PSI - Issue 14

Bimal Das et al. / Procedia Structural Integrity 14 (2019) 619–626 Das et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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nature. It is also noticed that material undergoing cyclic softening exhibit obvious relaxation of mean stress as compared to the cyclically hardened materials.

The phenomena of cyclic softening and mean stress relaxation behavior can be clearly understood from the analysis of hysteresis loops. First and half-life ( N f /2 ) hysteresis loops with strain ratio (R) of -1 and -0.43 at constant strain amplitude of 0.3% is illustrated in Fig. 4. The symmetric strain cycling (R= -1) at strain amplitude of 0.3% resulted in cyclic softening accompanying a decrease in height and an increase in width of the hysteresis loop. The center of the hysteresis loop shifts downward along the stress axis in the case of mean stress relaxation test with R= -0.43 and strain amplitude 0f 0.3%. (b) Fig. 3. Mean stress relaxation test at mean strain of 0.1% and stress amplitude of 0.3%. (a) Evolution of mean stress with number of cycles. (b) Variation of maximum and minimum peak stresses vs number of cycles. (a)

Fig. 4. First and half-life hysteresis loop ( N f /2) under different strain ratio.

4. Constitutive modeling In this section, the formulation of classical plasticity is developed in the rate independent framework. The basic