Many researchers adopt electrical resistance change (ERC) methods to detect damage in Carbon Fiber Reinforced Plastic (CFRP) laminates. They usually apply the method under tensile or bending loads. For compression tests, a block type specimen is used. The block type specimen, however, is too thick to obtain a uniform electrical current. This study starts with the design of a compression test specimen with uniform electrical current using a sandwich beam specimen. The four-point bending tests revealed that the piezoresistivity of the compression tests was the same as that of the tension tests. Using a three-point bending test, fiber-micro-buckling was obtained, which caused an increase in electrical resistance with residual compression strain. Non-linear behaviors observed during cyclic loading tests were investigated, and it was revealed that the plastic deformation at the loading point had large effect.

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With a view to examine the axial crushing behavior of thin-walled structures, which are used as energy-absorbing components of transports under various dynamic compressive loads, some thin-walled circular and regular polygonal tubes were investigated mainly by the FEM simulation. The former examination was focused on the effects of the reinforcement with circular ribs placed at regular intervals in the axial direction and the moderation of load undulations due to corrugated pattern on the load-displacement relation. On the other hand, the latter examination was focused on the effects of the shape of cross section (the number of apexes and the thickness). The absorbed energy per unit volume and some indexes of efficiency were used for the examination of those axially crushing tubes. Especially, the effective range of the interval between ribs, the aspect ratio of rib, the dimensions of corrugation, and the number of apexes were primarily discussed from the view point of the comprehensive efficiency which laid emphasis on the absorbed energy per unit volume.

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In order to investigate oxidation behavior and cracking susceptibility of the Ni-Cr alloys under extremely-low oxygen partial pressure, three Ni-Cr alloys (Ni-14Cr, Ni-22Cr and Ni-30Cr) were used as plate specimen and reverse U-bend specimen for oxidation experiments for 750 hours at 400 °C in two kinds of gas system (inert gas and dry steam) under various oxygen potential (Ni stable, Ni/NiO equilibrium and NiO stable). The Ni-Cr alloys cracked along grain boundary both in inert gas system (with trace O₂, without H₂O) and in hydrogenated steam. In the inert gas system, the cracking susceptibility was confirmed in near NiO stable condition. On the other hand, no crack was found in near Ni stable condition. In the dry steam system, the cracking susceptibility was confirmed in near Ni/NiO equilibrium. In contrast, no crack was found in near NiO stable condition. The cracking susceptibility was confirmed in near Ni/NiO equilibrium in hydrogenated steam as contrasted with higher oxygen potential in inert gas system. This result shows that potential range for the cracking susceptibility seemed to be different between the two kinds of gas system. Cracking severity was highest for Ni-14Cr and lowest for Ni-30Cr both in inert gas and steam; however, even Ni-30Cr was not immune to intergranular cracking in steam near Ni/NiO equilibrium.

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A Monte Carlo simulation model for the process of stress corrosion cracking (SCC) in structural materials under non-uniform stress condition has been proposed. The possible number of crack initiations is set for a given space and initiation times for all cracks are assigned by random numbers based on exponential distributions depending on stress level. Sites and lengths of the cracks are assigned by random numbers based on uniform distribution and normal distribution, respectively. Coalescence of cracks and subcritical crack growth are determined based on the fracture mechanics concept. Through the SCC process in the model, the influence of semi-elliptical surface cracks is taken into consideration. SCC simulations were carried out on an area around a weld line by taking account of residual stress distribution. Multiple parallel cracks were obtained along the weld line. Numerical examples exhibit the applicability of the model to describe the SCC behavior observed in real structures.

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This paper describes two user subroutines developed within ABAQUS to simulate coupled hydrogen transport equations. Developed user subroutines incorporate two key features in coupled hydrogen transport equations, such as the hydrostatic stress and plastic strain effects on hydrogen transport, and hydrogen-induced dilatational deformation rate. To validate developed subroutines, present simulation results are compared with published results, showing good agreements for all cases considered.

