担当区分：最終著者,　責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

<p>Many actual structures, such as piping and turbine shafts, are subjected to torsional low-cycle fatigue. However, there have been many studies on high-cycle fatigue due to torsion, but few studies on low-cycle fatigue due to torsion alone, and there are many unknown points. Fatigue tests were conducted in a torsion testing machine (490 Nm capacity) at room temperature in air, with both swings and controlled torsion angles over a specified total strain range. Cracks were observed using the replica method, in which replicas of the specimen surface were taken at regular intervals in each total strain range and observed with an optical microscope. In this study, it is shown that there is a grain size dependence of the Manson-Coffin law in torsional low-cycle fatigue and that the microcrack propagation rate is independent of crack length in torsional low-cycle fatigue.</p>

DOI： 10.1299/jsmemm.2023.mm0639

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その他リンク： https://www.jstage.jst.go.jp/article/jsmemm/2023/0/2023_MM0639/_pdf

担当区分：最終著者,　責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

<p>Fatigue behaviors differ between thin film and bulk materials, even if they are the same material. Reports show that the incidence of grain slip saturates at 0.1 when loading is applied in the shear direction. The purpose of this study is to clarify the behavior of slip and crack initiation in carbon steel thin films subjected to cyclic shear loading. We investigated the effects of carbon content and film thickness on slip and cracks. Pure iron, S10C and S45C are selected as specimens to investigate the effect of carbon content. Then, to investigate the effect of film thickness, tests are conducted with film thickness/grain size ratio <i>t</i>/<i>D</i> less than 0.8 and greater than 1.67. A torsion bending tester (Shimadzu TB-10) is used. As a result, in-plane slips and cracks are more likely to occur with higher carbon content, while out-plane slips are more likely to occur with lower it. Increasing the <i>t</i>/<i>D</i> increased out-plane slips, but not increasing in-plane slips and cracks. The following three points are considered from this study. In-plane slips occur more frequently when the volume fraction of pearlite is large, and is considered to be caused by the concentration of strain. Out-plane slips occur more frequently when <i>t</i>/<i>D</i> exceeds 1.67, suggesting that it is caused by the deformation of crystal grains in the film thickness direction. The larger the amount of in-plane slip, the more cracks are observed, suggesting that the cracks are caused by in-plane slip.</p>

DOI： 10.1299/jsmemm.2023.mm0604

CiNii Research

その他リンク： https://www.jstage.jst.go.jp/article/jsmemm/2023/0/2023_MM0604/_pdf

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

<p>In general, high-strength steel is known to occur an internally initiated fatigue fracture called "Fish-eye failure" in the very long life region. In addition, the fatigue life of a fish-eye failure is dominated by the ODA (Optically Dark Area) that forms around the fracture origin. Therefore, it is necessary to elucidate the formative mechanism of ODA in order to predict the fatigue life of fish eye failure. Besides, it has been reported that small surface cracks propagate at extremely low speeds below the lattice spacing in a vacuum simulating the interior of high-strength steel. However, it has not been confirmed that the growth of these small cracks forms ODA. In this study, fatigue tests were conducted from a very short crack to a long crack, which corresponds to internal failure in the very long life region, instead of the fatigue tests with a relatively long crack of around 150 μm that have been conducted so far. The results of intermittent observation of the growth behavior and the relationship between the crack growth rate, stress intensity factor, and maximum stress suggest that small cracks grow and form ODAs.</p>

DOI： 10.1299/jsmemm.2022.os0317

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その他リンク： https://www.jstage.jst.go.jp/article/jsmemm/2022/0/2022_OS0317/_pdf

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

<p>In the same materials, film and bulk materials show different mechanical properties. In fatigue testing of metallic thin film, several studies have been reported for axial and bending directions, however, there are few studies for shear direction. In addition, multiple parallel slips in the same grain are considered out-plane direction, a single linear slip in a grain is considered in-plane direction. Therefore, in this study we conducted fatigue tests under cyclic in-plane pure shear loading to S10C and S45C.We focused on the effect of pearlite volume fraction on slip generation and the relationship between cracks and slips. As a result, about 90% of the slip that occurred in S10C was out-plane direction. About 70% of the slip that occurred in S45C was in-plane slip. This is considered to be caused by the concentration of strain due to pearlite. In addition, more cracks were observed in S45C than in S10C, Consequently, cracks in the carbon steel film are considered to have grown from in-plane slip.</p>

DOI： 10.1299/jsmemm.2022.os0328

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その他リンク： https://www.jstage.jst.go.jp/article/jsmemm/2022/0/2022_OS0328/_pdf

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

DOI： 10.1299/jsmekyushu.2021.74.d44

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その他リンク： https://www.jstage.jst.go.jp/article/jsmekyushu/2021.74/0/2021.74_D44/_pdf

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

DOI： 10.1299/jsmekyushu.2021.74.d52

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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（研究会，シンポジウム資料等）

DOI： 10.1299/jsmekyushu.2021.74.d54

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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（研究会，シンポジウム資料等）

DOI： 10.1299/jsmekyushu.2021.74.d25

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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（学術雑誌）

<p>This paper proposes a technique to determine the dimensions of a CNRB specimen to be used for plane fracture toughness tests. First, the brittle fracture behavior satisfying the small-scale yielding condition is investigated through an elasto-plastic analysis. The analysis parameters are the shape parameters such as the notch ratio of the specimen based on the parallel part diameter and notch bottom diameter; tip radius; and notch angle. Based on the analysis results obtained, a fracture toughness test is conducted on a JIS-S45C (quenched and tempered) specimen to evaluate the small-scale yielding condition. The experimental results confirm a linear relationship between the square of the value obtained by dividing the plane-strain fracture toughness by the yield stress and specimen diameter. Further, the diameter of the CNRB specimen satisfying the small-scale yielding condition varies with the shape parameters. With these results, a function that can determine the CNRB specimen diameter at which brittle failure occurs under uniaxial tensile loading is proposed and validated.</p>

