Fatigue service life evaluation of spot-welding specimen with liquid metal embrittlement defects using equivalent structural stress

In recent years, the application of ultra-high strength steels has increased owing to improvements in the weight reduction of automobiles and the strengthening of collision safety regulations. However, their application has been delayed owing to liquid metal embrittlement (LME) defects during the spot-welding process of ultra-high strength steel galvanized steel sheets. This is because of the absence of test data for exact criteria about LME defects, but experimentally analyses of the various defect types and sizes are virtually impossible. Therefore, in this study, we apply the equivalent structural stress method to some spot-welding fatigue test results, and we derive a master stress - fatigue life curve regardless of the specimen shape and load type. In addition, we evaluated the effect of LME defects.