To clarify the loosening and coming out behavior, a ceramics sleeve is analyzed by using FEM when the sleeve is shrinking fitted to two steel shafts at both ends. Extremely low shrink fitting ratios are used to the ceramics roller because of the brittleness of the ceramics. Therefore the steel shafts shall be loosen out in such low shrink fitting ratios. In this study, therefore, two types of simulation are considered, one assumes an applied load to the shaft varying along the circumferential direction of the shaft at the certain interval to simulate rotating bending, and the other assumes pulling the shaft by tension. It is found that for the tensile pull out with decreasing the friction coefficient μ between the shaft and sleeve the separation happens more easily. However, for the rotating bending coming out, with decreasing different mechanism for separation may be seen depending on the number of cycle for loading, and sometimes unstably phenomenon is observed.

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Hearth rolls used in continuous annealing furnace for producing thin steel sheet, generally coated by thermal spraying's applied. The surface coating on the hearth roll needs enough adhesion and wear resistance. In this study we focus on the intensity of the singular stress appearing at the end of the JIS specimen used to investigate thermal shock strength. Then, we discuss the effect of thickness of the coat and the bond coat as well as the effect of material property on the intensity. It is found that with decreasing Y_2O_3 contents of the ceramic coat the intensity decreases.

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In this paper, the crack tip stress method is extended so that the intensity of the singular stress field of the SLJ with two real stress singularity orders can be analyzed. Two types of the reference models are proposed; one is the tensile force model; the other one is the shear force model. The intensities of the singular stress fields of the reference models are calculated by the reciprocal work contour integral method (RWCIM). The intensities of the singular stress field of the SLJ are calculated by superposing those of the reference models. Then the accuracy of the present method is discussed by comparing the present results with the solutions which are calculated by the RWCIM.

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Stress singularity frequently occurs at a vertex in an interface of joints due to a discontinuity of materials. The stress singularity fields are one of the main factors responsible for debonding under mechanical or thermal loading. The stress distribution near the vertex in the interface of joints is very important to maintain the reliability of joints. However, the intensity of singularity for 3D transversely isotropic piezoelectric bi-material joints has not been made clear until now. In this paper, intensity of singularity in transversely isotropic piezoelectric dissimilar material joints is analyzed. The stress and electric displacement distributions on an interface and the intensity of singularity at the vertex are investigated using BEM.

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Recent electronic device packaging, for instance, CSP has a bonded structure of IC chip and polymers, and delamination occurs frequently at the interface between IC and a resin. Furthermore, thermal stresses which are caused by a temperature variation in the bonding process of CSP and heat cycles for environment temperature will influence on the strength of interface. In the present paper, the strength of interface in multi-layered specimens composed of silicon, resin, silicon film and sapphire is investigated. Influence of layer thickness on the strength of interface is examined.

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The elastic-plastic constitutive equation with the stress-dependent effect on phase transformation is proposed, but there are few experimental examples to verify the accuracy of the equation. Therefore,the transformation induced plasticity (TRIP) strain during pealrite reaction of S45C was measured when the hollow specimen was subjected to tension-compression-torsion uniaxial stress. TRIP strain was identified from experimental results, which are reproducible results about torsional strain. In the case of axial strain, some results had variability under same stress condition. Then we found that the constitutive equation disagree with TRIP strain under tension-compression-torsion uniaxial stress.

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Three-point bending system has been developed to analyze the transformation plasticity (TP) behavior and obtain transformation plasticity coefficient. Two kinds of materials SCM440 steel and S45C steel have been studied. The specimens heated to austenite temperature and hold temperature constant for several minutes, then naturally cooled to room temperature, during cooling the bending stress applied to the specimen. The maximum transformation plasticity deflections due to bending stresses have been obtained experimentally and then transformation plasticity coefficient determined. By improving the loading system of test machine and changing one of simple support to fixed support the scattering of deflection decreased.

