Layered metal materials which consist of more than two kinds of metals can have great properties by taking advantage of good property of each metal material. The layered metal materials, however, could include various defects at the interface such as delamination and weak interface stiffness, which can be introduced during rolling and thermal treatment processes. The interface defects could accordingly deteriorate the properties of layered metal materials. Thus, it is important to non-destructively evaluate the interface property before its practical application. In this study, by using a method of resonant ultrasound spectroscopy (RUS), the delamination and the stiffness at interface between two copper sheets are evaluated. The modal analysis is conducted by the finite element method and the resonant frequency is measured by the RUS system.

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This paper reports on the observation method of 3D inicrostructure, 3D-EBSD method that combines serial sectioning method withEBSD observation technique. First, the procedure for 3D-EBSD Data Collection is described, about EBSD observation, mechanical polishing and measurement of polishing depth. Second, the procedure for 3D-EBSD Data Analysis is described, about extraction of grain, alignment of GrainMap and 3D reconstruction from serial sectioning images. Minimization of absolute value of and variation in the polishing amount is investigated to realize the higher-resolution 3D-EBSD observation by mechanical polishing. As a result, 3D shape and distribution of grain and grain boundary (S45C) is visualized by this method.

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For Caibon Fiber Reinforced Plastic (CFRP), electrical conductivity of caibon fiber can be used as a sensor for damage detection. The change of electrical resistance of the CFRP structure has been studied as a self-sensing system for monitoring damages. Todoroki et al. reported that the electrical resistance change meihod successfully monitored various damages like matrix cracking, fiber breakage and delamination in CFRP laminates. To apply the electrical resistance change method to practical structures, reliability of the electrodes is a key issue. This paper contains the proposal of "Lead-Wire Integrated Electrodes" and the investigation of the reliability of the proposed electrodes under cyclic load. The electrodes were bonded to CFRP surface by using copper plating after polishing of the specimen surface with sandpaper to remove the surface resin. Lead-Wire was put on the plating surface and bonded to the electrode by using copper plating, so the electrode and Lead-Wire were integrated. One of advantages of this proposed electrode is no initial defect Fatigue tests were carried out using a servo-hydraulic testing system. As a result, the electrodes had a fatigue life at the same level as the conventional strain gages under cyclic load.

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The effect of hydrogen on fatigue properties for S45C carbon steel tempered at 550℃ were investigated using smooth and notched specimens at frequencis of 0.02Hz through 30Hz under stress ratio of R=-1. In the case of smooth specimens, fatigue strength showed negligible difference between hydrogen charged and uncharged specimens. On the other hand, fatigue lives for notched specimens decreased with decreasing in frequency in the presence of hydrogen. However, the decrease in fatigue lives of hydrogen charged specimens was saturated with 1/10 of fatigue lives of uncharged specimens. The results of smooth and notched specimens show thst hydogen strongly influences on fatigue crak propagation rather than on fatigue crack initiation. The brittle fracture appearances such as the intergranular fracture were not found at the fracture origins even for hydrogen charged specimens. Accordingly, the decrease in fatigue life, that is, the acceleration of fatigue crack propagation for hydrogen charged specimens could be explained by the hydrogen enhanced localized plasticity model rather then by the hydrogen decohesion model.

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This paper describes the influence of cyclic loading condition and irreversible hydrogen on the fatigue crack propagation properties in a cold drawn eutectoid steel wire. Fatigue crack propagation tests were conducted for virgin samples and irreversible hydrogen charged samples. In the low ΔK_<eff> region irreversible hydrogen accelerated the fatigue crack propagation rate. However, in the high ΔK_<eff> region, the fatigue crack growth rate was not influenced by irreversible hydrogen. To elucidate the mechanism of the acceleration of the crack growth rate by irreversible hydrogen, the influence of stress cycle frequency and stress ratio was investigated. In the case of irreversible hydrogen charged sample, crack growth rate at a lower stress cycle frequency of 1 Hz was higher than that at a higher stress cycle frequency of 10 Hz. As the stress ratio become large in order of 0.1, 0.2 and 0.4, the fatigue crack growth rate increased in the irreversible hydrogen charged sample. These results were similar to the case of diffusible hydrogen.

