This paper describes the homogenization of fin layers in structural analysis of heat exchanger cores composed of flat tubes and wavy fins. It is assumed that uniform deformation prevails at the bonded interfaces between fins and tubes, and that the fins have the Y-periodicity in the fin layers. The homogenization method for 3D periodic solids is then shown to be applicable to the homogenization of fin layers provided the uniform deformation condition is imposed at the bonded interfaces between fins and tubes. The resulting homogenization method is applied to designed and real shapes of outer and inner fins in an intercooler. The evaluated homogenized elastic stiffnesses of fin layers are verified by performing finite element analysis using full-scale and homogenized models of tube-fin sections subjected to uniaxial compression.

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In this work, the thermal stress distribution in ultrafin plate-fin structures made of a Ni-based alloy subjected to a macroscopic temperature increment is simulated using a homogenization theory for thermoelasticity. The results show 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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Dislocation movement is impeded by grain boundaries (GBs) and thus, microscopic yielding can be realized by transfer of dislocation across a GB, or by the nucleation of dislocations in the near-field of GB due to the applied stress. These phenomena are determined by the crystallographic orientation and the multiaxial stress state around the GB. In the present paper, a boundary interaction criterion of L or L'-value is newly proposed, which considers both contributions of the geometric relationship between two grains and a GB, and the stress state applied to the representative volume containing the two grains and GB. The dynamic incorporation and transfer of dislocations nucleated by indentation to GBs were also examined using molecular dynamics simulations. The reaction process between the emitted dislocations and GB was, in detail, resolved and discussed on easiness of plastic deformation across GB in reference to the proposed boundary interaction condition.

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The fatigue tests under the out-of-plane compressive and slight tensile loading are conducted in order to investigate the fatigue strength of paper-based friction materials and evaluate the influence of the constituents of friction materials on fatigue strength. The out-of-plane compressive tests are also carried out to evaluate damage behavior of friction materials. The cross-section of the materials is observed by scanning electron microscope in order to evaluate damage evolution in microstructure of the material. The constituents of the friction materials are aramid, cellulose and phenolic resin. From the static and fatigue tests, the fatigue strength of the friction materials decreases with increasing the number of cycles. The static and fatigue strengths of the friction material composed of aramid fiber and phenolic resin are higher than that of the friction material composed of cellulose fiber and phenolic resin. From the out-of-plane compressive tests, the damage evolution, such as crack initiation and fiber breakage, is observed. The damage ratio of the cellulose-based friction material is higher than aramid-based friction material. The damage behavior of the friction materials under the out-of-plane compressive loading may affect the fatigue strength of the friction materials.

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The inhomogeneous compressive strain behavior of the friction material was analyzed by means of digital image correlation method (DICM). Macroscopic strain of the sample without cashew decreased monotonically with increasing molding pressure, and DICM indicated homogeneous strain distribution. While sample containing cashew showed peculiar molding pressure dependence in macroscopic strain, which the strain increased remarkably above 30MPa. The result of DCIM indicated that the void structure periphery of cashew caused the inhomogeneous strain distribution as well as larger deformation upon compressive load.

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The fatigue tests using solder alloys have been conducted by many researchers to ensure the fatigue strength of the solder joints in electronic packages. Some of the test results show that there is the strain rate effect on the fatigue life of solder alloys. The effect would be closely related to the creep deformation generated during the cyclic loading for the fatigue tests because the deformation behavior of solder alloys is dominated by the creep strain generated during a loading. Namely, the creep strain development behavior of solder alloys under a cyclic loading should be clarified to evaluate the fatigue characteristics of solder alloys. This paper shows a method which can investigate the creep strain development behavior of Sn-3.0Ag-0.5Cu (SAC) lead-free solder under cyclic loadings by employing stepped ramp wave (SW) loading. The validity of the method is verified by fractography using SEM. Then an estimation method for the fatigue life of the SAC solder is proposed based on the results of the creep strain analysis.

