論文 - 多田　直哉

Crystal plastic homogenization finite element analysis of Ti-6242 alloy subjected to in-plane reverse loading 査読

Takeshi UEMORI, Naoya TADA, Junji SAKAMOTO

Bulletin of the JSME, Mechanical Engineering Journal   12 ( 2 )   24-00340   2025年4月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1299/mej.24-00340

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Effect of artificial defect on tensile properties of thin titanium alloy wire 査読

Junji SAKAMOTO, Naoya TADA, Takeshi UEMORI, Koyo OISHI

Bulletin of the JSME, Mechanical Engineering Journal   11 ( 6 )   24-00129   2024年12月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1299/mej.24-00129

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Crystal Grain Rotation during Tensile Test of Polycrystalline Pure Titanium Thin Sheet Based on Surface Height and Crystal Orientation 査読

Naoya Tada, Hiroaki Ohashi, Takeshi Uemori, Junji Sakamoto

Journal of Physics: Conference Series   2892   012002   2024年11月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1742-6596/2892/1/012002

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Elasticity-based prediction of inhomogeneous deformation of polycrystalline metals 招待

Naoya TADA

Extended abstract of Asia-Pacific Conference on Fracture and Strength 2024 (APCFS 2024)   P001   2024年11月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Creep Fracture and Damage Evaluation Based on the Distribution of Cavies on Grain Boundaries 招待 査読

Naoya Tada

Abstract book of 2024 International Symposium on Structural Integrity (ISSI 2024)   178   2024年11月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Method for Predicting Crack Size Using Amplitude Change in Titanium Alloy under Bending Vibration 査読

J. Sakamoto, N. Tada, T. Uemori

Book of Abstracts: Europian Conference on Fracture 2024 (ECF24)   472   2024年9月

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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荷重制御疲労試験時のTi-6Al-4V細線の破壞形態 査読

坂本惇司, 多田直哉, 上森武

チタン   72 ( 3 )   39 - 43   2024年7月

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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セルロースナノファイバー強化天然ゴムの繰返し引張特性と膨潤試験から得られるバウンドラバー体積分率の関係 査読

奥井 健斗, 多田 直哉, 上森 武, 坂本 惇司, 榊原 圭太

日本機械学会論文集   90 ( 932 )   24-00008   2024年4月

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1299/transjsme.24-00008

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アルミニウム合金の曲げ振動下の振動変化とき裂進展 査読

坂本 惇司, 多田 直哉, 上森 武

日本機械学会論文集   90 ( 930 )   23-00246   2024年2月

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/transjsme.23-00246

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アルミめっきホットスタンプ鋼板の抵抗スポット溶接シミュレーション 査読

福本学, 多田直哉

自動車技術会論文集   55 ( 1 )   107 - 112   2024年1月

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.11351/jsaeronbun.55.107

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Prediction of slip activity of crystal grains around semi-circular and semi-elliptical notches in thin-sheet specimens of pure titanium using formulated macroscopic stress distribution and crystal orientation 査読

Naoya Tada, Takeshi Uemori, Junji Sakamoto

Engineering Failure Analysis   153   107623   2023年11月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.engfailanal.2023.107623

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抵抗スポット溶接における分流数理モデルの構築 査読

福本学, 多田直哉

溶接学会論文集   41 ( 4 )   302 - 310   2023年11月

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.2207/qjjws.41.302

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Prediction of active slip system for commercially pure titanium sheet by crystal plasticity finite element analysis 査読

Takeshi UEMORI, Naoya TADA, Junji SAKAMOTO, Masatoshi DOI

Extended abstract of The Advanced Technology in Experimental Mechanics and International DIC Society Joint Conference 2023 (ATEM-iDICs '23)   19-G05   2023年10月

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Effect of Surface Roughness and Oxidation Treatment on Joint Strength between Aluminum Alloy and High-Density Polyethylene 査読

N. Tada, T. Uemori, J. Sakamoto

Extended Abstracts of 17th International Conference on Advances in Experimental Mechanics   2023年8月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Microscopic Inhomogeneous Deformation of Polycrystalline Metals in Elastic and Plastic Regions 査読

Naoya Tada

Abstract of Materials Today Conference 2023   O4C.1   2023年8月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Tensile properties and slip deformation behavior of pure titanium thin wire with a small diameter-to-grain-size ratio 査読

Junji Sakamoto, Naoya Tada, Takeshi Uemori

Materials Science and Engineering A   863   144532   2023年1月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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

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Slip Activity of Crystal Grains around Notch in Thin Sheet Specimen of Pure Titanium 招待 査読

Naoya Tada, Takeshi Uemori, Junji Sakamoto

Books of abstracts, 17th Asia-Pacific Conference on Fracture and Strength and 13th Conference on Structural Integrity and Failure   19 - 19   2022年12月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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複素数階微分法の純チタン板材の結晶塑性解析への適用 査読

上森武, 多田直哉, 坂本惇司

チタン   70 ( 2 )   158 - 163   2022年4月

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

J-GLOBAL

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Effect of Mechanical Surface Treatment and Post-treatment Polishing on Tensile Strength and Fatigue Life of High-speed Tool Steel 査読

N.Karunathilaka, N.Tada, T.Uemori, J.Sakamoto, R.Hanamitsu, M.Fujii, Y.Omiya, M.Kawano

International Journal of Peening Science and Technology   2 ( 1 )   35 - 60   2022年

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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Effect of resin lamination on tensile strength characteristics of SUS304 stainless steel thin film 査読

