Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.msea.2020.139821

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Phase-separated glass (PSG) is being used widely for manufacturing scientific apparatus and kitchenware, owing to its advantages of high hardness and heat resistance, which can be attributed to its sea- and island-like structures on the nanoscale. There is a growing demand in the glass industry for methods for evaluating and visualizing the local stress distribution in such glass materials at the nanoscale in order to elucidate their fracture mechanism and to obtain more information to develop even harder glass materials. In this study, we clarified the correlation between the local stress in this type of glass material and its associated nanoscale structure using a nanoelectron probe based on scanning transmission electron microscopy and cathodoluminescence. The peak shift of an emission line corresponding to an intentionally doped rare-earth element was measured based on the piezospectroscopic effect. We found that the sea- and island-like structures, whose origins can be attributed to the difference in the thermal expansion coefficients of the two phases, mutually push each other. This result was confirmed by a simple finite-element method simulation. The present result suggests that the local mechanical properties of PSG can be well described by a coherent elastic continuum consisting of the phases that evolve during thermal treatment. (C) 2019 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

DOI： 10.1016/j.mtla.2019.100578

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

DOI： 10.1016/j.msea.2019.138218

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

The time-dependent crack initiation from the interface free-edge of adhesively bonded axisymmetric columnar butt joints (epoxy/SUS, edge shape: 90 degrees/90 degrees) was investigated in detail. With the change of applied stress level, sigma(n), the butt joints exhibited crack initiation life, t(C), that varied about four orders of seconds (10(2)-10(6) s). Such a clear time-dependent life property was then studied in terms of the fracture mechanics. The near-edge stress/strain field at the crack initiation was numerically evaluated with the finite element method (FEM) by applying the time-hardening creep law to the epoxy resin. It was found that the critical asymptotic stress field along the interface represented by the combination of two parameters, lambda(cr)(sigma) (creep stress singularity index) and K-sigma(cr) (creep stress intensity factor), satisfies a unique relation irrespective of (sigma(n), t(C)) sets. The same tendency was also confirmed when the near-edge total strain field parameters were employed. These results indicate that the K-lambda criterion, originally developed for static fracture problems, still holds its validity in the time domain. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.engfracmech.2017.08.017

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

In order to directly investigate the grain boundary (GB) hydrogen embrittlement in polycrystalline materials, a novel micro-mechanical testing method was developed. By combining a site-specific sampling technique and a high-voltage environmental transmission electron microscope (HV ETEM), the fracture property of micro-cantilever specimens fabricated from the same GB in a nickel-aluminide (Ni3Al) polycrystal was critically compared in environments with/without hydrogen (H-2) gas. For randomly oriented GBs, brittle fracture nucleation accompanied by plastic deformation was observed in a H-2-containing environment except for ones with small orientation difference. No GB fracture was observed for coherent Sigma 3 boundaries. It also appeared that the similitude of the hydrogen-enhanced de cohesion (HEDE) mechanism was still valid even for the submicron-scale specimens. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2016.03.035

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

The strength against interfacial fracture initiation from a free-edge of Si/Cu micro-components was evaluated. The micro-scale cantilever specimens containing dissimilar interfaces were fabricated with a focused-ion-beam (FIB) technique, and they were loaded with a quantitative nanoindenter holder operated in a transmission electron microscope (TEM). The specimens were successfully fractured along the Si/Cu interface, and the critical loads at fracture were measured. The critical stress distribution near the free-edge was evaluated with the finite element method (FEM). The near-edge stress distributions of 90°/90°-shaped specimens were scattered while those of 135°/135°-shaped specimens were in good agreement despite the difference in specimen dimensions. Such a difference was discussed in terms of the relation between the magnitude of stress singularity and the microstructures of material.

DOI： 10.4028/www.scientific.net/KEM.665.169

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The effect of additional solute magnesium (Mg) on mechanical and high-cycle-fatigue properties of 606146 aluminum alloy is investigated in detail. By adding 0.5% and 0.8% Mg to the 6061-T6 alloy with a normal stoichiometric Mg2Si composition (base alloy), the alloy exhibits eminent strain-aging characteristics demonstrated by the emergence of serrated flow, the negative strain-rate-sensitivity and relatively weakened temperature dependency of flow stress. The Mg-added new alloy also shows higher work-hardening rate than the base alloy particularly at initial flow regime and at lower strain rate. The SN curve of the new alloy shows a clear fatigue limit which is absent in the base alloy. The fatigue limit of the new alloy is shown to be controlled by the threshold against small crack growth. Moreover, the new alloy clearly exhibits a coaxing phenomenon (time-dependent strengthening) which is absent in the base alloy. The coaxing effect is attributed to the existence of a small quasi-non-propagating crack whose growth resistance gradually increases during stress amplitude step-ups. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2015.06.051

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

A novel experimental method that enables evaluation of interfacial strength of micro-components subjected to well-controlled various environments is proposed. The method combines a high-voltage transmission electron microscope (HVEM) equipped with an open type environmental cell (EC) and a quantitative nano-mechanical holder. The experiments were conducted by using focused-ion-beam-processed micro-cantilever specimens containing interfaces of dissimilar materials (silicon (Si) and copper (Cu)). The in situ observation of fracture phenomenon along a target interface (Si/Cu) and the simultaneous measurement of fracture load were successfully implemented under vacuum and gaseous environments (N-2 gas and N-2/H-2 mixed gas) whose maximum pressure was controlled at 5 x 10(3) Pa. The stress distribution at the onset of fracture was calculated in detail by finite element analysis. The strength against interfacial debonding was then evaluated by the local normal stress value at the interface free-edge. The proposed technique, which can also be combined with simultaneous electron probe analyses, is highly versatile when compared to the conventional nano-mechanical strength evaluations under limited environments.

DOI： 10.1007/s11340-015-0008-2

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

In order to investigate the fatigue limit micro-mechanism of a precipitation-hardened Al-Mg-Si alloy (6061-T6), the alloy was subjected to very-high-cycle fatigue (VHCF) of over 10(9) cycles by an ultrasonic fatigue method. Two kinds of specimens, one with smooth surface and the other with a small artificial hole on the surface, were compared. The smooth specimens showed no distinct fatigue limit. Conversely, the holed specimens showed clear fatigue limit which had been generally deemed to be absent in nonferrous alloys. In addition to the conventional fatigue crack growth (FCG) observation by replica technique, metallographically critical analyses by electron backscattered diffraction (EBSD) and cross-sectional focused ion beam (FIB) were conducted to reveal the micro-plasticity associated with FCG. It was found that the fatigue life of smooth specimens at low stress amplitude was controlled by an unstoppable FCG mechanism mediated by persistent slip bands (PSBs). On the other hand, the emergence of distinct fatigue limit in holed specimens was attributed to a non-propagating crack having mode I characteristics in essence. No coaxing effect was, however, confirmed for such non-propagating cracks. The above results, which were somewhat different from previous ones obtained by rotating bending under normal frequency, were discussed in terms of both metallurgical and mechanical points of view. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2014.07.039

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The fracture strength properties of single-crystalline Si micro-components fully processed via focused ion beam were successfully evaluated by an in situ nano-mechanical testing system. Fracture initiation of all tested specimen was completely brittle within the detection limit of the testing system. By using different types of cantilever specimens (smooth/notched), it was suggested that the fracture initiation along the {1 1 1} plane was controlled primarily by the critical normal stress component regardless of the magnitude of shear stress component. The average strength value for FIB-processed specimens (sigma(c) = 8.1 GPa) was found to be approximately the same as that of wet-etch-processed specimens while larger than that of dry-etch-processed specimens. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.sna.2013.11.037

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SOC TESTING MATERIALS  

In this study, we propose a method for assessing the applicability of an artificial flaw as a small initial crack for fatigue limit evaluation. The proposed method is applied to drill holes and sharp notches introduced using a focused ion beam (FIB) technique in annealed 0.45% carbon steel. It is found that under rotating bending fatigue, an FIB notch can be used as a small initial crack for fatigue limit evaluation, whereas a drill hole cannot, for root area of 50 mu m. Here, root area is the square root of the area obtained by projecting the defect onto a plane perpendicular to the load axial direction. The results indicate that an FIB notch can be used as a small initial crack for fatigue limit evaluation in a greater number of materials than those in which a drill hole can be used.

