Computational crack propagation modeling of welded structures under as‐welded and high frequency mechanical impact (HFMI) treatment conditions

Abstract

AbstractThe fatigue damage assessment of welded structures is of critical importance in the design of many engineering structures. The thermomechanical nature of the welding process leads to undesired tensile residual stresses, which results in fatigue performance degradation of welded structures. High‐frequency mechanical impact (HFMI) technique offers significant potentials to induce compressive residual stresses into the welded joints, thus improving fatigue life of welded parts. In this paper, a new crack propagation modeling approach considering effects of residual stress fields and the crack closure based on a modification of the Forman model is proposed to assess fatigue crack propagation performance of welded joints under as‐welded and HFMI treatment conditions. Experimental residual stress and fatigue data sets of 5083‐H321 aluminum, CSA 350W, ASTM A514, S355, and S960 steel welded joints are used to validate the proposed approach. Both predicted and experimental results show that the fatigue life improvement by the HFMI treatment depends on the applied stress level and material type. The fatigue life improvement is greater at the lower stress levels with a factor of more than 10–30 times, and the fatigue life increase becomes less at the higher stress levels with a factor of two to three times depending on the material type of welded joints. The fatigue life improvement by the HFMI is more significant with a higher material yield strength. Compared results showed that the proposed modeling approach provides efficient and accurate life predictions of the welded joints of five different materials under both as‐weld and HFMI conditions. The proposed modeling framework can be used as an effective analysis technique for fatigue crack propagation life of welded structures under pre‐ and post‐weld treatment conditions to account for residual stress fields.