One remarkable characteristic of grinding process is the sudden wear increase of grinding wheel. This phenomenon occurs when grinding force per a grain exceeds the strength of a bond bridge or the strength of a grain. This grinding force per a grain is defined as the average critical pressure. In this paper, the relationship between the composition of grinding wheels and the average critical pressure is analyzed. The results obtained are as follows :
(1) The average critical pressure depends on the grain sizes, the kind of grain, the sort of bond and the composition of grinding wheels, and it becomes one of the specific values which indicates the grinding ability of grinding wheels.
(2) The relationship between the composition of grinding wheels and the average critical pressure fc is given by
fc=d02√2γgEg/d0 [1-exp {-√γbEb/γbEg·υb/3υg2/3 (1-3√υg)}]
where d0, γg, γb, Eg, Eb, υg and υb are the side length of grain, the equivalent surface energy of grain, the equivalent surface energy of bond, the Young's modulus of grain, the Young's modulus of bond, the percentage of grain and the percentage of bond respectively.