Application of the Theory of Critical Distances to quasi-brittle fracture with a developed process zone

Abstract

The results of theoretical and experimental studies of quasi-brittle fracture of plaster plates containing a circular hole and subjected to non-uniformly distributed compression are presented. To predict the critical load at the instance of crack initiation in case of quasi-brittle fracture with a developed process zone, it is proposed to modify the failure assessment methods (fracture criteria) based on the Theory of Critical Distances (TCD). The modified methods contain a complex parameter which is associated with the fracture process zone and considers not only the material microstructure, but also the plastic properties of the material, the geometry of the specimen, and boundary conditions. Formulae are obtained for critical stresses in the problem of tensile crack initiation in a plate with a circular hole subjected to biaxial loading by tension along one axis and compression along the other axis. The deformation and fracture processes in quasi-brittle material are experimentally studied and the modified methods are verified. In the first series of tests, the effect of the hole size on the initiation of tensile cracks at the hole under constant boundary conditions is described, and in the second series of tests, the effect of boundary conditions on the initiation of tensile cracks at the hole of fixed diameter is investigated. The results of the calculations are in good agreement with the experimental data. It is indicated by the results obtained that the modified TCD methods properly describe the effect of both the hole size and the boundary conditions on the fracture of quasi-brittle material.