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Bulk ultrafine-grained (UFG) low carbon steel bars were produced by warm caliber rolling, and the impact and tensile properties were investigated. The microstructures in the rolled bars consisted of an elongated UFG structure with a strong α-fiber texture. The rolled bar consisting of spheroidal cementite particles that distributed uniformly in the elongated ferrite matrix of transverse grain size of 0.8-1.0μm exhibited superior strength-ductility balance and impact properties. In the rolled bars, cracks during an impact test branched parallel to the longitudinal direction of the test samples as temperatures decreased. Delamination caused by such crack branching remarkably appeared near the ductile-to-brittle transition temperature. In conclusion, the strength-toughness balance is improved by refining crystal grains and controlling their shape and orientation; in addition, delamination effectively enhances the low-temperature toughness.

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The present paper has investigated the effects of the laser peening treatment on the changes in residual stress, creep life and microstructure in modified 9Cr-1Mo steel. The X-ray diffraction analysis revealed that the peening treatment can change subsurface residual stress from tensile to compressive at an output laser power of 5.6〜22GW/cm^2. The creep life of the steel can be doubled by the peening treatment for σ=240MPa at 823 K in air. The EBSD/SEM analysis also revealed that laser treatment can coarsen crystal grains in the crept steel. This effect may have brought about longer creep life of the steel.

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A technique to heal a fatigue crack for a stainless steel by controlling a high-density electric current field was studied. The high-density electric current was applied at the crack tip using adjacent electrodes. Surface-activated pre-coating technique was used in order to improve adhesion of the crack surface. The crack on the specimen surface was observed by scanning electron microscope (SEM) before and after applying the high-density electric current to examine the effect of the fatigue crack healing. The experimental results showed that the fatigue crack was closed and the strength of a healed specimen was increased by the electrical stimulation.

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Structural interaction between solids and liquids are seen in various industrial fields, such as MEMS fabrication. A droplet between solid surfaces forms a liquid bridge, which provides a resistive or a desorption force due to surface tension. These forces can be ignored in large scale structures, but they show significant influence in micro scale. Since the deformation caused by liquid bridge has not been sufficiently studied, it is necessary to quantitatively evaluate these forces. In this study, two pillars that were aligned in parallel were prepared and the deformation caused by a liquid bridge was observed with different types of liquid. It is confirmed that the spacing between two pillars were getting closer and eventually attached with each other when silicone oil was used as liquid. But water did not cause any change in two pillars. The evaluation of the pillar deformation was conducted using a cantilever model, considering Laplace pressure and surface tension as drive forces. As a result, it was found that Laplace pressure has more significant influence than surface tension.

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Polycarbonate was one of the materials which has the highest impact strength in the high polymer materials. However, there was a problem that impact strength decreased in low-temperature environment. S In order to solve this problem, PC which copolymerized the poly dimethyl siloxane was developed. In this study, change by the load rate of impact strength was verified about PDMS-PC. By preserving ductile fracture, PDMS-PC had controlled the decrease in fracture energy.

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Influence of microstructure on the tensile properties and fracture behaviors of Hadfield steel at high strain rate was studied. Hadfield steels sample with different mean grain size with different existence of carbon (precipitates and/or supersaturated solid solution of carbon) were made by rolling at warm temperature and annealing. The sample with conventional grain size (a few 10μm to 100μm) and a small number of carbide shows ductility with local elongation at high speed tensile deformation at 10^3/s. Additionally, fracture surface changes from brittle manner (at 10^<-3>/s) to dimple pattern (at 10^3/s). On the other hand, the fine grained sample with carbides performs brittle fracture at any strain rate. The tensile test at elevated temperature lower than 300℃ at a quasi-static strain rate (10^<-3>/s) clarifies that the elongation recovers as a similar manner as in the change with strain rate. These tendency was discussed with the consideration of the dynamic strain aging as well as the emission of dislocation from clacks.

