In this study, a 2D model of a reinforced fiber is considered in matrix under pull-out force. Here, two intensities of singular stress fields (ISSF) are discussed appearing at the fiber end A and the intersection point E of the fiber and the surface. The analysis method focuses on the FEM stress at point A and E applying the same FEM mesh pattern to the unknown and reference models. To analyze the ISSF at A, the body force method solution is used as the reference model. To analyze the ISSF at E, the reciprocal work contour integral method (RWCIM) solution is used as the reference model. Then the two ISSFs are compared and discussed by varying the fiber bonded length lin. When lin is shorter, the ISSF at A is larger than the ISSF at E. When lin is longer, the ISSF at E is larger than the ISSF at A.

In this study, the strength evaluation method of the sharp notch plate under large scale yielding condition is considered. The tensile test of carbon steel JIS S45C specimen is carried out to obtain failure stress for various notch depths and angles. The values of plastic strain of notch tip node at the specimen are computed by elastic-plastic analysis under the same mesh pattern. As a result, it is found that the failure strength of the sharp notched specimens for various notch depths and angles can be estimated by using the plastic strain at the notch tip calculated by FEM.

Fully reversed tension-compression cyclic loading experiment is conducted for a copper single crystal micro-specimen with a single slip orientation under constant deformation amplitude control. Cyclic loading brings about nanoscale extrusion/intrusion on the specimen surface, which is not developed in monotonic loading. The size of extrusion/intrusion is much different from that of bulk counterpart. This indicates that micro-scale metallic materials possess a characteristic fatigue behavior.

To investigate the effects of surface oxide layer on fatigue crack propagation properties of submicrometer-thick metallic films, in situ field emission scanning electron microscope observations of fatigue crack propagation were conducted in approximately 500-nm-thick freestanding copper (Cu) films with roughly 1-nm-thick native oxide layer and with roughly 10-nm-thick thermal oxide layer. The fatigue crack in the films with native oxide layer propagated with intrusions/extrusions formation ahead of the fatigue crack tip, and then the fatigue crack stably propagated through the intrusions/extrusions. In contrast, obvious intrusions/extrusions were not formed and rapid fatigue crack propagation occurred in the films with thermal oxide layer. Fatigue crack propagation rate da/dN of the films with thermal oxide layer was higher than that of the films with native oxide layer.

Severe plastic deformation such as the equal channel angular pressing (ECAP) has been received attention in the field of grain refinement strengthening. There are several studies on low-cycle fatigue of ECAPed materials having fcc and bcc lattice structures, but low-cycle fatigue behavior has not been understood in an ECAPed materials having a hcp lattice structure yet. In the present study, a hot-extruded ZK60A magnesium alloy was processed by the ECAP for 1 to 8 passes at a die temperature of 200°C. Microstructure, tensile strength, and low cycle fatigue property of the ECAPed ZK60A alloy were investigated. The low-cycle fatigue test were conducted under a constant plastic strain amplitude of ε_pl=10^-3. In tensile deformation tests, the ECAPed samples processed for 1 and 2 passes revealed high tensile strengths. However, after 4 and 8 ECAP passes, tensile strengths decreased in comparison with the 1 and 2 pass samples. In low-cycle fatigue tests, the initial stress amplitudes of ECAPed samples were certainly higher than that of the as-extruded sample. Among the ECAPed samples, the 2-pass sample showed the highest intial stress amplitude. The initial stress amplitudes of the other ECAPed sample were almost equal, even though the 1-pass sample showed a higher tensile strength. Until 2000 cycles, all the ECAPed samples exhibited no significant cyclic softening behavior, while rapid softening has been observed in ECAPed samples including copper and strainless steel. The absence of the cyclic softening seems to be of advantage in an application for engineering purpose. In the 4- and 8-pass samples, stress amplitudes decreased gradually with increasing cycles. The fatigue life cycle of the 1-pass sample was less than 2000 cycles, which was shorter than the as-exruded sample. However, for the 4- and 8-pass samles, the fatigue life cycles were extended up to 6000 cycles.

EBSD analysis was carried out to investigate microstructures formed below a fracture surface. A push-pull fatigue test was conducted on a polycrystalline copper strip specimen having 3×3mm² cross section. From fracture surface observation, it is recognized that a primary fatigue crack was grown from right to left side, because striations arranged parallel to the left end. After the fracture surface observation, various positions in the fracture surface were milled by a focused ion beam (FIB) to obtain small flat planes normal to loading axis. The flat planes were analyzed with the EBSD system to estimate local lattice rotation. In a grain existing just below the fracture surface, gradual orientation change was detected. To estimate the orientation change quantitatively, lattice rotation gradient was calculated at each FIB-milled plane. According to the preliminarily-obtained relationship between the lattice rotation gradient and ΔK_I value, the distribution of the ΔK_I value over the fracture surface could be drawn. At lower ΔK_I value area of the fracture surface, change in the ΔK_I value was consistent with a crack growth direction that was estimated from fracture surface topology. However, the estimated ΔK_I value decreased at the left side of the fracture surface. Although there was no significant lattice rotation, grain refinement was recognized at the left side.

