In this paper stress intensity factors of double and multiple edge cracks in a semi-infinite plate is considered. The problem is considered by solving a system of hypersingular integral equations based on the body force method. First, two edge cracks A and B having different crack lengths and inclination angles are analyzed and the effect of crack B upon crack A is investigated. Then, stress intensity factor(SIF) of crack A is found to be almost constant independent of the wide variation of inclination angle B if the crack tip B is fixed. Second, periodic edge cracks are systematically analyzed with varying the number, distance and angle of cracks. Then the interaction effect is found to appear mostly from the distances of crack tip independent of the angle. Numerical results are also shown when crack parameters are slightly changed from average values in almost equally spaced multiple edge cracks.

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We present a new and simplified method of estimating residual stress in welded structures by using inherent strain. The method makes use of elastic analysis by means of the finite element method, and can be used to calculate the welding residual stress in three-dimensional structures. The method can be used to efficiently compute the residual stress remaining in complex welded structures. The inherent strain distribution at a welded joint of a small-diameter pipe penetrating a thick plate can be assumed to be present in a simple distribution, and the residual stress can be calculated by elastic analysis. Inherent strain distributions were inferred from those of welded joints with simple shapes. The estimated residual stress distributions using these inferred inherent strains agree well with the results of strain-gauge measurements of a mock-up specimen. The proposed method in this paper can estimate welding residual stress in three-dimensional structures of complicated shapes in a simple way.

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Impurity effects on grain boundary grooving in crystalline aluminum are studied using computer molecular-dynamics simulation. We use a Morse potential that includes equilibrium spacing(r_A1)and potential well depth(|u_A1|)to characterize aluminum/aluminum interaction, and a two-body interatomic potential that includes equilibrium spacing(r_m)and potential well depth(|u_min|)to characterize aluminum/impurity interaction. Simulations show that when r_m is smaller than r_A1 and when |u_min| is close to |u_A1|(within ±20% of it), grain boundary grooving is prevented. This effect is explained by a decrease in the ratio of grain boundary diffusion to surface diffusion. Diffusion coefficients obtained in our simulations show that impurities at grain boundaries which satisfy the above conditions(e.g. copper)strengthen surface diffusion without strengthening grain boundary diffusion.

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Sudden growth of an infinitesimal void to a finite size under equitriaxial tension is studied for elastic-plastic materials via a bifurcation approach. The analysis employs the Prandtl-Reuss model with finite deformation taken into account, for both strain-hardening and perfectly plastic solids. Expressions for critical stress and strain levels for finite void growth, namely, cavitation limits, are obtained in the form of integrals involving material parameters and hardening characteristics. Numerical results for the critical values and post-cavitation behavior are demonstrated for power-law hardening elastic-plastic materials, and the influence of hardening exponents as well as elastic compliance is discussed in detail.

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The propagation of stress waves and the concentration of dynamic stress in tapered lap adhesive joints with impact loading were investigated analytically and experimentally. Stress distribution and time variation of stress and strain in the joints under tensile impact loading were calculated using FEM, considering viscoelastic properties of the adhesive resin. Impact tests on the adhesive joints of aluminum alloy were conducted. Calculated results agreed with experimental results. The effects of taper length on the concentration of stress and strain were examined by comparing the calculated results with the experimental results. An increase in taper length is an effective way to reduce the concentration of stress and strain in adhesive lap joints under impact loading.

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The degree of the enhancement of the fracture resistance of an orthogonal three-dimensional composite of cabon fiber reinforced epoxy is experimentally determined using a DCB testing method. By analyzing the load-displacement curve and the energy change caused by the breaking of the bridging fiber yarn, the mechanism of the enhancement of the bridging fiber for the fracture resistance is considered. It was found that the greater the number of bridging yarns in the crack, the greater is the amount of deformation energy per cracking area necessary for crack propagation. An estimation method for the mode I fracture toughness of the material is presented.