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Machine structure under elevated temperature generally causes not only static stress but multiaxial cyclic stress. It is common to be subjected cyclic stress simultaneously with mean stress. The purposes of this research are to obtain of the experimental data with reliability under multiaxial cyclic stresses, and to construct of the constitutive equation. It carried out a tension - torsion cyclic tests using triangular stress wave and the tension-torsion cyclic experimental result was compared with finite element analysis result on three stress conditions at 260 °C. And finite element analysis using this constructive equation was conducted to the specimen which has a notch.

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Polymeric material is used in such fields as electricity and electronic parts. In this report, deformation behaviors of water absorbed nylon66 after pre-strain are investigated under biaxial stresses to establish the constitutive model. A series of equi-strain loci after tensile and torsional pre-strains can be expressed numerically in Mises type stress plane by considering hydrostatic pressure effect in flow stress. By using the obtained equations of the equi-strain loci and the normality rule with respect to plastic strain incremental vector, stress paths are calculated at loading along various strain paths with a corner of various angle. It is confirmed that rather good agreement can be obtained between experimental and predicted results on stress-strain curves of water absorbed Nylon66 in reloading after pre-strains.

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Si_3N_4-matrix SiC whisker reinforced composites (CMC) have higher fracture toughness if the size and the fraction of whisker or matrix powder, are appropriate. Though the condition is not apparent, it is concerned with the mechanical properties of grain boundary. In this study, the high temperature internal frictions of CMC and Si_3N_4 were measured by an inverted torsion pendulum Strength tests and fracture surface observation were also conducted. The relationship between higher toughness of CMC and these experimental data was investigated.

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This paper investigates the effect of the fiber discontinuity, caused by the prepreg cut in fabricating laminated structures, on the mechanical properties in CFRP laminates. The damage initiation and progress around the fiber discontinuity are also discussed. It has been found that stresses required to initiate debonding between the resin rich region and the fiber discontinuous plies, and interlaminar delamination between the continuous and discontinuous plies, decrease with the increase in thickness of the fiber discontinuous plies. Specimens type B, C and D contain 3, 5 and 7 discontinuous spots respectively and these spots form staggered geometries. Fracture stress varied with the different distribution of fiber discontinuity. If interval d is longer than 10mm in type B and type C, fracture stress did not change. Also, if interval d is longer than 20mm in type D, fracture stress did not change.

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In order to predict the behavior of the growth of microscopic voids which causes fracture in ductile metal materials, finite element analysis is valid. However, the large number of elements are needed to analyze model with voids distributed randomly. Therefore, the model which describes the effect of such voids by internal state variables is required. In this study, finite element analysis is performed using anisotropic Gurson's yield function which incorporates the damage tensor. And validation will be carried out by comparing with experimental results under uniaxial stress and analytical results under biaxial stress. As a result of comparison, it was found that the proposed mesoscopic model well describes the macroscopic deformation of perforated sheets.

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The amount of back stress formed in work-hardened IF steel was examined. The stress-strain curves of tension and those of compression tests were obtained by four-bending test, which used two strain gauges glued on the top surfaces to measure the fiber stresses there. Pre-strained bars after tensile deformation of 0.5,1,2,3,4, 10,20,30% strain were prepared, and subjected to the bending test. The result showed that the Bauschinger effect in subsequent compression was almost absent in the specimens prestrained below 4%. However, the effect was developed in specimens prestrained larger than 10% strain.

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In this study, we focus on the dry fabric forming simulation. Starting point of our approach is meso-scale simulations of both plain and satin weave textile to understand each of the dry fabric property especially under shear deformation. Significant differences between the responses to picture frame test and to bias-extension can be explained by the tension of yarns. Finally, the hemispherical forming simulations are performed.

