Strain-rate dependence in spot welds: Non-linear behaviour and failure in pure and combined modes I/II

When modelling assemblies for structural crashworthiness computations, fasteners are usually only characterised by their tension and shear strengths. However, for large deformations potentially leading to the failure of the assembly, joints are often loaded in combined modes, and the usual macro models fail to predict the assemblies' non-linear behaviour and rupture. In this paper, an advanced experimental procedure is proposed for testing and modelling spot-welded plates in pure and combined modes I/II under quasi-static and dynamic loading conditions. Obtained using a hydraulic jack and the Split Hopkinson Pressure Bar technique, the experimental results make it possible to analyse the mechanical strength (and the displacement rate dependence) of spot-welded plates. The non-linear behaviour and failure of experimental spot welds were proved to be strain-rate dependent in pure and combined mode I/II loading conditions. Our analysis showed that ultimate strengths in pure modes I and II would be particularly strain-rate dependent. Based on these results, a strain-rate dependent model was developed for ultimate loads in pure opening mode (tensile load) and presented in this paper. A computational approach for building a model for ultimate loads in pure shear mode is also discussed.