Research into metal cutting is an established area, whereas the behaviour of rock during cutting is somewhat more complex and not well understood. This makes the field of Rock Mechanics - in particular the use of Finite Element Analysis [FEA] in studying the behaviour of the rock under cutting conditions where many parameters are involved - a challenging area to explore. Here experimental results are needed to justify and verify the results from FEA modelling. Based on the Brazilian Test [1] this paper analyses three types of rocks namely - limestone, sandstone and shale, which belong to the sedimentary rock category with sandstone having greater strength than limestone and shale. The Finite Element-Discrete Element coupled method (FEM-DEM) used in the proposed modelling enables the facture process of the rock to be studied closely in relation to the cutting force component causing the start of fracture and the behaviour of the propagating crack during this process [2]. These results should prove to be useful in analysing the fundamental behaviour of the rock material at the extreme cutting edge of the tool.


Rock being a natural material presents a high degree of complexity in understanding its response to a given state of stress. Rocks are made up of different elements (Si, Na, Ca, Al, Fe, O, C, etc) which constitute the minerals that are bonded by a cementing agent, usually silicon. The most common minerals are Quartz, Feldspar and Mica; The different mineral make up, the temperature and pressure at which rocks are created, all add to the inherent anisotropy present in any rock mass. Furthermore it also contains discontinuities such as faults and fractures and fluid-filled pores. Rocks tend to be anisotropic, hence a finite element analysis technique employed to model the mechanical characteristics of the rock should be able to take into account the above mentioned discontinuities [3]. The most commonly used cutting tool materials are Tungsten Carbide and Polycrystalline Diamond Compacts. They are used in machining of rocks in various industries and tasks such as drilling for oil and gas, extraction of geothermal energy, mining, excavation, tunnelling, coring and for rocks used as building materials. Rocks are extremely variable substance such that studies based on one particular type of rock may not be applicable to other rock types. Rock fracture mechanics studies the failure criterion and the failure mechanisms of rock fracture and provides ways to either maximise or minimise rock fracture [2]. Wear and tear of the tools is inevitable and thus there is a greater need to understand the fracture mechanics of rocks in order to improve tooling. Numerical modelling has been successfully used to model material removal process in rock cutting [4], to understand the influence of friction on chip size [5], to study the material deformation of heterogeneous rocks [6–8], study of rock bolts [9], to name just a few. An exhaustive review of numerical modelling related to rock mechanics is provided by Jing [3].

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