Axisymmetrical elastic problems for a nonhomogeneous medium with a penny-shaped crack are treated theoretically. It is assumed that the nonhomogeneous material properties of shear modulus of elasticity G vary with the axial coordinate z according to the power product form, i.e., G(z)=G₀Z^m. As an analytical model, a nonhomogeneous infinite body or thick plate with a penny-shaped crack subject to uniformly distributed loading such as internal pressure on the crack surface is considered. The above-mentioned axisymmetric problems with a singular stress field are developed theoretically utilizing a fundamental equation system for such a nonhomogeneous medium derived in our previous paper. Thereafter, numerical calculations are carried out for several cases taking into account the variations of the nonhomogeneous parameter m of shear modulus of elasticity G and the thickness of the slab, and the numerical results for displacements, stresses and the stress intensity factor at a crack tip are shown graphically. The influences of the nonhomogeneous material property and the thickness on the elastic behavior such as displacements, stresses and the stress intensity factor are examined precisely.

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Intrinsic mechanical stresses exist in a general interface, because of an interface atomic structure changes relative to the bulk. This paper presents fundamental solutions using the interrelationships between surface stresses and bulk stresses deduced in the previous paper. The interfacial stresses have a close relationship with an interfacial energy and the geometry(mean curvature)of interface. In this paper, the fundamental solutions for a prismatic dislocation loop with a radius a in transversely isotropic materials are derived using the three-dimensional theory of elasticity. Furthermore, solutions and potential functions for a dislocation loop with an arbitrary shape loop in a two-phase transversely isotropic material were derived. The stress distributions taking into account of the interfacial energy were compared with that taking into no account. Stresses for the former were larger than the latter. Finally, we deduced the relationship between a prismatic dislocation loop and a dislocation-like deformation generated by changing locally the free energy in materials.

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This paper is concerned with the inverse problem of impact force, which is to estimate the impact forces acting on bodies from the measurement of their impact responses. As the authors have shown previously, both numerical Laplace transformation and its inversion are required to solve the inverse problem. Since the inverse analysis is based on experimental data and, in addition, the Laplace inversion is typical of ill-posed problems, straightforward computation tends to provide an unacceptable estimate of the true impact force. Therefore, regularization of the Laplace inversion is necessary to obtain a good estimate of the impact force. In this paper Tikhonov regularization is applied to the numerical Laplace inversion using FFT. Both numerical simulation and experimental results verify that the Tikhonov regularization is effective for improving the accuracy of the estimated impact force. In addition, it is shown that Hansen's L-curve method can be employed to determine appropriately the regularization parameter.

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The effects of stress on the Raman frequencies of crystalline silicon are studied using molecular dynamics simulation both for uniaxial stress along the[100]direction and for biaxial stress which is isotropic in the(001)plane. The Tersoff potential is used to represent the interaction among the silicon atoms. Simulation results showed that the tensile stress causes the Raman frequencies to decrease. The conversion coefficients that are needed for converting the shifts of the Raman frequencies into the stress were obtained by comparing the simulation results with the dynamical equations for optical modes. The values obtained for the coefficients agreed well with the experimental values obtained by other works. The obtained relationship between the uniaxial stress and the Raman frequency for vibration in the[001]direction also agreed well with the experimental result we obtained using microscopic Raman spectroscopy.

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A three-dimensional finite element computer code was developed to deal with a thermal stress analysis of a gadolinium orthosilicate(Gd₂SiO₅, hereafter abbreviated as GSO), a monoclinic single crystal, during Czochralski growth process. The GSO single crystal has strong anisotropy in the elastic constants and the thermal expansion coefficients, so a three-dimensional analysis is required for the exact calculation of thermal stress. A tensor transformation technique was used to obtain the components of the elastic constant matrix and the thermal strain or the thermal expansion coefficient vector corresponding to an arbitrary pulling direction. Using this computer code, thermal stress analyses of the GSO bulk single crystal were performed for various pulling directions in order to examine the relation between the magnitude and distribution of thermal stress in the bulk single crystal and the pulling directions. The b-axis pulling of the GSO bulk single crystal was proposed from the viewpoint of minimizing the thermal stress during the growth process.

