13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- Figure 4. Stress amplitude a and ferromagnetic martensite fraction (a), change in tofmean (b) and change in peakmean (c) vs. number of cycles N at ambient temperature Due to the change of tof and peak within one cycle, caused by the elongation of the specimen and change of the stress state of the specimen (Figure 7), an arithmetic mean value per load cycle for tof and peak was chosen to characterize the fatigue behavior [8]. The cyclic deformation behavior of the investigated austenite at ambient temperature is predominantly determined by the deformation induced austenite-martensite transformation. After a load dependent number of cycles N, the formation of ´-martensite starts and increases continuously with increasing number of cycles until specimen failure (Figure 4a). The a, N-curves illustrate the cyclic hardening processes, which lead
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