Recently, HALT (Highly accelerated limit test) is used for an accelerated test of electronic products to evaluate the reliability of the products. Solder joints are important parts in electronic devices. Therefore, clarification of the deformation behavior and fracture of the solder joints due to HALT is required. In this study, a series of biaxial loading tests using copper-solder joint specimens is carried out in order to reproduce the deformation and failure of solder joint in HALT condition. The authors are trying to construct a method for fatigue life estimation based on the biaxial ratcheting test of solder joints considering HALT. In this study, both the thermal cyclic and mechanical vibration load were simulated by the cyclic torsion load and small cyclic axial load in the biaxial ratcheting test. As a result, the ratcheting strain increment greatly increased with increase in the superposed stress. In addition, the vibration load increases the ratcheting strain. These results coincide with the tendency for solder joint to fracture earlier in the HALT condition. Moreover, linear relationship between the ratcheting strain rate and fatigue life was obtained by the single logarithmic plot. These results suggest that the ratcheting strain rate may be design parameter for estimating fatigue life of solder.

Natural fiber composites receive wide attention as a sustainable material. The composite is toughened by fibers. Nano-C/C composites using Bacteria Cellulose have been developed, and present good tribological properties. In this study, we consider a natural fiber reinforced composite with random orientation of fiber and make a multi-scale model of the composite in order to clarify the characteristic of scratching on composite materials. The fiber structure filled with polymer matrix forms a natural fiber reinforced composite. To investigate tribological properties of the composite, we simulate a scratch test of the composite. The model consists of macroscopically homogeneous medium, microscopically inhomogeneous medium and a sphere. As we evaluate effective properties of the composite as a macroscopic homogeneous medium, a homogenization theory is applied. We demonstrate micro scratching on composite materials to clarify relation between load variation in scratching test and micro structure of composites.

Honeycomb sandwich panels are kind of composite panels constructed by adhering thin surface plates such as CFRP laminates or metal sheets with honeycomb cores made of aluminum or aramid materials. Honeycomb sandwich panels have light-weight and high strength performances. So they are widely used in many fields such as the transportation equipment field, especially for light-weight mainly required aerospace field. On the other hand, the merit of the honeycomb sandwich panels is effective only in the limited environment. For example, it is strong only when uniform loads are applied on the surfaces of the panels, while honeycomb cores show vulnerability with local concentrated loads applied. Under concentrated loads, it is possible that the strength of whole panel should be reduced due to local buckling failure inside the honeycomb core. However, no data on local buckling properties of honeycomb structures are widely publicized and testing methods are not clearly stipulated. Therefore, the purpose of this study is to grasp the local buckling tendency of honeycomb structures affected by design variables like foil thickness, cell size and specimen size (length, width, height dimension) of honeycomb structures. Compression tests on honeycomb sandwich panels having different design variables are executed to examine buckling performance under local impact loading.

The aim of this study is to fabricate micro bell-shape Al alloy which have micro order bell-shape pore in its body, and investigate its vibration characteristic by sound absorption test and damping test. First, the aggregates consisting of glass capsules and zirconia particles were fabricated by rolling granulation method. Second, micro bell-shape Al alloys were fabricated using the aggregates and Al alloy powder by original method. Also, porous Al alloy and Al alloy without pores were fabricated. Third, their vibration characteristics were investigated by sound absorption test and damping test. As a result, micro bell-shape Al alloy presented significant absorption characteristic for sound absorption test. Furthermore, it was seen that the bell-shape structure gap enable us to control absorption characteristics.

Stability of particle-packing structure was numerically studied using distinct element method. Complete spherical shape was assumed for composing particles while the radii were distributed in a certain range. First, the particles were set on lattice points of face-centered cubic structure, and the stability against the gravity was investigated. As a result, the structure was broken when the difference in radii of the particles was large. Then the stability against external load was simulated. In this case, the instability was observed earlier when the radius distribution was wide, whereas the structure was very stable when all particles had the same radius.

Dewetting of a liquid film leads to the formation of self-organized structures of substances that are initially distributed in the film. This phenomenon has actively been exploited to spontaneously pattern nanomaterials on a solid substrate surface, and the location where the self-organized nanomaterials form can precisely be adjusted when the dewtting dynamics is regulated using micro-/nanopatterned templates. However, such templates are generally fabricated by lithography-based methods, which involve complex processes and specialized facilities that are not readily accessible. Here, we show that periodic ridges of a diamond-like carbon (DLC) film that arise as a consequence of a mechanical instability can effectively be used to manipulate the dewetting manner of a liquid film containing DNA molecules on a flat substrate, which results in the formation of DNA nanowires that align unidirectionally with a given spacing.

