13th International Conference on Fracture June 16–21, 2013,Beijing, China -8- Figure 5: Comparison between experimental data and prediction of the plasticity model under consideration of the martensite transformation. More results are summarized in Fig. 6, in which true stress at 10% plastic strain and ultimate stress of the SS304 under different pre-strains are plotted. Due to martensite transformation both stress at 10% plastic strain and ultimate stress can be different. The ultimate stress is taken from the maximum stress in the tension tests. The results show, however, that the stress monotonically grows with pre-strain, whereas the ultimate stress of the specimen is independent of initial deformations. Fig. 6(b) shows that the ultimate stress of SS304 is independent of loading history. The prediction of the plasticity model is acceptable. (a) True stress at 10% plastic strain (b) Ultimate stress Figure 6: Comparison between experimental data and prediction of the plasticity model under consideration of the martensite transformation. 5. Fracture and Fatigue Behavior Martensite phase transformation affects plastic behavior of the stainless steel SS304. Since Hχ in Eq. (15) is positive, the martensite phase will generally increase the hardening of the material. Due to enbrittlement through martensite phase, however, fracture toughness of SS304 decreases with growth of martensite content. Effects of the martensite phase to material failure have to be
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