Why does resistance to crack propagation increase as a microcracked ceramic crack grows longer?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

advanced structural ceramics Figure 1: Resistance to cracking in transformation-toughened zirconia. In a ceramic composed of tetragonal zirconia dispersed in a zirconia matrix, the stress field advancing ahead of a propagating crack transforms the small tetragonal particles to larger monoclinic particles. The larger particles exert a crack-closing force in the process zone behind the crack tip, effectively resisting propagation of the crack.

In advanced structural ceramics, resistance to crack propagation increases as a crack grows longer due to the formation of a process zone behind the advancing crack tip.

As the main crack propagates, microcracks open in the material adjacent to the crack path. These microcracks, located in the wake or process zone behind the crack front, result in a localized increase in volume. This volumetric expansion exerts a closing force on the main crack, effectively hindering its further advancement. Consequently, the resistance to propagation increases the farther the crack propagates, as the cumulative effect of these microcracks continues to exert a closing pressure on the crack tip.1