Effect of tensile stress on the corrosion potential of high pressure die cast aluminum alloy was examined by the tensile test in a corrosive environment with the electrochemical measurement. The aluminum alloy has an oxide film as a corrosion barrier, but the oxide film may partially break by the mechanical stress and the damage leads to a local corrosion such as pitting corrosion by the effect of local cell. To qualitatively evaluate the strength of corrosion fatigue or stress corrosion cracking, the effect of stress on the electrochemical property has to be clarified. The spontaneous potential difference was measured by the three-electrode system during the tensile test, and the relationship between the spontaneous potential and the tensile stress was evaluated. The results showed that the spontaneous potential certainly decreased within the elastic region and saturated after the yielding. The effect of casting skin was also examined, and the spontaneous potential decreased due to the deletion of the casting skin.

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It is known that residual stress in a structure effect on the fatigue life, especially tensile residual stress make the life shorter. Recently aluminum alloys widely used as structural parts of auto vehicles. In industry, it is very important to simulate the residual stress in the aluminum alloy part for the fatigue design. In this paper, numerical simulations for residual stresses in 6000 series aluminum alloy during press forming processes were achieved with a large scale parallel computing finite element method, ADVENTURECluster[○!R]. Residual stress is in press formed structures are depended on coefficient of friction between jigs and works.

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Mechanical surface treatments such as shot peening and cavitation peening are useful techniques to enhance fatigue strength of metallic materials. In order to establish mechanical surface treatments of mechanical components, the effects of geometry on enhancement of fatigue strength should be investigated. In the present paper, a plate with a hole as a typical shape, which had a corner and inner wall, was treated. The tested material was Duralumin Japanese Industrial Standards JIS A2017-T3. The plate was treated by shot peening and cavitation peening. Although the fatigue life of shot peened specimen was shorter than that of non-peened specimen, cavitation peening could improve fatigue life when the cavitation bubbles were shed and collapsed on the inner wall surface.

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Effect of humidity on the growth properties of a fatigue crack in an age-hardened Al alloy was investigated in relative humidity of 25% and 85% at loading frequencies of 50 and 6Hz. Macroscopic growth mode of a crack was a tensile one in low humidity, while the mode changed from the shear one to the tensile one with increase in fatigue life in high humidity. The crack in low humidity propagated by forming striation. On the other hand, in high humidity, most of fracture surface was occupied by many slip planes in the shear mode crack, and many granular facets in addition to striations were observed in the tensile mode growth. The difference in growth mechanism was explained by microstructure and cyclic softening behavior of the alloy and hydrogen content.

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Resonance frequency is an important parameter in the ultrasonic fatigue testing. This study investigated the effects of the resonance frequency by measuring stress amplitude and edge displacement under various resonance frequency conditions. The resonance frequency of the specimens varies according to the specimen length. When the resonance frequencies are equal between the specimen and the testing machine, errors of stress amplitude are negligible. However, if there are differences, the errors are increased. In these cases, the errors of edge displacement are increased as well. The errors of stress amplitude are therefore reduced by re-calculating the stress amplitude based on the measured edge displacement. This re-calculation is very close to feedback control of the edge displacement. A way to minimize the errors is however to match the resonance frequencies between the specimen and the testing machine. In this case, the feedback control is not always necessary.

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In this paper, the possibility of fatigue life prediction of spot-welded joint under two steps variable amplitude load was investigated. The constant amplitude load fatigue tests for the spot-welded tensile shear specimen and peeling specimen were carried out and the results were arranged by using the nominal structural stress. As a result of prediction using Miner's rule, the fatigue life of spot-welded joint under two steps variable amplitude load could be estimated by the nominal structural stress considering average load and fatigue crack closure. Further, it was suggested to be able to estimate the fatigue life without depending on the joint form. Therefore, the nominal structural stress parameter showed the possibility of evaluating the fatigue life of spot-welded joint under actual variable load.

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Multi-ply bellows is widely used because its flexibility and pressure tightness. However, the analytical treatment of its behaviors is difficult compared with that of single-ply bellows, since the uncertainty of friction between plies exists. In this paper the strength evaluation equations of multi-ply bellows are examined based on EJMA Standard and the friction effect between plies is investigated through FEM analyses including material plasticity.

