Since semi-crystalline polymer has very complex hierarchical structure, it is essential to construct a suitable multiscale mechanical model for the prediction of its mechanical characteristics. For the establishment of the triple scale mechanical model of semi-crystalline polymer, which can reflect the non-uniform deformations in micro-, meso- and macroscopic scales, computationally efficient model to relate structures and deformations in micro- to mesoscopic scales is indispensable. In this paper, to solve the problems, tangent modulus method was introduced into the constitutive equations for crystalline and amorphous phases consisting of the microstructure of semi-crystalline polymer. Furthermore, we proposed a new laminar composite model connecting deformations in micro- to mesoscopic scales based on the equilibrium of stress acting on the interface between the phases and the compatibility of deformation along the interface. Appropriate time steps for stable simulation and validity of the proposed model were examined through the computational simulation of uniaxial tension of single lamellar and spherulite models of high density polyethylene. It has been clarified that the proposed model could predict an elasto-viscoplastic deformation behavior of semi-crystalline polymer in markedly less computational time and memory.

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The present paper is concerned with the formulation of a constitutive model of skeletal muscle that describes material behavior in the context of a nonmonotonic stretch history. Firstly by examining some experimental data about muscle damage, we assumed that the damage degree of a muscle depends on the maximum strain in its history. Based on this hypothesis, we formulated a damage evolution equation for a second-order tensor expressing the muscle damage. Then, the damage model is incorporated into the constitutive model of skeletal muscle developed by Ito et al. on the basis of the hypothesis of total energy equivalence in the framework of continuum damage mechanics. Then, the proposed constitutive model is applied to a 3D finite element skeletal muscle model. Simulation results showed that the constitutive model can reproduce some experimental results: the mechanical property and the failure property under constant rate extension; distribution of internal damage induced by strain injury; the mechanical property and the failure strain in the context of nonmonotonic stretch history.

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In general, internal cells are required to solve unsteady thermo-elastoplastic problems using a conventional boundary element method (BEM). However, in this case, the merit of BEM, which is the easy preparation of data, is lost. The conventional multiple-reciprocity boundary element method (MRBEM) cannot be used to solve the thermo-elastoplastic problems, because the distribution of initial stress cannot be determined analytically. In this paper, it is shown that two-dimensional unsteady thermo-elastoplastic problems can be solved without the use of internal cells, by using the triple-reciprocity boundary element method and a thin plate spline. Initial stress formulation is adopted and the initial stress distribution is interpolated using boundary integral equations and a thin plate spline. A new computer program was developed and applied to several problems.

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The conventional boundary element method (BEM) needs a domain integral in unsteady thermal stress analysis with heat generation or initial temperature distribution. This paper shows that the three-dimensional unsteady thermal stress problem can be solved effectively by using the triple-reciprocity boundary element method without internal cells. In this method, the distribution of heat generation and initial temperature are interpolated by using integral equations. Time-dependent fundamental solutions are used. Therefore, by adding only the data of the values at internal points and on the boundary for the distributions of heat generation and initial temperature, the analysis of three-dimensional thermal stress for the unsteady state with heat generation and initial temperature distributions has become possible. A reduction of the dimensionality of the problem has been effectively achieved. A new computer program was developed and applied to solving several problems.

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In hydraulic turbine runner, accidents due to fatigue often occur. In this study, tension-compression and bending fatigue tests were carried out for the stainless cast steel cut out from the turbine runner crown, in order to clarify fatigue properties and mechanism of fractures on stainless cast steel SCS6 used as hydraulic turbine runner aged 27 years. The test results are summarized as follows:(1)The S-N curve of aged SCS6 used in this study has wide scatter and the tension-compression fatigue strength was lower than bending test data. (2)From SEM observation of the fracture surfaces, crack initiation sites were found to be the casting defect which consist of dendritic phase and pore. (3)It is possible to evaluate the fatigue life of aged SCS6 by using the casting defect size √area and the initial stress intensity factor calculated by defect size. The value of the threshold stress intensity factor obtained in this study were 2.6 MPa·m^1/2. (4)It was proposed that a critical volume of tension-compression test specimen where uniform stress was applied should be 20% of the region from the surface, because stress intensity factor of surface crack is larger than that of interior crack of the same size.