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The behavior of the defonnation-induced martensitic transformation in austenitic stainless steels was investigated under monotonic and cyclic loading. The volume fraction of martensitic phase was measured by ferrite scope in the tensile test and the axial fatigue tests. It was found that the martensitic volume fraction ζ, was not detected in early stage of fatigue process under cyclic loading below yield stress that was measured by the tensile test, and ζ increased with increasing in number of cycles. The behavior of martensitic transformation under cyclic deformation agree with the behavior of plastic strain such as cyclic softening and cyclic hardening. The process of martensite transformation can be represented as function of the cumulative plastic strain and the cumulative strain-energy density.

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In recent years, the demand has been increased for establishing nondestructive inspection technique for detection of pre-existing plastic strain to ensure integrity of the structure such as nuclear power plant. In this study, electrochemical technique (potentiostatic etching) is applied to detect and measure plastic strain imposed to austenitic stainless steel by tensile straining. After potentiostatic etching (1N HNO_3, -600mV_<SCE> 20min), the slip line appears as etched line on the surface of specimen. The etched slip line is observed by optical microscope and quantified as the etched slip line density. There is one to one relation between the etched slip line density and the amount of pre existing plastic strain in the range from 1% to 30%.

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The present paper describes the effect of cyclic stressing on aged microstructure in high-chromium ferritic stainless steel, Type 447. Hardness and tensile strength were largely increased by aging at 520℃ due to the 475℃ embrittlement. TEM observation revealed that the embrittlement could be attributed to the spinodal decomposition of Cr phase. Cyclic stressing during aging at 520℃ suppressed the spinodal decomposition and resulted in less hardness increase than that under static aging.

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Metallic thin films are now used as structural members of MEMS and electronic devices, and their fatigue properties may be different from bulk materials because of the difference in the crystalline orientation and grain size. In the present study, nickel nanocrystalHne thin films were produced by electrodeposition using sulfamate solution. Three types of thin films with different grain sizes were produced: CC films were made under constant current, PC films under pulse current, and CC-ally films under constant current with grain refinement additive. The grain size gets smaller in the order of CC, PC, and CC-ally films down to nanometers. The fracture strength and yield strength in tension tests follows the Hall-Petch relation. The fatigue strength increased with decreasing grain size, following the Hall-Petch relation down to lOnm. On the other hand, the resistance to fatigue crack propagation decreased for nano grain-sized films. The threshold stress intensity factor was the smallest for PC and CC-ally films. In the intermediate-rate range, the propagation rate increased with decreasing grain size when compared at the same stress intensity factor.

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Using Ultrasonic Nano-crystal Surface Modification (UNSM) method, adopted 3 kinds of strike number (34000 /mm^2,45000 /mm^2,68000 /mm^2) to modify the surface of S45C. Studying the hardness, surface roughness, residual stress and fatigue properties of S45C, several conclusions have been made. As the number of ultrasonic strike is more, the fatigue life is much longer. Though most of the cracks initiate from the surface of specimens, surface nano-layer makes the effect to delay the crack initiation.

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High-cycle fatigue tests were carried out on smooth specimens of ultrafine-grained copper produced by equal channel angular pressing(ECAP). Grain sizes of 300nm were formed after twelve passages of ECAP pressing by Be route. Fatigue tests were conducted using a rotating bending fatigue machine. A major crack, which led to the final fracture of the specimen, initiated from shear bands. After initiation, Hie growth rate increased with an increase in crack length. However, a decrease in growth rate with a change in growth path morphology occurred when the crack length 0.1<l<0.3 mm. The fracture surface showed a planar, granular, and striated surface in the range of l<0.1 mm, 0.1<l<0.3mm and l>0.3mm, respectively. This decrease occurred because of a change in the crack growth mechanism and is explained by considering the interrelation between grain size and the reversible plastic zone size at the crack tip.

