Comparative Study of ? Projection Method and Its Modified Forms on Creep Life Prediction

The phenomenological characteristics of theta projection method constrain its prediction accuracy, especially at the primary creep stage. Herein, the mathematical features of the classical theta projection method and its modified forms based on a group of creep curves of a newly designed low-cost heat-resistant steel are analyzed. A detailed data processing method is introduced, and the prediction accuracy is comparatively studied with respect to the relative error on different creep stages. Results reveal that the simplified 3-parameter method brings a balanced improvement on the residual errors by sacrificing the prediction accuracy on primary creep. However, the 5-parameter method can precisely predict the characteristics of primary creep, and the tolerance fitting process can further reduce the deviation at the tertiary creep stage. Furthermore, the 5-parameter method shows a larger reliable prediction region than the 3-parameter method, and the two methods present good consistency when the applied stress is larger than 134 MPa. Herein, theoretical guidance for the selection of different theta projection methods is provided.