PSI - Issue 52

Long Jin et al. / Procedia Structural Integrity 52 (2024) 12–19 Author name / Structural Integrity Procedia 00 (2019) 000–000

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(a)

(b)

Fig. 5. Cyclic stress response curves for as-received (a) and aged specimens (b)

Fig. 6. The maximum cyclic hardening ratio H max of as-received and aged specimens at different strain amplitudes

3.3. Fatigue life prediction model The parameters of half-life are generally used to predict the fatigue life. Figure 7 illustrates the relationship between the stress amplitude at half-life and the number of reversals. The fitted S - N curves of unaged and aged specimens are presented independently in Eq. (1) and Eq. (2). It is worth noting that although the aged and unaged specimens possess the similar tensile strength in Fig. 4a, the aged specimens clearly have lower fatigue life as shown in Fig. 7, and the gaps appear to enhance as the fatigue life increases. This appears to indicate that the effect of aging is minimal and the differences are not evident at single tensile test or fatigue test with lower fatigue life, however, it becomes more apparent with the increase of fatigue cycles. This indicates a higher susceptibility of fatigue strength to aging compared to tensile strength.

Fig. 7. Relationship between stress amplitude at half-life cycle and fatigue life for as-received and aged specimens