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In resin-metal composite structures such as electronic products with epoxy resin molding insulator, thermal stress is induced to epoxy resin during thermal cycle due to the mismatch of thermal expansion, and often the case it is a thermal fatigue problem of epoxy resin under out-of-phase loading. In this paper, the technique of predicting thermal fatigue crack growth rate in epoxy resin is studied. We proposed the evaluation temperature of crack growth characteristics where strain intensity factor K/E takes maximum value, based on K/E - da/dN relationship. In order to evalute thermal fatigue crack growth rate under out-of-phase loading, both crack propagation test by thermal cycle test and thermal stress evaluation by viscoelastic FEM analysis were carried out. As a result, it was fouond that crack growth rate under out-of-phase thermal fatigue test was nearly in accordance with that of iso-thermal fatigue test under the evaluation temperature.

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The finite element method (FEM) was used to calculate the J integral for a mode I crack in bulk plates and jointed specimens of lead-free solder under triangular loading wave. First, the path independence of the J integral was confirmed for both bulk plates and jointed specimens. The J integral for a center crack in bulk plates was computed as a function of the crack length under displacement and load controlled conditions. The variation of the computed J integral value agreed with the experimental results. The relation between crack-tip local parameters, such as inelastic strain and inelastic strain energy density, and the J integral was unique irrespective of the loading condition or the specimen type. The computed J integral was correlated to the experimental value of the crack propagation rate. The relation was unique for bulk plates, but the crack propagation rate was slower than the prediction for jointed specimens. This discrepancy for jointed specimens is ascribed to small interface cracks produced in the interface in the crack propagation experiments of jointed specimens.

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The effect of ratcheting strain on creep-fatigue strength was investigated in order to adjust the strain limit. Ratcheting creep-fatigue tests were conducted at 600℃ with lhr hold time. Creep fatigue lives did not decrease when the accumulated strain was superimposed within 5%. Therefore the effect of ratcheting on creep-fatigue strength is negligible when accumulated strain exceeds 2%.

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The effect of ratcheting strain on fatigue strength was investigated in order to adjust the strain limit. Ratcheting fatigue tests were conducted in various conditions for temperature and accumulated strain. As the result of these tests, the fatigue life reduction correlates with their maximum mean stresses, and this reduction can be explained using the modified Goodman diagram. When accumulated strain is less than 2%, the effect of ratcheting strain on fatigue strength is negligible.

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In this study, we investigated new bio-compatible piezoelectric materials in perovskite-type oxide ABO_3 through first-principles calculation. Firstly, stable combinations which satisfy the geometric stable were searched. Secondly, insulating substrates were discriminated with electric band structure. Then, phonon properties in cubic structures were analyzed and the possibilities of structural phase transition from cubic structure to tetragonal one were explored for the promising materials. As a result, we discovered 5 oxides for the bio-compatible piezoelectric material. Finally, their characteristics of stable tetragonal structure were analyzed. MgSiO_3 and CaTiO_3 were predicted to have higher piezoelectricity.

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External load turns the orientations of spontaneous polarization in microscopic domain structures of piezoelectric materials. This domain switching in microscopic structure dominates macroscopic piezoelectric performance. This paper presents a multiscale nonlinear finite element method through a crystallographic homogenization method to analyze ferroelectric hysteresis behaviors caused by domain switching. As a computational example, the electric field - strain and electric field - electric displacement relations were discussed for BaTiO_3 polycrystal with regular distribution of crystal orientations.

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Micro crystal morphology, which affects strongly on macro electromechanical response of polycrystalline piezoelectric ceramics, was analyzed by electron backscatter diffraction method. The obtained crystal morphology was applied to multiscale finite element analysis. Then a representative volume element of micro structure was investigated in the view points of macro homogenized properties and micro localized response.

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In this paper, we presented the performance assessment of a valve-less piezoelectric pump through piezoelectric-fluid interaction finite element analysis to support the design of piezoelectric actuator and channel in MEMS and u-TAS. At first, the effect of fluid interaction on the amplitude and phase of vibration was analyzed for bimorph piezoelectric actuator. Then, the velocity and Ihe flow rate in micro channel were investigated computationally.

