Extension of the Spot Weld Element to the Elasto-Plastic Case

The authors have developed an original spot weld finite element based on a theoretical solution condensed on the nodes that surround the spot weld region. The spot model was successfully used in the elastic case, which is useful for high cycle fatigue life predictions. An improved version accounted also for the progressive damaging due to fatigue evolution by means of appropriate stiffness reduction of the spot nugget. By this way, load redistribution under progressive damaging can be accounted. In this paper, the spot weld is studied when plastic deformations are experienced by the structure. This is the case of occasional overloads but also the more drastic case involving structure crashes. The groups of beams that connect the spot core to the metal sheets, already set up in the fatigue computation, are modified so that to account of irreversible deformations. Here again the developments are based on an analytical approach even if several simplifications reduce overall accuracy. However, the final result is much more accurate that any other finite element trick used in the past to model spot welds subjected to wide deformations.