DOI： 10.1299/mej.19-00621

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その他リンク： https://ci.nii.ac.jp/naid/130007887808

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

<p>The mechanical properties of steels are known to be improved by grain refinement and by smaller and more finely dispersed cementite particles. Super-rapid induction tempering can achieve smaller and more finely dispersed cementite particles, and super-rapid induction quenching can improve grain refinement. In this study, we investigated the fatigue properties of carbon steel treated by induction quenching and tempering using a super-rapid induction heating technique. Hollow test specimens were fabricated to observe the mechanical properties of the structure obtained by induction heating. Based on our observations, in the finite-life region, no difference was found between tempering conditions for each hardness value, but a transition to longer life due to differences in quenching conditions was observed. In addition, no clear grain refining effect was found in the fatigue limit of induction-quenched steel in the range of the quenching conditions of this study. However, a delay effect due to grain refinement was recognized at the initial stage of crack growth from the consideration of the crack growth rate of induction-tempered steel.</p>

DOI： 10.11395/aem.5.0_97

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その他リンク： https://ci.nii.ac.jp/naid/130007953457

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

<p>A low cycle torsional fatigue test of carbon steel S10C for machine structural use was performed with strain control. Using a mechanism that applied Martens's mirror device, the scale was read, and the torsional torque was increased or decreased to achieve a predetermined torsional angle, and experiments were performed with total strain widths γ = 1.0%, 1.5%, and 2.0%. As a result, the propagation behavior of cracks in low cycle torsional fatigue was connected and propagated by innumerable microcracks. The fatigue life calculated by the small crack propagation law, focusing on the main crack that caused the fracture, was equivalent to the fatigue life of the Manson-Coffin's law.</p>

DOI： 10.1299/jsmemm.2019.OS0303

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その他リンク： https://ci.nii.ac.jp/naid/130007846376

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

<p>At the same materials, mechanical properties of a film different from those of a bulk and we consider that fatigue property of a film is different from that of a bulk. In this study, According to a report by Ueda et al., It was reported that when a thin film experiment was conducted, the occurrence of slips and cracks was small. It has been reported that crystals also differ from in-plane and out-of-plane shear components．Therefore, in this study, we investigated the difference in the location and concentration of slip due to the pearlite volume fraction of carbon steel thin films, and the mode of occurrence of slip using EBSD and metallurgical factors.As for the form of slip, pure iron is near the grain boundary, and in S10C, several slips occur in parallel within the same grain. What was occurring was confirmed.S10C slips are considered to occur only in crystals that satisfy certain conditions, such as having multiple crystals in the film thickness direction and pearlite on both sides. Other non-slip crystals are considered to be plastically deformed due to the high pure shear applied, so slips are occurring but are considered to have been restored.</p>

DOI： 10.1299/jsmemm.2019.OS0302

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その他リンク： https://ci.nii.ac.jp/naid/130007846378

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

<p>High Strength Steel shows internal origin type fatigue failure as called Fish eye failure in low stress and high cycle region. In this failure, ODA is formed on the fracture surface. Although the explication of the mechanism of ODA formation is needed for the explication of the Fish eye failure mechanism, the explication is not yet accomplished. It’s reported that internal fatigue crack in high strength steel is propagating extremely slowly by recent investigations. And crack propagation rate was suggested that series of the low alloy steel depend on the maximum stress and ΔK. In this study, fatigue test of the same material was in vacuum environment. As a result, ΔK≤4 MPa√m as for crack propagation rate, it suggested that the test on condition of long initial crack was faster than the test on condition of short initial crack. Therefore crack progress speed depend on the test conditions as well as the maximum stress.</p>

DOI： 10.1299/jsmemm.2018.os1408

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その他リンク： https://www.jstage.jst.go.jp/article/jsmemm/2018/0/2018_OS1408/_pdf

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

<p>Small fatigue crack closure is observed as a thing with a possibility that the influence of change of the stress level and a stress ratio, etc. to the crack growth behavior can be explained, and until now various researches have been done. Although there is a method using the strain gage as the dynamic measurement method required for the elucidation of a minute fatigue crack, in respect of generating of minute fatigue cracks being directly contacted to a measuring object thing, and there is a problem in durability or measurement of the crack growth behavior, it may not necessarily be effective. Then, its attention was paid to the magnetostriction effect which is one of the magnetic actions of a ferromagnetic substance. Measurement of micro fatigue crack information under dynamic load without requiring a simple device and contact with the object was carried out and the change in the magnetic field around the test piece due to the magnetostrictive effect was measured using a coil. We investigated micro fatigue crack information from the information.</p>

DOI： 10.1299/jsmemm.2018.os0414

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その他リンク： https://www.jstage.jst.go.jp/article/jsmemm/2018/0/2018_OS0414/_pdf

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

<p>At the same materials, mechanical properties of a film different from those of a bulk and we consider that fatigue property of a film is different from that of a bulk. In this study, we think that formation of fatigue slip band of thin film materials of pure iron , S10C, and S45C, are different from each other and conducted a microscopic observation of the slip band of each thin films. Also we observed strains of each thin films by using Electron Back Scatter Diffraction Pattern (EBSD). As a result, we confirmed that slip bands occurred at the grain boundaries in pure iron, slip bands occurred in a wide range within the grains in S10C and slip bands occurred in a short range within the grains in S45C. Also we consider that strain occurred at the grain boundaries in pure iron, strains occurred in a wide range within the grains in S10C and strains occurred in a short range within the grains in S45C by EBSD. We indicate that in the case of carbon steel, forms of generation of strain within the ferrite crystal grain differs depending on the different in restraint of perlite.</p>