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CFRP laminates are used by about 50% weight ratio in the body of the Boeing 787 jet plane. Many kind of impact damage, for example due to the collision of small stone, bird, tool dropping and hail, may be introduced in the airplane body during the long time use. The effect of impact damage due to dropping weight on the flexural strength of the fabricated CFRP laminates with copper mesh sheet, were investigated. The flexural strength decrease strongly, depending on the impact damage. Effect of the cure condition on the strength of CFRP with copper mesh sheet was recognized. The strength of CFRP with copper mesh sheet against impact damage was good compared to the result of CFRP.

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The thermal strain and/or stress in CFRP plays an important rule in determining damage initiation and evolution at the fiber/matrix interface, it arise from the difference between the longitudinal and the transverse CTE of carbon fiber. Experimental investigation has been made on the effect of anisotropic microstructure of carbon fiber on inhomogeneous thermal strain in CFRP during thermal loading. The measurement method on thermal deformation and strain distribution at different length scales was investigated by in-situ FE-SEM observation. A heating/cooling stage by Joule-Thomson effect was installed into the FE-SEM chamber. The material used was high modulus pitch-based K13D carbon fiber reinforced epoxy matrix composite. The grid and random patterns were fabricated onto the CFRP surface. The nano scale thermal deformation inhomogeneity in CFRP was found at the interface due to the anisotropic microstructure of carbon fiber.

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We propose an estimation method for determining the anisotropic material properties of glass fiber reinforced plastic (GFRP) in this study. The anisotropic material properties had to be determined and taken into consideration to predict the GFRP deformation using finite element method (FEM). We used a homogenization method to calculate the anisotropic material properties. The material properties of the glass fiber and resin had to be inputted to do this. However, the material properties of the resin were sometimes unknown, due to the changes in the material properties based on the manufacturing condition. We predicted the anisotropic material properties of GFRP in this study by inputting the in-plane material properties of GFRP to response surface. The response surface was created by using an experimental design and a homogenization analysis. We applied this method to the GFRP for a print circuit board, and calculated the anisotropic material properties without any resin material properties.

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This paper evaluates the reliability of an aluminum based composite including vapor growth carbon fibers (VGCF) and carbon nanotubes (CNT). The composite is fabricated using spark plasma sintering and has high thermal conductivity. The correlation between the inelastic deformation and thermal conductivity of the composite is discussed. Specimens made from the composite are first subjected to tensile loading until inelastic strain occurs. After the tensile loading, the thermal conductivities of the specimens were measured to establish the differences in the thermal conductivity before and after the tensile loading. The FEM analyses are also conducted to evaluate the reliability of the composites. It was found that the thermal conductivity changed due to the inelastic deformation of the composites and that a FEM analysis considering the damage due to the deformation qualitatively estimates the differences in the thermal conductivity before and after the tensile loading.

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This paper deals with finite element analysis of a crack tip field in particulate-reinforced composites with debonding damage and containing various sized particles. The finite element method was developed based on a micromechanics model of particulate-reinforced composites which can describe the debonding damage of particles from matrix and particle size effect on deformation and damage. The micromechanics model based on the Eshelby's equivalent inclusion method and Mori-Tanaka's mean field concept has been extended to consider the particle size effect. The effect of the debonding damage evolution on a crack tip field is evaluated. The stress distribution ahead of a crack tip field shifts upward with decreasing particle size. The debonding occurs from a crack tip and progresses ahead of a crack tip. The stress reduction around a crack tip is attributed to loss of load carrying capability of particles by debonding between particles and matrix.

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This paper describes the effect of fiber orientation fluctuation on tensile strength of a green composite reinforced with slivers of flax fibers. To quantify the morphology of the fiber orientation, fiber orientation angles were measured on fine segments, divided into 1 mm × 1 mm squares on a photograph of the whole composite surface. The tensile strength obtained here did not show any appreciable relation to the average of measured fiber orientation angles. The concept of two-dimensional (2D) autocorrelation was used in the present study to express the degree of similarity between fiber orientation angles in two different local areas. Results show that, if high 2D autocorrelation coefficients occupy more area on a composite surface, then this composite possesses more regular fiber orientation and tends to exhibit higher tensile strength.

