Ductile-Brittle Transition in Geomaterials, Caused by Tensile Stress Concentration

Abstract

The possibility of using known nonlocal and stress gradient fracture criteria to describe brittle, quasi-brittle, and ductile fracture of materials with openings is analyzed. A common property of these criteria is the introduction of intrinsic material length characterizing its structure, which allows one to describe the size effect in conditions of stress concentration. At the same time, the scope of application of nonlocal criteria is limited to cases of brittle or quasi-brittle fracture with a small fracture process zone. To expand the scope of application, new fracture criteria are proposed, which are the development of the average stress criterion, and the stress gradient criterion, and which contain a complex parameter that characterizes the size of the fracture process zone and accounts not only for the material structure, but also plastic properties of the material, geometry of the sample, and its loading conditions. Expressions are obtained for the critical pressure in the problem of the formation of tensile cracks under compression in the samples of geomaterials with a circular hole. The calculation results are in good agreement with the experimental data on the fracture of drilled gypsum plates.