Fracture Toughness for Brittle Fracture of Elastic and Plastic Materials

The crack energy density causes a new expression of fracture toughness for brittle fracture, together with the concept of Barenblatt's characteristic distance d(c) of cohesive zone at the edge of the crack. The Griffith's formula for fracture toughness is modified by the ratio of sigma(T)/Sigma(T), which sigma(T) is the true fracture stress and Sigma(T) the maximum strength of the material obtainable by ordinary processing. The fracture toughness of elastic-plastic material, K-Ic* for brittle fracture is described by the product of sigma(T) and the root of the observed absorption energy by Charpy impact test corrected for instrumental effect, root I-cp(corrected). The characteristic distance d(c) depends linearly on the released elastic energy, which is the physical basis of above-mentioned estimation formula.