In this study, the change of the crystallographic quality of electroplated copper thin-film interconnections due to stress-induced migration was investigated by using an EBSD (Electron Back Scatter Diffraction) method. This EBSD analysis clearly showed that the crystallinity of the annealed electroplated copper thin-film was degraded during the storage of the interconnection even at room temperature without any loading. This is due to the stress-induced migration caused by high tensile residual stress which occurred in the film after annealing. Molecular dynamics simulations showed that the diffusivity of copper atoms along grain boundaries with low crystallinity was enhanced significantly by high tensile residual stress. Therefore, the grain boundary diffusion accelerated by tensile residual stress is the main reason for the degradation of crystallinity the thin film interconnection after annealing.

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This paper describes the influences of specimen size, focused ion beam (FIB) induced damage, and high vacuum annealing on the mechanical properties of silicon (Si) nanowires (NWs) evaluated by tensile testing in a FE-SEM. Si NWs made from silicon-on-nothing (SON) membranes are produced by deep reactive ion etching (DRIE) and annealing. FIB system's probe manipulation and film deposition functions are used to directly bond them onto the sample stage of a tensile test device and to fabricate Si NWs. The mean Young's modulus and strength of FIB-damaged NWs are 129.1 GPa and 5.6 GPa, respectively. After annealing, the Young's modulus is increased to 168.4 GPa, whereas the strength is decreased due to morphology degradation.

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In order to investigate the effect of material size on the fatigue behavior in less than micrometer-scale, resonant fatigue experiments are conducted using single-crystal gold specimens that possess test section with different sizes. The experimental result indicates that the width and fomiation stress of intrusion/extrusion, which appears on the test section surface due to fatigue, shingly depend on the material size.

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The mechanical conditions of fatigue crack initiation were evaluated on roughly 500 nm thick freestanding copper films. Fatigue experiments and fatigue damage observations by using field emission scanning electron microscope (FESEM) and electron backscatter diffraction (EBSD) analysis revealed that an intrusion/extrusion formed parallel to a Σ3 twin boundary, and fatigue crack then initiated from this intrusion/extrusion. On the basis of these results, anisotropic elastic finite element method (FEM) analysis considering grain shape and crystal orientation around the fatigue crack initiation sites was conducted in order to evaluate local stress distribution near fatigue crack initiation sites. FEM analysis results indicated that fatigue crack initiation occurred at the slip system which penetrated the film in thickness direction. Moreover, number of cycles to fatigue crack initiation showed a tendency to increase as resolved shear stress decreased.

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To investigate the creep crack growth properties of aluminum (Al) nano-films deposited by electron-beam evaporation, creep crack growth experiments for freestanding 356 nm- and 139 nm-thick film specimens with a center notch or a single edge notch were conducted. In both Al films, a creep crack stably propagated at first, and then the crack growth rate gradually accelerated, leading to unstable fracture. FESEM observation of fracture surface revealed that fine unevenness presented on the fracture surface of the stable crack growth region while ductile or chisel point fracture occurred in the unstable region. The stable crack growth is presumably due to intergranular fracture. For the 356 nm-thick films, the relationship between the creep crack growth rate and the stress intensity factor depended on the experimental conditions, whereas the creep J-integral at the steady state well characterized the creep crack growth rate regardless of the experimental conditions.

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The grain boundary (GB) engineering for improvement of fatigue property in SUS316L austenitic stainless steel was investigated. The fatigue crack was predominantly nucleated at high energy random GBs. The low-Σ coincidence site lattice (CSL) GBs with the lower GB energy showed the higher resistance to fatigue crack nucleation. In-situ observations of fatigue crack propagation revealed that the local crack propagation rate strongly depends on the spatial distribution of GBs having different character and structure. The local propagation rate of fatigue crack in crossing CSL GBs became lower than when propagated across random GBs and in grain interior. The local propagation rate along CSL GBs was lower than that in grain interior, while the fatigue crack propagation was accelerated when the crack propagated along random GBs. The specimen with the higher fraction of CSL GBs showed the higher fatigue strength than the specimen with the lower fraction of CSL GBs.

