In this overview the process of drilling is regarded from a continuum mechanical point of view. Starting with drilling into a material that is free of stresses, with drilling only as a process of cutting, the case of drilling into a pre-stressed material is investigated more precisely. The drilled material has either a metallic or a granular behavior. In particular, materials with a strain-softening behavior at the point of failure is considered. A complete analytical solution is presented for conditions of rotational symmetry, while for biaxial symmetry semi-analytical and numerical solutions are developed. The theoretical analysis is in good agreement with the experimental results.

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In a solid material with many cracks, the stress field is affected by the interaction of cracks. In the present paper, in order to investigate the interaction of many cracks, the torsional stress state of a cylindrical rod with three parallel ring-shaped edge cracks is considered on the basis of the theory of elasticity. The radius of the central crack is different from those of the others. Numerical results are illustrated for the distributions of displacement and of shear stress and for the variation of stress intensity factors with distance between cracks and with the crack size. The stress intensity factors for deep cracks are larger than those for shallow ones. The maximum stress intensity factor in a cylindrical rod with three cracks increases with increasing distance between cracks, and approaches that in the case of a single crack.

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This paper concerns the derivation of the nonsingular ordinary boundary integral equations for the tangential derivatives of boundary displacements. Having solved these equations after computation of tractions on the boundary, one can evaluate the stress tensor components at any boundary point. The present formulation can be implemented numerically using standard C⁰-continuous boundary elements for all the boundary densities. The number of integral equations which are to be solved is decreased as compared with the other formulations. Moreover, the formulatlon is presented in the most general form applicable to two- and three-dimensional problems.

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This paper presents a computational method of dynamic stress intensity factors (DSIF) in two-dimensional problems. In order to obtain accurate numerical results of DSIF, the boundary element method based on the Laplace transform and regularized boundary integral equations is applied to the computation of transient elastodynamic responses. A computer program is newly developed for two-dimensional elastodynamics. Numerical computation of DSIF is carried out for a rectangular plate with a center crack under impact tension. Accuracy of the results is investigated from the viewpoint of computational conditions such as the number of sampling points of the inverse Laplace transform and the number of boundary elements.

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Cylindrical shells subjected to lateral loads buckle in shear or bending modes. The bending buckling mode is a diamond-shaped pattern or an elephant-foot bulge at the edge. The effects of geometrical imperfections and combined loading on buckling loads and postbuckling behavior are investigated by developing a special-purpose finite element analysis (FEA) program using the 8-node isoparametric shell element. Four types of imperfections are considered and the relationships between the imperfection amplitude and the buckling load are obtained. Three types of loading are taken into consideration. For short cylindrical shells, shear buckling is dominant but elephant-foot bulges appear with an increase in bending moments and axial loads. Effects of axial loads on shear buckling and elephant-foot bulges are calculated. Postbuckling behavior which is closely related to imperfection sensitivity is also investigated

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The cyclic stress-strain response of copper under conditions where tensile deformation was followed by cyclic deformation and change in strain range occurred during cyclic deformation was estimated, extending the analysis proposed by the authors in their previous paper. At that time it was assumed that copper had inherent dislocation density in the controlled strain range at the stable stage in the cyclic deformation process, independent of the strain history to which copper was subjected. The cyclic softening occurring in cyclically deformed copper following the tensile deformation was successfully described through the present analysis. Moreover, the cyclic softening and hardening behavior induced by the change in strain range controlled in the cyclic deformation test was also satisfactorily calculated using the proposed method.

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In the preceding work we encountered several peculiar phenomena in plane strain upsetting of oxide-free pure copper blocks which are set in multilayered manners without bonding. That is, the interfaces of blocks under certain experimental conditions become strongly wavy, and shear-band fracture takes place under the condition that the blocks are precompressed up to an extremely high strain. Furthermore, when two tapered blocks are set in the forms of an hourglass and a barrel, the interface in each case remains slightly wavy. In this paper, numerical simulations by means of the elastic-plastic finite element method in plane strain conditions are carried out to ascertain whether these phenomena take place by nature or due to some experimental error. The results show that in the case of 2-, 3-, and 7-layered rectangular blocks where Cu-H is assumed as the material, the wavy interface reappears, and that in the case of 2-layered rectangular blocks where Cu-O is assumed, the interface remains almost flat. When the n-value, which describes the work-hardening property of the material, is assumed to decrease in proportion to the increase of equivalent strain, the interface becomes more wavy for the higher rate of the n-value's decrease. These numerical results imply strongly that such waviness of the interfaces is due to a diffuse -type plastic instability. Next, in the simulations of the shear-band formation, we see that such a band appears more readily for a lower n-value, at which extrusion of the material in the shape of a thin sheet is also observed at the bottom portion. This result shows that such shear-band formation is due to a localized-type plastic instability. Finally, regarding the hourglass- and barrel-type specimens designed with two tapered blocks, the interface shows smaller waviness as the tapering is sharper. Based on the calculations performed here, we conclude that the previous experimental results can be well simulated numerically, and that, therefore, these unexpected phenomena may take place by nature, not due to any error in the experimental operation.