To investigate the effects of oxide layer on fracture toughness of freestanding submicrometer-thick films, we conducted in situ field emission scanning electron microscopy (FESEM) fracture toughness tests in roughly 500-nm-thick Cu films with nanometer-thick oxide layer. In order to form oxide layer on specimen surface, heat treatment in dry air was conducted at 120°C-140°C. After the heat treatment, we removed oxide layer by argon ion sputtering method for some specimens. In all specimens, the notch root became blunt by applying a monotonic tensile load, and a crack was initiated from the blunted notch root. The critical crack tip opening displacement (CTOD) for crack initiation was evaluated on the basis of FESEM micrographs.

This paper presents plastic deformation behavior on silicon surface of both defect and hydrogen. Two groups of silicon sample with/without surface damage introduced by reactive ion etching (RIE) and exposure to hydrogen plasma to introduce hydrogen into crystal, thus four types of samples were prepared. Depth profile and trapping state of hydrogen atoms diffused into each samples were measured by TDS and TOF-SIMS. Nanoindentation curve of each samples were compared under deep and shallow indentation depth. As a results, there found on change in indentation depth under same load level between two case with/without exposure to hydrogen plasma. In contrast to this, surface damage and hydrogen had significantly deeper indents than the other cases. These results suggested that plastic deformation of silicon is enhanced due to synergy effect of both defect and hydrogen even at room temperature.

To investigate an interaction between macroscopic and microscopic nonuniform deformation of polycrystalline pure copper, uniaxial tensile tests using various specimens having different curvature and different crystal grain size were performed. Specimens were annealed by different to vary grain size, and radius of curvature was changed in gage section to induce various stress gradient. To evaluate heterogeneous strain field in the surface of specimen, digital image correlation method was used in this study. The maximum stress for each specimen under uniaxial tension was also evaluated. Similar to Hall-Petch relation, the maximum stress increases with decreasing grain size. The curvature of specimen also affects to the maximum stress. The macroscopic nonuniform deformation enlarges the microscopic nonuniform deformation, and it increases the hardening due to GND. This trend was found for each annealing temperature. In fine grain specimen, strain distribution depends on specimen shape. In contrast, if grain size is large, order of microscopic heterogeneity approaches order of macroscopic nonuniform deformation. In such case, strain distribution depends on not only specimen configuration, but also grain distribution.

Multiple slip deformation in dispersion hardening alloys are numerically analyzed by using a crystal plasticity finite element technique the characteristics of macroscopic strain hardening are discussed. Strain hardening in each of slip system estimated by the density of statistically stored dislocations (SSDs). The increment in the SSD density was evaluated with the value of slip strain and the dislocation mean free path. It was found show that the strain hardening ratio was overestimated with experimental one when the critical resolved shear stress (CRSS) and dislocation mean free paths for secondary systems was chosen as the same scale dependency with those for the primary one. The reason for the over estimation is due to excessive activity of the secondary slip systems. The values CRSS of secondary systems are given by higher than the primary one. The results show strain hardening ratio is in good agreement with experimental one.

The passivation is a key component of interconnections in the electronic devices because it works as an electrical insulator and a shield against mechanical deterioration and chemical corrosion. In the interconnections, the accumulation of atoms due to electromigration (EM), which is the physical phenomenon of atomic diffusion with high density electron flow, causes the passivation fracture through the formation of nano/micro-structures. The passivation fracture threatens the reliability of electronic devices because the open/short circuits caused by the failures of interconnections are easily formed. One of the countermeasures to prevent fracture initiation of passivation is the deposition of thicker passivation. Although the study of passivation thickness is important because the increase in the passivation thickness would increase the resistance against the passivation fracture and the reliability of interconnections, the effect of the passivation thickness on the lifetime of interconnections against EM has been still qualitatively reported so far. The clarification of the failure mechanism of nonconductive passivation is required to propose the suitable passivation thickness against the passivation fracture by accumulation of atoms. In the present study, to propose the strategy for determining the suitable passivation thickness, the effect of passivation thickness on passivation fracture is examined through the experiments using an Al line covered with tetraethyl orthosilicate passivation. The behavior of passivation fracture with passivation thickness is newly formulated and can be explained by considering the critical tensile stress in the circumferential direction at the inner wall of a long cylindrical tube subjected to internal pressure. A suitable passivation thickness for required resistance against passivation fracture can be determined based on this finding.

Alumina bicrystals with {1120}/<1100> low-angle tilt grain boundary and (0001)/[0001] low-angle twist grain boundary were fabricated by a diffusion bonding method, and dislocation structures of the grain boundaries were observed by high-resolution transmission electron microscopy. The {1120}/<1100> low-angle tilt grain boundary consisted of the 1/3<1120> edge dislocations, and they were dissociated into the 1/3<1010> and 1/3<0110> partial dislocations with a stacking fault on the {1120} plane. The (0001)/[0001] low-angle twist grain boundary consisted of 1/3<1120> screw dislocations. In contrast to the 1/3<1120> edge dislocation, the 1/3<1120> screw dislocation was not dissociated into partial dislocations. We will discuss the basal slip behaviour based on the observed dislocation core structures.