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Low cycle fatigue (LCF) properties were investigated on Fe-20%Cr ferritic stainless steel processed by equal channel angular pressing (ECAP). The Fe-20%Cr alloy bullets were processed for four pass through ECAP Routes-A,Bc and C. The ECAPed samples were cyclically deformed at constant plastic strain amplitude ε_<pl> of 5x10^<-4> at room temperature in air. All the samples showed the cyclic softening which continued until fatigue fracture. At initial stage of the fatigue test, 4C sample exhibited the lowest stress amplitude of 400MPa, while 4A and 4Bc samples showed higher stress amplitudes of 580MPa and 560MPa respectively. Fatigue lives of 4A, 4Bc and 4C samples were 13,000, 22,000 and 16,000 cycles, respectively. The difference in the initial stress amplitudes can be attributed to microstructure: dominant grain boundaries of the 4C sample revealing the low stress amplitude were low-angle grain boundaries while the 4A and 4Bc samples contained large amount of high-angle grain boundaries and fine grains of iglu diameter. The long fatigue life of the 4Bc sample can result from the equi-axed fine-grained structure which can inhibit crack growth towards various directions, in comparison with lamellar microstructure formed in the 4A sample.

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In this work, we investigate the effect of thickness ratio of Ti/Si constituent layer, bilayer thickness and total thickness on the self-propagating reaction behavior. It is presented that the Ti-Si multilayer films of Ti:Si = 1:2 show intensive self-propagating reaction. The films can react instantly by just applying mechanical shock. The multilayer films with the bilayer thickness of 〜25 nm appear to need the least energy to ignite the self-propagating reaction regardless of the Ti/Si thickness ratio.

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Capillary induced forces are widely observed in fine structures where liquid flows along solid surfaces, such as wet-etching process in micro/nano-pillar fabrication. Undesirable bending or collapse of the structure occurs if they are improperly considered in the structural design. In this study, liquid column formation between aligned polymer plates is observed and the resulting capillary induced force causing the plate deformation is evaluated. The plate dimension is sub-millimeter scale, which is rather large in observation of capillarity, in order to clearly measure deformation process of the aligned plates until their contacts. When the plates are immersed into liquid from the fixed end, gap between plates becomes smaller due to liquid columns formed far from the end. It is found that the deformation of the plates proceeds more unstably as the number of plates increase, but their contact is initiated at the similar plate length into liquid.

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Alkali halide crystals having the NaCl-type structure are generally brittle at low temperatures, but AgCl with the same structure is much more ductile than the other alkali halide crystals. In order to address this issue, first-principles calculations were performed to analyze energetics of slip deformation in NaCl and AgCl. We evaluated slip deformation resistance by using GSF energy and surface energy. In NaCl, only the GSF energy of the {100}<011> slip system was lower than twice the surface energy of {100}, which indicates that the slip system can be activated in NaCl. In case of AgCl, on the other hand, the GSF energies along several slip planes including {100} are lower than twice the surface energy of {100} and {110}. It can be said, therefore, that the several slip systems can be activated in AgCl, which may bring about the specific ductility of AgCl.

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A dislocation in a crystalline material has dangling bonds at its core and strong strain field in its vicinity. Therefore, it has a potential to exhibit peculiar physical properties. In this study, we investigated electric properties of dislocations in lithium niobate. In order to introduce dislocations in the crystal, we fabricated low-angle grain boundaries by a diffusion bonding technique. Owing to this method, we can arrange dislocations periodically in the crystal. It was found that electric properties of dislocations are different depending on the Burgers vector.

