Nature overcomes a similar issue by arranging natural composites, made of mostly brittle constituents, in discontinuous and hierarchical microstructures.
These are heterogeneous materials with brittle constituents, characterized by material inhomogeneities that are not negligible compared to the structure size.
The hard as well as brittle constituents are typically difficult-to-machined materials, and this character upsurges the machining cost.
Nacre, the inner layer of mollusk shells holds the key to the development of an effective composite system for protecting structures from extreme loads due to its superior fracture toughness, despite its brittle constituents.
A second critical issue is ensuring that the brittle ceramic cell constituents, i.e. the electrodes and electrolyte, exhibit high mechanical reliability by mitigating potential sources of thermal-mechanically induced stresses that can lead to fracture during operation and/or shutdown.
Incorporating softer constituents into brittle materials can alleviate stress concentration, leading to tougher and stronger composites.
Nacre in abalone shell exhibits prominently high toughness and remarkable inelasticity when subjected to the external loads, despite the brittle nature of its main constituent.
By adopting the tensile strength criterion and assuming either brittle or ductile failure of the constituent solid skeleton of the porous media, lower and upper bounds of the fracture toughness are obtained.
At this stage, each constituent is assumed to be brittle elastic.
Jarvie (2007) proposed BI definitions based on the mineral composition of the rock, dividing the most brittle minerals by the sum of the constituent minerals in the rock sample, considering quartz as the more brittle minerals; after Jarvie, some equations, Perez and Marfurt (2013), Nayak and Singh (2007), Altindag (2003), also used the following equation for BI calculation.