Braided structures which consist of warp and weft yarns has been used in many structural applications. Over the decades, the deformation behaviour of braided structure has been studied by many researchers. However, in most cases, the effect of slippage of yarns has been neglected, so their predictions overestimate the actual response. Although the existing studies considering slippage of yarns, there are some limitations for the movements of yarns. The main purpose of our study is to propose an estimation equation for the deformation and frictional response of braided structure based on FEM analysis. In particular, the effects of yarn’s geometries and material properties on the response have been investigated systematically.

Robots and apparatuses used as welfare equipment are conventionally made of metal as a structural material. In recent year, a light structure material for mobile equipment is required for improvement of physical support or help. Therefore, composite material for these uses is expected to satisfy high strength, high rigidity, and low density. In this study, Sirasu Balloons (SB), the micro glassy hollow spherical materials with improved interface bond strength, are used for reinforced composites. The matrix was epoxy resin. Its surface treatment was done by using silane coupling agent treatment, because the weak interfacial debonding between SB and a matrix was observed in recent work. The hybrid composite was designed by using reinforcing carbon fibers with core composite materials. Izod impact test was performed for cylindrical specimen of the composites. The impact properties were examined from the experimental results. By using scanning electron microscope (SEM), the observations for the interfacial debonding were performed from the viewpoint of micro-mechanical study. Consequently, the Izod impact strength of the composite was about ten times larger that of the core composite alone. In addition, silane coupling treatment improved the interfacial debonding because destroyed SB was observed from SEM photo for fracture surface. By controlling the interfacial strength, the crack growth resistance was increased.

Recently, solar power generation attracted attention among natural energy. There are various design methods for the steel structure on which solar panels are mounted. When we examine the strength and rigidity of photovoltaic system, we use beam model in FEM analysis. Therefore, we focused on snow load, which is one of design loads in this research. By comparing the experiment with the analysis and evaluating the buckling caused by the snow load. And we report on FEM model of the joint part which is the cause of buckling.

In this study, the elastoplastic bending collapse of thin-walled tubes subjected to statically pure bending has been studied by using finite element method (FEM).There are many researches about thin-walled tubes subjected to statically pure bending, but there are few researches about elliptic tubes. In Particular, the effects of tube's geometries (high length a, and width length b) and on the maximum bending moment were discussed by comparing with cylindrical tube. It is revealed that the maximum moment of the elastoplastic tubes are controlled by the flattening ratio of tube. Also, it is shown that the flattening ratio of tube can be expressed by axial and circumferential stress as function of the material and geometrical properties and curvatures. Based on FEM results, the stress distribution of elliptical tube is similar to that of cylindrical tube. On the other hand, the flattening ratio of elliptical tube is approximated by using the modified coefficient relating the aspect ratio (b/a). By approximating the flattening ratio of elliptic tube, maximum moment of elliptic tube can be estimated with a good accuracy.

Fracture of the bonded dissimilar materials generally initiates near the interface, or just from the interface edge due to the edge stress singularity. In this study, the stress intensity factor of an edge crack close to the interface between the dissimilar materials is considered. The small edge crack is strongly dominated by the singular stress field near the interface edge. The analysis of stress intensity factor of small edge crack near the interface in bi-material and butt joint plates is carried out by changing the length and the location of the crack and the region dominated by the interface edge is examined. It is found that the dimensionless stress intensity factor of small crack, normalized by the singular stress at the crack tip point in the bonded plate without the crack, is equal to 1.12, independent of the material combination and adhesive thickness, when the relative crack length with respect to the crack location is less than 0.01. Therefore, the stress intensity factor of the small edge crack can be simply evaluated not only in the bi-material plate but also in the butt joint plate.

In this study, the relationship between the impact speed and the compressive at failure stress of the micro lattice structure has been studied using the finite element method. Based on the numerical results, the following conclusions have been obtained. Firstly, the stress-strain diagram of the lattice structure is divided into two curves: plastic yielding of the center beam (Stage 1) and the crushing of the beam composed of inclined beams (Stage 2). The maximum load can be attained when the inclined beams yeild. Secondly, the maximum stress of the lattice structure varies with the impact speed, and it depends on the buckling mode.

In this study, the theoretical model for estimating the equivalent elastic modulus (tensile modulus E_eq and shear modulus G_eq) of composite structures has been proposed and compared with FE results. In this model, the displacement along the loading direction is assumed to describe the hyperbolic function, and the minimum potential energy scheme is used for deriving unknown parameters in the function. This model was applied to two cases of inhomogeneous structures (honeycomb core with defects and honeycomb sandwich panel), and the effects of the structure's geometry on the relative error were discussed.

