The fatigue fracture surfaces of a metallic alloy, and the stress corrosion fracture surfaces of glass are investigated as a function of crack velocity. It is shown that in both cases, there are two fracture regimes, which have a well defined self-affine signature. At high enough length scales, the universal roughness index ζ ≃ 0.78 is recovered. At smaller length scales, the roughness exponent is close to ζc ≃ 0.50. The crossover length ξc separating these two regimes strongly depends on the material, and exhibits a power-law decrease with the measured crack velocity ξc ∝ v −φ , with φ ≃ 1. The exponents ν and β characterising the dependence of ξc and v upon the pulling force are shown to be close to ν ≃ 2 and β ≃ 2.

The fracture surface of a Ti 3 Al-based alloy is studied using both an atomic force microscope and a standard scanning electron microscope. Results are shown to be quantitatively comparable. Two fracture regimes are observed. It is shown in particular that the roughness index characterizing the small lengthscales regime is equal to 0.5. Furthermore, the large lengthscales fractal domain is found to spread over nearly six decades of lengthscales.