Junji Sakamoto, Naoya Tada, Takeshi Uemori

The International Journal of Advanced Manufacturing Technology   116 ( 3-4 )   1081 - 1088   2021年9月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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その他リンク： https://link.springer.com/article/10.1007/s00170-021-07510-8/fulltext.html

Prediction of the Fracture Location by Tensile Tests of Gray Cast Iron Based on the Dimensional Changes of Graphite Flakes 査読

Naoya Tada, Takeshi Uemori, Junji Sakamoto

Journal of Pressure Vessel Technology   143 ( 2 )   2021年4月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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

Naoya Tada, Kentaro Kishimoto, Takeshi Uemori, Junji Sakamoto

American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP   3   PVP2020-21715   2020年10月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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

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Finite element study of the effect of internal cracks on surface profile change due to low loading of turbine blade 査読

Junji Sakamoto, Naoya Tada, Takeshi Uemori, Hayato Kuniyasu

Applied Sciences (Switzerland)   10 ( 14 )   4883   2020年7月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 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

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短繊維強化複合材料の可視化データによる破壊予測技術 査読

多田直哉

プラスチックエージ   66 ( 799 )   53 - 56   2020年3月

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担当区分：筆頭著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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引張および疲労負荷を受ける純チタン細線の破壊予測に向けた直流電位差および直径分布の変化の分析 査読

坂本 惇司, 高木 佑輔, 上森 武, 多田 直哉

日本機械学会論文集   86 ( 882 )   19-00351   2020年2月

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本機械学会  

<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

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積層セラミックコンデンサのプレス変形挙動 査読

成瀬文雄, 多田直哉

FCレポート，日本ファインセラミックス協会   38 ( 1 )   30 - 34   2020年1月

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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

Takashi Ishida, Naoya Tada, Takeshi Uemori, Junji Sakamoto

Proceedings of the International Conference on Advanced Technology in Experimental Mechanics 2019 (ATEM ‘19)   ( 19-402 )   2019年10月

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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

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

Metals   9 ( 7 )   783 - 783   2019年7月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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

Naoya Tada, Ming Jin, Takeshi Uemori, Junji Sakamoto

Conference Papers, ASME 2019 Pressure Vessels and Piping Conference (PVP2019)   PVP2019-93546   2019年7月

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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純チタン薄板における微視的な不均一変形が表面あれに及ぼす影響に関する結晶塑性有限要素解析 査読

上森武, 柿原大毅, 多田直哉

材料   68 ( 6 )   478 - 484   2019年6月

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.2472/jsms.68.478

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

Naoya Tada, Takeshi Uemori

Applied Sciences   8 ( 10 )   1907 - 1907   2018年10月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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

Naoya Tada, Takeshi Uemori

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

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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

Nuwan Karunathilaka, Naoya Tada, Takeshi Uemori, Ryota Hanamitsu, Masahiro Kawano

Procedia Manufacturing   15   488 - 495   2018年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Cyclic Stress Strain Resposes of AZ31 Magnesium Alloy Sheet Metal at Elevated Temperature 査読

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

Procedia Manufacturing   15   1792 - 1799   2018年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Elastic and Plastic Microscopic Undulation on the Surface of Polycrystalline Pure Titanium under Tension 査読

Naoya Tada, Takeshi Uemori, Toshiya Nakata

Transactions of the ASME, Journal of Pressure Vessel Technology   139 ( 6 )   061403   2017年12月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

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

Naoya Tada, Takuhiro Tanaka, Takeshi Uemori, Toshiya Nakata

Crystals   7 ( 8 )   255 - 255   2017年8月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：MDPI AG  

DOI： 10.3390/cryst7080255

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

Naoya Tada, Yafei Hu, Takeshi Uemori, Toshiya Nakata

2017 INTERNATIONAL CONFERENCE ON MECHANICAL, AERONAUTICAL AND AUTOMOTIVE ENGINEERING (ICMAA 2017)   108   01004   2017年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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Springback analysis of aluminum alloy sheet metals by yoshida-uemori model 査読

Takeshi Uemori, Kento Fujii, Toshiya Nakata, Shinobu Narita, Naoya Tada, Tetsuo Naka, Fusahito Yoshida

Key Engineering Materials   725   566 - 571   2017年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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

Naoya Tada, Takeshi Uemori

IMPACT 2017 Proceedings   319 - 322   2017年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Tensile Test of Copper-Cored Lead-Free Solder Joints Using Non-Contact Type Testing Device with Permanent Magnets 査読

N. Tada, T. Uemori, T. Nakata

SEM Annual 2017 Proceedings   478 - 478   2017年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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

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

Procedia Engineering   207   1594 - 1598   2017年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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Microscopic Height Change on the Surface of Polycrystalline Pure Titanium Plate Under Cyclic Tension 査読

Naoya Tada

INTERNATIONAL DIGITAL IMAGING CORRELATION SOCIETY   267 - 271   2017年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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Evaluation of bonding strength of thin copper wire and lead-free solder by pullout tests 査読

Naoya Tada, Takuhiro Tanaka, Hirotsugu Tabata, Takeshi Uemori, Toshiya Nakata

Proceedings of Technical Papers - International Microsystems, Packaging, Assembly, and Circuits Technology Conference, IMPACT   164 - 167   2016年12月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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Elastic and plastic microscopic deformation of polycrystalline pure titanium under tension 査読

Naoya Tada, Yuki Doi

American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP   3   PVP2016-63268   2016年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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Microscopic deformation of polycrystalline pure copper wire during tension 査読