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Columnar specimens were made of resin composites by light curing. The specimens were subjected to static compressive stress. The compressive stress was unloaded when the stress attained to the specified value. Then loading and unloading were repeated with the specified stress increased gradually. Young's modulus was evaluated by gradient of stress-strain curve just after starting unloading. Moreover, apparent density was also measured by the Archimedes' method. Then variation in Young's modulus and apparent density with maximum applied stress increased was clarified. On the other hand, change in residual strain after unloading was clarified in two cases. One is the case in which loading and unloading were repeated in a specimen with the maximum stress increased, and the other is the case in which a set of loading and unloading was made in a specimen once. In the latter case, the maximum stress was changed when a specimen was changed. Finally, a scalar damage variable was evaluated by the variation in Young's modulus from the initial value, and the features of damage development were discussed.

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The viscoplastic constitutive equation of epoxy resin reinforced with carbon nanofiber (CNF) is evaluated using a numerical approach based on the finite element method (FEM). Homogenization theory is employed to estimate the viscoplastic constitutive equation of the composite composed of matrix resin and carbon nanotube. Viscoplastic property of epoxy resin was evaluated by tensile tests under several strain rate. Viscoplastic constitutive equation of CFRP can be estimated numerically by homogenization theory with FEM. The effectiveness of the present study is verified by comparing the experimental and numerical results of stress-strain relation of the composite changing strain rates.

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The stitching yarn of Non-crimp fabric (NCF) composite brings the improvement of out-of plane strength and intricate microscopic structure. In order to estimate the effect of position of a hole and opening resin region on damage development of composites conveniently, a new modeling of NCF composites with a circular hole is proposed based on the mesh superposition method. The laminate parts and a hole part are modeled individually, and the mechanical behaviors under static tensile loading is estimated. The continuous model of NCF GFRP with a hole as the conventional model, and the super imposed model which is consisted of global model (laminate with opening resin region) and local model (a hole part) are generated. As the numerical results, the effects of opening resin region and a hole on the damage can be estimated with the proposed mesh superposition method. And it has been revealed that the proposed numerical modeling method is useful for design of the products composed of textile composites.

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Recently, piezoelectric material has a very important potential for its property showing high responsiveness as a MEMS (Micro Electro Mechanical Systems) actuator. In addition, the PZT (Lead Zirconate Titanate) is a piezoelectric material most general. Then, physical property changes greatly from changes in the composition ratio. Therefore, function improvement of PZT is tried widely by additive element. However, as for them, empirical method that requires enormous cost and lacking in quantitatively is mainstream. Thus, the application of the results is difficult. Accordingly, in this research, search of the additive element low-cost and quantitatively from the viewpoint of energy by using a first-principles calculation. In consequence, V and Mn can be substitute to the B site on PZT from the cohesive energy value. Moreover, it was confirmed that the structure of PZT is maintained when added in V, and Mn by tolerance factor. Furthermore, V and Mn are lighter than the Zr, so PZT piezoelectricity can be improved by adding V or Mn.

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This paper investigates theoretically and experimentally the cryogenic fracture behavior of cracked piezoelectric ceramics under electric fields. Fracture tests were performed in three-point bending with the single-edge precracked-beam (SEPB) specimens at room temperature (RT) and liquid nitrogen temperature (77 K), and the fracture loads under electric fields were obtained. Plane strain finite element analysis was also carried out using temperature-dependent material properties of the piezoelectric ceramics, and the dependence of the energy release rate on the electric field and temperature was discussed. In addition, possible mechanisms for cryogenic fracture were examined by scanning electron microscopy (SEM).

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This paper presents a FEM procedure for nonlinear magneto-striction materials, which take on a phenomenon that strain ε is a quadratic-like function of magnetic flux density B. In the procedure independent variables are mechanical displacement vector u and magnetic vector potential A, whose combination results in the variational formulation based on minimization of total potential energy. Modeling Helmholtz's free energy density having convexity is essential for accurate constitutive equations.

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We used a new method to fabricate micro porous bell-shape metal from glass microcapsules and liquid metal. Each pore structure behaves as a micro-bell. This metal, which is more than 20% lighter than bulk material, also shows a unique characteristic: high-frequency oscillation is greatly attenuated when propagated in its medium. This method offers great potential for size, shape, and conformation control, with changed the attenuation characteristics achieved merely by changing the mixing technique. In present study, we could fabricate some kinds of micro porous bell-shape metals with different bell-shape structure only by changing microcapsule size. Then, the attenuation characteristics and mechanical behaviors were measured for fabricated micro porous bell-shape metals.