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Torsional fatigue tests were conducted for circumferentially notched bars of austenitic stainless steel (JIS SUS316L) and carbon steel (JIS SGV410) under completely reversed cyclic torsion without static tension (Case A) and with static tension (Case B). The propagation behavior of cracks formed at the notch root was examined from a viewpoint of fracture mechanics. The length of crack was evaluated by the electrical potential method under the assumption of concentrical cracks propagating inward on the minimum cross section of specimens. For Case A of both steels, the crack propagation rate decreased with crack length, and turned to increase after taking the minimum rate point. Sharper notches gave rise to a slower rate for SUS 316L, while to a faster rate for SGV410. At the same stress amplitude, the crack propagation rate in SUS316L is lower than in SGV410. For Case B, the crack propagation rate was monotonically increased with crack length. Similar tendency was observed when the crack propagation rate was correlated to the stress intensity range. The J integral range was estimated from the hysteresis loop between torque and twist angle. For Case B, the crack propagation rate was expressed as a power function of the J integral range. For Case A, the crack propagation was lower than that for Case B, because of retardation due to the sliding contact between crack faces. The amount of retardation was larger for sharper notches at lower stress amplitudes in SUS316L, while blunter notches gave larger retardation in SGV410. The amount of retardation in Case A was closely related to the roughness or the acuteness of the factory-roof fracture surface.

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The purpose of this paper is to develop the evaluation method of interfacial strengths with a micro cutting system. The interfacial strength of thin films is crucial for the reliability assessment of electronics packages and MEMS devices. There have been a lot of experimental and theoretical studies about the measurement of interfacial strengths. However, it is still under developing stages, because it is quite difficult to measure it quantitatively for micro- and nano-thickness films. Recently, SAICAS(Surface and Interfacial Cutting Analysis System) has been developed and used for the evaluation of the mechanical properties in micro- and nano-thickness films. In this paper, we developed the theoretical model of SAICAS micro cutting tests and proposed the evaluation method of interfacial strength for thin films systems. The proposed method was applied to copper thin films on printed circuit boards and compared with 90° peel tests. The results show that the proposed method can exclude the plastic and friction dissipation energies during the SAICAS tests and quantitatively evaluate the interfacial strength.

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This paper presents the general solutions for many circular elastic inclusions that are perfectly bonded to an elastic medium(matrix) of infinite extent under the in-plane deformation. These many elastic inclusions have different radii, central points and possess different elastic properties. The matrix is subjected to arbitrary loading, for example, by uniform stresses at infinity. This solution is obtained through iterations of the Möbius transformation as a series with an explicit general term involving the complex potential functions of the corresponding homogeneous problem. This procedure is referred to as heterogenization. Using these solutions, several numerical examples are presented by the graphically.

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Powder magnetic core is a densely-packed material produced by compacting soft magnetic metal powders coated with an insulating surface layer tens of nanometers thick. This material exhibits low eddy current loss due to its high electrical resistivity, and can provide opportunities for new three-dimensional designs of electrical machines because of the magnetically isotropic characteristics and complex shape forming capabilities. However, the mechanical strengths of the magnetic powder cores are usually lower by a factor of one-third or one-tenth than those of the typical Fe-Cu-C sintered materials. In this study, the mechanical strengths of three typical powder magnetic cores were examined by three-point bending test, by tensile test and by fatigue test to discuss the basic mechanical strength characteristics of the magnetic powder cores. The fractured surfaces of the specimens were observed with an optical microscope and scanning electron microscope, and the mechanical strength fluctuation was discussed by Weibull analysis. As a result, the fracture of powder magnetic cores was generated in the insulating layer on the metal powder boundary and/or at the boundary of insulating layer and the metal powder. The Weibull moduli were approximately in 30 to 45 range, which is higher than that of the conventional ceramic materials. The relationship between static strength and fatigue strength of the powder magnetic cores was similar to that of a low-density sintered metal.

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Double network (DN) gel is one of high-strength strongest gels in the world. Its maximum stress in compression is over 30MPa, and its surface frictional coefficient is 0.0001 at suitable conditions. Thus the DN gels realize both anomalously high strength and extremely low friction at the same time. The DN gels will be possibly used as medical materials. Here a system, which can make 3-dimensional optical forming of the DN gels by using ultraviolet laser, was proposed in order to make an artificial blood vessel experimentally. A suitable forming scheme is found, and the mechanical strength of the vessel is evaluated. The artificial vessels formed by DN gels are promising, since this material can penetrate water, oxygen, etc. Thus, the vessel can work more naturally in human bodies.

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