Microstructural design of platelet reinforced ceramics

Platelet reinforcement can increase the fracture toughness of ceramics. However, the responsible mechanisms are still not clearly understood. In this paper we examine the role of residual stresses due to thermal expansion mismatch. The residual stress distribution can be calculated using the effective-field approximation for ellipsoidal inclusions. The three main toughening mechanisms (crack deflection, crack bridging, and microcracking) are affected differently by residual stresses. We show how the critical flaw size can be properly assessed once the role of residual stress is taken into account, and how the flaw size is related to microstructural features in the material. It follows that by optimizing the ratio of grain size to platelet size, and by controlling the residual stress distribution, the fracture toughness can be increased by platelet reinforcement by more than 50% without a significant decrease in strength.