The Competition Mechanism of WC–Co Coating Thickness and Interface Strength in Multiaxis Fatigue Failure of Damping Bolt

ABSTRACT The fatigue crack in 18Cr2Ni4WA helicopter damping bolts with WC–12Co coating occurs at the bolt shank; fatigue failure typically exhibits a competitive behavior between matrix‐through cracks and interface delamination cracks. To elucidate the dynamic interaction mechanism of these two crack types under cyclic loading, a synchronous simulation framework that couples multiaxial fatigue theory with a cyclic cohesive zone model is established. Based on the ABAQUS platform, a collaborative architecture integrating USDFLD and UMAT subroutines is developed to simulate matrix continuous damage evolution and interface fatigue delamination behavior. Using representative coating thicknesses (0.1–0.2 mm) and interface strength parameters (85–200 MPa), the simulation results reveal that crack competition is driven by axial strain energy and interface shear strain energy. The critical threshold of interface strength depends on thickness, which governs the transition of the dominant failure mode between matrix fracture and coating delamination. Although thicker coatings delay crack initiation, they tend to shift the competition toward matrix‐dominated failure. The competitive mechanism remains robust under the combined effects of residual stress and multiaxial load.