Faculty Profiles - UEMORI Takeshi

Microscopic deformation of thin sheet of polycrystalline pure titanium under tension Reviewed

Naoya Tada, Kentaro Kishimoto, Takeshi Uemori, Junji Sakamoto

American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP 3 2020

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

Prediction of Fracture Location in Tensile Test of Short-Fiber-Self-Reinforced Polyethylene Composite Plates Reviewed

Slip Deformation of Crystal Grains in Semi-Circular Notched Thin Sheet Specimen of Pure Titanium during Tensile Test Reviewed

Takashi Ishida, Naoya Tada, Takeshi Uemori, Junji Sakamoto

2019.10

Naoya Tada, Ming Jin, Takeshi Uemori, Junji Sakamoto

Volume 3: Design and Analysis 3 2019.7

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

Effect of Lubrication and Forging Load on Surface Roughness, Residual Stress, and Deformation of Cold Forging Tools Reviewed

Karunathilaka, Tada, Uemori, Hanamitsu, Fujii, Omiya, Kawano

Metals 9 ( 7 ) 783 - 783 2019.7

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

Crystal Plasticity Finite Element Analysis of Effects of Microscopic Non-Uniform Deformation on Surface Roughness of Pure Titanium Sheet Reviewed

Takeshi UEMORI, Hiroki KAKIHARA, Naoya TADA

Journal of the Society of Materials Science, Japan 68 ( 6 ) 478 - 484 2019.6

Springback Suppression of AZ31 Magnesium Alloy Sheet in Draw Bending at Elevated Temperature Reviewed

Takashi Katahira, Takeshi Uemori, Tetsuya Yoshida, Michihiro Takiguchi, Tetsuo Naka, Komgrit Lawanwong, Fusahito Yoshida

Key Engineering Materials Vol.794 127 - 132 2019.2

Microscopic Elastic and Plastic Inhomogeneous Deformations and Height Changes on the Surface of a Polycrystalline Pure-Titanium Plate Specimen under Cyclic Tension Reviewed

Naoya Tada, Takeshi Uemori

Applied Sciences 8 ( 10 ) 1907 - 1907 2018.10

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

Cyclic stress and strain responses of AZ31 magnesium alloy sheet metal at elevated temperatures Reviewed

Takeshi Uemori, Takashi Katahira, Tetsuo Naka, Naoya Tada, Fusahito Yoshida

Procedia Manufacturing 15 1792 - 1799 2018

Effect of Contact Pressure Applied on Tool Surface during Cold Forging on Fatigue Life of Tool Steel Reviewed

UEMORI Takeshi

Procedia Manufacturing 15 488 - 495 2018

Dimensional Changes of Graphite Flakes and Fracture in Tensile Tests of Gray Cast Iron Reviewed

Naoya Tada, Takeshi Uemori

Conference papers, ASME 2018 Pressure Vessels & Piping Conference PVP2018-85214 2018

Elastic and Plastic Microscopic Undulation on the Surface of Polycrystalline Pure Titanium Under Tension Reviewed

Naoya Tada, Takeshi Uemori, Toshiya Nakata

JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME 139 ( 6 ) 1180 - 189 2017.12

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

Commercial pure titanium has been widely used in the aerospace, chemical, and biomedical industries because of its light weight, high corrosion resistance, high strength, high heat resistance, and good biocompatibility. Pure titanium takes the form of a hexagonal closed-pack structure with anisotropic elasticity and plasticity, with most of its components being polycrystalline aggregates having different crystal orientations. Small mechanical loading under elastic conditions therefore always induces inhomogeneous microscopic deformation, and the resulting inhomogeneity brings about various defects such as inhomogeneous plastic deformation, microcracking, and necking. It is therefore important to investigate the microscopic inhomogeneous deformation under elastic and plastic conditions. In this study, a plate specimen of commercial pure titanium was subjected to a tensile test on the stage of a digital holographic microscope (DHM), and the microscopic deformation of grains in the specimen under elastic and plastic conditions were observed and measured. During the test, the grains' height distribution was measured in a fixed area on the specimen's surface at each tensile loading step, and the correlation between height distributions at different loads was examined. We found from the measurements that each grain shows a different height change even under elastic conditions with a small load. This inhomogeneous height change was enhanced as the load was increased to plastic conditions. A strong correlation between the height changes under elastic and plastic conditions was also found. This result suggests that the microscopic deformation experienced under plastic conditions is predictable from that observed under elastic conditions.

DOI： 10.1115/1.4038012

Evaluation of Thin Copper Wire and Lead-Free Solder Joint Strength by Pullout Tests and Wire Surface Observation Reviewed

Naoya Tada, Takuhiro Tanaka, Takeshi Uemori, Toshiya Nakata

Crystals 7 ( 8 ) 255 - 255 2017.8

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

Copper wires have been attracting much attention for Large Scale Integration (LSI) bonding because of their excellent mechanical and electrical properties, in addition to their low material cost. The ends of these wires are usually joined to pads or through-holes on a printed circuit board, and lead-free soldering is one of the popular bonding methods. Since the deformation resistance of solder is lower than that of copper, especially in slow deformation due to creep, the strain tends to be increased in the solder and concentrated near the copper/solder joint interface. Thus, fracture frequently occurs at this interface and may influence the quality of the 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 wire from lead-free solder were carried out, and the pullout behavior of the wires was observed. The bonding strength was evaluated based on the actual bonded area on the copper wire surface. Finally, the strength of the thin copper wire/solder joint was summarized using the shear and tensile strengths of the copper/solder interface as well as the tensile strength of the copper wire.