DOI： 10.1299/jsmemm.2017.os0533

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その他リンク： https://www.jstage.jst.go.jp/article/jsmemm/2017/0/2017_OS0533/_pdf

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

<p>Even if metal thin film is the same material, it does not know that different mechanical characteristics form a bulk material are shown, and general fatigue behavior showing a bulk material does not necessarily appear. The present condition is that research of the fatigue behavior in the repetition shear load of a metal thin film is not made compared with the thing of load direction axis and bending. From studies of thin films in the cyclic loading to date, a crack with a locally slip in S10C occurs. The cause such crack occurs, the strain in the ferrite by applying the cyclic shear loading occurs, pearlite is considered to crack been concentrated deformed part that is sandwiched between the pearlite harder than ferrite because no deformation occurs. In addition, with respect to micro fatigue crack propagation in the repeated shear load of the bulk material, it was confirmed that the stiff cracks were inhibited by hard pearlite crystal grains, but the propagating cracks also progressed into the pearlite grains. Therefore, in this study, fatigue cracks are generated and developed by applying a repeated shearing load to the thin film material of S10C, and the influence of the observation / microstructure of its progress process was examined. As a result, it was confirmed that the pearlite crystal grains of the thin film material prevented the crack growth as well as the bulk material, and the propagating cracks also progressed into the pearlite crystal grains.</p>

DOI： 10.1299/jsmemm.2017.os0534

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その他リンク： https://www.jstage.jst.go.jp/article/jsmemm/2017/0/2017_OS0534/_pdf

記述言語：日本語   掲載種別：研究論文（学術雑誌）

主要雑誌

DOI： 10.1299/transjsme.2014smm0185

CiNii Article

記述言語：日本語   掲載種別：研究論文（学術雑誌）

主要雑誌

DOI： 10.1299/transjsme.2014smm0149

CiNii Article

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

The general method is not always effective for the measurement of fatigue small crack growth properties by relation of accuracy and a device characteristic. Non-contact and the highly precise measurement are expected by the use of a magnetostriction effect to apply in this study. The small crack growth properties measurement by a magnetic field change with the magnetostriction effect that was one of a characteristic of magnetism of ferromagnetic substance was studied. Using a coil, a magnetic field change with magnetostriction effect was detected, and the waveform change of the output was inspected. The experiment result was revealed that the small crack affects a magnetic field change by a magnetostriction effect.

DOI： 10.1299/jsmemm.2014._OS2120-1_

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その他リンク： https://ci.nii.ac.jp/naid/110009939748

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

In this study, high-speed tensile testing for notched specimen is conducted to investigate the impact property of Polydimethylsiloxane copolymerized Polycarbonate (PDMS-PC) compared with Polycarbonate (PC). Depending on the test temperature and tensile speed, brittle or ductile fractures are observed for PC. However, only ductile fractures are seen for PDMS-PC even at the high speed 7000mmis and low temperature 243K. The impact properties are also considered in terms of the time-temperature superposition principle. Then, master curves for the final fracture elongation for both PC and PDMS-PC are constructed in terms of the strain rate at the notch in conjunction with shift factors.

DOI： 10.1299/jsmemm.2014._GS19-1_

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その他リンク： https://ci.nii.ac.jp/naid/110009939419

記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

It is known that high strength steel will cause the characteristic internal fracture called Fish eye fracture in very high cycle region. From this, in order to use high strength steel more efficiently and more safely, the elucidation of the mechanism of the Fish eye fracture produced in low stress and long-life and construction of the lifetime evaluation method of Fish eye fracture are desired. In this study, we did ΔK decrease fatigue test under vacuum environment, and examined the relation between internal fracture in very high cycle region and extremely slow fatigue crack growth behavior under vacuum environment. As a result, the influence of material strength was not seen under vacuum environment. Moreover, opening stress increases with increases of maximum stress.

DOI： 10.1299/jsmemm.2014._OS2103-1_

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その他リンク： https://ci.nii.ac.jp/naid/110009939732

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）

A metal thin film doesn't necessarily appear general fatigue behavior like a bulk material. By a balk and film material, there is difference of restricted state because of differing in the number of grains to the direction of film thickness. In this research the diagram of ratio of slipped grains and number of cycle was sorted by film thickness/grain size ratio in carbon steel thin film under cyclic shear loading. Then slip ratio under film thickness/grain size ratio 0.80 saturated. The influence of grain size was considered to slip band formation by examining grain's existence frequency to direction of film thickness. It was bringing close to actual grains by extending two dimensions grain size to three dimensions. As a result, there was the relation between the slip ratio and the grain's cumulate existence frequency in the value whose film thickness/grain size ratio are near 0.9.

DOI： 10.1299/jsmemm.2014._OS2109-1_

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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（研究会，シンポジウム資料等）

The following conclusions were obtained as a result of examining the fatigue strength characteristic and the relation of a damage process paying attention to damage to the resin/fiber interface in GFRP based modified PC. 1) Fatigue crack growth rate of the difference in the fatigue characteristics of PDMS-PC and PC-EP is the cause. 2) The damage process of PDMS-PC is a type of crack distribution destroyed while two or more GF end cracks connect.

DOI： 10.1299/jsmemm.2014._OS2110-1_

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その他リンク： https://ci.nii.ac.jp/naid/110009939739

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）

Engineering plastics provide superior performance to ordinary plastics for wide range of the use. For polymer materials, dynamic stress and strain rate may be major factors to be considered when the strength is evaluated. Recently, high speed tensile test is being recognized as a standard testing method to confirm the strength under dynamic loads. In this study, therefore, high speed tensile test is analyzed by the finite element method; then, the maximum dynamic stress and strain rate are discussed with varying the tensile speed and maximum forced displacement. The strain rate concentration factor found to be constant independent of tensile speed, which is defined t K μ as the maximum strain rate appeared at the notch root over the average nominal strain rate at the minimum section. The maximum strain rate is controlled by the tensile speed alone independent of the magnitude of the forced displacement. It is found that the difference between static and dynamic maximum stress concentration (σmax-σst) at the notch root is proportional to the tensile speed when u/t ≤ 5000mm/s. Copyright © (2013) by International Conference on Fracture.