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Carbon nanotubes and natural fibers are staple fibers. Staple fibers can be spun for making yarn. Yarn has several advantages over short fibers because each fiber almost align in the axial direction and yarns are easy to handle for composite fabrication. However, mechanics of yarn reinforced composites have been hardly developed. In this study, a new theory for yam reinforced composites based on a classical yarn theory was developed in order to predict Young's modulus of composite and calculate stress distribution in composite.

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Recently, carbon fiber reinforced plastics (CFRP) have been widely employed in various industrial fields. For realizing the low-carbon society, it is necessary to reduce the carbon dioxide that automobiles discharge. When CFRP is applied to an automotive body instead of steel, the weight becomes a quarter while the stiffness becomes twice.This paper presents experimental characterization of damage due to shear cut-in load in CFRP laminates. At first, damage was produced by cutting a CFRP plate with two rectangular edges using a universal testing machine. Surface and internal damages of the CFRP specimens were observed by using optical microscopy together with soft X-ray analysis. A damage process was then discussed on the basis of the experimental result. Next, the influence of clearance on the damage in the specimen was examined to optimize the clearance. Especially, the effect of clearance on delamination in cross-ply laminates was investigated. The result of the study enables us to obtain the optimum cutting conditions with minimum damages and burrs around the cutting plane.

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Notched fatigue behavior of woven fabric CFRP laminates is examined, and an analytical model is developed for prediction of notched fatigue life at room temperature. Fatigue tests are first performed at room temperature on unnotched and center-holed coupon specimens of a plain woven CFRP laminate for different stress ratios. The experimental results show that tension-dominated fatigue behavior turns insensitive to notch in a high cycle range due to matrix cracking that occurs predominantly at the edges of a hole along loading direction. By contrast, the compressive fatigue behavior remains notch sensitivity partly because of a different damage mode of transverse cracking. Then, a new engineering fatigue model is developed that explicitly takes into account the change in notch sensitivity due to fatigue loading and facilitates fatigue life analysis of notched CFRP laminates for any notch size, and it is shown to be valid for the notched fatigue behavior of the woven fabric CFRP laminate at room temperature.

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Sputtered niobium sulfide films having various argon contents, interplanar spacing and internal stresses were prepared by various argon pressures and positive bias voltage on stainless substrate during rf sputtering. The films were investigated by EPMA and XRD. Internal stress of films was derived from curvature of substrate with film. The obtained results are as follows: The sputtered films form rhombohedral crystal structure. An increase of argon pressure or bias voltage brings about decrease of argon contents, (00・3) interplanar spacing and internal stress in sputtered film.

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This study was conducted to investigate the effect of plasma-nitriding as a pre-treatment, and DLC (diamond like carbon) coating on the surface characteristics, hardness distribution and friction-wear properties of SCM440 steel. Four DLC layers with different hydrogen contents were generated by the UBMS method in order to clarify the relationship between hydrogen content and the friction-wear properties. The result showed that the thickness of each DLC layer was about 1.5μm. Plasma-nitriding formed the hardened layer possessing 150μm depth. The hardness distribution was unchanged by the DLC coating and its formation greatly improved the durability of the DLC layer. At room temperature under dry condition, the DLC coating drastically reduced the friction coefficient and improved the wear resistance of the base material. Furthermore, the DLC layer was contributed to a lower friction coefficient and higher durability with increasing hydrogen content.

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The purpose of this study was to understand the effects of thermal exposure temperature on residual stress in thermal grown oxide (TGO) on NiCrAlY coating. The residual stresses in the TGO layer were measured by photo-stimulated luminescence spectrum. High velocity oxygen fuel sprayed (HVOF) method was used to fabricate NiCrAlY coating on a nickel base superalloy. The thermal exposure tests were conducted inair at 900℃, 1000℃, 1100℃ for up to 1000 hours using an electric furnace. It was shown that the thickness of the TGO increases with an increase in thermal exposure time with a parabolic curve. The residual stress in the TGO layer increases in thermal exposure time up to 75 hours, and then, the residual stress in the TGO layer decreases slowly. The effects of surface roughness on the residual stress in the TGO were discussed based on experimental results and analysis.

