Optimal threshold strength of laminar ceramics

Laminar ceramics in which alternating layers of material are bonded togethe r exhibit a threshold strength if one set of layers has a compressive resid ual stress. The threshold strength is substantial if the mechanical propert ies of the component ceramics are chosen wisely. Optimization of the thresh old strength for a system with homogeneous elastic properties in terms of t he layer thicknesses, fracture toughness and residual stress is presented. The best result is shown to be associated with the toughest material and th e highest residual stress, but the choice of a laminar system exhibiting su ch features is limited to available ceramics. For each material system, the threshold strength is further optimized by making the layers as thin as po ssible. The thinness achievable will be limited by the technological proces ses used to make the laminar ceramic and by material stability. Given a lam inar ceramic system with a specific compressive layer thickness, the thresh old strength is optimized by selecting a ratio of tensile to compressive la yer thickness. If the system mechanical properties are favorable, the optim ized threshold strength can be comparable in magnitude or much larger than the compressive residual stress.