Cross-Scale Fatigue Crack Propagation in the Heat-Affected Zone of Welded Joints

This study presents a multiscale numerical simulation of the behavior of crack growth in the heat-affected zone (HAZ) of AH36 marine steel welded joints under fatigue loading from the micro-scale to the macro-scale. The MD-FEM method and the multiscale coupling-optimized XFEM method were used to simulate fatigue crack propagation from micro-scale to meso-scale and from meso-scale to macro-scale. A total of 10,900,788 tension–tension fatigue cycles was realized. Information across different scales was transferred via boundary displacement transfer, crack morphology equivalence, and tip tracking. Building upon our previous investigation into fatigue crack growth behavior at the micro-scale, in which crack extension was limited to 469 Å, the present study encompasses the complete process of fatigue cracking from micro-scale initiation to macro-scale instability. Furthermore, the crack tip morphology and propagation pathways obtained from micro-scale molecular dynamics simulations are employed to optimize and calibrate the corresponding XFEM simulations at both the meso- and macro-scales. Results demonstrate that the phenomenon of interconnection between voids and the main crack near the crack tip has a significant influence on the crack propagation rate and path. During cycling, the propagation rate of the main crack increases significantly during its interconnection with voids, whereas crack propagation is significantly hindered when the interconnection is completed or when voids undergo self-closure. Furthermore, both theoretical simulations and experiments revealed the occurrence of crack propagation instability at the meso-scale. The present examination of the entire fatigue crack propagation process indicates that the MD-FEM method and the multiscale coupling optimized XFEM method in this study are fundamentally accurate in representing both the crack propagation process and the crack tip morphology. The results obtained in this paper can serve as a reasonable prediction of fatigue damage mechanisms in the HAZ of AH36 marine steel welded joints.