Abstract
ABSTRACT There are two types of creep constitutive equation, one with a steady-state term (steady-state type) and the other with no steady-state term (non-steady-state type). We applied the Bayesian inference framework in order to examine which type is supported by experimental creep curves for a Grade 91 (Gr.91) steel. The Bayesian free energy was significantly lower for the steady-state type under all the test conditions in the ranges of 50–90 MPa at 923 K, 90–160 MPa at 873 K and 170–240 MPa at 823 K, leading to the conclusion that the posterior probability was virtually 1.0. These findings mean that the experimental data supported the steady-state-type equation. The dependence of the evaluated steady-state creep rate on the applied stress indicates that there is a transition in the mechanism governing creep deformation around 120 MPa.
Highlights
Creep is a time-dependent phenomenon and is controlled by various mechanisms depending on the stage
We concluded that the experimental data support the modified theta projection
Detailed analysis of the strain rate versus time plot showed that more than 50% of the creep deformation can be regarded as occurring in the steady state
Summary
Creep is a time-dependent phenomenon and is controlled by various mechanisms depending on the stage. We propose a Bayesian inference framework to judge whether there is an intrinsic steady state, on the basis of observed creep strain curves. For the non-steady-state model, we adopt the theta projection [1], which includes exponential-type deceleration and acceleration terms corresponding to the primary and tertiary stages, respectively. There is no study to apply the Bayesian inference framework to the model selection problem in creep constituent equations. Both equations have been used and there is no consensus on whether the steady-state term is necessary
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