Application of the coupled stress-energy criterion to predict the fracture behaviour of layered ceramics designed with internal compressive stresses

Abstract

One novel approach to improve the apparent toughness of ceramics is to design a multilayer architecture with embedded layers having compressive residual stresses. Surface cracks propagating during mechanical loading can be deflected within the compressive layers, in order to delay the final fracture of the whole structure. The design of high toughness laminates requires understanding the effect of residual stresses on the initiation and propagation of cracks in the material. In this work, a coupled stress-energy criterion is used to predict the initiation and propagation of surface cracks in ceramic laminates upon thermo-mechanical loading. Experiments were conducted on V-notched alumina-based laminates to show the effect of residual stresses and mechanical loading on their fracture behavior. The conditions for crack initiation as predicted for notched specimens agreed with the experimental observations. It is shown that the onset of cracks from V-notches is associated with (i) the tensile residual stresses in the first surface layer and (ii) the depth of the notch. The further propagation of the crack into the first embedded compressive layer was also studied. Based upon the coupled criterion, a short penetration of the propagating crack into the first compressive is foreseen. If the mechanical load is increased, the crack finally deflects within the compressive layer propagating with a certain angle which is also predicted with a good accuracy.