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In this paper, using the specimen which is already applied the pre-deformation of a large uni-axial tension, the estimation method for the yield stress when the cyclic loads of uni-axial tension and compression are applied with keeping the constant strain amplitude is described. Based on the Natural Strain theory, the yield stress is estimated by the tangent modulus of the principal deviatoric stress and the principal deviatoric strain curve. Especially, the relations between the change of the yield stress and the number of cycle are examined under the different size of the pre-deformation of uni-axial tension and the different amplitude of strain. Moreover, the results based on this method are compared with the results by conventional proof stress.

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This paper describes the methods for distributing the residual bending moment efficiently in a thin metal plate in order to generate a plastic deformation along the irradiation point when acting the bending moment again. The thermo-elasto-plastic deformational behavior of a thin metal plate when laser beam is irradiated to the surface of a plate with cooling its back side is investigated based on the limit analysis. In our previous study, the distributions of residual moment have been examined under the multipoint irradiation. However, it became clear that the residual moment cannot be distributed effectively in a plate by conducting the multipoint irradiation only once. Then, in this paper, the distribution of residual moment obtained under the overlapping irradiation is taken up as the next subject of this research. Especially, the methods for distributing the residual moment widely are examined by changing the conditions such as the positions of irradiation and the surface temperature.

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Stainless steel is mainly used as structural materials under severe environment. Therefor clarifying the fracture strength of stainless steel is important. The purpose of this study is to clarify the fracture toughness anisotropy of rolled stainless steel. Inclusion distribution is influenced by the rolling process. The stable crack grows by coalescence of voids which occur as nuclear inclusions. Therefore the distribution of inclusions affects the fracture strength of the material. In this study rolled SUS304 stainless steel with the thickness of 30mm was used. Specimens in the crack direction of the six were produced from this material. The fracture toughness values of these specimens were evaluated by direct current potential difference method. As a result, the fracture toughness of this material showed anisotropy. The specimen of which crack plane was parallel to the rolling plane showed lowest fracture toughness value. This tendency was the same as other the rolled metal material having ductile properties. As a result the orientation relationship between crack plane and rolled surface affects the fracture toughness. In addition, in case the large dimples are present in the fracture surface, the fracture toughness values of the specimens were low.

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Recently, a term of "Security and Safety" has been widely used instead of a single term of "Safety" not only in mechanical fields but also in various fields in Japan. In the previous study, its fundamental concept is made clear by using a mathematical concept of "Projective Transformation". In this study, clarification of its fundamental concept is attempted by using concept of "Expression and Representation" which was submitted by G. W. Leibniz.

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Creep crack growth tests using C(T) specimens are standardized by ASTM E1457. To realize uniform creep crack growth, C(T) specimens with side-groove are used for the tests. However, due to difference of creep ductility and creep crack growth behavior for each material, the optimum depth of side-groove has not been yet defined strictly. In this paper, to characterize the optimum depth of the side-groove, diffusion analysis of vacancy around a notch tip was conducted based on micro damage mechanics.

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Cr-Mo-V steel has been used as a material of turbine rotor of thermal power plant, and it will be used under the conditions of high temperature and creep. The life of creep crack growth for Cr-Mo-V heat-resistant steal is considered to be sensitive to differences in material micro-structure. In this study, creep crack growth tests were conducted using Cr-Mo-V steel with four kinds of materials with variation in micro-structural dimensions in order to clarify the effects of material structures such as grain size on the creep crack growth characteristics.

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Generally speaking, it is difficult to evaluate the degradation of components using destructive techniques, because conventional uniaxial creep specimens were sometimes too large to collect them from local area of target components. Miniature Creep (MC) tests have been recognized as a semi-destructive technique. They employ small specimens that can reduce the conventional uniaxial creep specimen in similarity. In this study, MC tests of 2mm in diameter were performed in Argon gas to measure creep properties, and compared them with uniaxial creep test results employing 2.25Cr-1Mo steel. It was shown that MC rupture lives were a bit shorter than those of uniaxial creep due to some oxidation and some addition of bending stress to nominal stress.

