Elastic Fracture Toughness of Ductile Materials

Linear elastic fracture mechanics has been widely used for fracture analysis of cracked metals. For ductile materials, it is known that the yielding of a crack front results in the easing of stress intensity at the crack front, which ultimately increases the total fracture toughness of the material. Therefore, to use linear elastic fracture mechanics for prediction of the failure of ductile materials requires the extraction of the elastic portion of the fracture toughness. The intention of this paper is to develop a new theory of fracture toughness for ductile materials. Two methods, namely the elastic-plastic parameter method and the failure assessment diagram method, are proposed to determine the elastic fracture toughness. After verification of derived models, the developed elastic fracture toughness theory is applied to ductile metal pipes. Factors that affect the elastic fracture toughness are also studied in the paper. It is found in this study that the elastic fracture toughness is a function of the geometry of cracked bodies, material properties, loading conditions, and mode mixity. The developed theory of elastic fracture toughness will enable accurate prediction of the fracture conditions for both brittle and ductile metals, which is essential to prevent catastrophic failures of structures made of ductile metals.