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Spot weld is the primary joining method to assemble the automotive body structure. In any crash events some separation of spot-welds can be expected. However, if this happens in critical areas of the vehicle it can potentially affect the integrity of the structure. It will be beneficial to identify such issues through CAE simulation before prototypes are built and tested. This paper reports a spot weld modeling methodology to characterize spot weld separation and its application in full vehicle crash simulation. A generalized two-node spring element with 6 DOF at each node is used to model the spot weld. Separation of spot welds is modeled using three alternative rupture criteria defined in terms of peak force, displacement and energy. Component level crash tests are conducted using VIA sled at various impact speeds to determine mean crush load and identify possible separation of welds.

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.