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To better understand the material properties of lead zirconate titanate (PZT) ceramics, the in situ mechanical and electrical properties have been investigated during cyclic mechanical loading. The elastic constant increases and the electrical properties (piezoelectric constant) decrease with increase of the applied load due to internal and external damage in the PZT ceramic, e.g., domain switching and electrode damage. The domain switching occurs randomly in the grains, and this causes lattice distortion leading to a high elastic constant On the other hand, the electrical properties decrease because of the domain switching as well as the damage in the electrode. Based upon the variation of the material properties, details of the damage characteristics are further discussed.

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Piezo-electric ceramics, PZT, are used as actuators in mechanical structures, therefore the log-term reliability of actuators is required. Crystalline structure of PZT is changed by the ratio of chemical compositions. PZTs have rhombohedral structure at high ratio of Zr, tetragonal structure at a high ratio of Ti, and morphotropic phase boundary (MPB) at same ratio of Zr and Ti. In this study, 4-point bending tests of PZTs with three types crystal structure were conducted. Bending strength and fatigue crack propagation behaviors were investigated. Bending strength for tetragonal PZT was highest, that for MPB PZT was lowest Fatigue crack propagation rate could be divided into three regions: Region I was the region where crack propagation rate decreased, Region II was the minimum constant rate region, and Region III was the acceleration region. In Region El of high crack propagation rate, crack propagation rates for three crystalline structures follow the Paris's law. But, the crack propagation rate less than 10^<-7> m/cycle in early Region III was lower than the rate predicted by the Paris's law. Fracture surfaces after fatigue test were dominated by intergranular fracture.

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This paper discusses the delayed fracture and localized polarization switching near a crack tip in three-point bending piezoceramics under electromechanical loading. Delayed fracture experiments were performed on the piezoelectric ceramics with single-edge precracked-beam method. A nonlinear finite element analysis was also employed to calculate the fracture mechanics parameters such as energy release rate for the permeable, impermeable, open and discharging crack face boundary conditions. The effects of applied electric field and localized polarization switching on the fracture mechanics parameters and lifetime vs energy release rate curves were then examined

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Nikel-Titanium (Ni-Ti) alloy is known for its shape memory properties. These properties are useful for various biomedical applications. However, a high percentage of nickel elements in Ni-Ti alloy elicit toxicity, allergic responses, and limits practical uses of the alloy. Therefore, further improvement of the corrosion resistance of Ni-Ti alloy is desirable for implant applications. In this study, the authors conducted a study by using Ni-Ti alloy on the new compound surface modification method consisting of a new electrical grinding technique (EG-X) based on ELID (Electrolytic In-process Dressing) grinding and Thermal Oxidation (TO). The results showed that the new compound surface modification method can achieved high quality surface compared with the conventional TO treated surface.

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In order to develop a brain spatula made of shape memory alloy (SMA), the mechanical characteristics of copper and TiNi SMA used for the brain spatula were compared based on the tensile deformation properties, and the dimensions of the SMA-brain spatula were discussed. The fatigue properties of both materials were investigated by the alternating-plane bending test. If the thickness of the rolled-SMA spatula is 1.9 times and that of the casted-SMA spatula is 1.2 times as large as that of the copper spatula, the SMA-brain spatula can be bent by the same force as the case of the copper spatula. The fatigue life of the SMAs is longer than that of copper.

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Solid oxide fuel cell (SOFC) has been attractive as a way to solve global energy and environmental problems. As the SOFC has layered structure consisting of different materials, there is significant residual and thermal stresses produced during sintering process and operating, which could affect the power performance of the SOFC. hi the present study, the effect of the stress on the ionic conductivity of 8 mol% yttria-stabilized zirconia electrolyte has been investigated by molecular dynamic simulation, allowing for the direction of the crystal axis. The results show that there is an optimum stress state for the oxygen migration.

