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Using experimental and finite element analysis methods, the effects of electrode forging force are investigated on fatigue behavior and residual stress of spot welded joints of aluminum alloy 5182. Results show that applying forging force significantly reduces the residual stresses in the heat affected zone and the fatigue cracks no longer initiate from there; instead, all cracks begin from the nugget edge. In addition, the mitigation of residual stress by forging force decreases the driving force for crack propagation and leads to longer fatigue life. It can be concluded that applying forging force appropriately has a positive effect on the fatigue strength of resistance spot welded joints.

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A nonlinear finite element model is built to study the self-piercing riveting process. In this model, the elasto-plastic properties of sheets and rivet, i.e., the dependency of flow stress on effective strain is considered. The adaptive meshing technology is used for the separation of sheet material. The piercing operation on two 2 m m-thick 5754-O aluminum sheets is simulated, and the results obtained are in agreement with the published experimental results. Using this method, residual stress and strain are calculated under different die tip heights and rivet strengths, to obtain insights into the local mechanical behavior of the joints and the effect of process variables. It is found that the hoop residual stress is the main stress that affects the mechanical properties of joint. Higher riveting pressure is needed for higher die tip and higher rivet strength. Both the die tip height and river strength can affect the joint shape and residual stress.