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Small Punch (SP) creep test has been recognized as a practical procedure to examine creep rupture lives only sampling a very small volume. However the standard test method of SP creep has not been established yet. In this study, SP creep tests in air and in vacuum were carried out at 600℃ employing 2.25Cr-1Mo Steel and using two types of loading balls which vary in a diameter of 2.0mm and 2.38mm. As a result, creep rupture lives with the loading ball of 2.38mm in diameter were longer than these with that of 2.0mm. On the other hand, there were little difference among the test results in lower applied load levels in air and in vacuum regardless of the loading ball diameter. Ratio of applied load in the SP creep test to stress in the uniaxial creep one was changed from 1.7 to 2.0mm^2 with the loading ball of 2.0mm and from 2.1 to 2.2mm^2 with these of 2.38mm.

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Recently, composite materials are used in various products, above all, GFRP (Glass Fiber Reinforced Plastic) is relatively inexpensive and widely used as a structure member of watercraft, or aircraft. Hat-Shaped stiffener is used as a structural member of a ship. The rising part of the GFRP Hat-Shaped stiffener, delamination occurs before the compressive stress of BWR layer of the flat part reaches the limit value. In this case, rising part is subjected to bending moment in the direction of opening the bend. The bending moment may be the cause of the delamination. In this study, we conducted the four-point bending test of GFRP curved plate and reveal the delamination strength of GFRP curved plate when subjected to bending loads.

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This study proposes a method for identifying damages induced by an impact force acting on aluminum and CFRP sandwich panels with honeycomb core. The impact location and the impact history are identified using strain data measured by biaxial strain gauges. Experimental transfer matrices, which relate the impact force and the sensor response, are used to identify the force history. The present paper reveals that the impact damage in aluminum and CFRP sandwich panels can be estimated by the shape and the peak value of identified force history of the impact force.

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The through hole connects each layer and conducts electric signals to the layers of the printed circuit board. The irregular shape was occurred on printed circuit board due to that the through hole was created by drilling process. The printed circuit board was stacked structure of glass fiber rich layers and resin layers. The stress concentration was occurred on the irregular shape of through hole. In this study, inelastic thermal stress simulation was performed by using a large scale simulator ADVENTURECluster which was based on FEM to study fatigue strength around through hole of printed circuit board.

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

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The wear performance between Si_3N_4/ SiC composite plate and Si_3N_4 ball under dry conditions was investigated. The wear depth of Si_3N_4/SiC with shot-peening was shallower than that of Si_3N_4/ SiC without shot-peening in the sliding wear test under low Hertzian contact pressure. This result is achieved by the compressive residual stress which is introduced by shot-peening and this result indicate that shot-peening is effective method to make use of ceramics as a slide member.

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Carbon nanotubes (CNTs) have extremely high tensile strength and elastic modulus, good flexibility and low density. In addition, CNTs are expected to have lubrication properties like other carbon-derived materials including graphite and diamond-like carbon. In this study, alumina ceramics reinforced with multi-walled CNTs (MWCNTs) were prepared by a flocculation method and the effects of the MWCNT content on mechanical and tribological properties of the composites were investigated. The results showed that the bending strength and fracture toughness simultaneously increased for the composite containing 10.0 vol.% MWCNTs. The friction coefficient of the composites containing 5.5 vol.% MWCNTs was about 0.15, measured by the ball-on-disk wear tests using alumina balls as a counterpart in air. Microstructural observations of the fractured and polished surfaces of the composites implied that the size of a MWCNTs agglomerate is one of the important factors for improving friction properties of the composite. It is suspected that there may be an optimal MWCNTs content for improving the mechanical and friction properties of the composites.

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For the box beams which compose the frame structure of a vehicle, and consist of thin plates, an approximate expression are derived from the knowledgement of the shear buckling stress, and the exact expression from the energy methods under compressional force assuming the coupling of the adjacent plates. The accuracy of these expressions is investigated as compared with the results acquired in the buckling eigenvalue analysis by the finite element method (FEM). As the results, the difference of compressional buckling stresses between the approximate expression and FEM is less than about 6% as for the aspect ratio of the cross section between 0.3-1.0.

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The coral reef is the important producer in the eco system. It is known that formation of skeleton in branching coral is affected by environmental factors. However, bending strength property of the skeleton is not really investigated in the field of biological engineering. In this study, branching coral (Acropora nobilis) was conducted 4-point bending test based on JIS R 1601 standard. And internal structure of skeleton in branching coral was investigated by using the X-ray CT technique. The results show that the bending characteristics depend on the inhabiting environments of polyps and density of the branching coral.

