PSI - Issue 71

Shreebanta Kumar Jena et al. / Procedia Structural Integrity 71 (2025) 34–41

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2.3. Monotonic stress-strain response: The tensile properties of the selected low-alloy C-Mn steel material have been determined by conducting a standard tensile test following the ASTM E08 (2024) procedure. A total number of three tensile tests have been carried out at room temperature (28) in an air environment under axial strain controlled conditions. The tensile properties, such as lower bound tensile yield strength, ultimate tensile strength, Young’s modulus and total percentage elongation, which come out to be 290 MPa, 492 MPa, 204.8 GPa and 40%, respectively, have been obtained by averaging the test results over three standard tensile tests. The monotonic stress-strain curve showing different phenomena is presented in Figure 3. 2.4. Low cycle fatigue test on unnotched solid specimen: After successful completion of monotonic tensile tests and determination of tensile properties, LCF tests on solid specimens have also been performed following the standard test procedure of ASTM E606 (2021). A total number of seven LCF tests have been carried out under completely reversible pure

axial strain-controlled conditions. The strain amplitude has been varied from ±0.25% to ±1.25% to generate the baseline fatigue data. During the test, test parameters such as axial load/torque cell reaction, elongation and the number of cycles for crack initiation have been recorded. The fatigue initiation event is decided by the earliest occurrence of any of the two events, which are either the appearance of a visible crack with a size of 1 mm or a 25% drop in peak load value from the saturated value. The stress and strain values have been estimated by dividing the corresponding cross-sectional area and gauge length with the corresponding load and elongation value. 2.4.1. Masing/non-Masing study The saturated material test response (typically corresponding to the half-life of the LCF test) under pure axial conditions has been investigated w.r.t. Masing/non-Masing idealisation. For this, the saturated loops were first shifted to have their common minima at the origin in ( − ) − − ( − ) space. It was observed that the loading arms of these saturated loops were not matching with one another; therefore, the smaller strain amplitude loops were translated along the elastic line to an extent such that their post-yielding behaviour can be compared. Thus, the hysteresis loops are now compared on shifted axial stress-versus-axial strain loops in ( − + − ℎ )− − ( − + 100× − ℎ ) space. It has been observed from all these analyses that the material exhibits Masing idealisation with a linear shift along the elastic line. The details of the massing idealisation have been shown in Figures 4 (a) & (b).

Figure 3. Monotonic stress-strain curve

(a) (b) Figure 4: Cyclic saturated hysteresis loop (a) linear shift to the origin (b) rigid shift for common post-yield behaviour.