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To evaluate the effect of size of polycrystalline microstructure on a macroscopic non-uniform deformation field, computational simulations of micro- to macroscopic deformations of the polycrystalline metals with different sizes of microstructure were performed using the rate-form second-order homogenization method. For all gauss integration points in the hole-introduced tensile specimen macroscopic model, periodic polycrystalline microstructures, in which the plastic deformation is modeled by the conventional crystalline plasticity theory, were given. For the model with smaller size of microstructure, decrease in macroscopic load was emphasized in the later stage of deformation. In such model, rapid reduction of the cross section around the hole was confirmed. This difference was caused by the deformation of the microstructure, which was strongly characterized by the macroscopic strain gradient and the size of the microstructure.

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Intrinsic multiferroic properties of native vacancies in BiFeO_3 are investigated by density-function calculations. Oxygen vacancies characteristically exhibit the strong anisotropy in ferroelectric polarization and locally enhance the magnetic moment of its neighboring Fe atoms, while the other Bi and Fe vacancies have less influence on the multiferroic properties. Furthermore, the positive-charged state of oxygen vacancies is found to dramatically enhance their ferroelectric properties, but suppress the magnetic properties. We reveal that these multiferroic properties are characterized by the distinct defect electronic state of each vacancy.

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The ferroelectric phase transition of lithium niobate (LiNbO_3) has theoretically been analyzed using lattice vibrational analyses based on first-principles calculations. The phonon dispersion relation of the paraelectric phase has four imaginary vibrational modes at the vicinity of the Γ point, which have imaginary frequencies in the wide region of the Brillouin zone including the zone boundaries. This suggests that the ferroelectric phase transition in LiNbO_3 is not the conventionally-accepted displacive type but should be a complicated mixture of displacive and order-disorder type.

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In this study, the contact and adhesion problems of power-law profile indenter and wavy surface is considered. The solution of contact problem based on the axisymmetric contact is solved. The adhesion problem is solved based on the JKR theory. The solution is compared with the adhesion analysis based on the JKR theory.

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The purpose of this study is to estimate the shape of ablated crater with sufficient accuracy when the multi-shot of the ultra-short pulse laser are irradiated to glasses. In this analytical model, the complex dielectric function of the Lorentz model is applied, in order to consider that glasses are dielectrics and to evaluate the damage by the laser ablation. Simultaneously, the time evolutions of free electrons density for distinguishing the ablation region and the damage region are calculated, and finally the threshold fluences are able to be computed quantitatively to various laser irradiation conditions. The absorption coefficients and threshold fluences which were obtained by this analysis were applied to the Beer-Lambert law, and it was well in agreement with the crater depth obtained from this analysis. Moreover, the crater shapes over the multi-shot channels in consideration of the laser fluence dependences of the absorption coefficients and the threshold fluences at the first shot were well in agreement with experimental results.

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It has recently been clarified that ductile fracture in aluminum alloys occurs predominantly through coalescence of hydrogen micropores. This type of ductile fracture was investigated by the image-based finite element analysis using the 3D image taken by X-ray tomography. The studied FE model consists of Al_2Cu particles and pores. The analysis revealed the distribution of local stress, strain and the stress triaxiality developed within the real material's structure, providing important clues to anticipate the location that would undergo significant damage.

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We have developed a modified three-dimensional x-ray diffraction (3DXRD) microscopy, which enables us to obtain three-dimensional orientation map non-destructively. In other study we have examined the plastic behavior for polycrystalline iron by the 3DXRD experiment. In this study we performed the crystal plasticity finite element (CPFE) analysis which corresponds to the 3DXRD observation. The plastic deformation state of the finite element model was computed by means of CPFE analysis based on the body centered cubic (BCC) crystal with slip system of {011}<111>, {112}<111>and {123}<111>. Both the experimental observation and the numerical analysis showed that the most of the grains rotated toward the preferred orientation <110> along the tensile axis and that intra-granular orientation spread and multi-directionally rotated as the tensile strain increased, which was caused by inter-granular interaction. Remaining discrepancy was due to the observation technique and/or the constitutive model adopted in the present study.

