Abstract
Creep-rupture strength and creep strain curve are popularly evaluated by TTP method and θ projection concept, respectively, where TTP method can extrapolate creep-rupture data by a TTP function compensating temperature difference and polynomial of stress, and θ method, one of unsteady creep constitutive equations, predicts creep strain curve including the tertiary stage. However, the parameter estimation procedures for the conventional methods have some statistical and numerical difficulties e. g., inversion of the creep-rupture curve, nonconvergence and so on.
In order to improve the accuracy of estimation and to eliminate these difficulties, the authors have proposed two parameter estimation procedures employing nonlinear programming. One is for TTP method and another is for θ projection concept.
According to estimation examples from calculated data referring to literatures and experimental data, these procedures can successfully predict the creep-rupture strength and the creep strain curve obtained for some steels.
