13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- Figure 9. Schematic representation of single overload spectrum Figure 10. CTOD variation at each loading cycle in Figure 9 (a) R=0.33 (b) R=0.025 Figure 11. Illustration of the crack opening stress level variation One important hypothesis in the classical crack closure theory is that the effective stress intensity 0 5 10 15 20 25 30 35 40 0 1 2 3 4 5 6 7 8 9 101112131415161718 K (MPa·m0.5) Nth cycle 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 10 20 30 40 CTOD (um) K (MPa·m0.5) Test 1 Test 2 CycleA 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 0 10 20 30 40 CTOD (um) K (MPa·m0.5) Kmax of the constant amplitude load part Cycleb CycleB 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 10 20 30 40 CTOD (um) K (MPa·m0.5) CycleC 0 0.05 0.1 0.15 0.2 0.25 0.3 0 10 20 30 40 CTOD (um) K (MPa·m0.5) CycleD A B C D
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