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記述言語：日本語   掲載種別：研究論文（学術雑誌）

This study considered the behavior of tensile and fatigue damage, and the effect of reinforcement of the interface strength given to a damage process by observing the microscopic damage to the fiber interface of glass fiber reinforcement polycarbonate. As a result, the following thing became clear. 1) In both tensile and fatigue process, damage was initiated from the fiber end in the early stages, and the debonding propagated along the fiber interface. 2) The GF/PC interface strength improved by adding the epoxy resin. 3) The debonding along the fiber interface was inhibited by improving interface strength. © 2012 The Society of Materials Science, Japan.

DOI： 10.2472/jsms.61.441

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記述言語：日本語   掲載種別：研究論文（学術雑誌）

主要雑誌

記述言語：日本語   掲載種別：研究論文（学術雑誌）

主要雑誌

DOI： 10.1299/kikaia.78.609

Scopus

CiNii Article

記述言語：日本語   掲載種別：研究論文（学術雑誌）

主要雑誌

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

It has been well known that mechanical properties of steels are improved by gain refinement, smaller cementite particle and finely dispersing cementite particle, It is enabled by super rapid induction tempering the the smaller cementite particle and the finely dispersing cementite particle. In this study, mechanical properties of induction quenching and tempering carbon steel using super rapid induction heating system were investigated. Dtail, the effect of quenching time on tensile properties is examined. The quenching time was changed in four steps of 0.44 s (1163 K), 10 s (1233 K) +10 s (1153 K), 20 s (1273 K) and 20 s (1433 K). As a result, it was found that the tensile strength of QT steel indicated an increase tendency with hardness. The yield strength was in proportion to a square root of grain size. However, the ductility improvement effected by super rapid induction quenching was not found, reduction of area did not depend on grain size.

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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（学術雑誌）

We focused our attention on microstructure control and improvement of mechanical properties of induction tempering carbon steel using super rapid induction heating system. We examined the effect of tempering time on tensile properties. The tempering time was changed in two steps of 0.35s and 1.15s. As a result, it was found that the QT steel obtained super rapid induction tempering had both high strength and high ductility. The ductility of the super rapid induction tempering steel was 10% larger compared with the usual tempering steel. The reason for this phenomenon was explained in that cementite particle of super rapid induction tempering steel became small and dispersed finely in comparison with usual tempering steel.

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記述言語：日本語   掲載種別：研究論文（学術雑誌）

主要雑誌

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

A high strength steel shows fish-eye failure in very long life fatigue. In this region, the fatigue crack growth in ODA (Optically Dark Area) controls the fatigue process. However, ODA's formative mechanism is unknown. Therefore, to predict fatigue life of fish-eye failure, it is important to know ODA's formative mechanism. So, the present study examined for the influential factors on ODA in the fatigue process through uniaxial push-pull fatigue tests in vacuum as well as computer simulation. In experiment, vacuum environment is employed to simulate fish-eye type crack growth on surface of specimens becase of shutting off supply of air. The test results in vaccum showed that the fatigue life property of surface failure has corresponded to fish-eye fatigue life. And the site of inclusion which has fracture origin size determines whether surface failure or internal failure in vacuum. The results of fractographic observation of crack initiation showed that the rough area of surface fracture in vacuum was formed by mechanism of ODA type crack. Furthermore, the fatigue life of numerical simulation in vacuum showed that the fatigue life which was necessary to form ODA on specimen surface corresponded experimental life.

DOI： 10.2472/jsms.54.1213

Scopus

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記述言語：日本語   掲載種別：研究論文（学術雑誌）

主要雑誌

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）

2004年04月  -  2004年04月

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）

2004年04月  -  2004年04月

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）

A fundamental study of relieving or attenuating weld residual stress was done by applying cyclic load. Two kinds of tests were done. First, bead-on welding was done onto front surface of plate specimen. Then, the distribution of initial welding residual stress was measured in terms of X ray diffraction method. To relieve this initial residual stress, cyclic load was applied to the specimen in a vibrating machine. The change of stress cycle-dependent residual stress was measured. Secondary, this method was applied to a box-shaped rahmen structure. Both results showed that the initial welding residual stress can be relieved when the summation of stress component of the residual stress plus externally applied cyclic stress exceeds the yield stress of the material.

Scopus

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記述言語：日本語   掲載種別：研究論文（学術雑誌）

主要雑誌

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）

2003年04月  -  2003年04月

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）

In this study, we simulate nanoscale copper precipitation process based on the vacancy jump model using Lattice Monte Carlo (LMC) method, where an activation energy is calculated from the first neighboring interaction model. We confirmed that status of copper clustering at temperature of 300 K is different from those of 600 K and 900 K at the same potential energy decrease, and copper clusters are formed more rapidly at higher temperature. We obtained a fact that process of copper clustering consists of the two phases which are formation phase, and coalescence and/or absorption phase.

DOI： 10.1299/kikaia.69.538

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/110002370340

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

In this study, we simulate nanoscale copper precipitation process based on the vacancy jump model using Lattice Monte Carlo (LMC) method, where an activation energy is calculated from the first neighboring interaction model. We confirmed that status of copper clustering at temperature of 300 K is different from those of 600 K and 900 K at the same potential energy decrease, and copper clusters are formed more rapidly at higher temperature. We obtained a fact that process of copper clustering consists of the two phases which are formation phase, and coalescence and/or absorption phase.

