Experimental study of fracture surface roughness on rocks with crack velocity

In this paper we address the question of the influence of crack velocity on the fractured surface roughness. We studied samples made of Berea sandstone, chosen for their good macroscopic homogeneity and their granular microstructure. The samples were fractured in a double cantilever geometry, which allowed for a controlled crack speed that was maintained constant for each sample using an imposed displacement quadratic in time. The range of speed covered in the experiments was 5×${10}^{\mathrm{-}4}$ m ${\mathrm{s}}^{\mathrm{-}1}$ to 2×${10}^{\mathrm{-}1}$ m ${\mathrm{s}}^{\mathrm{-}1}$. Systematic profilometry measurements of the fractured surfaces revealed a self-affine geometry characterized by a roughness exponent, which was found to be independent of the crack speed. © 1996 The American Physical Society.