Brittle wear of silicate materials by Hertzian rubbing contact

We studied the tribological properties of a structural series of 11 silicate materials to identify the main physical parameters that control the brittle wear of these materials. First, for each material we characterized Young's modulus E by ultrasonic microscopy, roughness sigma by atomic force microscopy and crack pressure P-c by Hertzian indentation testing. Second, we measured the static and dynamic friction coefficients mu(S) and mu(D), respectively, with a ball probe tribometer for each material and for three hardnesses of the ball probe. The experiments showed that crack density, which quantified the brittle wear of the materials, was controlled by an adimensional number, C-r = P-c/mu E-S. We show in this paper how this number takes into account the combined effects of the mechanical properties, the lubricating coating layer and the residual internal stresses of these materials.