Recently, composite materials are used in various products, above all, GFRP (Glass Fiber Reinforced Plastic) is relatively inexpensive and widely used as a structural member of watercraft, or aircraft. As a new light weight structural materials, GFRP sandwich panels have been proposed. However, the strength properties of GFRP sandwich panel are not understood enough. In this study, we conducted the four-point bending test of GFRP sandwich panel and discuss the strength properties of GFRP sandwich panel.

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The interfacial strength between carbon and phenolic resin is studied by using molecular dynamics simulations in order that carbon reinforced carbon matrix composites (C/C composites) has better strength development rates. Simulations are performed by two carbon fiber models, one of which has only carbon atoms and the other has carbon atoms and some fluorinated carbon groups. Carbon fiber models are regarded as two-layer graphite and phenolic resin model is treated as simple cross linked structures. All force field parameters are based on Dreiding force field. Tensile stress and interfacial fracture energy are calculated for the estimation of adhesive strength. Results of the model including fluorinated carbon groups get lower interfacial strength than that of having only carbon atoms.

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Bacterial Cellulose is the natural cellulose, characterized by a three-dimensional structure network of micro fibril. BC possesses an array of unique properties, including high crystallinity, high tensile strength, therefore, it has been an interesting topic in the field of research and development. In this paper, the effects of state of bacterial cellulose on wear characteristics were investigated for BC-Carbon/Carbon composites. Two types of samples were prepared by using milled bacterial cellulose gel or freeze-dried BC. The test results were also shown for the effect of various carbonizing temperature.

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The thermal exposure tests are conducted to evaluate high temperature durability of nylon 6 clay hybrid nanocomposite (NCH). The degree of crystallinity is reduced by the thermal exposure at 120 ℃ and 150 ℃, based on the Differential Scanning Calorimetry (DSC) analysis. The tensile strength, elongation and fatigue strength are also decreased by the thermal exposure. As a result, the fracture origin is changed from the surface in as-received specimens to interior in exposed specimens.

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In this research we use uncoupled analysis to evaluate the impact resistance of multi-layer coatings. We conduct high strain-rate simulation by ANSYS. Then the results of stress and strain are in put to damage analysis program which employs the elasto-viscoplastic damage constitutive equation based on continuum damage mechanics. Both of tensile fracture analysis and drop impact analysis have almost agreed well with the corresponding experimental results. Uncoupled analysis for dynamic damage mechanics problems can be expected to be used as a computational tool for the evaluation and the design of multi-layer coatings.

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Creep fatigue life analyses based on the concept of continuum damage mechanics were conducted for the bi-propellant thruster's chamber in a space satellite. FEM analyses and post damage calculations were conducted under the conditions that the maximum temperatures on a chamber surface were at 1250℃ and 1500℃. The analyses results show that the calculated chamber's life at 1500 ℃ was one-third of that at 1250℃.

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We carried out the basic research in order to reveal the deformation behavior of solder joints in compressive stress field. We have developed a new element test method in which we could apply uniform and constant pressure on solder joints in the specimen up to 150℃. We confirmed that the shape of voids in solder joints changed drastically in the element test. We found that the creep deformation at high temperature in the solder joints contributes to the deformation of voids.

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Ni/ZrO_2 multi layered and functionally graded materials (FGMs) with high heat resistance are developed with a powder molding. High-temperature strength of the FGMs are measured. Binder gradient is used for reducing thermal stress in the FGMs. Five kinds of the compounds with various compositions are obtained by mixing Ni powder and ZrO_2 powder with a binder which includes wax and a thermoplastic resin. The compound with higher amount of Ni has higher amount of the binder. The five layered FGMs are made from the compounds. The creep rupture tests are carried out for the FGMs using free plasma jet equipment at about 2000 K. Ni/ZrO_2 FGMs can be developed and their high-temperature strength can be evaluated.

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A casting precursor method is proposed as a manufacturing method of large aluminum foams with complex shape. The aim of this study is to clarify the effectiveness of the casting precursor method. The columnar precursor with 15 mm diameter was obtained by adding and mixing TiH_2 powder as a foaming agent with aluminum melt. The specimen was machined from the precursor for the foaming test. The free foaming tests were carried out by heating the specimen over the decomposition temperature of TiH_2. The same experimental conditions such as heating temperature and holding time were used for the all free foaming tests in order to investigate the homogeneity of the precursor. The columnar compression test specimen was obtained by foaming the precursor inside a mold. The porosity of the specimens obtained from the free foaming varied. This is because that the TiH_2 particles distribute in the precursor inhomogeneously. The compressive behavior of the foamed specimen is similar to the typical compressive behavior of low density foam.