Atomistic simulations were performed to reveal the pressure dependence of grain boundary structure and point defect segregation for symmetric tilt boundaries in MgO. We found that most of the boundaries studied transform to a different atomic arrangement at each threshold pressure more than once. In addition, the driving force for segregation of intrinsic vacancy was found to increase with the increase of pressure.

In order to investigate the effect of sessile dislocation on the fracture strength of nanoscale materials, fracture tests were carried out for nano-scale SrTiO₃ single crystal specimens with an array of sessile dislocations. The fracture strength of the specimens was about 30 % lower than that of a specimen without dislocation array. High resolution transmission electron microscope (HRTEM) observation indicated the fact that the dislocation can be a fracture starting point in nanoscale materials.

Dislocations, a lattice defect in crystals, have been believed to play an important role in determining plastic behavior of materials due to their mobility. Recently, a new role of dislocations as an initiation of brittle fracture was suggested by experiments. Here, we demonstrate fracture phenomena from dislocation cores and the mechanics using quantum-mechanics/molecular-mechanics (QM/MM) simulations. Our QM/MM simulations successfully reproduce fracture stress/strain and fracture morphology obtained by experiments. We also find that sequential local bond breaking of dislocation cores with loading is an origin of brittle fracture of dislocation. Therefore, we provides an insight into the new role of dislocations in crystals.

A dislocation in crystalline materials has dangling bonds at its core and strong strain field in its vicinity. Therefore, it has a potential to exhibit unusual physical properties. In this study, we investigated atomic structure and electric properties of dislocations in strontium titanate (SrTiO₃). In order to introduce dislocations in SrTiO₃, we fabricated a bicrystal with (001) low-angle grain boundaries by a diffusion bonding technique. TEM and STEM observations showed that a (001) low-angle tilt grain boundary mainly consists of [001] dislocations. This is consistent with the past reports. Then we carried out electrical measurement along dislocations at the boundary. It is suggested that electric conductivity along dislocations is different from that in bulk.

Zinc oxide (ZnO) is a representative wide band gap semiconductor and have long been used as a main constituent material of varistors because of its highly nonlinear current-voltage characteristics. Recently, ZnO has received growing interest due to its potential application in short wavelength optoelectronic devices as a substitute to gallium nitride. Although a large number of studies have been performed so far, most of them aimed to further develop the applications or to control point defects and grain boundaries, both of which play an important role on functional properties in ZnO. On the other hand, it seems that structure of dislocations, which dominate mechanical property and also affect functional property, have not been studied enough. In the present study, therefore, we aim to investigate atomic structure of a basal dislocation in ZnO using bicrystal experiment. It is suggested that a basal dislocation dissociate into two partial dislocations.

We investigate the emergence of single atomic scale multiferroics by a hole polaron in paraelectric and nonmagnetic CaTiO₃ using first-principles calculations. A hole localizes on one oxygen in CaTiO₃ with local lattice distortions, namely forming a hole polaron. Polarization is emerged at the local area of about 8 Å × 4 Å × 4 Å around a hole polaron because of lattice distortions induced by a hole polaron. In addition, magnetization is emerged on one oxygen where a hole polaron is formed because of spin polarization of a hole. The emergence areas of both properties are smaller than critical size where they vanish. Therefore, the local area where a hole polaron is formed exhibits polarization and magnetization and can be considered as a single atomic scale multiferroics.

Ferroelectric behavior in strained SrTiO₃ nano porous is investigated using phase-field method. We find, in the strained nano-porous, ferroelectric regions with some polarization vortices emerge around each pore. The ferroelectric region expands and connects each other with increasing strain, and finally forms a periodic structure in which the polarization vortex arrays with the unusual pattern. These findings suggest that we can mechanically tailor complex shape ferroelecirc nano structures, which leads to new functional devices.

Polymer foam is widely used in the engineering field because of various properties, e.g., lightweight, shock absorbing, insulation. However, the strength of the foam material dramatically decreases with the increase in the volume fraction of the pore. Therefore, evaluating the mechanical response and the strain distribution provides important information to understand mechanical properties of the polymer foam. In this study, three-dimensional non-uniform deformation behavior of low density polyethylene foam specimens having curvature of gage area during the tensile test is investigated by using the three-dimensional digital image correlation method. Effects of foaming method, expansion ratio and specimen size on the tensile test are evaluated. The microscopic structure such as cell size and connection of cells is observed by using X-ray CT. A remarkable strain concentration in the tensile direction was caused by the curvature of specimen. The strain in thickness direction distributed non-uniformly as well as the strain in tensile direction. However, the strain in width direction shows almost uniform distribution even in large deformation range. Large volume change caused in open-cell foam microstructure while almost no volume change was confirmed in closed-cell foam.

