Wear of geo-materials by mechanical impulse

Shear along rock faults is always associated with wear of the sliding blocks that commonly results in the production of fine powder called gouge. We experimentally analyzed intensity of wear-rate and frictional strength during shear of dolomite and granite samples at slip-velocity of V = 0.001-1.0 m/s, and normal stresses of σ_n = 0.25-4.5 MPa. The experiments showed that the friction coefficients of these rocks depend on the mechanical power-density, which is the rate of energy dissipation during slip. The wear-rates, WR, showed dependency on the mechanical-impulse of the form WR = a · [τ/V]^b where τ is shear stress, V is the slip-velocity, and a and b are material constants. This relation of wear-rate to loading indicates that for rocks, the Archard (1953) model is only a special case for low slip-velocity. We propose here a model based on microfracturing wear at stressed asperities that explains the observed dependency of wear-rates on the mechanical impulse.