Conversion of the hot torsion test results into flow curve with multiple regimes of hardening

Khoddam, S. and Hodgson, Peter 2004, Conversion of the hot torsion test results into flow curve with multiple regimes of hardening, Journal of materials processing technology, vol. 153-154, pp. 839-845, doi: 10.1016/j.jmatprotec.2004.04.171.

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Title Conversion of the hot torsion test results into flow curve with multiple regimes of hardening
Author(s) Khoddam, S.
Hodgson, Peter
Journal name Journal of materials processing technology
Volume number 153-154
Start page 839
End page 845
Publisher Elsevier BV
Place of publication Switzerland
Publication date 2004-11-10
ISSN 0924-0136
Keyword(s) hot torsion test
singular value decomposition
constitutive parameters
flow curve
dynamic recrystallisation
varying hardening indices
parametric modelling
Summary The method of Fields and Backofen has been commonly used to reduce the data obtained by hot torsion test into flow curves. The method, however, is most suitable for materials with monotonic strain hardening behaviour. Other methods such as Stüwe’s method, tubular specimens, differential testing and the inverse method, each suffer from similar drawbacks. It is shown in the current work that for materials with multiple regimes of hardening any method based on an assumption of constant hardening indices introduces some errors into the flow curve obtained from the hot torsion test. Therefore such methods do not enable accurate prediction of onset of recrystallisation where slow softening occurs. A new method to convert results from the hot torsion test into flow curves by taking into account the variation of constitutive parameters during deformation is presented. The method represents the torque twist data by a parametric linear least square model in which Euler and hyperbolic coefficients are used as the parameters. A closed form relationship obtained from the mathematical representation of the data is employed next for flow stress determination. Two different solution strategies, the method of normal equations and singular value decomposition, were used for parametric modelling of the data with hyperbolic basis functions. The performance of both methods is compared. Experimental data obtained by FHTTM, a flexible hot torsion test machine developed at IROST, for a C–Mn austenitic steel was used to demonstrate the method. The results were compared with those obtained using constant strain and strain rate hardening characteristics.
Language eng
DOI 10.1016/j.jmatprotec.2004.04.171
Field of Research 091399 Mechanical Engineering not elsewhere classified
HERDC Research category C1 Refereed article in a scholarly journal
Copyright notice ©2004, Elsevier BV
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