Semi-crystalline polymer (SCP) has very complex hierarchical structure consisting of a laminar structure of crystalline and amorphous phases in nm scale and a spherulite structure in μm scale. The inelastic mechanical behavior of SCP is usually explained by the slip deformation in crystalline phase. However, the folded molecular chain in crystal phase changes to the highly oriented structure in a large strain range. This change cannot be explain using only the slip deformation and a rigid rotation accompanied by the slip. In the present study, the inelastic deformation behavior of SCP is modeled by introducing the separation and recombination of the physical bonding of molecular chain into the rubber elasticity model. In-situ observation of elongation process of the spherulite of polypropylene revealed that the prominently localized deformation occurred in the equator area of spherulite. The softening due to the separation of the physical bonding may cause such a microscopic local deformation in the spherulite. The mechanical model was then constructed based on the separation and recombination of the physical bounding. The relationship of the stress and strain under the uniaxial tensile test predicted by the proposed model represented the softening followed by the hardening due to the orientation of molecular chain. Furthermore, the propagation of the local deformation zone, which is often seen in the tensile test of polymeric material, was also predicted by FEM simulation with the proposed constitutive equation.

The armchair-type graphene nano-ribbon (AGNR) with the width less than about 70 nm has the band gap at room temperature, and the band gap increases monotonically with the decrease in the width of AGNR. However, the electronic structure, in particluar band gap value varies frequently as a function of the number of carbon atoms along its width direction. In order to control the large variation of the band gap of AGNR, the electronic structure of various dumbbell-shape structure of AGNR was analyzed by first-principle calculations based on the density functional theory. By applying the dumbbell-shape AGNR structure, the large periodic variation of band gap appeared in perfect AGNRs was successfully decreased, though the electronic structure and the band gap of dumbbell-shpe AGNRs cahnged depending on the number of carbon atoms.

It is important to evaluate the magnetic property of magnetic storage devices which has very small size due to minitualization and high density. In this study, we propose a new scanning magnetic sensor combined by Atomic Force Microscopy (AFM) system and conductive nanocoil probe. Conductive nanocoil probe having an AFM tip combined with conductive micro/nano coil is possible to be used for magnetic evaluation according to the principle of electromagnetic induction. Furthermore, the conductive nanocoil probe has a distinctive feature which unites both observation and control of magnetic state at very small size, because the magnetic control is possible by the impressing current to the coil. To fabricate nanocoil on the AFM tip, the method of fabricating micro/nano coils which is based on a mechanical process, i.e., a straight nanowire is bent by depositing a thin film with a circumferentially nonuniform thickness on the nanowire, was used. The bending of nanowire is due to the misfit strain of the coated film. In order to enhance the bending, the heat treatment was conducted to induce a creep flow in the nanocoil, and to release the constraint of the nanowire on elastic bending due to film strain. From the result, the fabrication of nanocoil on the AFM tip with a high conductivity on the scale of 10⁶ Ω・m was achieved successfully.

In order to clarify the mechanical criterion of stress-induced chemical reaction of Ti/Si multilayered-nano-films, we conducted compression experiments for specimens with a notch fabricated from the Ti/Si multilayer by focused ion beam. Compressive displacement in the stacking direction was applied to the specimen by a diamond flat-punch tip using a nano-indenter under in situ field emission scanning electron microscopy observation. In the experiments, stress relaxation occurred when the displacement was held in the region where the nominal stress was 3000 MPa or higher. The stress relaxation also increased as the stress increased. In addition, transmission electron microscope observation after compression showed that a new layer with no multilayered structure was generated on the free surface at the notch. These results suggest the presence of a mechanical criterion of the stress-induced chemical reaction.

In a tensile test of a thin sheet specimen made of SUS304 at low strain rate, anomalous deformation behaviour accompanied with generation and propagation of an X-shaped region with higher strain can be observed in a later stage of deformation after maximum force point. Some past studies have considered the anomalous deformation behaviour is caused by strengthening because of strain-induced martensitic transformation (SIMT), however, the mechanism of the generation and propagation is still unclear. Since SUS304 indicates complicated deformation behaviour due to SIMT, a numerical simulation is necessary to clarify the mechanism. In this study, a 3D finite element analysis with a consideration of initial imperfection on yield of austenite is performed for the tensile test at low strain rate using a sheet specimen made of SUS304 by including a modified damage model.

In this study, the effects of random laminate misalignment on the microscopic mechanical behavior of ultrafine plate-fin structures are statistically investigated using the Monte Carlo simulation. For the mechanical analysis, thehomogenization theorybased on unit cell analysis is used. Moreover, the substructure method is introduced into the theory to deal with random laminate misalignment. The present method is applied to the analysis of microscopic stress and strain distribution and their concentration in ultrafine plate-fin structures made of Ni-based alloy with random laminate misalignment. Then, the analysis results are statistically examined using histograms. It is shown that the effects of random laminate misalignment on the mechanical behavior of the plate-fin structures become remarkably strong depending on the loading condition.

