Language：Japanese   Publishing type：Research paper (scientific journal)  

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/transjsme.24-00008

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

In this study, aluminum alloy specimens were subjected to bending vibrations at different vibration frequencies near the first resonance frequency in order to investigate the vibration changes associated with crack propagation. Bending displacement, crack length, and strains at several parts of the specimen were measured during the bending vibration tests. As a result, it was confirmed that when the vibration frequency was lower than the initial first resonance frequency, the vibration amplitude increased with the crack length, and when the vibration frequency was higher than the initial first resonance frequency, the vibration amplitude decreased with an increase in the crack length. This is due to the decrease in the first resonance frequency due to the material damage. The relationship between the change of bending displacement amplitude and the crack length during vibration of the specimens can be organized using the slope (dΔε_x2/df_v) of the relationship between the strain range and the vibration frequency for the undamaged specimen. This might be due to the strong correlation between the decrease in the first resonance frequency and the crack size when the crack initiation location is limited in the material. Moreover, based on the relationship between the change of bending displacement amplitude and the crack length, the stress intensity factor range (ΔK) was estimated by incorporating the load change into the crack length. By using the modified ΔK, the crack growth rate during bending vibration could be predicted.

DOI： 10.1299/transjsme.23-00246

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.11351/jsaeronbun.55.107

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.engfailanal.2023.107623

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2207/qjjws.41.302

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

To investigate the tensile properties and slip deformation behavior of pure titanium thin wires with a small ratio of the diameter to the grain size, tensile tests and a stepwise tensile test were performed using specimens with a diameter of approximately 170 μm and grain sizes of 17 and 87 μm, corresponding to diameter-to-grain-size ratios of 10 and ∼2, respectively. The specimen with a diameter-to-grain-size ratio of 10 fractured through the growth of voids. The fracture morphology was similar to that of the bulk specimens. On the other hand, for specimens with a diameter-to-grain-size ratio of 2, fracture occurs owing to the local deformation, in which primary slip systems are activated in each grain. The stepwise tensile test of the specimen with a diameter-to-grain-size ratio of 2 indicated that the slip deformation tended to occur from the large grains. Moreover, the activities of the slip systems of grains were evaluated using the Schmid factor (SF) and critical resolved shear stress (CRSS) of each slip system. It was noted that slip systems with the highest SF∙CRSS−1 were activated for 30 out of 33 grains.

DOI： 10.1016/j.msea.2022.144532

Scopus

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)  

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

The objective of this study is to clarify the effect of resin lamination on the tensile strength characteristics of SUS304 stainless steel thin films. We conducted tensile and stepwise tensile tests using several types of specimens prepared with 20-μm- and 40-μm-thick SUS304 films, 25-μm-thick polypropylene (PP) film, and 6-μm-thick polyethylene terephthalate (PET) film. Their macroscopic and microscopic tensile deformation behaviors were observed using an optical microscope and a reflection-configured digital holographic microscope, respectively. As a result, laminating the PP or PET films onto the SUS film did not significantly change the macroscopic and microscopic strain changes against the tensile load or microscopic surface changes in the low-strain region. Laminating the PET film onto the SUS film did not reduce the fracture strain, whereas laminating the PP film onto the SUS film did reduce it. One of the reasons may be that burrs formed on the side surface of the PP/SUS laminate. Polishing the side surface of the PP/SUS laminate may suppress the reduction in its fracture strain. The reduction of the fracture strain due to the PP lamination in the 20 μm thick SUS film was larger than that of the 40-μm-thick SUS film. In thin SUS films, small stress concentrators that have almost no effect on macroscopic and microscopic deformation might significantly reduce the fracture strain.

DOI： 10.1007/s00170-021-07510-8

Scopus

researchmap

Other Link： https://link.springer.com/article/10.1007/s00170-021-07510-8/fulltext.html

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME International  

<title>Abstract</title>
Gray cast iron has been used as a component in various mechanical parts, such as the blocks and heads of automobile and marine engines, cylinder liners for internal combustion engines, and machine tool bases. It is desirable because of its good castability and machinability, damping characteristics, and high performance-to-cost ratio. On the other hand, weak graphite flakes present in gray cast iron serve as stress concentrators and adversely affect the material strength. Therefore, it is crucial to examine the relationship between the distribution of graphite flakes and the strength or fracture of gray cast iron. In this study, tensile tests on gray cast iron were carried out using a plate specimen and observed by scanning electron microscopy, and the microscopic deformation was observed on the specimen surface. Particularly, the change in the size of graphite flakes during the tensile tests was examined, and the observed trend was discussed. The experimental results reveal that the dimensional changes in the graphite flakes vary in the observed area and that the final fracture occurs in an area where a large dimensional change is observed, suggesting that the fracture location or critical parts of gray cast iron can be predicted from the dimensional changes of the graphite flakes at an early stage of deformation.

DOI： 10.1115/1.4048063

Scopus

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Copyright © 2020 ASME. Commercial pure titanium has been widely used in aerospace, chemical, and biomedical industries for its lightweight, high corrosion resistance, high strength, high heat resistance and good biocompatible properties. The market of pure titanium thin sheets is expected to increase in medical, dental, civil engineering, and acoustical engineering fields. On the other hand, pure titanium takes hexagonal closed-pack structure with anisotropic elasticity and plasticity. Inhomogeneous microscopic deformation always occurs by mechanical loading from the elastic condition. The inhomogeneity brings about various damages such as localized plastic deformation, microcracking, necking, and so on. Since the inhomogeneity is significant in thin sheets, it is important to investigate its deformation behavior. In this study, a tensile test was carried out using a thin sheet specimen of polycrystalline pure titanium, and the microscopic deformation of grains was measured by the digital holographic microscope. During the test, the height distribution of grains was measured in a fixed area on the front and back surfaces of the specimen at each tensile load step and the results at different load steps were compared. It was found from the measurement results that inhomogeneous deformation began at the small load due to anisotropic elasticity of crystal grains and expanded with the load by their anisotropic plasticity. Grain heights at grain center and those along grain boundaries were related with each other, and the grain heights on the front surface were inversely correlated with those on the back surface.

DOI： 10.1115/PVP2020-21715

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

© 2020 by the authors. Turbine blades for thermal power plants are exposed to severe environments, making it necessary to ensure safety against damage, such as crack formation. A previous method detected internal cracks by applying a small load to a target member. Changes in the surface properties of the material were detected before and after the load using a digital holographic microscope and a digital height correlation method. In this study, this technique was applied in combination with finite element analysis using a 2D and 3D model simulating the turbine blades. Analysis clarified that the change in the surface properties under a small load varied according to the presence or absence of a crack, and elucidated the strain distribution that caused the difference in the change. In addition, analyses of the 2D model considering the material anisotropy and thermal barrier coating were conducted. The difference in the change in the surface properties and strain distribution according to the presence or absence of cracks was elucidated. The difference in the change in the top surface height distribution of the materials with and without a crack was directly proportional to the crack length. As the value was large with respect to the vertical resolution of 0.2 nm of the digital holographic microscope, the change could be detected by the microscope.

DOI： 10.3390/app10144883

Scopus

researchmap

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>Pure titanium thin wires have been used for medical fields. It is important to investigate the possibility of non-destructive inspection of pure titanium thin wires for the safety utilization of them. In order to investigate a fracture prediction method for a pure titanium thin wire, we performed tensile and fatigue tests and a finite element analysis to analyze the changes of direct current potential difference and diameter distribution of the pure titanium thin wire during tensile and fatigue tests. It was found that a direct current potential difference method may be available for evaluating the tensile and fatigue damages of the pure titanium thin wire. In the tensile and fatigue tests, the normalized direct current potential difference increased almost linearly with an increase in the nominal strain, and a sign of an increase of the normalized direct current potential difference was observed when the fatigue crack propagated. Therefore, the nondestructive inspection could be conducted by setting a tolerance value of the normalized direct current potential difference, or detecting a sign of an increase in the normalized direct current potential difference. In addition, a method of predicting the fracture location from the diameter distribution change of the pure titanium thin wire was studied. The method could be applied to tensile and fatigue fractures.</p>

DOI： 10.1299/transjsme.19-00351

CiNii Article

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)  

researchmap

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Cold forging is a metal forming that which uses localized compressive force at room temperature. During the cold forging process, the tool is subjected to extremely high loads and abrasive wear. Lubrication plays an important role in cold forging to improve product quality and tool life by preventing direct metallic contact. Surface roughness and residual stress also greatly affects the service life of a tool. In this study, variations in surface roughness, residual stress, and specimen deformation with the number of cold forging cycles were investigated under different forging conditions. Specimens that were made of heat-treated SKH51 (59–61 HRC), a high-speed tool steel with a polished working surface, were used. The specimens were subjected to an upsetting process. Compressive residual stress, surface roughness, and specimen deformation showed a positive relationship with the number of forging cycles up to a certain limit and became almost constant in most of the forging conditions. A larger change in residual stress and surface roughness was observed at the center of the specimens in all the forging conditions. The effect of the magnitude of the forging load on the above discussed parameters is large when compared to the effect of the lubrication conditions.

DOI： 10.3390/met9070783

researchmap

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Society of Mechanical Engineers  

<title>Abstract</title>
Composite materials such as carbon-fiber-reinforced plastics (CFRP) and glass-fiber-reinforced plastics (GFRP) have been attracting much attention from the viewpoint of lightweight solution of automobiles and airplanes. However, the recyclability of these composite materials is not sufficient and the environmental load is large. Recently, self-reinforced polymer (SRP), in which similar polymer is used for reinforcing fibers and matrix, has been proposed. High-density polyethylene (HDPE) reinforced with ultra-high-molecular-weight polyethylene (UHMWPE) fibers, so-called self-reinforced PE (SRPE), is one of the promising thermoplastic composites. In this study, SRPE plates were made and the tensile tests were carried out. After the effect of reinforcement of UHMWPE fibers was evaluated on the basis of the tensile strength, the relationship between the distribution of UHMWPE fibers and the location of the final fracture line was examined. It was found from these experimental results that the fracture tends to occur along the regions with low area fraction of fibers or along those with low area fraction of fiber/matrix boundaries. This fact suggests that the fracture location of SRPs is predictable from the distribution of reinforcing fibers.

DOI： 10.1115/pvp2019-93546

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Society of Materials Science, Japan  

DOI： 10.2472/jsms.68.478

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

A cyclic tensile test was carried out using a plate specimen of commercial pure titanium on a digital holographic microscope stage. Microscopic deformation of the grains was observed, and their height distribution was measured on the specimen surface. Each grain showed nanoscopic movement up and down, as well as reverse movement corresponding to specimen loading and unloading. We suggest that the different grain-specific changes in height were caused by microscopic inhomogeneities in the material, such as differences in the crystal orientation and geometries of both the surface and subsurface grains. Changes in grain height increased with tensile load, and a strong relationship was found between the height changes that occurred under elastic and plastic conditions. This suggests that microscopic plastic deformation is predictable from microscopic elastic deformation. In order to investigate the plastic deformation of grains in more detail, slip-line angles were measured after the tensile test. We found slip lines with similar angles in neighboring grains, suggesting that the plastic deformation of grains was not independent, but rather was related to that of surrounding grains and influenced by the deformation of subsurface grains.

