Optimal threshold strength of laminar ceramics

Laminar ceramics in which alternating layers of material are bonded together exhibit a threshold strength if one set of layers has a compressive residual stress. The threshold strength is substantial if the mechanical properties of the component ceramics are chosen wisely. Optimization of the threshold strength for a system with homogeneous elastic properties in terms of the layer thicknesses, fracture toughness and residual stress is presented. The best result is shown to be associated with the toughest material and the highest residual stress, but the choice of a laminar system exhibiting such features is limited to available ceramics. For each material system, the threshold strength is further optimized by making the layers as thin as possible. The thinness achievable will be limited by the technological processes used to make the laminar ceramic and by material stability. Given a laminar ceramic system with a specific compressive layer thickness, the threshold strength is optimized by selecting a ratio of tensile to compressive layer thickness. If the system mechanical properties are favorable, the optimized threshold strength can be comparable in Magnitude or much larger than the compressive residual stress.