In this study, the development of an elastic-viscoplastic macroscopic constitutive model for woven composites and its implementation in the finite element analysis code LS-DYNA are conducted for structural analyses of woven composites. To this end, an elastic-viscoplastic macroscopic constitutive model which is able to express strong anisotropy of woven composites is introduced, and the material parameters in the model are determined based on the results of triple-scale homogenization analysis using mesoscopic and microscopic structures (unit cells). Then, the constitutive model is implemented in the LS-DYNA through a user defined material subroutine. The present method is then applied to a bending analysis of a cantilever beam made of quasi-isotropic plain-woven carbon fiber-reinforced plastic (CFRP) laminates with two types of laminate configurations. It is found that the present method can express strong anisotropy and inelastic behavior of woven composites. It is also shown that the present method can analyze their different behavior depending on the laminate configuration.

In this paper, we perform eigenvalue buckling analysis to investigate a defect of domain walls (DWs) in a diamond plate pattern (DPP), which is caused by swelling-induced pattern transformation in porous gel films. It is found that DWs in a DPP can be captured as long wavelength buckling. The critical stress of DWs in a DPP is higher than that of a uniform DDP, but as periodic units increase, both are identical. This means that this defect, i.e., DW, is hardly eliminated in DPPs. Further, the pattern of DWs consists of 4 basic buckling modes, which are obtained from extending the buckling mode of the DPP using the Bloch wave.

In this study, the authors incorporate the electrochemical analysis in the numerical plate testing (NPT) for multistage analysis by considering thermal strain, reduction strain and creep deformation of solid oxide fuel cell (SOFC). First, we perform an electrochemical analysis for an unit microstructure of flat plane SOFC classified into a composite plate composed of in-plane periodic structures. Based on the obtained distributions of oxygen potential and temperature from the electrochemical analysis, reduction and thermal strains are calculated. Considering these strains, we conduct a NPT for the unit microstructure by a commercial FEM software. Finally, we compare the NPT results with and without consideration of data from electrochemical analysis.

The Villari effect of magnetostrictive materials, a change in magnetization due to an applied stress, is used for sensor/energy harvesting applications. In this work, magnetostrictive fiber/polymer composites are fabricated for the first time by embedding strong textured Fe-Co fibers in an epoxy matrix, and their stress-rate-dependent output voltage characteristics are investigated. Compression tests are first conducted to measure the output voltage of a sample. A simple magnetomechanical coupling model of the magnetostrictive fiber/polymer composite is then established. The output voltage is predicted, and domain wall dynamics is discussed in relation to the macroscopic inverse magnetostrictive response (known as the Villari effect). The results show that the output voltage density of this novel Fe-Co fiber/polymer composite dramatically increases with increasing stress-rate and becomes larger than that of Fe-Ga alloy. Our work represents an important step forward in the development of magnetostrictive sensor and energy harvesting materials.

Metallic micro- or nano-wires show higher strength compared with their bulk counterparts due to their fine crystalline structures. Instead, they become brittle and the workability is decreased. In this study, for improving ductility, the crystalline grains of the 25 μm-thick Cu microwire are grown by Joule heating caused by supplying current through the wire. Moreover, small-span bending test was performed for the Cu microwires with and without heating, and it was confirmed that the yield stress of the Cu microwire was decreased by the heating.

The miniature specimens made from Sn-3.0Ag-0.5Cu (SAC) solder tend to show larger variation in the tensile strength than the ordinary size specimen. This means that the comparison of the internal structure between high-strength specimens and low-strength specimens will give valuable information to propose a method for giving high strength to solder joints in electronic equipment. Therefore, in this study, the tensile tests using miniature SAC solder specimens made by casting were conducted. The shape and distribution morphology of primary Tin crystal in the specimen after the tensile test were also investigated, and they were compared between high-strength specimens and low-strength specimens. The shape of each Tin crystal was represented as an ellipse by employing an image processing method. The length and the angle to the loading direction of the major axis of an approximating ellipse were used for representing the size and the distribution morphology of a tin crystal, respectively. Tin crystals the size of which was in the range from 10 μm to 15μm were most frequently observed irrespective of the strength of the specimen. Meanwhile, the orientations of the tin crystals in the size range were different depending on the strength. Namely, tin crystals the orientation of which made low-angle to the loading direction were observed frequently in the high-strength specimens, but not in the low-strength specimens.