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The tensile deformation behavior of polytetrafluoroethylene (PTFE) hollow fiber membranes was studied. The present PTFE membrane has sub-micron pores with open cell structure, which plays a critical role of water purification. One of the main challenges of water purification is that the pore structure is covered with biofouling, leading to blocking pores. To maintain the ability of water purification, physical cleaning along with mechanically deformation is usually conducted. Thus, it is crucial to understand the mechanical properties, in particular the deformation behavior of the membrane fibers. Using uniaxial tension experiments, we established a finite element model in order to describe the deformation behavior of porous structure. The present model enables the prediction of the macroscopic deformation behavior of the membrane by taking into account the changes of pore structure. The result may be useful for the fabrication of porous membrane and provide insights for reliable operation of water purification.

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This paper describes the method of finite strain measurement based on image analysis. The effectiveness of this measurement method based on the Naomi Strain Theory has been verified by comparing the strain measurement by the image analysis with the conventional measurement based on the displacement meter. The behaviors of the local deformation under uni-axial tension have been investigated in on previous study. However, the detail studies on the local defamation for simple shear have not been examined yet. So, in this study, the simple shear, which is gemmed under different deformation path, are discussed. Especially, developments of local deformation generated under different types of deformation history, which are obtained by applying the simple shear to the reversed direction alter the forward direction, are examined.

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Impact test at subsonic level is developed and applied to the evaluation of deformation behavior of soft materials such as biological soft tissue. The deformation resistance modulus of quasi-static examination is compared with that of the impact test at subsonic level. The results of the impact test at subsonic level are much higher than that of quasi-static examination in all materials. The material emulating a chicken are almost equivalent with a chicken breast in terms of deformation resistance modulus and behavior of the destruction. As a result of impact test simulation using the viscoelastic model applied deformation characteristic of chicken breast, the behavior of specimen crushed surface at the moment of ball collision is confirmed.

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The ultrasonic guided wave technique has been applied to pipes and thin structures. However, the guided wave usually has a dispersive nature, and the received signal becomes more complicated and of longer duration compared with the input signal. The dispersed waveform is a function of the elastic wave velocities, the plate thickness, and the propagation distance. Using this relation, in this study, the elastic wave velocities and the plate thickness identification method using dispersion analysis is suggested. The effectiveness of the suggested method is investigated by both numerical calculation and numerical simulation. The identification errors of the elastic wave velocities and plate thickness are discussed.

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The pertinent translation rule is proposed for the elastic-core, i.e. similarity-center of the sub-loading surface to the normal-yield surface in addition to the generalization of nonlinear anisotropic hardening rule. Incorporating them, the subloading surface model formulation is refined for the hypoelastic-based plasticity and the hyperelatic-based plasticity with the multiplicative decomposition of deformation gradient. The plastic spin and the dissipative spins of the anisotropic hardening variables are also formulated rigorously based on them.

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Formation of curious deformation bands has been reported as one of the deformation mechanisms occurring in a Mg-based long period stacking ordered (LPSO) phase. The origin of the deformation band is still unknown, and the possibility of the deformation kink band and/or the deformation twin has been discussed. To clarify this, the crystallographic nature of deformation bands formed in the LPSO phase was examined by scanning electron microscope-electron backscatter diffraction (SEM-EBSD) pattern analysis. The deformation band in the LPSO phase was found to show three arbitrariness on its crystallographic nature: an ambiguous crystal rotation axis that varied on the [0001] zone axis from band to band; an arbitral crystal rotation angle that was not fixed and showed relatively wide distributions; and a variation in crystal rotation angle depending on the position even within a deformation band boundary itself. These features were coincident with those observed in the deformation bands formed in Zn polycrystals, suggesting that the formed deformation bands in LPSO phase crystals are mainly deformation kink bands.

