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How does microcracking increase a ceramic material's resistance to crack growth?
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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, microcracking serves as a mechanism to increase fracture toughness by impeding the propagation of a main crack. This process occurs in single-phase polycrystalline ceramics with anisotropic grains or in intentionally biphasic microstructures through two primary effects:1
- Energy Absorption: As a main crack advances, tiny microcracks form on either side of its path. The energy required to create these subsidiary cracks increases the total energy demand for the main crack to propagate further.1
- Crack Closure: Microcracks that open in the process zone—the area adjacent to the main crack but behind the crack front—result in a localized increase in volume. This volumetric expansion exerts a closing force on the main crack, effectively resisting its continued growth.1
Consequently, the material's resistance to crack propagation increases as the crack extends further into the microstructure.1