Criteria for Crack Deflection-Penetration in EBC Coated Ceramics: A Parametric Study

Abstract

This article discusses results obtained from a parametric study to analytically evaluate the impingement of a crack at the interface of an environmental barrier coating (EBC) and a monolithic Silicon nitride (Si 3 N 4 ) layered ceramics substrate. The study establishes a correlation that leads to determine if the crack is arrested or advanced by either penetrating or deflecting along the EBC/substrate interface. A finite-element-based fracture mechanics methodology is utilized to perform these calculations. Critical parameters determining penetration-deflection conditions in relation to EBC's physical characteristics, such as porosity level, voids, and mini cracks, are determined for a single layer and multi-layered coating system coordinating the interactions between the EBCs (Mullite, Mullite mixture, Silicon nitride, etc.) and the substrate structure. Results showing thermo-mechanical stresses and stress/strain energy release relations with respect to crack penetration-deflection are presented and discussed as the crack is advanced. = stress at the interface r and = radial distance and the polar angle f ij ( ) = angular distribution of the singular stress field = defines the strength of stress singularity ␣ and ␤ = Dundurs bi-material parameters E' j = E j is for plane stress E' j = E j /(1 -j ) for plane strain (1 and 2 denote the material) = shear modulus [MPa] G d = (material 1) is the strain energy release rate associated with the "deflected" crack or adhesive failure G p = (material 2) is the strain energy release rate associated with the "penetrated" crack (or cohesive failure of adjacent material) G pc = cohesive or penetrated fracture energy G dc = adhesive or deflected fracture energy, respectively K 1 and K 2 = stress intensity factors for the interface crack ε = a function of material constants Keywords

Numerical study on crack bifurcation of self-healing fiber-reinforced ceramic matrix composite

“…However, most studies focused on composite material having two-layered structures, while there were few studies related to the crack bifurcation of composite materials having an interlayer of constant thickness (such as three-layered shFRC). In addition, although crack bifurcation criteria based on fracture strength and fracture energy at the interface were studied (e.g., Abdul-Aziz et al, 2015;Ahn et al, 1998;He and Hutchinson, 1989;Martinez and Gupta1994;, Parmigiani and Thouless, 2006), studies on the effects of the sintering characteristics of each layer have not been conducted, to the best of the author's knowledge. It is widely known that the relative density, pore size, and grain size of ceramics, which relate to the mechanical properties, depend on the sintering.…”