13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- The comparison between the theoretical curves predicted by inverse deduced equations and analysis data obtain from the fractography is shown in Fig. 7. It can be seen from Fig. 7 that the theoretical curves are well fitted with analysis data, which indicates that the inverse deduced equations can be used to accuratelly describe the crack propagation behavior in the steady propagation region. 45 90 135 10-4 10-3 10-2 R=0.02 R=0.1 R=0.2 R=0.4 da/dN/(mm.cycle−1) ΔK/MPa.m1/2 Figure 7. Inverse deduced curves of crack propagation rate Following, these inverse deduced equations (from Eq. (25) to Eq. (28)) are generalized to describe the whole process of fatigue crack propagation. At various stress ratios, the comparisons between theoretical curves of fatigue crack propagation rate and experimental data are shown in Fig. 8. 45 90 135 180 10-5 10-4 10-3 10-2 R=0.02 da/dN/(mm.cycle−1) ΔK/MPa.m1/2 (a) 45 90 135 180 10-5 10-4 10-3 10-2 R=0.1 da/dN/(mm.cycle−1) ΔK/MPa.m1/2 (b) 45 90 135 180 10-5 10-4 10-3 10-2 10-1 R=0.2 da/dN/(mm.cycle−1) ΔK/MPa.m1/2 (c) 45 90 135 180 10-5 10-4 10-3 10-2 10-1 R=0.4 da/dN/(mm.cycle−1) ΔK/MPa.m1/2 (d) Figure 8. Crack propagation rate curves obtained by inverse deduced equations It can be seen from Fig. 8 that the theoretical curves are basically consistent with experimental data, indicating that the inverse deduced equations derived from the analysis data obtained by measuring damage striations in steady propagation region of fracture surface, can still be used to predict the whole process of fatigue crack propagation. Furthermore, it can be found that if only the stress
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