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Finite-element analysis(FEM) wasperformed to characterize the deformation behavior of ceramic composite material during static and dynamic bending. Normal and shearing stress distributions were clarified by FEM with respect to elastic anisotropy and the specimen height-to-span ratio(H/L), and the tensile and shearing fracture behaviors were well understood in terms of the predicted stress distributions. Well-ramped impact bending leads to almost identical stress distributions as static bending and, consequently, the fracture strength of brittle materials can be measured at a high deformation rate. Tensile and shearing strengths increased significantly with the rise in the deformation rate.

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The shear strength of adhesive joints at high loading rates is evaluated with the split Hopkinson bar technique using a pin-and-collar specimen. A commercially available cyanoacrylate adhesive(commonly termed an instantaneous adhesive)and two different adherend materials are used in the tests. The impact shear strength of the cyanoacrylate adhesive joints is determined from the applied shear stress history at failure initiation. Comparative shear tests at low loading rates are carried out on an Instron testing machine. The influences of loading rate, thickness of adhesive layer, and adherend materials on the shear strength of the cyanoacrylate adhesive joints are examined. The test results indicate that the shear strength increases significantly with increasing loading rate, and is greatly affected by both the adhesive layer thickness and adherend materials. It is shown that the shear strength increases to a maximum at an adhesive layer thickness of about 25 μm and subsequently decreases. The advantages and limitations of the technique are also discussed.

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In this paper, the axisymmetric torsion problem of compound infinite hollow cylinder with an external annular crack is considered on the basis of the three-dimensional theory of elasticity. The cylinder is composed of two layers of different materials. The problem is reduced to solution of an infinite system of simultaneous equations. The distribution of displacement and shear stress as well as the stress intensity factor K_III are computed for various combinations of the elastic modulus for the inner and outer layers.

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Recently, joints that combine a shrink fit with anaerobic adhesives have been used in order to increase joint strength. In this study we deal with the stress analysis and strength evaluation of bonded shrink fitted joints subjected to torsional loads. The stress distributions in the adhesive layer of bonded shrink fitted joints are analyzed by using the axisymmetric theory of elasticity when an external torsion is applied to the upper end of the shaft. The effects of the outer diameter and the stiffness of rings on the interface stress distributions are analyzed by the numerical calculations. Using the interface stress distributions, the joint strength was predicted. In addition, the value of the joint strength was obtained experimentally. It is seen that a rupture in the adhesive is initiated from the upper edge of the interfaces when a torsion is applied to the upper end of the shaft. The numerical results show more conservative values than the experimental results. It is found that the joint strength of bonded shrink-fitted joints is greater than that of shrink-fitted joints.

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Pure bending with a constant curvature-rate followed by creep(hold constant moment for a period of time)or relaxation(hold constant curvature for a period of time)tests were conducted to investigate the effect of prior curvature-rate at preloading stage on the subsequent creep of relaxation behavior. Thin-walled tubes of 304 stainless steel were used in this investigation. The curvature-ovalization measurement apparatus, designed by Pan et al.⁽¹⁾ was used for conducting the present experiments. It has been found that the curvature-rate at the preloading stage has a strong influence on the subsequent creep or relaxation deformation under pure bending.

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In the case of ball bonding process in LSI packaging, complex non-steady-state metal flow occurs in a wire ball during the process, and solid-phase bonding is accomplished between the wire ball and an electrode pad. We proposed a physical simulation method to analyze the above ball bonding process. The physical ball bonding simulation and detailed numerical analyses, using enlarged plane-strain models of a capillary tool made of SKD-61 steel and the wire ball and the electrode pad made of 1050 aluminum, were carried out. The outer profile change of the wire ball and the changes in and distributions of flow velocity, strain rate and strain in the wire ball during the process were revealed quantitatively. The simulation method will aid in the optimization procedures for tool configuration and other operating conditions, in order to achieve sound bonding with narrow electrode pad pitch spacing.

