Abstract: The multifractal spectrum theories are applied to the material fatigue damage based on the physical sense of multifractal spectrum. Surface cracks for low cycle at high temperature are studied, the notched specimens of 20 steel is experimentally studied. A series of binary images of the damage evolution are obtained by image processing. The multifractal spectrum theories are adopted to describe the damage evolution on material surface, and introduced the spectral width Δa and spectral height Δf to describe the fatigue crack distribution complexity. The study indicates that the multifractal spectrum f(a) is a characteristic parameter which enables the quantitative analysis and explanation of material fatigue damage from multifractal perspective, and the spectral width Δa and spectral height Δf with the fatigue life by a certain trend development. In order to explore the inherent law between the fatigue life and the fractal characteristics on the crack surface figure of material, a new method is established.

Key words: Crack, Damage, High temperature low cycle fatigue, Multifractal spectrum