Suppression of edge cracking in layered ceramic composites by edge coating

A strategy is proposed to reduce surface tensile stresses that develop in ceramic microlaminate structures. As a specific example, surface stresses, which can lead to unwanted edge cracking, appear within a thin alumina/mullite layer bounded by thicker alumina layers after fabrication at some elevated temperature and subsequent cooling. A stress analysis is performed using the finite element method on a geometry in which the (edge) surface of the ceramic sandwich structure has been coated with an overlayer of the alumina/mullite material with thickness proportional to the initial buried layer thickness. These analyses show there is a critical thickness of the overlayer at which the surface tensile stresses can be reduced to zero. Stress concentration factors are calculated numerically for cracks propagating through this structure, and thus the resistance to surface cracking is quantified.