Scopus

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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）

In order to characterize small mode III crack growth torsional fatigue tests were done using circumferentially notched prefatigue-cracked specimens. The change of the shape of hysteresis loop during crack growth was monitored in terms of two wire strain gauges mounted on the surface perpendicularly across the notch. Then, the change of compliance during fatigue crack growth was evaluated in terms of the hysteresis loop. Regarding to characteristic growth behavior of the small mode III fatigue crack, the small crack first grew in the coaxial plane. Then it gradually changed growth plane out of that coaxial plane. Finally the crack was propagated in the direction 45° inclined to the cross sectional plane. That means, the change of three dimensional crack plane was found to correspond to so-called factory roof pattern, common at the first stage of fatigue crack growth from the notch root in torsional fatigue condition. The fatigue crack growth rate varied in accordance with that mode change of small crack growth. In addition, the crack growth rate was considerably affected by the friction force acting on the crack surface. Increasing crack length in mode III crack growth condition decelerated the crack growth, which reflected increase in friction force. The change of compliance during crack growth was found suitable for estimating the effect of the friction force on crack growth rate. In lower ΔKeff region, the friction force was successfully characterized using a parameter of compliance. In case of large scale yielding condition, ΔJeff parameter including the effect of friction force-generated increase of torque was found to be a suitable parameter to estimate crack growth rate. The friction force acting on the unit area of crack plane was constant, irrespective of crack length and loading condition.

DOI： 10.1299/jsmeatem.2003.2._OS12W0360

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/110009968302

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）

China   Dunhuang   2002年08月24日  -  2002年08月27日

記述言語：日本語   掲載種別：研究論文（大学，研究機関等紀要）

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/110000151722

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Mode III fatigue crack is usually observed at the root of circumferentially notched round bar. As the crack grows in the depth direction of specimen, the growth rate of crack decreases. In this respect, crack mode transition from mode III to mode I is understood responsible. However, quantitative evaluation on crack mode transition has been hardly done. Therefore, values of stress intensity factor K1 under mode III fatigue crack growth tests on a low carbon steel were calculated with using principal stress, as crack mode transition began. Then KI values were compared with crack growth rate curve of mode I. As the result, it was observed that the condition of crack mode transition was given by the crack growth curve of mode I.

DOI： 10.2472/jsms.50.1098

Scopus

CiNii Article

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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）

Portugal   Lisbon   2001年06月25日  -  2001年06月28日

記述言語：日本語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）

2001年04月  -  2001年04月

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）

2001年04月  -  2001年04月

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

In order to examine the mechanism of so-called fish eye-pattern fatigue failure, usually being caused by initiation and growth of internal small crack, uniaxial push-pull fatigue tests were carried out on a high strength low alloy steel in vacuum, for modifying the environment during internal crack initiation and growth on specimen surface. The test results showed that the fatigue life was elongated and the crack growth rate was delayed in vacuum. Furthermore, the results of fractographic observation of crack initiation at inclusions revealed that the surface type crack initiation in vacuum resembles the internal fish eye-type crack initiation in atmosphere. Finally the fish eye-type fatigue life was well evaluated in terms of small crack growth law in vacuum.

DOI： 10.2472/jsms.48.1107

Scopus

CiNii Article

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記述言語：日本語   掲載種別：研究論文（学術雑誌）

記述言語：日本語   掲載種別：研究論文（学術雑誌）

記述言語：日本語   掲載種別：研究論文（学術雑誌）

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）

1999年04月  -  1999年04月

記述言語：日本語   掲載種別：研究論文（学術雑誌）

記述言語：日本語   掲載種別：研究論文（学術雑誌）

記述言語：日本語   掲載種別：研究論文（学術雑誌）

記述言語：日本語   掲載種別：研究論文（学術雑誌）

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）

1997年04月  -  1997年04月

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

A surface hardening technique for improving the wear resistance of ductile cast iron (DI) is proposed by fabricating molten DI with stainless steel. The essential idea is concerned with using the chromium source in stainless steel and the carbon source in DI to form chromium carbides. It was demonstrated that the surface of the fabricated DI consisted of firstly a layer of high chromium white cast iron ((Cr,Fe)7C3 eutectic carbides), which was originally stainless steel, and then a layer of medium-low-chromium white cast iron ((Fe,Cr)3C eutectic carbides), which was originally DI. Thus the hardness of the surface layer became 2-3 times that of the baseline ductile cast iron. Applying austenitic stainless steel produces a much better hardening effect than applying ferritic stainless steel. The depth of the hardened surface layer depends on the pouring temperature of the iron melt, the wall thickness of the iron casting and the cooling rate of the casting mold. The present strategy is, in principle, possibly applied to complete as well as local surface hardening of various kinds of ductile iron castings.

DOI： 10.1016/0921-5093(95)10058-X

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）

1996年04月  -  1996年04月

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）

1996年04月  -  1996年04月

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）

1996年04月  -  1996年04月

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）

Two kinds of ferritic ductile cast iron, having same chemical composition and different nodule count, i.e., high nodule count material (HNC) and low nodule count material (LNC), were low-cycle fatigued under stress-controlled cycling. The difference of nodule count induced difference in cyclic hardening behavior, LCF strength and fatigue mechanism. When LCF life was evaluated in terms of cyclic plastic strain range which includes the effect of cyclic hardening properties, both materials showed same fatigue strength. Although spheroidal graphite (SG) played an important role as a crack initiation site at an early stage of fatigue process, subsequent fatigue process was differed between HNC and LNC. In case of HNC, the fatigue process was dominated by the growth of a single crack. On the contrary, independent growth of subcracks without forming a leading crack controlled the whole fatigue process in material LNC. In addition, contradictory to number of nodule counts, the density of the initiated subcracks was higher in LNC than in HNC. Statistical analysis of three dimensional (3D) distribution of SG revealed that the difference in fatigue mechanism mentioned so far was mainly caused by the difference of distribution of SG size. Finally image processing analysis of 3D fracture surface showed that the roughness in crack growth area was larger in LNC than in HNC.