Naoya Tada, Yoshitaka Matsukawa, Takeshi Uemori, Toshiya Nakata

2015 10th International Microsystems, Packaging, Assembly and Circuits Technology Conference, IMPACT 2015 - Proceedings   229 - 232   2015年12月

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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Computational simulation of micro- to macroscopic deformation behavior of cavitated rubber blended amorphous polymer using second-order homogenization method 査読

Makoto Uchida, Naoya Tada

Key Engineering Materials   626   74 - 80   2015年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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FINITE ELEMENT ANALYSIS FOR THE EVALUATION OF CRACKS AT A PIPE-FLANGE WELDED PART BY THE DIRECT-CURRENT POTENTIAL DIFFERENCE METHOD 査読

Naoya Tada, Masaki Kosaka

PROCEEDINGS OF THE ASME PRESSURE VESSELS AND PIPING CONFERENCE - 2015, VOL 5   PVP2015-45484   2015年

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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Surface Undulation of Pure Titanium Grains under Elastic and Plastic Tensile Conditions 査読

Naoya Tada

Extended Abstracts of 10th International Conference on Advances in Experimental Mechanics   2015年

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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ポール側面衝突時の車体変形と四角形鋼管を用いたその実験的モデル化

小野 忠則, 清水 一郎, 多田 直哉, 田久保 宣晃

日本機械学会論文集   81 ( 826 )   14 - 00542-14-00542   2015年

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記述言語：日本語   出版者・発行元：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

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POTENTIAL DIFFERENCE DISTRIBUTION ON FLAT PLATE AROUND SEMI-ELLIPSOIDAL THINNING ON THE BACK SURFACE

Naoya Tada, Makoto Uchida, Manabu Nohara

ASME PRESSURE VESSELS AND PIPING CONFERENCE - 2014, VOL 5   PVP2014-28684   2014年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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Evaluation of Tensile Strength of Copper-Cored Lead-Free Solder Joints in Air, Distilled Water, and NaCl Solution Using Testing Device with Permanent Magnets

Naoya Tada, Hiroyasu Masago

IMPACT-EMAP 2014 Proceedings   237 - 240   2014年

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担当区分：筆頭著者,　責任著者  

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NON-DESTRUCTIVE DETECTION OF CRACK IN HDPE PLATE BY NANOMETRIC CHANGE IN SURFACE PROFILE

Naoya Tada, Makoto Uchida, Yoshitaka Matsukawa

PROCEEDINGS OF THE ASME PRESSURE VESSELS AND PIPING CONFERENCE - 2013, VOL 5   PVP2013-97732   2014年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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Micro-, meso- to macroscopic modeling of deformation behavior of semi-crystalline polymer 査読

Makoto Uchida, Naoya Tada

INTERNATIONAL JOURNAL OF PLASTICITY   49   164 - 184   2013年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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Remotely-Controlled Tensile Test of Copper-Cored Lead-Free Solder Joint in Liquid Using Permanent Magnet

Naoya Tada, Hiroyasu Masago

IMPACT-IAAC 2013 Proceedings   372 - 375   2013年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Investigation of Deformation Mechanism under Indentation Testing of Metastable Beta-type 査読

Ichiro SHIMIZU, Noriaki KIMURA, Naoya TADA, Yoshito TAKEMOTO

Proceedings of the 8th International Symposium on Advanced Science and Technology in Experimental Mechanics   ( 62 )   2013年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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枠無しプレスによる積層セラミックコンデンサーブロックの変形挙動

成瀬 文雄, 多田 直哉

日本機械学会論文集 A編   79 ( 800 )   442 - 454   2013年

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記述言語：日本語   出版者・発行元：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

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巨視的なひずみ勾配に対する特性変位関数を導入した２次均質化法に基づく有限要素法による変形解析法の構築

内田 真, 多田 直哉

日本機械学会論文集 A編   79 ( 806 )   1486 - 1503   2013年

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記述言語：日本語   出版者・発行元：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

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格子点配列マークを用いた平行溝付多結晶純チタン試験片の往復曲げにおける微視的塑性変形評価

多田 直哉, 清水 一郎

日本機械学会論文集 A編   79 ( 800 )   420 - 432   2013年

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記述言語：日本語   出版者・発行元：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

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片状黒鉛鋳鉄の微視的構造を考慮した有限要素解析によるディーゼルエンジンシリンダブロックの強度評価

井口克之, 多田直哉, 清水一郎

日本機械学会論文集 A編   79 ( 799 )   281 - 293   2013年

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記述言語：日本語   出版者・発行元：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

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Study on Deformation of Rectangular Metal Tube during Dynamic Three-Point Bending for Modeling of Pole Side Impact of Vehicle

Tadanori Ono, Ichiro Shimizu, Naoya Tada, Nobuaki Takubo

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 ・・・   No.A122   2012年

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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

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Study on Compressive Forming Limit of Cast AZ31 Magnesium Alloy under Non-Proportional Strain Paths

Ichiro Shimizu, Naoya Tada, Daisuke Akiyama, Seiki Hirano

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 ・・・   61   No.0110 - 382   2012年

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記述言語：日本語   出版者・発行元：日本材料学会  

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

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Tensile Test of Small Lead-Free Solder Joint Using Permanent Magnet 査読

Naoya Tada, Ryo Nishihara, Hiroyasu Masago

2012 7TH INTERNATIONAL MICROSYSTEMS, PACKAGING, ASSEMBLY AND CIRCUITS TECHNOLOGY CONFERENCE (IMPACT)   346 - 349   2012年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.
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NON-DESTRUCTIVE CRACK DETECTION BY NANOMETRIC CHANGE IN SURFACE PROFILE USING DIGITAL HOLOGRAPHIC MICROSCOPE 査読