DOI： 10.3390/app8101907

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

DOI： 10.3390/cryst7080255

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications Ltd  

During the last few decades, the enhancement of prediction capability of the sheet metal forming have been increasing dramatically. High accurate yield criteria and wokhardening model (especially, non-linear kinematic hardening model) have a great importance for the prediction of the final shapes of sheet metal. However, the predicted springback accuracy of aluminum alloy sheet metal is not still good due to their complicated plastic deformation behaviors. In the present research, the springback deformation of aluminum alloy sheet metals were investigated by finite element calculation with consideration of initial anisotropy and the Bauschinger effect. In order to examine the effect of the initial and deformation induced anisotropy on the springback deformation, several types of high accurate yield function and hardening rules are utilized in the present research. The calculated springback by Yoshida 6th yield function [1] and Yoshida-Uemori model [2] shows an excellent agreement with the corresponding experimental data, while the other models underestimate the springback.

DOI： 10.4028/www.scientific.net/KEM.725.566

Scopus

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier Ltd  

For the last two decades, strong demands for the light weighted structures of automobiles have been increasing in all over the world. In order to satisfy the demands, the high strength steel sheets (hereafter HSSs) have been widely utilized in the various automobile related companies. However, for the companies, it is still one of the hard tasks to apply HSSs for the automobile parts with complex shapes, due to low ductility and large springback of the HSSs. In the present research, we assumed fracture limits in stretch bending are theoretically obtained with the assumption that fracture occurs when stretching force reaches its maximum value. The authors proposed an explicitly theoretical analysis method based on the maximum load criterion that can easily and rapidly allow us to predict the fracture and springback of HSSs by using two no dimensional parameters (limited wall stretch L/L0 (L: limit wall length of a sheet, L0: initial wall length) and bending radius t/R (t: sheet thickness, R: bending radius)). For the evaluations of this method, the comparisons between stretching bending experiments of HSSs and the corresponding theoretical calculations were conducted. From the comparisons, the calculated results by our proposed method have good agreements with the experimental observations.

DOI： 10.1016/j.proeng.2017.10.1054

Scopus

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER  

A cyclic tensile test was carried out using a plate specimen of commercial pure titanium on the stage of digital holographic microscope. The microscopic deformation of grains was observed and their height distribution was measured on the specimen surface. Each grain showed different height change from small elastic loading due to microscopic inhomogeneity, and the height change increased with the tensile load. It was found that the height change under elastic condition was correlated with that under plastic condition.

DOI： 10.1007/978-3-319-51439-0_64

Web of Science

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：E D P SCIENCES  

Thin metal films deposited on polymers have been attracting much attention in flexible electronics. Various combinations of film and polymer substrate are expected to be developed. In this paper, deformation and fracture of thin metal film on polymer substrate was briefly analysed and the influencing factors were summarized. After that, focusing on the shape and thickness of thin metal film on polymer substrate, cracking behavior of small rounded-rectangular thin gold films called "strips" with a thickness less than one micrometer was observed under cyclic and stepwisely-increased trapezoidal tensions. The strips were deposited on a polycarbonate plate specimen, and wide and narrow strips with different thickness were prepared for the tests. The cracking behaviour was successfully observed and the increasing rate of crack number with the load or strain was examined. Since most cracks were initiated from the small defects, the crack initiation behavior was correlated with the distribution of defects.

DOI： 10.1051/matecconf/201710801004

Web of Science

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE Computer Society  

Recently, copper wires have been attracting much attention for LSI (Large Scale Integration) bonding because of its excellent mechanical and electrical properties, and low material cost. On the other hand, the end of these wires are usually joined to the pads or through-holes on the printed circuit board, and lead-free soldering is one of the popular bonding methods. Since the solders are weaker than copper wires, the stress and strain tend to be concentrated on the interface of solder/wire interface. The fracture frequently occurred there and may influence the quality of product. It is therefore important to evaluate the bonding strength of thin copper wire and lead-free solder. In this paper, pullout tests of thin copper wires from lead-free solder were carried out and the pullout behavior of the wires were observed. A method of bonding strength evaluation was proposed and the results were examined.

DOI： 10.1109/IMPACT.2016.7799989

Scopus

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Society of Mechanical Engineers (ASME)  

Commercial pure titanium has been widely used in aerospace, chemical, and biomedical industries for its lightweight, high corrosion resistance, high strength, high heat resistance and good biocompatible properties. Pure titanium takes hexagonal closed-pack structure with anisotropic elasticity and plasticity, and most of the components are polycrystalline aggregate with different crystal orientations. Therefore, inhomogeneous microscopic deformation always occurs by mechanical loading from the elastic condition and the inhomogeneity brings about various damages such as inhomogeneous plastic deformation, microcracking, necking, and so on. It is therefore important to investigate microscopic inhomogeneous deformation under elastic and plastic conditions. However only a few researches deal with the microscopic inhomogeneity because it is not easy to measure a small deformation of crystal grains under elastic condition or very small load. Recently, digital holographic microscope has been developed and a high-speed measurement of surface height of materials became possible with an accuracy of less than a micron meter in a relatively wide area. In this study, a tensile test of a plate specimen of commercial pure titanium was carried out on the stage of digital holographic microscope, and the microscopic deformation of grains was observed and measured under elastic and plastic conditions. During the test, the distribution of height of grains was measured in a fixed area on the specimen surface at each tensile loading step and the height distributions at different loads were correlated. It was found from the measurement results that each grain shows different deformation even under elastic condition with a small load, and the inhomogeneous deformation expanded with increasing the load to plastic condition. Also, a strong correlation was found in the height distributions under elastic and plastic conditions. This fact suggests that the microscopic deformation under plastic condition is predictable from that under elastic condition.

DOI： 10.1115/PVP2016-63268

Scopus

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

In order to clarify the inhomogeneous deformation of thin copper wire, an interrupted tensile test was carried out on the stage of the digital holographic microscope (DHM). The inhomogeneity was evaluated based on the non-uniform change in height distribution on the surface of thin wire specimen during the test. Microscopic plastic deformation by a unit of crystal grain and large gradient in height distribution along grain boundaries were observed. The increase in average height of grain between two earlier loading steps corresponded to that between two later loading steps. This result suggests that the microscopic deformation at the latter stage of tension is predictable from that at the early stage of the tension.

DOI： 10.1109/IMPACT.2015.7365226

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications Ltd  

To evaluate the effect of the size of the microstructure on the mechanical property of the cavitated rubber blended (voided) amorphous polymer, the FEM simulation based on the rate form second-order homogenization method, in which rates of the macroscopic strain and strain gradient are given to the microstructure, was performed. Computational simulations of micro- to macroscopic deformation behaviors of amorphous polymers including different sizes and volume fractions of the voids were performed. Non-Affine molecular chain network theory was employed to represent the inelastic deformation behavior of the amorphous polymer matrix. With the increase in the volume fraction of the void, decrease and periodical fluctuation of stress and localized deformation in the macroscopic field were observed, and were more emphasized with the increase in the size of the void. These results were closely related to the non-uniform deformation and volume increase of the void in the microscopic field. © (2015) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/KEM.626.74

Scopus

researchmap

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

The use of a flange joint is a popular method to close the end of pipes or connect pipes in manufacturing industries. As the pipes are often subjected to vibrations and cyclic bending, fatigue cracking may occur at the welded part between the pipe and flange. It is therefore important to detect and monitor the cracking in this part to ensure safety of the whole piping system. The direct-current potential difference method (DC-PDM) is known as a suitable non-destructive technique to monitor the initiation and growth of cracks and it has been applied to cracks and wall thinning on the inner surface of pipes. In this study, finite element analyses were carried out to clarify the relationship between the size and location of cracks at the pipe-flange welded part and the potential difference. An evaluation method of circumferential crack length angle by DC-PDM was proposed.

Web of Science

researchmap

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Pole side impact is one of the most common types of vehicle collisions. The pole side impact at high vehicle speed induces not only local collapse but also bending of the vehicle body. However, the estimation method of the vehicle speed with consideration of the bending has not been established yet. In the present study, the deformation of the vehicle body at the pole side impact experiment with impact speed of 80 km/h was investigated. The results revealed that the collapse deformation first occurred and then the bending deformation followed. In order to understand the deformation of the vehicle at high-speed pole side impact, lateral local compression test and three-point bending test of rectangular steel tubes were performed. It was found that the deformation of the tube was similar to that of the vehicle at the pole side impact experiment, when the specimen was subjected to the sequential test of lateral local compression and three-point bending. The change in the energy absorbed by the deformation of tube in the sequential test was also found to be similar to that in the vehicle experiment. These similarities are useful to investigate the vehicle collision speed at high-speed pole side impact based on the deformation and the absorbed energy of rectangular metal tubes.

DOI： 10.1299/transjsme.14-00542

CiNii Article

researchmap

Authorship：Lead author,　Corresponding author  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

When a mechanical load is given to a cracked material, an undulation appears in surface profile around the crack. The undulation is caused by stress-strain concentration at the crack tip and its release near the crack center. If the load is very small and within the elastic deformation range, the material recovers the original shape after unloading and no damage remains. Therefore, this surface undulation by a small mechanical load can be used for detection of crack on the material surface. In this study, non-destructive crack detection method by nanometric change in surface profile is proposed, and the experiment and related finite element analyses were carried out for notched high-density polyethylene (HDPE) plates. Non-uniform height change by a small mechanical load around the notch on the surface of HDPE plate was measured by a laser scanning microscope. The height change distribution agreed with the analytical result.

Web of Science

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

Local wall thinning is one of serious problems in aged power generating plants and is known to occur mainly by Flow Accelerated Corrosion (FAC) and Liquid Droplet Impingement (LDI) erosion. As the thinning grows inside the pipes, it is difficult to detect and evaluate it from the outer surface of pipe. The direct-current potential difference method (DC-PDM) is thought to be a suitable non-destructive technique to monitor the initiation and growth of these damages. In this study, an approximate analysis method of the potential difference around a semi-ellipsoidal thinning on the back surface of flat plate is presented and the accuracy is discussed based on the results obtained by the finite element analyses.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

To represent the elasto-viscoplastic deformation behavior of semi-crystalline polymer (SCP), which has a complicated hierarchical structure, a micro-, meso- to macroscopic computational model was developed. A laminar composite model and FE-based homogenization method were used to relate the mechanical behaviors in micro- to mesoscopic and meso- to macroscopic scales of the material. Using the proposed model, elasto-viscoplastic deformation behaviors of high density polyethylene under several macroscopic boundary conditions were computationally investigated. Material's parameters used in the constitutive equations for microstructure of SCP were defined by fitting the calculated stress-strain relation into the experimental data. Then, the effects of deformation mode and crystallinity on deformation behavior of SCP were investigated. Obtained stress-strain relations represented the experimentally observed characteristics such as an anisotropic strain hardening rate depending on the deformation mode and an increase in the Young's modulus and the flow stress with the crystallinity. Then, the neck propagation process in the uniaxial tension with different strain rate was investigated. The present model represented a development of macroscopic non-uniform deformation characterized by the mechanical response of micro- to mesoscopic deformation. (c) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijplas.2013.03.007

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To investigate the deformation behavior of multi-layered ceramic capacitors (MLCCs) during production press process is very important to reduce over all MLCC size and increase the capacity of the MLCC through the enlargement of the electrode area. In the previous paper, the deformation of MLCC blocks in the uniaxial compression test was observed and the filling mechanism was clarified based on the measurement results. In this study, the non-frame press tests of MLCC blocks were carried out to realize the high precision press, in which the lateral compressive stress was given in addition to the longitudinal one. The deformation process was clarified based on the results of cross-sectional observation. In the edge part of the MLCC block, the interlayer space in Side-Gaps L and W was decreased by longitudinal strain and the lateral strain, whereas, at the central part of the MLCC block, the interlayer space in Side-Gaps L and W was decreased only by longitudinal strain. Since the difference in the deformation behavior between the central part and the edge part generated variations in the thickness of MLCC block, the width of the internal electrode part and the width of the Side-Gap, it was concluded that non-frame press was not suitable for high precision press of MLCC block.