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Isotropic graphite has homogeneous characteristic such as thermal expansion in all direction, high strength due to fine-grain structure and low characteristic variation in addition to characteristics of general graphite. It is used as a material of manufacturing equipment for semiconductor, solar cell, LED, and core structure in nuclear systems. Since graphite is porous material containing 20% of porosity, the characteristics of graphite strongly depends on shape and volume distribution of pore. It is essential to establish the production method for further reducing the characteristic variation of graphite to produce high quality graphite. Therefore, it is necessary to establish the simple method for prediction of the characteristics of graphite. Although they have been characterized as a function of porosity, it is necessary to characterize them as a function of some detailed factors in order to further reduce the characteristic variation and to characterize them with high accuracy. The authors have been developing the method for predicting the characteristics of graphite by analysis of shape and volume distribution of open pore and closed pore using two and three dimensional images in order to characterize graphite with high accuracy. In the present study, quantity of open pore and closed pore analyzed by a digital image analysis was compared with that measured by a mercury porosimeter. Both results indicated that open pore increased with increasing porosity and closed pore showed almost constant value. However, the volume of closed pore by the mercury porosimeter was measured up to 5% larger than that by the digital image analysis. It is necessary to clarify the correlation between the volume of closed pore analyzed by the digital image analysis and that measured by the mercury porosimeter to measure closed pore with high accuracy by the mercury porosimeter in the next step.

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The crack initiation mechanism of cast aluminum alloy was addressed to quantitatively evaluate the fatigue strength. The synchrotron radiation microtomography was employed to visualize the three-dimensional damage around pores and Si particles. Two types of specimens were prepared for the low cycle fatigue test. The temperature of solution treatment was different, and it yields a difference in the shape of Si particles. After a certain cycles of fatigue, a catastrophic damage around many Si particles happened and they connected to each other so as to form a crack. The scanning electron microscopy after the test showed that the type of damage was the break of long Si particles or the interface debonding around round Si particles.

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There is large difference of strain between surface and inside materials in strain singular field. It is important to analyze strain field material in 3D/4D, because almost all of grains exist inside material. We use technique amalgamating a transmission X-Ray diffraction (XRD) experiment with grain boundary tracking (GBT) that has been developed by the present authors. This technique combines X-ray micro tomography (CT), this novel technique which is called the diffiaction-amalgamated grain boundary tracking (DAGT) technique, provides accreted crystallographic deformation of individual grains dining deformation of material. It makes non-destructive and in-situ characterizing of materials possible up to plastic defamation near failure event. We success to realizes strain during tensile test and grain orientation before tensile test by using DAGT technique in previous study. It is necessary to realizes grain orientation during tensile test to analyze crystallographic deformation immediately before destruction. For this raison, technique ofthe addition for DAGT was developed in this research.

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Aluminum foam is a multifunctional material with light weight and high energy absorption. In this study, three-layered functionally graded ADC12 aluminum alloy foam with different pore structures was fabricated by varying amounts of blowing agent added and amounts of gases in ADC12 aluminum alloy die castings as starting materials. From X-ray computed tomography (X-ray CT) observations of the pore structures of fabricated three-layered functionally graded porous ADC12 aluminum, it was found that it has three layers with layer A (high porosity and large pore diameter), layer B (middle porosity and small pore diameter) and layer C (low porosity and small pore diameter). The deformation of the fabricated three-layered functionally graded porous ADC12 aluminum during compression tests started from the low strength layer A, and thereafter the middle strength layer B and high strength layer C sequentially deformed.

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Porous aluminum (Al) was fabricated by a tool traversing friction powder compaction process with the sintering and dissolution process. In this process, a mixture of Al powder and NaCl as spacer particle was the starting material. After the powder mixture was placed in a mold, sintering was conducted only by the traversing of a rotating tool. Namely, no external heat source was used in fabrication of porous Al except for the friction heat generated by the traversing of the tool. In this study, increasing in size of porous aluminum was conducted by applying multi-pass process. Fabricated porous Al had a length and width equal to the tool traversing area. By a X-ray computing tomography observation, fabricated porous Al had uniform pore distribution. In a compression test, it was found that fabricated porous Al had almost the same mechanical properties, regardless of the position in the tool traversing area.