Naoya Tada, Makoto Uchida, Yuki Uenoyama

PROCEEDINGS OF THE ASME PRESSURE VESSELS AND PIPING CONFERENCE, PVP 2012, VOL 5   251 - 257   2012年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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Effect of Spherulite Size on Macroscopically Non-Uniform Deformation of Semi-Crystalline Polymer 査読

Makoto Uchida, Naoya Tada

Proceedings of PLASTICITY '12: The Eighteenth International Symposium on Plasticity and Its Current Applications   316 - 318   2012年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Computational Simulation of Polymer RVE Model under Boundary Condition with Macroscopic Strain Gradient 査読

M. Uchida, N. TADA

Proceedings of 4th International Conference on Computational Methods   ID197   2012年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Sequential evaluation of continuous deformation field of semi-crystalline polymers during tensile deformation accompanied by neck propagation 査読

Makoto Uchida, Naoya Tada

INTERNATIONAL JOURNAL OF PLASTICITY   27 ( 12 )   2085 - 2102   2011年12月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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リバース式差動回転直動変換機構を用いたプレス装置の開発 査読

清水 一郎, 關 正憲, 松井 崇史, 多田 直哉, 藤井 正浩, 吉田 彰

設計工学   46 ( 1 )   40 - 47   2011年1月

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本設計工学会  

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解説 デジタルホログラフィック顕微鏡を用いた材料表面特性評価 査読

多田直哉, 内田真

非破壊検査   60 ( 10 )   592 - 598   2011年

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担当区分：筆頭著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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解説 直流電位差計測に基づくき裂評価手法の展開

武尾文雄, 多田直哉

非破壊検査   60 ( 10 )   572 - 578   2011年

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担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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解説 直流電位差法を用いた配管内外表面き裂と肉厚評価の最新技術 査読

多田直哉

検査技術   16 ( 5 )   21 - 28   2011年

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担当区分：筆頭著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本工業出版  

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A method of crack detection in the turbine blade using digital holographic microscopy (DHM) 査読

Naoya Tada, Seiichi Hamada, Tetsuo Teramae, Shin Yoshino, Takehiko Suzuki

American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP   5   211 - 216   2011年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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

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Influence of Plastic Anisotropy on Compressive Forming Limit of AZ31 Magnesium Alloy

Ichiro SHIMIZU, Kosuke Okada, Seiki Hirano, Naoya TADA

Proceedings of International Symposium on Advanced Science and Technology in Experimental Mechanics (6th ISEM '11-Sendai/Kansai)   121   2011年

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Experimental Modeling of Vehicle Deformation in Pole Side Impact by Means of Lateral Compression of Rectangular Steel Tube

Tadanori Ono, Ichiro Shimizu, Naoya Tada, Nobuaki Takubo

Proc. International Conference on Advanced Technology in Experimental Mechanics 2011 (ATEM '11)   2011 ( 10 )   OS09-4-2 - 4-2-1"   2011年

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記述言語：英語   出版者・発行元：一般社団法人日本機械学会  

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Deformation Behavior of Multilayered Ceramic Sheets with Printed Electrodes under Compression

Fumio Naruse, Naoya Tada

Proc. International Conference on Advanced Technology in Experimental Mechanics 2011 (ATEM '11)   6 ( 6 )   OS18F003 - 770   2011年

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記述言語：英語   出版者・発行元：一般社団法人 日本機械学会  

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

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Effect of Distribution of Spherulite on the Non-Uniform Plastic Deformation Behaviour of Semi-Crystalline Polymer

M. Uchida, N. Tada

Computational Plasticity XI, Fundamentals and Applications (COMPLAS XI)   2011年

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Detection of stress corrosion cracking by direct-current potential difference method 査読

Naoya Tada, Makoto Uchida, Hiroki Maeda, Atsushi Hozuki

American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP   5   217 - 224   2011年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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

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積層複合体モデルに基づく結晶性高分子材料のミクロ・メゾスケールの変形挙動のモデル化

内田 真, 多田 直哉, 冨田 佳宏

日本機械学会論文集 A編   77 ( 778 )   902 - 915   2011年

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出版者・発行元：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

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Finite element simulation of deformation behavior of semi-crystalline polymers with multi-spherulitic mesostructure 査読

Makoto Uchida, Tsuruyo Tokuda, Naoya Tada

INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES   52 ( 2 )   158 - 167   2010年2月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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解説 高温における材料寿命予測法

多田直哉

検査技術   15 ( 10 )   23 - 29   2010年

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担当区分：筆頭著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本工業出版  

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解説 直流電位差法を用いたき裂評価技術の現状 査読

多田直哉, 浜田晴一

非破壊検査   59 ( 5 )   204 - 208   2010年

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担当区分：筆頭著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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NUMERICAL SIMULATION FOR IDENTIFICATION OF SEMI-ELLIPTICAL CRACK ON THE INNER SURFACE OF PIPE BY MEANS OF DIRECT-CURRENT ELECTRICAL POTENTIAL DIFFERENCE METHOD WITH MULTIPLE-PROBE SENSOR 査読

Naoya Tada, Makoto Uchida, Hiroki Ishikawa

PROCEEDINGS OF THE ASME PRESSURE VESSELS AND PIPING CONFERENCE 2009, VOL 5   257 - 263   2010年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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A Study on the Fatigue Life Evaluation of Vibration Insulator Considering the Effect of Creep 査読

