Effect of surface roughness on the multiaxial fatigue behavior of WC-12Co coated bolts in a helicopter rotor system

The damping bolt with a tungsten carbide coating is a critical component of the helicopter rotor system, and its fatigue life directly influences operational safety. This study introduces a mesoscale numerical simulation approach to examine the effect of surface roughness on the fatigue crack propagation behavior of WC-12Co-coated bolts. The method integrates the SWT critical plane theory with continuum damage mechanics. By correlating the geometric features of interface surface roughness with the multiaxial fatigue response of WC-12Co-coated bolts, the results demonstrate that increasing interface roughness Ra markedly deteriorates the coating’s mechanical properties, leading to a systematic reduction in fatigue life. In addition, the elastic modulus mismatch between the coating and the substrate further aggravates deformation incompatibility, accelerates interface damage accumulation, and promotes preferential crack growth toward the coating side. Moreover, the spatial distribution of roughness parameters (e.g., correlation length R 1 ) exhibits a non-monotonic influence on interface life. Overall, the findings indicate that surface roughness characteristics have a significant influence on the multiaxial fatigue life of coated bolts.