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In the present work, austenitic stainless steel 316L (SS316L) samples were implanted with Ni and Ni-Cr. A nickel-rich layer about 100 nm in thickness and a Ni-Cr enriched layer about 60 nm thick are formed on the surface of SS316L. The effects of ion implantation on the corrosion performance of SS316L are investigated in a 0.5 M H₂SO₄ with 2 ppm HF solution at 80°C by open circuit potential (OCP), potentiodynamic and potentiostatic tests. The samples after the potentiostatic test are analyzed by XPS. The results indicate that the composition of the passive film change from a mixture of Fe oxides and Cr oxide to a Cr oxide dominated passive film after the potentiostatic test. The solutions after the potentiostatic test are analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). The results reveal that Fe is selectively dissolved in all cases and a proper Ni and Ni-Cr implant fluence can greatly improve the corrosion resistance of SS316L in the simulated polymer electrolyte membrane fuel cells (PEMFCS) environment. They are in agreement with the electrochemical test results that the bare SS316L has the highest dissolution rate in both cathode and anode environments and the Ni and Ni-Cr implantation reduce markedly the dissolution rate. After the potentiostatic test the interfacial contact resistance (ICR) values are also measured. Ni and Ni-Cr are enriched in the passive film formed in the simulated PEMFC cathode environment after ion implantation thereby providing better conductivity than that formed in the anode one. A significant improvement of ICR is achieved for the SS316L implanted with Ni and Ni-Cr as compared to the bare SS316L, which is attributed to the reduction in passive layer thickness caused by Ni and Ni-Cr implantation. The ICR values for implanted specimens increase with increasing dose.

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Ni-base alloy is widely used in light water reactor component and the recent study has shown stress corrosion cracking (SCC). Over the years various attempts have been made to obtain mechanism of SCC but it still require more fundamental study to understand clearly. This study presents an approach based on the multiscale modeling, to assess the influence of alloy composition and stress intensity on the initial stage of solid state oxidation of the Ni-Cr alloy. The multiscale modeling considers different length scales such as finite element method (FEM) / quasi-continuum (QC) / quantum chemical molecular dynamics (QCMD), for analyzing crack tip molecular domain. The compact tension (CT) specimen of alloy 600 has been loaded for stress intensity, after that the micro region has chosen for the QC model which is a combination of continuum and atomic method. Finally, the deformed atomic position has picked for the QCMD simulation with some water molecules. The simulated results show that the chromium segregates faster than nickel atoms from the surface and make preferential bonding with oxygen. The preferential bonding forms a passive film. Applied stress intensity deformed the structure which may increase the atomic distance. As distance increases the absorption of water molecule or OH or oxygen into lattice increases. The stress intensity raises the crack tip solid state oxidation that may enhance SCC initiation.

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The mechanical behaviors of solid-liquid two-phase materials are affected by environmental conditions because of the moist structure of the materials. Therefore, material tests to investigate the solid-liquid interactions in these materials should be conducted by considering various conditions such as multiaxial stress, temperature, and fluid concentration. Here, the deformation of biological soft tissues having high liquid content is also dependent on multiaxial conditions including hydrostatic stress. However, it is difficult to evaluate the condition dependency of tissues because no equipment has been developed to realize low-load sensing under hydrostatic stress conditions. In this study, a pressure vessel for a tensile testing system is developed to evaluate the pressure dependence of biological soft tissues. This vessel can be attached to the tensile testing system that can be used to evaluate the viscoelasticity of tissues. A non-friction sealing system with a film on the vessel wall is adopted to measure the load; this load is verified by carrying out a tensile test with a linear spring under pressure conditions. In particular, the error caused by the opened/closed condition of the vessel is calibrated by the verification results, and the load applied to the specimen is precisely measured by using the tensile system with the pressure vessel. After the calibration, a tensile test for biological soft tissue is carried out under varying pressure conditions. The experimental results indicate that the stress-time curves for each condition exhibit good agreement and the tensile system with the pressure vessel has good applicability to evaluate the pressure dependency of viscoelastic behavior.

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In this research, the Osteoarthritis of Hip Joint was pick up, the 3-dimensional stress freezing method of photoelastic method was applied, and the state of the stress in the normality hip joint and the transformable hip joint was examined. The direction and the singular point of principal stress and stress distribution were experimentally examined. At result, The Osteoarthritis of Hip Joint touches by 2 points, Osteoarthritis of Hip Joint occurrence of the new singular point with flat of the femoral head, They change the direction of the principal stress line in an existing singular point is cause.

