Abstract: From the physical point of view, the solid containing cracks is actually a non-linear dissipation system, so it can be described by fractal theory. The propagation of short fatigue crack is a fractal curve, the irregular path can be described by fractal dimension. The fractal dimension of the crack implicates many physical factors, such as microstructure of material and loading conditions. The short crack for low cycle at high temperature is studied. The material 20 steel in various stress state is experimentally studied, the evolution process of initiation, propagation and coalescence of short cracks on the specimen surface are observed. By analyzing experiment results, characters of crack fractal dimensions evolving with the cycle process are as follows, the behavior of short fatigue cracks satisfies fractal feature, with the development of the fatigue process, the fractal dimension is increased.

Key words: Complex stress state, Fractal, Fractal dimension, High temperature low cycle fatigue, Short crack, Acoustic elasticity theory, Acoustic microscopy, Elastic constants, Silicon crystal, Surface acoustic waves