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The energy absorptivity of porous aluminum depends on the pore structures of porous aluminum. The pore structure can be captured by the micro-focus X-ray computed tomography, and the finite element model can be also automatically generated by using the uniform cubic element. In this study, elastic-plastic finite element analysis for the fmite element model and compression test of porous aluminum were carried out. The analytical result gives a good estimation of the initial gradient of the nominal stress-strain curve obtained by the test. Moreover, it was concluded that the compressive collapse behavior was affected by the elastic-plastic property of material along with the high stress concentration from the beginning of compression load and the plateau region was realized by the fmite deformation of the cell walls.

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Concept of assurance of structural integrity has been taken into accounted for large structures like energy related structures where flaw evaluation is conducted based on the fracture mechanics and non-destructive inspections. When its application is attempted to welded locations, welding residual stresses must be given qualitatively, and it is relatively difficult as the X-ray technique gives only information near the structure surface and the thermo-elasto-plastic simulation gives only the qualitative information due to complexity of welding process. Moreover, prediction of welding deformation is also required in the design process. So, development of a new evaluation method of both welding deformation and residual stresses that can be applicable to the finite element (FEM) analysis is desired. In this study, by incorporating the eigen-strain method, a new method is proposed where estimation of both welding deformation and residual stresses can be conducted. In the proposed method, three dimensional eigen-strain distribution is estimated by using "the Truncated Singular Value Decomposition (TSVD)" method and the penalty method. The validity of the proposed method is made clear by numerical analysis.

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In this paper, thermo-electro-elastic fracture behavior of two parallel cracks in arbitrary positions of a FGPM strip under thermo-electric loadings is considered. The crack faces are supposed to remain thermally and electrically insulated. We assume that all material properties depend only on the coordinate z (perpendicular to the crack faces) in such a way that properties are some exponential functions of z. Fourier transform techniques are used to reduce the mixed boundary value problems to two systems of singular integral equations. Numerical calculations are carried out, and detailed results are presented to illustrate the influence of the geometric and material parameters on the stress and electric displacement intensity factors. The results for the temperature and electro-elastic field are also included.

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This study applies linearized couple-stress theory to evaluate the dynamic stresses around two collinear cracks in an infinite elastic medium that is subjected to an incoming shock stress wave impinging normal to the cracks. The boundary conditions with respect to the cracks are reduced to dual integral equations using a Fourier transform in the Laplace domain. To solve these equations, the differences in the displacement and rotation at the cracks are expanded by a series of functions that are zero-valued outside the cracks in the Lapace domain.

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We propose flexible sports protectors whose outer shells harden only under impact loading by virtue of the strain rate effect on mechanical properties due to the viscoelasticity. In the present study, we investigated the compressive mechanical properties of soft epoxy resins as an outer shell material of flexible sports protectors. The effect of the strain rate on the compressive behavior of the soft epoxy resin was clarified by conducting static compression and split-Hopkinson-pressure-bar (SHPB) tests. The experimental results reveals that the soft epoxy resin is suitable as outer shell material.

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This paper deals with evaluation of singular stress field for V-shaped notch specimen by using the small crack problem. In this study, a stress intensity factor of small crack at V-shaped sharp notch is analyzed by the crack tip stress method. The dimensionless stress intensity factor of small crack, normalized by the intensity of V-shaped notch without the crack, is independent of the notch depth and the loading conditions. By applying the evaluation of fracture strength for V-shaped notch specimen, it is found that the fracture toughness K_<IC> of small crack problem is almost constant independent of the notch depth and the loading conditions.

