Abstract: Fracture surface analysis is an important means for judging failure mode, finding failure reason and preventing failure. Under constant amplitude cyclic loading, the pattern of a fatigue fracture surface and the crack numbers depend on the loading type as well as the stress level, while the problem is much complex under variable amplitude cyclic loading because of the cyclic dependent property of the material. According to principle of microstructure stability in metallic systems as well as cyclic dependent property, the author studied systematically the effect of cyclic dependent property on accumulative damage and fracture surfaces of the fatigue specimens. The conclusions are that under the same loading history. There are different fracture surface characteristics for cyclic hardening material and cyclic softening ones, and that in the case of high-low stress levels the number of crack at the fracture surface depends not only on the level of the first high stress but also on its cyclic number and the cyclic dependent property of material.

Key words: fatigue fracture surface, cyclic property, strengthening effect