Fatigue Life Prediction of Spot Welds with Direct Strain Measurement

Fatigue is the most critical failure mode of spot-welded joints in automobiles. Although various approaches have been proposed for fatigue life estimation of spot welds, a practical tool for spot welds in a fully built vehicle has not been thoroughly established. Since the spot welds in the assembled vehicle generally are situated in complex geometries under multi-axial loading, the most effective tool for fatigue life estimation might be the direct strain measurement. Here, a practical and reliable technique for fatigue life prediction of spot-welds based on direct strain measurement is proposed. The developed technique shows that the fatigue life of spot welds can be estimated by a multiple strain-gauge pattern attached to the outer surface of the overlap sheets near the spot weld. The designed pattern measures strain signals from circumferentially aligned strain gauges, which effectively provide information for fatigue life prediction after a simple conversion process. The developed technique is verified by experiments using specimens under multi-axial loading condition, and validated with data measured from the on-vehicle tests.