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The thermo-mechanical fatigue tests of a protective coated Ni-base superalloy were carried out. The substrate of Ni-base superalloy,IN738LC, was coated with CoNiCrAlY protective coating sprayed by cold spray process. The damage behaviors during thermo-mechanical fatigue were investigated comparing with those during iso-thermal low-cycle fatigue. In this paper, the influence of thermo-mechanical loading on fatigue strength was discussed and fatigue strength of the cold sprayed protective coatings was compared with that of low-pressured plasma sprayed one.

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High-temperature coating systems, which were used in gas turbine engines, usually consist of a ceramic Thermal Barrier Coating (TBC) as a top coat (TC), an intermediate metallic-bond coat (BC) and a superalloy substrate. During service, a Thermally Grown Oxide (TGO) layer grows at the interface between the TC and the BC. The TGO is predominantly comprised of α-Al_2O_3 and provides protection of the underlying substrate against high-temperature corrosion. However, upon cooling of the component from high temperature, thermal-mismatch strains can generate within the TGO. In this study, the influence of bond coating process for a thermal barrier coating (TBC) on thermally grown oxide (TGO) growth was investigated. The bond coats (BCs) were sprayed by different spray techniques, namely the low pressure plasma spraying (LPPS) and the cold spraying (CS). The coatings were oxidized isothermally at 1273K for different time periods up to 1000h and their TGO growth were compared and fully discussed by measuring their TGO thickness, accounting their TGO oxidation rate k. As a result, it can be found that the TGO growth of the TBC with CS-BC was less than that of the TBC with LPPS-BC. And also, in the TBC with CS-BC, formation of mixed oxides, which has harmful influence on delamination of the top coating, was less than LPPS-BC.

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Failure behavior of thermal barrier coatings (TBCs) was investigated by using of a new testing system. The system consists of a "can" type of combustion system and a servo-electro hydraulic material testing system, and it can apply thermo-mechanical loadings to a test sample in a simulated gas turbine combustion environment. By means of this apparatus, failure behavior of a thermal barrier coating (TBC) specimen was studied under a condition of cyclic burner heating on which a constant tensile load was superimposed. The experimental results demonstrated that the test samples indicate as the non-elastic elongation as topcoat clacking. The strain rate of sample deformation was remarkably higher than laboratory creep tests. Thermo-mechanical deformation model, took account the effect of temperature gradient in the substrate, can give one possible understanding on the higher strain rate.

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Thermal barrier coatings (TBCs) have been employed in turbine blades in order to degrade the temperature of the substrate. The elasticity of the TBC is anisotropic because of the lamella structure. In this study, the anisotropic elastic properties and the sintering behavior of a yttria-stabilized-zirconia TBC deposited by atmospheric plasma spraying were investigated. The elastic moduli at high temperatures up to 1373K were successfully measured by the resonance ultrasound spectroscopy (RUS) system. Following experimental results were obtained. The out-plane Young's modulus was significantly lower than the in-plane modulus. It was because of lamella cracks preexisting in the TBCs. These Young's moduli of as-sprayed TBC ranged from room temperature to 873K gradually decrease with an increase of the testing temperature. On the contrary, the moduli from 1073K to 1373K gradually increase because of sintering. The other high temperature elastic moduli, Poisson's ratios and shear moduli of elasticity, were also evaluated by the RUS.

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In this study, applicability of porous ceramic coatings to transpiration cooling system for gas turbine blade was examined. The results in this study can be summarized as follows. Hot gas flow test simulating the exposure environment surrounding the gas turbine blade was conducted using the porous ceramic coated plate-shaped sample. It was recognized that the surface temperature of the sample was considerable reduced at a center of the cooling hole and then spread along a rear field in a hot gas flow with the increase of coolant gas pressure. Based on our experimental results, the amount of coolant gas needed in transpiration cooling system was calculated roughly. The calculation revealed that the amount of coolant gas in transpiration cooling system is very few in comparison with the current cooling system in gas turbine under the same level of the blade metal temperature.

