Evaluation of Strain Rate-Sensitive Constitutive Models for Simulation of Servo Stamping: Part 1 Theory

Strain-rate sensitivity has been neglected in the simulation of the traditional stamping process because the strain rate typically does not significantly impact the forming behavior of sheet metals in such a quasi-static process, and traditional crank or link mechanical presses lack the flexibility of slide motion. However, the recent application of servo drive presses in stamping manifests improvement in formability and reduction of springback, besides increased productivity and energy savings. An accurate simulation of servo stamping entails constitutive models with strain-rate sensitivity. This study evaluated a few strain rate-sensitive models including the power-law model, the linear power-law model, the Johnson-Cook model, and the Cowper-Symonds model through the exercise of fitting these models to the experimental data of a deep draw quality (DDQ) steel. Curve fitting over segmented strain ranges and grouped strain rates were conducted so that the uniqueness of the identified parameters of each model could be analyzed. The findings of each model’s suitability to be used in finite element software herein can help users select the appropriate constitutive models for simulation of servo stamping.