A Program for the Fatigue Analysis of Automotive Spot-Welds Based on Finite Element Calculations

A Software system has been developed which permits fatigue life predictions to be made for automotive spot welds joining two steel sheets, based on finite-element analyses. The method requires the spot welds in a structure to be modelled as stiff bar elements in a relatively coarse mesh, with the bar elements acting as force transducers. The method uses the bar element cross sectional forces and moments to calculate the “structural stresses” in each spot-weld nugget and the adjacent sheets.

The system permits the user to play complex loading histories through a finite element model, using either a quasi-static or transient approach to stress history determination. The method provides a convenient way to predict the locations and lives of fatigue sensitive spot welds, and includes graphical tools to assist in interpretation of results. Studies so far indicate that in a typical application such as an automotive body structure, the system correctly identifies all the spot welds that are likely to give rise to durability problems. Using generic S-N curves, life predictions made so far have tended to be somewhat conservative. When S-N curves are used which are more representative of the material from which the component is constructed, more accurate life predictions can be made.