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In this study, the effect of heating temperature, heating time, thermal growth oxidation(TGO) layer thickness and adhesive strength of top coat(TC) are investigated experimentally by scraping shear test. In addition, the effect of TGO layer thickness, Young's modulus of TC and crack length in TC on adhesive strength are investigated analytically by FEM simulation. As the result, (1) Adhesive strength of TC increases apparently at the first stage of heating, then it decreases slightly in the second stage. This is because that both of adhesive strength and TC strength increase by heating effect in the first stage and TGO grows up in the second stage. (2) It is considered that adhesive strength of the TC is dominated by the interface strength at the beginning and then the TC strength at the second stage. (3) On the basis of the stress analysis, the initiation and the direction of crack propagation can be clarified in this scraping shear test.

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A three dimensional EBSD (3D-EBSD) analysis was applied to characterize microstructure and crystallographic orientation in thermal barrier coatings (TBC) exposed at 1173 K for 300 hours. In this study, the new analysis method of morphology and crystallographic orientation, Dual-Scanning Majority (DSM) Method, was proposed and the c-axis direction of tetragonal phase in TBC was determined by this method. The c-axis direction in splat grains was perpendicular to interfaces between splat grains. 3D-EBSD analysis was conducted by three-dimensionally reconstructing a series of inverse pole figure (IPF) maps of cross sections milled by focused ion beam (FIB) method. The slice thickness was about 185nm. From 3D-microstructure obtained by 3D-EBSD analysis, large and small columnar crystals along tetragonal axis c in splat grains were observed. Then, the crack initiation occurred at the ends of small columnar crystals or interfaces between splat grains.

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Nondestructive-continuous detection and monitoring of the delamination crack of the ceramic top coat in thermal barrier coatings (TBCs) was explored using an AC impedance technique. It was shown that the measurement of capacitance enabled us to continuously monitor the delamination crack which initiated and propagated in a ring shape of TBC specimen. An electric model has been also constructed to rationalize the changed in the electric capacitance with the delamination crack advance.

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In this research, in order to investigate the adhesive strength of thermal sprayed coating, the scraping shearing test was developed. It was found that the adhesive strength of WC-Co thermal sprayed coating is depending on the dimension of the test piece and the loading position around the interface. That is because the apparent critical shear stresses increase with increasing height of the test piece and decrease with increasing width of the test piece. Also, it is confirmed that the critical distributions of shearing stress and bending stress around at the interface edge depend on the dimension of the test piece by three-dimensional FEM analysis.

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Effects of the rolling temperature on the stretch formability and mechanical properties of the rolled Mg-3Zn and Mg-3Zn-0.1Ca alloys (mass%) were investigated. The surface appearance of the rolled Mg-3Zn alloys was improved with an increase in the rolling temperature. On the other hand, that of the rolled Mg-3Zn-0.1Ca alloys was deteriorated with an increase in the rolling temperature, due to the precipitation of inter-metallic compounds (Ca3Zn), whose melting point (664 K) were around the rolling temperature. The rolled Mg-3Zn alloys exhibited almost the same stretch formability with that of the commercial AZ31 Mg alloys. On the other hand, the rolled Mg-3Zn-0.1Ca alloys showed significant stretch formability corresponding to the rolled aluminum alloys, which was attributed to the appearance of the TD-split texture. The stretch formability of the rolled Mg-3Zn and Mg-3Zn-0.1Ca alloys was slightly improved with an increase in the rolling temperature. The intensity of basal plane texture for the Mg-3Zn and Mg-3Zn-0.1Ca alloys decreased with an increase in the rolling temperature.

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Magnesium alloys have special features such as light weight, high specific strength and good reusability. However, information on the flow behavior and formability of magnesium alloys in multi-axial compressive stress conditions is highly limited, nevertheless of their importance for plastic working processes such as forging and extrusion. In the present study, the uniaxial and biaxial compression tests along proportional strain paths were conducted at room and at elevated temperatures, and thus the influence of strain paths and temperature upon mechanical properties and compressive forming limit were discussed. The results revealed that the flow stress scarcely changes with the test temperature in the range from 493 K to 523 K. On the other hand, the compressive forming limit was found to be dependent on the temperature as well as the strain paths.