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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 SEM observation. Particular emphasis is laid on the aspect of kinks, which is one of the characteristic microstructures generated in the LPSO phase. Mg alloys containing some transition metals such as 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 microstructures of LPSO phase. The kinks were generated by working such as extrusion in the LPSO phase, which raises the strength of LPSO phase. Then, such hard LPSO phase should contribute to the increase of yield and tensile strength of the alloy. SEM-EBSD analysis revealed the many wedge-shape microstructures with high angle boundaries, which indicates that the kinking occurred by the compression test. In order to clarify the details of such kinking behavior, high-precision marking method using electron beam lithography has been employed. Large distortion of markers and migration of kink wall were observed on the specimen surface. The formation mechanism of such microstructural inhomogeneity in the LPSO phase is discussed.

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In this study, a finite element analysis based on a dislocation-based crystal plasticity model is performed to investigate a kink band formation and its evolution in an α-Mg/LPSO polycrystalline alloy. The present analysis model is composed of two α-Mg matrix phases and a LPSO phase, both having a rectangular shape, and tilt grain boundaries and a shape imperfection are introduced. The results show that a wedge-like deformation region formed on the free surface of the α-Mg phase propagates to the LPSO phase. In consequence, an arbitrary crystal lattice rotation is brought about locally and a kink band across the specimen is formed. In addition, the basal slips other than the predominant basal one and the non-basal slips are activated by stress concentration in the α-Mg phases around the phase interface in the kink band.

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Effects of volume fraction of long-period stacking order (LPSO) phase on work hardening of cast Mg-Zn-Y alloys were investigated. Stress-strain curves for Mg-Zn-Y alloys with four volume fractions of LPSO phase were obtained by tension-compression cyclic loading tests with a constant strain amplitude under a constant strain rate. The results showed that the stress amplitude of the alloy with high volume fraction of LPSO phase continuously increased up to 50^<th> cycle. With increase in volume fraction of LPSO phase, the increase in the stress amplitude became significant. The evaluation of the contributions of isotropic hardening and kinematic hardening to cyclic hardening indicated that the amount of kinematic hardening significantly increased during cyclic loading in Mg-Zn-Y with high volume fraction of LPSO phase.

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Tensile deformation behavior of two phase Mg-Zn-Y alloy containing of alpha Mg matrix and 18R long period stacking ordered (LPSO) phase 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 Mg matrix and LPSO phase, which was called as phase stresses. Beyond the onset of plastic flow, micro-yielding, almost no change of the phase strain in magnesium matrix was detected with increase of the applied stress. On the other hand, phase strain in LPSO phase was continuously increased. These results show good agreement with the predictions by a simple two-phase model: the strong LPSO phase yields higher stress than macro-yield stress, resulting in high strengthening of two phase Mg-Zn-Y alloy.

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Deformation behaviors of the LPSO and α-Mg phases in the microstructure of a high-strength Mg alloy of LPSO type were studied by a crystal plasticity software code. Results showed that in the LPSO phase , large stress was generated and accumulation of GN dislocation corresponding to kink deformation was observed. In α-Mg phase, deformation was highly nonuniform due to the anisotropy of the HCP structure, but kink deformation did not occur.

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Effect of aging on activity of twinning in magnesium alloy AZ91 was investigated. The experimental results showed that stress-strain curves during reversed loadings were different between tension after compression and compression after compression. The difference in stress-strain behavior decreased with the increase in aging time. Crystal plasticity finite element analysis revealed that the difference of activities of twinning and detwinning resulted in the difference in stress-strain behavior during reversed loadings, which suggested that the decrease of difference in the stress-strain curves with the increase in aging time related to the decrease in the activity of twinning.

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An extended model of deformation twinning based on phase-field and crystal plasticity models to represent both the rapid growth of a tip of twin-band and a large plastic deformation is developed. The phenomena of growth of twins are decoupled into two scenarios that is the lengthening and the thickening. Regarding the lengthening as a kinematic movement of twin dislocations, a convection-like term is newly added to the phase-field equation. Simple models of twin-nucleation and back-stress-like effect evolving with the twin microstructure are also presented here. To avoid the difficulties of the boundary problem and to evaluate the microscopic mechanical and morphologic response to the macroscopic mechanical load, homogenization method is applied to compute the present model via a FE analysis on polycrystalline pure Mg. The obtained results show that the strain localization occurs around the twin boundaries and the relaxation and the concentration of the stress arise respectively in the twinned phase and the matrix.