DOI： 10.1520/JTE20120176

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The goal of this study was to confirm the presence of fatigue limit in a plain specimen of a new precipitation-hardened aluminium alloy. The alloy was fabricated by adding 0.53% excess Mg to the standard 6061-16 aluminium alloy with a balanced Mg2Si composition. There were two challenges in this study: verification of the existence of fatigue limit in this new alloy and interpretation of the large scatter in specimen life at the low stress level amplitude. For the former, the existence of a fatigue limit was confirmed by a coaxing effect test. For the latter, the initiation and growth behaviors of a small fatigue crack at low stress amplitude were observed by plastic replica method not only with an optical microscope but also with a scanning electron microscope (SEM). The study results showed that the large scatter in specimen fatigue life at the low stress level amplitude was due to the anomalous initiation and growth behaviors of the small fatigue crack, which in turn was strongly influenced by local conditions. Finally, a conservative S-N curve of this new alloy evaluated by using a plain specimen could be obtained where a distinct knee point showed at cycles of about 10(6). (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijfatigue.2012.06.001

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

New aluminium alloys were developed by adding excess Mg to the ordinary precipitation-hardened aluminium alloy, JIS 6061-T6. By analyzing the results of the fatigue tests and the coaxing effect test, the existence of a distinct fatigue crack propagation limit in these new aluminium alloys was confirmed using a small-holed specimen. Moreover, by comparing the fatigue process with that of the 6061 alloy, the possibility of generating the fatigue limit in face-centred cubic metals, which has been considered to be absent, was discussed. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2012.03.018

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

The mechanism controlling the fatigue life of a precipitation-hardened Al-Mg-Si alloy (6061-T6) at a high-cycle fatigue (HCF) regime of over 10(7) cycles was investigated in detail. It was found that over 90% of the total fatigue life was occupied by the growth process of a microstructurally small crack at relatively low stress amplitude. The small crack was often found to be arrested and halted for a long period (more than 106 cycles) before it began to grow again, which resulted in a significantly slow growth process. The small crack was then analyzed not only by the conventional fractography but also by the cross-sectional observation of the crack tip region using a focused ion beam and transmission electron microscopy. These observations, supplemented also by a grain orientation analysis using electron backscattered diffraction, explicitly revealed the following points: (i) the small crack growth observed on the specimen surface is primarily related to facet-type cracking that occurs exclusively at the specimen surface; (ii) the growth direction of the small crack has strong anisotropy (i.e. surface-induced growth); (iii) the facet-type cracking is related to the formation of persistent fine slip bands that accompany no structural change of the matrix. On the basis of these results, the micromechanism of small crack growth and its relation to the concept of fatigue limit at the HCF regime is discussed in detail. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2012.01.023

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

The effect of hydrogen on dislocation structures around a mixed-mode fatigue crack tip in a single-crystalline iron silicon alloy was investigated by cross-sectional electron backscatter diffraction and high-voltage electron microscopy. In contrast to the previously reported results in an inert environment, no dislocation cells were formed around the crack tip in a hydrogen environment. The microscopic features around the crack tip suggest that hydrogen promotes a mode I-type crack growth mechanism, which reasonably explains the observed macroscopic crack growth property. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2010.12.032

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

A microscopic analysis of sub-critical hydrogen-assisted cracking (HAC) in a single-crystalline iron silicon thin sheet was conducted and revealed the following points: (i) crack tip geometry and crack growth unit (striation spacing) are constant even when crack length (i.e. apparent stress intensity) and crack velocity (da/dt) significantly change; and (ii) da/dt monotonically increases with plastic zone size. These findings suggest that the effect of large-scale plasticity on the rate-limiting process should be explicitly considered in the kinetic modeling of the HAC mechanism. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2010.11.035

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

Dislocation structures around a mixed-mode fatigue crack tip introduced into a single-crystalline iron silicon alloy is characterized by cross-sectional electron backscatter diffraction and high-voltage electron microscopy. The results show that the crack growth is preceded by the formation of a cell band and the crack grows along cell boundaries. Crack growth rate and width of the cell band are constant despite the monotonic increase in stress intensity, which is anomalous in terms of the conventional fracture mechanics concept. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2010.09.033

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The microscopic feature of hydrogen-induced quasi-brittle fatigue fracture in low-strength carbon steel was investigated by transmission electron microscopy and electron backscatter diffraction These analyses, aided also by fractography, explicitly revealed the following points, i) brittle striation is formed by extensive slip at the crack tip, ii) quasi-brittle facet is not crystallographically related to the (100) cleavage plane, and iii) crack growth process is stable These results may suggest that the crack growth, despite its brittle appearance, is essentially a combined process of extensive slip and significantly localized ductile cracking, which is distinct from the normal slip-off growth mechanism (C) 2010 Elsevier B V All rights reserved

DOI： 10.1016/j.matlet.2010.08.019

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A novel specimen holder that enables in situ observation of crack-tip deformation and/or fracture under a controlled environment is developed for a high-voltage electron microscope (HVEM). A window-type environmental cell (EC) that incorporates a uniaxial straining apparatus is built into a side-entry-type single-tilt specimen holder. The gas control in EC, straining apparatus design, limited field of view for crack-tip observation, and specimen preparation for the specimen holder are presented in detail. Experimental results successfully demonstrate that the developed specimen holder is quite useful for the dynamic observation of crack-tip deformation and/or fracture subjected to a hostile environment, such as hydrogen gas. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ultramic.2010.07.011

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The effect of gaseous hydrogen on cyclic slip behavior around a fatigue crack tip introduced along the {1 1 0} plane in a Fe-3.2 wt.% Si alloy is precisely investigated by cross-sectional transmission electron microscopy and fractography. The results clearly suggest that the fatigue crack growth rate is promoted by hydrogen, whereas the number of dislocations emitted per load cycle is reduced. In addition, dislocation distribution is localized around the crack, causing quasi-brittle crack morphology. A sustained load test confirms that no subcritical crack growth caused by cleavage or micro-void coalescence exists along the {1 1 0} plane, which indicates that the observed increase in the fatigue crack growth rate is correlated solely to the intrinsic effect of hydrogen on the cyclic slip-off process around the crack tip. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2009.11.040

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

In order to investigate the brittle-striation formation mechanism of low carbon steel JIS S10C in hydrogen gas environment, TEM/EBSD observations corresponding to fractography were conducted. Main results are as follows. (1) Quasi-cleavage (QC) facets plane with brittle striations does not coincides with (100) cleavage plane. (2) Slip deformation distributions reflecting the brittle striation formation processes are observed with TEM. One of the conceivable brittle-striation formation mechanisms which can explain these results is as follows. A striation line is formed during the loading part of the cycle as a trace of blunting by slip. Then, stable ductile crack growth starts. These processes were similar to those in the normal ductile fracture from a crack, that is, ductile tearing process in tension.