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The purpose of this study is to manufacture the aluminum foam with high porosity by recycling of cheap aluminum foil chips. Aluminum foil chips are mixed with TiH_2 powder as a foaming agent, Al_2O_3 powder as a thickening agent and Zn powder as a sintering agent. The precursor is obtained by compressing the mixture at elevated temperature. Equal channel angular pressing (ECAP) is applied to the specimen without Zn in order to obtain dense precursor. The precursor is cut to columnar specimens. The foaming tests are carried out using the columnar specimens. The compressive tests are carried out of the foamed specimens for clarifying the compression behavior. The compressive tests are also carried out of ALPORAS. Conclusions are as follows. (1) Maximum porosity 36 % is obtained by heating the precursor with Zn powder. (2) The compressive behavior of the foamed specimen with Zn powder is not closed to ALPORAS and is close to dense aluminum, this is because the porosity of the specimen is much smaller than ALPORAS.

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The problem of stress intensity factor of penny-shaped crack with imperfect crack tip shape for a tensile loading is formulated based an energy principle perturbed when crack tip is changed from a complete circle line. In this study, the perturbed crack line α-ε(1+cosmθ), which is variation of circle with radius a, was assumed inside an infinite elastic media subjected to uniform tensile stress. Approximated stress intensity factor solution associated with penny-shaped crack with imperfect crack tip was obtained by general perturbation scheme under small amount of ε. It was shown that the approximated solution matched with the results of three dimensional finite element analysis, consequently.

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Ductile fracture behaviors were experimentally and analytically investigated with fracture tests in various loading conditions. Fracture limit curves, which are the relationships between stress triaxiality factor and equivalent plastic strain at the location of fracture initiation, were obtained in the wide range of stress triaxiality, including negative triaxiality range. It was found that the trend of fracture limit curves were different depending on triaxiality. In order to confirm the applicability of the limit curves to fracture assessment after large deformation, load reverse tests were carried out. As a result, it was found that fracture initiation point in load and displacement curve could be predicted using the limit curves obtained in this study as fracture law in FE-analysis.

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This paper investigates a method for identifying the location and the force history of an impact acting on isogrid-stiffened panels using the radiated sound. Sound waves radiated from the structure during the impact are measured with microphones. The impact location is identified using the differences in arrival times of sound waves at each microphone. The force history is identified by minimizing the deviation between the time histories of the measured sound pressure and the estimated one. The estimated time history of sound pressure is calculated from transfer matrices which relate the impact force and the sound pressure. Impact force identification is performed experimentally, and the identified impact locations and force histories are compared with the measured ones to verify the accuracy of the identification method.

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In the result obtained from the drop weight impact test of honeycomb core sandwich panel (Hereafter, HSP for brevity), the two concentric circles were observed in the dent formed on the face sheet. It was considered that the cell wall under beneath the outer circle supported the resistance force, because the cell wall was unbroken. Moreover, in the inside of the inner circle, the deep drawing process was observed. Therefore, it is considered that the cell wall arranged in the circumferential direction affects the local compression property of HSP. In this study, the sandwich panel where the cell wall was arranged in the circumferential direction was prepared. In addition, the sandwich panel where the cell wall was arranged in the radial direction was also prepared, because cell walls in the HSP arranged in various directions. By using these panels, serious of drop weight impact tests were carried out in order to investigate effects of the cell walls on the local compression property.

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The wear performance between a shot-peened zircinia-silicon carbide composite (ZrO_2/SiC) plate and a silicon nitride ball under dry conditions was investigated, in order to improve the wear resistance of ZrO_2/SiC frictional parts. The wear resistance of a ZrO_2/SiC plate with shot peening was higher than that of a ZrO_2/SiC plate without shot peening in the sliding wear test under low hertzian contact pressure. The hardness and the compressive residual stress in the near-surface layer of the ZrO_2/SiC plates were increased by shot peening, which improved the wear resistance of a ZrO_2/SiC plate.

