Numerical study of strengths of spot-welded joints of steel

A resistance spot-welding (RSW) joint consists of several material zones with different microstructure and properties as a result of the thermal, metallurgical and mechanical deformation process. Detailed material properties are essential to accurately simulate the mechanical behavior of a joint and its dependency on some key structural parameters (e.g. nugget size, sheet thickness etc.). The work presented in this paper utilises an inverse modelling methodology combining numerical modelling and indentation tests with a standard hardness test to characterise the detailed properties of different weld zones of spot-welded joints. The yield and strain hardening parameters of the three zones (nugget zone, HAZ: heat-affected zone and base zone) were determined and the predicted stress–strain curves for base zone were compared with standard tensile tests results. A 3-D finite element model based on the predicted constitutive material laws for different zones coupled with a fracture model was developed to predict the deformation of spot-welded joints beyond the onset of initial yield under tensile-shear loading. The deformation mode and force–displacement result showed good agreements with experimental data. The effect of nugget size and sheet thickness on the tensile-shear strength of welded joints was further systematically studied using a high performance computing system.