DOI： 10.1299/kikaia.79.442

CiNii Article

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To evaluate effect of a relative scale of microstructure to macrostructure, a simulation procedure using second-order homogenization based finite element method was proposed. In this method, a microscopic characteristic displacement function for macroscopic strain gradient was added to the conventional first order homogenization method. Then, a procedure to solve a macroscopic boundary problem was established based on the principle of virtual work in macroscopic scale represented by the microscopic characteristic displacement function. To validate the proposed second-order homogenization method, computational simulations of deformation behavior of cavitated rubber (void) blended amorphous polymer were performed using the proposed second-order homogenization. From the result of bending deformation where tension or compression was given to upper side or lower side of the macroscopic model, the material containing larger void required a larger energy for the bending of the model. With decrease in the void size, the energy converged to that predicted by first-order homogenization method. Basically, the deformation behavior predicted by proposed homogenization model was qualitatively and quantitatively similar to that predicted by full scale model. The proposed model is expected to be applied for computational prediction of the scale-dependent deformation in various cases because the model does not limit the form of constitutive equation, shape of the unit cell and deformation mechanisms and structure of the material.

DOI： 10.1299/kikaia.79.1486

CiNii Article

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A single-cycle bending test of polycrystalline pure titanium was carried out using a rectangular specimen with a pair of parallel grooves. The plastic deformation in a long part between these grooves was observed at every quarter cycle of back-and-forth bending. Before the test, multiple square marks of gold were made at the lattice points having a mutual distance of 12.5 μm in the region of interest by ion-coater. The strain and rotation during the test were evaluated based on the displacement of these gold marks. The following results were obtained: (1) The region of interest between grooves showed plastic deformation during bending, and the deformation was mainly caused by slips. Twining was also observed in some grains. (2) The strain and rotation during the bending were not uniform grains to grains. The shearing strain was small compared with the normal strains and rotation. (3) The region, which showed a larger normal strain at the first quarter cycle, continued to show a relatively large strain at the following quarter cycles in an opposite direction. Rotation showed a similar behavior. (4) Crystal orientation analysis was performed for grains with clear slip lines. The plastic deformation of these grains seemed to occur mainly by the prismatic slip.

DOI： 10.1299/kikaia.79.420

CiNii Article

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Stress distribution of gray cast iron was analyzed by the finite element analysis based on the actual distribution of graphite flakes embedded in pearlite. Three types of two-dimensional FE-models were used: (1) "true model" where graphite flakes were distributed in pearlite as observed, (2) "voids model" where graphite flakes were replaced by voids of the same geometries, and (3) "single void model" where one of selected voids which showed higher stress in the vicinity of void tip in the pearlite. As the voids model showed higher stress in the vicinity of each void tip, it was concluded that the voids model was appropriate for the safe-side evaluation of gray cast iron strength. Furthermore, a simplified method of strength evaluation was proposed by comparing the results of the voids model with those of the single void model. Since the maximum ratio of the stress near the void tip was 6.27 between the voids model and the single void model, tensile and fatigue strengths of gray cast iron was evaluated by the stress intensity factor multiplied by 6.27 using the maximum length of graphite flakes, the threshold stress intensity factor range and fracture toughness of pearlite about the tested diesel engine cylinder block. The method validated the safety of cylinder block of the tested diesel engine.

DOI： 10.1299/kikaia.79.281

CiNii Article

researchmap

Language：Japanese  

CiNii Article

CiNii Books

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Since solder materials are often used for electric connections in various electric devices, the strength of solders and that of interfaces to the other metallic materials are very important. After the restriction of lead solder usage according to the European Union Waste Electrical and Electronic Equipment (WEEE) and Restriction of Hazardous Substances (RoHS) Directives, various lead-free solders have been developed and their optimized joining condition is being investigated. The mechanical test of solder joints is one of the best ways to check the joining condition and it gives us useful information to secure the safety of electric devices. From the viewpoint of mechanical testing, it is not easy to handle the solder materials because of their very low deformation resistance and small size. In this paper, a new method of tensile test is proposed using permanent magnet, and the results are discussed. By using the permanent magnet, various non-contact tensile tests are going to be possible. The present paper is a basic study to realize the non-contact tensile tests for micro materials.
[GRAPHICS]
.

Web of Science

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

When a material is subjected to a small mechanical load, it shows a small elastic deformation of the order of nanometer. If there is a crack on the surface or underneath the surface, small elastic deformation shows non-uniformity around the crack. In this study, a non-destructive crack detection method by nanometric change in material's surface profile is proposed, and a tensile test of notched plate specimen was carried out. A non-uniform height change by mechanical load appeared near the notch. This fact suggests that the proposed method is available as an NDE method.

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Proceedings of Joint International Conference of the 2nd International Symposium on Experimental Mechanics, The 11th Asian Conference on Experimental Mechanics and 2012 Society for Experimental Mechanics Fall Conference, 7th International Symposium on Advanced Science and Technology in Experimental Mechanics

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The localized deformation field of high density polyethylene and polypropylene during a tensile test accompanied by neck propagation was quantitatively evaluated based on the network digital image correlation method. In the proposed method, the continuity of the deformation field around a point of interest was introduced for accurate evaluation of the displacement. The accuracy of the proposed method was verified through test images. Using the proposed method, the development of a non-uniform displacement field during tensile tests was evaluated from sequential digital images. The local strain rate was almost uniform until the nominal stress reached its maximum value. After the maximum stress was reached, non-uniform deformation developed at a part of the gauge region of the specimen. A decrease in nominal stress induced a reduction of the local strain rate at regions other than the necked zone. In this study, the cross section average local true stress, strain, and strain rate can be evaluated from the local displacement field. Thus, the relationship between these quantities was evaluated during the tensile tests. Using the proposed method, the local response under wide ranges of strain and strain rate can be evaluated from a few test conditions of tensile strain rate and a small range of tensile strain. Finally, the relationships between gradients of stress, strain, and strain rate under uniaxial tension are discussed. These non-local quantities deviated from those predicted by constitutive equations when the domain size used to evaluate the local quantities was large. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijplas.2011.07.009

Web of Science

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)  

CiNii Article

CiNii Books

researchmap

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本工業出版  

CiNii Article

CiNii Books

researchmap

researchmap

Language：English   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：English   Publisher：The Japan Society of Mechanical Engineers  

Deformation behavior of multi-layered ceramic capacitors (MLCCs) during production press process is very important to reduce over all MLCC size and increase the capacity of the MLCC through the enlargement of the electrode area. In this study, compression tests of MLCC blocks, which were composed of stacked ceramic dielectric sheets and printed internal electrodes, were carried out, and the deformation process was clarified based on the results of cross-sectional observation. Deformation of MLCC block was modeled and predicted using the area fraction of dielectric sheets, internal electrodes, and internal space. The prediction agreed well with the experimental results and helps the optimization of MLCC design.

DOI： 10.1299/jmmp.6.760

CiNii Article

researchmap

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Stress corrosion cracking (SCC) is one of serious damages occurred in power generating plants, petrochemical plants, and gas pipelines. However, it is not easy to detect and evaluate SCCs because their shapes are complex and they are usually initiated in the weldment composed of base metal, weld metal, and heat-affected zone. In this study, the direct-current potential difference method (DC-PDM) was applied to SCCs artificially introduced in plate specimens and the applicability of DC-PDM to their detection was discussed. It was found from the measurement results that the potential differences near SCC were higher than those away from SCC. This fact suggests that SCC is detectable by DC-PDM. Copyright © 2011 by ASME.

DOI： 10.1115/PVP2011-57913

Scopus

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

The authors proposed an NDE method of detecting the crack developed in the turbine blade by means of digital holographic microscopy (DHM). UT procedures sometimes have limitations in particular cases of in-service-inspections such as the detection and sizing of a creep crack developed in the air-cooled casting blade of the combined cycle gas turbine. The local displacement at the blade surface near the crack during a mechanical loading is different from that of a noncracked blade. This small different can be detected by DHM. The authors discussed whether this difference affected by the mechanical load between the cracked blade and the noncracked is detectable by means of DHM or not. In this paper, the authors verified the practical validity of the proposed NDE method using the finite element analyses. Copyright © 2011 by ASME.

DOI： 10.1115/PVP2011-57299

Scopus

researchmap

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

researchmap

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

CiNii Article

researchmap

Publisher：The Japan Society of Mechanical Engineers  

Since semi-crystalline polymer has very complex hierarchical structure, it is essential to construct a suitable multiscale mechanical model for the prediction of its mechanical characteristics. For the establishment of the triple scale mechanical model of semi-crystalline polymer, which can reflect the non-uniform deformations in micro-, meso- and macroscopic scales, computationally efficient model to relate structures and deformations in micro- to mesoscopic scales is indispensable. In this paper, to solve the problems, tangent modulus method was introduced into the constitutive equations for crystalline and amorphous phases consisting of the microstructure of semi-crystalline polymer. Furthermore, we proposed a new laminar composite model connecting deformations in micro- to mesoscopic scales based on the equilibrium of stress acting on the interface between the phases and the compatibility of deformation along the interface. Appropriate time steps for stable simulation and validity of the proposed model were examined through the computational simulation of uniaxial tension of single lamellar and spherulite models of high density polyethylene. It has been clarified that the proposed model could predict an elasto-viscoplastic deformation behavior of semi-crystalline polymer in markedly less computational time and memory.

DOI： 10.1299/kikaia.77.902

CiNii Article

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Elasto-viscoplastic deformation behavior of semi-crystalline polymer with multi-spherulitic mesostructure was investigated using large deformation finite element homogenization method. Multispherulitic mesostructure was modeled in representation volume element (RVE) by Voronoi polygons, and the deformation behavior during tension in different directions was numerically investigated. Mesoscopic stress strain relations were almost similar for different mesoscopic structures except for a quarter spherulite mesoscopic models, and its anisotropy decreased with increase in the number of spherulites in RVE. Although anisotropy in mesoscopic stress strain relation disappeared for enough number of spherulites, highly heterogeneous distribution of local strain and stress was observed in each spherulite. Distribution of lamellar orientation in the spherulite caused the heterogeneity and played an important role in the local deformation field. (c) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijmecsci.2009.09.002

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

Remaining life evaluation has been attracting much attention to secure the safety of aged power generating plants. A crack on the outer surface of pipe is a typical kind of damage observed in aged plants. Accurate information of crack largely helps the remaining life evaluation based on fracture mechanics. The direct-current potential difference method (DC-PDM) is known as one of the suitable non-destructive techniques to monitor the initiation and growth of crack in the pipes. Usually, numerical analyses are necessary to evaluate the geometry of crack from the potential difference because no analytical solution was given in most cases. In this study, a solution of the potential difference around a semi-elliptical crack on the outer surface of pipe is presented and the result is compared with that obtained by finite element analysis.

