Rio de Janeiro-RJ-Brazil

The present study was designed to determine the role of the microstructure length-scales in fracture mechanisms in heterogeneous media. Therefore, materials of various grains sizes, i.e. nanophase TiO2 (grains size around 300 nanometers), zirconolite ceramics (grains size around 10 micrometers) and glass ceramics (grain size around 100 micrometers) were fractured in both dynamic and sub-critical stress corrosion regime. Combinations of Atomic Force Microscopy and stylus profilometry were used to measure the topography of post-mortem fracture surfaces. In glass ceramics, these surfaces are found to be self-affine, with a roughness exponent ζ ~ 0.5, significantly smaller than ζ = 0.8 as commonly observed for homogeneous glass. In nanophase TiO2, ζ was found to be even smaller, close to zero. Development of roughness during crack propagation was also investigated. Influence of both grain size and cohesion strength between grains on self-affine properties of post-mortem fracture surfaces will finally be discussed.