Nonlocal Criteria for Brittle and Quasi-Brittle Fracture of Geomaterials and Rocks

Sergey Suknev,I Rasskazov,S Kornilkov,S Tkach

doi:10.1051/e3sconf/20185602003

Abstract

Nonlocal criteria are used for prediction materials and rock mass failure near stress concentrations (pores, faults, openings, excavations). A common property of nonlocal fracture criteria is the introduction of the intrinsic material length characterizing its microstructure, which allows one to describe the size effect in conditions of stress concentration. At the same time the scope of their application is limited to cases of brittle or quasi-brittle fracture with a small fracture process zone. To expand the scope of the criteria for cases of fracture with a developed fracture process zone, it is proposed to abandon the hypothesis of the size of this zone as a material constant, associated only with the material structure. New fracture criteria are proposed, which are the development of the average stress criterion, and point stress 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.

Highlights

Nonlocal fracture criteria are based on the concept of the formation of a fracture process zone in the material, in which there is local redistribution of stresses, whereas the main material is deformed elastically until fracture [1,2,3,4,5,6,7,8]
On the basis of the analysis of existing nonlocal fracture criteria, whose distinguishing feature is the introduction of the additional material constant characterizing its structure, it is shown that the scope of their application is limited to cases of brittle or quasi-brittle fracture with a small fracture process zone
To expand the scope of application of the criteria for cases of quasi-brittle fracture with a developed fracture process zone, it is proposed to abandon the hypothesis of the size of the fracture process zone as a material constant associated only with its structure

Summary

Introduction

Nonlocal fracture criteria are based on the concept of the formation of a fracture process zone in the material, in which there is local redistribution of stresses, whereas the main material is deformed elastically until fracture [1,2,3,4,5,6,7,8]. Typical representatives of such quasibrittle materials are geomaterials (concrete, gypsum), and rock. Paper considers the possibility of expanding the scope of application of nonlocal criteria for cases of fracture with a developed fracture process zone

Fracture criteria

Average stress criterion

Point stress criterion

Experimental verification and discussion

Findings

Conclusion