Abstract
This paper reviews recent research concerned with identifying and subsequently reducing sources of uncertainty in strain measurement associated with the ubiquitous use of extensometer ridges in the design of high-temperature creep testpieces. Both experimental and theoretical procedures have been employed. Three principal sources of strain uncertainty have been identified: firstly, the interaction of deformation fields due to the hoop constraints associated with each extensometer ridge; secondly, the notch effect caused by any differences in bar diameter between the gauge length side and loading shank side of the ridge; and thirdly, time-variation of the testpiece temperature during the test. It is shown by theory and experiment that an efficacious means of eliminating the first source of uncertainty is to machine multiple axial slits within each extensometer ridge. This is shown to be particularly advantageous for the short gauge lengths used in LCF testing. The uncertainty in measured creep strains due to the “notch” effect has been reduced by displacing the step outwards and away from the gauge section side of the ridges. To reduce the uncertainty in strain measurement due to temperature variability, it has been proposed that temperature histories throughout each test should be accurately measured and recorded. These data, along with measured strain histories, can then be used to calibrate appropriate constitutive equations to enable more accurate strain/ time histories to be computed.KeywordsConstitutive EquationCreep RateGauge LengthCreep StrainCreep CurveThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
Published Version
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