On material fracture criteria

Based on the nonlinear mechanics of material fracture, a model of the fracture of materials with actual (discrete) structures has been constructed. The model is supported by proofs that crack resistance $K_{1c}$ and fracture toughness $G_{1c}$ obtained from the energy conservation law without using the assumptions adopted in the linear material fracture mechanics serve as the force and energy criteria in the nonlinear fracture mechanics. It has been shown that energy criterion $G_{1c}$ in the nonlinear mechanics is much greater than $G_{1c}$ in the linear fracture mechanics.