13th International Conference on Fracture (ICF13) June 16–21, 2013, Beijing, China diagram, as shown in Figure 3. For a fracture mechanics specimen the limiting threshold for crack propagation in SCC is KISCC, as calculated by EAC testing. Similarly to the original Kitagawa diagram, these two limiting conditions, σth and KISCC, can be used to develop an envelope diagram describing where crack propagation by SCC is expected to occur. By considering both stress related propagation and long crack condition, the diagram describes an SCC “safe” area and an SCC “unsafe” area. The failure diagram for SCC can be described by the following equation: σ ୦ ൌK୍ୗେେ/ሺYሺaܽ ௌሻඥπሺaܽ ௌሻ ሻ (4) Similarly, for corrosion fatigue, a Kitagawa like diagram can be envisioned, where the endurance stress in environmentally assisted fatigue, e_CF , is combined with the stress intensity threshold in aggressive environment, Kth_CF. The failure diagram will have the form: ∆σ େ ൌ∆K୲୦_େ/ሺYሺaܽ ிሻඥπሺaܽ ிሻ ሻ (5) Conceptually, a combined Kitagawa-like diagram with more than one mode of failure can be constructed for any material; it is the interest of this paper to ilustrate a failure diagram for CF, SCC and pure fatigue. The diagram can be pictured to look like Figure 3: the outermost Kitagawa-like diagram is expected to be the one representing SCC, with th and KISCC as limiting values, the innermost Kitagawa-like diagram is expected to be the one representing CF, with e_CF and Kth_CF as limiting values. The Kitagawa diagram for pure fatigue is pictured to lie between CF and SCC, with e and Kth as limiting values. A failure diagram in aggressive environment can be constructed by considering only the outermost and innermost limiting conditions: CF and SCC. Let’s suppose that a component is subjected to fatigue loading in aggressive environment by cyclic stressing at a high R-ratio, as shown in Figure 4. In this situation we can infer that the component will be subjected to corrosion fatigue at a stress amplitude and mean stress m. Since the cyclic loading occurs at a high R-ratio, we can also infer that the component is subjected to stress corrosion cracking at a stress level m. In this situation the Kitagawa-like diagram that can be applied are two: one for CF and one for SCC. Two limit state functions need to be written for the failure diagram in EAC, one considering the CF and one the SCC damaging process; the limit states can be written as follows: ۖ۔ ۖە ݃ۓ ሺܺ ሻி ൌΔ ߪ െ ∆_ಷ ටగ൫ାబ ಷ൯൫ାబ ಷ൯݃ ሺܺ ሻ ௌ ൌ ߪ െ ೄ ටగ൫ାబ ೄ൯൫ାబ ೄ൯ (6) m , Stress t, time Figure 4: example loading in EAC.
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