A constitutive model for the superplastic material ALNOVI-1 including leak risk information

For some applications, it is important that a formed sheet of material is completely gas tight, therefore it is beneficial to be able to predict whether a formed sheet will be leak tight for gases or not. Superplastic materials show the ability to attain very high plastic strains before failure. These strains can only be reached within a small range of tempera-ture and strain rate. In thecase of the alu-minium alloy ALNOVI-1 by Furukawa Sky Aluminium, the optimum superplastic be-haviour is found at 520 °C and at strain rates roughly between 10-4 to 10-2 s-1. Under these conditions, the mechanical behaviour of the material is highly strain rate depend-ent. This article describes a proposal for the constitutive model of ALNOVI-1, as can be incorporated into an FE code (like a user-defined material UMAT in ABAQUS), in which the leak risk can be implemented, as function of the cavity volume fraction. This will be done in a phenomenological way, using the results of uniaxial tensile and biaxial bulge experiments