Influence of Specimen Geometry on Crack Propagation and Arrest Toughness

Abstract

A number of crack propagation experiments on four different specimen geometries were performed in order to investigate the existence of a unique relationship between crack propagation toughness and crack-tip velocity. For one geometry, dynamic finite-element method (FEM) calculations were found to be necessary in order to obtain proper stress-intensity factors, whereas quasi-static FEM-calculations were found to be sufficient for the other geometries. Crack-tip velocities were determined from continuous recordings of crack length versus time, which was measured by an impedance method. The stress-intensity factor and the instantaneous crack-tip velocity were obtained for a number of crack lengths for each experiment. The experimental results do not contradict the hypothesis of a unique relationship between these two quantities at low load levels; neither do they contradict the hypothesis of a geometry-independent crack arrest toughness. At high load levels a deviation from the uniqueness was observed. The height of the specimens was found to influence the crack propagation toughness level at the beginning of deviation from the unique relationship.