Nearly brittle fracture of solids, that is, brittle fracture without appreciable plastic deformation has been divided into two types. One is low stress fracture in. nearly elastic large structures, which occurs before general yielding. The other is brittle fracture of small laboratory specimens below the ductility transition temperature, which occurs immediately after the general yeilding, or during yeilding and where microeracks are observed prior to fracture. The fracture is not considered in either case as consisting of a single process.
However, as far as fracture criterion is concerned, it may be described by a certain single event, although it may involve the previous history of stress and strain. In the present paper, the energy balance considerations are assumed in the process, and the fracture criteria for both types of fracture have been obtained respectively. We have taken the line of considerations that as many behaviors as possible in the same materials should be explained by any proposed fracture criterion, or at least the criterion should not be inconsistent with any one of many data on the materials established experimentalllΒ’.