A new strain rate dependent spotweld failure model for automotive crash applications

New spotweld failure models in a range of sheet steel grades have been developed for use in the virtual testing of automotive crash structures, to ensure compliance with international safety requirements. An important feature of this paper is the desire to balance the cost to develop the data input to spotweld failure models and their application capability in crash simulation tools to predict spotweld failures. The paper describes a new strain rate dependent spotweld failure model for use with hexahedron elements in automotive crash applications. The enhanced functional capabilities of the spotweld model allow the strength hardening effect at higher strain rate to be defined for the hexahedron spotweld element. A Force-based failure description using maximum shear and tension force as a function of strain rate may each be defined independently for the hexahedron spotweld element. The new model has been programmed and tested in a finite element software code. The results suggest the new spotweld failure model is capable of reproducing the static and dynamic test data generated in the IARC laboratory with a high degree of accuracy. The paper discusses the development of high rate test procedures, with particular attention on the repeatability of the dynamic test data. Shear and tension spotwelded joint specimens in a variety of automotive sheet steel materials with thickness varying in the range 0.8 to 2 mm have been tested at low and high speed. The joint specimens have been spotwelded under controlled laboratory conditions and simulated factory assembly conditions to compare performance, to validate spotweld models for industry application. All spotwelded specimens are tested under controlled laboratory conditions. At low rate, spotwelds are tested at 1 mm/s and these may be referred to as quasi-static tests. At high rate, spotwelds are tested at 2 m/s and these may be referred to as dynamic tests. Accordingly test procedures were developed and refined to support the development of quasi-static and dynamic test results. In total some two hundred tests were performed.