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A three-dimensional maxillary bone model was constructed using CT-images. The distribution of Young’s modulus was also estimated from the bone mineral density distribution. Four or six implants were embedded into the maxillary model and a metal prosthesis was attached to the implants. Computational analysis of the maxilla model was performed in order to characterize effects of the number of embedded implants on the stress state of the maxilla under two different loading conditions. For the two loading conditions, the distribution of strain energy density was severely concentrated especially around the right-molar implant, suggesting bone damage and absorption in this region. The 4-implants model with rear implantation and shortened prosthesis showed almost the same value of strain energy density in the 6-implants model. It is thus concluded that this kind of 3-D modeling could clinically be used for predicting the optimal position of implantation corresponding to each patient.

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To improve the strength of adhesively bonded composite joints, surface modification of composites by nanoimprint lithography (NIL) is investigated. Since microstructures can be fabricated during the curing of composites, this technique reduces the time required and costs involved in conventional surface preparation such as chemical etching or sand blasting. Since structural adhesives are susceptible to peeling, a pyramidal microstructure is chosen for the surface modification pattern. Such a pattern divides the stress at the interface into peel and shear components; thus, the apparent joint strength is greater than that of an untreated joint with a flat surface. We fabricated the pyramidal microstructure on carbon fiber reinforced plastic and determined the adhesive strength both analytically and experimentally. In the analysis, interfacial stresses were calculated using the finite element method and the interfacial fracture was defined using the peel and shear mixed-mode criterion based on the average stress criterion. In the experiment, tensile butt joint tests were performed for NIL and untreated joints and the apparent strengths were measured. The NIL joint was found to be 52% stronger than the untreated joint according to the finite element method calculation and 67% stronger according to the tensile tests.

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Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combination. This paper deals with a central interface crack in a bonded infinite plate and finite plate. Then, the effects of material combination on the stress intensity factors are discussed. A useful method to calculate the stress intensity factor of interface crack is presented with focusing on the stress at the crack tip calculated by the finite element method. For the central interface crack, it is found that the results of bonded infinite plate under remote uni-axial tension are always depending on the Dunders’ parameters α, β and different from the well-known solution of the central interface crack under internal pressure that is only depending on β . Besides, it is shown that the stress intensity factor of bonded infinite plate can be estimated from the stress of crack tip in the bonded plate when there is no crack. It is also found that dimensionless stress intensity factor F_I <1 when (α+2β)(α-2β) >0, F_I >1 when (α+2β)(α-2β) <0, and F_I =1 when (α+2β)(α-2β) =0.

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Epoxy-Steel composites have been used widely for lightening and strengthening mechanical structures. This paper deals with the stress analysis and strength estimation of epoxy-steel composite joint in which a hollow cylinder (epoxy) is fitted at the outside surface of a solid cylinder (steel) subjected to torsional loads. The interface stress distributions in the epoxy-steel composite cylinders under external torsion are analyzed using an axisymmetrical theory of elasticity as a two-body contact problem. In the numerical calculations, the effects of Young’s modulus and the diameter of the solid cylinder on the interface stress distributions are examined. It is found that the shear stress increases as Young’s modulus and the diameter of the solid cylinder decrease. A valid method for estimating the singularity is proposed. Using the interface stress distributions and analogous tests, the joint strength is predicted. In addition, the values of the joint strength were obtained experimentally. It is seen that a rupture initiates from the upper edge of the interface area when the torsion is applied to the upper end of the solid cylinder. For verification of the present analysis, FEM calculations are carried out. The numerical results are in fairly good agreements with the experimental results and the FEM results.

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In this study, effect of bond thickness upon the strength and fracture toughness of epoxy adhesive dissimilar joint is investigated. Tensile and three-point-bending (abbreviated as 3PB hereafter) fracture tests are conducted. Finite element method (abbreviated as FEM hereafter) analysis is also executed to analyze the stress distribution at an interface corner of dissimilar joint. From FEM analysis results, it is found that the stress singularity in the dissimilar joint exists pronouncedly at the SUS304/adhesive interface corner and the order of stress singularity in the tensile model is higher than that in the 3PB model. Moreover, the order of stress singularity in the dissimilar joint having bond thickness of 1.0 mm is quite identical to the value obtained from analytical solution under the plane stress condition. From 3PB test and tensile test, it has been confirmed that the failure stress of dissimilar joint slightly increases with the decreasing bond thickness and can be well predicted by using the interface corner toughness, Hc parameter. The failure of dissimilar joints always originates from the SUS304/adhesive interface corner and the failure stress for dissimilar joint of 3PB test is higher than that of tensile test. For the specimens failed at the ALU/adhesive interface corner, the poor wettability of ALU adherend’s surface plays an important role. For the dissimilar joint with an interfacial crack, the fracture toughness, Jc is calculated by J integral method in FEM analysis. Fracture toughness, Jc for cohesively fractured specimens is more or less constant but shows some dependency on bond thickness for interfacially fractured specimens. Locus of fracture can be best interpreted in terms of stress singularity order at the interfacial crack tip.