Scopus

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記述言語：日本語   掲載種別：研究論文（学術雑誌）

記述言語：日本語   掲載種別：研究論文（学術雑誌）

記述言語：日本語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）

1995年04月  -  1995年04月

記述言語：日本語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）

1994年04月  -  1994年04月

記述言語：日本語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）

1993年04月  -  1993年04月

記述言語：日本語   掲載種別：研究論文（学術雑誌）

記述言語：日本語   掲載種別：研究論文（学術雑誌）

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）

1990年04月  -  1990年04月

開催期間： 2023年03月06日   記述言語：日本語   開催地：鹿児島  

開催期間： 2022年09月26日 - 2022年09月28日   記述言語：日本語   開催地：弘前  

In the same materials, film and bulk materials show different mechanical properties. In fatigue testing of metallic thin film, several studies have been reported for axial and bending directions, however, there are few studies for shear direction. In addition, multiple parallel slips in the same grain are considered out-plane direction, a single linear slip in a grain is considered in-plane direction. Therefore, in this study we conducted fatigue tests under cyclic in-plane pure shear loading to S10C and S45C.We focused on the effect of pearlite volume fraction on slip generation and the relationship between cracks and slips. As a result, about 90% of the slip that occurred in S10C was out-plane direction. About 70% of the slip that occurred in S45C was in-plane slip. This is considered to be caused by the concentration of strain due to pearlite. In addition, more cracks were observed in S45C than in S10C, Consequently, cracks in the carbon steel film are considered to have grown from in-plane slip.

開催期間： 2022年09月26日 - 2022年09月28日   記述言語：日本語   開催地：弘前  

In general, high-strength steel is known to occur an internally initiated fatigue fracture called "Fish-eye failure" in the very long life region. In addition, the fatigue life of a fish-eye failure is dominated by the ODA (Optically Dark Area) that forms around the fracture origin. Therefore, it is necessary to elucidate the formative mechanism of ODA in order to predict the fatigue life of fish eye failure. Besides, it has been reported that small surface cracks propagate at extremely low speeds below the lattice spacing in a vacuum simulating the interior of high-strength steel. However, it has not been confirmed that the growth of these small cracks forms ODA. In this study, fatigue tests were conducted from a very short crack to a long crack, which corresponds to internal failure in the very long life region, instead of the fatigue tests with a relatively long crack of around 150 µm that have been conducted so far. The results of intermittent observation of the growth behavior and the relationship between the crack growth rate, stress intensity factor, and maximum stress suggest that small cracks grow and form ODAs.

開催期間： 2021年09月15日 - 2021年09月16日   記述言語：日本語   開催地：名古屋  

High Strength Steel shows internal origin type fatigue failure as called Fish eye failure in low stress and high cycle region. In this failure, ODA is formed on the fracture surface. Although the explication of the mechanism of ODA formation is needed for the explication of the Fish eye failure mechanism, the explication is not yet accomplished. It’s reported that internal fatigue crack in high strength steel is propagating extremely slowly by recent investigations. And crack propagation rate was suggested that series of the low alloy steel depend on the maximum stress and ΔK. In this study, fatigue test of the same material was in vacuum environment. As a result, ΔK≤4 MPa√m as for crack propagation rate, it suggested that the test on condition of long initial crack was faster than the test on condition of short initial crack. Therefore crack progress speed depend on the test conditions as well as the maximum stress..

開催期間： 2021年09月15日 - 2021年09月16日   記述言語：日本語   開催地：名古屋  

Small fatigue crack closure is observed as a thing with a possibility that the influence of change of the stress level and a stress ratio, etc. to the crack growth behavior can be explained, and until now various researches have been done. Although there is a method using the strain gage as the dynamic measurement method required for the elucidation of a minute fatigue crack, in respect of generating of minute fatigue cracks being directly contacted to a measuring object thing, and there is a problem in durability or measurement of the crack growth behavior, it may not necessarily be effective. Then, its attention was paid to the magnetostriction effect which is one of the magnetic actions of a ferromagnetic substance. Measurement of micro fatigue crack information under dynamic load without requiring a simple device and contact with the object was carried out and the change in the magnetic field around the test piece due to the magnetostrictive effect was measured using a coil. We investigated micro fatigue crack length from the information.

開催期間： 2021年09月15日 - 2021年09月16日   記述言語：日本語   開催地：名古屋  

Many actual structures suffer from low cycle torsional fatigue, such as pipes and turbine shafts. However, there have been many studies on high cycle fatigue due to torsion, but there are few studies on low cycle fatigue using torsion alone, an there are many unclear points.It is widely known that in low-cycle fatigue, the Manson-Coffin rule that allows the fatigue life to be organized by the plastic strain width is established. The relationship is not clear. In recent years, there has been a report on the specific fatigue crack initiation behavior in studies of pure shear low cycle fatigue of thin film materials.Therefore, in this study, repeated low-cycle torsional fatigue tests were performed using S10C hollow specimens, and focusing on the main crack that caused the fracture, was the Manson-Coffin rule equivalent to the microcrack propagation law? It was investigated.

開催期間： 2021年03月10日   記述言語：日本語   開催地：オンライン  

開催期間： 2021年03月10日   記述言語：日本語   開催地：オンライン  

開催期間： 2021年03月10日   記述言語：日本語   開催地：オンライン  

開催期間： 2021年03月10日   記述言語：日本語   開催地：オンライン  

開催期間： 2019年11月02日 - 2019年11月04日   記述言語：日本語   開催地：九州大学  

At the same materials, mechanical properties of a film different from those of a bulk and we consider that fatigue property
of a film is different from that of a bulk. In this study, According to a report by Ueda et al., It was reported that when a thin
film experiment was conducted, the occurrence of slips and cracks was small. It has been reported that crystals also differ
from in-plane and out-of-plane shear components．Therefore, in this study, we investigated the difference in the location and
concentration of slip due to the pearlite volume fraction of carbon steel thin films, and the mode of occurrence of slip using
EBSD and metallurgical factors.As for the form of slip, pure iron is near the grain boundary, and in S10C, several slips occur
in parallel within the same grain. What was occurring was confirmed.S10C slips are considered to occur only in crystals that
satisfy certain conditions, such as having multiple crystals in the film thickness direction and pearlite on both sides. Other
non-slip crystals are considered to be plastically deformed due to the high pure shear applied, so slips are occurring but are
considered to have been restored.