We study the snapping responses of a hemispherical arch with the inhomogeneity distribution of bending rigidity contacting in a rigid plane. We first introduce the elastica model with the inhomogeneity distribution of bending stiffness depending on the arc-length. Since the elastica involves geometrical nonlinearity and a contact problem involves unknown moving contact boundary, the problem yields a nonlinear free boundary value problem. To solve the problem numerically, we transform the free boundary value problem to the fixed boundary value problem by making a change of variables and then we use a continuation scheme with a relaxation method. We examine how the inhomogeneity distributions of bending rigidity affect the load-displacement responses and the critical loads for the snapping as well as the dropping loads after the snapping. We demonstrate that the snapping response can be tuned by controlling the distribution of bending rigidity of the arch.

This paper investigates the tangle deformation of a loop body connected with elastic tube segments and revolute hinges. We prepared three types of segment geometry: a straight tube, a necking tube, and a bellows tube. Demonstrating the traction tests for these elastic loop structures, we observed that the bellows-type model only formed the tangle conformation induced by torsional rotations of the discrete hinges while the structures having the other types of segments shrank without torsional rotation. According to the mechanics of materials, we discuss about the relationship between bending and torsional stiffness of each segment to clarify the tangle mechanism of the proposed structures.

An axisymmetrical partial sphere-shaped crack problem was analyzed by body force method. Though the treated problem can be considered as one of the simplest curved surface crack problem, a reliable reference solution could not be found in the literature. In the present study, we developed special program base on the standard body force method to improve the mesh-free body force method which is recently developed by authors.

People who have lost a part of their bones due to accidents, injuries or illnesses are subjected to bone graft surgery. This study focuses on metallic implants used for artificial bone grafts. There are three bone graft methods for bone defects caused by diseases such as cancer and accident injuries: Autogenous bone grafts, Allografts and Artificial bone grafts. This study focuses on metallic implants used for artificial bone grafts. Conventionally used implants of titanium alloys have the problems that the burdens on the patient are increased due to their excessive rigidity and overweight than human bones. Meshed GUM Metal plates with lower elasticity, high strength and high biocompatibility are introduced to solve the over stiffness & weight problems of ready-used metal implants. Basic mesh shapes are designed and applied to GUM Metal plates using 3D CAD modeling tools. Bending properties of prototype meshed GUM Metal plates are evaluated experimentally and analytically. Meshed plate specimens with 180°, 120° and 60° axis-symmetrical types were fabricated for 3-point bending tests. The pseudo bending elastic moduli of meshed plate specimens obtained from 3-point bending test are ranged from 4.22 GPa to 16.07 GPa, within the elasticity range of natural cortical bones from 2.0 GPa to 30.0 GPa. Analytical approach method is validated by comparison with experimental and analytical results for evaluation on bending property of meshed plates.

There are concerns about strength reduction and fatigue fracture due to stress concentration in currently used medical stents. To address these problems, meshed stents applied by mesh structures were interested for achieving long life and high strength perfromance of medical stents. The purpose of this study is to design basic mesh shapes to obatin three dimensional (3D) meshed stent models for mechanical property evaluation. The influence of introduced design variables on compressive characteristics of meshed stent models are evaluated through finite element analysis using ANSYS Workbench code. From the analytical results, the compressive stiffness are changed periodically with compressive directions, average results need to be introduced as the mean value of compressive stiffness of meshed stents. Secondly, compressive flexibility of meshed stents can be improved by increasing the angle proportional to the arm length of the mesh basic shape. By increasing the number of basic mesh shapes arranged in stent's circumferential direction, compressive rigidity of meshed stent tends to be increased. Finaly reducing the mesh line width is found effective to improve compressive flexibility of meshed stents.

Recently in Japan, degenerative intervertebral discs have a sign of epidemic as one of diseases caused by aging and lifestyle habits. Degenerative intervertebral discs include lumber disc herniation, intervertebral disc herniation and cervical disc herniation. Currently practiced treatments called spinal fusion surgery using pure titanium or titanium alloy implant products have the problem that the loads on the natural-bone of the human body are large and will cause overloading on healthy nature bones. GUM Metal has characteristics of lower elasticity rigidity, large elastic deformation, higher strength and biocompatibility etc. When it is used for implant applications, there is still problem like overloading on the natural-bone because of its high rigidity compared with the human bones. Therefore, the purpose of this study is to create more flexible meshed plates for implant applications from the viewpoints of elastic rigidity and volume density. Basic mesh shapes are designed, devised and applied for meshed GUM Metal plates using three dimensional (3D) CAD tools. Experimental evaluation on tensile fatigue characteristics of meshed GUM Metal plate specimens are carried out. Analytical approaches on stress evaluation are also executed through finite element method to obtain the S-N curve for fatigue characteristic evaluation.