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Stress singularity frequently occurs at a vertex in an interface due to a discontinuity of materials. The stress singularity fields are one of the main factors responsible for debonding under mechanical or thermal loadings. The stress distribution near the vertex in the interface is very important to maintain the reliability of joints. In this paper, stress singularity at a vertex in transversely isotropic piezoelectric dissimilar material joints are analyzed. Eigen analysis based on FEM is used for stress singularity field analysis of piezoelectric dissimilar material joints. The eigen equation is used for calculating the order of stress singularity, and the angular function of elastic displacement, electric potential, stress and electric displacement. Stress and electric displacement fields demonstrate that the values near stress singularity line of the joint are larger than that at the inner portion. From the numerical result, it is suggested that delamination of the interface may occur at the interface edge of the dissimilar piezoelectric material joints due to the higher angular function at the free edge.

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In the present paper, an influence of interlayer thickness on the singular stress field in 3D adhesive joints with three layers are investigated using eigen analysis formulated by finite element method (FEM) and boundary element method (BEM) using fundamental solutions for two-phase materials. A model for analysis is a three-layered block joint composed of Si, resin and FR-4.5 (Flame Retardant type 4.5, a kind of glass epoxy resin), which constitutes CSP (Chip Size Package) in the electric device. All stress components are expressed as spherical coordinate systems where their origins are located at the vertex of each interface. Firstly, the orders of stress singularity for vertex and lines characterizing singular stress fields are calculated from eigen analysis. Secondly, distributions of stress for the model subjected to an external load are calculated using BEM. Then, the intensity of singularity is derived from these results. Furthermore, 3D intensity of singularity is determined for evaluating a bonding strength in the 3D three-layered bonded joints. A relationship between the 3D intensity of singularity and the thickness of interlayer is finally examined. It was found that the 3D intensity of singularity becomes a small value when the interlayer thickness reduces, and the 3D intensity of singularity attains an upper limit when the interlayer thickness is larger than the width of the model.

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The objective of present study is to present solution to determine the stress and displacement fields around an interface edge of a joint formed by quarter planes in which materials behaves as an elastic and a power-law hardening material. J₂-deformation plasticity theory under plane strain condition is assumed for the power-law hardening material. Both the balance of force and the continuity of displacements are satisfied on the interface iteratively. The stress fields are found to be singular with the type of r^{λ_i -1} singularity from the i-th order approximation, where r is the radial distance from the interface. The power of r in the stress equation depends on the hardening exponent n. (i +1) or more singular terms exist in the i-th order approximation for n < (i +1)/i .As n is increased the absolute value of the i-th order of singularity, |λ_i-1| ,tends to be decreased to zero when λ_i-1<0.

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A method to evaluate pick-up performance of four kinds of adhesive tape materials with different thickness has been studied numerically and experimentally. Needles peel an IC chip with an adhesive film off the base material in the pick-up process, by pushing the back of the base material. In our evaluation method, the dependence of the peel energy on the peel speed was measured using a peel test. The finite element method was applied to calculate the energy release rate of the pick-up process for various peel lengths. The pick-up time was obtained from the results of the peel tests and the finite element analysis. Our results indicate that the peel energy is the dominant property influencing the pick-up performance, and the difference in energy release rate in the pick-up process between the samples is not significant. Furthermore, the minimum needle displacement was estimated from the calculated pick-up time using our method. The minimum needle displacement of the experimental pick-up values was in good agreement with the estimated result.