DOI： 10.1299/kikaia.76.1335

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

Local cyclic slip behavior around an oblique fatigue crack tip in single-crystalline Fe-3.2 wt.% Si alloy is precisely observed by using cross-sectional transmission electron microscopy (TEM). The observation successfully reveals the existence of different dislocation structures (vein, ladder, labyrinth, cell) around the crack tip. The results clearly suggest that the crack growth is strongly related to the formation of dislocation cell structures. Additional fractographic observation suggests that the crack growth, the path of which is found to be the boundary between hard cell region and soft matrix, accompanies the formation of striation pattern along the boundary.

DOI： 10.1299/kikaia.76.251

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Authorship：Lead author   Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The effect of hydrogen on local cyclic behavior around an oblique fatigue crack tip in single-crystalline Fe-3.2wt.%Si alloy is precisely investigated by using cross-sectional transmission electron microscopy (TEM). The observation successfully reveals that the crack propagation is strongly correlated to the formation of dislocation cell structure in an inert atmosphere, whereas no cell structure is formed around the crack tip in a hydrogen atmosphere.

DOI： 10.1299/kikaia.76.1002

CiNii Books

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Authorship：Lead author   Language：Japanese   Publisher：The Japan Institute of Metals and Materials  

DOI： 10.2320/materia.48.609

CiNii Books

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

The effect of hydrogen on cyclic slip behavior around a fatigue crack tip in a bulk Fe-Si alloy is successfully observed by high-voltage electron microscopy. The observation explicitly reveals the following points: (i) hydrogen reduces the amount of cyclic slip whereas it promotes crack growth rate; and (ii) hydrogen induces a quasi-brittle crack growth that accompanies localized slip in the crack periphery. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2009.03.020

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

The cyclic slip behavior around a fatigue crack tip originally located inside a bulk Fe-Si alloy was successfully observed by a high-voltage electron microscope in combination with a novel specimen preparation method. The method, by taking advantages of ion milling and focused ion beam techniques, ensures that the original shape of the crack tip is preserved without introducing additional slips. The observation confirms that the slip bands emitted from the fatigue crack tip are bounded by a labyrinth-like wall structure. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2009.01.002

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

Fatigue crack propagation tests using a single-crystalline Fe-3.2 wt.%Si alloy are conducted for the purpose of investigating the effect of hydrogen gas on cyclic slip around the crack tip. The crack propagation rate is found to be larger in hydrogen gas than in non-hydrogen (helium) gas. The fracture surface and the near-tip cross-section of {110} crack are observed in detail by using a scanning electron microscope (SEM) and a transmission electron microscope (TEM), respectively. The observation reveals that, in helium atmosphere, the propagation is attributed solely to a ductile plastic rocess. In hydroen atmosphere, the propagation can be also attributed to a ductile plastic process except that the amount of plastic deformation is small and the cyclic slip is concentrated around the crack tip region. Different types of slip systems are found to be operative in helium and in hydrogen gas atmospheres, which is postulated to be correlated to the slip concentration and the increased propagation rate.

DOI： 10.1299/kikaia.75.1082

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

To clarify the mechanics of time-dependent crack initiation at all interface edge in submicron thick elements due to creep, delamination experiments are Conducted using a micro-cantilever bend specimen with a tin/silicon interface edge. After the specimen time-dependently deforms under a constant load, a delamination crack is initiated at the Sn/Si interface edge. In addition, the steady state creep property of Sn is estimated by performing an inverse analysis using a finite element method based oil creep deformation experiments conducted for different specimens. Stress analysis using the obtained creep property reveals that stress and strain rate singularities exist at the Sn/Si interface edge under creep deformation. The intensity of the Singular field time-dependently increases as the creep region expands, and eventually it becomes a steady state. The stress and strain rate intensities at the steady state correlate well with the crack initiation life, which indicates that the singular stress field near the interface edge governs the creep crack initiation. (c) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.engfracmech.2008.01.007

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

DOI： 10.1016/j.tsf.2007.08.062

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

In order to elucidate the role of plasticity on interface crack initiation from a free edge and crack propagation in a nano-component, delamination experiments were conducted by a proposed nano-cantilever bend method using a specimen consisting of ductile Cu and brittle Si and by a modified four-point bend method. The stress fields along the Cu/Si interface at the critical loads of crack initiation and crack propagation were analyzed by the finite element method. The results reveal that intensified elastic stresses in the vicinity of the interface edge and the crack tip are very different, although the Cu/Si interface is identical in both experiments. The plasticity of Cu was then estimated on the basis of the nano-cantilever deflection measured by in situ transmission electron microscopy. The plasticity affects the stress fields; the normal stress near the interface edge is intensified while that near the crack tip is much reduced. Both the elasto-plastic stresses are close to each other in the region of about 10nm. This suggests that the local interface fracture, namely, the crack initiation at the interface edge and the crack propagation along the interface, is governed by elasto-plastic normal stress on the order of 10 nm.

DOI： 10.1007/s10704-007-9079-0

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

The interface strength of low-dimensional nano-components such as films and islands formed on substrates has been investigated in this project, and the focus is put on the mechanics of crack initiation from the free interface edge and propagation along the interface. The series of experiments elucidates the applicability of fracture mechanics concept on the structures. We proposed experimental methods for evaluating the initiation strength of an interface crack in submicron films and islands deposited on substrates. The initiation is governed by the singular stress field, and the criterion is prescribed by the stress intensity parameter. Using special loading apparatus built in a TEM, we developed a crack initiation method for nano-components and the role of plasticity on the delamination is clarified. Subcritical crack growth along an interface between submicron films under fatigue was also investigated by modified four-point bend method.

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

A novel in situ TEM fracture testing method is developed to elucidate the mechanics dominating crack initiation at an interface edge in nano-structures. The testing system includes a special mechanical apparatus equipped with a piezo-actuated stage and a diamond loading tip attached to a MEMS load sensor, which enables us to control specimen position and perform quantitative load measurement with enough precision. Nano-scale cantilever specimens with interfaces are fabricated from a multi-layered material (Si/Cu/SiN) using FIB process technique. The validity of the testing method is demonstrated by conducting interfacial crack initiation experiments for the specimens with different size. The applied load and the specimen image have been successfully monitored and recorded during the experiments. For each specimen, the crack is initiated from the free-edge of interface between Si/Cu at a maximum load, PC, and the specimen is instantly separated at the interface. Using the experimental results the stress fields along the Si/Cu interface at the crack initiation are analyzed for each specimen by finite element method. This reveals that the crack initiation of the Si/Cu interface is governed by the normal stress on the interface near the edge.