Prabhakar Soma, Naoya Tada, Makoto Uchida, Kazunari Nakahara, Tetsuya Miyake

Conference Proceeding (Programme and Abstracts), International Rubber Conference & Exhibition 2010   426 - 429   2010年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Influence of Initial Texture on Plastic Behavior of Pure Titanium in Biaxial Compression 査読

Ichiro SHIMIZU, Junya IDEI, Naoya TADA

Proceedings of the 5th International Symposium on Advanced Science and Technology in Experimental Mechanics   2010年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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POTENTIAL DIFFERENCE AROUND SEMI-ELLIPTICAL CRACK ON THE OUTER SURFACE OF PIPE FOR NON-DESTRUCTIVE EVALUATION OF CRACK BY DC-PDM 査読

Naoya Tada, Makoto Uchida, Hiroki Maeda

PROCEEDINGS OF THE ASME PRESSURE VESSELS AND PIPING CONFERENCE 2010, VOL 5   215 - 222   2010年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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Plastic behaviour and forming limit during biaxial compressions of magnesium alloy AZ31 at room temperature

I. Shimizu, N. Tada

ICEM 14: 14TH INTERNATIONAL CONFERENCE ON EXPERIMENTAL MECHANICS, VOL 6   6   16001-1-16001-2   2010年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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The Effect of Heterogeneity of Microstructure on the Micro- to Macroscopic Non-Uniform Elasto-Viscoplastic Deformation Behavior of Polymeric Material

Makoto Uchida, Naoya Tada

Proceedings of PLASTICITY '10: The Sixteenth International Symposium on Plasticity and Its Current Applications   298 - 300   2010年

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Evaluation of Orientation-Dependent Geometry of Micro Triangular Indentation on Grain of Polycrystalline α-Titanium

Ichiro Shimizu, Naoya Tada, Takahisa Ishida

Programme & Abstracts Book of ICEM 2009 4th International Conference on Experimental Mechanics in conjunction with 8th Asian Conference on Experimental Mechanics, ICEM 2009 Organising Committee   7522   60 - 60   2010年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1117/12.851502

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Numerical Study on Reducing Methods of Static Strain along the Fillet on Upper Deck of Diesel Engine Cylinder Block 査読

Katsuyuki Iguchi, Naoya Tada, Ichiro Shimizu, Kouji Iwasaki

Proc. the 12th International Conference on Fracture   2009年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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A Fracture Mechanics Approach for Evaluating the Effects of Heat Aging on Fatigue Crack Growth of Vulcanized Natural Rubber 査読

Prabhakar Soma, Naoya Tada, Makoto Uchida, Kazunari Nakahara, Yoshifumi Taga

Proc. of the Asian Pacific Conference for Materials and Mechanics 2009, The Japanese Society of Mechanical Engineers   a138   2009年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Research and Education in the Field of Applied Solid Mechanics 査読

Naoya Tada

Proc. 2009 International Symposium on Total Engineering Education, East China University of Science and Technology   167 - 174   2009年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Regional Identification by Digital Height Correlation of Nanolevel Surface Profile

TADA N.

SEM 2009 Fall Symposium Technical Program, Advanced Image-Based Measurement Methods : Recent Developments and Applications in Engineering and Medicine   15 - 15   2009年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：The Society for Experimental Mechanics, Inc.  

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Electric Field Analysis of Simultaneous Evaluation of Crack on Inner Surface of Pipe and Pipe Wall Thickness Using Direct-Current Potential Difference Method of Multiple-Probe Type 査読

Naoya Tada, Makoto Uchida

Abstract book the 12th International Conference on Pressure Vessel Technology, Korean Society of Pressure Vessels & Piping   563 - 570   2009年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Evaluation of Geometry of Semi-Elliptical Crack by Direct Current Potential Difference Method Based on Potential Difference Distribution in Two Orthogonal Directions

Makoto Uchida, Hiroki Ishikawa, Naoya Tada

Conference Handbook of the 13th Asia-Pacific Conference on Non-Destructive Testing, The Japanese Society for Non-Destructive Inspection   248   248 - 248   2009年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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APPLICATION OF DIRECT-CURRENT POTENTIAL DIFFERENCE METHOD TO EVALUATION OF VARIOUS DAMAGES IN CONDUCTIVE MATERIALS 査読

Naoya Tada

PROCEEDINGS OF THE ASME PRESSURE VESSELS AND PIPING CONFERENCE, VOL 5   183 - 189   2009年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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ヘッドボルトの締め付けによって生じるディーゼルエンジンシリンダブロックのトップデッキ隅部における静ひずみに関する有限要素解析

井口 克之, 多田 直哉, 清水 一郎

日本機械学會論文集. A編 = Transactions of the Japan Society of Mechanical Engineers. A   74 ( 744 )   1053 - 1059   2008年8月

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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熱応力駆動型引張り試験による純チタン切欠き薄膜の引張り

多田 直哉, 清水 一郎, 上森 一真, 多田 寛之

日本機械学会論文集. A編 = Transactions of the Japan Society of Mechanical Engineers. A   74 ( 737 )   137 - 144   2008年1月

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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純チタンにおける微小圧痕形状に及ぼす結晶方位の影響 査読

清水 一郎, 多田 直哉

材料   57 ( 3 )   249 - 254   2008年

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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ゴム充てん結晶性ポリマーの変形挙動に及ぼす引張方向とひずみ速度，メゾ構造の影響 査読

内田 真, 北乘 吉晴, 多田 直哉

材料   57 ( 3 )   243 - 248   2008年

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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Experimental study of three-dimensional identification of semi-elliptical crack on the back surface by means of direct-current electrical potential difference method of multiple-point measurement type 査読

