PSI - Issue 71

Sudarshan Solanki et al. / Procedia Structural Integrity 71 (2025) 95–102

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● The fatigue crack initiation is likely to happen in SS base region for peak equivalent strain amplitudes of 0.75% and 1% under remote pure axial and pure torsion loading conditions. ● SS weld region is more prone for fatigue crack initiation with peak equivalent strain amplitudes of 0.35% and 0.5% under remote pure axial and pure torsion loading conditions. This study would be helpful for subsequent fatigue experimental programme on DMW specimens. Acknowledgements • The low cycle fatigue test data on SA-508 Gr.3 Cl.1 have been generated at National Metallurgical Laboratory, Jamshedpur under BARC, Mumbai designed and funded experimental project. • The supporting efforts of Mr. Shreebanta K. Jena are sincerely acknowledged. Appendix This section aims to present the details of the cyclic plasticity material model (Chaboche) used in the present study. von-Mises yielding criterion and incremental plasticity flow rule are used in the Chaboche three-decomposed model as described below Chaboche et al. (1991) and given by equation (1). ( , )=√ 3 2 ( − )( − )− =0 and = 1 is the stress tensor, is the total back stress tensor, is the deviatoric part of , is the deviatoric back stress tensor, is the size of yield surface, is the plastic strain tensor, is increment in , and is a positive scale factor of proportionality. Total stress ( ) at any material point in uniaxial stress-strain hysteresis loop, is the sum of yield strength ( ) and total back stress ( ) is given by equation (2). = 0 + 2 Further, the total back stress can be represented in equation (3) the summation of three back stress components. =∑ 3 =1 = 1 + 2 + 3 3 Also, incremental deviatoric back stress tensor can be expressed sum of three deviatoric back stress tensor and evolution of each incremental deviatoric back stress tensor is given in accordance to Armstrong-Frederick hardening rule in equation (4) = ∑ 3 =1 4 = 2 3 pl − ̅̅̅ In this equation, ( ) : deviatoric back stress tensor increments for i th segment, ( ) : deviatoric back stress tensor for i th segment, pl : plastic strain increment tensor and ̅̅̅ : equivalent plastic strain increment. Each segment of three decomposed Chaboche material model representing the post yield behaviour is given in equation (5). For first segment, 1 = 2 3 1 pl − 1 1 ̅̅̅ 5 For second segment, 2 = 2 3 2 pl − 2 2 ̅̅̅ For third segment, 3 = 2 3 3 pl − 3 3 ̅̅̅ The calibrated constants ( ( ) ( ) for 1≤ ≤3 ) were used to verify the simulated hysteresis loops with corresponding test responses. As all the selected grade of material in the present study exhibits Masing behaviour with linear shift and the saturated cyclic yield strength corresponding to a given strain amplitude was varied manually.