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Prediction, not extrapolation

Wed 11th December

Prediction not extrapolation

J.W.Brooks

School of Metallurgy and Materials, University of Birmingham,

Edgbaston, Birmingham B15 2TT

j.brooks@bham.ac.uk

The risks of extrapolating mechanical property data beyond the understanding of the relevant deformation regime are well known. This paper highlights some of the problems that can be encountered and suggests that deformation models which capture the physical behaviour of a material across the temperatures and strain rate regimes encountered in service can provide more reliable estimates of long term performance. Some physically based approaches are presented for flow stress, fatigue and creep which attempt to capture the significant metallurgical features which determine the mechanical properties and provide some predictive capability. The flow stress model is based on dislocation and grain size interaction to allow the prediction of the sigmoidal log stress-log strain rate behaviour and captures the shift from creep (Regime I) through superplasticity (Regime II) to work hardening behaviour (Regime III). The fatigue approach has been demonstrated for titanium alloys and is based on the interactions of dislocations with alpha-beta lamellae and grain boundary necessary dislocations (GNDs). The creep model is based on the dislocation particle interactions that are relevant to the mechanical performance of superalloys.

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