Thoriated tungsten alloy (ThO2-W) has been used as cathode material in discharge lamp and for TIG welding rod because of its excellent thermoelectric emission properties. However, ThO2 is one of radioactive substances, therefore development of thoria free tungsten is desired. In this study, hafnium carbide (HfC) was used as an alternate material of ThO2. The material used, HfC-W alloys was produced with spark plasma sintering (SPS) and tensile strength of the alloy at elevated temperature was evaluated. Tensile strengths at 1300 and 1500°C increased with increasing sintering temperature. Increase of sintering pressure also enhanced tensile strength from 250 MPa to 281 MPa at 1300°C. According to microstructure observation by SEM-EDS in the materials used, coarse aggregates of HfC were observed in HfC-W sintered by SPS. It is considered that aggregate of HfC with lower relative density affects tensile strength of the materials used. Therefore, the high temperature strength is possibly improved by increasing sintering temperature and pressure due to dense aggregate of HfC. Moreover, strength may be improved by dispersing small HfC particles in the W-matrix to avoid formation of aggregate of HfC.

Stress corrosion cracking (SCC) is a degradation phenomenon induced by a combination of tensile stress and environment, and involves multiple processes ranging from micro (grain-sized) crack initiation to macro (millimeter-sized) crack coalescence and propagation. To evaluate the SCC life, it is necessary to consider the SCC process of crack initiation. In this study, to make clear nucleation behavior of stress corrosion cracks in a type 304 austenitic stainless steel (SUS304), oxalic acid etching test and constant load tests in tetrathionate solution were carried out using sensitized SUS304. As the results of etching test, nucleation of intergranular corrosion (IGC) was affected by grain boundary (GB) characters; low-angle GBs (less than 10 deg.) and some specific CSL GBs (∑3,∑5,∑11,∑13a, ∑15and ∑17a) exhibited the high resistance to IGC, although random GBs and the other CSL GBs were susceptible to IGC. As the results of constant load tests, stress corrosion cracks initiated at the random GBs and some specific CLS GBs. Based on the comparison of susceptibility of GBs to IGS with that to SCC, stress corrosion cracks selectively occurred at some GBs which exhibited susceptibility to IGC. Other factors, such as microscopic stress acting at GBs, may affect the susceptibility of GBs to SCC.

The authors have recently developed a first-order perturbation based stochastic homogenization (FPSH) method to predict the variability in the macroscopic properties of composite materials before manufacturing. Both geometrical and physical uncertainties at the microscale were considered in the stochastic multiscale modeling, i.e., the generation of RVE (representative volume element) models. The parameterization and statistical measurement of uncertainties have also been reported. As an extension of FPSH method, this paper mainly describes the formulation to predict the probabilistic density of microscopic strain under uniform macroscopic strain and damage probability. Short fiber reinforced composite materials are considered in this study, where RVE models were generated using Meshman_ParticlePacking.

Equivalent expression is derived for an ellipsoidal misfit double inclusion which consists of a nested sequence of two inhomogeneous inclusions whose electro-magnetic properties and orientations of semi axes are different from each other. The die-electric constant of the composite containing many misfit double inclusions is derived successfully by using the resultant equivalent expression. Moreover, by focusing on any inclusion in the cluster consists of many misoriented ones and by smearing out of its surroundings, the cluster can be regarded as the misfit double inclusion. Therefore, the die-electric constant of the composites containing such clusters is derived by using the same resultant equivalent expression.

Various models are proposed to the composite materials including clusters of reinforcements. In such models, the concentration of reinforcements in the cluster is generally very high or low compared to the outside region of the cluster. However, in realistic composite materials, the difference of concentrations inside and outside of the cluster is relatively small. In the present study, such a low-level clustering of reinforcements is modeled by replacing the cluster with the mixed double inclusion of the first kind by focusing on some reinforcement and smearing out of its surrounding. As a result, the total internal stresses occurring in the composite material are good agreement with those obtained by Taya et.al (JSME A,43-1(2000), pp.46-52.) in the high-level clustering of reinforcements. Moreover, they also agree with those of the random distribution of reinforcement as a limit of low-level clustering,

Tensile creep behavior of an injection molded short carbon fiber-reinforced polyamide (ICF/PA) composite was examined at room temperature with a particular emphasis on stress-dependence and orientation-dependence. Furthermore, a phenomenological creep model was developed and evaluated by comparing with the creep behaviors observed. Constant stress creep tests were performed on dumbbell-shaped specimens that are oriented from the flow direction at 0°, 45° and 90°, respectively. Creep strain was measured by means of a digital image correlation (DIC) method. It was observed that creep deformation develops more significantly with increasing off-axis angle from 0° to 90°. In addition, it was observed that creep deformation increases with increasing creep stress, regardless of specimen orientation. Transient creep behavior and steady creep behavior was observed over the range of time in this study, regardless of specimen orientation. An engineering model to describe the anisotropic creep deformation was developed taking into account the time-, stress-, and orientation-dependence of the creep behavior observed. It is based on the classical Bailey-Norton law that was extended to describe the creep behavior of transversely isotropic media. It is shown that the anisotropic creep behavior of ICF/PA can approximately be described by means of the transient creep model developed.