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The aim of the present study is to understand the twinning behavior in a commercial pure titanium (CP-Ti) sheet. Stress-strain curves and microstructure evolutions were examined under various loading paths. The activity of twinning was larger under compression than under tension and, moreover, the activity of detwinning was observed during tension following compression. On the other hand, unlike Mg alloys, the effects of the twinning and detwinning on the work hardening behavior seemed to be small.

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The deformation twinning is an important deformation mechanism of magnesium and other HCP metals. This paper provides a framework of crystal plasticity model involving the effect of deformation twinning of HCP metals. The lattice rotation due to the deformation twinning is introduced into a conventional crystal plasticity framework, and the volume fraction of deformation twinning is considered. A numerical example is conducted to evaluate the evolution of volume fraction of twinned region in polycrystalline pure mangesium, and an evolution equation of volume fraction of twinning is quantitatively discussed.

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Compressive creep behavior and dislocation substructures in hot-rolled (40%) Mg-Y based alloys have been investigated in this study. Creep strength of magnesium is significantly improved by the simultaneous addition of yttrium and zinc. Apparent activation energy for creep in Mg-Y and Mg-Y-Zn solid solution alloys are around and/or more than 200 kJ/mol at the temperature range from 455 to 700 K. These values are higher than the activation energy for self-diffusion coefficient in magnesium (135 kJ/mop. Many stacking faults, which are planar type defects are observed on the basal planes of the magnesium matrix in Mg-Y-Zn ternary alloys. Transmission electron microscopic observation has been revealed that the non-basal slip of the a-dislocations is activated by these alloys during creep above 480 K. The rate controlling mechanism of Mg-Y based solid solution alloys are considered to the cross-slip controlled dislocation creep.

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A compatible-symmetric-type bicyrystal model and incompatible-type bicrystal models having inclined grain boundary were employed to conduct crystal plasticity analysis of unidirectional tensile tests, and we investigated changes in patterns of Geometrically Necessary dislocation (GND) bands when nominal strain was 1 %. The results showed that GND bands, where the inclination angle was about 45°, developed from the intersection point of the grain boundary with the upper or bottom edge, and the bands inclination was unalterable independently of angles of the grain boundary inclination. On the other hand, sign of densities of GN dislocations within the bands was changed when the grain boundary inclination was changed from 45° to 46°. This is because the mechanical restraint at the upper and bottom edge and the grain boundary strongly affects formation of GND bands rather than the inclination of grain boundary.

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For wide application of magnesium(Mg), it is necessary to quantitatively evaluate the activation condition of each deformation mode observed in deformation experiments of Mg. In usual experiments, critical resolved shear stress(CRSS) is used for quantitative evaluation of deformation. However, recent work on deformation of Mg via atomistic simulations indicates that normal stresses applied in the crystal also contribute to CRSS. In this work, we evaluate the activation free energy of the nucleation of a basal edge dislocation pair in an Mg single crystal under the application of the shear stress in slip direction and the normal stress in one direction via atomistic simulations. Our results show that the activation free energy of a dislocation nucleation is strongly dependent on the normal stresses along [1120] and [0001] directions though it is not sensitive to the normal stress along [T100] direction. We attribute this dependence to the elastic deformation of the crystal due to the normal stress, which brings the change in the magnitude of Burgers vector and distance between atomic planes.

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We investigate effects of solute atoms on twin boundaries and surfaces of Mg alloys by First-principles calculations. Most of solute atoms are stable or unstable at each twin boundary sites, depending on the atomic radius; solute atoms larger than Mg are stable at the extension site on twin boundaries and unstable at the compression site. On the other hand, the surface energy of the basal plane is lowest. Solute atoms at surfaces affect the surface energies. The variation of the surface energy reflects the cohesive energy of the solute element.

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First-principles calculations were performed to understand the relationship between grain boundary energy and free volume in magnesium. A linear relationship between grain boundary energy and free volume was found not only in pure Mg grain boundaries, but also in segregated grain boundaries. This indicates that the free volume is determined by both the mechanical effect (e.g. misfit strain) and the chemical effect (e.g charge transfer), and even strong covalent-like bonding cannot break down the linear relationship. However, only Ca and Y segregated grain boundaries deviated from the linear relationship. The origins of deviation for the Ca and Y segregated grain boundaries are discussed.

