Optimisation and confidence region estimation of constitutive parameters in equations for hot metal deformation

Rist, Martin; Mulyadi, M.; Edwards, Lyndon and Brooks, J.W. (2005). Optimisation and confidence region estimation of constitutive parameters in equations for hot metal deformation. In: Banabic, D. ed. Proceedings of the 8th Esaform Conference on Material Forming, Volume 1. Bucuresti, Romania: The Publishing House of the Romanian Academy, pp. 61–64.

Abstract

This paper surveys a range of numerical methods for the optimisation of material parameters in a single state-variable constitutive model applied to the hot deformation of Ti-6Sn-2Zr-4Mn-6Mo. Minimisation of an objective function, describing the least squares difference between experimental results and model output, was carried out using several methods: Nelder-Mead direct search, quasi-Newton gradient, trust-region Newton and genetic algorithms. The most robust approach involved gaining an initial estimate of parameter values using the genetic algorithms and then refining this with a Nelder-Mead search. A scheme for estimating the confidence limits of the derived parameters is also presented.

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