DOI： 10.1115/PVP2010-25286

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：E D P SCIENCES  

The plastic behaviour and compressive fracture of AZ31 magnesium alloy were examined at room temperature. The uniaxial compression tests and biaxial compression tests along linear and nonlinear strain paths were carried out until fracture using a unique biaxial compression testing machine developed by author. The results revealed the evolution of plastic anisotropy in biaxial compressions, that is the strain path dependency of work hardening. The adaptability of several forming limit criteria to the compressive fracture of AZ31 alloy was discussed. It was found that the uniform estimation of compressive forming limits by uniaxial and biaxial compressions was difficult by Freudenthal criterion and Oyane criterion. The result of Tresca energy criterion suggested that the criterion based on shear stress has possibility to predict the compressive forming limits at room temperature of AZ31 alloy.

DOI： 10.1051/epjconf/20100616001

Web of Science

researchmap

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

In microindentation testing, an indentation size is smaller than the average grain size of industrial polycrystalline metals, so that the indentation shape is affected by the crystallographic orientation of grain on which the indentation is imposed. Hence, clarification of the relation between the crystal orientation and the indentation shape leads to the possibility of estimating the crystal orientation by microindentation testing. In the present study, influences of crystal orientations upon indentation shapes on grains of polycrystalline titanium were investigated. The crystal orientations of grains were measured by an electron backscattered diffraction method, and indentation tests with a triangular pyramidal indenter were performed on the grains. The indentation shapes were thus observed by a laser-scanning microscope and an optical microscope. The results revealed that the direction of the most bulged position of edges from the apex of triangular indentation agreed well with an a-axis direction. It was also found that deviation of the indentation edge from the ideal one became smaller with larger angle of inclination of c-axis for the sample surface, owing to the limited slip direction of titanium. Those results suggest the possibility to evaluate the crystal orientation of titanium grain directly from the observed indentation geometry.

DOI： 10.1117/12.851502

Web of Science

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

The direct-current potential difference method (DC-PDM) is known as one of the promising non-destructive methods to evaluate the crack in the conductors. This method utilizes the change in the current path or the potential difference which is caused by the crack. In the previous study, a method of three-dimensional evaluation of semi-elliptical crack on the back surface of plate was proposed and its theoretical validity and practical utility were shown based on the results of numerical analyses and experiments. In this study, the method is extended to the identification of semi-elliptical crack on the inner surface of pipe and the related electric field analyses are carried out by the finite element method. The results show that the crack on the inner surface of pipe can be evaluated by the proposed method based on the distribution of potential difference measured on the outer surface of pipe. The present extension will be very useful for various practical cases which are often seen in the piping of power-generating and petrochemical plants.

Web of Science

researchmap

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本工業出版  

CiNii Article

CiNii Books

researchmap

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

CiNii Article

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

CiNii Article

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

The direct-current potential difference method (DC-PDM) is known as one of the best techniques to evaluate the damage initiated in structural materials. However, it is not still very popular and has not yet been widely used. One of its main reasons is that the potential difference measured is not supported based on the physical background and the relationship between the damage and the potential difference is not clarified quantitatively. In this paper, DC-PDM is classified into several categories based on the distribution of defects, the number of potential measurement probes, and the location of current supply probes. Characteristics of all categories are described.

Web of Science

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The distribution of static strain along the fillet on an upper deck of cylinder block and its dependency on the depth of thread engagement for cylinder head bolts were evaluated for a diesel engine by the finite element method. Since the fillet on upper deck is one of the critical parts in the cylinder block that may be cracked by stress and strain concentration, the static strain along the fillet was focused on in this study. In the model, the static tightening force of cylinder head bolts balanced with the total force acting on the cylinder block. A uniform surface pressure calculated by the total force divided by the contact area was given to the upper deck. The following results were obtained.<BR>The static strain along the fillet was dependent on the circumferential direction of cylinder and its value was varied with the depth of thread engagement for cylinder head bolts. The optimum depth of thread engagement was determined to be about 100 mm from the viewpoints of the overall magnitude of strain, the circumferential fluctuation of strain, the change rate of strain against the depth of thread engagement, and the length of cylinder head bolt. The calculated circumferential distribution of the static strain and the tightening force were compared with the measurement results under the optimum depth of thread engagement condition. Both results agreed well and this fact suggests that the present analysis is useful for optimizing the structural design of cylinder block for diesel engines.

DOI： 10.1299/kikaia.74.1053

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00318143567?from=CiNii

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Tensile tests of notched thin film of pure titanium were carried out on the stage of a digital microscope. Tensile load was generated by the thermal expansion of a pair of polycarbonate loading plates by which the specimen was sandwiched. Since the thermal expansion coefficient of polycarbonate is much larger than that of pure titanium, the specimen was elongated with an increase in the temperature and successfully fractured at the end of the tensile test. The plastic deformation of the notched part of specimen was observed during the test and the stress and strain were evaluated. The obtained stress-strain curve situated between two curves by a commercial tensile testing machine at the room temperature and at 363 K, which approximately corresponds to the maximum temperature of the thermal stress-actuated tensile test. As the mechanism of the proposed tensile test is simple, it is expected to be applicable to much smaller specimens in the future.

DOI： 10.1299/kikaia.74.137

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00307954976?from=CiNii

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Society of Materials Science, Japan  

A micro indentation testing has been used to investigate the local mechanical properties of engineering materials. Since the size of indentation becomes much smaller than the average grain size of ordinary metallic materials by that testing, the results must be influenced more or less by the characteristics of each grain in which the indentation is imposed. However, the influences of crystal orientation of the grain upon the indentation results have scarcely been investigated for polycrystalline metals. In the present study, the micro indentation tests were performed on the grains of commercially pure titanium, of which the crystal orientations were evaluated beforehand by an electron back scattering diffraction technique. The relationships between the crystal orientation and the resultant indentation shapes as well as the indentation hardness values were then experimentally investigated. The results showed clear orientation dependences of the indentation shape and indentation hardness for the titanium grains. The anisotropy and the distortion of indentation profile tended to increase, while the obtained indentation hardness tended to decrease with increase in the angle between <0001> direction and the surface normal direction. The distortion of the indentation shape was found to appear due to the pile-up of materials in the limited area around the indentation by the restricted plastic flow with regard to the crystal orientation. These results are supposed to indicate the possibility to use an indentation made on grain's surface for the identification of its crystal orientation in polycrystalline titanium.

DOI： 10.2472/jsms.57.249

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00310940850?from=CiNii

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Society of Materials Science, Japan  

To elucidate the deformation behavior of rubber blended semi-crystalline polymers, the micro- to mesoscopic structure and its mechanical behavior was modeled by using large-deformation finite element homogenization method. In this paper, the effect of direction and strain rate of tensile loading, volume fraction of rubber particle and distance between rubber particles was investigated by numerical simulations of uniaxial tension of semi-crystalline polymer with uniformly distributed rubber particles. A series of computational result clarified the followings. The stress in earlier stage of the deformation, where the stress increases linearly with the strain, is high when the volume fraction of rubber particles is small, when distance between rubber particles is small, and when the load is applied parallel to the nearest neighbor direction. That in following stage, where the stress increases non-linearly with the strain, is high when the volume fraction of rubber particles is small and when tensile strain rate is high. Furthermore, change in the local strain rate and mean stress distribution with the increase in the global tensile strain rate is closely related to the distance between rubber particles and tensile direction.

DOI： 10.2472/jsms.57.243

CiNii Article

researchmap

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本工業出版  

CiNii Article

CiNii Books

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Solder materials are often used for electrical connections in various electric devices. In most cases, solders have interfaces with the other metal substrates and their interface strength is more important than the internal strength of solders. Since most of lead solders have been replaced by lead-free solders from the viewpoint of environmental conservation, the evaluation of interface strength between lead-free solders and metal substrates [1, 2] and the continuous monitoring of interface damage [3, 4] have been attracting much attention. However, it is not easy to evaluate the interface strength and damage because of a short-term experience of lead-free soldering in comparison with that of traditional tin-lea soldering, the difficulty in the mechanical analysis of interface based on constitutive equations obtained from macroscopic mechanical tests, and microscopic scatter of the material or structure on the interface arising from the relatively large microstructure in comparison to the volume of solder portion. From these points of view, the authors proposed a non-destructive method to evaluate the interface crack during the mechanical test by direct current potential difference method (DC-PDM). In the previous studies, cyclic tension tests under a constant temperature condition [5] and the related electric field analyses [6] were carried out. In this study, cyclic tension tests were carried out under fluctuating temperature condition and the growth of interface crack was monitored.

DOI： 10.1109/EMAP.2008.4784271

Web of Science

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

A method for identification of a semi-elliptical crack existing on the back surface of the material by means of direct-current electrical potential difference method of multiple-point measurement type was proposed. The geometry of the crack was given by the two-dimensional location of the crack center, the surface and inward angles of the crack, and the length and depth of the crack. The identification was carried out based on the distribution of potential difference on the surface. The related experiments were carried out using six metal plates with various semi-elliptical cracks made on the back surface by electric discharge machining. The geometry of the crack was successfully identified by the proposed method and the results were discussed.

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：Japanese   Publisher：The Japanese Society for Non-Destructive Inspection  

In the conventional direct-current potential difference method (DC-PDM), uniform current is supplied by a pair of probes set far from a crack and the change in the potential difference by the crack is measured by another pair of probes near the crack. The identification of the crack is done based on the measurement result. But when the crack exists on the back surface, the change in the potential difference is not large and the identification is usually difficult. In this study, it was assumed that current was supplied by a pair of remote probes and a pair of adjacent probes to a plate with a crack on the back surface. The distribution of electric potential and the potential difference between a pair of potential measurement probes on the surface were analyzed by the finite element method. When the adjacent current-supply probes were set in between the potential measurement probes, larger normalized potential difference was obtained than the case where only the remote current was supplied. Furthermore, it was found that the increase in the potential difference by the adjacent current depends on the distance between adjacent current-supply probes and the crack depth. Based on this characteristic, a method of crack depth evaluation was proposed.

DOI： 10.11396/jjsndi.56.643

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To elucidate the toughening mechanism in rubber particle modified semi-crystalline polymers in which the average matrix ligament thickness plays important roles, the micro-to mesoscopic deformation behavior of rubber/semi-crystalline polymer blends was modeled by using large-deformation finite element homogenization method. In this paper, the deformation behavior of three kinds of models which have different size of rubber particles was investigated. A series of computational simulation clarified that highly localized deformation is induced by the initial orientation of lamellae at interface region for the case of smaller size of rubber particles, and it produces larger strain in the matrix due to localization and propagation of the deformation zone. Furthemore, the microscopic deformation is mainly absorbed by not only a slip along chain direction in the crystalline phase, but also interlamellar shear in the amorphous phase, which must be closely related to the toughening mechanism of the rubber/semi-crystalline polymer blends.

DOI： 10.1299/kikaia.73.73

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00289895106?from=CiNii

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Society of Materials Science, Japan  

A simulation method of the creep damage progress combining the random fracture resistance model and FEM elastic-creep analysis was proposed and was applied to the evaluation of Type III and Type IV creep damage respectively in the coarse and fine grain heat affected zone (HAZ) in welded joints of 2 1/4Cr-1Mo steel. Firstly following the previous work on the fine grain HAZ, parameters for the coarse grain HAZ were identified for simulating the increase of number density of small defects on the basis of the random fracture resistance modeling. Secondly the simultaneous damage simulation for both fine and coarse grain HAZ was applied to both the welded joint model test and the burst test of elbow. A possibility of predicting the final failure time of welded joint was also discussed on the basis of the effective stress against the final failure surface. The proposed simulation successfully reproduced the increase of the number density of small defects in the fine and the coarse grain HAZ, and could predict the failure time of welded joints.

