Toughening mechanisms of structural ceramics

Toughening mechanisms in polycrystalline ceramics were discussed based on Griffith's energy equilibrium. These mechanisms were classified into three groups: (1) The frontal process-zone toughening mechanism, which is related to the intrinsic fracture energy of a material, and creates a damaged zone ahead of the crack tip. This mechanism generates intrinsic fracture toughness in a material, (2) The crack-surface-bridging mechanism, which is caused by stress shielding, resulting from bridging and/or interlocking in a process-zone wake, and creates an extrinsic increase in crack resistance. (3) The macroscopic crack deflection mechanism, in which the crack deflection decreases the energy-release rate and, consequently, the stress-intensity factor at the crack tip, thus apparently enhancing the fracture toughness.