Reliable Ceramic Structural Composites Designed with a Threshold Strength. Laminar Ceramics That Exhibit a Threshold Strength

Abstract : We demonstrate that thin, compressive layers within a laminar ceramic both arrest large cracks (surface and internal) and produce a threshold strength, allowing for the first time, the potential for an engineer to reliably design with brittle materials. The stress intensity factor derived for a crack sandwiched between two compressive layers suggests that the threshold strength is proportional to the residual, compressive stress and the thickness of the compressive layer, and inversely proportional to the distance between the compressive layers. Laminates composed of thick alumina layers (605 +/- 11 nm) and thin mullite/alumina compressive layers (37 +/- 1.4 nm) fabricated for this study had a threshold strength of 482 +/- 20 MPa, which is in fair agreement with the theory.