Symmetrical Propagation of a Central Crack in Orthotropic Material

Abstract

A central crack which propagates symmetrically in an orthotropic composite plate is investigated using the techniques of Fourier and Laplace transforms. The crack is located along one of the principal axes of the material. Complete contour integrations are carried out in the evaluation of the Laplace inversion integrals. For the crack tips running at a constant speed, exact expressions for the dynamic crack shape and the dynamic stress distribution with singularities in the crack plane are obtained in terms of anisotropic material constants and crack speed. The dynamic expressions are evaluated numerically by using graphite/epoxy and glass/ epoxy composites and an isotropic material as sample materials. The dynamic solution reduces to the static solution at zero crack speed. During crack propagation, the deviation between dynamic and static solutions is governed by dynamic correction factors which are nondimensional functions of the ratios among anisotropic material constants and the ratio of crack speed to shear-wave speed. Values of these dynamic factors are obtained for the sample composites at a large range of crack speed. The dynamic stress intensity factor vanishes at the corresponding Rayleigh wave speed.