FRACTURE-MECHANICS PRINCIPLES

The principles of linear elastic fracture mechanics (LEFM) were develo ped in the 1950s by George Irwin (1957). This work was based on previo us investigations of Griffith (1920) and Orowan (1944). Irwin (1957) d emonstrated that a crack shape in a particular location with respect t o the loading geometry had a stress intensity associated with it. He a lso demonstrated the equivalence between the stress intensity concept and the familiar Griffith criterion of failure. More importantly, he d escribed the systematic and controlled evaluation of the toughness of a material. Toughness is defined as the resistance of a material to ra pid crack propagation and can be characterized by one parameter, K-IC. In contrast, the strength of a material is dependent on the size of t he initiating crack present in that particular sample or component. Th e fracture toughness of a material is generally independent of the siz e of the initiating crack. The strength of any product is limited by t he size of the cracks or defects during processing, production and han dling. Thus, the application of fracture mechanics principles to denta l biomaterials is invaluable in new material development, production c ontrol and failure analysis. This paper describes the most useful equa tions of fracture mechanics to be used in the failure analysis of dent al biomaterials.