Keywords: silicon carbide, pre-stressed machining, discrete element method, cluster, simulation, scratching test.

Ceramic materials have been widely used as functional materials as well as structural materials in many industrial fields because of their excellent properties, such as high-temperature strength, good chemical and wear resistance and low thermal expansion coefficient etc. However, due to their inherent high hardness and brittleness, grinding has become the main machining method. In the process of machining ceramics material, the damage that caused by tools contact with the ceramics surface is mainly reflected in the surface or sub-surface cracks and residual stress [1]. Clearly, owing to the high machining cost of ceramic components and the difficulty of controlling and measuring the damage of machined surface, its wider application is limited. Therefore, the study of damage and control mechanism has become an important research topic of ceramic machining and its application.

Pre-stressed cutting method was first proposed by Zhou [2] in the machining of metallic materials, which had been used in turning, grinding and milling. With the development of computer technology, especially the emergence of high performance computers, new kinds of models and simulation methods are used to simulate the machining processes, such as discrete element method (DEM). The DEM can represent the ceramic at the grain scale by particles bonded together, and the damage is represented as broken bonds or grains explicitly and naturally. So it brings a breakthrough point to research the machining mechanism of ceramic materials.

In this paper, based on the theory of metal pre-stressed machining, the method of suitable for pre-stressed ceramic materials machining was presented. And the DEM model of SiC ceramic was established which could describe the mechanics behavior of inter-granular and trans-granular fracture. The crack's initiation and propagation in the cutting processes with different pre-stress were simulated, and the scratching tests were carried out to confirm the validity of simulation. Both the DEM simulation and the experimental study showed that in certain pre-stressed conditions, with the increasing of pre-stress, the number of radial cracks reduced and the transverse cracks replaced the radial cracks to some extent, and also caused the material removal in the form of smaller fragments. Using the method of pre-stressed machining can decrease the machining damage and improve the surface quality; and further prove that the application of the discrete element method to simulate the machining of pre-stressed SiC ceramic was feasible.

1

R. Hessert, B. Eigenmann, O. Vöhringer, D. Löhe, "Fracture mechanical evaluation of the effects of grinding residual stresses on bending strength of ceramics", Materials Science and Engineering A, 234-236, 1126-1129, 1997. doi:10.1016/S0921-5093(97)00407-3

2

Z.H. Zhou, D.T. Guo, "Pre-stressed machining: combined use of heuristics and optimization methods", In "Proceedings of IX the ICPR", Cincinnati, 1, 257-262, 1987.

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