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We investigated the effect of stress on the electrochemical property of high pressure die cast aluminum alloy in sodium chloride solution at room temperature. As an electrochemical property, the polarization curve was measured under the constant tensile stress. Since the polarization curve depends on the metallographic structure of the specimen surface, the casting skin and mirror-polished surface were individually examined. To evaluate the effect of the stress, the four levels of stress were employed under the proof stress. The results showed that the spontaneous potentials of polished surface were lower than that of casting skin regardless of the level of applied stress. Moreover, the spontaneous potential tended to decrease, as the applied stress increased under the proof stress.

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Barrel, nozzle and screw are plasticization parts of injection molding machines that works under high processing temperature. These parts are also exposed to corrosive gas and acid environment came from molten plastics. These combined factors cause considerable corrosion damage on plasticization parts. Furthermore, frictions with glass-filled polymers in molten plastic give rise to wear damages simultaneously on plasticization parts. In this study, the electrochemical test has been conducted on SKD61 specimens in the solute H_2SO_4 dissolving nylon66-25wt.% fiberglass. It was found that oxide film formation was promoted due to the oxidation reaction between SKD61 surface and the solution while the regenerative ability of the oxide film of SKD61 was deteriorated. The corrosion wear test was also conducted by using Alumina ceramics ball on SKD61 disk specimens. Destruction of the oxide film of SKD61 due to friction was confirmed. The regenerative ability of oxide film was also verified in the test.

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Silicon is a promising anode material for lithium-ion battery application due to its high specific capacity. However, when silicon is lithiated, it can undergo a volume expansion, which leads to an extensive fracturing. This is thought to be a primary cause of the rapid decay in cell capacity routinely observed.. To solve this problem, a more thorough understanding of how the material degrades is necessary to help cycling techniques that may be capable of reduce capacity fading. In this study, we report in situ acoustic emission and laser microscope observation of volume change in Si negative electrodes. The largest number of emissions occurred on the first lithiation and corresponding to volume change of the silicon negative electrode. this study demonstrates that AE and laser microscope observation is a powerful tool to survey the real-time mechanical damage and electrochemical degradation in the electrode.

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Lanthanum-based perovskites has emerged to be a promising candidate as cathode for solid oxide fuel cells (SOFCs) and as oxygen separation membrane. With regard to mechanical properties, anomalous behavior, known as ferroelasticity, has been reported in recent years. Systematical and experimental investigation relates to ferroelastic material has not been conducted to date. In the present study, we conducted X-ray diffraction (XRD), observing crystal surface with scanning electron microscope (SEM) and uniaxial compression test in room temperature to discover relation between lanthanum-based perovskites and addition ion. Both rhombohedral crystal and orthorhombic crystal perovskites showed ferroelasticity, but orthorhombic crystal showed slightly. With regard to rhombohedral crystal perovskites, when crystal lattice distortion (cubic based) is large, critical stress is higher value, residual strain is large.

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A flame combustion method enables the synthesis of diamond using acetylene-oxygen gas in ambient atmosphere. It has various advantages over other methods, but most diamond films delaminate as a result of thermal stress during cooling. In this study, to improve abrasion resistance of a Co-Cr alloy surface for artificial hip joint, diamond films were synthesized by the flame combustion method. Moreover, in order to archive good adhesion synthesized diamond films on the Co-Cr alloy, surface roughness of the Co-Cr alloy were varied by pretreatment. According to the result, diamond films were able to synthesize on the Co-Cr alloy surface by the flame combustion. The crystallite morphology of synthesized diamond films can be changed.

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It is necessary for a damage evaluation of Thermal Barrier Coatings (TBC) to understand temperature and thermal stress fields in turbine blade. Those fields had been estimated based upon start-up, steady-state and stop operation. However, turbine blade surface temperature vary randomly due to fluctuation in combustion temperature. For the purpose of improving reliability of TBC damage evaluation, the effect of harmonic oscillation on a steady state temperature field of TBC and Porous-TBC (P-TBC) was clarified. As a result, it was found that the heating wave was reflected from pores, and temperature amplitude was attenuated. Furthermore, it is confirmed that the thermal diffusion length decreased with increasing angular velocity.

