Precision Grindability of Granite in Relation to Discrete Distribution Parameters of Microhardness and Microbrittleness

The natural granite includes various hard and brittle minerals with different material behaviors. In this paper, the discrete distribution parameters of microhardness and microbrittleness are proposed to describe its micron-scale material behavior. The objective is to evaluate and predict the precision grindability of various granites by using its microhardness and microbrittleness. First, the relative values of microhardness and microbrittleness were defined by measuring diagonal length and crack spreading length of micron-scale indentation in a micro-indentation experiment; then the microhardness, the microbrittleness, and their average deviations were introduced as discrete distribution parameters with regard to the weighted coefficients of various minerals in granite; finally, a precision grinding experiment was carried out to investigate the grinding force and surface roughness with regard to different grinding variables. It is found that grinding force and surface roughness have good and very good correlations with the microhardness and its average deviation, respectively, but they have no obvious relations with the microbrittleness. The ground surface can be improved when grinding the granite with high microhardness and its uniform distribution even if leading to large grinding force. For grinding variables, the grinding force increases with the decrease in the depth of cut and the work speed in brittle-mode grinding, but it has little correlation with work speed when approaching ductile-mode grinding. It is concluded that the precision grindability of granite may be evaluated and predicated by the relative microhardness and its average deviation.