It would be possible to understand the mechanism for forming a compressive residual stress field around the crack tip by measuring the stress directly. It would also be possible to contribute to the construction of a crack growth model that enables us to explain a retardation effect on crack growth. In this study, the process of the forming a compressive residual stress field around the crack tip caused by overloading was examined using the X-ray diffraction method. In order to examine the effect of overloading, the stress intensity factor of 30MPa√m was applied to the specimen, which K=25MPa√m had been applied. The measured stress near the crack tip after the overloading was reduced to by 23-44% in comparison with before the overloading was applied. Through this experimental approach, a formation of the compressive residual stress field around the crack tip as well as the effect of the overloading on a stress reduction was revealed.

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Triphasic theory has been proposed to integrate mechanical, electrical and chemial phenomena for hydrated soft tissues. Though having been applied to biomaterials such as cardiomyocyte and cartilage, the following two difficulties have prevented the theory from wide range of applications. The first is huge calculation cost; ”multiphysics” makes degree of freedoms large, and chemical or electrical phenomena limit the time step. The second is difficulty of parallelization due to interaction complexity. Therefore size of the model is restricted to unproductively small. To achieve large-scale analysis, we propose an effective algorithm on time discretization and parallelization. We separated mechanical, electrical and chemical variables and updated with different timesteps, sufficient for each phenomenon. Separate time discretization and incorporation of properly updated interaction terms achieved low-calculation-cost interactive analysis. With regard to parallelization, the whole analysis was partitioned based on spatial segmentation of mechanical mesh. Electrical and chemical meshes are generated after separation so as to use communication methods commonly and to access other physical quantity directly within each processor. Finally, the algorithm was applied to cardiomyocyte model of 17 million degree of freedoms and a parallel computation with 256 processor cores was presented.

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In this paper, time-dependent dimensional change in quasi-isotropic laminates induced by relaxation of thermal residual stress and physical aging was predicted by the classical lamination theory. CFRP with pitch-based carbon fiber and cyanate ester resin was chosen for the study. Viscoelastic properties were investigated by performing tensile creep test for unidirectional laminates in the transverse direction. In addition, shrinkage strain induced by physical aging was studied by measuring the strain change of unidirectional laminates as well. Shrinkage strain in off-axis layers was calculated by using the coordinate-transform method. Shrinkage strain in 60° and 45° laminates were measured and the results were compared with the calculation. From the comparison, it was found that shrinkage strain of off-axis layers can be calculated by using the coordinate-transform method. Experimental results were applied to the classical theory in order to predict the time-dependent dimensional change of quasi-isotropic laminates. The strain change in quasi-isotropic laminates was obtained experimentally, and the result was compared with the prediction. It was verified that the time-dependent deformation of quasi-isotropic laminates can be predicted with a με-order by using proposed prediction method.

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Rolling contact fatigue tests of JIS-SUJ2 steel were performed using plate specimens having a small drill hole with various diameters and depths. In all the tests, fatigue crack initiated at the edge near the bottom of the hole just after starting the fatigue test, and then propagated by shear mode. Even in the unbroken specimens tested up to N = 2×10⁸ cycles, a short fatigue crack was found at the edge. Fatigue life, N_f, plotted against the maximum contact pressure, q_max, was greatly varied according to the diameter and depth of the hole. The effect of the depth at crack initiation on the fatigue life N_f was uniquely characterized by using the nominal shear stress amplitude, τ_a, instead of q_max. Further, based on the consideration of the rolling contact fatigue strength as a small shear-mode crack problem, the fatigue life data were plotted using the novel parameter, τ_a/(√area)^-1/6, where the √area is a projected area of the hole. Consequently, all the fatigue life data were successfully fitted on a unified line irrespective of the diameter and depth of the hole, i.e. a defect size dependence in the rolling contact fatigue strength was manifested in a small crack regime. Moreover, the fatigue life data for smooth specimens fractured from an internal non-metallic inclusion were also in accordance with the data for the drill holes in the plot of N_f versus τ_a/(√area)^-1/6. The result infers that a lower limit of the rolling contact fatigue strength of bearings with various dimensions can be evaluated by means of the following two dominant parameters: (i) maximum inclusion size predicted by the statistics of extremes in a given control volume and (ii) the maximum value of nominal shear stress amplitude produced under the rolling contact.

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In general, internal cells are required to solve deformation of thin plate with arbitrary distributed thermal load using conventional boundary element methods (BEM). However, in this case, the merit of BEM, which is the easy preparation of data, is lost. In this paper, it is shown that deformation analysis of thin plate with arbitrary distributed thermal load can be solved without the use of internal cells by using the triple-reciprocity boundary element method. Distribution of arbitrary thermal load is interpolated using boundary integral equations. The problem of thin plate according to Kirchhoff's theory is formulated by means of two coupled Poisson's equations to be expressed in integral form using the second theorem of Green in the classical way. A new computer program was developed and applied to several example problems.

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The roll used in a heat treating furnace is called hearth roll, which has been changed very frequently. This is because high temperate of a furnace induces wear on the roll surface in short period. This paper deals with a new roller structure consisting of ceramics sleeve connected to two steel shafts by shrink fitting because the ceramics has high temperature resistance and high corrosion resistance. However, attention should be paid for the risk of fracture due to the thermal expansion difference between ceramics and steel. In this study the finite element method is applied to calculate the stress appearing at connecting parts with varying the geometries of the shaft. To design the structure safety, it is found that tapered shaft with smaller thickness is most designable for the ceramic hearth roll.

