International Journal of Rock Mechanics & Mining Sciences ] (]]]]) ]]]–]]] www.elsevier.com/locate/ijrmms
A 3D FEM methodology for simulating the impact in rock-drilling hammers
Luciano E. Chianga,Ã, Dante A. Elı´ asb
´lica de Chile, 4860 Vicuna Mackenna Avenue, Santiago, Chile Department of Mechanical Engineering, Pontiﬁcia Universidad Cato b ´lica del Peru 1801Universitaria Avenue, Lima, Peru ´, ´ Department of Mechanical Engineering, Pontiﬁcia Universidad Cato Received 27 January 2007; received in revised form 26 July 2007; accepted 21 August 2007
Abstract A three-dimensional (3D) ﬁnite element approach for modeling impact as it occurs in impact tools used in rock drilling is presented. The model permits one to simulate the energy transmission to therock, the bit–rock interaction, and the process of rock fragmentation, all of which are important in the study and evaluation of such tools. The ﬁnite elements method (FEM) analysis allows one to simulate the impact in 3D stress–strain problems, to consider linear material properties, and to include post failure fracture propagation. Anisotropic elements have been used to model the rock postfailure behavior. Inﬁnite domain elements have been used to characterize boundary conditions far away from bit–rock interaction. The accuracy of the model has been evaluated both theoretically by comparing the result to those obtained with a model based on impulse–momentum principle as well as experimentally. r 2007 Elsevier Ltd. All rights reserved.
Keywords: Impact tools; Finite element; Rockdrilling; Percussion drilling; Impact hammer
1. Introduction Impact tools are used in a wide variety of applications. In the mining industry they are used for rock drilling and rock breaking. Similarly, in the construction industry they are used for concrete and pavement drilling and breaking. From a design standpoint, these applications can be described using the generic conﬁguration of an impacttool as shown in Fig. 1. The process begins when a piston is accelerated to a certain velocity by some means such as air or hydraulic pressure (or even gravity in the more elementary tools). The piston collides with a second body, usually known as bit, so that some of the kinetic energy of the piston is transferred to the bit by means of a stress wave. The stress wave travels through the bit until itreaches the end in contact with the medium to drill or break. This is usually rock or concrete. High point stresses must be developed at the bit–rock interface so that the rock
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E-mail addresses: firstname.lastname@example.org (L.E. Chiang), email@example.com (D.A. Elı´ as). 1365-1609/$ - see front matter r 2007 Elsevier Ltd. All rightsreserved. doi:10.1016/j.ijrmms.2007.08.001
can be fragmented. For this purpose, tungsten-carbide inserts are mounted on the bit face. A thrust force may be applied to the entire hammer and it can be continuously rotated. At each body interface and also at every geometric singularity within each body (i.e. section change), the stress wave originated by the impact is partially reﬂected andtransmitted. Hence at any instant the stress wave pattern can be very complex. The stress wave energy actually transmitted to the rock is a fraction of the stress wave energy originated in the impact between rock and bit. The rock itself, while absorbing the energy from the incoming stress wave, will also reﬂect a certain amount back to the hammer and its supporting structure. Some of the energy passedto the rock will produce failure and fracture, and the rest is elastic energy that is eventually dissipated far away from the damaged zone. Due to their practical importance, impact tools have been studied for many years. Percussion drilling has been characterized as being a very complex phenomenon. This is because during the operation of these tools, the interaction both between hammer...