Yoshiji Niwa

Coupling of numerical Green's matrix and boundary integral equations for the elastodynamic analysis of inhomogeneous bodies on an elastic half-space

Abstract A coupled system of integral equations (of the domain and boundary types) is formulated for the elastodynamic response analysis of a locally inhomogeneous body on a homogeneous elastic half-space. The method uses the fundamental solution for homogeneous elastostatics in the inhomogeneous domain owing to the lack of a fundamental solution in inhomogeneous elastodynamics. The integral representation of displacements in the inhomogeneous domain is formulated with the help of this elastostatic fundamental solution by considering the term induced by the inhomogeneity of materials and the acceleration term as the body force term. Then the Greens matrix is obtained numerically from this integral representation and combined with the ordinary boundary integral equations, which are valid in the exterior homogeneous half-space. Some numerical examples show the efficiency and the versatility of this coupled method.

Elastodynamic analysis of inhomogeneous anisotropic bodies

Abstract The integral equation method is presented for elastodynamic problems of inhomogeneous anisotropic bodies. Since fundamental solutions are not available for general inhomogeneous anisotropic media, we employ the fundamental solution for homogeneous elastostatics. The terms induced by material inhomogeneity and inertia force are regarded as body forces in elastostatics, and evaluated in the form of volume integrals. The scattering problems of elastic waves by inhomogeneous anisotropic inclusions are investigated for some test cases. Numerical results show the significant effects of inhomogeneity and anisotropy of materials on wave propagations.

In-Situ Determination of Stresses in Orthotropic Rock

The interpretation of deformations, strains and stresses in rocks on the assumption that the rock behaves as a medium homogeneous, isotropic and linearly elastic, is not always practically valid.The paper describes a theoretical analysis of stresses and strains in an orthotropic linearly elastic rock, and proposes a method for practical determination of initial or variational stresses by using the stress-relief technique. The determination of initial stresses by the aid of photoelastic plug is worked out in detail.

Fracture Criterion of Cement Mortar Subjected to Triaxial Compression

The most general fracture criterion of cement mortar subjected to triaxial compression is experimentally obtained. The criterion is expressed in the principal stress space as a convex surface with space diagonal of its axis. The surface expands almost isotropically with an increase of hydrostatic pressure. The right sections of the fracture surface have a slightly bulged shape as compared with the equilateral triangle. The fracture criterion obtained by the authors can be approximated by Mohrs envelope of parabola.It is also found that the fracture criterion is independent of loading paths within the experimental range.