PSI - Issue 71

Prakash Bharadwaj et al. / Procedia Structural Integrity 71 (2025) 26–33

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(a) (b) Fig. 6. Variation of (a) Plastic strain in loading direction with no of cycle and (b) Stress with plastic strain, at different locations for RT and 300 °C Fig. 7, illustrates the influence of R and temperature on plastic strain accumulation relative to the number of cycles and stress with plastic strain in the loading direction for a crack size of 23.02 mm. The point is located 29 microns ahead of the crack tip, where the variations are captured. It can be seen that for the R = -1, there is a lower plastic strain accumulation occurs relative to R = 0.1 at a given temperature. The increased accumulation of plastic strain at positive R occurs because the loading cycle maintains a tensile-dominated state of stress, which enhances plastic deformation mechanisms. Negative R, characterized by alternating tensile and compressive loads, diminish net plastic strain by facilitating partial elastic recovery and reducing crack tip plasticity [Dowling (2004)]. For a given R, strain accumulation rate is lower at RT as compared to 300 °C.

(a) (b) Fig. 7. Variation of (a) Plastic strain in loading direction with no of the cycle and (b) Stress with plastic strain, at a distance 29 microns ahead of the crack tip for R = 0.1 and -1 at RT and 300 °C

Conclusions These studies related to CPZ and ratchetting rate would be useful for deducing a cyclic plasticity-based crack driving force variable for fatigue crack growth rate assessment. Such crack driving force variable is expected to result in single material specific FCGR curve, independent of R. The observations of finite element study related to cyclic plasticity and ratcheting behaviour on SA333Gr6 material at RT and 300 °C is summarised below, 1. The size of the CPZ is approximately 1/3 rd of the size of the MPZ at both the RT and 300 °C.