Finite Element Analysis for Fracture Toughness Testing

The physically important effects of material anisotropy and nonlinearity on a fracture toughness parameter, the J-integral, are investigated numerically for some representative testing geometries. An anisotropic nonlinear model, calculating stress as a function of strain to second order, was computer coded for implementation in a finite element program. Analyses were then performed for two common testing geometries, namely the standard "compact tension" specimen and the internally pressurized radially-cracked jacketed annulus. After obtaining the resulting states of stress and strain by finite element discretization, the J-integral was calculated along several paths around the crack, to confirm path-independence. For a linear transversely isotropic material it was discovered that crack orientation can strongly affect the toughness calculated for given loading conditions, and can even remove geometric domains of stable crack growth or relevance of conventional formulas; appreciable nonlinear effects are also found. The two chosen geometries, exemplifying stable vs. unstable crack growth, also provide an interesting contrast in their response to these various material characteristics.