The effect of strain rate sensitivity evolution on deformation stability during superplastic forming

The most important characteristic of superplastic materials is the high sensitivity of flow stress to deformation rate. In general, a constant strain rate sensitivity index value is usually used for calibrating models describing superplastic deformation. However, experimental results indicate that the strain rate sensitivity index depends on strain rate, strain and does not remain constant during deformation. In this work, the effects of strain rate sensitivity variation on the stability of deformation during superplastic forming are examined using finite element simulations in conjunction with a microstructure-based constitutive model. The model is experimentally calibrated and validated for the AZ31 magnesium alloy. The results clearly show the importance of accounting for the variation of strain rate sensitivity in modeling and simulating superplastic forming.