A microcrack evolution-based fatigue damage model for assessment of laser-arc hybrid welded joints in TC4 titanium alloy

High cycle fatigue (HCF) failure in titanium alloy welded structures is predominantly caused by microcrack initiation and propagation induced by microscopic defects during fatigue loading. In this work, an idealized microcrack density-balanced evolution system was employed to characterize microcrack evolution during fatigue loading, and a fatigue damage evolution model was proposed to assess damage progression and predict the fatigue life of TC4 laser-arc hybrid welded joints. Microcrack number density was selected as the damage characterization parameter. A finite element model of the welded joint was developed in ABAQUS, and the fatigue damage evolution process was simulated through the implementation of a user material subroutine (UMAT). The cycle jumping technique was simultaneously employed to substantially decrease computational cost while preserving accuracy. This work adopted the aforementioned method to propose a HCF damage model for welded joints featuring parallel macro-microscale development. Fatigue experimental validation demonstrated good agreement between experimental data and simulation results, with the experimental fatigue life data predominantly lying within the twofold error band of the predicted values.