Abstract
The fracture strengths of grinding wheel materials with vitrified bonds are theoretically analysed. The matrix is idealized as a system composed of spherical grains with bonds, an ellipsoidal force distribution around a grain is assumed, the relation between the microscoptic force acting on the adja-cent grains and the macroscopic stress is deduced and the inter- and trans-grain fracture conditions are derived. The following conclusions are obtained : (1) The intergrain tensile fracture strength is proportional to the strength of bonds and the square of the ratio of the radius of bond and the distance between the adjacent grains. (2) The intergrain shear fracture strength depends on the properties of bonds. If the bonds are subjected to the shear fracture according to the maximum shearing stress theory, the fracture conditions similar to those of von Mises hold, while if they are subjected to the shear fracture according to the Mohr failure envelope, so is the matrix. (3) The transgrain fracture strengths are given by the products of the grain strengths and the volumetric ratio of grains.
