An analysis of the effect of continuous nucleation and coalescence on cavitation during hot tension testing

A numerical model which treats continuous nucleation, growth, and coalescen ce of cavities was developed to describe the ductile failure of metals duri ng superplastic and conventional hot deformation processes. The evolution o f the fraction of coalesced cavities and the average cavity size as a funct ion of strain were the principal model predictions. For typical material pr operties, it was found that cavity coalescence begins at low cavity volume fractions (similar to 1%), independent of the individual, isolated cavity g rowth rate and the cavity nucleation rate N. The true strain epsilon(CB) at which coalescence begins was determined; above this strain, the fraction o f coalesced cavities depended only on the difference (epsilon-epsilon(CB)) and was independent of N. In addition, a relation to describe the evolution of the average cavity radius as a function of strain: the individual cavit y growth rate, and the cavity volume fraction was derived from the numerica l simulations and compared with published cavitation measurements. This com parison revealed that the model predictions provide a lower-bound estimate of the actual kinetics, primarily because of the assumption of a constant, steady state nucleation rate. It was also established that an upper-bound t o the cavity growth behavior is obtained by assuming a pre-existing cavity array without continuous nucleation. (C) 2000 Acta Metallurgica Inc. Publis hed by Elsevier Science Ltd. All rights reserved.