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A bi-layer cantilever beam dielectric elastomer actuator (DEA) is developed by using fiber-stiffened active layer and flexible carbon conductive grease electrodes. When a voltage is applied through the thickness of the sheets, large actuation strains are achievable in the direction vertical to fiber axial direction. The fiber-stiffened elastomer actuator shows more stable and larger flexural deformation than the normal elastomer actuator. The curvature of the fiber-stiffened elastomer actuator is measured and can well be predicted by an electro-mechanical model. Moreover, the deformation of the new dielectric elastomer actuator can be controlled by the fibers compared to the dielectric elastomer actuator without fibers.

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Currently, the solar cells are mainly made of silicon. However, due to the high cost and shortage of silicon, new materials for solar cells are still needed. It has been proved that Cu_2O solar cells have a high theoretical energy conversion efficiency with a very low cost. However, the actual efficiency of Cu_2O solar cell is much lower than theoretical one. In this research, Cu_2O/Cu core-shell nanowires are fabricated on the surface of the solar cell by the template method to increase light receiving area. Then, elemental analysis for core-shell nanowires is carried out by Electron Energy-Loss Spectroscopy. As a result, we succeed in fabricating Cu_2O/Cu core-shell nanowires. The area of the solar cells is increased to about 220 times, which is convinced to improve the solar energy conversion efficiency.

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Nanowires have been expected to be utilized in various applications. Recently, many researchers have reported about single crystal or polycrystalline nanowires where the single crystal nanowires are shown to have a higher conductivity compared to the polycrystalline ones. In our previous study, we investigated the fabrication process of single crystal nanowires by stress migration. However, because the mechanism of fabrication was not clear, the generation density of single crystal nanowires was low for this method. In this study, we suggested a new method to increase the generation density of single crystal nanowires. An etching process was added to the previous fabrication method and the conditions of the substrate surface were changed. By doing this, the stress generated around the concentrated Al atoms was larger than the threshold stress needed to fabricate the nanowires. As a result of the added etching process, we achieved a nanowire generation density 100 times that of the conventional fabrication method.

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It was revealed that a metalic nanodendrite with dendritic shape has catalytic activity. Therefore, the metalic nanodendrite is expected to be applied as a catalyst. An electrodeposition method has been used for fabrication of nanodendrite. However, this method has large environmental loads because it uses metal salt solution. Electrochemical migration that is called ionic migration (IM) is known as the phenomenon which causes insulation deterioration for electronic devices due to deposition of dendrite. Since this phenomenon occurs in the presence of moisture and DC bias, IM can be applied as a method for fabrication of dendrite with a lower environment load than the electrodeposition method. The purpose of this study is to show possibility of IM as a new method for fabrication of nanodendrite. In this study, a water-drop test was conducted to observe deposition process of Ag dendrite.

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This paper describes the homogenization of fin layers for structural analysis of heat exchanger cores composed of flat tubes and wavy fins. By considering a wavy fin sandwiched by two plates, a first-order homogenization method is proposed on the assumption that uniform deformation prevails at a distance h^^- away from the fin layer in the stacking direction while the wavy fin has periodicity in the in-layer directions. The bilayer model developed by Tsuda and Ohno (2011) is then used to identify the homogenized fin-layer elastic stiffness D^^〜_<ijkl>^H. This method is applied to outer- and inner-fin layers in an intercooler. It is shown that the effect of h^^- is fairly large with respect to two components of D^^〜_<ijkl>^H but is negligible in fin-homogenization-based analysis of tube-fin structures subjected to compression and bending.

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Influences of various preloads on the mechanical properties of extruded AZ31 magnesium alloy rod were studied by mechanical tests. For the yield surface after a compressive preload, the yield stress of a compressive loading is higher than the yield stress of a tensile loading. For the yield surface after a torsion preload, a reduction of the tensile yield stress was observed. For the yield surface after a tensile preload, an increase of yield stress of a compressive loading and a torsion loading was observed.

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In this study, biaxial compression tests along proportional and non-proportional strain paths were performed on binary titanium-niobium alloys (Ti-Nb alloys) of different niobium contents, in order to clarify the deformation behaviors of those alloys under biaxial loadings. The influences of strain path and niobium content upon the compressive deformation behavior were then investigated. It was found that there were differences on stress-strain relations of Ti-Nb alloys owing to the different primary plastic deformation mechanisms. The clear influence of strain path change on the compressive behavior of Ti-35Nb alloy was observed, probably because of the activation of new twin systems after the path change.

