Session: MF-16-01 Creep and Creep-Fatigue Interaction

Paper Number: 82064

82064 - A Datum Temperature Calibration Approach for Long-Term Minimum-Creep-Strain-Rate and Stress-Rupture Prediction Using Sine-Hyperbolic Creep-Damage Model 

This study introduces a datum temperature (DT) calibration approach for improved extrapolation of minimum-creep-strain-rate (MCSR) and stress-rupture (SR). The ASME B&PV code III outlines the stringent requirements for approval of new candidate materials to be tested 10000+ hours per heat to be qualified for service. Additionally, components operating at a range of service conditions require tests to be performed at many combinations of stress and temperature. Subsequently, it takes years to decades for new creep-resistant alloys to be implemented due to the number of tests, duration, and costs involved. The increasing demand for new alloys for IGT applications and the desire to reduce qualification time driven the urge for rapid qualification testing, calibration, and modeling techniques. To that end, a datum temperature (DT) calibration approach is applied to a contemporary creep-damage model for improved long-term extrapolation of creep data. In the DT approach, data across multiple temperatures are mathematically transferred to a datum temperature creating a wide range of parametric data. This expansion of data in essence reduces the amount of data needed to calibrate a model. Next, the model is calibrated against the parametric data to the datum temperature; afterward, the model is transferred back to original temperatures. A DT approach can significantly reduce the overall duration of creep testing, effort for model calibration, and eliminate the requirement for temperature-dependent material constants.

                  In this study, the DT calibration method is applied to the continuum-damage-mechanics (CDM)-based Sine-hyperbolic (Sinh) model to extrapolate the MCSR and SR for 18Cr-8Ni stainless steel. The MCSR and SR data across multiple isotherms are gathered from the National Institute for Material Science (NIMS) database. The Sinh material constants are calibrated to fit the data across a single temperature (DT) instead of calibration against multiple temperatures.  Mathematical rules to transfer data to a datum temperature are developed for the Sinh MCSR and SR equations. The model is shifted back to original temperatures and extrapolation credibility is assessed. The coefficient of determination (R²) and normalized mean square error (NMSE) statistics are employed to analyze the prediction quality. The extrapolation at low stress and high temperature and vice versa is observed to be devoid of any inflection point. The DT approach for Sinh is further verified and validated by comparing against additional MCSR and SR data for 18Cr-12Ni-Mo steel that were not used for calibration. It is observed that the Sinh model can accurately extrapolate over three times the maximum MCSR and SR. Based on the goodness-of-fit of the extrapolation credibility, a recommendation to use DT approach for the past and modern creep-damage models is provided.

Presenting Author: Md Abir Hossain The University of Texas At El Paso

Presenting Author Biography: Mechanical Engineering Ph.D. student at UTEP exploring career opportunities in Academia and Industry. I am a theorist - I enjoy studying constitutive laws and inherent statistical analysis. As a member of the computation and simulation branch of team MERG, I explore different creep modeling schemes, quantify the uncertainty, and simulate the long-term prediction.

Authors:

Md Abir Hossain The University of Texas At El Paso
Mohammad Shafinul Haque Angelo State University
Calvin M. Stewart The University of Texas at El Paso