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Damping properties of foamed plastics is analyzed experimentally using an impulse technique. To investigate the influence of expansion ratio on vibration damping characteristics, vibration tests are implemented. The results show that the damping ratio of sandwich materials decreases with increase of the expansion ratio of foamed plastics. It is recognized that the damping properties of aluminum/foam/aluminum sandwich materials are depend on the expansion ratio.

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A diaphragm made of stainless steel sheet is widely used as switching part in electric devices, which controls on/off of electric signal supply. Making trial pieces based on experience is a common way for designing diaphragm with certain click characteristics and fatigue life, which is time consuming and costly. In this study, a designable space method for designing diaphragm considering both click characteristics and fatigue life is proposed. This approach consists of three procedures. Firstly, design space of click characteristics is constructed based on the results of numerical simulation. Secondly, the fatigue reliability is evaluated based on the stress history of every element obtained from numerical simulation and the fatigue limit diagram with fatigue probability. Finally, design space considering fatigue reliability can be constructed by combing the click characteristics design space and fatigue reliability together. It is revealed that the proposed method is very useful for designing diaphragm considering fatigue reliability.

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The objective of this study is to evaluate the stress/strain distribution on a cast aluminum alloy (AC4CH-T6) employing image based nonlinear elasto-plastic finite element analysis. The numerical analysis was performed to simulate a uni-axial tension test. The geometry of the finite element model includes an aluminum matrix, silicon and inter-metallic particles which were obtained by the synchrotron X-ray micro-computed tomography (XMCT) technique. In order to create a proper finite element mesh, the Standard Triangle Language (STL) generated from the XMCT segmented volume was treated to remove geometric and structural irregularities. Results are discussed in terms of the number of elements necessary to accurately represent the stress/strain fields and the necessary computational time to simulate the problem. Additionally, results enabled visualizing the stress/strain distributions, stress concentration, and the stress/strain evolution on the three solids of interest.

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In this paper, the numerical simultion about press molding of glass lens using the finite element method is investigated. Thermo-viscoelastic properties of the glass were estimated using undirectional compression creep test based on traditional thermoviscoelastic theory. Numerical simulation for molding press of the glass was carreid out by finite element method using universal FEM code (ANSYS ver.12.0). Relation between molding temperature and pressure for complete transcription was investigated and the adaptive condition of press molding was predicted. The effect of cooling rate for residual stress and shape error was investigated by the present numerical simulation.

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In this work, the thermal stress in ultrafine plate-fin structures made of a Ni-based alloy subjected to a macroscopic temperature increment is simulated macroscopically and microscopically, using a homogenization theory for thermoelastoviscoplasticity. For this purpose, the homogenization theory for thermoelastoviscoplasticity is constructed by introducing the effects of thermal expansion into the homogenization theory for time-dependent materials. The present theory is then applied to the thermal stress simulation of ultrafine plate-fin structures, in which two cases of macroscopic temperature rates are considered. The results show that the higher the macroscopic temperature rate is, the higher the thermal stress is. Moreover, it is shown that the stress concentration occurs at joint regions between plates and brazing parts, and at some parts of fins, indicating the importance of thermal stress analysis of ultrafine plate-fin structures.

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To understand deformation mechanisms of magnesium, ball indentation tests were carried on pure Mg and Mg-Al single crystals. In both crystals, indentation on (0001) was round shape, while indentation on (1210) was oval shape. Size of the indentation on (0001) was decreased by A1 addition, while the size on (1210) was similar in both crystals. Formation mechanism of the indentations was also analyzed by using MD simulation method. From these results, we conclude that the indentation on (0001) is made by activation of basal slip and pyramidal slip, and the indentation on (1210) is made by activation of basal slip and {1012} twin.