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Nondestructive evaluation of adhesively bonded interfaces is of high importance to ensure the structural integrity. In this study, the adhesive interface is modeled as a nonlinear spring interface, and the guided wave propagation in a laminated plate is studied numerically using the finite volume method. Continuous harmonic wave excitation is given at the end of the laminate plate, and the amplitude of a generated second-harmonic guided mode is evaluated using the two-dimensional Fourier transform. As a result, it is found that the amplitude ratio of the second-harmonic mode and the fundamental mode increases monotonically at a certain frequency, which is close to the frequency satisfying the theoretical phase-matching condition.

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In this study, resonance behavior of an imperfect joint of plates for the incidence of the lowest-order symmetric (S0) mode is investigated theoretically. To this purpose, a semi-analytical method termed hybrid finite element method (HFEM) is employed to analyze the interaction between the incident S0 mode and an imperfect joint of plates. A linear spring-type interface is introduced for modeling an imperfect joint of plates. This model is characterized by two parameters called normal and tangential stiffness. As a result of analysis, it is revealed that an imperfect joint shows resonance behavior at two frequencies below the cut-off frequencies of the higher-order symmetric Lamb modes. At these resonance frequencies, the out-of-plane displacement amplitude of the imperfect joint rapidly increases. Furthermore, it is shown that the resonance frequencies of an imperfect joint of plates monotonically increase with the interfacial stiffnesses.

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The purpose of this study is to examine spatial distribution of heat flux at a spot of concentrated light emitted from solar simulator on the surface of a heat receiver and thermo-elastic behaviors of the receiver. A mathematical analysis of a transient thermal stress problem of a circular plate subjected to plane axisymmetrical partial heat supply by the concentrated light is developed. Performing numerical calculation based on the analytical solutions, spatial distributions and time-evolutions of temperature change, thermal stresses and thermal deformations of the plate are examined. The effect of spatial distribution of heat flux is considered under a condition that the quantity of heat per hour flowing into the plate is kept at a constant value.

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Mechanoluminescence (ML) is one of a luminescence phenomenon, which is excited by the mechanical energy, such as strain energy. Thus, ML is expected to use as a stress sensor. In this paper, in order to investigate the relationship between the bending stress and ML, a four point bending test is carried out by using an epoxy resin specimen containing ML material. The equation, which describes the relation between the emission intensity, the loading velocity ,and the maximum displacement, is proposed. The efficiency of the proposed equation is confirmed.

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The perovskite ferroelectric materials, such as Pb(Zr_xTi_<1-x>)O_3 (PZT), consist of multiple crystal systems at morphotropic phase boundary (MPB) and they exert a huge piezoelectric response depending on domain switching and structural phase transition. In the present work, a multiscale nonlinear finite element method based on crystallographic homogenization theory was developed to evaluate nonlinear hysteresis behaviors at MPB. We employed the energy-based criteria and the incremental constitutive law taking into consideration with material property changes caused by domain switching and structural phase transition. The developed computation was applied to a PZT polycrystal and then the relation between macrostructural hysteresis behavior and microstructural crystal orientation change was discussed.

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A conductive elastomer is applied to detect damage in GFRP laminating with a hole. As the electrical resistance changes due to deformation of the material, strain distribution in the composite structure is measured using the conductive elastomer. It is an advantage to apply sensing in wide area along the conductive network. Possibility of the damage detection is demonstrated in comparison with measured strain distributions using the method.

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Fiber reinforced thermoplastic composites has poorer matrix resin impregnation to fiber reinforcement, because of extreme high viscosity of molten thermoplastics. Intermediate materials using Micro-Braiding technique have been developed to overcome these difficulties. In this study, composite textiles plates were fabricated under various fabrication conditions, and their impregnation were investigated experimentally and predicted by theoretical formulae. As a result, impregnation increased with molding pressure and time, and impregnation of single-ply textiles is improved compared with that of multi-ply textiles because they have more collapsed fiber bundles, hence closer impregnation distance. On another front, the analytical predictions were in disagreement with the experimental results.

