Unveiling fracture mechanics of a curved coating/substrate system by combined digital image correlation and numerical finite element analyses

A mechanism of coated, curved substrate failure is characterized via a C-ring compression test and multiscale modeling analysis. Coating crack formation is driven by sudden through-thickness cleavage in accordance with Mode I fracture type. The fracture is arrested at the coating/substrate interface. The cracks continue to widen as the underlying substrate experiences periodic regions of high stress under the crack and regions of relaxed stresses under the remaining intact coating. An analytical, closed form solution model developed via curved beam theory captures the hoop stress in the axis transverse to external loading and predicts the external load at crack initiation. After the onset of cracking, the system transitions to cleavage driven failure, which is simulated via element deletion failure in a small-scale explicit dynamics finite element model. The macroscale explicit dynamics finite element model, analytical solution, and bulk experimental results agree. The correlation between coating microstructure and deposition method is also investigated and reveals that high interfacial roughness and equiaxed grain morphology correspond to higher loader carrying capability and lower crack density while low interfacial roughness and smooth columnar grains correspond to higher strain to coating failure.