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Ni-Ti alloys are typical shape-memory materials. It is suggested that the atomic-scale phase transformation between martensite and austenite crystalline phases is responsible for such function. However, it is reported that these alloys sometimes show also amorphization together with nanocrystal under severe deformation. The mechanism of amorphization should compete against martensitic (crystalline) transformation (MT). This study focuses on the atomistic relation between amorphization and MT in Ni-Ti alloys. Molecular dynamics simulation is performed by using our simplified potential built on the MEAM framework. The change in crystalline state is identified and traced mainly by developing common neighbor analysis (CNA) method. Under amorphization from B2 cubic structure, the characteristic topological change in CNA cluster around a transforming atom is detected. By applying simple shear in periodic specimen, it is found that the martensite phases appear first then amorphous phases are formed. The nucleation of amorphous phases is strongly dependent on choice of shear plane, e.g. {100}, {110} or {111} plane. When the shear direction does not match to the orientation of inherent slip system, amorphous phase is nucleated with relative ease and remains for a long time. It is recognized that dislocation slip (plastic deformation), MT and amorphization are closely related in atomic scale. The direction of phase transition is mostly "B2(austenite)"→"B19'(martensite)"→"amorphous", except for the case of {111} shear plane which possesses "pre-amorphous" structures. It is found that the "pre-amorphous" is once formed and then disappears, preceding martensite phase or principal and later formation of amorphous phase.

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For the investigation of nature of mechanical instability in a large-scale atomic system, we propose a simplified analytical method that can describe unstable deformation with reduced degrees of freedom by introducing linear elements. The approach is applied to a three-dimensional atomic structure with a crack under tension, and it successfully reproduce the minimum eigenvalue of the Hessian matrix of the potential energy before the dislocation emission, namely instability criterion, as well as its deformation mode at the junction of the crack tip and surface. The computational load is considerably reduced in comparison with the original method, enabling us to address the mechanical instability issues in a large-scale atomic system. Moreover, the critical area that mainly dominates unstable deformation can be determined using the proposed method.

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This paper is to study the impact of partially-debonding damage on the effective elasticity of particle reinforced composites (PRC). The particles would lose a part of load-carrying capacity after the interface partially-debonding happens. The damage degree is determined by damage variable parameters in terms of the debonding angle. Two sets of prevailing definitions of damage variable parameters, i.e. Zhao’s and Liu’s, are verified by finite element method (FEM), and the deficiencies of them are clearly demonstrated. To better characterize the effect of the partially-debonding damage, damage variables proposed by Wada are incorporated into an explicit micromechanics model to predict the effective properties of PRC. Finally, the accuracy and efficiency of the developed method are confirmed. In order to deeply understand the inherent damage mechanism, FEM is utilized to analyze the specific stress distribution in and around a debonded particle, and the evolution of the average particle stress with the debonding angle is revealed.

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Since a solid-state heat engine using a shape memory alloy (SMA) works at the temperature difference of several ten degrees, the development of the SMA-heat engine to use the low-temperature thermal energy around 373K is greatly expected from a view-point of global warming prevention. The working principle of the SMA-heat engine is discussed based on the recovery stress of the SMA. The output power characteristics of a tilt-disk offset crank SMA-heat engine and the basic working properties of a solar-powered car using an SMA-heat engine are investigated. The subjects for the development of the SMA-heat engine are also discussed.

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Sputter-etching was applied to type 303, 304, 430 and 420 stainless steels to form conical or ring-shaped protrusions on the surface, and the tensile test of the substrate with protrusions, the press and scratch tests of protrusions were carried out. The tensile test shows that the conical protrusion is ductile, and the delamination and dropping out of the protrusions from substrate never occur before fracture of the substrate. The press test of the protrusions reveals that the conical protrusion is so strong to form deep hole on the counter rod of aluminum alloy although the tip of the protrusion is flattened. The scratch test of the surface with conical protrusions shows a large change of friction force with increasing scratch distance, whereas relatively small change of friction force for ring-shaped protrusions due to a smaller height and a narrow space between each ring wall. The maximum scratch force for a typical conical protrusion is about 40mN.

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Recrystallization microstructure evolution in cold rolled low carbon compact strip production (CSP) steel was observed by means of optical microscope and transmission electron microscope (TEM).The influence of fine precipitates on microstructure of strip steel during the recrystallization annealing was analysed by using Small Angle X-ray Scattering (SAXS) technique, and the textures evolution was investigated by means of ODF analysis. It was found that the deoxidation residual solute precipitate at the grain boundary during rapid cooling in the CSP process, these fine particles responsible for retarding ferrite grain coalescence and growth during annealing, thus the recrystallization microstructure of CSP strip steel show unique characteristics.

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