DOI： 10.2472/jsms.55.1073

Scopus

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

In order to examine the mechanics of crack initiation at the free interface edge of a microcomponent on a substrate, delamination tests are carried out for two specimen shapes of Cr microdots on a SiO2 substrate. The microdots of the first specimen are shaped like the frustum of a round cone. The Cr microdots are successfully delaminated from the SiO2 substrate in a brittle manner and the critical load is measured by atomic force microscopy (AFM) with a lateral loading apparatus. Stress analysis reveals that a singular stress field exists near the interface edge and the strength for the crack initiation is governed by the intensified normal stress field. The critical stress intensity parameter is evaluated as K-sigma C approximate to 0.24 MPa m(0.39). Similar delamination tests are conducted for microdots shaped like the frustum of an oval cone. The stress distributions at the crack initiation of this specimen shape show a higher normal stress than the first specimen shape in the region near the interface edge of about x < 40 nm, while it is lower in the region of about x > 50 nm (x: distance from the edge). This suggests a limitation of conventional fracture mechanics: namely, the crack initiation in these specimens is not uniquely governed by the intensity of the singular field. It is found that the delamination crack is initiated when the averaged stress sigma(ya) in the region of 90-130 nm reaches 190-270 MPa, regardless of the specimen shape. This indicates that the dominant stress region of crack initiation is roughly estimated as 90-130 nm and the criterion is given in terms of the averaged stress in the region. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.engfracmech.2006.04.019

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Authorship：Lead author  

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Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Powder and Powder Metallurgy  

DOI： 10.2497/jjspm.23-00075

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

DOI： 10.1299/transjsme.23-00271

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

This study aims to understand the mechanical properties of cellulose nanofibers (CNFs), a nano-sized material element of woods or plants. We develop all-atom (AA) molecular dynamics models of cellulose microfibrils (CMFs), which are the smallest constituent of CNFs. The models were designed for the process of structural failure or the degradation of a hierarchical material of multiple CMF fibers, due to shear deformation. It was assumed that two CMFs were arranged in parallel and in close contact, either in a vacuum or in water. The CMF models in water were built by surrounding AA-modeled water molecules with a few nanometers. Shear deformation was applied in the axial direction of the CMF or in the direction parallel to molecular sheets. Shear moduli were measured, and they agree with previous experimental and computational values. The presence of water molecules reduced the elastic modulus, because of the behavior of water molecules at the interface between CMFs as a function of temperature. In the inelastic region, the CMF often broke down inside CMFs in a vacuum condition. However, in water environments, two CMFs tend to slip away from each other at the interface. Water molecules act like a lubricant between multiple CMFs and promote smooth sliding.

DOI： 10.3390/applmech4010013

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

Due to great interest in the development of electric vehicles and other applications, improving the performances of lithium-ion batteries (LIBs) is crucial. Specifically, components of electrolytes for LIBs should be adequately chosen from hundreds of thousands of candidate compounds. In this study, we aimed to evaluate some physical properties expected for combinations of molecules for electrolytes by microscopic simulations. That is, the viscosity, ionic conductivity, degree of dissociation, diffusion coefficient, and conformation of each molecule were analyzed via molecular dynamics (MD) simulations. We aimed to understand how molecular-sized structures and properties collaboratively affect the behavior of electrolytes. The practical models of molecules we used were ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (GBL), γ-valerolactone (GVL), dimethyl carbonate (DMC), ethyl-methyl carbonate (EMC), diethyl carbonate (DEC), and lithium hexafluorophosphate (LiPF6). Many molecular systems of electrolytes were simulated, in which one molar LiPF6 was mixed into a single or combined solvent. It was found that small solvent molecules diffused with relative ease, and they contributed to the higher ionic conductivity of electrolytes. It was clarified that the diffusion coefficient of lithium (Li) ions is greatly affected by the surrounding solvent molecules. We can conclude that high-permittivity solvents can be selectively coordinated around Li ions, and Li salts are sufficiently dissociated, even when there is only a small content of high-permittivity solvent. Thus, we can confirm solely by MD simulation that one of the better candidates for solvent molecules, formamide (F), will exhibit higher performance than the current solvents.

DOI： 10.3390/batteries8030027

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

DOI： 10.2472/jsms.71.167

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

DOI： 10.1299/transjsme.22-00019

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Publishing type：Research paper (scientific journal)   Publisher：Trans Tech Publications, Ltd.  

Sulfide was used as solid lubricant, and MoS₂ was popular. It was used industry as powder shape. Sulfur as oil additive; ZDDP, MoTDC were also well known. These composites make tribofilm which prevent seizure, scoring and some tribological troubles. In this paper, sulfides were synthesized by powder metallurgy technics. In addition, these sulfides were mixed with bronze powders and sintered as cylindrical specimen. As a result of the friction test in the lubricated condition, tribofilm were covered with specimen surface. By XPS observation, sulfides and oxides were detected on the specimen surface. In the test, additive was not contained in the lubricant because PAO as base oil was adapted. However, sulfide in the specimen affect the making the tribofilm, especially when bornite (Cu₅FeS₄) was used.

DOI： 10.4028/www.scientific.net/kem.901.164

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Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Powder and Powder Metallurgy  

DOI： 10.2497/jjspm.68.317

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Publishing type：Research paper (scientific journal)   Publisher：Hindawi Limited  

As a sustainable ecosystem, the general firing process for ceramics emits large amounts of CO2 gas; thus in ceramics production, the focus is the nonfiring process; however, the solidification and strengthen mechanism of this nonfiring system, which essentially reacts between surface-activated ceramic particles and a solvent, has not been elucidated to date. The nonfiring process had three steps, i.e., particle surface activate process by grinding process, maintaining the active state until starting nonfiring solidification begins, and nonfiring solidification process. Thus, in this study, the reaction of silica and water was simulated by adapting molecular dynamics based on LAMMPS with ReaxFF potentials. Reproducing the activated silica surface state, three ended models called O model, Si model, and OH model were prepared which indicated ended molecules of each surface. These models and a water molecule as a solvent were bonded in the atomic scale, and the energetic state and mechanical properties were evaluated. A reacted or structured O-H-O bond was reproduced in the nonfiring process in the O-ended model. The bond was a hydrogen bond. A Si-O-Si bond was produced when a Si atom was ended on the interface. The bonded interface was able to tensile. However, the tensile strength was weaker than that of the solid silica model. The nonbonded OH model did not have tensile strength.

DOI： 10.1155/2020/8857101

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Other Link： http://downloads.hindawi.com/journals/jnm/2020/8857101.xml

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

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DOI： 10.4236/snl.2019.94004

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

DOI： 10.1299/transjsme.19-00206

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DOI： 10.1088/1757-899X/461/1/012074

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：European Powder Metallurgy Association (EPMA)  

In recent years, with the development of powder metallurgy technology, sintered materials have been tried for bearings. However, parts made by powder metallurgy are porous and therefore have low strength. Therefore, this research was conducted using bimetal which is excellent in strength and sliding property. In this experiment, a friction test was carried out using sulfide bronze and metallic powder of brass and phosphor bronze with blended solid lubricant (graphite or sulfide) These materials were sintered in vacuum condition. As a result, in the friction test, the phosphor bronze had the lowest coefficient of friction and a stable friction. Also the amount of wear on phosphor bronze was small. This is thought to be due to the improvement of the abrasion resistance by adding phosphorus and the solid lubricant. In conclusion, among these three copper alloys, phosphor bronze was found to be the most excellent in wear resistance.

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

The strength against fracture initiation from an interfacial edge in bonded micro-components (Si/Cu and Cu/SiN) is quantitatively evaluated by using a novel technique that combines a minute mechanical tester (nano-indenter) and a special high-voltage transmission electron microscope (TEM) equipped with an environmental cell. The micro-component specimens having an interfacial edge of controlled geometry are prepared by a focused-ion-beam (FIB) based micro-sampling technique. The fracture initiation strength is particularly analyzed in terms of the fracture mechanics concept. In the case of Si/Cu interfacial edge, the scatter of strength value is significantly affected by the edge singularity: The higher singularity (wedged specimen) leads to the smaller scatter of strength. The effect of gaseous hydrogen (H2) on the strength of Cu/SiN is then evaluated by two kinds of wedged specimens. It is found that the strength is eminently reduced by the existence of H2 gas and, moreover, the strength reduction is dependent on specimen shape.