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In this research, a technique has been developed for quantitatively evaluating the amount and distribution of tensile and compressive residual stresses by using combined strain measurements under the spherical indentation loading together with the finite element method (FEM). When the spherical indentation is applied to the top surface of a steel plate, the elastic strain at an optimized position near the indentation is measured by strain gauges, where the residual stresses and applied indentation stresses are largely superimposed. In order to analyze the residual stress, FEM analysis has been conducted to establish the relationship between the elastic strain adjacent to the indentation and the indentation load for steel plates subjected to various uniformed tensile and compressive bending stresses, also it has employed using the physical property values appeared in different substrates in accordance with Young's modulus and yield strength. A strain energy term (U^*) has been newly introduced by integrating along the trajectory between the indentation load and elastic strain in a range from 0 to the maximum load. We have obtained the certain relationship between a strain energy term (U^*) and residual stress in influence of physical property values which is expected to contribute for enhancing reliability verification of steel parts.

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Self-sensing Carbon Fiber Reinforced Plastics (CFRP) is one of the attractive multifunctional composites. That multifunctional composite has structural strength/stiffness and sensing function using electrical resistance changes. For the self-sensing, electrical contact between the lead wire and the carbon fibers is the most important issue. The present study focuses on the effect of the long term cyclic loading of lower applied strain range than the fatigue damage initiation level. Cyclic loading tests of the lower applied strain range are performed in the present study with measuring electrical resistance changes. The temperature change compensation method is proposed here for the long term tests. As a result, the electrical contact resistance at the copper electrode increased with the increase of cycles. That means the electrical change at the electrodes must be considered for the long-term self-sensing monitoring system. Moreover, angle-ply laminates has plastic deformation caused by shear loading, and that causes electrical resistance decrease during the cyclic loading.

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Shot peening is one of the most effective techniques for surface modification. Fatigue strength of dental prosthesis is increased by the peening introducing compressive residual stress and work-hardening into sub-surface of metallic materials. In this study, in order to improve mechanical properties of dental materials, five kind of dental materials, i.e. Au-Cu-Pt-Ag, Ag-Pd-Cu-Au, Co-Cr, cp-Ti and Ti-6Al-7Nb, were treated by shot peening. Residual stress, Vickers hardness, the number of cycle to failure and the yield stress of shot peened materials were measured by the two-dimensional detector in X-ray analysis, the Vickers hardness test, the fatigue test and the inverse problem analysis based on results of indentation test, respectively. It was concluded that the yield stress of dental material increases due to the shot peening and the relationship between the yield stress obtained by inverse problem analysis and the fatigue life had higher correlativity than that between the Vickers hardness and the fatigue life.

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The effect of hydrogen on fatigue crack growth properties was investigated for two heats of SCM435 steel used for storage cylinder in hydrogen stations. Fatigue crack growth tests were performed for hydrogen-charged and uncharged specimens at stress ratios R = 0.1, 0.4, 0.7 and under the condition fixing the maximum load. An additional tests in 90 MPa hydrogen gas were also carried out at R = 0.1 and 0.5 at 1 Hz. As the results, the threshold stress intensity range ΔK_th of the hydrogen-charged specimens obtained at 50 Hz was almost equal to that of the uncharged specimens. This result meant that hydrogen effect was negligible on ΔK_th. The results obtained in the 90 MPa hydrogen gas supported this conclusion. In the middle ΔK region, the fatigue crack growth was accelerated by hydrogen. The acceleration, which depended on frequency, was saturated below 0.2 Hz. Maximum acceleration was about 30 times regardless of the stress ratio and the heat of the materials. Also in the hydrogen gas, the fatigue crack growth was accelerated, while the maximum acceleration was coincident with that of the hydrogen-charged specimens. Moreover, the fitted line of Paris low in the hydrogen gas was parallel to that in air in the high ΔK region. Accordingly, the fatigue crack growth in hydrogen gas could be predicted from the test results of the hydrogen-charged specimens.

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Based on shock wave theory one of the authors derived the criterion of the micro-crack nucleation, namely the micro-crack nucleation is caused by the jump of the velocity along the intersected crossing line between two different stationary discontinuity bands characterized by vanishing velocity of an acceleration wave. In the previous paper, to consider dependence of the progress of ductile fracture of crystal solids on crystal orientations, the algorithm of acoustic tensors derived from the proposed model was built into finite element crystal plasticity model (FEPM) and the progresses of the ductile fracture in FCC bi-crystal and tri-crystal were analyzed. Then, the role of the crystal orientation and the grain boundary in the trigger of the transcrystalline fracture or intercrystalline fracture in the bi-crystal and also the role of the grain-boundary triple junction in the trigger of the ductile fracture in the tri-crystal were studied. In the present paper, the dependence of the ductile fracture progress on the grain-boundary is examined due to the FCC tri-crystal model consisted with 3 grains which are chacterized by single slip system, in-plane 4 slip systems and out-of-plane 4 slip systems.

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A vibration measurement of a mechanical element in liquid hydrogen was conducted using a fiber Bragg grating (FBG) sensor. The monitored mechanical element was an 8-mm diameter stainless-steel rod connected to a bearing cartridge of a ball-bearing, which is an element of a liquid rocket engine. The rotation of the ball-bearing vibrates both the cartridge and the rod to be monitored. The vibration was measured during a rotational test where the test temperature and the maximum rotational speed were 26 K and 30,000 rpm, respectively. The FBG-sensor signals were recorded at the sampling frequency of 50 kHz. The vibration of the rod was measured successfully up to 25 kHz despite the root-mean-square level of the dynamic strain smaller than 10x10^-6. The frequency analysis revealed that the FBG-sensor signal corresponded well with the rotational speed of the ball bearing. The peak frequency agreed with the first-order frequency of the rotational speed of the ball-bearing. The experiment demonstrates that FBG sensors are available to mechanical measurements of liquid rocket engines during operational tests, and also seem to be useful for mechanical measurements of fuel cell cars and hydrogen engine cars.

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