Frontal Process Zone Toughening Mechanism of Ceramic-Based Nanocomposites

摘要

Toughening mechanism for ceramic-based nanocomposites will be presented based on residual stresses around second-phase nano-particles dispersed in matrix grains. The residual thermal stresses around a spherical particle within a concentric sphere of a matrix grain were analyzed to clarify the effects of residual stresses on the toughening mechanism in the frontal process zone. An indirect estimation technique for assessing a critical size of the frontal process zone in ceramics was also proposed using a SEVNB (Single-Edge V-Notched Beam) technique. A three-point flexure test was carried out for nanocomposites and monolithic materials with various depths of a sharp V-shaped notch, and then a critical local stress was calculated at a distance from the notch tip. The frontal process zone size at the beginning of crack propagation, namely, the critical frontal process zone size, was determined as the distance from the notch tip to the point where the local stress has the same value as the flexural strength of the material. The results revealed that both the strength and the critical frontal process zone size must be increased for enhancement of the fracture toughness of ceramics.