Fatigue assessment of welded thin-walled automotive steels using effective stress methods

Abstract

Local weld toe geometry is a determining factor in the fatigue strength of as-welded joints. Nevertheless, it is still unknown how real weld geometry can be incorporated into fatigue assessments using notch stress-based approaches. This study aims to investigate the use of effective stress methods to account for different local weld geometries in fatigue assessments. The fatigue strength of welded overlap joints made of automotive and structural steel thin sheets is experimentally and numerically studied. The experiments included specimens with different geometrical characteristics: welds with undercut defects, normal quality welds with sharp transition, and welds with blunt notches with high weld toe radii. The different geometrical weld qualities demonstrated significantly different fatigue resistances, with endurable characteristic stresses at two million load cycles ranging from 54 to 114 MPa. By considering the overlap joint eccentricity and angular imperfections through strain gage measurements, three different base metal-independent fatigue resistances were obtained, corresponding to the studied weld qualities. The use of effective stress concepts consolidated the fatigue data of the different weld qualities into a single scatter band with scatter range index values of 1:Tσ < 1.3. However, the critical distance and stress averaging length that minimized scatter were much less than conventionally recommended for welded connections. The findings of this work suggest that the effective stress concepts can be regarded as approaches to incorporate real weld geometries into fatigue assessments.