Naoya Tada, Makoto Uchida, Akira Funakoshi, Hiroki Ishikawa

PROCEEDINGS OF THE ASME PRESSURE VESSELS AND PIPING CONFERENCE 2007, VOL 5   Paper No.PVP2007-26299   143 - 150   2008年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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Computational Simulation of Mechanical Behavior of Semi-Crystalline Polymers with Randomly Distributed Rubber Particles 査読

M.Uchida, N.Tada, Y.Tomita

Proc. International Conference on Computational & Experimental Engineering and Sciences ICCES'08, Tech Science Press   405 - 411   2008年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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解説 マルチスケールで信頼性・健全性評価が可能な直流電位差法 査読

多田直哉

検査技術   13 ( 9 )   1 - 7   2008年

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担当区分：筆頭著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本工業出版  

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Monitoring of Interface Crack between Solder Ball and Copper Plate Subjected to Cyclic Tensile Loading under Fluctuating Temperature by Direct Current Potential Difference Method 査読

Naoya Tada, Yusuke Ezaki

2008 EMAP CONFERENCE PROCEEDINGS   232 - 235   2008年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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Effect of Bead Position on Stress Distribution along the Fillet on Upper Deck of Diesel Engine Cylinder Block with Dry Liner Structure 査読

Katsuyuki Iguchi, Naoya Tada, Ichiro Shimizu, Kouji Iwasaki

Proc. ACMFMS2008, Shimane University, Japan   409 - 412   2008年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Strain Path Dependent Plastic Behavior of Aluminum by Unidirectional and Cyclic Biaxial Compressions 査読

Ichiro Shimizu, Naoya Tada

Proc. ACMFMS2008, Shimane University, Japan   165 - 168   2008年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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複数の電流供給端子を用いた直流電位差法による背面き裂の評価に関する有限要素解析

内田 真, 船越 亮, 石井 祐介, 多田 直哉

非破壊検査 = JOURNAL OF THE JAPANESE SOCIETY FOR NON-DESTRUCTIVE INSPECTION   56 ( 12 )   643 - 648   2007年12月

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記述言語：日本語   出版者・発行元：一般社団法人 日本非破壊検査協会  

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

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ゴム粒子を充填した結晶性ポリマーの変形挙動のマルチスケールモデリング

内田 真, 多田 直哉, 冨田 佳宏

日本機械学会論文集. A編 = Transactions of the Japan Society of Mechanical Engineers. A   73 ( 725 )   73 - 79   2007年1月

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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２ １／４Ｃｒ‐１Ｍｏ鋼溶接部Ｔｙｐｅ ＩＩＩおよびＴｙｐｅ ＩＶクリープ損傷のミクロ・マクロシミュレーション 査読

川島 扶美子, 猪狩 敏秀, 時吉 巧, 多田 直哉

材料   56 ( 2 )   106 - 113   2007年

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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Tensile test of notched metal film by means of thermal expansion of plastics 査読

Naoya Tada, Ichiro Shimizu, Kazumasa Uemori

2007 INTERNATIONAL CONFERENCE ON ELECTRONIC MATERIALS AND PACKAGING   114 - 120   2007年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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Plastic behavior of polycrystalline aluminum during biaxial compression with strain path change 査読

Ichiro Shimizu, Naoya Tada

ENGINEERING PLASTICITY AND ITS APPLICATIONS FROM NANOSCALE TO MACROSCALE, PTS 1 AND 2   340-341   883 - +   2007年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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,

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直流電位差法を用いたはんだボール/銅接合界面き裂のモニタリングに関する有限要素法解析

多田 直哉, 安藤 貴宏, 神谷 徹

日本機械学会論文集. A編 = Transactions of the Japan Society of Mechanical Engineers. A   73 ( 724 )   1825 - 1831   2006年12月

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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多点測定型直流電位差法による表面き裂の3次元的同定に関する実験的検討

多田 直哉, 岩本 淳, 岡田 眞禎

日本機械学会論文集. A編 = Transactions of the Japan Society of Mechanical Engineers. A   72 ( 715 )   332 - 339   2006年3月

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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Evaluation of interface crack between solder ball and copper based on the non-destructive monitoring of direct current potential difference 査読

Naoya Tada, Takahiro Andou

2006 INTERNATIONAL CONFERENCE ON ELECTRONIC MATERIALS AND PACKAGING, VOLS 1-3   659 - 665   2006年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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

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3615 補助電流を付加した直流電位差法による背面き裂の同定に関する有限要素法解析(S13-4 疲労特性と設計,S13 実用構造材料の疲労問題と健全性評価)

多田 直哉, 船越 亮, 石井 祐介

年次大会講演論文集   2006   767 - 768   2006年

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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P65 圧痕の形状変化に基づく材料表面の3次元的ひずみ評価に関する解析的検討(GS1)

杉本 義展, 多田 直哉, 細井 康成

材料力学部門講演会講演論文集   2006   647 - 648   2006年

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

DOI： 10.1299/jsmezairiki.2006.0_647

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多結晶金属の引張塑性変形に伴う表面あれの自己相関関数による検討

宋 華林, 阿部 武治, 多田 直哉

材料   54 ( 4 )   407 - 413   2005年4月

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記述言語：日本語   出版者・発行元：社団法人日本材料学会  

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

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多結晶高純度アルミニウムの引張塑性変形に伴う微視的表面形状変化 査読

