PSI - Issue 75

D. Tousse Tchamassi et al. / Procedia Structural Integrity 75 (2025) 450–456 Tousse Tchamassi / Structural Integrity Procedia (2025)

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Fig. 2. Low cycle fatigue behavior of the initially undeformed material. (a) First, mid-life, and last stress-strain loops, ±0.8%; (b) evolution of the stress amplitude during the tests; (c) mid-life loops for all tests; the lower left corners have been superimposed to evidence the Masing effect.

3.1.2. Cyclic deformation behavior after prior deformation The effects of prior plastic deformation on the cyclic behavior were the same for all prescribed strain amplitudes. They are illustrated in Fig. 3. Whatever the amount of strain applied before the fatigue test, cyclic softening occurred (Fig. 3a); however, the stress amplitude remained slightly higher (by about 20 MPa) for the undeformed material than for the specimens previously deformed in tension. On the other hand, the stress amplitude of the expanded industrial material was identical to the one of the undeformed material. The amount of strain applied to the expanded material was similar to that applied by tension to the prestrained fatigue specimens. Nevertheless, the stress triaxiality is expected to be different between tension and expansion; this suggests that in addition to the cumulative plastic strain, the loading path slightly affected the cyclic deformation behavior, even after a high number of cycles. Despite these slight differences, the shapes of the stress-strain hysteresis loops at mid-life were very similar (Fig. 3b).

Fig. 3. Effect of prior deformation on the low cycle fatigue deformation behavior, total strain amplitude of ±0.8%. (a) Evolution of the stress amplitude during the tests; (b) mid-life loops; the lower left corners have been superimposed to compare the shapes of stress-strain curves.