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Plane bending fatigue test had been conducted to investigate fatigue crack initiation mechanism in coarse-grained magnesium alloy, AZ31, under different mean stress. The initial crystallographic structure was analyzed by an electron backscatter diffraction (EBSD) method. When the test had been conducted at the load ratio R=-1, secondary twin operated in a primary twin and resulted in the fatigue crack initiation. On the other hand at R=0.1, dual twin was activated and crack has initiated along the grain boundary.

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The bending fatigue tests were performed using the micro-cantilever-shaped specimens of AZ31 magnesium alloy fabricated by the focused ion beam (FIB) processing to investigate the effects of the scale and the grain orientation on the fatigue behavior. The configuration of specimen was the rectangular cross section of 3μm × 8μm and the height of 40μm. For the fatigue test of micro cantilever specimens, the fatigue testing apparatus was constructed using the piezo actuator and the high resolution microscope for controlling the very small displacement. Before fatigue tests, crystallographic orientations of the specimens were analyzed by EBSD technique. The micro cantilever specimens exhibited the higher fatigue strengths than the bulk-sized ones. The fatigue strengths of micro cantilever strengths were strongly affected by the crystallographic orientations. When basal slips mainly operated, fatigue lives were the shortest. But the operation of non-basal slip systems resulted in the longer fatigue lives, where Schmid factors of basal slip systems were very low.

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The repeated roll bending process was carried out on AZ31 magnesium alloy sheet to improve formability at room temperature. Influences of applied bending strain per pass by roll bending process on mechanical property and formability were investigated changing pushing amount of upper bending roll. The larger applied bending strain per pass was effective to increase hardness at the surface of the sheet, due to additional shear deformation. Although the hardness after repeated roll bending and subsequent annealing at 400 ℃ for 1hour was lower than that of initial sheet, the tensile strength is almost same for the initial sheet. The Eriksen value was increased by roll bending process and subsequent annealing with little decreasing the strength of the sheet.

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Ejecta size of a LPSO-type magnesium alloy were examined when aluminum alloy projectiles struck in hypervelocity. The size of ejecta collected from the test chamber was measured. We compared with the difference in ejecta size distribution by changing impact velocity. The results of LPSO-type magnesium alloy were compared with those of aluminum alloy.

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A modeling methodology of polycrystalline aggregate has been studied to define the representative volume element (RVE) within finite element analyses of a periodic microstructure which enable us to estimate the deformation state of the microstructure and the corresponding macroscopic material response. In general, a polycrystalline aggregate contains multiple crystal grains and its heterogeneity is defined by the difference of crystallographic orientations. In this study, a modeling approach has been developed to generate a morphology of a periodic polycrystalline aggregate on the basis of the given frequency distribution of grain size with Voronoi tesselation and also finite element mesh under the constraint of periodic boundary condition.

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The cyclic deformation behavior of AZ31 magnesium alloy sheet metal have been investigate in order to reveal the general material elasto-plastic behaviors related with its texture, such as Bauschinger effect and flow stress during stress reversal, by finite element analyses. To discuss these phenomena of AZ31 magnesium alloy sheet at the room temperature to 200 degree [Celsius], the crystal plasticity material models, which can take into account the size effect of twined region proposed by Kitayama was introduced into the commercial finite element code. The calculated results by the applied model can describe moderately the corresponding experimental data at the room temperature to 200 degree.

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Plastic slip deformation in α phase grains of Ti-6Al-4V alloy polycrystal models is studied by a crystal plasticity finite element analysis. Models consist of 30 crystal grains and their crystal orientations are given randomly. Critical resolved shear stress for prismatic slip systems is the lowest and that for basal systems is slightly higher than that for the prismatic systems. Results show that slip deformation is highly non-uniform at the deformation stage of macroscopic yielding point and not only prismatic but also basal systems operate in a small number of crystal grains in the model, while no slip deformation occurs in other grains.

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Ti-6Al-4V, consisting of a and fi phases, is one of the most popular Ti alloys, and the detailed mechanical properties are required in the product design; however, they are not fully understood. In this study, unidirectional tensile tests of α-Ti of Ti-6Al-4V alloys were numerically simulated with a bicrystal plasticity model, and we investigated changes in activities of the basal and prismatic <a> slip systems with changing in the critical resolved shear stress (CRSS) of the basal slip systems. The results showed that higher stress was observed in the crystal grain with c-axis closer to the loading direction, and slip on the basal plane occurred easier than that of prismatic <a> when CRSS of the basal slip systems equals to or slightly higher than that of the prismatic <a> slip systems. The activity of basal slip systems decreased with an increase in their CRSS while that of the prismatic <a> slip systems increased.