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Tension-compression asymmetry of plastic deformation of magnesium alloys has been known to affect plastic formability in several metal forming processes. However, in most of works on the tension-compression asymmetry, the result of uniaxial tension was compared with that of uniaxial compression. In the present study, the plastic deformation behavior of AZ31 magnesium alloys in uniaxial tension was investigated and compared with those in equi-biaxial compression, in which the macroscopic deformation was equivalent to that of uniaxial tension. It was found that the equi-plastic work point obtained by equi-biaxial compression was on the same isotropic yield curve with that by uniaxial tension, in the early stage of plastic deformation. The crystal orientation measurement results also revealed that the twin area fractions as well as active twin systems by uniaxial tension were almost the same with those by equi-biaxial compression. These results imply that the difference between deformation patterns by uniaxial tension and by uniaxial compression is primary cause of the tension-compression asymmetry of magnesium alloys.

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The yield surface and the deformation mechanism of the extruded AZ31 magnesium alloy rod at room temperature were studied. The uniaxial tensile, compressive and pure shear tests with the simultaneous observation of the microstructure were carried out for specimens sampled along different directions in an extruded rod. In the plane-stress condition within the plane perpendicular to extrusion, the yield surface almost fits the Tresca's criterion for isotropic materials, because of the activation of the basal slip or {1012} twinning, regardless of the loading direction. The deformation mechanism with higher critical resolved shear stress than those of basal slip or {1012} twinning is driven by the tensile loading parallel to extrusion, due to the texture with the direction of its c-axis perpendicular to tensile direction. Therefore the tensile yield stress for this direction increase more than compression or shear, and the twinning pattern at the yield for tensile loading does not appear.

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Biaxial tensile tests of commercial pure titanium sheet, JIS #1, were performed using a servo-controlled multiaxial tube expansion testing machine developed by one of the authors [Kuwabara, T. and Sugawara, F., Multiaxial tube expansion test method for measurement of sheet metal deformation behavior under biaxial tension for a large strain range, Int. J. Plasticity, 45 (2013), 103-118.]. Tubular specimens with an inner diameter of 54 mm were fabricated from an as-received sheet sample with a thickness of 0.5 mm by roller bending and TIG welding. Many linear stress paths in the first quadrant of stress space were applied to the tubular specimens to measure the biaxial work hardening behavior of the test sample. Following conclusions were obtained: (1) the test material exhibited significant differential work hardening (DWH); (2) the work contour for ε^p_0= 0.05 was in fair agreement with that calculated using the Yld2000-2d yield function; (3) the work contour forε^p_0 =0.15 was in fair agreement with that calculated using Hill's quadratic yield function.

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The deformation mechanism of the extruded AZ31 magnesium alloy rod under various temperature conditions was studied. The purpose of this study is to find the yield mechanism of this material in the thermoplastic deformation conditions. When this material is subjected to tensile stress parallel to the extruded direction to which a transgranular deformation and grain boundary sliding are hard to occur by the crystallographic texture, the non basal slip whose critical resolved shear stress decreases with increasing temperature can act as the yield mechanism. After the yield was induced by the non basal slip, two different deformation mechanisms occur according to the environmental temperatures. The c-axis compression twinning which has the temperature dependency occurs at a relatively low temperature. On the other hand, the grain boundary sliding which was promoted by the dynamic recrystallization acts as the plastic deformation mechanism at the higher temperature.

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This paper deals with the influence of deformation twin on fatigue crack propagation in extruded AZ31 magnesium alloy (average grain size: approximately 120μm). In order to introduce the deformation twins, the specimens were compressed along the extrusion direction at several strain levels: 1%, 3% and 5%, respectively. Compact tension (CT) specimens were machined from the pre-compressed materials. Fatigue crack propagation tests were performed on an Electro-hydraulic testing machine at a stress ratio R=0.1 and a frequency of 10 Hz at room temperature in air. The fracture surfaces and the crack paths of the fatigue fractured specimens were observed by SEM and SEM-EBSD. The fatigue crack propagation rates of the specimens introduced the deformation twins are comparable to that of the as-received specimen. It appears that the fatigue crack growth is not controlled by the deformation twins at the crack tip.

