Abstract
Linear elastic fracture mechanics principles are widely applied for the analysis of crack problems in rock fracture mechanics. Rock indentation is an important and complicated problem among rock engineering issues. In this paper, in addition to the fracture criterion of maximum tangential stress adjacent to crack tip, the higher order displacement discontinuity method (which is a version of the indirect boundary element method) has been used for modeling the crack propagation mechanism under blunt indenters. In order to achieve more accurate results, higher order boundary elements i.e. quadratic elements, has been used to calculate displacement discontinuities and also to reduce the singularities of stress and displacement fields near the crack tip, the special crack tip elements has been used to calculate the stress intensity factors (SIF) at the crack tips. In this modeling, the effect of crack angle on stress intensity factors has been investigated. The numerical results of stress intensity factors obtained from some example problems were compared to the theoretical and experimental results cited in the literature which always show a percentage error less than one percent. The simulated results may pave the way for increasing the efficiency of mining and drilling by improving the design of tools and indentation equipments.
Highlights
One of the complex issues in the field of rock engineering is the rock cutting and the rock indentation processes
In addition to the fracture criterion of maximum tangential stress adjacent to crack tip, the higher order displacement discontinuity method has been used for modeling the crack propagation mechanism under blunt indenters
For investigating the effect of different angles on the value of stress intensity factors, each free surfaces boundary are divided into 20 elements, 10 elements is considered along the crack and blunt indenter is divided to 10 elements
Summary
One of the complex issues in the field of rock engineering is the rock cutting and the rock indentation processes. Howarth and Roxborough have studied the application of blunt indenters in the form of disc cutters using as cutting tools for Tunnel Boring Machines (TBM). They experimentally investigated the effect of penetration depth, joint width and disc edge angle on the thrust force and the specific energy (SE) may be required for (a). Singularity is an inevitable problem in crack issues, this problem has been solved using special crack tip element concept In this analysis based on the linear elastic fracture mechanics (LEFM) principles, both Mode I and Mode II stress intensity factors are computed. The numerical results obtained here are in good agreement with those cited in the literature
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