Effect of frequency of free level fluctuations and hold time on the thermal ratcheting behavior

• Time independent and dependent ratcheting behavior model is compared.
• The relative contribution of viscoplasticity in ratcheting strain is highlighted.
• The effect of frequency of free level fluctuations in ratcheting strain is compared.
• Implicit plastic integration formulation using Newton's method is discussed.
• Contribution of thermal ratcheting strain with hold time is predicted.

Investigation of cyclic strain accumulation behavior of a thin cylindrical shell (SS 316L) due to thermal ratcheting, in the framework of time independent (Model-1) and dependent formulations (Model-2) is carried out. The effect of frequency of free level fluctuations by varying cycle time (CT) is compared for Model-1 and Model-2. Contribution of strain due to high frequency and low frequency level fluctuations is quantified. Further, the contribution of ratcheting strain with hold time is evaluated to highlight the effect of free level hold on radial deformation of the cylinder. Improvement in predicting ratcheting strain is observed using semi-implicit plasticity integration method. Implicit plastic increment formulation is derived using Newton's method. Validation of code for Model-1 is done by comparing the results with the existing experimental results. Strain controlled cyclic characteristics and uniaxial monotonic loading at different strain rate is analyzed to validate the code for Model-2.