Fatigue life evaluation for ring-welded lap joints of stainless steel based on fracture mechanics approach

Abstract

This study aims to evaluate the fatigue life of ring-welded lap joints of stainless steel with various geometries. It involves welding morphologies observations, static and fatigue tests under tensile-shear loading, and fatigue life evaluation based on fracture mechanics approach. Test results show that the interfacial failure occurs for each specimen under the static loading, and the static strength increases with an increase in weld area, as well as the degree of bending deformation during the test. In addition, three failure modes were identified under fatigue loadings, with crack propagation from the weld root to the weld metal surface accounting for over 90% of the fatigue life for most specimens. Taking into account the fatigue failure modes, a fracture mechanics-based method was used to unify the Fa-Nf curves of ring-welded lap joints with different geometries. This unified curve considers the effects of specimen geometries, crack length, loading ratio, and bending deformation. The analysis demonstrates that the fatigue life of ring-welded lap joints increases with an increase in the thickness of the sheet with a hole and the hole diameter, while decreases with the increasing loading ratio and bending deformation. By utilizing this method, the predicted fatigue life of various ring-welded lap joints can be controlled within a range that is four times of the measured values.