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CFRP unidirectional laminates were cut by shearing with some clearances, and the damage extension and the morphology of cut specimens were observed. Damage extension was then predicted by smoothed particle hydrodynamics (SPH), and the unidirectional laminate was divided into fibers and resin in the model. By comparing the damage pattern between the experiment and the analysis, we discussed the mechanism of shear-cutting, i.e., extension of fiber breaks and resin failure. Compression failure of the resin was generated from the vicinity of the upper blade contacting point, and the fracture was then developed toward the lower blade. There was no significant difference in the damage extension due to clearance, but the area of resin compression failure increased with decreasing clearance.

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A thermoplastic CFRP sheet with an excellent balance of mechanical properties and press molding workability, as well as high suitability for high-volume production through press molding, has been developed for vehicles. This material consists of a mat of discontinuous, in-plane randomly oriented carbon fiber impregnated with thermoplastic resin. Thorough the use of press molding, consistent quality is achieved while allowing for excellent workability; the product is also well suited for mechanical simulation due to its high homogeneity.

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In the molding of thermoplastic composites, impregnation of thermoplastic resin into fiber bundles is difficult because of its high melt viscosity. Powder Impregnated Fabric (PIF) has been developed as an intermediate material of thermoplastic resin powder on surface of carbon woven fabric for easier impregnation. In this study, the relation between impregnation state, interfacial properties, mechanical properties, and molding conditions in the molding of CFRTP with PIF was investigated. Excellent impregnation state of less than 0.5% unimpregnation ratio was obtained in every molding time by using PIF. Although impregnation state was almost the same, tensile strength was increased with increase in molding time. From SEM micrograph of fracture surface, interfacial properties were improved by longer molding time. It was suggested that interfacial properties was improved by changing molding condition after completed impregnation.

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We propose a numerical method for predicting the distribution of mechanical properties, such as elastic modulus and yield stress, which appear in an injection molded part. In this method, the mechanical properties are directly predicted from the fiber orientation, the thermal history and the flow one of fiber-reinforced thermoplastics experienced during an injection molding process. Multivariate polynomial equations are derived with a neural network method, as prediction equations. Predicted mechanical properties agree well with measured ones for specimens cut out from several locations in a molded plate of fiber-reinforced polypropylene.

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Since interlaminar strength is weak point and difficult to predict, flaw is usually assumed in design of CFRP structures with stress discontinuity (e.g.: hole, ply drop-off slope). In this study, tensile tests for CFRP flat plate with ply drop-off slope were conducted, and numerical simulation with VCCT (virtual crack closure technique) were also conducted. The test specimen, which is based on a part of aircraft structure, includes an artificial flaw. From comparison with test results and previous studies, appropriation of the simulation method for present issue was verified. Furthermore, on the basis of the simulation as a trial, expected improvement for fracture toughness was discussed for realizing delamination-free CFRP structures and weight saving of structure.

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Numerical simulations for composite structure with stress concentration (e.g.:hole, slit) have been conducted under simple loading (ex. tensile loading), but rarely have been conducted under combined loading. In this study, strength tests of plane specimen with a slit under combined loading (tension and shear) and observation were conducted. Furthermore, numerical simulations considering both in-plane and interlaminar failure were also conducted to investigate the failure mechanisms. Detail observation showed difference of failure mode according to loading pattern. Numerical simulations showed good agreement with failure mechanism. Furthermore, failure load was predicted in various loading patterns with practically sufficient accuracy by use of band broadening stress as compressive strength.

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I suggest assessment method of the mean stress in the fatigue strength design of the short fibers CFRP from the fatigue test result in various stress ratios with completely reversed fatigue data in the standard specimen, creep rupture test data and product structure in this report.