DOI： 10.2472/jsms.56.106

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00289912612?from=CiNii

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

Biaxial compression tests with an abrupt strain path change have been performed on polycrystalline aluminum to investigate the plastic deformation behavior under complex strain histories. Attentions are paid especially to the rapid change in the normal stresses due to the abrupt strain path change. The influences of the prestrain amplitude and the angular relation of sequential strain paths on the stress changes were also studied. The results showed that the transient increase of the normal stresses related to the latent hardening phenomenon with strain path change as well as the plastic anisotropy increase with the pre-straining amplitude. The transient increase in the stress was also affected by the strain histories in the sequential compression tests with the strain path change. The transient stress increment became large to the maximum then decreases with the angle between the sequential paths,

Web of Science

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Tensile tests of notched thin film of pure titanium were carried out on the stage of a digital microscope. Tensile load was generated by the thermal expansion of a pair of polycarbonate loading plates which sandwiched the specimen. Since the thermal expansion coefficient of polycarbonate is much larger than that of pure titanium, the specimen was elongated with an increase in the temperature and successfully fractured at the end of the tensile test. The plastic deformation of the notched part of the specimen was observed during the test and the stress and strain were evaluated. The obtained stress-strain curves were compared with those obtained by a tensile testing device with a piezoelectric stage at the room temperature and 363 K which approximately corresponds to the maximum temperature of the thermal stress-actuated tensile test.

DOI： 10.1109/EMAP.2007.4510292

Web of Science

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In order to validate the applicability of the direct current potential difference method (DC-PDM) to identification of interface cracks, electric field analysis was carried out for a copper plate with a solder ball joined on the surface by the finite element method. The analysis was carried out for different crack depths under the following four conditions; (a) when the shape of interface cracks between solder ball and copper changes, (b) when the radius of solder ball changes, (c) when the distance between the bottom of the copper wire and the interface changes, and (d) when the angle of copper wire changes. It was found from the analysis that the larger crack area ratio gave the larger increase in potential difference and that the effect of the crack shape and the angle of copper wire on the potential difference was small. Finally, the relationship between the crack area ratio and the increase in potential difference was given by a single formulated curve for all the conditions discussed in the present analysis

DOI： 10.1299/kikaia.72.1825

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00289043842?from=CiNii

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A method for identification of a crack on the surface of the material by means of direct-current electrical potential difference method of multiple-point measurement type was proposed and related experiments were carried out to verify the proposed method. The geometry of the crack was given by the two-dimensional location of the crack center, the surface and inward angles of the crack, the length and depth of the crack. The experiments were carried out for metal plates with various surface cracks made by electric discharge machining. When most of the area of potential disturbance by a crack was included in the measurement area, the geometry of the crack was successfully identified by the proposed method based on the potential differences measured at multiple locations around the crack.

DOI： 10.1299/kikaia.72.332

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00277226295?from=CiNii

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

An evaluation method of interface crack between solder ball and copper based on the non-destructive monitoring of direct current potential difference was proposed. The validity of the method was examined based on the results of electric field analysis by the finite element method. In the analysis, it was assumed that a solder ball was simply joined on the surface of a copper plate and the interface crack was evaluated by the potential difference between the top of the wire inserted into the solder ball and the copper plate. It was found from the analysis that the relationship between the crack area ratio and the increase in the potential difference was given by a single formula for all the conditions assumed in this study. As an experimental verification, a cyclic tensile test was carried out for the interface between Sn-3Ag-0.5Cu lead-free solder balls and a plate specimen of pure copper. Similar relationship between the crack area ratio and the increase in the potential difference held for the test. This suggests that the proposed method is applicable to the evaluation of actual interface cracks initiated in the specimens or in various electric packages.

DOI： 10.1109/EMAP.2006.4430649

Web of Science

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In conventional direct-current potential difference method (DC-PDM), uniform current is supplied far from a crack and the change in the potential difference by the crack is measured. The identification of the crack is done based on it. But in the case of a crack on the back surface, the change is not large enough and the identification is usually difficult. In this study, auxiliary current is supplied in addition to the remote uniform current and the improvement of identification of the crack existing on the back surface is investigated using the finite element method. Based on the analysis results, effect of the location of the auxiliary current and its strength on the measured potential difference is discussed.

DOI： 10.1299/jsmemecjo.2006.1.0_767

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmezairiki.2006.0_647

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Society of Materials Science, Japan  

The microscopic plastic deformation and the surface roughening behavior of free surface of polycrystalline aluminum sheet during uniaxial tension were experimentally investigated. The free surface roughness profiles are measured during plastic deformation with a confocal laser-scanning microscope. The surface roughness curve was analyzed employing the autocorrelation function and simplified model of surface roughness curve. It is shown that the average inclination of the surface profile curve increases lineally with increasing applied strain, and the grain rotation out of the surface plane is dominant contributor to the surface roughness. The roughness in grains are less than 30% and the roughness of slip bands are less than 7% , respectively, of the total surface profile roughness. The wavelength of the surface roughness curve is about 5〜9 times the averaged grain size, which increases with the applied tensile strain. Discussions are made on the autocorrelation length, the wavelength of surface profile and the grain boundary position on the surface profile.

DOI： 10.2472/jsms.54.407

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00249206751?from=CiNii

Language：Japanese   Publishing type：Research paper (scientific journal)  

CiNii Article

CiNii Books

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

A simulation method for microscopic creep damage at grain boundaries in the fine-grain heat-affected zone of low-alloy steel welds involving high energy piping was proposed on the basis of the combination of elastic-creep FEM (finite element method) analysis and random fracture resistance modeling of the materials. The procedure to determine the initiation and growth-driving forces of small defects were briefly described. Then, a simulation procedure combining the stress distribution from elastic-creep FEM and the random fracture resistance model was proposed, and this procedure was applied to the simulation of the microscopic damage progress in a welded joint model test and in actual power piping. The results in terms of the simulated number density of small defects throughout the wall thickness were in good agreement with the observed results.

Scopus

researchmap

Language：Japanese   Publisher：The Society of Materials Science, Japan  

The microscopic plastic deformation behavior of aluminum sheet during uniaxial tension is experimentally investigated by a confocal laser-scanning microscope. The surface roughening is closely related to the inhomogeneity of polycrystalline metals, that is, to the inhomogeneous plastic deformation of respective grains. In order to clarify the deformation behavior of polycrystalline metals, new measuring methods and 4 types of strains of grains are introduced and inhomogeneous of strain of grains are investigated. Digital image processing technique is applied to the surface image taken by the CCD camera for measurement. It is shown that the grain-area strain, the maximum dimension and mean dimension strain, the grain-boundary length strain and the standard deviations of these parameters statistically increase in proportion to the applied strain. Discussions are made on the differences between these measuring methods of strain parameters of grains, variations of measured statistical results including comparison with equilateral polygon model during tensile deformation.

DOI： 10.2472/jsms.53.473

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00239810968?from=CiNii

Language：English   Publishing type：Research paper (international conference proceedings)  

A method of three-dimensional identification of a semi-elliptical surface crack by direct-current electrical potential difference method with a multiple-probe sensor was proposed and its validity was numerically examined. The condition of the surface crack embedded in a conductive plate was specified by the two-dimensional location of the crack center, (yc, z c), length and depth of the crack, c and a, and the surface and inward angles of the crack plane, θsur and θ in. Identification was carried out based on the distribution of the electrical potential difference around the crack measured on the surface of the plate with the "multiple-probe sensor" which is composed of many probes aligned in two orthogonal directions. The location, (yc, zc), and surface angle, θsur, were evaluated using the line and point symmetries of the potential difference distribution. The inward angle, θin, was determined by the magnitude of symmetry of potential difference distribution with reference to the evaluated crack line. Finally, length and depth of the crack, c and a, were determined using the exact solution of potential difference for an inclined inner elliptical crack which yields similar potential difference to that of the inclined semi-elliptical surface crack. The validity of the method was numerically confirmed by carrying out the evaluation based on the result obtained by finite element analysis.

DOI： 10.1115/PVP2004-2245

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

Microscopic plastic deformation behavior of aluminum sheet during uniaxial tension is experimentally investigated by a confocal laser-scanning microscope. The surface roughening is closely related to the inhomogeneity of polycrystalline metals, that is, to the inhomogeneous plastic deformation of respective grains. Image measuring method of rigid rotation of grain is proposed. It is shown that the averaged grain rotation on the surface plane is much less than the averaged grain rotation out of the surface plane. The averaged grain rotation, the grain-area strain and the mean size strain and the standard deviations of these parameters increase statistically in proportion to the applied strain. The grain rotation in the material is less than that on the surface, thus it is considered that deformation inhomogeneity of grains in the material is less than that of grains on the surface of the material. This fact may indicate that the surface roughness is mainly affected by inhomogeneous deformation of the surface layer. Discussions are made on the grain rotation, the inhomogeneous deformation of the grains and the free surface roughening mechanism.

Web of Science

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A method of evaluation of six components of grain strain in polycrystalline metal was proposed. In the present method, the electron backscattered diffraction (EBSD) technique and the digital image processing were efficiently combined. Four components of grain strain, ε_x, ε_y, ε_z and γ_xy were evaluated based on the change in average aspect ratio of the number of pixels inside the grain which was obtained by an optical microscope and digital image analysis, where xy-plane is set on the specimen surface and z-axis is directed perpendicularly to the surface. The other two components, γ_yz, γ_zx, were calculated by taking into consideration the restriction of plastic deformation of each grain which was derived on the assumption that the plastic deformation occurred by crystallographic slipping on a single set of slip plane. An angle of the slip planes was 3-dimensionally identified by observation of the slip line by a scanning electron microscope and EBSD technique. Grain strain of polycrystalline copper during tension was evaluated by the proposed method and the results were discussed from the viewpoints of the distribution of grain strains and the deformation restriction by neighboring grains.

DOI： 10.1299/kikaia.69.972

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00229769016?from=CiNii

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Relationship between the slip line and the orientation of grains in polycrystalline copper during tensile plastic deformation is studied. Slip plane of each grain is calculated from the orientation obtained using EBSD technique, and the slip line of specimen surface is observed by SEM image. A method of estimation of active slip plane in each grain of polycrystalline copper during tensile plastic deformation is proposed based on the experimental results. Direction of slip line is calculated from the geometrical relationship between the specimen surface and the slip plane whose orientation is obtained using EBSD method. The estimated results and the observed results are compared by use of their correlation factor. The constraint between grains in the normal direction to the specimen surface is expected to be smaller than that between grains in the surface plane. Namely, the active slip plane is decided from the condition that the component of the specimen inward direction or the direction on the specimen surface of the shearing stress on the slip plane is maximum. It is also shown that the small size grain deforms on the slip plane whose orientation is close to the active slip plane of the neighboring grain with the maximum size. The estimated results are in good agreement with the experimental results.

DOI： 10.1299/kikaia.69.924

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00208632522?from=CiNii

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

Change in crystal orientation and strain of individual grains during tensile plastic deformation are studied to clarify on the microscopic deformation behavior of polycrystalline copper. The orientation of grain is measured by electron backscatter diffraction technique in the scanning electron microscope. The principal strain of grain is also measured by obtaining the approximated ellipse of strain distribution. The deformation of grains dependent on their initial orientation and the rotation of the principal strain during uniaxial tension are clarified.

