ROUGHNESS OF A CRACK FRONT PINNED BY MICROSTRUCTURAL OBSTACLES

The morphology of crack fronts stopped during their propagation at pin ning microstructural obstacles in two different metallic alloys is ana lysed, and their ''in-plane'' roughness index is determined for the fi rst time. In the case of the 8090 Al-Li alloy, which has a very anisot ropic microstructure, the roughness of the tensile crack front propaga ting along the grains length is equal to zeta = 0.60 +/- 0.04. On the other hand, the roughness of the purely three-dimensional fatigue crac k front in the Super alpha(2) Ti3Al-based alloy is equal to zeta = 0.5 4 +/- 0.03.