In this paper, the Battelle structural stress method for evaluating the fatigue life of welded joints is applied to weld-bonded joints. In order to overcome the complexity of modeling and analyzing both crack paths in weld-bonded joints, a superposition approach is proposed as a reasonable and effective alternative for fatigue design purpose.
The superposition approach for evaluating the fatigue life of weld-bonded joints uses two simplified finite element (FE) models: a spot weld model and an adhesive bond model. Each simplified FE model is required to represent the fatigue behavior properly and to minimize the modeling effort without sacrificing the accuracy of the results. The superposition concept can be used in practice if the life evaluation results using the superposition are comparable with the experiments. For the spot welds, the recently developed simplified procedure and master fatigue S-N curve is employed [1]. The spot-weld master fatigue S-N curve is applicable to a wide range of spot-weld diameters, sheet thicknesses, and loading directions. For adhesive bonded joints, a new procedure that combines shell and solid elements is developed and a corresponding master fatigue S-N curve is constructed.
Recently, Auto/Steel Partnership (A/SP) has undertaken an investigation of the fatigue performance of advanced high strength steel spot welds [2]. The proposed superposition approach was validated using A/SP's fatigue test results from adhesive bonded and weld-bonded joints of HSLA340 steel and DP600 steel. A comparison of the observed fatigue lives with those predicted using the superposition procedure that was based on the Battelle structural stress method demonstrated the effectiveness of the proposed tool for fatigue design assessment and optimization purposes.
The key contribution of the development of this procedure is that a consistent approach using the Battelle structural stress method based on nodal forces/moments, now can be applied to adhesive joints and to weld-bonded joints, and as has already been established, can be applied successfully to spot-welded joints and fusion-welded joints.