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

The change in the surface morphology of polycrystalline titanium during tensile plastic deformation is studied mainly using the scanning probe microscope. The observation shows that slip occurs mainly near grain boundary at the strain range of epsilon&lt;0.05. The slip develops with the applied strain, and the slip on the second slip system or the crossing of slip lines appear. The surface roughness increases linearly with the applied strain. The height difference between the grain boundary area and the inner grain area also increases with the applied strain, though the increasing rate decreases after the applied strain of about 0.3. The nano-scale height difference of the surface step between slip lines increases with the applied strain, though it remains almost constant after the applied strain of 0.4.

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：EAST CHINA UNIV SCIENCE AND TECHNOLOGY PRESS  

Creep cavities were observed in smooth bar and notched plate specimens of low alloy steel. The material was specially heat-treated to obtain the fine grain structure in the heat-affected zone adjacent to the weld of actual pipes in fossil power boiler. Creep tests were carried out and the interrupted specimens were made for observation in addition to the ruptured 19 specimens. The distribution of cavities was observed by scanning electron microscope on the cross-section of specimens. The areal density, size, and total length of cavities were measured in each specimen and their increasing rates against time were discussed. Change in the distribution of cavities on the cross-section of notched specimens was compared with the stress distribution obtained by finite element analysis and a method of prediction of cavity distribution was proposed.

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

CiNii Article

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SOC EXPERIMENTAL MECHANICS INC  

Creep-fatigue tests of Type 304 stainless steel were carried out using smooth bar specimens. Cavities, which were initiated on grain boundaries inside the specimens, were observed on the cross-section. From the early stage of creep-fatigue life, cavities were initiated on grain boundaries one after another without reference to the direction of grain boundaries against the stress axis. However, the only cavities that existed on grain boundaries perpendicular to the stress axis grew. Moreover, four kinds of creep damage parameters, area fraction of cavities, areal cavity density, fraction of cavities on grain boundary lines, and A-parameter, were evaluated, and the results were discussed taking into account the physical meaning of each parameter.

Web of Science

researchmap

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Society of Materials Science, Japan  

In order to investigate the fracture process of CFRP with high toughness, a plate specimen of a uni-directionally reinforced AS4/PEEK is subjected to transverse tension at room temperature. The results obtained are summarized as follows ; (1)At 83% of fracture stress, small cracks are initiated along the interfaces of fiber and matrix in a group on or near the edge of specimen. (2)The cracks are semi-circular and they are arrested just after the initiation. (3)Although the number of the cracking regions increases as the applied stress increases, the area of each cracking region does not grow due to the crack arrest. (4)The boundary element analysis and the finite element analysis reveal that the arrest is caused by the cylindrical shape of the interface. (5)The cracks restart to grow and make coalescence when the stress field near the crack tip satisfies the condition of crack kinking. (6)The main crack formed brings about the specimen breaks down when the stress intensity factor reaches the macroscopic toughness, which is evaluated by DCB specimen.

DOI： 10.2472/jsms.48.1022

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00063348118?from=CiNii

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A method for evaluating the distribution of electrical potential around multiple spherical defects was proposed. As the method is based on the known solution for a single defect, the electric field can be efficienly analyzed in comparison with the other methods, such as the finite element method. The electric field in a conductive material with multiple spherical defects at random locations is estimated by the method. The analysis shows that the increase in the potential difference normalized by the potential difference without defects, ΔV/V₀, is in proportion to the product of the volumetric density of defects and the mean of cubed defect radius, n_v [r³]_m. The universal relationship is independent of the location of defects and the distribution of defect radius. Thus, the damage due to the multiple defects can be evaluated by the increase in potential difference.

DOI： 10.1299/kikaia.65.693

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00059919001?from=CiNii

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Stress analysis was conducted for a transversely reinforced composite laminate with an edge crack in the matrix or along an interface by the boundary element method (BEM). The laminate is submitted to the tensile stress perpendicular to the laminate in plane strain condition. The results obtained are summarized as follows ; (1) When the laminate is composed of such two materials as don't show the free edge effect, the stress intensity factor (SIF) for a small edge crack coincides with that for a small inner crack. (2) In the case that the free edge effect is remarkable, when a crack is very small (or thort), the change in normalized SIFs, K₁ (K₁=K₁/K_lh, K_lh is SIF for a crack in a homogeneous orthotropic body) for a matrix crack and K₁, K₂ and K₁ for an interface crack depend on the magnitude of stress singularity by free edge effect. (3) As a crack becomes larger (or longer), K₁ for a matrix crack and K_i for an interface crack tends to converge on the constant values. The convergent values are calculated by the energy release rate for a crack in the homogeneous orthotropic body which has the same elastic constants as those of the composite macroscopically. (4) The magnitude of SIF for a small edge crack can be calculated by the stress distribution near the edge without a crack.

DOI： 10.1299/kikaia.65.538

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00059805069?from=CiNii

Language：Japanese   Publisher：The Society of Materials Science, Japan  

In order to investigate the fracture process of a sintered silicon nitride at high temperatures, tensile, static creep, and fatigue tests were carried out at temperatures from room temperature up to 1573K, and the fracture surface of each specimen was carefully observed by means of optical and scanning electron microscopes. Fracture of the silicon nitride can be classified into two types from the viewpoint of cracking morphology. One is"single cracking type"where only a single crack brings about the fracture. As the crack is initiated at the largest pre-existing defect, distribution and size of the defects greatly affect the fracture strength. The other is"multiple cracking type"where several cracks were observed on the fracture surface as well as on the specimen surface. As the cracks are initiated by viscous sliding of grassy phase along grain boundaries, pre-existing defects affest little the fracture strength. The latter type is apt to appear in the tests with lower tensile stress or lower stress rate at higher temperature.

DOI： 10.2472/jsms.48.173

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00059446088?from=CiNii

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Chin Acad Sci  

Creep-fatigue test was carried out using smooth round bar specimens of Type 304 stainless steel. Cavities and small cracks on the cross-section of the specimen were carefully observed by a scanning laser microscope. Moreover, direct current electrical potential method (DC-EPM) was applied in order to evaluate non-destructively the distribution of internal cracks. The distribution evaluated by DC-EPM agrees well with the actual one.

Scopus

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Stress analysis was conducted for a traversely reinforced composite plate with an interface crack at the center under tension in plane strain condition by the boundary element method (BEM). The results obtained are summarized as follows ; (1) When the normalized crack length, a=a/d, (a : crack length, d : thickness of matrix layer) is much smaller than unity, the magnitude of stress intensity factors (SIFs), K₁, K₂, and K_i=(K²₁+K²₂)^1/2, are close to the SIFs for an interface crack in a dissimilar infinite body. The crack is termed as the small crack for composite materials. (2) As a becomes larger, the normalized SIF, K_i decreases and shows the minimum near a=1, where K_i is the SIF, K_i, divided by the SIF for a homogeneous orthotropic body composed of a Mode I crack, K₁h. It increases and converges on a constant value as a increases. (3) The energy release rate calculated from the convergent K_i coincides with that of the crack in a homogeneous orthotropic body where the elastic constants are determined by a mixture of those in the matrix and fibers. The crack is termed as the large crack for composite materials. (4) Since the region of oscillated stress distribution is confined in the vicinity of the crack tip, the stress intensity is represented by K_i, of which values are nearly equal to the SIF of the large crack in a homogeneous orthotropic body.

DOI： 10.1299/kikaia.63.2338

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00050234615?from=CiNii

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Stress analysis is conducted for a traversely reinforced composite with a Model 1 crack in plane strain condition using the boundary element method (BEM). The crack is introduced in the matrix at the center of the layered composite plate. The results obtained are summarized as follows. (1) When the normalized crack length, a^*=a/d, (a : crack length, d : thickness of matrix layer) is much smaller than unity, the high stress region near the crack tip is confined to the matrix. The magnitude of stress intensity factor (SIF), K, is close to K₀ for a homogeneous body composed of a single matrix material. The crack is called a small crack for composite materials. (2) As a^* becomes longer, the normalized SIF, K^*=K/K₀, decreases due to the constraint by the adjacent fibers. K^* shows a minimum near a^*=1 and increases when a^* increases. (3) K^* tends to be saturated as a^* exceeds 5. The energy release rate calculated by the asymptotic magnitude of K^* coincides with that of the homogeneous orthotropic body where the elastic constants are determined by a mixture of those in the matrix and fibers. The crack is called a large crack for composite materials.

DOI： 10.1299/kikaia.63.2077

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00049752588?from=CiNii

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The electric field in a conductive material with multiple circular cracks is analyzed by means of the crack-flow modification method (CFMM). It is found that the increase in the potential difference of the cracked meterial normalized by the potential difference without cracks, ΔV/V₀, is in proportion to the product of the effective volumetric crack density and the mean of the cubed crack radius, n_eff[γ³]_m. This universal relationship is also valid for multiple semi-circular cracks on the surface of the material and gives the physical meaning of damage detected by the direct current electrical potential method.

DOI： 10.1299/kikaia.63.2235

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00049752779?from=CiNii

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ASME  

Creep-fatigue tests were conducted using smooth specimens of a Type 304 stainless steel at 923K through 1073K and the characteristics of small cracks were observed. The morphology of the fracture was classified into three types
(1) transgranular cracking on the specimen surface, which is similar to that in room temperature fatigue, (2) intergranular cracking on the specimen surface due to creep, and (3) intergranular cracking inside the specimen due to creep. Type (2) was mainly caused by grain boundary sliding at the specimen surface where the constraint was weak, while Type (3) was brought about by cavities due to grain boundary diffusion coupling with creep deformation of grains, which showed the shortest fatigue lives. The creep-fatigue failure map was constructed in terms of three types of cracking in the 3D-expression of tensile strain rate, compressive strain rate and temperature.

Scopus

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Analytical discussion was given on the relationships between actual cavity distribution and creep damage parameters such as volume fraction of cavities, effective cross-sectional area and the 'A' parameter. The relationships between cavity distribution and these damage parameters were derived using a very simple probabilistic model where creep cavities on a grain boundary facet were initiated and grew, depending only on the macroscopic stress (or strain rate) acting on the facet. The exact relationships were represented by Eqs. (16), (20) [or (23)] and (26), respectively. These expressions take into account the effect of the size and direction of grain boundary facets. Damage evolution during creep and creep-fatigue can be calculated using these equations.

DOI： 10.1299/kikaia.59.2074

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00022973115?from=CiNii

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

This paper deals with a method for predicting the three-dimensional distribution of internal defects from the two-dimensional observation of intercepted defects on an inspection plane by an inverse analysis. At first, the fundamental relationships between them were analytically derived on the basis of a statistical model where multiple penny-shaped cracks in an infinite body were intercepted by an inspection plane. The validity of the method was confirmed by a numerical simulation. It was, moreover, applied to small creep fatigue cracks distributing in a smooth specimen of a Type 304 stainless steel, and the volumetric density and the distribution of crack size were successfully evaluated.

DOI： 10.1299/kikaia.59.381

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00019660639?from=CiNii

Language：Japanese   Publisher：The Society of Materials Science, Japan  

Fracture process of creep fatigue in a Type 304 stainless steel at 923K can be divided into two types ; "crack initiation type" and "crack growth type". The former is characterized by multiple small cracks initiating one after another along grain boundaries on the specimen surface and coalescing each other at the late stage of failure life, when the material is subjected to relatively large strain ranges in slow tension-fast compression (so called c-p type) strain waveforms. This failure is mostly governed by crack initiation. The latter is distinctive of the initiation and growth of little coalescence, which is revealed under small strain ranges and/or in slow-slow (c-c type) or slow very slow (c-s type) strain waveforms. Therefore, the failure life is controlled by the growth rate of small cracks in this case. In this study, a numerical simulation was done based on a model of two kinds of driving forces for crack initiation and crack growth with random fracture resistance of grain boundaries, in order to distinguish between the two types of fracture process and to estimate the failure life in relation to the cracking behavior.

