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A Statistical Test for Identifying the Number of Creep Regimes When Using the Wilshire Equations for Creep Property Predictions / Mark Evans

Metallurgical and Materials Transactions A, Volume: 47, Issue: 12, Pages: 6593 - 6607

Swansea University Author: Mark Evans

Abstract

A new parametric approach, termed the Wilshire equations, offers the realistic potential of being able to accurately lift materials operating at in-service conditions from accelerated test results lasting no more than 5000 hours. The success of this approach can be attributed to a well-defined linea...

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Published in: Metallurgical and Materials Transactions A
ISSN: 1073-5623 1543-1940
Published: Springer Science and Business Media LLC 2016
Online Access: Check full text

URI: https://cronfa.swan.ac.uk/Record/cronfa29679
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Abstract: A new parametric approach, termed the Wilshire equations, offers the realistic potential of being able to accurately lift materials operating at in-service conditions from accelerated test results lasting no more than 5000 hours. The success of this approach can be attributed to a well-defined linear relationship that appears to exist between various creep properties and a log transformation of the normalized stress. However, these linear trends are subject to discontinuities, the number of which appears to differ from material to material. These discontinuities have until now been (1) treated as abrupt in nature and (2) identified by eye from an inspection of simple graphical plots of the data. This article puts forward a statistical test for determining the correct number of discontinuities present within a creep data set and a method for allowing these discontinuities to occur more gradually, so that the methodology is more in line with the accepted view as to how creep mechanisms evolve with changing test conditions. These two developments are fully illustrated using creep data sets on two steel alloys. When these new procedures are applied to these steel alloys, not only do they produce more accurate and realistic looking long-term predictions of the minimum creep rate, but they also lead to different conclusions about the mechanisms determining the rates of creep from those originally put forward by Wilshire.
Keywords: Activation Energy; Creep Rate; Regime Change; Stress Regime; Creep Mechanism
College: College of Engineering
Issue: 12
Start Page: 6593
End Page: 6607