In recent years, the number of patient of locomotive syndrome has been increasing due to advancement of aging society. Knee osteoarthritis is one of those pain. In order to prevent this symptom, we develop shoes sole fitting to personal walk characteristics. In this research, we measured the sole pressure of a subject by using the measurement apparatus by which three dimensional ground reaction force can be measured. We examined the characteristic of the right foot of a man of the 23 years-old physically unimpaired person. The shoe sole pattern areas was designed by following aspects; (1) At the heel area, the vertical reaction force was concentrated at the central part rear of the heel area and the horizontal reaction force was observed highly at the front of the heel area. Therefore, we design the sole pattern by embedding a shock absorbent material into the central part of the rear heel area and an abrasion-resistant material into the rear heel area. (2) The horizontal reaction force varies direction back and forth at rear of MP joint in the toe area. For the design of the sole pattern, an abrasion-resistant material is put into this area. (3) The vertical reaction force was concentrated near the second finger. Therefore, we design the sole pattern by embedding the material with high bending rigidity into the whole area of the toe. The effect of designed shoe sole on the change of personal walk characteristics was discussed from the experiments.

In the present study, a theoretical analysis of the one dimensional unsteady thermal stress problem is dealt with. The beam has the inhomogeneity in the material properties which are expressed in the form of power of the coordinate variable in the height direction. It is assumed that the inhomogeneous beam is subjected to cyclic heat supply at the upper surface, and the lower one is insulated thermally. Analytical solution of temperature change is derived from the unsteady heat conduction equation for the inhomogeneous beam by means of the Laplace transform and inverse one using the residue theorem. The solution is able to express the temperature change in the beam whose specific heat capacity has inhomogeneity in the form of power with arbitrary real index. Analytical solutions of axial displacement, deflection, and thermal stress resulted from the temperature change are derived from the equations of equilibrium for the inhomogeneous beam under the condition of simple supports. Performing numerical calculation, the effect of the inhomogeneity in the specific heat capacity on the temperature change, axial displacement, deflection, and thermal stress is discussed briefly. As the inhomogeneity parameter in the specific heat capacity increases, the phase lag in the temperature change of the inhomogeneous beam increases, and the temperature amplitude decreases.

A low cost solid sensible heat storage system using concrete and industrial waste as a heat storage medium has been considered in the heat storage system of concentrating solar thermal power generation plant. Ferronickel slag produced as a by-product in the refining of ferronickel can be used as a low cost solid sensible heat storage medium. In this study, the effect of ferronickel slag mix on heat storage in the mortar hollow circular cylinder block using ferronickel slag as a fine aggregate is evaluated by both heating test of the heat storage block and numerical calculation of heat storage based on unsteady heat conduction analysis.

It is important for industry products to keep enough adhesive strength between inorganic materials and organic materials. Therefore silane coupling agents are employed for various applications. Silane coupling agent consists of the hydrolyzable group which reacts to an inorganic material, and the organic functional group which reacts to organic material. The most suitable combination of hydrolyzable and organic functional groups must be found and the efficient design of molecular structure is desired. The adhesive strength was investigated for various silane coupling agents by experimental and numerical approaches, but it is not enough. In this paper, the influence of the molecular structure of the silane coupling agent on the adhesive strength with the metal layers was investigated through first-principles calculation. Chromium layer was used for metal layer, γ-mercapto propyl tri methoxy silane and γ-amino propyl tri methoxy silane were selected for silane coupling agent. The cohesion energy of two silane coupling agents were compared to discuss the difference of adhesive strength. Calculations indicated two silane coupling agents are found similar energy curve, and γmercapto propyl tri methoxy silane generates higher adhesive strength with metal layer than γ-amino propyl tri methoxy silane as silane coupling agent.

FEM analysis was conducted with the joint as the contact area, and the stress concentration factor of the male wood and female wood was calculated. Based on the results, we proposed a formula to calculate the stress concentration coefficient of male wood and female wood. From the calculation formula, it was possible to obtain the optimum sickle jaw width S when the length of the head portion length L was determined. In addition, a sickle joint was made by using homogeneous material acrylic, a tensile test was conducted, and the validity of the proposed stress concentration calculation formula was examined. As a result, the trends of the experimental result and the analysis result roughly agreed. Therefore, it can be said that the proposed formula is valid.

Wooden materials and biodegradable polymers have attracted much attention as promising materials to achieve carbon neutrality and biodegradability. To ensure the quality of wooden materials, nondestructive evaluation techniques need to be developed. On the other hand, the films and fibers made of poly-L-lactic acid, as one of biodegradable polymers, are expected to be employed in the human-machine interface devices and surgery instruments. For safe operation of applications using these materials, the thermoelectroelastic field inside the material must be elucidated. From a mesoscopic viewpoint, both materials are considered to have D_∞ symmetry, which is characterized by an infinite rotation axis and a two-fold rotation axis perpendicular to it. In this study, we analyze the thermoelectroelastic field in a body with D_∞ symmetry. As an example, we treat a semi-infinite body subjected to a combined load of the surface shear and temperature fluctuation. Following the summary of the analytical method derived by us, the elastic, piezoelastic, and thermoelastic displacement potential functions are obtained by applying that analytical method and the Fourier transform techniques, and the thermoelectroelastic field quantities are explicitly formulated. By numerical calculation, the field quantities are investigated qualitatively and quantitatively. As a result, the importance of thermal considerations in the sensor applications using D_∞ bodies.