DOI： 10.1109/MHS.2018.8886975

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DOI： 10.1088/1757-899X/307/1/012039

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：International Conference on Fracture  

The effect of hydrogen (H2) gas on grain boundary fracture was evaluated with a novel micro-mechanical experimental method. Micro-specimens were fabricated from the same discrete grain boundary (GB) in a bulk poly-crystalline alloy. The specimens were then mechanically loaded in a special transmission electron microscope (TEM) equipped with an environmental cell (EC). It was shown that brittle GB fracture preceded by plasticity occurred only in a H2-containing environment. The GB fracture tendency appeared to be related to the orientation difference between the constituent grains.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：European Powder Metallurgy Association (EPMA)  

Sufides as MoS2 are known as solid lubricants. These materials are also known as thermoelectric materials. However, there is no material satisfying both functions at the same time. In this study, sulfides powders such as Cu2S (chalcocite), TiS2, SnS, Cu5FeS4 (bornite) were synthesized under vacuum condition. Some specimens of sintered sulfides were evaluated by friction tester and their lubricity. As a result it was found that SnS had indicated better friction properties. Other specimens were evaluated in terms of Seebeck coefficients, which is one of the thermoelectric properties. Experimental results of the Seebeck coefficients were compared with simulation results. For thermoelectric properties, the Seebeck coefficient of Cu2S had matched with experiments and simulation. Totally, Cu2S (chalcocite) and SnS has superior properties both, as solid lubricant as well as thermoelectric material.

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Language：English   Publisher：Japanese Society of Tribologists  

In order to clarify the plastic deformation mechanism of silicon carbide in cubic phase (3C-SiC), molecular dynamics (MD) simulations are performed on the nanoindentation using a spherical indenter. Transition from elastic deformation to plastic deformation has been confirmed by the phenomenon called pop-in in the load-displacement curves during nanoindentation. Dislocations on {1 1 1} slip planes are found during indentation. In order to analyze internal defects, common neighbor analysis (CNA) is slightly modified so that it is suitable for the analysis of slips of zinc-blend structure. In our method, the CNA is applied separately to sub-lattice of Si or C in the same SiC. By this method, structural changes are confirmed in a region with the shape of square pyramid when the pop-in behavior occurs. By measuring the atomic distances along the region of misalignment, it was confirmed that there is certainly atomic sliding by crystalline slip. Furthermore, it is found that, with increase of loading, dislocation loops spread along {1 1 1} slip planes.

DOI： 10.2474/trol.11.183

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Elsevier B.V.  

The strength against fracture nucleation from an interface free-edge of silicon-nitride (SiN)/copper (Cu) micro-components is evaluated. A special technique that combines a nano-indenter specimen holder and an environmental transmission electron microscope (E-TEM) is employed. The critical load at the onset of fracture nucleation from a wedge-shaped free-edge (opening angle: 90°) is measured both in a vacuum and in a hydrogen (H 2 ) environment, and the critical stress distribution is evaluated by the finite element method (FEM). It is found that the fracture nucleation is dominated by the near-edge elastic singular stress field that extends about a few tens of nanometers from the edge. The fracture nucleation strength expressed in terms of the stress intensity factor (K) is found to be eminently reduced in a H 2 environment.

DOI： 10.1016/j.prostr.2016.06.174

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A6061-T6 alloy has been used in the liner material of high-pressure hydrogen gas storage container that is mounted on a fuel cell vehicle. The degradation of the properties such as strength, toughness and hydrogen embrittlement resistance, etc., has been pointed out, because the grain structure of the mouthpiece part of the liner becomes coarse in the manufacturing process. The tensile and fatigue test for the specimens with different grain size were done, and the detected AE signals during the testing were analyzed. In the tensile test, the characteristics of the signals on dislocation motion, transgranular and intergranular fracture were extracted. In the fatigue test, it was shown that the possibility of which the damage is evaluated by the spectral analysis that utilizes the slope of an approximation straight line in the both logarithmic scale display of FFT analysis result. Then we proposed the amplitude ratio R_v that is the parameter which divided the maximum amplitude of signal for intergranular fracture by that of detected signal, and the correlation between the grain size and the R_v was recognized. These proposed information are able to be utilized in order to evaluate the damage of the container.

DOI： 10.1299/transjsme.2014smm0292

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：HINDAWI PUBLISHING CORPORATION  

Fiber Bragg grating (FBG) is an optical fiber sensor and is suitable for acoustic emission (AE) measurements of structures such as chemical plants that require water resistance, explosion proofing, and so forth, However, directionality has been a problem in conventional usage which glues the grating range of an FBG to the inspection surface. This study proposes a cylinder-FBG (C-FBG) sensor with the FBG glued to a cylindrical sensor holder. Effectiveness of the sensor was evaluated by characterizing directionality and frequency sensitivity of the sensor and by comparing the detected AE signals in a 3-point bending test of a carbon fiber reinforced plastic (CFRP) laminate against a conventional wide-band piezoelectric AE sensor. The features of the detected signals were similar to the signals detected by the wide-band AE sensor. These results show that it is possible to produce a wide-band cylindrical sensor without the directionality limitations of the conventional usage of FBG.

DOI： 10.1155/2014/274071

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

The giga-cycle property of a newly developed Al alloy, which contains 0.5vvt.% excess Mg solute compared to a standard age-hardened 6061 alloy (6061-T6), was investigated by using smooth specimens subjected to ultrasonic fatigue. The fatigue strength of the new alloy was higher than that of a normal 6061 alloy particularly at relatively low stress amplitude level. Several analyses (surface crack observation, fractography, FIB cross-sectioning, etc.) were also conducted to reveal the micro-mechanism of the observed strength properties. The following results were obtained: i) No fatigue limit was confirmed for both 6061 and new alloy. ii) Total life (N-f) of 6061 and new alloys was determined by a single fatigue crack initiated from a surface PSB crack. iii) Crack initiation resistance defined by N-25 (number of cycles to reach rho = 25 mm(-2), where rho is the PSB crack number density) for new alloy was higher than that of 6061. iv) The higher fatigue strength of new alloy was explained by the effect of excess Mg solute which increased the resistance against the formation of PSB cracks.

DOI： 10.4028/www.scientific.net/KEM.577-578.293

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

In general, aluminum alloy does not exhibit distinct fatigue limit (knee point) in the S-N diagram. The growth of a small fatigue crack of precipitation-hardened Al-Mg-Si system alloy (6061-T6) was investigated to clarify the mechanism of non-appearance of distinct fatigue limit (knee point) in the S-N diagram. The small crack was analysed in detail by replica method, scanning electron microscope (SEM), and Electron Back Scatter Diffraction Patterns (EBSD). On the other hand, the existence of distinct fatigue limit (knee point) of new developed aluminum alloy by adding excess Mg to the 6061 alloy was found. In this study, the resistance of small crack growth of the developed alloy was compared with standard 6061 alloy. It was revealed that the resistance of crack growth of new developed alloy was higher than that of standard 6061 alloy in short crack region (l<1.0 mm).