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This paper is concerned with the dynamic treatment of a transient thermoelastic problem for an infinite plate with arbitrarily prescribed temperature field. The material of the structure is continuously nonhomogeneous with thermal and mechanical properties varying linearly with the thickness of the plate. The curvilinear characteristics in the space-time plane are transformed into straight lines of equal slope so that the numerical errors can be minimized. The problem is then solved using appropriate characteristic equations on boundaries while using more convenient explicit finite -difference approximations at all other points in the transformed space-time plane. The numerical calculations are carried out for the propagation and reflection of thermal stress waves in a nonhomogeneous plate subjected to ramp-type heating on one of the plane boundaries while the other plane boundary is maintained at a constant temperature.

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The macroscopic fracture behavior of composite laminates is now being clarified to be controlled by the extension of microscopic cracks. On the basis of released elastic strain energy accompanied by microcrack extension, we present simple equations which enable us to predict the fracture behavior of the laminate with arbitrary ply thickness by using the experimental results of the laminate with standard ply thickness. We come to the conclusion that the damaged region ahead of notch tips in laminates extends to a size proportional to the ply thickness under the same apparent critical stress intensity factor. The difference in the maximum apparent critical stress intensity factor sustained by the laminate with different ply thicknesses is also quantitatively examined. The predicted fracture behavior is in good agreement with the experimental results of continuous glass fiber-reinforced epoxy cross-ply laminates with three different ply thicknesses.

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It was found that measurement of electrical resistance in the CFGFRP (carbon fiber-glass fiber reinforced plastic) composites during and after loading is a very promising method for monitoring residual damage. CFGFRP composites containing three types of carbon fibers along with 31.6 V% glass fibers were tested. With loading, the CFGFRP specimens were able to withstand load/strain beyond the point where carbon fibers alone were fractured. At the transition point a tremendous change in electrical resistance was seen, and this point could be controlled through suitable selection of the type of carbon fibers according to their values of ultimate elongation. The signal is very distinct and the method is very simple. The design concept for explicit warning of fracturing is to combine a conductive material with a small value of ultimate elongation and an insulating material with a large value of ultimate elongation.

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The residual stress in silicon substrates after thermal oxidation is discussed experimentally. Microscopic Raman spectroscopy is used for the stress measurement. A 1-μm-diameter Ar⁺laser beam is irradiated into the silicon substrate and the back-scattered light is detected by a photon multiplier. It is confirmed that the peak position of the Raman spectra shifted almost linearly with existing stress. After plane oxidation, tensile stress occurred near the silicon substrate surface due mainly to the volume expansion of the newly grown oxide film. However, complicated stress change occur-red in the substrate after local thermal oxidation. The stress change is explained by considering the curvature change of the Si/SiO₂ interface during local thermal oxidation.

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A new method was proposed for measuring normal strain using a high-frequency diffraction grating. A laser beam illuminated the grating attached on the surface of a specimen. The frequency of the grating was 900 lines/mm. The shift of diffracted beam spots from the grating was measured with two PCD linear image sensors connected to a personal computer in order to determine the normal strain and out-of-plane rotation angle caused by an applied load. The measured light intensity profile was approximated by a Gaussian function and the location of the intensity profile was determined as the main axis of the function. This method was applied to measurement of elastic normal strain of a cantilever steel beam. The strain measured using this method agreed well with the strains measured using a strain gage and calculated from the elasticity theory.

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In order to investigate the basic properties of pseudoelasticity of TiNi shape memory alloy, tensile tests with various maximum strains at constant temperature were performed. Based on the experimental results, dependence of the stress-strain curve in the pseudoelastic region on maximum strain and temperature was discussed. The results are summarized as follows. If maximum strain occurs in the stress-induced martensitic (SIM) transformation region, the reverse transformation stress assumes a constant value at each temperature. The modulus of elasticity decreases in proportion to maximum strain. This occurs due to the fact that the fraction of the martensitic phase increases. The residual strain increases in proportion to the amount of SIM transformation strain and temperature. The dissipated strain energy increases in proportion to the amount of SIM transformation strain, but depends slightly on temperature. The recoverable strain energy increases in proportion to maximum strain and temperature.

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This paper discusses the effect of fiber orientation upon weld strength of short-fiber-reinforecd polymer composites. The fiber orientations of an injection-molded parent and weld were studied by microscorpic methods. The appearence of fiber orientation in the mold was named either a flowerlike pattern in a wide area or a volcanolike pattern in a narrow area. In addition, whether the matrix or the orientation of glass fiber at weld regions has the greater effect on weld strength was discussed. The tensile strength of the parent and weld is greatly affected by fiber orientation within the angle of 45^o, but over 45^O the effect of matrix properties on strength is greater than that of fiber orientation. The polymer composite material used in this experiment is a polycarbonate with amorphous structure, such as general engineering plastics, including 30% short glass fibers. The specimen used is the dumbbell-type tensile and three-point bending specimen with a weld line, made by means of double-gate injection molding. The microtoming technique was used for slicing ultrathin sections from molded polymer parts. Microstructural analysis of fiber orientation at the injection weld was carried using a light-transmission microscope and an image analyzer.

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A qualitative model on the remodeling of fibrous connective tissues is proposed, from which it follows that the dynamic component of tensile strain induces strengthening of tissues, and their static component induces lengthening of tissues. Based on these hypotheses, we examine the design rules for compliant prostheses, the use of which will enhance the growth and reorganization of reconstructed tissues enveloping the prostheses. We constructed artificial ligaments for rabbit anterior cruciate ligaments, and carried out animal experiments. Unfortunately, considerable inflammation responses were induced, for which wear debris was believed to be responsible.

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