DOI： 10.2472/jsms.41.1545

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00017478090?from=CiNii

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In order to achieve the objective of securing the reliability of high-temperature components, it is necessary to establish a method for predicting the remaining life of their materials subjected to severe creep-fatigue damage. It was reported by the authors that multiple small cracks initiated along grain boundaries on the specimen surface at the very early stage of life in creep-fatigue and their growth and coalescence formed the main crack which induced the failure. Moreover, the process of small crack initiation and growth showed random behavior due to microstructural inhomogeneity. A stochastic model was proposed and the failure process was numerically simulated by means of the Monte Carlo method. This paper provides a scheme of the small-crack-simulation-method for the evaluation of remaining life of the materials in high-temperature components, which is an integration of our previous studies and is summarized in a flow chart.

DOI： 10.1299/kikaia.57.1732

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00010853924?from=CiNii

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

It is necessary for determination of crack size and shape by means of D.C. potential drop technique to know electric potential distribution at the surface of cracked body beforehand. The potential distribution on a body with semi-elliptical surface-crack is investigated in this paper. The results obtained are summarized as follows. (i) Exact distribution is derived as Eqs. (1)∼(3) for semi-infinite body with a semi-elliptical surface-crack. As it requires numerial integral to evaluate the potential, a simple approximation method (Eqs. (14) and (15)) is proposed for convenience. It is confirmed by numerical analysis that the error of approximation is very small. (ii) We propose an easy method to make a cracked body with an arbitrary crack shape and size for the calibration of electric potential distribution. Plate specimens with a semi-elliptical surface-crack are made of a wood metal, and the potential distribution is examined experimentally. The values measured coincide the solution of infinite body (see (i)) except that the crack depth is nearly equal to the thickness of plate. It implies that specimen's back surface affects fairly little on the potential distribution at the front surface.

DOI： 10.1299/kikaia.56.259

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00000700672?from=CiNii

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In order to elucidate the microstructural effect on initiation and growth of intergranular small cracks under creep-fatigue conditions, we discuss the randomness of grain-boundary length and inclination. This study consists of the following investigations; (1) the length and inclination of grain boundaries of a stainless steel, SUS 304, are measured by means of image analysing system; (2) a numerical generation method of polycrystal grains is developed on the basis of an isotropic grain growth model; and (3) the crack length and inclination are measured by means of an image analysing system under creep-fatigue conditions. The results obtained from each investigation are summarized as follows, respectively. (A) The grain-boundary inclination of the steel is uniformly distributed and the length between adjacent triple points has a wide scatter between 10 and 100 μm. The length and the inclination are independent of each other (B) The simulated length and inclination of grain-boundaries coincides well with the actual grains of the steel. This method is useful for the stochastic simulation of initiation and growth of microstructurally small cracks, which will be reported in the next paper. (C) Cracks preferentially initiate on the grain boundaries perpendicular to the stress axis by a span between adjacent triple points. The crack growth rate shows a little dependence on the crack tip angle.

DOI： 10.1299/kikaia.56.702

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00002568416?from=CiNii

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In order to clarify the effect of the compressive strain rate on initiation and growth of small cracks under creep-fatigue condition, the following tests were conducted using smooth specimens of Type 304 stainless steel at 650°C in air, (i) slow-tension and fast-compression (c-p type fatigue), (ii) slow-tension and slow-compression (c-c type fatigue), and (iii) slow-tension and very-slow-compression (c-s type fatigue). The results obtained are summarized as follows. (1) Multiple small cracks initiated and grew at random along grain boundaries being nearly perpendicular to the stress axis at each specimen surface. (2) The compression-going strain rate affected the crack initiation life and the crack density. The c-p type fatigue brought about the shortest initiation life and the highest crack density, and the c-s type fatigue did the longest and the lowest. (3) The crack growth rate was not influenced by the compression-going strain rate but was primarily governed by the tension-going strain rate. (4) The difference of life between c-p type and c-s type fatigue was caused by the difference of crack initiation life and crack coalescence. The highest crack density in the c-p type fatigue made the crack coalesce easily to bring about a long crack.

DOI： 10.1299/kikaia.56.575

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00001677843?from=CiNii

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Publ by ASME  

A stochastic model and a method of simulation of the initiation and the early propagation of creep-fatigue small cracks along grain boundaries were proposed. In the model, grain boundaries between two adjacent triple points were projected and linked on a straight line perpendicular to the applied stress axis, and their length was given as random variables of a normal distribution. The grain boundaries had their own fracture resistances, the magnitudes of which were given as uniform random numbers. The fracture resistance of each grain boundary decreased by a constant magnitude corresponding to the driving force of one fatigue cycle. When the resistance became zero or a negative value, the grain boundary was assumed to fracture and to yield an intergranular facet of small crack.

Scopus

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A stochastic model and a method of simulation of the initiation and the early propagation of creep-fatigue small cracks along grain boundaries were proposed. In the model, grain boundaries between two adjacent triple points were projected and linked on a straight line perpendicular to the applied stress axis, and their length was given as random variables of a normal distribution. The grain boundaries had their own fracture resistances, the magnitudes of which were given as uniform random numbers. The fracture resistance of each grain boundary decreased by a constant magnitude corresponding to the driving force of one fatigue cycle. When the resistance become zero or a negative value, the grain boundary was assumed to fracture and to yield an intergranular facet of small crack. Based on this model, a numerical calculation was done for a smooth specimen of 304 stainless steel subjected to the slow-fast strain cycle of 1%-total strain range at 923K in a vacuum. The result of simulation on crack density, cumulative probability of crack length, and crack propagation rates coincided with the experimental results.

DOI： 10.1299/kikaia.54.1312

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00220856098?from=CiNii

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In order to investigate crack propagation behavior of thermal fatigue on the basis of non-linear fracture mechanics, crack propagation tests were conducted for isothermal fatigue at several temperatures and for cyclic temperature fatigue. The results obtained were summarized as follows. (1) The fracture mechanics laws in isothermal fatigue dl/dN-ΔJ_f and dl/dN-ΔJ_c relations where dl/dN was crack propagation rate, ΔJ_f was fatigue J-integral range and was ΔJ_c was creep J-integral range) showed little dependence on temperature. (2) A simple evaluation method of the values of ΔJ_f and ΔJ_c in thermal fatigue was proposed. (3) Crack propagation under cyclic temperature could be divided into two types which were cycle-dependent and time-dependent. dl/dN had good correlations with ΔJ_f and ΔJ_c for each type, respectively. (4) The transient condition between two types was given by a function of ΔJ_f and ΔJ_c. (5) The same fracture mechanics laws were obtained in isothermal and cyclic temperature fatigue.

DOI： 10.1299/kikaia.53.1030

CiNii Article

CiNii Books

researchmap

Other Link： https://jlc.jst.go.jp/DN/JALC/00215095136?from=CiNii

researchmap

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Authorship：Lead author   Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Authorship：Last author   Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

J-GLOBAL

researchmap

Language：Japanese  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Javanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmecs.2021.59.02b5

CiNii Article

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmecs.2021.59.02d2

CiNii Article

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmecs.2021.59.02d1

CiNii Article

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)   Publisher：The Japan Society of Mechanical Engineers  

<p>To investigate effects of dislocation density on microscopic stress distribution and macroscopic stress-strain relation, we conducted crystal plastic homogenization finite element analysis of Ti-6242 alloy subjected to in-plane reverse loading with dislocation density calculation. As a result, Statistically Stored (SS) dislocation density increased with occurrence of slip deformation for all conditions. On the other hand, Geometrically Necessary (GN) dislocation density was less likely to accumulate at the interface in the parallel relationship between primary slip systems of hcp and bcc. Although GN dislocations only develop near the interface, a large increase in GN dislocation density affects the macroscopic stress-strain relation.</p>

DOI： 10.1299/jsmemecj.2020.J03115

CiNii Article

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Authorship：Lead author   Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmecs.2020.58.02c1

CiNii Article

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmecs.2020.58.03b3

CiNii Article

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Authorship：Lead author   Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Authorship：Lead author   Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：English   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

researchmap

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To evaluate the effect of non-uniform deformation on the elastic and viscous strain during unloading of the polymeric material, strain distribution after loading, unloading were measured by digital image correlation method. Local viscous strain was obtained by removing the elastic strain from total strain cased during unloading. Obtained results clarified that the strain recover in necked region was very small while those caused in necked surrounding region was large.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this study, biaxial compression tests along proportional and non-proportional strain paths were performed on binary titanium-niobium alloys (Ti-Nb alloys) of different niobium contents, in order to clarify the deformation behaviors of those alloys under biaxial loadings. The influences of strain path and niobium content upon the compressive deformation behavior were then investigated. It was found that there were differences on stress-strain relations of Ti-Nb alloys owing to the different primary plastic deformation mechanisms. The clear influence of strain path change on the compressive behavior of Ti-35Nb alloy was observed, probably because of the activation of new twin systems after the path change.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Tensile tests were performed using plate specimens of self-reinforced polyethylene (SRPE) with short ultra-high molecular weight polyethylene (UHMWPE) fibers. The effect of fiber length on the properties was investigated. The specimens were made by hot-pressing the stacked HDPE films with short UHMWPE fibers distributed between each film at high temperature. The SRPE specimens showed much larger elastic modulus and tensile strength than monolithic HDPE specimens while their fracture took place at smaller strain than the monolithic HDPE specimens. Focusing on the effect of UHMWPE fibers, the specimens reinforced with longer fibers of 120 μm showed larger elastic modulus and tensile strength than those reinforced with shorter fibers of 60 μm. It was considered that the difference was attributed to the shearing force between fibers and matrix or pull-out force of fibers during tension taking into consideration the feet that lots of pulled-out fibers were observed on the fracture surface.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The elasto-plastic deformation behaviors of an IF steel sheet during stress path changes were investigated by performing nonproportional tension-compression tests. To evaluate the developed constitutive models in describing nonproportional deformation behaviors, numerical simulations of stress-strain responses were conducted for the same stress paths as the experiments. From the comparisons of experiment and calculations, it was found that the proposed constitutive model can describe well every deformation behaviors of an IF steel sheet during stress path changes.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Tensile test of high-density polyethylene (HDPE) was performed on the stage of digital holographic microscope (DHM) using plate specimen. The surface height of the order of nano meter was evaluated during tensile test and its change was discussed. Microscopic undulations were observed at small load and the undulations became larger at higher load or displacement. As the height distribution in observation area was similar throughout the tensile test, it seemed that the microscopic deformation was predictable from the surface undulation under small loadings.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Titanium alloys with beta-stabilizing elements have excellent characteristics such as high specific strength, good plastic formability and good corrosion resistance. However, the deformation behaviors of those alloys under biaxial loadings are still not clarified. In this study, uniaxial and biaxial compression tests of binary titanium-niobium alloys (Ti-Nb alloys) of different niobium contents were performed. The influences of niobium contents upon the compressive deformation behavior were then investigated. It was found that the primary plastic deformation mechanism changed with the niobium content and with deformation pattern. As a consequence of that, the different type of anisotropic hardening appeared. The niobium content dependency of constitutive relation of Ti-Nb alloys was then discussed using equivalent stress variation based on an anisotropic yield function and plastic work.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

