A Novel Spot Joint Element for Fatigue Evaluation of Spot Welds and Fasteners in Lightweight Automotive Structures

Due to the spot weld and mechanical fastener share the similar characteristics to join sheets together with only differences in deformation behavior around joint region, a novel spot joint element (user-defined element) consists of regular Mindlin shell elements and equations for different kinematic constraints is proposed to simplify the spot joint representation in lightweight automotive structures. The novel spot joint element can not only provide accurate deformation behavior around joint region but also output mesh-insensitive structural stresses at virtual nodes with the use of traction-based structural stress method for fatigue failure analysis. In this investigation, the structural stress distributions around joint peripheral in the lap-shear specimens with spot weld or fastener are first calculated to validate the accuracy of the novel spot joint element. Then, the structural stresses along different cross-sections emanating from joint are also calculated for the specimens with fasteners to investigate the potential failure mode dependence on sheet thickness. Finally, the fatigue data correlation based on the novel spot joint element and traction-based structural stress method using available literature data are presented and served as an example application.