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[in Japanese]

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Higher performance large scale integration (LSI) requires copper (Cu) instead of aluminum (Al) as a wiring metal because of its superior electrical conductivity. These LSI also requires lower dielectric constant to decrease line-to-line capacitance. Recently, porous low-k dielectrics are introduced for low-k dielectrics because of its ultra lower dielectric constant. However, their poor mechanical strength causes fractures of porous low-k dielectrics during Chemical Mechanical Polishing (CMP) process. Therefore, it is important to keep the mechanical strength of porous low-k dielectrics during increasing porosity. In this paper, we studied the mechanical property and dielectric property of porous low-k dielectrics by finite element method and U^* method. U^* expresses a degree of connection between a loading point and an internal arbitrary point. To estimate dielectric property, we expanded the U^* method to the electrostatic field problem. The effects of pore arrangements on the mechanical property and dielectric property of porous low-k dielectrics were discussed.

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High strength magnesium alloys with a long period stacking ordered (LPSO) structure have been developed in Mg-Zn-Y alloys. The Mg-Zn-Y alloys are mainly consisted of two phases, which are LPSO and ot-Mg phases, and their mechanical properties are improved drastically by plastic deformation. In this study, we have tried to construct a constitutive formulation of the yield strength for the extruded LPSO Mg_<97>Zn_1Y_2 alloy as a model alloy. The effect of extrusion ratio and speed on the yield strength and microstructure of the LPSO Mg_<97>Zn_1Y_2 alloy has been investigated. The extruded LPSO Mg_<97>Zn_1Y_2 alloy was composed of three regions which were LPSO phase, dynamic recrystallized and un-recrestallized regions of α-Mg phase. On the basis of a composite model consisted of three regions, a constitutive formulation of the yield strength of the extruded LPSO Mg_<97>Zn_1Y_2 alloy has been constructed from the investigations of the microstructure and mechanical properties of extruded alloys with a singe LPSO phase and a single α-Mg phase. The yield strength calculated from the constitutive formulation represented the experimental yield strength with an accuracy of 7%. This result reveals that the composite model can be applied to the yield strength of LPSO magnesium alloys.

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Mg_<97>Zn_1Y_1RE_1 (RE=La, Ce, Nd and Sm, at. %) alloys were prepared by high-frequency induction melting in an Ar atmosphere. The rods were extruded with an extrusion ratio of 10 at 623K and a ram speed of 2.5mm s^<-1>. The microstructure and mechanical properties of the extruded alloys were investigated. Mg_<97>Zn_1Y_1Nd_1 and Mg_<97>Zn_1Y_1Sm_1 alloys consisted of just 2 phases of α-Mg and Mg-RE intermetallic compound. The Mg_<97>Zn_1Y_1La_1 and Mg_<97>Zn_1Y_1Ce_1 alloys consisted of 3 phases of α-Mg, Mg-RE intermetallic compound and Mg_<12>ZnY corresponding to a long period stacking ordered (LPSO) structure. Specially, after extrusion, the Mg_<97>Zn_1RE_1 alloys with α-Mg, Mg-RE intermetallic compound and LPSO phase had the stratified structure. The Mg_<97>Zn_1Y_1RE_1 alloys with LPSO phase exhibited higher mechanical properties than the Mg_<97>Zn_1Y_1RE_1 alloys without LPSO phase. The yield strength and ultimate tensile strength at room temperature of Mg_<97>Zn_1Y_1La_1 and Mg_<97>Zn_1Y_1Ce_1 alloys consisting 3 phases were 390-393 MPa and 439-442 MPa, respectively. Their ultimate tensile strength at the elevated temperature of 473 K was more than 330 MPa.

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Ternary Mg-Zn- Y alloy sheets with a Long Period Ordered (LPO) phase were prepared by hot-rolling at 623K. Volume fraction of the LPO phase was estimated more than 85% in a Mg_<85>Zn_6Y_9 (at.%) cast alloy. (00018) pole figure showed basal plane of the LPO phase has a tendency to orient a plane of sheet by hot-rolling. However, it was considered that the basal texture of the LPO phase is difficult compare with Mg phase, due to introduce a kink formation. Compression test was performed in Mg_<85>Ni_6Y_9 (at.%) cast alloy at room temperature. Yield strength of the Mg_<85>Ni_6Y_9 (at.%) cast alloy was 365MPa which is higher than that of pure-Mg. Also, deformation kink bands were frequently observed in deformed LPO phase, like as observed in hot-rolled Mg-Zn-Y alloy sheet. It was observed that the basal plane of the LPO phase has tendency to orient a compression plane by compression test at room temperature.

