The results of numerous tests show that quantitative estimation of accumulated fatigue damage may effectively be conducted by computer-aided optical analysis of the surface state. The method may be applied for alclad alluminium alloys which are used for modern aircraft skin manufacturing. The developed optical system and its software allow to determine the density of the areas with slip bands (damage parameter D), and a set of surface pattern fractal dimensions. These parameters allow to indicate more dangerous points of aircraft structures, predict fatigue crack under full scale test of aircraft structures as well as estimate residual service life.
