Impact of angular distortion on the fatigue performance of high-strength steel T-joints in as-welded and high frequency mechanical impact-treated condition

In general, distortion has significant effects on the assembly process of welded structures and remarkable influences on the strength of the welds. Therefore, this work focuses on the effect of angular welding distortion on fatigue strength to improve transferability of specimen results to components. Experimental investigations cover manufacturing and fatigue testing of three single-sided transversal stiffeners series exhibiting different angular distortions. The fatigue test results of as-welded specimen show a distinct link between fatigue performance and initial angular distortion. However, in case of a high frequency mechanical impact (HFMI)-treated weld toe, the fatigue strength increases up to base material level and is independent of the distortion. A comprehensive numerical analysis reveals a complex interaction between the applied nominal load, initial specimen distortion and the local stress field. In this context, an engineering-feasible assessment is derived to estimate the local effective stresses featuring the acting local stress range as well as the stress ratio. The application of this distortion factor enables the set-up of a uniform S/N-curve with a significantly reduced scatter band.