DOI： 10.4028/www.scientific.net/MSF.794-796.313

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

The growth of a small crack controlling the high-cycle fatigue life of a precipitation-strengthened 6061-T6 aluminium alloy was critically investigated. As the applied stress lowered, the small crack was arrested for a long period (over 10(6) cycles) at grain boundaries before regrowth, which resulted in a significantly slow growth process. The morphological and crystallographic details of the small crack were then analyzed with focused ion beam and transmission electron microscopy. It was revealed that the small crack was formed along fine persistent slip bands (PSBs) whose structure was fairly different from that reported for other metals. The concept of PSB-limited fatigue strength may be extended to include the present material type.

DOI： 10.4028/www.scientific.net/KEM.525-526.213

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Language：Japanese   Publisher：Kansai University  

CiNii Books

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Other Link： http://hdl.handle.net/10112/7509

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

The aim of this study is firstly to investigate the applicability of a sharp notch with Focused Ion Beam (FIB) as a crack for fatigue limit evaluation. Secondly we investigate a condition in which artificial defects (drilled hole, FIB notch) can be used as a crack for fatigue limit evaluation. To achieve the aim, the growth behaviors and the non-propagating crack sizes of small fatigue cracks initiated from a FIB notch and a drilled hole are carefully compared with those of an annealed fatigue crack which imitates an ideally sharp crack. The results show that a FIB notch can be used as a crack for fatigue limit evaluation under some conditions. The results also show that the condition which controls the applicability of an artificial defect as an ideal crack for fatigue limit evaluation is strongly dependent on the relation between (i) the length of a non-propagating fatigue crack and (ii) the crack length when the small fatigue crack growth behaviors from an artificial defect and an ideal pre-crack become almost the same. It is found that the length of (ii) can be obtained by the analyses using the number of cycles from a certain crack length to failure.

DOI： 10.4028/www.scientific.net/KEM.488-489.319

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：European Conference on Fracture, ECF  

In this study, we propose a method for assessing the applicability of an artificial defect as a small initial crack for fatigue limit evaluation. The proposed method is applied to drill holes and sharp notches introduced using a focused ion beam (FIB) technique in annealed 0.45% carbon steel. It is found that under rotating bending fatigue, an FIB notch can be used as a small initial crack for fatigue limit evaluation, whereas a drill hole cannot, for of ∼50 μm. Here, is the square root of the area obtained by projecting the defect onto a plane perpendicular to the load axial direction. The results indicate that an FIB notch can be used as a small initial crack for fatigue limit evaluation in a greater number of materials than those in which a drill hole can be used.

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Publisher：The Japan Society of Mechanical Engineers  

The laser welding methods are widely used for manufacturing the products that the high quality welding conditions are required. Therefore, the establishment of the evaluation method for the melting conditions is desired. In the previous paper, the method by using the features of detected AE signals, when the irradiation energy was changed at the pulse width, was proposed. The results showed the following: (1) The frequency range of the signal of melting is near 300 kHz. (2) The correlation coefficients of the regression equations that evaluate the melting conditions from the AE energy of transversal wave components showed the high value. (3) The high correlations were recognized with the equations that evaluate the conditions by the led largest Lyapnov exponents from the wavelet transform results of the longitudinal wave component. However, it was proven that the frequency range of the thermal shock wave overlaps to the range of the melting, when the temperature rise rate lowers with the decrease of the lamp input voltage. Therefore, the evaluation method in the previous paper is not able to use in case of the evaluation of the melting conditions under the condition for changing the irradiation energy at the voltage. The method for evaluating the melting conditions, when the irradiation energy is changed by the voltage and the pulse width, is proposed in this paper. Concretely, the detected signals in the range (<i>i.e.</i> after 2 ms from the irradiation completion) that the influence of the thermal shock wave fades out, and the temperature of the irradiation part keeps the over melting point are analyzed with chaos and wavelet transform analysis method. The summaries of the result in this study are like the following. The correlation coefficients of the regression equations that evaluate the melting conditions from AE parameters showed the high value. One of the parameters is the correlation dimension <i>Cd</i> of transversal wave component, and the rest are the largest Lyapnov exponent <i>LLy</i> and the correlation dimension <i>Cd</i> of the time fluctuation waveform on the energy rate of the wavelet coefficient of longitudinal wave component. From the above results, it was shown to be possible that the melting conditions can be evaluated with the proposed method in this study, when the irradiation energy is changed by the lamp input voltage and the pulse width.

DOI： 10.1299/kikaia.77.1518

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

In order to investigate the effect of gaseous hydrogen on cyclic slip behavior around an early stage (stage Ifatigue crack tip, fatigue crack growth (FCGtests using a single-crystalline Fe-3.2wt.%Si alloy are conducted respectively in a hydrogen atmosphere and in a helium atmosphere. The cross-sectional observations of the crack tips by both electron backscatter diffraction (EBSDmethod and transmission electron microscopy (TEMsuccessfully reveal the following points. In helium atmosphere, FCG is preceded by formation of cell structures and crack propagates along cell boundaries. In hydrogen atmosphere, on the other hand, no cells are seen, and crack growth process is similar to that observed in a stage II type FCG. Crack extension resistance in hydrogen is postulated to be lower than that in helium, indicating that the mode of FCG in hydrogen is more critical than that in helium.

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

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Other Link： http://orcid.org/0000-0002-4982-257X

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The authors have previously observed a marked effect of hydrogen on cyclic slip behavior around a {110} fatigue crack tip in Fe-3.2wt.%Si alloy (Scripta Mater, 61(2009),145). In this study, a sustained load test is conducted to confirm the possible effect of hydrogen-assisted cracking (HAC). The result shows that no HAC exists along the {110} plane, demonstrating that the observed effect of hydrogen is limited solely to the cyclic slip mechanism. Crack growth process is then further discussed.

DOI： 10.1299/jsmemecjo.2009.1.0_69

CiNii Books

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

The effect of hydrogen on the crack tip cyclic slip deformation is investigated using a single-crystalline Fe-3.2 mass%Si alloy. The fracture surface and the neartip cross-section are observed in detail by SEM and TEM respectively. The cyclic slip-off process by a pair of symmetrical slip system about the crack ((11̄2̄)[11̄1]/(11̄2)[1̄11] pair) is operative in helium atmosphere. On the other hand, other types of slip system ((011)[11̄1]/(101)[1̄11]/(1̄01)[11̄1]/(01̄1)[1̄11] pair) are also found to be operative and the slip is localized around the close vicinity of the crack in hydrogen atmosphere.

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

The plasticity of a copper (Cu) nano-component is experimentally evaluated by a cantilever specimen with multi-layered structure. The cantilever is monotonically loaded by a diamond tip and the deflection at the free-end is precisely measured by a transmission electron microscope (TEM). The plastic deformation of the Cu nano-component is successfully monitored through the non-linear behavior of applied load, P, and cantilever deflection, delta. The plastic constitutive quation of the Cu component is inversely analyzed by finite element method (FEM) assuming that the component obeys the Ramberg-Osgood law. The parameters in the R-O law (sigma(0), n and alpha) are optimally fitted to reproduce the experimentally evaluated P-delta relation. The resultant parameter set is derived as (sigma(0), n, alpha) = (345 MPa, 3.2, 1.25). The Cu nano-component has a much higher yield stress and a hardening rate compared with the ones in a bulk Cu.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Kluwer Academic Publishers  

DOI： 10.1007/1-4020-4972-2_368

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Event date： 2017.9

Venue：埼玉大学  

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Venue：名城大学  

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Venue：札幌  

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Event date： 2016.9

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Event date： 2016.6

Venue：仙台国際センター  

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Event date： 2016

Language：English  

The strength against fracture nucleation from an interface free-edge of silicon-nitride (SiN)/copper (Cu) micro-components is evaluated. A special technique that combines a nano-indenter specimen holder and an environmental transmission electron microscope (E-TEM) is employed. The critical load at the onset of fracture nucleation from a wedge-shaped free-edge (opening angle: 90 degrees) is measured both in a vacuum and in a hydrogen (H-2) environment, and the critical stress distribution is evaluated by the finite element method (FEM). It is found that the fracture nucleation is dominated by the near-edge elastic singular stress field that extends about a few tens of nanometers from the edge. The fracture nucleation strength expressed in terms of the stress intensity factor (K) is found to be eminently reduced in a H-2 environment. Copyright (C) 2016 The Authors. Published by Elsevier B.V.