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Accumulative roll-bonding (ARB) is one of the severe plastic deformation techniques, using rolling. In this study, the dependence of sheet direction on the fatigue properties in commercially pure Ti sheets ARB processed by 6-cycle was investigated. In the fatigue tests, the two kinds of the loading directions were used: parallel and perpendicular to the rolling direction of the ARB processed sheet. The ARB processed sheet consists of the equiaxed and elongated grains, and the mean grain sizes were 131 nm and 95 nm, respectively. Texture becomes stronger with increasing ARB cycle. In the ARB processed Ti sheets with texture, the fatigue crack initiation life depends on the sheet direction. This dependence can be explained by the slip and twin activities.

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A tensile test of pure titanium plate specimen was performed on the stage of digital holographic microscope, and a change in the height of each grain on the surface was evaluated during the tests. The load was increased stepwise in the tensile test and the distribution of height change of each grain was evaluated at all steps in nanometer order. The identification of region before and after each loading step was done by the Digital Height Correlation Method (DHCM). The height change of each grain between low loading levels corresponded to that between relatively high loading levels, which suggests that the height change in plastic deformation occurred mainly by crystallographic slips can be predicted by that in elastic deformation. Slip lines after the plastic deformation were observed and the correlation of the slip lines and height change of the grain was discussed.

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Recently lower costly alloy, Ti-Cr(Fe)-0(N) which shows strength as high as Ti-6A1-4V alloy has been in common use. Both nitrogen (N) strengthened (Ti-4Cr-0.2N (mass%)) and oxygen (O) strengthened (Ti-4Cr-0.20) titanium alloys have been studied for their utilization on the structural materials. Their tensile deformation behavior was investigated by in-situ neutron diffractmeter "TAKUMI". Lattice spacing was measured with increase of the applied stress. The internal stress was partitioned into the grain interface between alpha phase and beta phase, which was called as phase stresses. Phase strains were measured in the axial and transverse direction determined lattice parameters by Reitveld refinement. Beyond the onset of plastic flow, micro-yielding, almost no change of the phase strain in alpha phase was detected with increase of the applied stress. On the other hand, phase strain in beta phase was continuously increased. Furthermore, the N (O) adjunction increased the yield stress and tensile strength. These results show good agreement with the predictions by a simple two-phase model: the strong beta phase yields higher stress than macro-yield stress, resulting in high strengthening of (alpha + beta) dual phase titanium alloys.

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In the present paper, the deformation behavior of AZ31 cast magnesium alloy sheet was investigated both experimentally and numerically. Although the sheet had random crystallographic orientations, an asymmetric deformation was observed between tension and compression; the stress level was higher under tension than under compression, and the stress-strain curve was affected by a loading path as in the case of a rolled magnesium alloy sheet. A crystal plasticity finite-element method was used to examine the mechanism that causes such asymmetry. The simulation results showed that the activities of twinning and nonbasal slip were clearly different between tension and compression, leading to the asymmetric deformation behavior in the cast magnesium alloy sheet.

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The non-normality effect of magnesium alloy AZ31 is numerically investigated using the crystal plasticity approach. A homogenization-based finite element method is introduced to compute the macroscopic material behaviors with a crystalline scale structure. The strain path abrupt change method is utilized and the non-normality, which is the difference between the normal to yield surface and direction of plastic deformation, is quantitatively evaluated. The effect of activities of each slip system on the non-normality is discussed.

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In this study, a multi-phase-field (MPF) model describing evolution of twin microstructure with two or more variants of twin is developed. Three kinds of free energy namely elastic energy, barrier energy and interfacial energy are considered. In order to introduce the strong anisotropy of interfacial energy, nonlinear form of its functional is adopted. The MPF model is coupled with dislocation-based crystal plasticity model, which is developed previously by the authors, via order parameter and resolved shear stress acting on twin system that plays a role of driving force of twin microstructure development. Using the above model, a uniaxial tensile FE analysis on pure magnesium including two variants of twin is carried out. From the result of the present analysis, compression stress considered to be occurred by twin shear is seen at the triple junction among matrix and two twins. In addition, basal slip and accumulation of dislocation is observed in the vicinity of twin interface, especially at the triple junction.