開催期間： 2019年11月02日 - 2019年11月04日   記述言語：日本語   開催地：九州大学  

A low cycle torsional fatigue test of carbon steel S10C for machine structural use was performed with strain
control. Using a mechanism that applied Martens's mirror device, the scale was read, and the torsional torque was
increased or decreased to achieve a predetermined torsional angle, and experiments were performed with total strain
widths γ = 1.0%, 1.5%, and 2.0%. As a result, the propagation behavior of cracks in low cycle torsional fatigue was
connected and propagated by innumerable microcracks. The fatigue life calculated by the small crack propagation law,
focusing on the main crack that caused the fracture, was equivalent to the fatigue life of the Manson-Coffin’s law.

開催期間： 2018年01月   記述言語：日本語  

<p>High Strength Steel shows internal origin type fatigue failure as called Fish eye failure in low stress and high cycle region. In this failure, ODA is formed on the fracture surface. Although the explication of the mechanism of ODA formation is needed for the explication of the Fish eye failure mechanism, the explication is not yet accomplished. It's reported that internal fatigue crack in high strength steel is propagating extremely slowly by recent investigations. And crack propagation rate was suggested that series of the low alloy steel depend on the maximum stress and ΔK. In this study, fatigue test of the same material was in vacuum environment. As a result, ΔK≤4 MPa√m as for crack propagation rate, it suggested that the test on condition of long initial crack was faster than the test on condition of short initial crack. Therefore crack progress speed depend on the test conditions as well as the maximum stress.</p>

CiNii Article

開催期間： 2018年01月   記述言語：日本語  

<p>Small fatigue crack closure is observed as a thing with a possibility that the influence of change of the stress level and a stress ratio, etc. to the crack growth behavior can be explained, and until now various researches have been done. Although there is a method using the strain gage as the dynamic measurement method required for the elucidation of a minute fatigue crack, in respect of generating of minute fatigue cracks being directly contacted to a measuring object thing, and there is a problem in durability or measurement of the crack growth behavior, it may not necessarily be effective. Then, its attention was paid to the magnetostriction effect which is one of the magnetic actions of a ferromagnetic substance. Measurement of micro fatigue crack information under dynamic load without requiring a simple device and contact with the object was carried out and the change in the magnetic field around the test piece due to the magnetostrictive effect was measured using a coil. We investigated micro fatigue crack information from the information.</p>

CiNii Article

開催期間： 2017年01月   記述言語：日本語  

<p>Even if metal thin film is the same material, it does not know that different mechanical characteristics form a bulk material are shown, and general fatigue behavior showing a bulk material does not necessarily appear. The present condition is that research of the fatigue behavior in the repetition shear load of a metal thin film is not made compared with the thing of load direction axis and bending. From studies of thin films in the cyclic loading to date, a crack with a locally slip in S10C occurs. The cause such crack occurs, the strain in the ferrite by applying the cyclic shear loading occurs, pearlite is considered to crack been concentrated deformed part that is sandwiched between the pearlite harder than ferrite because no deformation occurs. In addition, with respect to micro fatigue crack propagation in the repeated shear load of the bulk material, it was confirmed that the stiff cracks were inhibited by hard pearlite crystal grains, but the propagating cracks also progressed into the pearlite grains. Therefore, in this study, fatigue cracks are generated and developed by applying a repeated shearing load to the thin film material of S10C, and the influence of the observation / microstructure of its progress process was examined. As a result, it was confirmed that the pearlite crystal grains of the thin film material prevented the crack growth as well as the bulk material, and the propagating cracks also progressed into the pearlite crystal grains.</p>

CiNii Article

開催期間： 2017年01月   記述言語：日本語  

<p>At the same materials, mechanical properties of a film different from those of a bulk and we consider that fatigue property of a film is different from that of a bulk. In this study, we think that formation of fatigue slip band of thin film materials of pure iron , S10C, and S45C, are different from each other and conducted a microscopic observation of the slip band of each thin films. Also we observed strains of each thin films by using Electron Back Scatter Diffraction Pattern (EBSD). As a result, we confirmed that slip bands occurred at the grain boundaries in pure iron, slip bands occurred in a wide range within the grains in S10C and slip bands occurred in a short range within the grains in S45C. Also we consider that strain occurred at the grain boundaries in pure iron, strains occurred in a wide range within the grains in S10C and strains occurred in a short range within the grains in S45C by EBSD. We indicate that in the case of carbon steel, forms of generation of strain within the ferrite crystal grain differs depending on the different in restraint of perlite.</p>

CiNii Article

開催期間： 2016年01月   記述言語：英語  

<p>High strength steel shows the unique fatigue fracture called Fish eye failure, that's internal originated fatigue failure, in very long cycle region with the stress below a fatigue limit. Therefore, in order to build the lifetime method evaluation in a very high cycle region, an elucidation of the mechanism of internal fatigue failure is desired. It's reported internal fatigue crack in high strength steel is propagating extremely slowly. However, it is not clear whether this extremely slow fatigue propagation is a phenomenon peculiar to high strength steel. In this study, the materials which were changed hardness of high strength steel SNCM439 were used, and the crack propagation by ΔK decrease fatigue test in vacuum were observed. And it was inquired whether the extremely slow crack propagation would be very peculiar to high strength steel.</p>