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A high-strengih Mg-Zn-Y alloy was developed, with increased ductility and a multimodal microstructure. The microstructure of the extruded Mg-Zn-Y alloy consisted of three regions: a dynamically recrystallized α-Mg fine-grain region with random orientation, a hot-worked α-Mg coarse-grain region with strong basal texture, and a long-period stacking ordered (LPSO) phase region with kink deformation bands. An increase in dynamically recrystallized α-Mg grains having random crystallographic orientation improved ductility; the effective dispersion of the hot-worked α-Mg grains with a strong basal texture and a kink-deformed LPSO phase brought about strengthening of the alloy.

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Mg-Zn-Y alloy with a long period stacking ordered (LPSO) structure was produced by extrusion, and the effects of annealing on its microstructure and mechanical properties were investigated. Heat treatment at temperatures up to 623 K improved the elongation of the alloy from 5.4 % to 9.6 % but caused no changes in either yield stress or tensile strength, which remained at 391 MPa and 432 MPa, respectively, because the LPSO phase prevented grain growth, and the α-Mg phase kept the fine grain sizes and kink deformation remain in the LPSO phase and the Mg_3Zn_3Y_2 phases finely dispersed. When the alloy was heat treated at 773 K, the α-Mg and Mg_3Zn_3Y_2 phases became coarse, which reduced the yield stress and tensile strength to 210 MPa and 320 MPa, respectively, while the elongation improved to 23 %. The study showed that the ductility of the alloy could be improved while keeping the strength high by heat treatment.

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Plastic formability of HCP metal has disadvantage comparing with FCC and BCC because HCP has few number of active slip systems, typically three on the early stage of deformation at room temperature, and other slip systems have the higher critical resolves shear stress. To improve the formability of HCP, the development of a numerical procedure based on the multiscale modeling is expected. Polycrystal information such as texture In this study, Local necking behavior is the important phenomenon to trigger ductile failure of metal materials. Therefore, in this study, a macro-micro coupled analysis scheme based on the homogenization method is utilized for HCP materials and a macroscopic necking behavior caused by strain localization is analyzed. The effects of microstructures on the macroscopic strain localization are discussed.

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The instrumented wire-brushing process was applied to the AZ31B alloy sheets, and microstructure and mechanical properties of wire-brushed AZ31B alloys sheets by four different conditions were investigated. Two different loads (1kgf and 3kgf) and feed speeds (High and Low) were used: 1-H, 3-H, 1-L and 3-L. Nanocrystals were obtained near surface after the wire-brushing. The size of nanocrystals depends on the feed speed rather than the load. The 0.2% proof stress and tensile strength increased after the wire-brushing on most conditions, although the elongation decreased. The increasing 0.2% proof stress and tensile strength would result from the grain refinement. On the other, 0.2% proof stress, tensile strength and elongation of the wire-brushed sheet were smaller than those of the starting sheet when the surface is rough after the wire-brushing, because the stress-concentration factor increases with increasing roughness.

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To form magnesium alloy sheets without heating, friction stir incremental forming process was developed. AZ31 and AZ61 sheets with 0.5mm or 0.7mm thickness were used and formed into frustum of pyramid shapes. Tool rotation rate, tool feed rate and half apex angle of pyramid were changed. Not only formability but also hardness and tensile strength of formed part were measured. From the experimental results, AZ31 sheet with 0.5mm thickness formed into a frustum of pyramid shape with the half apex angle of 25° by the developed method showed 137% elongation, and its tensile strength was about 10% higher than that of not formed one. AZ31 sheet with 0.7mm thickness and AZ61 sheet with 0.5mm thickness were also formed into a frustum of pyramid shape with the half apex angle of 45°, successively.

