The Development of a Simplified Spot Weld Model for Battelle Structural Stress Calculation 2011-01-0479

The nodal force based Battelle structural stress method has shown its mesh insensitivity in the stress analysis of spot welds as well as fusion welds. In the conventional structural stress simulation procedure, the structural stress is calculated at the nodes along the nugget periphery. However, implementing a nugget into each spot weld is cumbersome and time consuming not only in preparing mesh for FE analysis but also in preparing a series of structural stress calculation after finishing the FE analysis. Therefore, the efficiency of the current Battelle structural stress practice for spot welds can be improved significantly for structures with a large number of spot welds. The simplified modeling procedure presented here delivers reliable structural stresses at spot welds and these stresses can then be utilized for fatigue life prediction using a master S-N Curve approach that is applicable to wide range of spot welding techniques.

In this paper, a Battelle-structural-stress based simplified procedure for modeling and simulation of spot welds is proposed. The simplified procedure can be summarized as employing shell/plate elements for plates and a beam element for each weld nugget with the plate failure as the major concern. The key contribution of this procedure is that a consistent approach for calculating the Battelle structural stress based on nodal forces and moments is developed for a given nugget with nominal size. The robustness and accuracy of the simplified procedure for spot welds is demonstrated by the fact that a large amount of fatigue data from various loading conditions and specimen geometries can collapse onto a fatigue master S-N curve. Finally, it is found that the fatigue master S-N curve for weld toe failure of fusion welds can be also utilized for sheet failure of spot welds. Furthermore, the simplified procedure demonstrates good mesh insensitivity and can significantly reduce the effort for modeling/simulation of spot welds without sacrificing the accuracy of the results.