王 暁群, 阿部 武治, 多田 直哉, 清水 一郎

軽金属   55 ( 2 )   68 - 74   2005年2月

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：軽金属学会  

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Evaluation of Multiple Through-Cracks with Random Angles by Direct Current Electrical Potential Difference Method 査読

Naoya TADA

Proc. the Third US-Japan Symposium on Advancing Applications and Capabilities, The American Society for Nondestructive and Testing   2005年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Tensile Test of Thin Titanium Plate Actuated by Thermal Expansion of Polycarbonate 査読

Naoya Tada, Ichiro Shimizu, Keigo Kanamura, Hiroyuki Tada

Proc. the Sixth International Congress on Thermal Stresses (Thermal Stresses 2005), Vienna University of Technology   2005年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Micro-macro damage simulation of low-alloy steel welds subject to type IV creep failure

T. Igari, F. Kawashima, T. Tokiyoshi, N. Tada

Acta Metallurgica Sinica (English Letters)   17 ( 4 )   393 - 399   2004年8月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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.

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走査型レーザ顕微鏡による多結晶アルミニウムの微視的塑性変形挙動の評価

宋 華林, 阿部 武治, 清水 一郎, 多田 直哉, 鳥居 太始之

材料   53 ( 5 )   473 - 480   2004年5月

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記述言語：日本語   出版者・発行元：社団法人日本材料学会  

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

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Three-dimensional identification of semi-elliptical surface crack by means of direct-current electrical potential difference method with multiple-probe sensor 査読

Naoya Tada, Masayoshi Okada, Jun Iwamoto

American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP   471   85 - 92   2004年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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

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Microscopic Damage Analysis of Welded Joints under Type III and Type IV Creep Failure 査読

T.Igari, F.Kawashima, T.Tokiyoshi, N.Nishimura, N.Tada

OMMI (Power Plant: Operation Maintenance and Materials Issues)   2004年

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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Observation of microscopic plastic deformation of polycrystalline aluminum during uniaxial tension by confocal laser-scanning microscope 査読

H Song, T Abe, Shimizu, I, N Tada, T Torii

ADVANCES IN ENGINEERING PLASTICITY AND ITS APPLICATIONS, PTS 1 AND 2   274-276   337 - 342   2004年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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EBSD法と画像処理を併用した多結晶銅の引張りにおける結晶粒の3次元的塑性ひずみの評価

近藤 了嗣, 阿部 武治, 多田 直哉

日本機械学会論文集. A編 = Transactions of the Japan Society of Mechanical Engineers. A   69 ( 682 )   972 - 979   2003年6月

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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EBSD法による多結晶銅の引張塑性変形における活動すべり面に関する検討

近藤 了嗣, 阿部 武治, 多田 直哉, 清水 一郎

日本機械学会論文集. A編 = Transactions of the Japan Society of Mechanical Engineers. A   69 ( 681 )   924 - 931   2003年5月

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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Numerical Simulation of the Microscopic Damage progress in Type IV Creep Failure of Low Alloy Steel Welds 査読

T.Igari, F.Kawashima, T.Tokiyoshi, N.Nishimura, N. Tada

Proc. Seventh Workshop on the Ultra-Steel, "Ultra Steel: Requirements from New Design of Constructions", National Institute for Materials Science   2003年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Orientation change measured by the EBSD method and the plastic deformation of grains in polycrystalline copper 査読

T Abe, R Kondou, N Tada, Shimizu, I

ENGINEERING PLASTICITY FROM MACROSCALE TO NANOSCALE PTS 1 AND 2   233-2   535 - 540   2003年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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Observation of the tensile deformation behavior of polycrystalline titanium with the scanning probe microscope 査読

T Abe, Y Li, N Tada

ENGINEERING PLASTICITY FROM MACROSCALE TO NANOSCALE PTS 1 AND 2   233-2   529 - 534   2003年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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Advanced Creep Damage Analysis of Low-Alloy Steel Welds Considering the Microscopic Damage Progress 査読

Fumiko Kawashima, Takumi Tokiyoshi, Toshihide Igari, Akira Shibashi, Naoya Tada

Proc. International Conference on Advanced Technology in Experimental Mechanics 2003, The Japan Society of Mechanical Engineers   2003年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Observation of creep cavity growth in smooth and notched specimens of low alloy steel in the heat-affected zone 査読

N Tada, H Maruyama, T Igari, F Kawashima

STRUCTURAL INTEGRITY AND MATERIALS AGING   113 - 118   2003年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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Fatigue Fracture of Third Generation Nickel-Base Single Crystal Superalloy CMSX-10 at High Temperature -Acceleration of Cracking by Stress Hold- 査読

Naoya TADA, Ryuichi OHTANI, Masanori SHIBATA, Shigeaki TANIYAMA

Proc. Fourth Japan-China Bilateral Symposium on High Temperature Strength of Materials, The Society of Materials Science, Japan   2001年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Prediction of Inner Cracking Behavior in Heat-Resistant Steel under Creep-Fatigue Condition by Means of Three-Dimensional Numerical Simulation 査読

TADA N.