Recently, it is urgent to reduce the energy consumption rate from environmental problems such as global warming and the exhaustion of fossil fuels. However, it is difficult to reduce the weight and to improve the efficiency of cooling by using existing materials. In recent years, carbon fiber (CF) having high thermal conductivity, electro conductivity, and strength properties are used as reinforcing material in composite material. The Aluminum (Al) based composite material containing CF has higher thermal conductivity than pure Al. In addition, the extrusion method is a relatively inexpensive manufacturing method, and it has been found that it has high hardness and high filling rate. However, measurement of mechanical properties of the composite material comes short. In this study, the thermal conductivity and Vickers hardness of the composite material prepared using extrusion method are evaluated. According to these results, as the content of carbon fiber was increased, the filling rate decreased, but the thermal conductivity and Vickers hardness tended to increase.

The strength of glass fiber reinforced plastics (GFRP) was evaluated based on Puck's rule for validating as wind turbine blade materials. Glass fiber reinforced unsaturated polyester (GRU) resins and epoxy (GRE) resins were subjected to static strength tests. The strength dependence of GRU on the fiber direction was also evaluated according to the Tsai-Wu failure criterion. GRU showed higher values of tensile fiber failure (FF) and inter fiber failure (IFF) criteria of Mode B than GRE. On the other hand, GRU indicated lower compressive FF and IFF criteria of Mode A and Mode C than GRE. Furthermore, the tensile strength dependence of the GRU on the fiber direction followed Tsai-Wu failure rule. When the fiber direction was inclined by 4° from the loading direction, the strength of GRU decreased 50 % from the fiber directional value. We could define the manufacturing tolerance of the fiber direction quantitatively by the Tsai-Wu failure criterion for blade materials.

Titanium (Ti) alloy matrix composites (TMC) attract attention as aerospace materials owing to their outstanding specific mechanical properties in compared with the conventional Ti alloys. Among the candidates of reinforcement for TMC, Titanium boride (TiB) is one of the best candidates because TiB is chemically stable in Ti matrix and does not make any intermediate layer at Ti/TiB interface. However, it has been reported that TiB reinforced Ti alloy matrix (Ti-TiB) composite has the brittle fracture behavior in previous studies, and the relationship between the microstructure and fracture properties of Ti-TiB composite has not been discussed enough. In this study, we fabricated Ti-3Al-2.5V-TiB composites by the powder metallurgy process, and revealed that the fracture toughness of Ti-3Al-2.5V-7.5vol% TiB composite was 23 MPa√m. During the fracture toughness test, Ti-3Al-2.5V-TiB composites were immediately fractured when the load achieved to the critical value to propagate the crack. The SEM micrographs of fracture surface of Ti-3Al-2.5V-TiB composites implied that the crack selectively propagated inside of TiB whiskers. Therefore, it is likely that the optimization of microstructure in Ti-3Al-2.5V-TiB composites can improve the their fracture properties.

Cellulose nanofiber-reinforced composites have lower impact on the environment, but their poor mechanical properties are one of the major drawbacks. Therefore, we focused on the orientation control of the cellulose nanofibers in the composite matrix by applying a stretch treatment. This study examined the effect of the stretching treatment on the microstructural features and the mechanical properties of gelation PVA/cellulose nanofiber composites. The composite samples were subjected to apply larger amount of stretching strain (maximum stretching strain was 25%). The tensile strength was increased with increasing the applied stretching strain. Compared to the original sample (without stretching treatment), tensile strength of the stretched sample was increased by 180%. Consequently, it was found that larger stretching strain lead to higher strength and this increase seemed to be derived from the alignment of the cellulose nanofibers.

Effects of random R-ratio loading on fatigue life of a quasi-isotropic woven fabric CFRP laminate have been studied. A new methodology for generating random R-ratio loading is first developed with the help of the anisomorphic constant fatigue life diagram approach. In the random fatigue testing, different R-ratio waveforms of different stress levels are randomly generated for two constant values of life, respectively, and they are alternately sequenced to form a block that is repeatedly applied to specimens of the composite. Random loading test results suggest a strong interaction between the waveforms consecutively applied. It is demonstrated that the Miner life based on the controlled original waveforms in the random R-ratio loading is excessively optimistic. In contrast, the use of the Miner rule in conjunction with the rain flow method allows much better prediction of fatigue life with an accuracy of a factor of two.

The statistical distribution of fatigue life for a short carbon fiber-reinforced polyamide-6 composite and the effect of stress ratio on it are examined. A procedure for predicting S-N relationships for different constant values of probability of failure P, i.e. P-S-N curves, is proposed. Constant amplitude fatigue tests are first performed to obtain statistical samples of fatigue life at different stress levels and stress ratios (R = 0.1, 10 and R = χ = σ_UTS/σ_UCS), respectively. Static tensile and compressive strength data are also collected. To quantify the scatter of fatigue life, Weibull and lognormal distributions are fitted to the fatigue data obtained. The plot of fatigue data on a probability paper and the goodness-of-fit tests using the modified Kolmogorov–Smirnov suggest that both Weibull and lognormal distributions are acceptable as the distributions for the static strength data as well as the fatigue life data. The P-S-N curves at different stress ratios for different probabilities of failure (10%, 50% and 90%) are predicted for the two cases using the experimental data and using the anisomorphic CFL diagrams for different constant values of probability of failure, respectively, and they are compared to each other to evaluate the accuracy of the proposed theory.

