Energy Principle of Elastic‐Plastic Fracture and Its Application to the Fracture Mechanics of a Polycrystalline Graphite

Abstract

Utilizing loading‐unloading procedures on the basis of nonlinear energy principles, an empirical method for evaluating the nonlinear fracture mechanics parameters, i.e. the nonlinear energy toughness G c , the crack growth resistance R , the J c value, and the plastic energy dissipation rate φ p , was established. These parameters were experimentally determined for an isotropic polycrystalline graphite enabling the elastic‐plastic fracture mechanics of graphite to he addressed. The graphite exhibits a typical elastic‐plastic fracture with ×38% of the total fracture energy consumed as plastic energy. It was concluded that the widely used assumption of the applicability of linear elastic fracture mechanics to polycrystalline graphites can lead to erroneous results if the fracture tests are conducted with the usual specimen size. The proposed experimental method for evaluating elastic‐plastic fracture parameters is potentially very effective for studying various nonlinear fractures in other ceramic materials.