Fracture Mechanics

This chapter describes fracture toughness as the mechanical resistance or the ability of a crack-containing material to absorb strain energy at the crack tip for subsequent crack growth and propagation under an applied stress. For comparison, the modulus of toughness or simply toughness is the ability of an initially crack-free material to absorb strain energy to deform or fracture under applied strains. The modulus of toughness is a short term for the strain-energy density (U) that defines the ability of a material to absorb energy and plastically deform without fracturing. It is graphically illustrated as the area under a stress-strain curve under quasi-static conditions. On the other hand, Charpy impact strain energy is also referred to as the impact fracture toughness of a notched specimen under a dynamic condition evaluated at a temperature range. Moreover, quasi-static condition prevails at low loading rates describing linear-elastic fracture mechanics (LEFM) of brittle materials, which allow a very small plastic zone ahead of crack tips. The main emphasis is to define the quasi-static plane-strain fracture toughness as a dimensional-independent property for several crack configurations, the crack growth rate and the impact toughness of cracked specimens.