DOI： 10.3390/cryst7080255

Time-Dependent Fracture of Copper-Cored Lead-Free Solder Ball and Nickel Rod Joints in Air, Distilled Water, and NaCl Solution Reviewed

Naoya Tada, Takeshi Uemori

Proceedings of Technical Papers - International Microsystems, Packaging, Assembly, and Circuits Technology Conference, IMPACT 2017- 319 - 322 2017

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE Computer Society

Solder joints have been used for electric connections in many electronic devices, and the joints are subjected to mechanical loadings such as static or cyclic tension/compression and shearing under various environments. Since the melting point of solder is very low comparing with the other normal metals, the time-dependent damage accumulation and fracture are often found in the solders even at the room temperature. In this paper, tensile tests of copper-cored lead-free solder ball and nickel rod joints were carried out in air, distilled water, and salt water environments using a unique testing device with permanent magnet. The time-dependent fracture of the joints was investigated from the viewpoint of damage accumulation.

DOI： 10.1109/IMPACT.2017.8255911

Description of closure of cyclic stress-strain loop and ratcheting based on Y-U model Reviewed

Fusahito Yoshida, Hiroshi Hamasaki, Takeshi Uemori

Key Engineering Materials 725 351 - 356 2017

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

This paper proposes a cyclic plasticity model to describe the closure of a cyclic stress-strain hysteresis loop based on the Y-U model. In this model, the backstress moves in a cyclic memory surface following a newly proposed kinematic hardening law. For this model just the same Y-U parameters can be used, and no additional material parameters are needed. By using a supplementary rule, this model is also able to describe ratcheting.

DOI： 10.4028/www.scientific.net/KEM.725.351

Effect of Hardening Rule for Spring Back Behavior of Forging Reviewed

Shinobu Narita, Kunio Hayakawa, Yoshihiro Kubota, Takafumi Harada, Takeshi Uemori

Procedia Engineering 207 167 - 172 2017

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

Geometrical discrepancy between formed part and designed one is one of the major problems for metal forming processes. Spring back behavior is one of the most important factors on the discrepancy, in not only sheet metal forming but also cold forging process. For cold forging process, it is difficult to observe the change in geometry of forgings before and after release of tools/dies, since the workpiece during forging is covered by tools/dies in most cases. Uncertainty remains for the precision on geometrical prediction after spring back of the cold forged part. In the present research, the diameters of extruded shaft at the bottom dead center and after the release of tools/dies were measured to investigate the spring back behavior in the cold forging process. As a result of experiment, the diameter of extruded shaft was increased at the bottom dead center by spring back and decreased after the release by re-extrusion. For these series of change in diameter, FE analyses using isotropic and kinematic hardening models were performed in order to evaluate influence of spring back on the material hardening models in forging process. For kinematic hardening model, Yoshida-Uemori model modified for large strain region was employed. As a result of calculation, both the isotropic and kinematic hardening models showed the similar tendency on the change in diameter with the experimental one.

DOI： 10.1016/j.proeng.2017.10.756

Theoretical predictions of fracture and springback for high tensile strength steel sheets under stretch bending Reviewed

Takeshi Uemori, Tetsuo Naka, Naoya Tada, Hidenori Yoshimura, Takashi Katahira, Fusahito Yoshida

Procedia Engineering 207 1594 - 1598 2017

Asymmetric-shaped bending of adhesively bonded sheet metals Reviewed

Taro Tokuda, Takeshi Uemori, Tetsuya Yoshida, Michihiro Takiguchi, Fusahito Yoshida

Key Engineering Materials 725 630 - 635 2017

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

In sheet metal industries, press-formed sheet elements are usually adhesively bonded together at the final stage of assembly. Instead of such a conventional process, the present authors proposed a new technique that first flat sheets are adhesively bonded together and then press-formed into the final products [1]. In previous study, the problem of the die-bending (V-bending and hat-shaped bending) with symmetrical shape has studied. In this study, asymmetric-shaped bending of adhesively bonded sheet metals was investigated by experiments and FEM analysis method. In the case of asymmetric-shaped bending, it was found that the timing of contact from the die corner to the die hypotenuse is early in the press-forming process compared with symmetrical bending (V-bending and hat-shaped bending). For the FEM analysis results, the maximum shear strain in asymmetric-shaped bending was smaller than that in symmetric-shaped bending at the hat-shaped side. Thus, the shape of the die has a large influence on the die-bending of adhesively bonded sheet metals.

DOI： 10.4028/www.scientific.net/KEM.725.630

Influence of Bauschinger Effect and Anisotropy on Springback of Aluminum Alloy Sheets Reviewed

Takeshi Uemori, Satoshi Sumikawa, Tetsuo Naka, Ninshu Ma, Fusahito Yoshida

MATERIALS TRANSACTIONS 58 ( 6 ) 921 - 926 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN INST METALS

For accurate springback calculations, the development of accurate constitutive equation Yoshida-Uemori model must always be taken into account. However, several springback calculations of other sheet metals by Yoshida-Uemori model have shown wrong agreements with the corresponding experimental data. The reason is why most of them have been calculated from the view point of the accuracy of Bauschinger effect without the strong anisotropy of sheet metal. In the present paper, we have investigated how the initial anisotropy affects the amount of springback for aluminum sheet metals with Bauschinger effect. Specifically, hat bending experiments in R.D. and T.D. were compared with the corresponding calculations. From the above mentioned comparisons, we found that the optimum combination of an anisotropic yield functions and Yoshida-Uemori model is very important for accurate springback analysis.

DOI： 10.2320/matertrans.L-M2017812

Cracking behavior of thin gold strip deposited on polycarbonate plate under Cyclic and stepwisely-increased tension Reviewed

Naoya Tada, Yafei Hu, Takeshi Uemori, Toshiya Nakata

MATEC Web of Conferences 108 01004 - 01004 2017

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