researchmap

Language：Japanese   Publisher：The Japan Society for Technology of Plasticity  

DOI： 10.9773/sosei.56.129

CiNii Article

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The compressive deformation behavior in micro areas of industrial pure titanium was investigated, by using a new method in which the deformation constraints from the neighboring areas were reduced by fabricating micro parallel grooves or V-shaped cross-section grooves, by focused ion beam machining. Uniaxial compression test was performed in the direction parallel to the grooves, and the deformation behavior in the areas between the grooves was observed by scanning electron microscopy. The parallel grooves were fabricated to across the deformation twin that appeared by pre-compression, and then the influence of deformation constraint on twinning was discussed. Meanwhile, the V-shaped cross-section grooves were fabricated on several grains to examine the crystal orientation dependency of the deformation of the micro areas. In both cases, the possibility was found to change the primary deformation mechanism in the areas by fabricating micro grooves.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Metastable beta type titanium alloys have been attracting attention in various industrial fields because of their special properties such as high specific strength, good formability, high corrosion resistance, and biocompatibility. However, plastic deformation characteristics of the titanium alloys have scarcely been clarified especially under biaxial loading conditions, despite of their importance on metal forming processes. In the present study, uniaxial and biaxial compression tests were performed on titanium-niobium (Ti-Nb) alloys with four different niobium contents, in order to investigate the influences of beta stabilizer content upon compressive deformations. The microstructure of Ti-Nb alloys was found to change from α, α' to p structure with increase of the niobium content. With this change of microstructure, the primary plastic deformation mechanisms were revealed to change from slip and stress-induced martensite to deformation twin and coarse slip with increase of the niobium content and thus the change influenced on the uniaxial and biaxial compressive plastic behaviors.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Tension-compression asymmetry of plastic deformation of magnesium alloys has been known to affect plastic formability in several metal forming processes. However, in most of works on the tension-compression asymmetry, the result of uniaxial tension was compared with that of uniaxial compression. In the present study, the plastic deformation behavior of AZ31 magnesium alloys in uniaxial tension was investigated and compared with those in equi-biaxial compression, in which the macroscopic deformation was equivalent to that of uniaxial tension. It was found that the equi-plastic work point obtained by equi-biaxial compression was on the same isotropic yield curve with that by uniaxial tension, in the early stage of plastic deformation. The crystal orientation measurement results also revealed that the twin area fractions as well as active twin systems by uniaxial tension were almost the same with those by equi-biaxial compression. These results imply that the difference between deformation patterns by uniaxial tension and by uniaxial compression is primary cause of the tension-compression asymmetry of magnesium alloys.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A tensile test of pure titanium plate specimen was performed on the stage of digital holographic microscope, and a change in the height of each grain on the surface was evaluated during the tests. The load was increased stepwise in the tensile test and the distribution of height change of each grain was evaluated at all steps in nanometer order. The identification of region before and after each loading step was done by the Digital Height Correlation Method (DHCM). The height change of each grain between low loading levels corresponded to that between relatively high loading levels, which suggests that the height change in plastic deformation occurred mainly by crystallographic slips can be predicted by that in elastic deformation. Slip lines after the plastic deformation were observed and the correlation of the slip lines and height change of the grain was discussed.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The direct-current potential difference method (DC-PDM) is an inspection technique to evaluate defects in structures. Although the method needs large direct current and relatively large equipment, many studies on the applicability of DC-PDM to non-destructive inspection have been performed because of low cost, cheap, and good reproducibility of results. DC-PDM has been applied to evaluate general wall thinning. But very few papers deal with the application of DC-PDM to local wall thinning. In this study, approximated solution for electric potential field analysis of a semi-ellipsoidal wall thinning existing on the back surface of a conductive plate was proposed and its validity was examined by comparing with the results by finite element method. The approximated solution agreed with the finite element analysis.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Polycrystalline metals are composed of grains with different crystal orientations and sizes, and show inhomogeneous elastic-plastic deformation behavior. Especially for grains on the surface, the inhomogeneous deformation appears accompanied by the change in the height distribution. On the other hand, recently, digital holographic microscope is used to measure the height distribution on the materials surface with high accuracy in a short time. In this study, a cyclic tensile test of polycrystalline pure titanium was carried out and the change in the height distribution was studied using the digital height correlation method. Increase in average height of each grain by unit load in elastic region correlated with those in plastic region, which suggests that the plastic deformation is predictable from the elastic deformation.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In the present study, a new method to reduce deformation constraint in a grain of industrial polycrystalline pure titanium was introduced, by fabricating micro parallel grooves in the grain by means of a focused ion beam method. Uniaxial compression test was then performed in the direction parallel to the grooves, and the influence of reduced deformation constraint upon the characteristics of plastic deformation in the area between the grooves was investigated. The comparisons of the plastic deformation of the area with that without grooves revealed that the plastic deformation behavior as well as the deformed feature of the grain clearly changed by the presence and absence of the deformation constraint. The influence of deformation constraint upon the plastic deformation behavior of titanium grain was thus discussed with taking into consideration the crystallographic orientation.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Metastable β-type titanium alloys have many features such as high specific strength, good ability of plastic deformation, excellent corrosion resistance, biocompatibility, and low Young's modulus, which are useful in aerospace, biomedical and chemical industries. However, plastic deformation behaviors of metastable β-type titanium alloys under multi-axial compressive conditions have not been clarified. In the present study, four types of Ti-Nb alloys, Ti-20mass%Nb, Ti-30mass%Nb, Ti-35mass%Nb, and Ti-45mass%Nb were prepared. The uniaxial and biaxial compression tests with proportional strain paths were then performed on Ti-Nb alloys by using a biaxial compression testing machine. The results of uniaxial compression tests revealed that stress induced martensite transformation, deformation twin, coarse slip occurred on Ti-20 and 30Nb, Ti-35Nb, and Ti-45Nb, respectively. It was found by biaxial compression tests that the plastic deformation behavior including anisotropic hardening also changes with Nb content.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Detection of cracks initiated at pipe-flange welded part by using direct current potential difference method had been proposed and the related researches have been conducted. However, the evaluation of the position and shape of the crack has not been discussed. In this study, three-dimensional electric potential field analysis was carried out by finite element method assuming that crack was initiated at the interface between flange and weld metal and effect of the circumferential angle and the central position of the crack on change in potential difference at the boundary between weld metal and flange was evaluated. As a result, potential difference along the circumferential direction significantly changed around the both tips of crack and the position where potential difference shows extreme value approximately corresponded to the crack tips.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Gray cast iron is used as structural materials for many machines. It has been assumed homogeneous when its strength was evaluated. But it has a composite structure of perlite and graphite. It is necessary to consider its microstructure for accurate strength evaluation of reliable products. In this study, the distribution of graphite was observed by SEM and its area ratio A_G was evaluated in equally divided areas of parallel part of specimen. It was found that high A_G region corresponded to the fracture surface of tensile test. This fact suggests that the position of fracture surface is predictable by the distribution of graphite.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Recently, aluminum alloys are important structural materials because of high specific strength, lightweight, excellent in recycling. Various surface treatments for aluminum alloys have been developed for improvement of corrosion and wear resistances. Among them, environment-friendly anodizing in which oxide coating is formed on the material surface with easy process has been applied to a wide range of structural material. Also, plasma electrolytic oxidation (PEO) treatment was developed. Since KURACERA coating, it is classified PEO coating, is harder than anodic oxide coating, it is expected spacious application. In this study, in order to research the effect of oxide coating on deformation and fracture behavior, hard anodizing and KURACERA treated test specimen were observed with microscope during tensile test and the results were compared. The following results were obtained. With increasing the coating thickness, longitudinal elastic constant of coating, tensile strength and strain at fracture decreased. Longitudinal elastic constant of KURACERA coating was larger than that of hard anodic oxide coating. Also, since surface roughness was large in specimens with thick coating, more stress concentration occurred in thick coating larger and made necking and cracking easy.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this study, Direct-Current Potential Difference Method (DC-PDM) was proposed for quantitative evaluation of crack initiation and propagation on joining between copper-cored lead-free solder ball and copper plate specimen when copper plate specimen was subjected to cyclic tension. Finite element method was used for three dimensional potential analysis to clarify the relationship between change in potential difference and change in crack depth. In addition, influence of crack depth and joint condition on potential difference was considered. It was found that the relationship between crack size and potential difference is represented by a master curve with modification coefficient of core independently of joint condition.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Magnesium alloys have special features such as light weight, high specific strength, and good reusability. However, information on the compressive formability of magnesium alloys in multi-axial compressive stress conditions is still limited, nevertheless of their importance in plastic working processes such as forging and extrusion. In the present study, biaxial compression tests of initially isotropic cast AZ31 magnesium alloy were performed along proportional and non-proportional strain paths at room temperature. In the tests, the change of microstructure was observed using a scanning electron microscope. The results revealed that the compressive forming limit of AZ31 magnesium alloy was affected not only by the maximum shear stress but also by the hydrostatic stress. The area fraction of twin, which influences on the compressive flow behavior, was found to vary according to the strain paths.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

researchmap

Language：Japanese   Publisher：The Society of Materials Science, Japan  

DOI： 10.2472/jsms.62.472

CiNii Article

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Magnesium alloys have special features such as light weight, high specific strength and good reusability. However, information on the flow behavior and formability of magnesium alloys in multi-axial compressive stress conditions is highly limited, nevertheless of their importance for plastic working processes such as forging and extrusion. In the present study, the uniaxial and biaxial compression tests along proportional strain paths were conducted at room and at elevated temperatures, and thus the influence of strain paths and temperature upon mechanical properties and compressive forming limit were discussed. The results revealed that the flow stress scarcely changes with the test temperature in the range from 493 K to 523 K. On the other hand, the compressive forming limit was found to be dependent on the temperature as well as the strain paths.

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Titanium is one of materials with hexagonal close-packed structure, in which mechanical twinning often occurs and the plastic behavior becomes rather complicated. In recent years, the compression testing technique of a micropillar fablicated in a grain of metallic material has been developed for the purpose to study the deformation properties of a single crystal structure in a polycrystalline aggregate. In the present study, micropillars with rectangular cross section were fablicated in grains of industrial pure titanium by Focused Ion Beam (FIB) technique. The micro-compression tests were then performed in order to investigate the compressive behavior of single crystal micropillars. It was found that the load-displacement relations obtained by compression tests varied according to the crystal orientation and dimensions of the micropillars. Several traces of mechanical twinning were found to appear on the side surfaces of micropillars after the compression test, when the compressive force was applied in <0001> direction of the titanium grains.

CiNii Article

CiNii Books

researchmap

Language：Japanese  

CiNii Article

CiNii Books

researchmap

Language：Japanese  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Publisher：The Society of Materials Science, Japan  

DOI： 10.2472/jsms.61.S2

CiNii Article

researchmap

Language：Japanese  

CiNii Article

CiNii Books

researchmap

Language：Japanese  

CiNii Article

CiNii Books

researchmap

Language：Japanese  

CiNii Article

CiNii Books

researchmap

Language：Japanese  

CiNii Article

CiNii Books

researchmap

Language：Japanese  

CiNii Article

CiNii Books

researchmap

Language：Japanese  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

CiNii Article

CiNii Books

researchmap