Modelling grain growth evolution and necking in superplastic blow-forming

A stability analysis is carried out to investigate necking in superplastic materials characterised by the sinh-law constitutive equation (epsilon) over dot (P) proportional to sinh(beta sigma). The effects of load and the strain rate sensitivity parameter beta on necking are quantitatively studied and a necking map is obtained for conditions of uniaxial loading. Finite element simulations of a superplastic blow-forming process are carried out in order to investigate both non-uniform thinning and grain size distribution which result from the use of the sinh-law constitutive equation. The pressure cycle required to ensure a target maximum strain rate is not exceeded in the material is obtained. The effects of strain rate and the magnitude of the parameter beta on the grain size and through-thickness strain distributions for the formed part are investigated, (C) 2000 Elsevier Science Ltd. All rights reserved.