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Magnesium (Mg) alloys with long-period stacking ordered (LPSO) phase (LPSO-type Mg alloys) have attracted considerable attention because of much higher strength compared with the conventional Mg alloys. The strength of LPSO-type Mg alloys is drastically improved due to metal forming processes such as extrusion and rolling. Consequently, as same to the conventional wrought Mg alloys, deformation behavior becomes anisotropic because the strong crystallographic texture developed during the forming processes. To reduce anisotropy in wrought LPSO-type Mg alloys with the aim of wide range of applications, the process optimization based on crystal plasticity simulation is one possible approach. In this study, a constitutive model for cast LPSO-type Mg alloys is developed based on experimental observation.

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The influence of loading direction on microstructural evolution of rolled AZ31 magnesium alloy (average grain size: approximately 40μm) was investigated. 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. As increasing plastic strain, deformation twins were developed uniformly in tensile loading, on the other hand, deformation twins were developed locally in compressive loading.

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Among advanced magnesium (Mg) alloys, Mg alloys containing long period stacking ordered (LPSO) phase (LPSO-type Mg alloys) have attracted considerable attention because of the superior strength compared with conventional Mg alloys. Extensive researches on LPSO-type Mg alloys show that one possible strengthening mechanism for LPSO-type Mg alloys is the contribution of a number of kink bands in LPSO phase which are formed during metal forming processes. In this study, kink band formation process in LPSO-type Mg alloys subjected to extrusion is numerically investigated. The analysis model is consisted of a-Mg phase with random texture and LPSO phase with strong extrusion texture. For the boundary conditions, equi-biaxial compressive loading is applied by displacement control. The results show that significant misorientations are introduced in LPSO phase during the deformation. Quantitative evaluation of the changes in crystal orientation suggests that intragranular misorientations should be developed both parallel to and perpendicular to the extrusion axis.

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A mean-field model is established for solving the interaction between a twin and a parent. A twin is modeled as a thin plate embedded in the parent. The compatibility and force equilibrium on the twin boundary are enforced. Integrating this model to a finite element method, strain localization in AZ31 sheet is simulated. This approach is able to predict the occurrence of contraction twin and fracture induced by accumulation of slips in the twin region.

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In the present study, the effect of twinning activity on thickness strain evolution in a rolled Mg alloy sheet was investigated both experimentally and numerically. An evolution of thickness strain and a twinning activity were examined during tension following compression. The decrease in thickness strain was more pronounced during the initial stage of tension than that during the latter stage. A result of crystal plasticity finite-element analysis showed that the difference in the evolution of thickness strain occurred because of the detwinning activity. More specifically, thickness strain in the initial stage of tension was induced by both slip and detwinning activities, whereas in the latter stage the effect of detwinning was negligible and thickness strain was induced solely by slip activity. The above results indicated that twinning can play a significant role in thickness strain evolution in a rolled Mg alloy sheet.

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We computed atomistic pathways of deformation twinning with First-principles calculation, and quantified the pathways by two variables: strain γ, and shuffling I which describes non-affme displacements of the internal degrees of freedom. We also computed activation energy of twin boundary nucleation and migration. Based on these activation energies, we constructed coarse grained kinetic Monte Carlo model. With this model, we computed the critical necessary stress of twinning deformation activation and its temperature dependency.

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o estimate CRSSs of slip systems in hcp crystals, shear tests of magnesium single crystals were carried out at room temperature. In the shear test, basal slip occurred within shear deformation area, and CRSS of the basal slip was estimated as 0.35MPa. However, specimens for prismatic slip deformed with {101^^-2} twin. The test result shows that CRSS of prismatic slip in magnesium will be more than 90MPa. To estimate CRSS of the prismatic slip precisely, alternate specimens for shear test should be necessary.