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The deformation behavior accompanied by the formation of deformation kink in synchronized LPSO-phase was examined by comparing the behavior in the hcp-Zn single crystal. Deformation process of the LPSO phase DS crystal accompanied by the formation of deformation kink was investigated by dynamical observation and the features were compared to that in Zn single crystal. In both crystals the formation of deformation kink bands were confirmed in specimens that were compressed along the direction parallel to the basal plane. The characteristic features of the deformation kink band showed many similarities in them.

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Inhomogeneous deformation behavior in a magnesium alloy which is almost occupied by long-period stacking order (LPSO) phase has been investigated by using high-precision marker method and TEM. Particular emphasis is laid on the aspect of a microstructure called "kink" generated characteristically in the LPSO phase. Mg alloys containing Zn and rare earth elements such as Y or Gd have a characteristic microstructure including the LPSO phase and the usual hcp matrix phase. The superior mechanical properties of the Mg alloy should be closely related not only to the microstructural inhomogeneity induced by the difference in the deformability of the dual phases but also to the characteristic deformation behavior of LPSO phase. The hard LPSO phase should contribute to the increase of yield and tensile strength. A characteristic microstructure called "kink" was generated by working such as extrusion in the LPSO phase, which raise the strength of LPSO phase. In order to clarify the details of kinking behavior, high-precision marking method using electron beam lithography has been employed. After compression test, many wedge-shape microstructures accompanying large distortion of markers were observed on the specimen surface, which indicates that the kinking occurred by the compression test. In addition, TEM observation revealed that basal plane was bended in the area including the kinks. The formation mechanism of such microstructural inhomogeneity in the LPSO phase is discussed.

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Within exliuded Mg_<89>Zn_4Y_7(at%) alloysontaining a long period stacking ordered(LPSO) phase,a unique defomation mode refemation mode referred to as "kink deformation"is found to occur within the LPSO phase grains, frming kink bands that are each represented by an array of geometnically necessary dislocation. Intragranular misonentation axis(IGMA) analysis suggests that this kink dformation results in lattic rotation predominately about the <1100>,<0110>,<0001>,and<1210>axes of the 18R-type LPSO structure. IGMA analysis is based on slip-induced lattioe rotation and determination of its rotation axis(Taylor axis). Therefore,it is possible to determine the dominant slop mod in a grain that is defoemed, by matching the Tayloeaxis for agiven slip system to its experimentally obtained IGMA destnbution. In this study,the study, the strong preferenoe of<1100>and<0110>Taylor axes suggests that kinking occurs through a basal <a> slip mode. The<0001> Taylor axes suggest that kink bands form through a prismatic<a>slip mod. These axes are categorized as "principal rotation" axes, which result from one Burgers vector of dislocations. Kink bands with a <1210> Taylor axis are produced through combination of dislocation. It is concluded that IGMA analysis can be effectively used to study and geometrically classify kink bands.

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In this research, the kink band formation probability in polycrystalline LPSO single phase alloy was investigated quantitatively. First, the uniaxial compression test was performed in order to introduce the kink bands into LPSO phase. Distributions of crystal orientations in undeformed and deformed specimens were measured using SEM/EBSD. Comparing the initial distribution of crystal orientations with the deformed one, the regions where kink bands were formed were specified by Kernel Average Misorientation (KAM). From the relationship between the probability of kink band formation and the misorientation angle between neighboring grains, it was found that the probability was less than 80% even at regions with high misorientation angles.

