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

A numerical model which treats continuous nucleation, growth, and coalescence of cavities was developed to describe the ductile failure of metals during superplastic and conventional hot deformation processes. The evolution of the fraction of coalesced cavities and the average cavity size as a function of strain were the principal model predictions. For typical material properties, it was found that cavity coalescence begins at low cavity volume fractions (∼1%), independent of the individual, isolated cavity growth rate and the cavity nucleation rate N. The true strain εCB at which coalescence begins was determined; above this strain, the fraction of coalesced cavities depended only on the difference (ε−εCB) 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 cavity growth rate, and the cavity volume fraction was derived from the numerical simulations and compared with published cavitation measurements. This comparison 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 to the cavity growth behavior is obtained by assuming a pre-existing cavity array without continuous nucleation.