Plastic constants of fracture

Based on the theory of an ideal rigid-plastic body, an approach is formulated for determining fracture constants on the basis of standard mechanical tests on uniaxial extension of plane and cylindrical samples. Instead of the experimentally determined characteristics of fracture of materials (dimensionless elongation and constriction of the sample during its fracture), two invariant tensor characteristics of the degree of sample deformation are introduced, which correspond to the moment of origination of a macrocrack and critical strain at the crack tip determining the process of crack propagation.