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In plastically deformed hexagonal close-packed (HCP) metals, kink bands are frequently formed. The one possible formation mechanism for kink bands is the significant lattice rotation due to localized accumulation of basal slip. Therefore, the details of accumulation of basal slip during plastic deformation should be made clear to gain understandings of formation mechanism of kink bands. In this study, the localization of basal slip during compressive loading in single crystal magnesium with the dominant activation of basal slip system is numerically evaluated using a crystal plasticity finite element analysis method. The influences of initial crystal orientation, lattice rotation, hardening rate and strain rate sensitivity are studied.

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Mg alloys with long-period stacking ordered structure (LPSO) phase show excellent mechanical properties such as high specific strength. Although it is known that kink band formation in LPSO phase during plastic working strengthens the alloy, there is not much information about how the kink bands progress in the alloy. Also, the effect of misorientation between crystals has not been investigated sufficiently. We developed a dislocation-based crystal plasticity model suitable for crystals of LPSO phase and demonstrated two-dimensional FE analysis for single crystal of Mg-based LPSO phase. In this study, we carry out FE compression analysis for polycrystalline Mg alloy with LPSO phase in which single crystal of LPSO phase is sandwiched between two crystals of a-Mg phase. We use same computational model mentioned above for both LPSO phase and a-Mg phase of the alloy, however we distinguish each phase by assigning different CRSS to respective slip systems in each phase. Through this numerical simulation, we discuss the effect of a-Mg phase on kinking of LPSO phase.

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Nucleation of a dislocation loop in the process of the basal slip of a magnesium single crystal has been investigated via atomistic simulations. Metadynamics method was applied in order to realize the nucleation of a dislocation loop in atomistic simulations which inactivate in the time scale used in usual molecular dynamics simulations except for cases where extremely higher stresses are applied. Activation free energy for nucleation of a dislocation loop was also evaluated from metadynamics method. We found that the activation free energy decreases as the applied shear stress increases and dependence of the activation free energy on temperature decreases for high applied shear stress.

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Crack propagation in Magnesium is investigated using molecular dynamics simulations. By providing atoms in a disk-shaped simulation cell with the displacement evaluated by the anisotropic elastic theory, propagation of a crack is carried out. For an embedded atom method (EAM) potential, basal and first-pyramidal surfaces are favorable cleavage planes due to relatively low surface energies. MD simulations using EAM show brittle fracture behavior with basal or first-pyramidal cleavage surface. On the other hand, a generalized embedded atom method (GEAM) potential, the basal plane has larger critical stress intensity factor by the Griffith's formula. Consequently, in GEAM simulations of crack propagation, ductile fracture occurs as dislocations and deformation twins are generated in the vicinity of the crack front.

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In this study, the activation energy of dislocation motion in Mg at finite temperature is evaluated using the combination of nudged elastic band method and constraint molecular dynamics method. In tha case of edge dislocation, while the energy barrier at 0 K for prismatic slip is found to be twice larger than that for basal slip, their energy level is significantly small. On the other hand, energy barrier for screw dislocation glide on prismatic plane is quite large, and the obtained result suggests that the process of recombination and redissociation of partial dislocations is a key factor to understand the temperate dependence of activation energy for dislocation motion.

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First-principles shear and tensile tests were performed on pure Mg, Mg-Zn-Ca, Mg-Ca, and Mg-Zn models, and the generalized stacking fault energy for basal and prismatic slip systems and the surface energy of the {0001} plane were investigated to understand the origins of the high-stretch formability of Mg-Zn-Ca alloy. The calculations suggested that the high formability of Mg-Zn-Ca alloys is attributable to improved plastic anisotropy, not to the enhanced surface energy.

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We report on our in-situ visualization experiments for nucleation and growth of cavities during the debonding process of soft adhesives. Based on the experimental observations, we propose a simple model describing the relationship between the cavitation and the mechanical properties. Through our work, we will stress the importance of deformation dynamics of soft viscoelastic materials in mesoscopic scales.

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The thermoplastic copolyester elastomer is a polymer material which has both characteristics of a flexible elastomer and processing properties of engineering plastic. For shock absorbing use, we had the high-speed tensile tests and obtained the material properties.

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