Identification of thermal material parameters for thermo-mechanically coupled material models

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.

On the determination of thermal boundary conditions for parameter identifications of thermo‐mechanically coupled material models

“…According to [15], a locally unique fit of the thermal material parameters (i.e., thermal expansion 𝛼 exp , heat conduction 𝜅 therm , heat capacity c 0 , and the parameter scaling latent heat, respectively dissipation 𝛽) is possible for the specific combination of model and material at hand and yields thermal material parameters close to literature values. In that publication, it was assumed that the boundary coefficients can be prescribed as 𝛼 air con = 0 and 𝛼 cl con = 10 8 W/(m 2 K) since the heat exchange through the clamping jaws appears to dominate.…”

“…A speckle pattern was applied to one side and a black coating with a known emission coefficient of 0.98 to the other side of the specimen. An example of the speckle pattern quality can be found in [15]. The two measuring systems were then placed on either side of the specimen and started simultaneously by means of a trigger signal, as depicted in Figure 2.…”

“…The model is valid for large deformations and uses the classic multiplicative split of the deformation gradient into an elastic and plastic contribution. The capability of this model to represent the main aspects of the aluminum alloy under consideration was already demonstrated in [15], where a detailed derivation of model equations can also be found. Hence, only three equations are highlighted within this section, since the main focus of the work at hand lies on the general identifiability of thermal parameters and thermal boundary conditions and less on model specific properties.…”

“…All model equations are summarized in this section. A detailed derivation of this model can be found in [15].…”

Simulation of PLC Effect Using Regularized Large-Strain Elasto-Plasticity

“…In fact, these papers and the present one belong to the broad field of research on thermo-mechanics of heterogeneous/composite materials and structures. The thermo-mechanical couplings are constantly a subject of intensive scientific activity; see, for instance [34][35][36][37][38][39][40][41].…”