Mechanism of plastic void growth during superplastic flow

Existing models for plastic hole growth have been re-evaluated in terms of their applicability to superplastic flow. The Cocks and Ashby model is modified to include more properly the effect of void shape, and the effect of simultaneous strain hardening is also discussed. Some new experimental data on the growth of artificial holes drilled in a sheet sample of Coronze 638 are presented and compared with data on the development of general cavitation damage in the same material without artificial holes. The difference between the two sets of results is explained in terms of a coalescence effect during general damage. Cavitation rates are found to be independent of strain in both sets of experiments. This result is explained by including the effect of strain hardening (brought about by strain enhanced grain growth) in the models. MST/461