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Event date： 2015.11

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Venue：Toyohashi, Japan  

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Venue：JSMS  

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Venue：Sydney  

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Venue：Osaka, Japan  

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Venue：Dresden, Germany  

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Venue：同志社大学  

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Venue：同志社大学  

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Venue：九州大学伊都キャンパス  

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Venue：九州大学伊都キャンパス  

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Venue：東洋大学川越キャンパス  

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Venue：東洋大学川越キャンパス  

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Venue：東洋大学川越キャンパス  

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Venue：立命館大学  

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Venue：立命館大学  

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Venue：立命館大学  

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Venue：立命館大学  

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Venue：福井大学  

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Venue：徳島大学  

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Venue：神戸商工会議所  

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Venue：神戸商工会議所  

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Venue：神戸商工会議所  

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Venue：産業技術総合研究所  

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Venue：山形大学  

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Venue：産業技術総合研究所  

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Venue：熊本大学  

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Venue：関西大学  

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Venue：関西大学  

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Venue：関西大学  

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Venue：関西大学  

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Venue：関西大学  

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Venue：関西大学  

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Venue：関西大学  

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Venue：関西大学  

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Venue：関西大学  

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Venue：ウインクあいち  

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Venue：高知工科大学  

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Venue：高知工科大学  

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Venue：高知工科大学  

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Venue：代々木オリンピックセンター  

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Venue：国立オリンピック記念青少年総合センター  

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Venue：高知工科大学  

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Venue：摂南大学  

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Venue：摂南大学  

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Venue：摂南大学  

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Venue：Kyoto, Japan  

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Venue：近畿大学  

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Venue：埼玉大学  

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Venue：近畿大学  

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Event date： 2017.9

Venue：北海道大学  

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Event date： 2017.9

Venue：埼玉大学  

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Event date： 2017.9

Venue：近畿大学  

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Event date： 2017.9

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Event date： 2017.9

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Event date： 2017.9

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Event date： 2017.6

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Event date： 2017.3

Venue：大阪大学  

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Event date： 2017.3

Venue：大阪大学  

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Event date： 2017.3

Venue：大阪大学  

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Event date： 2017.3

Venue：大阪大学  

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Event date： 2017.3

Venue：大阪大学  

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Event date： 2017.3

Venue：大阪大学  

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Event date： 2017.3

Venue：大阪大学  

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Event date： 2017.3

Venue：大阪大学  

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Event date： 2017.3

Venue：大阪大学  

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Event date： 2017.3

Venue：大阪大学  

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Event date： 2017.3

Venue：大阪大学  

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Event date： 2017.3

Venue：大阪大学  

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Event date： 2017

Language：Japanese  

Sufides as MoS₂ are known as solid lubricants. These materials are also known as thermoelectric materials. However, there is no materials satisfied both functions at the same time. In this study, sulfides powders such Cu₂S (chalcocite), SnS, Cu₅FeS₄ (bornite) were synthesized under vacuum condition. Some specimens were evaluated by friction tester and their lubricity, not only sintered sulfied but also blended and sintered sulfides with bronze powders were compared. Other specimens were evaluated their seebeck coefficients, that is one of the thermoelectric properties. Experiments results of the seebeck coefficients were compared with simulation results. As a result, it was found that SnS and blended SnS with bronze had indicated better friction properties. For thermoelectric properties, seebeck coefficient of Cu₂S had matched with experiments and simulation. Totally, Cu₂S (chalcocite) has superior properties as both solid lubricant and thermoelectric material.

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Event date： 2017

Language：Japanese  

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Event date： 2016.10

Venue：神戸大学  

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Event date： 2016.9

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Event date： 2016.9

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Event date： 2016.9

Venue：名古屋大学  

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Event date： 2016.9

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Event date： 2016.9

Venue：名古屋大学  

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Event date： 2016.9

Venue：九州大学  

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Event date： 2016.9

Venue：名古屋大学  

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Event date： 2016.8

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Event date： 2016.6

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Event date： 2016.6

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Event date： 2016.6

Venue：仙台国際センター  

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Event date： 2016.6

Venue：新潟コンベンションセンター  

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Event date： 2016.5

Venue：京都工芸繊維大学  

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Event date： 2016.5

Venue：富山大学  

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Event date： 2016.3

Language：Japanese  

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Event date： 2016.3

Language：Japanese  

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Event date： 2016.3

Language：Japanese  

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Event date： 2016.3

Language：Japanese  

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Event date： 2016.3

Language：Japanese  

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Event date： 2016.3

Language：Japanese  

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Event date： 2016.3

Language：Japanese  

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Event date： 2016.3

Venue：大阪電気通信大学  

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Event date： 2016.3

Venue：大阪電気通信大学  

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Event date： 2016.3

Venue：大阪電気通信大学  

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Event date： 2016.3

Venue：大阪電気通信大学  

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Event date： 2016.3

Venue：大阪電気通信大学  

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Event date： 2016.3

Venue：大阪電気通信大学  

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Event date： 2016

Language：Japanese  

<p>Recently, the fuel consumption improvement by weight saving is required in transportation machine. Therefore, Mg alloy is expected as the alternative material of Al alloy and resin material, because it is the lightest in the practical metals and its specific intensity is high. However, twin crystal deformation occurs easily, and there are the two kinds types (i.e. {10<span style="text-decoration: overline;">1</span>2} and {10<span style="text-decoration: overline;">1</span>1} twin crystal) in that deformation. It has been reported that the {10<span style="text-decoration: overline;">1</span>2} twin crystal has work to relax the stress concentration and the {10<span style="text-decoration: overline;">1</span>1} twin crystal has close relation to fracture. Our aim is to evaluate the kinds and the conditions of those types with AE method. In this study, Mg alloy AZ31 was used, and the AE signals of the alloy were detected in compression, tensile and CT test. After that, the analysis of those signals were done. From the results obtained under this experimental conditions, the following things became clear. (1) The frequency components near 250, 550 and 850 kHz are caused by slip, twin crystal deformation and crack growth respectively. (2) It is possible that the two kinds crystal deformation types are discriminated by the identification standards decided by the AE count and fractal dimension Fd of the detected signals.</p>

