Optimisation based material parameter identification using full field displacement and temperature measurements

2021

Meccanica

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.

Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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

Rose

2021

Meccanica

“…The implementation of the parameter identification closely follows the work in [51]. The goal of the objective function g is to quantify the difference between the response of the simulation and the physical specimen during the experiment.…”

Section: Objective Functionmentioning

confidence: 99%

“…By dividing the difference in the displacement of two neighbouring measurement points by their distance, a simple strain-like quantity Δu is obtained, which is less sensitive to rigid body motions, cf. [51]. Since the displacement field in the experiment is evaluated at different measurement points than the finite element nodes of the simulation, it is necessary to interpolate the measured displacement field to the finite element nodes-a linear interpolation in time and space is performed.…”

Section: Objective Functionmentioning

confidence: 99%

“…Experiments on one specimen geometry are used for parameter identification. The parameter identification approach incorporating full-field measurements chosen in this work is directly based on [51] and uses an objective function formulated in terms of the force and the displacement field. The experiments on the other specimen geometry are used to validate the identified parameter set.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A large strain gradient-enhanced ductile damage model: finite element formulation, experiment and parameter identification

Sprave

2020

Acta Mech

A gradient-enhanced ductile damage model at finite strains is presented, and its parameters are identified so as to match the behaviour of DP800. Within the micromorphic framework, a multi-surface model coupling isotropic Lemaitre-type damage to von Mises plasticity with nonlinear isotropic hardening is developed. In analogy to the effective stress entering the yield criterion, an effective damage driving force—increasing with increasing plastic strains—entering the damage dissipation potential is proposed. After an outline of the basic model properties, the setup of the (micro)tensile experiment is discussed and the importance of including unloading for a parameter identification with a material model including damage is emphasised. Optimal parameters, based on an objective function including measured forces and the displacement field obtained from digital image correlation, are identified. The response of the proposed model is compared to a tensile experiment of a specimen with a different geometry as a first approach to validate the identified parameters.

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

Rose

2022

GAMM-Mitteilungen

Self Cite

Identifiability and sensitivity of thermal boundary coefficients identified alongside thermal material parameters by means of full field measurements during a simple tension test are shown empirically using a simple tension test with self heating as a proof of concept. The identification is started for 10 different initial guesses, all of which converge toward the same optimum. The solution appears to be locally unique and parameters therefore independent, but a comparison against a reference solution indicates high correlation between three model parameters and the prescribed external temperatures required to model heat exchange with either air or clamping jaws. This sensitivity is further analyzed by rerunning the identification with different prescribed external temperatures and by comparing the obtained optimal parameter values. Although the model parameters are independent, optimal values for heat conduction and the heat transfer coefficients are highly correlated as well as sensitive with respect to a change, respectively, measurement error of the external temperatures. A precise fit on the basis of a simple tension test therefore requires precise measurements and a suitable material model which is able to accurately predict dissipated energy.