Coupling fatigue cohesive zone and magnetomechanical model for crack detection in coating interface

Abstract Coatings have been used extensively to extend the service life of components. During their service process, fatigue crack may initiate and propagate along the interface between coating and substrate. In order to evaluate the interfacial crack properly by magnetic nondestructive testing, the concept of cohesive zone and the phenomenon of spontaneous magnetization are introduced, and the fatigue cohesive zone-magnetomechanical coupling model is established. The interfacial crack initiation time and propagation behavior can then be predicted, and a new magnetic characteristic indicator dHmax/dN is further proposed to characterize the crack propagation rate. In the case of three point bending fatigue loads with the maximum amplitude at 0.25 mm, calculation results show that crack initiation occurs when the loading cycle number reaches 354, and the corresponding magnetic field intensity increases to the threshold Hmax = 238.1A/m. Furthermore, the magnetic field accumulation rate dHmax/dN is linearly related to the crack propagation rate at the fatigue crack stable propagation stage. In order to verify the theoretical model, the magnetic signals along interface are collected and analyzed under three point bending fatigue test. It indicates that the experimental result is consistent with the theoretical calculation, and the established model can support magnetic nondestructive testing of coatings.