Qualitative description on channel cracking in ceramic type coatings due to substrate tension using 3D discrete element method

Abstract

The objective of this work is to simulate qualitatively the initiation and propagation mechanism of channeling cracks in ceramic coatings due to uniaxial and biaxial substrate tension. Most of the previous simulations on damage evolution in coating/substrate structures were performed in 2D; however, in the current study, to demonstrate the damage evolution both in coating thickness and surface, several numerical simulation was performed in the 3D space frame. To this end, a FORTRAN code of Discrete Element Method (DEM) with Euler-Bernoulli beam bond elements and the random spherical arrangement was developed. Furthermore, the brittle fracture criterion was assigned for the coating while the substrate was considered to have linear elastic and isotropic behavior and to remain intact during loading. Three unit cells with the same dimensions and different coating thicknesses were considered. It was found that the coating thickness affects the damage initiation mechanism. In both uniaxial and biaxial tension, the increase of the coating thickness resulted in damage initiation near the interface and propagation to the top surface. At the surface view, the results showed that the free surfaces and edges could be susceptible to damage initiation in thin coatings.