Multiple crack localization and debonding mechanisms for thin thermal coating films

Abstract

Experimental tests, carried out on small scale alloy specimens covered on one side with a thin thermal coating, have shown complex failure mechanisms. The failure mechanisms observed are due to the competition between two fracture mechanisms. The two mechanisms are: (i) Vertical tensile coating surface cracks and (ii) debonding shear decohesion mechanisms along the interface between the coating and the substrate. The present paper analyzes the mechanical problem of the nonlinear behavior thin film on a stiff substrate adopting a computational approach. Namely, incremental 2D nonlinear finite element simulations. The stiff superalloy substrate is modeled as a thermo-elastic material. The coating film is constitutively modeled as quasibrittle material with a nonlocal elastic-damage constitutive relation. The formation and propagation of cracks between the coating film and the superalloy substrate is modeled by a zero-thickness cohesive-frictional mechanical interface. Finite Element results are analyzed with respect to the distance between the surface cracks and the debonding at the interface coating/substrate. A final consideration on the influence of the thickens of the coating is discussed.