Abstract

A computational method to simulate rock cutting is developed and evaluated. It aims to obtain the forces on the pick during cutting. The explicit FEM is chosen to model the pick-rock interaction. It allows accelerated calculations due to parallelization, a robust contact algorithm and superior material description with constitutive equations. A damage-plasticity law is chosen and modified with user-subroutines. The introduction of an element deletion routine evades the expected critical mesh distortions. Infinite elements model the boundary of the model in order to suppress acoustic wave reflection and unrealistic interference. Fitting the yield function numerically to stress states that cause fracture calibrates the constitutive equations. These stress states are obtained from inexpensive Brazilian tests and uniaxial compression tests. The tensile strength concept is extended to a two-parameter description of tensile strength and loaded volume using the Weibull theory.

1 Introduction
1.1 Principles of Excavation

Roadheaders (Figure 1) are widely used for excavation and mining purposes but high material strengths limit their usability (Tockner 1999). Nowadays a challenge is to extend their field of application to harder and more abrasive rock materials. The forces on the pick are of great importance and determine wear and especially the efficiency of the machine. Additionally the cutting capability is naturally limited by the weight of the machine, which makes the reduction of reaction forces by optimizing the process parameters rewarding (Tockner 1999). Cutting brittle materials is a stepwise phenomenon of separation and removal of a large segment, the so-called chip (Chiaia 2001). The basic physical phenomenon during rock cutting is fracturing and fragmentation of the rock induced by the mechanical cutting tool (Rojek et al. 2011). The tool-rock interaction determines the forces on the pick and thus the required work. The reduction of tool forces at steady excavated volume is rewarded with increasing cutting efficiency (Tockner 1999). Three forces are distinguished in rock cutting: The normal force, acting in the direction of excavation, the cutting force which acts in line with the cutting direction and finally the side force which is transverse to both other forces (Su & Akcin 2011). Figure 2 shows the principle of cutting and the predominant forces. Variation of pick geometry, cutting depth or attack angle will result in an alteration of these forces and determine the efficiency of the process (Tockner 1999).

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