Extending the theory of critical distances to quasi-brittle fracture

The results of theoretical and experimental studies of brittle and quasi-brittle fracture of plaster plates containing a circular hole and subjected to non-uniformly distributed compression are presented. This paper summarizes the results, partially published by the author earlier. To predict the critical load at the instant of crack initiation in case of quasi-brittle fracture with a developed process zone, it is proposed to modify the fracture criteria based on the theory of critical distances. The modified criteria 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 brittle and quasi-brittle geomaterials under non-uniformly distributed compression are experimentally studied and the developed criteria 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 developed TCD-based criteria properly describe the effect of both the hole size and the boundary conditions on the fracture of quasi-brittle material.

Automated summary

The paper presents the results of theoretical and experimental studies on brittle and quasi-brittle fracture of plaster plates with a circular hole under non-uniform compression. Modified fracture criteria based on the theory of critical distances are proposed to predict the critical load at the instant of crack initiation. Experimental verification indicates that the developed criteria can effectively describe the influence of hole size and boundary conditions on the fracture of quasi-brittle materials.