Ceramic fracture mechanics, basics

Since fibrous monolithic ceramics are intended for use in applications where stresses are primarily generated due to bending, strength and work-of-fracture in flexure are measured to evaluate their basic mechanical properties. In addition, factors determining the manner of crack propagation should be... 

Despite the fact that ceramics are inherently brittle, a variety of approaches have been used to enhance their fracture toughness and resistance to fracture. The essential idea behind all toughening mechanisms is to increase the energy needed to extend a crack, that is, in Eq. (11.11). The basic approaches are crack deflection, crack bridging, and transformation toughening. 

The fracture toughness is primarily determined by the strength of the chemical bonds within the ceramic because this determines the energy needed to create fresh surface. Beyond that, other effects within ceramics can occur that impede crack propagation because they require additional energy and thus increase the fracture toughness. The basic mechanisms are discussed in this section in section 7.5, we will see how they can be utilised to strengthen ceramics. 

Depending on the behavior of materials under mechanical actions, they can be classified, vis-a-vis mechanosynthesis or mechanical alloying processes, into two major groups ductile and brittle materials. The former are essentially the materials showing plastic deformation, that is, metals and alloys, and the latter are basically the materials fracturing under mechanical action without noticeable plastic deformation, that is, ceramics. Most of the perovskites are considered in the latter group. 

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