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Carbon fiber reinforced thermo plastics (CFRTP), which is expected to reduce the weight of transportations and is made higher speed and lower cost than these of CFRP, was cut by a CO_2 gas laser (10.6μm, 800W, CW(continuous wave), 1 m/min), single-mode fiber laser (1.07μm, 300W,350W or 2000W, CW, 1-7m/min) and machining with milling. Although the high-power laser cutting processes make it possible to improve cutting rate of CFRTP, the laser-cut specimens clearly showed a thermal damage with a heat-affected zone (HAZ) identified by a micro X-ray CT observation. These laser-cut specimens were lower tensile strength than milling-cut specimens. From the results of thermo-elastic stress analysis, low-stress field was generated in the HAZ, led to the cause of strength degradation.

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Micro-materials attract attention with their remarkable properties, including mechanical, thermal, electrical attribute. Various techniques have been developed for fabricating micro-materials. The fabrication technique by utilizing electromigration (EM), which is the physical phenomenon of atomic diffusion in a metallic line with a high-density electron flow, is one of the fabrication methods for generating micro-materials. EM technique can generate micro-materials with a high-aspect ratio, pure Al components, an arbitrary form, and a single-crystal structure. Whereas EM has significantly advantages, multiple micro-materials are difficult to fabricate simultaneously. The technique using conductive passivation and comb pattern has been recently developed for fabricating multiple micro-materials by the authors. The present study demonstrates the multiple fabrication more than previous research, and provides the approach for improving fabrication of multiple micro-materials by EM.

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This research proposes a method for fabricating CuO nanostructures by utilizing atomic diffusion including electromigration and stress migration. The samples are subjected to a current stressing under different combinations of current density and temperature. After current stressing, the samples are kept in atmosphere or in vacuum. The factors affecting the formation of CuO nanostructures, which are current density, temperature and storage environment, are studied. The current density can cause an effective Cu atomic diffusion and induce a gradient of atomic density along the direction of film thickness. However, a much higher current density induces a direct formation of mass CuO nanostructures on the Cu film due to Joule heating. In addition, CuO nanostructures are formed in the atmosphere more easily than in vacuum.

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Characteristic of nanowire is gradually attracting many researchers with potential applications of nano-devices, nano-sensors, solar-cells and so on. This paper describes fabrication and evaluation of silicon nanowire array with the metal-assist chemical etching. To fabricate Si nanowire array, five steps are needed. First of all, Si wafer is cleaned and hydrophilization. Second, polystyrene spheres are coated on Si wafer by spin coater. Third, the arranged polystyrene sphere array is etched by reactive ion etching to reduce the diameter of the polystyrene spheres. Fourth, Au film is evaporated on the Si wafer of the arranged polystyrene to work as a catalyst. Fifth, the Si nanowire array is formed via wet etching by 4.6M HF and 0.44M H_2O_2 solution. After the wet etching, the Si nanowire array is dried by the supercritical drying method. After all, the highly ordered Si nanowire arrays are obtained with the diameter of 250-900 nm, the length of 0-12 μm and the density of 1.1×10^7-1.0×10^8 NWs/cm^2.

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A micro-coil can be fabricated by turning a thin wire on core wire, but the plastic deformation is difficult to be induced into such thin wire due its higher strength compared with bulk. Then, it is necessary to soften a micro-wire for improving the ability of the plastic deformation. In this paper, we heat-treated the copper micro-wire using Joule heat, and it was soften in very short time. Using the heat-treated copper micro-wire, we made a micro-coil. The ratio of the diameter of the coil to the diameter of the wire used was only 3, and the electromagnetic function of the fabricated micro-coil was investigated.

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It is useful to join micro/nano materials with Joule heat because the melting and the following solidification at the contact of materials occur in self-completed manner. By the way, it is very important to join dissimilar metals for producing high quality micro/nano mechanical systems. In this paper, we join dissimilar-metal wires with Joule heat and measure the current for joining. By comparing the current for joining dissimilar-metal wires and that for cutting the wires, we investigate the condition for welding dissimilar-metal wires with Joule heat.

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