The effect of specimen dimensions on mixed mode ductile fracture

The results from a series of experiments are presented to determine the effect of specimen dimensions on the ductile tearing resistance of A508 Class 3 forged steel at ambient temperature. Single edge notch tension specimens were subjected to Mode I, Mode II and combination of Modes I and II. Mode I tests on various specimen sizes reveal characteristic features found in earlier work, such as decreasing slope of the tearing resistance with increasing constraint (or specimen size). In contrast, for Mode II the tearing resistance is shown to be independent of specimen size, although dependent on initial crack length. The tests show that there is a competition between void growth and shear localisation as mechanisms for ductile crack extension. The dominance of one mechanism over the other is shown to be related to the local Mode I and Mode II components of the J-integral.