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The authors discuss the first step in the approach to the fundamental mechanism of small-scale local fracture near the contact surface between a rigid traveling roller and a viscoelastic plate which has a deep groove on the upper edge of the plate, which simulates pitting or surface cracking around the contact surface. The photoviscoelastic method is applied to investigate the time-dependent stress and strain state under the condition of nonproportional loading, taking a typical case of the interaction of stress fields due to a traveling contact load and a surface groove into account. Complicated variations of the time-dependent photoviscoelastic fringe pattern are observed near the tip of the surface groove. The time variations of not only the principal stress difference and principal strain difference, but also principal directions of stress, strain and birefringence are evaluated using a convenient computer-aided photoviscoelastic technique under the temperature at which the material shows marked viscoelastic behavior. Time variations of stress intensity factors, K_I and K_II are also evaluated using the least-squares method following the technique proposed by Sanford and Dally.

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Experiments on the temperature difference for exfoliation of a three-dimensional joint have been performed to investigate crack initiation and the difference between two- and three-dimensional joints(2D and 3D) using specimens made from resin and steel. When the edge angle is less than 90 degrees, a crack initiates at the side; therefore, the temperature difference for exfoliation of the 3D joint equals that for exfoliation of the 2D joint. When the edge angle is greater than or equal to 90 degrees, a crack initiates at the corner and the temperature difference of the 3D joint is slightly less than that of the 2D joint.

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The delamination arrest between die pad and resin should be an efficient method to prevent resin cracking of LSI packages. In some LSI packages, dimples arranged on the die pad are effective for delamination arrest. In this study, the effects of dimples on delamination arrest are examined based on boundary element analyses of LSI packages under conditions of thermal and steam pressure loading. To evaluate this effect, the stress intesity factor, K_i, for an interface crack was calculated using the contact between interface crack surfaces. The following main results were obtained. (1)The dimple decreases K_i under both thermal and steam pressure load conditions. (2)The main reason for decreasing K_i is to prevent shearing deformation between crack surfaces under thermal load conditions. Conversely, the reason for the decrease is the kinking of interface crack tips under steam pressure load conditions. (3)The effect of delamination arrest increases as the dimple depth increases.

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The boundary element method(BEM) is developed for the dynamic analysis of thin elastic plate bending problems with arbitrary boundary conditions. The formulation employs Laplace-transform technique, where the boundary integral equations are obtained on the Laplace transformed domain with the fundamental solutions derived from Kelvin's functions. The accuracy of the numerical results mainly depends on those of numerical estimation of the singular integral derived from the static term of the fundamental solutions. In the present paper, an BEM formulation based on a single boundary integral equation of the deflection, which employes a source point on both the boundary and outer region, is discussed in detail. A non-singular boundary integral equation is introduced on the transformed domain, which is obtained by superposition of the analyzed field and the referenced field with a uniform gradient of deflection. Numerical results obtained by the proposed method are compared with the analytical solutions and the other numerical solutions by means of several numerical examples. These examples also serve to illustrate the use of the proposed method.

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A general higher-order approximation theory for analysis of static and/or dynamic behavior of laminated composite structures with interlayer slip is developed. Theoretical characteristics and validity of the theory are clarified using numerical examples. The theory is formulated by using a modified Hamilton's principle with relaxed displacement continuity requirements, after expanding displacements of each lamina using power series of the thickness coordinate. The independent unknown variables of this theory are the displacement coefficients of each lamina and interlamina stresses. It is shown that the present theory includes so many previous theories, and overcomes the defects of those theories.

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For a nonhomogeneous medium, both the heat conduction equation and the governing equations of an associated thermoelastic field are nonlinear in general. Therefore, theoretical treatment of these nonlinear equations is very difficult and an exact solution is almost impossible to obtain. By introducing a laminated composite model, we derived a one-dimensional temperature solution for a nonhomogeneous plate in a transient state in our previous work. In the present work, making use of this temperature solution, we describe the optimization of material composition to minimize the transient thermal stress. As a numerical example, two nonhomogeneous plates, one composed of zirconium oxide/titanium alloy and the others of alumina/aluminum alloy, are considered. Then the optimum material composition is determined by calculation. Furthermore, the temperaturedependence of material properties is discussed.

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