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To investigate the deformation behavior of a magnesium sheet, the finite element calculation was carried out under tension and in-plane cyclic tension-compression test. From the experimental data, the twin deformation was observed during the tensile deformation after uniaxial compression. For the accurate description of the above mentioned twin deformation, we have developed the constitutive equation of twining behavior. From the comparison, it is found that the developed constitutive equations can calculate stress-strain response accurately.

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The effect of microstructural factor, such as grain size, on the deformation behavior near the crack tip region during the fracture toughness test was investigated using wrought Mg-Al-Zn alloy. The stress distributions related to {10-12} twinning was predicted by FEA, and the microstructural evolutions were confirmed through experiments. This type of twinning was formed at the beginning of the fracture toughness test due to the creation of a large stress field near the crack-tip region. The formation region of twinning became small with grain refinement because of the changes in the dominant plastic deformations. The results from microstructure observations showed similarities to the stress distribution from FEA. These results can be used to predict the macroscopic deformation features near the crack-tip.

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Long-Period-Stacking-Ordered phase which is frequently observed in recently developed magnesium alloy systems of Mg-TM-RE shows "kink" deformation in the microstructure and this phenomena is believed to be playing a crucial role in macroscopic mechanical response. In this study, we employ single crystal specimens of the LPSO phase and relation between the magnitude of kink and strain hardening of basal slip is examined by means of crystal plasticity simulations.

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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. The features of the band like deformation product in LPSO-phase is similar to those of the deformation kink proposed in Zn single crystal, suggesting that the similar mechanism may govern the formation behavior of the deformation kink. However, the size of the deformation band and the migration speed of the interface were largely different between them. This implies that the crystal structure, morphology of the grain, loading orientation, etc. may affect the formation behavior of the deformation kink.

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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 using high-precision markers drawn by electron beam lithography. 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. Mechanical properties of this alloy are remarkably improved by warm-extrusion, comparing to that in the as-cast alloy. The superior mechanical properties of this 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. After the extrusion, a characteristic microstructure called "kink" was generated in the 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. The formation mechanism of such microstructural inhomogeneity in the LPSO phase is discussed.

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Effects of initial crystal orientation on microstructure in pure Mg single crystals after an equal channel angular pressing (ECAP) pass were investigated. Four kinds of Mg single crystals with different initial crystal orientations were prepared. Basal planes in samples 1 and 4 are parallel and perpendicular to extrusion direction. Basal planes in samples 2 and 3 are parallel and perpendicular to theoretical shear plane in an ECAP die. ECAP was carried out at room temperature. A crack propagated in the sample 1, and the fracture surface was parallel to (1124). On the other hand, deformation behaviors of the samples 2 and 3 were about the same. Basal slip lines were observed throughout the sample surface. In addition, a large {10 12} twin was observed throughout the surface where passed through the shear plane. The crystal orientations of the samples 2 and 3 after an ECAP pass rotated due to basal slips and {1012} twins, and they were agreements with the initial crystal orientation of sample 4. In the sample 4, the crystal orientation also rotated due to basal slips and {1012) twins. Crystal orientations of the samples 2, 3 and 4 were about the same after an ECAP pass despite the different initial orientations. The results in this study explain the texture formation of pure Mg polycrystals by an ECAP pass.

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The mechanism of twin region development during spherical indentation in pure magnesium single crystal is investigated using a crystal plasticity finite element analysis method. For deformation modes, basal slip, prismatic slip <a>, pyramidal-1<a> slip, pyramidal-1<a+c> slip, pyramidal-2<a+c> and tensile twinning systems are considered in the calculation. The indentation analysis on (0001), {10-10} or {11-20} surface are performed. The results of calculations show the significant anisotropy in surface displacement and twin region which qualitatively agree with the experimental results in the past report.

