A statistical analysis of the fatigue behaviour of single and multi-spot welded joints

Several models exist for predicting the fatigue behaviour of a spot welded joint based on geometric data. However, the accuracy of these models tends to diminish as the number of spot welds and complexity of the joint increases. This paper reports on the findings of an investigative study to assess the applicability of a statistical approach to modelling the fatigue behaviour of multi-spot welded joints, based on data obtained from testing single spot welded joints that are geometrically equivalent to the individual welds in the multi-spot joint. A range of fatigue tests were carried out using Staircase and Pro bit techniques to determine the fatigue strength distribution of a range of multi-spot welded joints, which were subsequently compared to those predicted using the proposed statistical model. The comparison indicated an excellent correlation between predicted and experimentally determined values for standard deviation and a marginal difference for mean fatigue strength values. This difference is potentially attributed to the effects of a degree of load redistribution occurring part way through testing in the multi-spot joints, which is currently not adequately accounted for in the proposed statistical model.