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Event date： 2016

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Event date： 2016

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Event date： 2015.11

Venue：愛知県産業労働センター（ウインクあいち）  

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Event date： 2015.11

Venue：愛知県産業労働センター（ウインクあいち）  

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Event date： 2015.10

Language：Japanese  

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Event date： 2015.10

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Event date： 2015.10

Language：Japanese  

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Event date： 2015.10

Venue：横浜国立大学  

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Event date： 2015.10

Venue：横浜国立大学  

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Event date： 2015.5

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Event date： 2015.5

Venue：慶應義塾大学  

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Event date： 2015.5

Venue：山形大学  

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Event date： 2015.3

Language：Japanese  

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Event date： 2015.3

Language：Japanese  

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Event date： 2015.3

Language：Japanese  

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Event date： 2015.3

Language：Japanese  

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Event date： 2015.3

Language：Japanese  

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Event date： 2015.3

Language：Japanese  

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Event date： 2015

Language：Japanese  

Magnesium alloy is the lightest material in all practical metals, and has the excellent mechanical properties. From such reasons, the alloy is noticed as the attractive material in various fields. However, the alloy has the weak points that are inferior for heat and corrosion resistance. Therefore, it will be possible to guarantee the safety security of structure parts, if the information on the fracture strain and life, etc. are evaluated by the signals detected from the alloy under those use environment. The three type specimens of the virgin, the heat history (<i>i.e.</i> repeatedly gave the heating to the virgin specimen) and the corrosion specimen (<i>i.e.</i> immersed the virgin specimen into solution) are prepared in this study. Then, the tensile test was carried out for each specimen, and the AE signals emitted in the testing were detected. Frequency and fractal dimension analysis were carried out in order to extract the features of those signals. From such analysis results, the feature extraction of the signal by the elasticity twin deformation was done, because that deformation participates in the degradation of mechanical properties. As the result, the following things became clear under the experimental condition in this study: The frequency component of the signals caused by that deformation is near 550 kHz. The fractal dimensions <i>Fd</i> of those signal show the value over 1.85. Then, it was examined whether the fracture strain is evaluated by the <i>Ib</i> value (Improved <i>b</i>-value) led from the frequency distribution of the <i>Fd</i>. As the result, the effectiveness of this method proposed under the experimental conditions in this study was confirmed. Therefore, the possibility for the prediction of that strain by the AE signal detected in elastic region was shown.

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Event date： 2014.11

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Event date： 2014.11

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Event date： 2014.11

Venue：岩手大学  

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Event date： 2014.11

Venue：岩手大学  

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Event date： 2014.7

Language：Japanese  

Molecular dynamics (MD) study on copper sulfide (Cu_2S) crystal which is subjected to sliding condition is performed. The hexagonal crystal structure of Cu_2S is determined by first-principle calculation, first. Values on the optimized structure are adopted to the construction the potential function which includes three-body term as well as pair term, resembling MoS_2 case. In MD simulations, a Cu_2S crystal undergoes relaxation and compression processes at first, then it is applied shear deformation and is slid on the hexagonal basal plane. The dependency on sliding direction with regard to hexagonal slip system and on sliding velocity is investigated. It is found that layers of Cu_2S slide without retaining their prescribed crystal stacking and shape. Under various temperature conditions, the sliding of the crystal is simulated and the shear resistance (averaged shear stress) shows a certain temperature-dependency, indicating stick-slip motion in some cases.

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Event date： 2014.7

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Event date： 2014.6

Venue：アルカディア市ヶ谷(東京)  

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Event date： 2014.5

Venue：広島大学  

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Event date： 2014.5

Venue：福岡大学  

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Event date： 2014.5

Venue：福岡大学  

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Event date： 2014.5

Venue：福岡大学  

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Event date： 2014.3

Language：Japanese  

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Event date： 2014.3

Language：Japanese  

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Event date： 2014.3

Language：Japanese  

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Event date： 2014.3

Language：Japanese  

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Event date： 2014.3

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Event date： 2014.3

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Event date： 2014.3

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Event date： 2014.3

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Event date： 2013.12

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Event date： 2013.12

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Event date： 2013.12

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Event date： 2013.11

Language：Japanese  

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Event date： 2013.10

Language：Japanese  

In order to investigate the mechanism of brittle-striation formation in low-carbon steel fatigued in hydrogen gas, fractographic observations were performed after programmed load fatigue tests and crystallographic cross-sectional observations were made using high-voltage electron microscopy. The results indicate that the processes of brittle-striation processes were microscopically similar to the normal ductile tearing process. In particular, they consist of a crack-tip blunting process and a stable ductile crack growth process. Hydrogen enhanced the occurrence of microscopic ductile tearing processes. Furthermore, the localization of hydrogen near the crack tip enhanced this process further. Based on the experimental results, a mechanical model for the brittle-striation-formation was proposed in which the microscopic ductile tearing fracture was enhanced by local hydrogen.

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Event date： 2013.9

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Event date： 2013.5

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Event date： 2013.5

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Event date： 2013.5

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Event date： 2013.3

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Event date： 2013.3

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Event date： 2013.3

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Event date： 2013.3

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Event date： 2013.3

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Event date： 2013.3

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Event date： 2013.3

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Event date： 2013.3

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Event date： 2013

Language：Japanese  

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Event date： 2012.11

Venue：Okinawa, Japan  

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Event date： 2012.11

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Event date： 2012.10

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Event date： 2012.10

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Event date： 2012.10

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Event date： 2012.10

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Event date： 2012.5

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Event date： 2012.3

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Event date： 2012.3

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Event date： 2012.3

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Event date： 2012.3

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Event date： 2012.3

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Event date： 2012.3

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Event date： 2012.3

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Event date： 2012.3

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Event date： 2012.3

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Event date： 2012.3

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Event date： 2012.3

Language：Japanese  

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Event date： 2012.3

Language：Japanese  

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Event date： 2012.3

Language：Japanese  

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Event date： 2012.3

Language：Japanese  

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Event date： 2012.3

Language：Japanese  

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Event date： 2012.3

Language：Japanese  

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Event date： 2012.3

Language：Japanese  

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Event date： 2012.3

Language：Japanese  

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Event date： 2012.3

Language：Japanese  

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Event date： 2012.3

Language：Japanese  

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Event date： 2012

Language：Japanese  

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Event date： 2011.9

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Event date： 2011.9

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Event date： 2011.9

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Event date： 2011.7

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Event date： 2010.5

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Event date： 2010.2

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Event date： 2010

Language：Japanese  

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Event date： 2010

Language：Japanese  

In order to clarify the micromechanism of transgranular type time-dependent subcritical crack growth under hydrogen environment (hydrogen-assisted cracking; HAC), a sustained load cracking test using a single-crystalline Fe-3.2wt.%Si alloy was implemented in hydrogen gas. Crack growth rate, da/dt, along (001) plane showed linear dependence on stress intensity factor, K. Same type of periodic striation pattern was observed on the fracture surface irrespective of daldt; striation spacing, AS, was found to be constant over daldt range of five orders, daldt may be related to diffusion of hydrogen at the crack tip.

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Event date： 2009.10

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Event date： 2009.8

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Event date： 2009.7

Language：Japanese  

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Event date： 2009.3

Language：Japanese  

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Event date： 2009.3

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Event date： 2009.1

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Other Link： http://orcid.org/0000-0002-4982-257X

Event date： 2009

Language：Japanese  

The authors have previously observed a marked effect of hydrogen on cyclic slip behavior around a {110} fatigue crack tip in Fe-3.2wt.%Si alloy (Scripta Mater, 61(2009),145). In this study, a sustained load test is conducted to confirm the possible effect of hydrogen-assisted cracking (HAC). The result shows that no HAC exists along the {110} plane, demonstrating that the observed effect of hydrogen is limited solely to the cyclic slip mechanism. Crack growth process is then further discussed.

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Event date： 2009

Language：Japanese  

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Event date： 2009

Venue：Ottawa, Canada, 2009.7.12-17  

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