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It is important to research activation of the slip systems in HCP crystals to understand deformation behavior of the crystals. In this study, pure zinc, cadmium, magnesium and titanium single crystals were tested by [112^^-0] and [0001] tension in various temperatures. In zinc and cadmium, {11^^-22}<<11>^^-23> second order pyramidal slip is activated. In magnesium, the pyramidal slip and {101^^-2} twin occurred depend on the tensile direction. In titanium, prismatic slip and {101^^-2} twin occurred in [112^^-0] tension and [0001] tension, respectively. However, {101^^-1}<<11>^^-23> first order pyramidal slip also occurred in [0001] tension depend on oxygen content.

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The nonlinear and anisotropic elastic properties of magnesium are studied through first-principles calculations based on density functional theory (DFT). The method of homogeneous deformation is combined with DFT total-energy calculations to determine high-order elastic constants for single-crystal hexagonal close-packed (hcp-) and face-centered cubic (fcc-) magnesium. Lagrangian strain tensors characterized by multiple strain components are applied to the crystal lattice and the elastic strain energy is calculated from first principles. A thermodynamically continuum description of the elastic response is formulated by expanding the elastic strain energy density in a Taylor series in strain truncated after fifth-order term. A total of 455 independent elastic constants for both lattice types are determined by least-squares fit to the ab initio calculations. The obtained high-order elastic constants provide the nonlinear continuum description for infinitesimal and finite strains under arbitrary loading.

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In this study, a new phase-field model for deformation twinning coupled with the crystal plasticity theory is developed. In the present model, elastic strain energy on twin plane and anisotropic interfacial energy between matrix and twinned region are adopted in Ginzburg-Landau free energy as the bulk energy and the gradient energy, respectively. In order to describe the twining-detwinning behavior, which are an evolution and a shrink of the twined region, the sign of the resolved shear stress acting on the twin plane is taken into account. The phase-field model derived in a conventional manner is incorporated in the dislocation-crystal plasticity model for HCP crystals, which is previously developed by the authors, through a phase field parameter and resolved shear stress. Using the above model, a numerical simulation on cyclic loading test along the a-axis for Mg single crystal plate is carried out by means of FEM and we find that the twinning-detwinning behavior can be reproduced by the present model. Also, slip deformation in twinned region during the twinning or detwinning is observed. The mechanism of the above phenomena is discussed.

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The initial and subsequent yield surfaces of magnesium alloy are numerically evaluated based on the crystal plasticity approach. A homogenization-based finite element method is introduced to compute the macroscopic material behaviors with a crystalline scale structure. The present method can represent the yield behavior of magnesium alloy under arbitrary stress paths. The obtained yield surface qualitatively coincides with the experimental one. The anisotropic hardening is observed and the pyramidal slip system plays an important role on the mechanism of anisotropic hardening.

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To simulate texture development during actual rolling process of magnesium sheet, rolling analysis was performed using two numerical methods with application of crystal plasticity model. First, the explicit finite element method DYNA3D is used for simulation of symmetric rolling process. Then, strain distribution was calculated by Orowan theory. Analysis by homogenization method was performed using the strain distribution. As a result, it was confirmed that the analysis by homogenization method considering shear strain is valid.

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In order to clarify the atomic structure of deformation twin boundary in pure magnesium, 99.9 % purity magnesium single crystal was prepared by modified Bridgeman technique. Thin foils were thinned by a mechanical polishing, a mechanical gliding and ion-beam thinning. The microstructure and the atomic structure of the twin boundary of magnesium were observed by transmission electron microscopy (TEM) and high resolution TEM. In this study, all of the observed twins were lenticular {1012} twins with curved and straight regions. In both regions, it was found that these twin boundaries consisted of the symmetric tilt boundary planes and the (0001) faceted planes. The atomic structure of symmetric tilt boundary plane on these twins corresponded to the calculated atomic structure of {1012} twin boundary. It was also found that the curved region was a step-like structure and the straight region was a zig-zag structure.

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