A New Strain Rate Dependent Spot Weld Model for Automotive Crash Applications

New spot weld failure models in a range of sheet steels have been developed for use in the virtual testing of automotive crash structures to ensure compliance to international safety requirements. The desire to balance the cost to develop the data input to spot weld failure models and their capability to predict failure in simulation tools is central to the method. Full vehicle crash simulations suggest confidence in the predictive capability of the models. This paper describes a strain rate dependent spot weld failure model for use with hexahedron (solid) elements. A spot weld may comprise one, or a cluster of four, eight or sixteen solid elements. The enhanced functional capabilities of the new spot weld model allow a force-based failure for a solid element in which maximum shear force and tension force may be a function of strain rate, and each may each be defined uniquely using a load curve. Further the strength hardening effect at higher strain rate may be defined for the solid element using a simple constitutive expression which relates the properties of the spot weld to plastic strain rate. The new model has been programmed and tested in the finite element software code LS-DYNA®. The results suggest the new spot weld model is capable of reproducing the quasi-static and high rate physical test responses with a high degree of accuracy.