Application of Ramberg-Osgood Plasticity to Determine Cyclic Hardening Parameters

Critical components of modern turbomachinery are frequently subjected to a myriad of service conditions that include diverse mechanical loads at elevated temperatures. The cost, applicability, and accuracy of either numerical or analytical component-level simulations are largely dependent on the material model chosen for the application. A non-interaction (NI) model derived from individual elastic, plastic, and creep components is developed in this study. The candidate material under examination for this application is 2.25Cr-1Mo, a low-alloy ferritic steel commonly used in chemical processing, nuclear reactors, pressure vessels, and power generation. Data acquired from literature over a range of temperatures up to 650°C are used to calibrate the creep and plastic components described using constitutive models generally native to general-purpose FEA. Traditional methods invoked to generate coefficients for advanced constitutive models such as non-linear kinematic hardening employ numerical fittings of hysteresis data, which result in values that are neither repeatable nor display reasonable temperature-dependence. By extrapolating simplifications commonly used for reduced-order model approximations, an extension utilizing only the cyclic Ramberg-Osgood coefficients has been developed to identify these parameters. Unit cell simulations are conducted to verify the accuracy of the approach. Results are compared with isothermal and non-isothermal literature data.