In this paper, the fracture problem of a functionally graded thermal barrier coating (FGTBC) containing a crack parallel to the interface between the FGTBC and a homogeneous substrate is considered. The problem is solved for the laminate that is suddenly heated from the upper surface of the FGTBC. The bottom surface of the homogeneous substrate is maintained at the initial temperature. The crack faces are supposed to be completely insulated. Material properties are assumed to be exponentially dependent on the distance from the interface. By using both the Laplace and Fourier transforms, the thermo-mechanical fracture problem is reduced to a singular integral equation and a system of singular integral equations which are solved numerically. The stress intensity factors of the crack are computed and presented as a function of the normalized time for the various values of the nonhomogeneous and geometric parameters.

In this study, a one-dimensional dynamic electro-elastic problem in an infinite functionally graded piezoelectric (FGP) thin plate subjected to mechanical and electrical loadings is analyzed by employing the method of characteristics, assuming that material properties vary in the thickness direction according to a power low distribution. Utilizing the electrical constitutive equation and the equation of electrodynamics as well as the electrical initial and boundary conditions, the dielectric flux density is expressed in terms of the displacement at the boundary surface and the applied voltage. It follows that the dynamic electro-elastic field is governed by the elastic constitutive equation and the equation of motion. By introducing the particle velocity which is the partial differentiation of the displacement with respect to the time variable, this problem finally reduces to numerically solving two characteristic equations established on two characteristic lines. Numerical simulation has been carried out for the FGP thin plate composed of PZT-4 and steatite. The effect of the applied voltage on the unsteady oscillation of dynamic stress is investigated for various values of the volume fraction exponent and the applied voltage which completely cancels the unsteady oscillation from the time history of dynamic stress is determined for each volume fraction exponent by using the trial-and-error method.

This work deals with the dynamic bending and energy harvesting characteristics of tennis rackets for smart devices both numerically and experimentally. First, static loading test was performed to measure the strain on the frame of commercial tennis racket. And, experimental data were then employed to determine the applied load to the tennis racket model of finite element analysis (FEA). After determination the load for analysis, FEA was conducted, and the strain and stress in the racket frame and grip were predicted. Next, the tennis racket model including piezoelectric plate under concentrated load was analyzed and the stress in piezoelectric plate was discussed in detail. And, the induced voltage was evaluated and examined the dependence between the induced voltage and position of the implant also. The impact energy harvesting ability for smart device was then discussed in detail. It was found that the tendency of strain of FEA is good agreement with experimental measurement. There are some stress gaps at the interface between CFRP and Urethane. And, z-direction normal stress in Urethane is almost zero and the normal stress in CFRP is dominant. The induced voltage increases with approaching the fixed end of the grip.

The hydrogen atom interacts various lattice defects and secondary particles in a material, causing a degradation in the tensile strength and elongation, well-known as hydrogen embrittlement (HE). Such material-hydrogen interaction should be extensively investigated to elucidate a precise mechanism of the HE. This study investigated hydrogen-entry properties and hydrogen state of an aluminum alloy 6061-T6 exposed to high-pressure hydrogen gas by means of thermal desorption analysis (TDA) and secondary ion mass spectrometry (SIMS). The TDA revealed that the hydrogen entry in the alloy occurred under the present hydrogen-exposure condition and the hydrogen was trapped by an extremely-deep trapping site, compared to ordinary trapping sites (lattice, dislocation, and vacancy) previously reported. To detect reliable signals of hydrogen trapped in the alloy by SIMS, removal of background-originated hydrogen derived from water or hydrocarbon molecules and verification of false signals produced due to a difference in sputtering rate between the phases were thoroughly conducted. Consequently, it was revealed the hydrogen was trapped by micrometer-sized intermetallic particles.

In order to experimentally verify the fracture mechanism of a precipitation-hardened superalloy with internal hydrogen, we performed SEM observation of fracture surface and cross sectional area beneath the fracture surface of an A286 iron-based superalloy subjected to an internal hydrogen tensile testing, which was carried out in air after being charged with hydrogen under 100-MPa hydrogen gas at 270 oC. The internal hydrogen drastically deteriorated the ductility of the precipitation-hardened A286, accompanied by formation of many facets on the fracture surface. The presence of hydrogen may make dislocations easier to pile up at grain boundaries, inducing nanovoids, followed by microcracking along the grain boundaries. Consequently, many tiny dimples occurred in numerous facets on the fracture surface. The observation results imply most of the facets were formed due to dislocation pile-ups at the grain boundaries which were enhanced by the presence of hydrogen and subsequent growth to the microcracks.

