Simulation of crack coalescence mechanism underneath single and double disc cutters by higher order displacement discontinuity method

Mohammad Fatehi Marji

(1Faculty of Mining & Metallurgy, Yazd University, Yazd, Iran)

Abstract:The present research is focused on the numerical crack coalescence analysis of the micro-cracks and cracks produced during the cutting action of TBM disc cutters. The linear elastic fracture mechanics (LEFM) concepts and the maximum tangential stress criterion are used to investigate the micro crack propagation and its direction underneath the excavating discs. A higher order displacement discontinuity method with quadratic displacement discontinuity elements is used to estimate the stress intensity factors near the crack tips. Rock cutting mechanisms under single and double type discs are simulated by the proposed numerical method. The main purposes of the present modeling are to simulate the chip formation process of indented rocks by single and double discs. The effects of specific disc parameters (except speed) on the thrust force F_t, the rolling force F_r, and the specific energy E_S are investigated. It has been shown that the specific energy (energy required to cut through a unit volume of rock) of the double disc is less than that of the single disc. Crack propagation in rocks under disc cutters is numerically modeled and the optimum ratio of disc spacing S to penetration depth P_d (i.e. S/P_d ratio) of about 10 is obtained, which is in good agreement with the theoretical and experimental results cited in the literature.

Key words:TBM disc cutter; double discs; cracks coalescence; higher-order displacement discontinuity method; specific energy