Anthony Ezanno

Numerical simulation of low-cycle fatigue behavior of welded joints for naval applications: influence of residual stresses

A methodology is described and evaluated for the numerical prediction of the low-cycle fatigue strength of welded assemblies taking into account the effect of local residual stresses. The methodology involves (i) modeling the cyclic behavior of base metal and heat affected zone materials of welded joints, (ii) establishing a simplified method to analytically predict the local notch fatigue behavior, (iii) defining a crack initiation criterion including mean stress effect. Notched specimens are first designed to produce a first configuration without residual stresses, a second one with tensile residual stresses, and a third one with compressive residual stresses. Cyclic tests are performed under repeated tensile loading. These tests allowed describing the influence of the initial residual stress states on the fatigue life quantified and analyzed on the basis of experiments. The application of the simplified method managed to capture the impact of residual stresses on the local cyclic behavior and the crack initiation resistance. Finally, the fatigue life prediction method is applied on thick welded T-joints. The deep hole drilling and the contour method are used to determine residual stresses in the weld toe. The proposed modeling approach is finally evaluated and discussed by correlating numerical predictions with experimental results obtained on T-joints loaded in four-point bending fatigue.