Geomaterials, 2013, 3, 132-137 http://dx.doi.org/10.4236/gm.2013.34017 Published Online October 2013 (http://www.scirp.org/journal/gm) Numerical Crack Analysis of Blunt Rock Indenters by an Indirect Boundary Element Method Narges Sadat Tayarani 1 , Mohammad Fatehi Marji 2 1 Faculty of Mining and Metallurgy, Yazd University, Yazd, Iran 2 Mine Exploitation Engineering Department, Faculty of Mining and Metallurgy, Yazd University, Yazd, Iran Email: n.tayarani@gmail.com Received March 30, 2013; revised April 30, 2013; accepted May 7, 2013 Copyright © 2013 Narges Sadat Tayarani, MohammadFatehi Marji. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT Linear elastic fracture mechanics principles are widely applied for the analysis of crack problems in rock fracture me- chanics. 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 dis- continuity 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 ele- ments i.e. quadratic elements, has been used to calculate displacement discontinuities and also to reduce the singulari- ties 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 com- pared 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. Keywords: Numerical Modeling; Boundary Element Method; Rock Indentation; Linear Elastic Fracture Mechanics (LEFM) 1. Introduction One of the complex issues in the field of rock engineer- ing is the rock cutting and the rock indentation processes. In the mechanical rock breakage, the cutting tool is in- truded into the rock to generate large and small frag- ments and internal cracks. The process is characterized as a rock indentation process [1,2]. Indenters may be di- vided into two general categories: sharp indenters (e.g. a cone or pyramid) and blunt indenters (e.g. a sphere) as shown in Figure 1. Study on rock fragmentation by these two indenters can be found in the experimental and analytical works of some researchers [1-6]. In some of these studies the at- tempt was to apply different mechanisms such as Hert- zian contact mechanics or cavity expansion model to the indentation of rocks with moderate thrust forces and to investigate the limits of these methodologies. Blunt indenters were widely used in disc cutters and some other excavation machines using chisel picks (Fig ure 2). Howarth and Roxborough have studied the appli- cation of blunt indenters in the form of disc cutters using as cutting tools for Tunnel Boring Machines (TBM). They experimentally investigated the effect of penetra- tion depth, joint width and disc edge angle on the thrust force and the specific energy (SE) may be required for (a) (b) Figure 1. Indentation phenomena. (a) sharp indenter. (b) blunt indenter. Copyright © 2013 SciRes. GM