A Two-Dimensional Electrothermal Model for Resistance Spot Welding with Temperature-Dependent Electrical Contact Resistance formulation

A 2D axisymmetric electrothermal model of resistance spot welding (RSW) was proposed topredict weld nugget formation under different welding currents. The model considers flat-facedelectrodes and incorporates nonlinear temperature-dependent thermophysical propertiestogether with the latent heat of fusion and solidification. To describe the transient electricalcontact conditions at the faying interface, a new temperature-dependent contact resistanceformulation was proposed, in which the contact resistance is represented by an exponentialtemperature-dependent form combined with a liquid-fraction correction factor to account forthe additional reduction in constriction resistance during interface melting. The model wasvalidated by comparing the predicted weld nugget diameters with experimental measurementsobtained on mild-steel sheets for welding currents ranging from 4 to 12 kA. The numericalresults reproduce the nonlinear dependence of nugget diameter on welding current andaccurately capture the successive stages of nugget development, including incubation, rapidgrowth, and saturation. In addition, the simulated evolution of the dynamic electrical resistancewas found to be consistent with the predicted transition from interface-dominated heating tovolumetric Joule heating during nugget formation. Overall, the proposed contact resistanceformulation provides a simple approach for representing the transient interfacial electricalbehaviour at the faying interface while maintaining good agreement between predictions andexperimental observations in terms of nugget diameter, shape, and growth stages.