IUTAM Symposium on Creep in Structures, (2001)   2001年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Kluwer Academic Publishers  

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Mesurement of cavities and evaluation of creep damage parameters 査読

N Tada, R Ohtani

PROCEEDINGS OF THE SEM IX INTERNATIONAL CONGRESS ON EXPERIMENTAL MECHANICS   409 - 412   2000年

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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直流電位差法による半楕円表面き裂の寸法, 形状および位置の推定 査読

多田 直哉, 中山 英介

非破壊検査   48 ( 10 )   697 - 704   1999年10月

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担当区分：筆頭著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本非破壊検査協会  

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AS4/PEEKの横方向引張における微小き裂の発生と停留

江嶋 恒行, 小泉 匡永, 多田 直哉, 北村 隆行, 大谷 隆一

材料   48 ( 9 )   1022 - 1028   1999年9月

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記述言語：日本語   出版者・発行元：社団法人日本材料学会  

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

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多数球形欠陥まわりの直流電位場解析

多田 直哉, 中山 英介, 北村 隆行, 大谷 隆一

日本機械学会論文集. A編 = Transactions of the Japan Society of Mechanical Engineers. A   65 ( 632 )   693 - 700   1999年4月

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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横方向引張を受ける複合材料の端部微小き裂に関する応力解析

江嶋 恒行, 多田 直哉, 北村 隆行, 大谷 隆一

日本機械学会論文集. A編 = Transactions of the Japan Society of Mechanical Engineers. A   65 ( 631 )   538 - 544   1999年3月

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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常圧焼結窒化けい素の高温における引張, クリープ, 疲労, クリープ疲労破壊(<特集>高度強度)

多田 直哉, 北村 隆行, 大谷 隆一, 木倉 真, 田中 豊延

材料   48 ( 2 )   173 - 180   1999年2月

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記述言語：日本語   出版者・発行元：社団法人日本材料学会  

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

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Evolution of creep-fatigue damage in type 304 stainless steel and its detection by electrical potential method

N. Tada, T. Kitamura, R. Ohtani, E. Nakayama

Acta Metallurgica Sinica (English Letters)   11 ( 6 )   463 - 469   1998年

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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.

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複合材料における微視き裂から巨視き裂への遷移 (界面き裂を有する横方向積層板のBEM解析)

江嶋 恒行, 坂口 昌平, 多田 直哉, 北村 隆行, 大谷 隆一

日本機械学会論文集. A編   63 ( 615 )   2338 - 2344   1997年11月

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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複合材料における微視き裂から巨視き裂への遷移 (Mode Iマトリックス中央き裂を有する横方向積層板のBEM解析)

坂口 昌平, 江嶋 恒行, 多田 直哉, 北村 隆行, 大谷 隆一

日本機械学会論文集. A編   63 ( 614 )   2077 - 2083   1997年10月

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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多数き裂型損傷を受けた材料の直流電位差に関する解析

多田 直哉, 林 義仁, 北村 隆行, 大谷 隆一

日本機械学会論文集. A編   63 ( 614 )   2235 - 2242   1997年10月

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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Relationship between creep damage parameters and distribution of creep cavities on grain boundaries 査読

N. Tada, T. Kitamura, R. Ohtani

Computer Aided Assessment and Control of Localized Damage - Proceedings of the International Conference   535 - 542   1996年

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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Characterization of creep-fatigue fracture of type 304 stainless steel based on initiation and growth of small cracks

T. Kitamura, R. Ohtani, N. Tada, W. Zhou

American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP   303   377 - 382   1995年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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内部微小欠陥分布の逆解析による推定

多田 直哉, 大谷 隆一, 北村 隆行, 山田 雅也

日本機械学会論文集 A編   59 ( 558 )   381 - 386   1993年

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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キャビティ分布と各種クリープ損傷パラメータの関係についての解析的検討

多田 直哉, 北村 隆行, 大谷 隆一

日本機械学会論文集 A編   59 ( 565 )   2074 - 2080   1993年

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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粒界き裂の発生と成長挙動の相違から見たクリープ疲労の破壊プロセスと寿命特性

多田 直哉, 北村 隆行, 大谷 隆一

材料   41 ( 469 )   1545 - 1550   1992年10月

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記述言語：日本語   出版者・発行元：社団法人日本材料学会  

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

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クリープ疲労微小き裂発生・成長の数値シミュレーションによる高温構造材料の余寿命診断方法

北村 陸行, 多田 直哉, 大谷隆 一

日本機械学会論文集 A編   57 ( 540 )   1732 - 1737   1991年

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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直流電位差法による半だ円表面き裂形状・寸法測定のための電位解析

多田 直哉, 坂之上 悦典, 北村 隆行, 大谷 隆一

日本機械学会論文集 A編   56 ( 522 )   259 - 264   1990年

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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ＳＵＳ３０４の結晶粒界長さおよび角度分布とそのクリープ疲労微小き裂発生・成長に及ぼす影響

北村 隆行, 多田 直哉, 栗山 義英, 大谷 隆一

日本機械学会論文集 A編   56 ( 524 )   702 - 707   1990年

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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クリープ・疲労条件下の微小き裂発生・成長に及ぼす圧縮ひずみ速度の影響

北村 隆行, 多田 直哉, 阿部 宗昭, 弓田 正人, 大谷 隆一

日本機械学会論文集 A編   56 ( 523 )   575 - 581   1990年

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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Numerical simulation of initiation and early propagation of creep-fatigue small cracks based on a model of random fracture resistance of grain boundaries

R. Ohtani, T. Kitamura, N. Tada

American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP   163   123 - 127   1989年

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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.

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粒界破壊抵抗分布モデルによるクリープ疲労微小き裂の発生と初期伝ぱのシミュレーション

大谷 隆一, 北村 隆行, 村山 英明, 多田 直哉

日本機械学会論文集 A編   54 ( 503 )   1312 - 1316   1988年

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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変動温度下の高温疲労き裂伝ぱ

大谷 隆一, 北村 隆行, 多田 直哉

日本機械学会論文集 A編   53 ( 490 )   1030 - 1036   1987年

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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

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