In order to investigate the effects of hydrogen gas pressure and temperature on fatigue crack growth characterizations of low carbon steel JIS-SM490B and low alloy steel JIS-SCM435, fatigue crack growth tests using a CT specimen were conducted in pressurized gaseous hydrogen in various temperature. In low-pressure hydrogen gas, the fatigue crack growth rate was decreased with increasing of temperature. On the other hand, in high-pressure hydrogen gas, the fatigue crack growth rate was not depending on temperature. The mechanism of fatigue crack growth under hydrogen environment with various temperature and pressure was discussed based on the theory of dislocation trapping of hydrogen.

In order to clarify the effect of hydrogen on the fatigue life properties of austenitic stainless steel welds, 317L and 308, fatigue life tests were performed in 115 MPa-hydrogen gas at room temperature. The specimens for fatigue life test were extracted from a weldment by tungsten inert gas (TIG) welding. The base metals of multi-pass weldment were SUS316 (hi-Ni) bar for 317L steel weld, and SUS304 plate for 308 steel weld. Two series of weld metals were tested; one was as-welded (AW) metal having coarse columnar grain with dendrite and δ-ferrite, and the other was post-welded solution-treated (PWST) metal having coarse equiaxed grain without dendrite and δ-ferrite. In high-pressure hydrogen gas, the fatigue limits both as 317L and 308 welds were not decreased, as compared with that obtained in air. In modified S-N curves that considers the deference of tensile strength between AW and PWST metals, the fatigue life properties of 317L steel weld showed good agreement in that of base metals, whereas there was a large discrepancy between the fatigue life properties of 308 steel weld and base metal. The fatigue life property of AW metal was higher than that of PWST metal both in 317L and 308 steel welds.

It is regarded as an important issue for achievement of hydrogen society to use safety and economical steels in the high pressure hydrogen gaseous environment. Materials used for high pressure hydrogen tank in FCV (Fuel Cell Vehicles) are high Ni balance austenitic stainless steels because of those high hydrogen embrittlement resistance. However, for spread of FCV the usage of economical and commonly used material like SUS304 is expected. Therefore, an applicable test method and criteria to evaluate the hydrogen embrittlement susceptibility of materials is being studied in high pressure gaseous hydrogen environments. The material compatibility is measure by SSRT (Slow Strain ate Technique) test and fatigue life test under the most severe environment. Materials which meet criteria in the high pressure hydrogen environment by SSRT test will be compared a fatigue limit in high pressure hydrogen environment and that in the atmospheric environment. The test results will be discussed from the standpoint of stability of microstructure and hydrogen embrittlement mechanism.

For the storage and transportation of compressed gaseous hydrogen in forthcoming hydrogen energy-based society, hydrogen-assisted fatigue crack growth (HAFCG) in structural steels is one of the most considerable problems from the perspective of life-cycle assessment or safety use of the hydrogen-containing components. In this study, fatigue crack growth tests of a commercially pure iron were conducted in laboratory air and 0.7 MPa gaseous hydrogen at room temperature, in order to elucidate the fundamental mechanism dominating the crack growth acceleration in steels with BCC lattice structure. The tests revealed dramatically accelerated crack growth rate in presence of hydrogen in association with significant change of fracture morphology (ductile striations to quasi-cleavage). The mid-thickness fracture paths in air and hydrogen were analyzed by using several characterization techniques including electron-backscattered diffraction (EBSD), electron channeling contrast imaging (ECCI), and transmission electron microscopy (TEM), achieving critical and direct evidence indicating that hydrogen dramatically suppressed the evolution of dislocation structure beneath the fracture surface and enhanced the fracture along {100} plane . These results implicate that the cause of HAFCG in BCC steels is the hydrogen-induced reduction of the interatomic cohesive force, leading to the fracture along cleavage plane, in addition to the localization of plasticity into the crack tip region as was reported in previous research.

Burst test of Type-3 FW vessel (normal working pressure: 19.6MPa, capacity: 2.1L) wound with and without GFRP layer were examined. Observing the cross section of the CFRP layers, microscopic structures such as fiber volume fraction Vf and the edge part of the hoop layer was measured. Analyzing the stress by FEM model considering inhomogeneity of fiber packing the burst pressure was predicted.

Type III FRP pressure vessels were used in hydrogen stations because of lightweight and long lifetime. However, fatigue cracks occur due to repetitive charging and discharge of hydrogen. Therefore, nondestructive inspection technique is required in order to prevent an accident. In this study, we analyzed the AE signal propagating in Type III pressure vessels and we investigated the characteristics of Acoustic emission (AE) propagation as a function of AE source position. Pulse YAG laser was used as artificial AE source to simulate the damage of Type III pressure vessels. Wavelet transform of waveform detected by PZT sensor was carried out. When aluminum liner was used as a sound source, low frequency component of A₀ mode in aluminum was detected, while it was not seen the waveform packet of lamb wave of carbon fiber reinforced plastic (CFRP). From this result, the possibility of classifying whether the AE generating member is aluminum liner or CFRP was classified.