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The viscoplasticity theory based on overstress(VBO) has been employed to model the uniaxial cyclic deformation of 316FR steel at high temperature. The experiments show that the stress strain response is rate independent in monotonic tension or the initial stage of cyclic straining, while the observed cyclic strain hardening is rate dependent. Also, the subsequent holding of strain results in a particular stress relaxation. These interesting deformation behaviors relating rate effects cannot be well reproduced by the conventional viscoplasticity theory. In the present paper extensions of VBO are introduced to reproduce these behaviors. The first extension admits a rate independent asymptotic solution. The second one produces the time(rate)dependent cyclic hardening. Good agreement is found between the experimental data and the numerical simulations by the present model.

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Nonlocal elastic constants have been related to atomistic properties through a macro-micro linking approach proposed in a previous paper(Trans.of JSME, Vol.62, No.601, A(1996), p.2054-2059). Using the derived relations, these material constatns can be estimated only by atomistic quantities of force constants and neighboring lattice configuration. In the present study, centrosymmetric homogeneous bulk is first taken up. Agreement between the number of independent components of these elastic constants and the results from analytical estimation by invariance of transformation on an isotropic tensor is demonstrated. Then, the less symmetric surface and the high Σ-value grain boundary are computationally constructed by molecular dynamics simulations in order to examine inhomogeneous nonlocal effects. It is found that atomistic inhomogeneity increases nonlocal material properties, while the characteristic length derived from the ratio of the 6th-order to the 4th-order elastic constants is smaller than a lattice parameter.

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The problem of the effect of thermal loads on buckling strength is important in buckling research for fast breeder reactors, because an axial temperature gradient is produced in the main vessel and significant thermal stress is induced at the surface of sodium. In this paper, we focus on two types of reactor vessels(loop type and pool type)and investigate the effect of thermal loads accompanied by axial temperature changes near the sodium surface. In addition, the reduction of the buckling strength due to thermal loads is evaluated.

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Nanoindentation measurement for tungsten(001)single crystal was conducted with an AFM ultra-micro hardness tester. For electrolytically polished tungsten(001)single crystal, sudden increase of penetration by around 50 nm occurred at 1.3 mN with a three-sided pyramidal indenter of an apical angle of 115°, and 0.24 mN with an indenter of 60°. Deformation was purely elastic under this critical force. However, these behaviors did not occur for mechanically polished surface, where a deformed layer of no more than 6 μm thickness exists. These facts lead an idea that such phenomena come from the same source of upper and lower yield points in tensile tests for B.C.C.crystals. Normalized shear stress τ_max/G at upper yield point was estimated as 0.22 and 0.24. Also, curvature radius of indenters, that is of great importance in nanoindentation, was estimated from both force-penetration depth curves and AFM topographic images.

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A grid method is applied to measure the specimen's strain during dynamic deformation in the split-Hopkinson torsional bar(SHTB) experiments. A streak camera is used to record the motion of an inclined grid pattern(5 lines/mm)previously formed on the outer surface of the specimen. The average shear strain of the metal matrix composites(MMC) is successfully obtained in a large strain range by analyzing frequency of the streak image. The nominal shear strain evaluated by the conventional SHTB method agrees well with the directly measured strain for these materials. Microscopic strain distribution in MMC is also measured by observing a diffraction grating(600 lines/mm)on the specimen's surface in quasi-static testings. Localization of the shear strain becomes strong with increasing volume fraction of the reinforcement, and would reduce ductility of the composite materials.

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The effects of mechanical stimuli on fibroblasts have been investigated, using the collagen gel culture method. A specimen of thin collagen gel membrane, involving cells, was supported by stainless steel wire mesh and subjected to static or dynamic uniaxial tensile/compressive load in an incubator. The cell alignment, the shrinkage of collagen gel matrix, and mechanical properties of the specimens have been examined. We found that both of static and dynamic loads strengthened the collagen matrix. From the morphological evidences, the dynamic stimuli were concluded to be effective in matrix strengthening. However, since the specimens were not strengthened uniformly and portions of compressive stresses remained weak, the macroscopic tensile test failed to show the differences of the mechanical properties between the specimens under static and dynamic stimuli.

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