Numerical simulation of cavity damage evolution in superplastic bulging process

Superplastic bulging is a typical process widely used in the aeronautical and astronautical industries; however, the microstructure variation, especially the cavity damage evolution, has a negative influence on the formability and service properties of the parts. In this paper, a yield criterion suited for the superplastic forming process and a cavity damage evolution model deduced from continuum damage mechanics are applied to the finite element formulation, and a rigid–viscoplastic finite element code is developed to simulate numerically the superplastic bulging processes. Examples of the cavity volume fraction distribution are given for the free bulging of a hemisphere and for the die bulging of cylinder parts, and the influence of cavity damage on deformation is pointed out. In addition, the evolution curve of cavity damage with respect to effective strain is presented, the calculation results of which compare very well with the experimental results. The influence of material constants on cavity damage evolution is also studied carefully. The computation models in this paper can be generalized to other kinds of superplastic forming problems.