CRITICAL DISTANCE APPROACH TO PREDICT FRACTURE

The term 'Failure' of a material may be defined as its fragmentation or separation, under the action of an external force, into two or more parts. It may occur as a sudden breaking up of a material either as the result of extensive plastic deformation or as a result of fatigue in a part of the material. The term 'Fatigue Failure' may be defined as the fracture which takes place under repeatedly applied fatigue stresses. It occurs at stresses well below the tensile strength of the materials. The 'Fatigue Failure' takes place due to initiation of the micro cracks at the surface of the material. The micro cracks act as the points of stress concentration. The theory of critical distances (TCD) proposes that the failure of a body containing a stress concentration (e.g. a crack or notch) can be predicted using elastic stress information in a critical region close to the notch tip. The critical region is defined in terms of a characteristic material length constant L, which is a function of the fracture toughness Kc and a failure stress oo.