# Elastic Plastic Fracture Mechanics

When a plastic zone of considerable size appears near the crack tip, it is no longer possible to describe the stress and strain fields using a single parameter, as was the case with the stress intensity factor, KI, not is it possible to define the fracture toughness of the material using its critical value. Hence, it is necessary to introduce parameters which are not limited by linear-elastic material behaviour, such as the crack tip opening displacement and the J integral.

Unlike the linear-elastic fracture mechanics, in the case of elastic-plastic fracture mechanics, stable crack growth may occur prior to reaching of critical parameter values, thus in this case the fracture is ductile rather than brittle.

The J-integral represents a way to calculate the strain energy release rate, or work (energy) per unit fracture surface area, in a material.The theoretical concept of J-integral was developed in 1967 by Cherepanov and in 1968 by Jim Rice independently, who showed that an energetic contour path integral was independent of the path around a crack. Later, experimental methods were developed, which allowed measurement of critical fracture properties using laboratory-scale specimens for materials in which sample sizes are too small and for which the assumptions of Linear Elastic Fracture Mechanics do not hold...