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The effect of texture and grain boundary on indentation behavior was investigated using single crystal and fine-grained magnesium with an average grain size of 2-3 μm. Hardness of prismatic plane had 10-20% higher than that of basal plane. The fine-grained magnesium also showed slightly harder as compared with those of single crystal in the high strain rate ranges. However, these differences in hardness were very small as compared with the strength obtained from uniaxial testing methods, i.e., tensile and compression tests. The activation volumes indicated cross-slip as the rate-controlling mechanism during indentation tests, and they were not influenced by the initial microstructures. This was related to the formation of deformation twinning. The simulation results showed that the deformation twinning formed beneath tip with shaper radius at the beginning of indentation, irrespective for indentation planes, due to the creation of complex and large stress state.

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In this study, a finite element analysis based on a dislocation-based crystal plasticity model considering a size dependence of a critical resolved shear stress (CRSS) is performed to reproduce a size dependence of yield stress in a micropillar composed of single crystal of Mg-based LPSO phase. The CRSS model in which a size-dependent term is proportional to the inverse of a pillar diameter is applied and a numerical parameter is identified from experimental results. We consider four initial crystal orientations where a basal slip, prismatic slip, pyramidal slip and kink deformation are likely to occur. The results show that the applied model reproduces the size dependence of the yield stress. In addition, in the initial orientation where a kink deformation is tend to occur, the deformation mode changes according to the specimen size.

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The generalized stacking fault energy (GSFE) curves of the basal and second-pyramidal slips in Magnesium are investigated by first-principles calculations. For the basal slip, the unstable and I_2-type stacking fault energies are decreased with increasing the normal strain perpendicular to the slip plane. In Mg-Y, the I_2-type stacking fault energy is significantly reduced. For the second-pyramidal slip, relaxation of atoms in the slip plane in the in-plane direction perpendicular to the slip direction gives rise to a stable stacking fault in the GSFE curve.

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The roles of grain boundaries in the plastic deformation of hexagonal close packed metals are not still clear despite of its importance, especially, for sufficiently small size of grains. In this work, we performed molecular dynamics simulations of uniaxial deformation tests of magnesium bicrystals with [1^^-100] symmetric tilt grain boundaries. We observed that not only the yield stress but also the active deformation mode itself is sensitively dependent on the misorientation angle of the bicrystal and the loading direction. In particular, ease of nucleation of basal dislocations from grain boundaries could be qualitatively explained by dependence of the grain boundary energy on the misorientation angle.

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We investigated the nature of the interactions between I1-type stacking faults (SF) and non-basal dislocations, which are suggested as the important deformation mode to improve the formability without decreasing the strength in Mg-Y alloys. The atomic models of pure Mg including the I1-SF were deformed using molecular dynamics calculations. We observed the dissociation reaction at both ends of I1-SF, where the partial dislocations on the pyramidal plane, Shockley partial dislocations on the basal plane, and stair-rod dislocations were nucleated. We suggest that the I1-SF is not likely to work as the nucleation source of "multiple" (c+a) dislocations, but as the faults to assist and accommodate the c-axis deformation.

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To keep a position using Shape Memory Alloy (SMA) actuators, the SMA actuators must be continued to be heated. To save the energy, a control method utilizing hysteresis in deformation was proposed for an antagonistic SMA system. To show feasibility of the control method, a fundamental experiment was performed. When a pulsed current was applied to the two SMA wires alternately, the equilibrium position changed between two positions alternately. To confirm the behavior, numerical simulation was also performed. The one-dimensional phase transformation model [Ikeda, Proc. SPIE 5757 (2005), 344-352] was applied to predict the deformation behavior of the antagonistic SMA system. The simulated result agreed with the experiment qualitatively. The feasibility of the proposed control method could be indicated both experimentally and numerically and the validity of the mathematical model also could be proved.

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Sharp memory alloy (SMA) is one of the functional material which shows the shape memory effect and superelasticities. Since the shape recovery temperature of Ti-Ni system SMA is below at 373K, this alloy is expected the element of heat-engine driven by low-temperature thermal of energy. Previous SMA heat-engines have not became commonplace because of short product life. Therefore, we developed SMA spiral spring actuator to improve life cycle of SMA heat-engine, and produced the spiral spring type SMA heat-engine. However, the spiral spring type SMA heat-engine needs pumps for flowing hot and cold water into the actuator. As a result, this heat-engine become complex mechanism. Therefore, we developed and produced the planetary geared type SMA heat-engine using SMA spiral spring actuator. This engine operates by the energy of hot water when this engine is submerged in hot water. In this research, we investigated the operating characteristic of this type heat-engine.

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