Abstract
The possibility of accurately identifying thermal material parameters on the basis of a simple tension test is presented, using a parameter identification framework for thermo-mechanically coupled material models on the basis of full field displacement and temperature field measurements. Main objective is to show the impact of the material model formulation on the results of such an identification with respect to accuracy and uniqueness of the result. To do so, and as a proof of concept, the data of two different experiments is used. One experiment including cooling of the specimen, due to ambient temperature, and one without specimen cooling. The main constitutive relations of two basic material models are summarised (associated and non-associated plasticity), whereas both models are extended so as to introduce an additional material parameter for the thermodynamically consistent scaling of dissipated energy. The chosen models are subjected to two parameter identifications each, using the data of either experiment and focusing on the determination of thermal material parameters. The influence of the predicted dissipated energy of the models on the identification process is investigated showing that a specific material model formulation must be chosen carefully. The material model with associated evolution equations used within this work does neither allow a unique identification result, nor is any of the solutions for the underlying material parameters close to literature values. In contrast to that, a stable, that is locally unique, re-identification of the literature values is possible for the boundary problem at hand if the model with non-associated evolution equation is used and if cooling is included in the experimental data.
Highlights
Accurate material parameters are the basis of every predictive simulation
No final answer exists and it will be the focus of this work to compare two thermodynamically consistent model formulations which differ only in the amount of predicted dissipation in the context of a parameter identification
While the aforementioned publication shows that a stable optimisation is possible on the basis of a specific example, it states that the resulting, optimal parameters may vary for different material model formulations
Summary
Accurate material parameters are the basis of every predictive simulation. The optimal values of these parameters are usually determined by means of a parameter identification. While the aforementioned publication shows that a stable optimisation is possible on the basis of a specific example (simple tension test with monotonous loading, associated evolution equations without possibility to scale dissipation independently), it states that the resulting, optimal parameters may vary for different material model formulations. Two different experiments are used as the basis of the identifications to see what kind of data is necessary to obtain a (locally) unique solution and to investigate if monotonous loading (as is used in almost all of the publications mentioned above) holds enough information to find a parameter set which can represent several loading scenarios, i.e. plastic heating and conduction based cooling of the specimen. The objective function can be extended to include additional measurable quantities, such as the integral reaction force, see [14] or [13]
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