Local approaches and XFEM used to estimate life of CFRP repaired cracked welded joints under fatigue loading

Abstract

Three different local approaches, the Theory of Critical Distances (TCD), the Notch Stress Intensity Factor (NSIF) and the Strain Energy Density (SED), and the Extended Finite Element Method (XFEM) were applied to estimate the fatigue life of unrepaired and CFRP patches repaired cracked welded joints. The effects of CFRP modulus and thickness on the fatigue life of welded joints with different initial crack depths were investigated. The fatigue damage evolution equation using the loading frequency as a new damage variable was used to describe the degradation process. Fatigue life assessment results and crack growth paths compared with experimental results using these methods. The results show that the fatigue life and fatigue strength decrease as the increase of the initial crack depth. Three different fatigue failure modes can be observed from experimental results. The TCD, NSIF, and SED can reliably predict the fatigue life of welded joints without CFRP patches, but it needs to further investigate the values of estimation parameters of welded joints with CFRP patches for the NSIF and the SED. Fatigue crack growth paths and lives predicted by the XFEM and actual results are in good agreement, and the accuracy and reliability are validated by test data.