1800 MPa-class ultra-high strength steel bar with an ultrafine elongated grain structure was fabricated through multi-pass caliber rolling at 500 °C for a 0.4C-2Si-1Cr-1Mo steel (mass%) with a tempered martensitic structure. The steel bar with an ultrafine elongated grain structure was warm formed into JIS M12 hexagon head bolts with a nominal length of 60 mm, and then their tensile properties were investigated by a wedge tensile test. Bolt heading was performed at 700 °C, and screw part was warm formed at 500 °C with a set of thread-rolling dies. In the ultrafine elongated grain structure, its transverse grain size was measured to be 0.3 μm, and a spheroidized carbide structure and a strong <110>//rolling direction fiber texture were developed through the warm caliber rolling. Such ultrafine elongated grain structure was also maintained in the bolt screw part. When the developed bolts were tensioned, all of them were failed at screw part. Delamination fracture, in which cracks propagated in the longitudinal direction of the bolt, occurred in the thread root. Hence, fracture appearance of the developed bolts was different from that of conventionally quenched and tempered bolts with a tempered martensitic structure. The developed bolts were demonstrated to be ductile and tough compared to the quenched and tempered bolts at ultra-high tensile strength level of 1800 MPa.

To investigate the interparticle bonding process of the powder particles during the compression shearing method at room temperature, unidirectional friction tests with different normal loads and number of sliding passes were carried out to uniaxial-compressed samples. Pure Cu is chosen as a material in this study and Pure Cu powder was compressed under the uniaxial normal stress of 1000 MPa in order to get compressed samples with the target size of 20 × 20 × 0.25 cm³. The relationship between the normal loads applied, the number of the sliding passes, and the bonding condition of the powder particles was investigated by observing the surface structure and the fracture surface of the samples after the friction test. The surface of the powder particles were deformed and bonded each other by applying a repetitive unidirectional sliding process. The thickness of the bonded each other region from the surface increased 1.0 to 4.0 μm by increasing normal load applied 4.0 to 27 N. The thickness of the bonding region did not change by increasing of the number of the sliding passes from 100 to 200. From these results, it was clarified that the normal load more effective for deformation and the bonding of the powder particles than the number of passes.

The strength reliability of fine solder joints must be evaluated by conducting a finite element analysis (FEA) considering the presence of the Cu/Sn intermetallic compounds (IMCs) layer, which consists of Cu3Sn and Cu6Sn5, generated at the interface between solder and copper wiring. To conduct such FEA accurately, the tensile stress-strain curves of the Cu/Sn IMCs are needed. Therefore, we proposed a method to estimate the stress-strain curve of the IMCs by conducting the tensile test using the miniature composite solder specimen with IMCs layer. The stress-strain curve estimated by the proposed method suggested that the both IMCs have material nonlinearity. This finding needs to be verified in some way, because the IMCs have been regarded as elastic materials for a long time. In this study, the shear tests using a copper-solder joint specimen, in which the solder joint has the IMCs layer, were conducted both experimentally and numerically. The numerical tests were conducted as FEAs, and the FEAs employed two different constitutive models of elastic model and elasto-plastic model to describe the deformation behavior of the IMCs. Collate the experimental results and the results of FEAs, we discussed the presence or absence of the material nonlinearity of the Cu/Sn IMCs.

In this paper, it is reported that an analyzing method of the elasticity and other deformation characteristics can be established by the reaction force of indentation testing. This method is adopting the analyzing procedure of indentation force to derive the deformation characteristics of materials in the ball indentation testing which is one of most fundamental testing. A flow of analyzing procedure of various behavior on the deformation of materials is also shown for the profile of variation of reaction force due to indentation test. Especially, the evaluation possibility of various behaviors included in complicated and nonlinear relationship of a profile of the reaction force due to the indentation test is shown by the inverse-analytical comparison between the force and the proofed indentation theories.

The subject of this paper is to calculate the residual stress occurred during heat treatments of the large forged steel using Finite Element Method (FEM). The analysis was carried out using a cylindrical FEM model of ASTM-A-470 used in rotor shafts for power stations. First, a heat transfer analysis was performed to obtain a temperature history, which is used to calculate material properties at varied temperatures. Then, using the temperature history, structure analyses were conducted considering both the creep deformation and the transformation plasticity. The residual stresses calculated by the structure analysis were compared with the value measured by experiments. As a result, the calculated residual stresses have the same tendency as the measured residual stresses when both the creep and transformation plasticity are considered. Therefore, the importance of both the creep and transformation plasticity for the structural analysis of the heat treatment of the large forged steels was confirmed. In addition, the effect of the cooling rate to the residual stress was also discussed.