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Twinning behavior of Mg-Zn alloy single crystal is investigated. It was found that both the work-hardening rate and the number of serration in the stress strain curve of the specimen depends on the stress axis ([1010] or [1120]) by which the number of operative twi systems changes. In order to understand the effect of grain boundaries on the twinning in Mg alloys, twin boundaries are introduced to single crystal specimens as pseudo grain boundaries. Using EBSD analysis, the importance of the strain compatibility at grain boundaries for introducing twins is confirmed by examining the microstructure evolution of the specimens with pseudo grain boundaries.

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It is important to research activation of the slip systems in magnesium crystals to understand deformation behavior of magnesium. In this study, pure magnesium single crystals were stretched in [112^^-0] and compressed in [0001] in the range of 77K to 573K. to investigate the deformation behavior by non-basal slip. The active slip system was investigated by the observation of slip bands. In both case, {112^^-2} <1^^-1^^-23> second order pyramidal slip is activated in all magnesium and magnesium alloy single crystals, and its yield stress shows anomalous temperature dependence in the range from 77K to 293 K, however, the yields stress decreased rapidly with increasing temperature above 293 K. [112^^-0] compression and [0001] tensile test was also carried. {101^^-2} twin occurred at 5-10MPa in both case. Deformation behavior of magnesium single crystal strongly depends on the loading orientation.

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In this study, homogenized elastic-viscoplastic behavior of an ultra-fine plate-fin structure fabricated for compact heat exchangers is investigated. First, the homogenized behavior is numerically analyzed using a fully implicit mathematical homogenization scheme of periodic elastic-inelastic solids. A power-law creep relation is assumed to represent the viscoplasticity of base metals at high temperatures. The plate-fin structure is thus shown to exhibit significant anisotropy as well as noticeable compressibility in both the elastic and viscoplastic ranges of the homogenized behavior. Second, a non-linear rate-dependent macroscopic constitutive model is developed using the quadratic yield function proposed for anisotropic compressible plasticity. The resulting constitutive model is shown to be successful for simulating the anisotropy, compressibility and rate-dependency in the homogenized behavior in multi-axial stress states.

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Strain-amplitude-dependent cyclic loading behavior of compatible type FCC bi-crystal is investigated by crystal plasticity finite element analysis. Bi-crystal models without and with subgrain (slight mis-orientation in each grain of the bi-crystal) are used to evaluate accumulations of geometrically necessary dislocations (GNDs) during cyclic loading with constant strain amplitudes. The result of the analysis shows that GNDs norm density distribution and the increase in the average GNDs norm density are affected by the crystal orientation. Comparing to the result of bi-crystal model without subgrain, additional increase in the average GNDs norm density can be found in the result of bi-crystal model with subgrain. The result also shows the qualitatively different increase in the average GNDs norm density during cyclic loading depending on the strain amplitude. The difference is discussed from the viewpoint of the strain-amplitude-dependent activation of secondary slip system.

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We have attempted to reveal the deformation mechanism of amorphous metal from the unique viewpoint of "local lattice instability" or the positive definiteness of atomic elastic stiffness coefficients, B^α_<ij>. LLIA distinguishes the "unstable atoms" as "defects" from the disordered structure of amorphous metals. In the previous report, we have compared mechanical conditions and roles of unstable atoms in monatomic amorphous metals of Ni and Al. As a result, it was clarified that the deformation mechanism between Ni and Al amorphous are different. In the present study, we have carefully discussed about changes in unstable atoms during relaxation to clarify the influence of fluctuations of B^α_<ij> by atomic vibrations. Atoms that have become detB^α_<ij> > 0 and detB^α_<ij> < 0 during relaxation feel tensile stresses. It was found that these atoms contribute to the deformation of amorphous metals.

