Fracture Toughness of Ionic and Covalent Single Crystals

Griffith and Irwin theories encounter difficulty in analyzing cleavage phenomenon from atomic level. Here, a new definition of the fracture toughness is proposed from the point of view of chemical bond. We find that the fracture toughness can be defined by the bond strength (the appropriate elastic modulus) and the bond density. This appropriate elastic modulus of single crystals is obtained using the complex variable function method. The calculated results of fracture toughness and surface energy of typical ionic and covalent crystals by the present formulae are in agreement with the experimental values of cleavage planes. It demonstrates that our method offers a concise tool for predicting the cleavage toughness, the energy release rate and the surface energy of crystal cleavage planes.