The meso-scale simulation, where the carbon fiber bundle structure with resin is explicitly handled, seems promising for rational setting of burst criteria of Type IV hydrogen vessel. Material properties including fracture models both for carbon fiber and resin can be directly introduced. The stress and strain concentrations caused by fiber bundles crossing are adequately analyzed to predict burst pressure in terms of carbon fiber strain. The advantage of the proposed methodology is demonstrated by the numerical example and future possibility is discussed.

This paper presents the fatigue life evaluation method for TypeIIICarbon Fiber Reinforced plastic (CFRP) accumulators. Using axisymmetric FEM model, we performed stress analysis, and calculated stress amplitude of liner based on the 2015 ASME Boiler & Pressure vessel code to evaluate the fatigue life of the vessel.

Failure analysis of hydrogen compressor (hydrogen pressure : 20 MPa, number of cycles to failure : 6.1×10⁶ cycles) was conducted. Chemical composition analysis, Microstructure observation, tensile test and Vickers hardness measurement showed that the material used was SCM440H which was sound. SEM observation of fracture surface showed that the connection part of hydrogen compressor was fatigue-failured. The maximum stress σ_max = 573 MPa of cyclic loading was estimated from fracture toughness K_IC = 199 MPa・m^1/2 for SCM435. It was inferred from the maximum stress σ_max = 573 MPa and S-N diagram (stress ratio R = 0) of SCM440 that the connection part was fatigue failured at the number of cycles to failure N_f = 6.1×10⁶ cycles.

The effect of hydrogen on flaking and fatigue cracking in contact compressive fatigue of SUJ2 bearing steel were investigated using steel ball having artificial small hole. In this study, compressive fatigue test up to 10⁷ cycles were carried out in 3 different environment : 1) 70 MPa high-pressure hydrogen, 2) ambient air and 3) 10^-5 Pa high vacuum. In cases of high-pressure hydrogen, crack was initiated in all steel balls. on the other hand, in case of vacuum, there are no flaking. Therefore, it is seemed that hydrogen diffused to steel ball was harmful to fatigue properties of steel ball. But, in this time, there are no white etching area (WEA) at the flaking part of steel balls.

In order to evaluate the influence of local stress and hydrogen concentration on delayed fracture property for high tensile strength steel, we have carried out SSRT, Slow Strain Rate Technique and CLT, Constant Load Test, of notched specimens under cathodic hydrogen charging. As a result, quantitative relationship between diffusible hydrogen content and tensile strength was obtained by notched specimens. There is little difference between these experimental methods, SSRT and CLT.

In order to inspect the inside of a small diameter metal pipe easily, an endoscope using a camera or a visual observation has been put into practical use. But there are a lot of problems to inspect a pip, for example, internal scratches can not be judged. Therefore, an ultrasonic probe installed in a pip using an electromagnetic acoustic transducer has been studied.

Carbon-fiber-reinforced plastic (CFRP) is one of the composite materials which have been employed widely in our society. In addition to the low density of CFRP, the tensile strength is 10 times higher than that of the conventional steel. Due to various fields used, the production amount has increased in recent years. However, there is a problem for CFRP: lack of recycling method for used CFRP. In the present work, an attempt was made to propose recycled CFRP (rCFRP) technology, in which used CFRP was crushed with two different sizes: 0.1 mm × 0.007 mm (milled CFRP) and 30 mm × 2 mm (chopped CFRP). In addition, two different resins were employed: epoxy and unsaturated polyester. The tensile properties were experimentally investigated. With increasing the chopped CFRP, the tensile strength increased for both unsaturated polyester and epoxy resin samples, while the reduction of ductility occurred. Thus, chopped CFRP reinforced both resins. On the contrary, the material ductility enhanced with increment of the milled CFRP until 20%, which is attributed to the change of the material characteristics: dimple based failure occurred with addition of the milled CFRP. However, rCFRP for a high content of milled CFRP 30% made the large size of blow holes leading to low ductility.

Nanowire is a cylindrical object with nano-order diameter. Because of its low number of defects such as dislocations and twins, nanowire has very high strength. However, its relatively large surface volume fraction compared to bulk materials, enhances its corrosion. This problem inhibits its application. Corrosion of nanowire can be treated as a diffusion of impurity atoms into a base material. This phenomenon is modeled by a diffusion equation. When impurity atoms intrude into the base material, volume expansion occurs. The volume expansion induces internal stress. This stress effects on the diffusion. To count this effect into the diffusion equation, we defined chemo-mechanical potential, which includes internal stress (mechanical effect) to a chemical stress (mechanical effect). A very large volume expansion may causes yielding. Because the stress and the diffusion are coupled, the yielding causes a non-contiguous effect on the diffusion. So we considered the effect of yielding. And we also considered blocking effect, decrease of apparent diffusion coefficient induced by high impurity concentration. We modeled hydrogen diffusion in nickel nanowire counting these effects. We numerically solved the diffusion equation. The obtained results tell that yielding delays the diffusion and it suggests the possibility of diffusion control by external stress.