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In the paper, deformation of two-phase polymer blends were analyzed by mesoscale simulation based on molecular dynamics to obtain relation between mechanical properties and higher order structures of the polymer blends. To express higher order structures in the analysis, the models were microstructures of two polymer phases with different molecular-chain lengths; unit cells including cylindrical phase, laminated unit cells, randomly distributed cells having different mixture ratios of the two components. Tensile stress-strain curves of the models until breaking were evaluated by using software OCTA. As the results, strain energy density of each cell model until breaking was shown. The strain energy densities were strongly dependent on not only the mixture ratios but also the microstructures, since initiations of the breaking were determined by the microstructures. Therefore, mechanical properties can be improved by designing higher order structures of polymer blends.

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The crystal condition of the poly lactic acid that was a crystalline polymer was changed (degree of crystallization etc.), and the tensile test was done. Then the influence of crystal condition on the mechanical attribute was examined. Therefore, heat-treatment was first given to the material based on the melting point and the crystallization temperature of the material requested from differential scanning calorimetry (DSC), and the material that changed the degree of crystallization was made. Next, when the change in the degree of crystallization in the extensional deformation was confirmed because the crystallinity dependence was seen in the extensional deformation as a result of doing the tensile test and having examined it, it was understood that the degree of crystallization had changed by the extensional deformation.

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This study investigated hydrogen embrittlement cracking (HEC) in high strength steel subjected to contact loading using a Vickers indentation. When the indentation test was applied to the high strength steel, the steel absorbed hydrogen produced several cracks around the impression, while as-received steel without hydrogen absorption did not produce any cracks. An experimental/computational framework was employed to elucidate the mechanism of such indentation cracks due to hydrogen embrittlement. We utilized acoustic emission technique (AET) to clarify when the crack initiated during the test. In parallel with the experiment, finite element analysis (FEA) was carried out to compute the stress field surrounding the impression. Based on the results of AET and FEA, we discussed the mechanism of crack initiation and critical stress to nucleate the crack.

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This paper intends to clarify the effect of inhomogeneity in grain aggregate scales on the Bauschinger behavior of polycrystals, which crucially affect the springback characteristics during the stamping processes, from a novel viewpoints based on the field theory of plasticity. A series of crystal plasticity-based FE simulations is carried out on dual phase polycrystalline models with 50% volume fraction of the hard phase. The relationship between elastic strain energy and incompatibility tensor field at maximum tensile stress is extensively examined. Linear relationships are found to hold for all the models. Furthermore, the slopes of the relations are demonstrated to be precisely predicted based on the correlation functions of the fluctuating field quantities.

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Regardless of any scale, space structures are widely applied for the field of engineering by using the enhanced mechanical properties, e.g., high stiffness and strength-to-weight ratio. Flexibly jointed structure as a type of space structure is constructed of flexible joints and beam members. Li this study, we proposed a newly structure with flexible multi-linkages and re-entrant spaces, and we evaluate its elastic characteristics as Poissoris ratio, which is a mechanical criterion for solid deformation. The numerical results show that the propose structure exhibits negative Poisson's ratio for high joint flexibility, and it also produce an expansion deformation subjected to local rotational moments.

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Since the high-density electronic package employs electroplating copper foils for micro wiring, the characteristics of deformation of electroplating copper foils must be clarified to ensure the reliability of the micro wiring technique. Therefore, the authors have investigated them and it became clear that copper foils show time-dependent deformations, such as strain rate effect, creep, stress relaxation and ratchetting deformation. In these time-dependent deformations, the ratchetting deformation has a possibility to cause fatigue failure due to the accumulation of strain. Then, a constitutive model which can describe the ratchetting deformation of electroplating copper foils must be constructed to design electronic equipments with high-reliability. Especially, since tfie ratchetting deformation is caused by the creep deformation, the creep constitutive model for electroplating copper foils should have high accuracy. In this study, the characteristics of ratchetting deformation of an electroplating copper foil were investigated by conducting cyclic tension-unloading tests under several conditions. Also the micro structures of the specimens after the tests were examined by conducting EBSD analyses to discuss the causes of the ratchetting deformation characteristics. Based on these results, the principle for constructing a creep constitutive model was discussed.

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