Fatigue strength assessment of spot-welded lap joint using strain energy density factor

One of the recent issues in design of the spot-welded structure such as the automobile body is to develop an economical prediction method of the fatig ue design criterion without additional fatigue test. In this paper, as one of basic investigation for developing such methods, fracture mechanical app roach was investigated. First, the Mode I, Mode II and Mode III, stress int ensity factors were analyzed. Second, strain energy density factor (S) synt hetically including them was calculated. And finally, in order to decide th e systematic fatigue design criterion by using this strain energy density f actor, fatigue data of the DeltaP-N-f obtained on the various in-plane bend ing type spot-welded lap joints were systematically re-arranged in the Delt aS-N-f relation. And its utility and reliability were verified by the theor y of Weibull probability distribution function. The reliability of the prop osed fatigue life prediction value at 10(7) cycles by the strain energy den sity factor was estimated by 85%. Therefore, it is possible to decide the f atigue design criterion of spot-welded lap joint instead of the DeltaP-N-f relation.