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In order to clarify the effect of additive elements on mechanical properties in solid solution strengthened titanium alloy, pure titanium (CP-Ti), Ti-1 mass% Al (Ti-1Al) and Ti-1 mass% Cu (Ti-lCu) alloys were prepared. The tensile tests at various temperature and the microstructure observation were carried out. In this study, it was found that the tensile strength and the 0.2% proof stress of Ti-1Al and Ti-1Cu were higher than those of CP-Ti and the total elongation of Ti-iCu was higher than that of Ti-1Al. The 0.2% proof stress of Ti-1Cu from 100℃ to 500℃ was highest among them. A lot of deformation twins were observed in CP-Ti and Ti-1Cu deformed at room temperature. From these results, the increase of the tensile strength and the total elongation are considered to be due to the number of twin in Ti-1Cu.

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Metastable beta type titanium alloys have been attracting attention in various industrial fields because of their special properties such as high specific strength, good formability, high corrosion resistance, and biocompatibility. However, plastic deformation characteristics of the titanium alloys have scarcely been clarified especially under biaxial loading conditions, despite of their importance on metal forming processes. In the present study, uniaxial and biaxial compression tests were performed on titanium-niobium (Ti-Nb) alloys with four different niobium contents, in order to investigate the influences of beta stabilizer content upon compressive deformations. The microstructure of Ti-Nb alloys was found to change from α, α' to p structure with increase of the niobium content. With this change of microstructure, the primary plastic deformation mechanisms were revealed to change from slip and stress-induced martensite to deformation twin and coarse slip with increase of the niobium content and thus the change influenced on the uniaxial and biaxial compressive plastic behaviors.

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Formability of AZ31 sheet under biaxial stretching modes is investigated. Forming limit strains of specimen are measured by using stretch forming experiment. RD-ND plane of fractured specimen was observed by an optical microscope and it is found that a visible local thinning was not created before fracture. Finite element simulations were conducted based on a crystal plasticity model, which incorporates only slip mechanism and twinning is excluded. The strain distribution simulated by finite element method reveals that the strains easily localize at several narrow portions in the specimen for the equi-biaxial stretching and plane stretching modes. On the other hand, the intensity of such localization is weakened when the specimen undergoes uniaxial tension. The nonuniformity of the deformation leads to the premature fracture of AZ31 for biaxial stretching modes.

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The aim of this study is to construct a simplified numerical method that can predict an actual texture development during hot rolling in AZ61 Mg. First, stress-strain and Lankford value-strain relations were experimentally investigated in a hot rolling temperature range (350℃) for AZ61Mg alloy sheets. Next, based on the experimental data, identification of material parameters in a crystal plasticity model was carried out using crystal plasticity finite element analyses. Strain histories for a material point near the surface of an AZ61 sheet were calculated using the Orowan's theory. The texture developments at the material point were computed with a finite element homogenization method. It was confirmed that the present method can reproduce qualitatively the actual texture development of the AZ61Mg sheets.

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The deformation mechanism of extruded AZ31 magnesium alloy rod under various temperature conditions was studied. The deformation mechanism was made clear by the changes of microstructures. The clarified mechanism was particularly what acts on the orientation for which trans granular sliding and grain boundary sliding are restrained. From the result, the yield mechanism of AZ31 magnesium alloy is non basal slip to 673K from 423K. The non basal slip works before the fracture under the temperature below 573K. At a temperature of 573K or higher, grain boundary sliding is activated.

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In the present paper, the deformation behavior of a rolled Mg alloy sheet with compressive pre-strain was investigated both experimentally and numerically. The rolled Mg alloy sheet showed remarkable in-plane anisotropy in the stress-strain curves. A crystal plasticity finite-element method was used to examine the mechanism that caused the anisotropy. The simulation predicted the qualitative tendency of the anisotropy well. The simulation results showed that the activities of detwinning and prismatic slip significantly differed depending on the angle between the first and second loading directions, leading to the anisotropy in the stress-strain curves.

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The influence of loading direction on cyclic deformation behavior of rolled AZ31 magnesium alloy (average grain size: approximately 40μm) was investigated. Cyclic tensile and compressive loading-unloading tests were carried out using cylindrical smooth specimens. Pseudoelastic behaviors were observed in tensile and compressive loading-unloading tests. The large anelastic strains and work hardening coefficient were observed in compressive stress-strain hysteresis loops of the S specimen.

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