In order to give creep resistance to the PTFE gasket, a particulate-filler is compounded. Indentation test was carried out using TMA with Berkovich indenter to evaluate the viscoelastic characteristics of a PTFE based sheet gasket. The time-temperature superposition principle using W.L.F equation was applied to obtain the master curve of the creep compliance of gasket material at elevated temperature. We found that the higher the blending ratio gets, the stronger the creep resistance becomes by examining the influence of this particulate-filler blending ratio on creep characteristics of gasket.

Blanking process is very efficient because it can be processed at once by using a press machine. Therefore, the blanking process is used in wide range of fields. The cutting surface of the blanking process is composed of sag, shear surface, fracture surface. The sag and fracture surface may be problem in products. Thus, it is important to suppress the occurrence of sag and fracture surface. To suppress them, even if many dies are proposed, they cannot be tried in terms of time and cost. Owing to this background, the prediction of cutting surface by numerical method such as finite element method (FEM) is useful. In the previous studies, blanking process analyses were carried out in several materials, process conditions and ductile fracture criteria and the cutting surface that coincided well with the experimental result was obtained. However, it is necessary to investigate whether this prediction method of the cutting surface can be applied to other materials and processing conditions. In this study, the prediction of shear length was carried out by using the critical fracture value in ductile fracture criteria proposed by Cockcroft and Latham and Ayada in the blank element at the tip of the punch. The results show that Ayada fracture criterion is more applicable to predict the shear length under the current condition than that of Cockcroft and Latham fracture criterion.

Judo has been compulsory at junior high school in Japan since 2012. However, judo has a higher mortality rate than other sports, and countermeasures are urgently required. The main cause of death accidents in judo is acute subdural hematoma (ASDH). ASDH is caused by the brain moving in the cranium due to a strong impact on the head and rupture of the bridging vein connecting the brain and skull. The purpose of this study is to examine the head protection material which can suppress the relative displacement at the time of head collision based on the relation between the strain of the bridging vein and the relative displacement of the brain and skull. As a result of optimizing the cranial deceleration curve, relative displacement decreased by about 20 %. And in the experiment using the head model, the deceleration curve and the relative displacement in the combination of buffer materials were measured. The results showed that the relative displacement was minimized in the combination of buffer materials that was closest to the deceleration curve obtained by optimization. Therefore, the result obtained by optimization is considered to be reasonable, and the optimal combination of buffer materials is low repulsion urethane 10 mm and cardboard with honeycomb structure 20 mm.

Bercovich tip indentation was performed with an instrumented hardness testing machine in order to measure dynamically indentation load-depth curves. The hardness of a high purity aluminum tricrystal was examined and the depth profile of indents was measured with a laser confocal scanning microscope. It was found that sink-in was formed around the indents. A constant value of hardness was obtained when the load was 100mN or larger. However, the hardness increased with decreasing the load when it was below 100mN.

A wooden baseball bat may break after hitting. The breakage occurs in various forms and the causes are still unknown. In this study, the stress generated by impacting a ball was obtained with three-dimensional finite element analysis. The analysis includes the impact force due to the ball and also the inertial force generated by the moving bat in swinging. The FEM shows the variation of stress distribution with the collision points. As compared with the observation of more than 150 broken bats, the model can successfully locate the points of breakage.

Much attention has been paid to composites made from biocompatible ceramics and metals in the medical field because the composites are expected to exhibit high biocompatibility and mechanical performance. The mechanical properties of interface between ceramic phase and metal phase should be elucidated to evaluate the mechanical properties of the composites. In this study, we fabricated square pillar-shaped specimens with an Al₂O₃/Ti interface by a spark plasma sintering (SPS) technique under various sintering conditions to investigate the sintering process of the Al₂O₃/Ti interface. Firstly, their microstructure was observed with an optical microscope and element diffusion near the interface was measured with an electron probe microanalyzer (EPMA). Then, the Vickers hardness tests and bending tests were carried out to evaluate their mechanical properties. As the results of EPMA measurement, Al atoms were diffused into the Ti phase, while Ti atoms were not diffused into the Al₂O₃ phase. The thickness of reaction layer created at the interface in Ti phase increased with increasing sintering time. As the results of hardness tests, the Vickers hardness was constant in the Al₂O₃ phase, while that in the reaction layer in the Ti phase was low, compared with that in the Ti phase. As the results of bending tests, brittle fracture occurred at the Al₂O₃/Ti interface, and the bending strength was lower than that of monolithic Al₂O₃ and their composites.