ELASTIC CONTACT ON ROUGH FRACTURE SURFACES

There is now ample evidence that fracture surfaces are self-affine. The elastic contact on such surfaces is expected to give rise to a power law dependence of the normal force on the penetration depth, whose exponent alpha depends on the roughness index of the surface, zeta. This problem is studied experimentally using three different fracture surfaces (bakelite, graphite and plaster) in contact with a flat rubber punch. After an initial regime which can be attributed to the contact of the most salient asperity of the rough surface, the experimental data are consistent with theoretical arguments presented earlier, leading to the relation alpha = 1 + 1/zeta. Numerical simulations of this problem on artificially generated self-affine surfaces also support this result.