Effective Fracture Toughness in Al2O3-Al2O3/ZrO2 Laminates

During the processing of laminar ceramics, biaxial residual stresses can arise due to the thermal mismatch between different layers. For ceramic multilayers, the beneficial consequences of compressive stresses at the surface are well known: increase in strength, apparent toughness and reliability. Nevertheless, the resulting tensile stresses may induce a negative influence in the effective fracture toughness if the tensile stresses are high. The weight function technique is used to assess the stress intensity factor corresponding to the residual stresses field. The influence of geometrical parameters such as thickness, number of layers and tension/compression thickness ratio is analyzed. For different multilayers (Al2O3 -xAl2O3/(1-x)ZrO2), effective R-curves are presented. The existence of an optimal architecture that maximizes the toughening is exposed as well as two tendencies on the apparent R-curve that define different fracture patterns: brittle failure or layer-by-layer fracture.