A composite model description of internal stress superplasticity

A simple two component composite model, each component having a different coefficient of thermal expansion, is used to describe internal stress superplasticity due to temperature cycling. The model adopts a creep rather than a plasticity approach and uses a single equation set to describe accelerated creep and the transition to normal creep behaviour at higher applied stresses. This is in contrast to some other descriptions where a separate equation is required for each type of behaviour and average values for material properties such as diffusion coefficients are used. The numerical solution makes the proposed method readily applicable to design situations, since actual temperature cycles can be taken into account. Results from the model are compared to previously published experimental work on zinc and results obtained during the present investigation.