CiNii Article

開催期間： 2016年01月   記述言語：英語  

<p>Even if metal thin film is the same material, it does not know that different mechanical characteristics form a bulk material are shown, and general fatigue behavior showing a bulk material does not necessarily appear. The present condition is that research of the fatigue behavior in the repetition shear load of a metal thin film is not made compared with the thing of load direction axis and bending. From studies of thin films in the cyclic shear loading to date, a crack with a locally slip in S10C occurs. The cause such crack occurs, the strain in the ferrite by applying the cyclic shear loading occurs, pearlite is considered to crack been concentrated deformed part that is sandwiched between the perlite harder than ferrite because no deformation occurs. So, in this study we used S45C that is high perlite volume fraction and has many of ferrite sandwiched perlite, observed intergranular crack, transgranular crack, and crack with locally slip. As a result, we confirmed difference of crystal orientation near the crack and the crack initiated along slip plane and not reached back face. And we considered that crack was initiated by local concentration of deformation.</p>

CiNii Article

開催期間： 2016年01月   記述言語：英語  

<p>Small fatigue crack closure is observed as a thing with a possibility that the influence of change of the stress level and a stress ratio, etc. to the crack growth behavior can be explained, and until now various researches have been done. Although there is a method using the strain gage as the dynamic measurement method required for the elucidation of a minute fatigue crack, in respect of generating of minute fatigue cracks being directly contacted to a measuring object thing, and there is a problem in durability or measurement of the crack growth behavior, it may not necessarily be effective. Then, its attention was paid to the magnetostriction effect which is one of the magnetic actions of a ferromagnetic substance. Measurement of the opening stress of the minute fatigue crack under dynamic load and crack length performed by measuring the magnetic field change by the magnetostriction effect, without needing the contact to an object with simple equipment.</p>

CiNii Article

開催期間： 2016年01月   記述言語：英語  

<p>In the soundness and safety assessment based on fracture mechanics of equipment and a structure, the nondestructive evaluation of a crack is indispensable. In recent years, various the evaluation method is also developed and studied with remarkable progress of a sensor. An inspection method magnetic also in nondestructive evaluation is an effective inspection method from being safe and being able to automate. In this research, a possibility that the position of crack can be measured was considered by against a rotating test piece of measuring the magnetic flux leakage using the hole sensor. As a result, it is possible to measure position of crack of 2.6mm or more by two-dimensional distribution of magnetic flux leakage.</p>

CiNii Article

開催期間： 2015年11月21日   記述言語：日本語  

FRP can have various properties by compositing materials that have different mechanical property, but the fracture mechanism is very complicated. So far, it is known that strength property of Glass Fiber Reinforced Plastics (GFRP) is greatly changed by modifying the interface between resin and fiber. Consequently, coupling agents are applied to the interface for improving the interface strength. In our research, to improve the interface strength we used Epoxy resin that has similar structure with Polycarbonate (PC) used for matrix, and resin copolymerizing Polydimethylsiloxane (PDMS) that has siloxane bond (Si-O-Si) that is similar structure with glass. About these GFRTP, We did fatigue test and crack propagation test. After that, we considered influence of appearance of micro crack propagation on fatigue behavior of GFRTP

CiNii Article

開催期間： 2015年11月21日   記述言語：日本語  

Metal thin films don't necessarily appear general fatigue behavior like a bulk material. By a balk and film material, there is difference of restricted state because of differing in the number of grains to the direction of film thickness. In previous report the diagram of ratio of slipped grains and number of cycle was sorted by film thickness/grain size ratio in carbon steel thin film. Then slip ratio dramatically changed film thickness/grain size ratio 0.81 to 1.00. The influence of grain's existence frequency to direction of film thickness was considered to slip band formation. In this research cross section of carbon steel thin film was observed. As a result, slip deformation occurred over two grains to film thickness. Slip band were faced out of plane when slip system was specified by EBSD.

CiNii Article

開催期間： 2015年09月13日   記述言語：日本語  

Small fatigue crack closure is observed as a thing with a possibility that the influence of change of the stress level and a stress ratio, etc. to the crack growth behavior can be explained, and until now various researches have been done. Although there is a method using the strain gage as the dynamic measurement method required for the elucidation of a minute fatigue crack, in respect of generating of minute fatigue cracks being directly contacted to a measuring object thing, and there is a problem in durability or measurement of the crack growth behavior, it may not necessarily be effective. Then, its attention was paid to the magnetostriction effect which is one of the magnetic actions of a ferromagnetic substance. Measurement of the opening stress of the minute fatigue crack under dynamic load and crack length performed by measuring the magnetic field change by the magnetostriction effect, without needing the contact to an object with simple equipment. Moreover, it measured by having changed cross-sectional shape of the specimen. Resulting in, opening stress of the minute fatigue crack opening stress was able to measure about specimen regardless of the cross-sectional shape of the specimen. However, at this stage, it is possible to perform a crack length measurement can only specimen having a circular cross-section.

CiNii Article

開催期間： 2015年09月13日   記述言語：日本語  

It's well known High Strength Steel shows internal origin type fatigue failure called Fish eye failure in low stress and high cycle region. In this failure, ODA(Optically Dark Area) is formed and this ODA occupies the great portion of fatigue life of Fish eye failure. Although the explication of the mechanism of ODA formation is needed for the explication of the Fish eye failure mechanism, the explication is not yet accomplished. It's reported that internal fatigue crack in high strength steel is propagating extremely slowly by recent investigations. However, it is not clear the relationship between the extremely slow fatigue crack growth behavior and the mechanism of ODA formation, and whether it is a peculiar phenomenon of high strength steel. In study, fatigue test was done in vacuum environment. As a result, fractography suggest that more obvious ODA is formed by smaller stress ratio when internal crack is extremely slowly propagating.

CiNii Article

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