Strain-Rate Characterization of Automotive Steel and the Effect of Strain-Rate in Component Crush Analysis

The effects of strain-rate and element mesh size on the numerical simulation of an automotive component impacted by a mass dropped from an instrumented drop tower was investigated. For this study, an analysis of a simple steel rail hat-section impacted by a mass moving at an initial velocity of 28Mph was performed using the explicit finite element code Radioss. Three constitutive material models: Elasto-Plastic (without strain rate), Johnson-Cook, and Zerilli-Armstrong were used to characterize the material properties for mild and high strength steel. Results obtained from the numerical analyses were compared to the experimental data for the maximum crush, final deformation shape, average crush force and the force-deflection curve. The results from this study indicate that the mechanical response of steel can be captured utilizing a constitutive material model which accounts for strain rate effect coupled with an average mesh size of 6 to 9mm. Larger mesh sizes (> 12mm) generally make the model stiffer and inclusion of strain rate further stiffens the structure making the correlation less robust. Overall, higher fidelity correlation was achieved with the Johnson-Cook material model for the commercial code utilized in this study (Radioss).