Investigation of the viscoelastic material behaviour of filled elastomers under multiaxial deformations

• Applicant: Professor Dr.-Ing. Stefan Diebels
• Subject Area: Mechanics
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 260169457

Nowadays filled rubber materials play an important role in industrial assemblies. The diversity in the different possible combinations of polymer bulk materials and filler particles can influence the material behavior to achieve the requirements of the application which shows the relevance of this material class. In our project we will investigate a carbon black-filled EPDM as a representative material for the class of filled rubber. Investigations have proved the transferability of the stress-strain relations to different elastomer-filler combinations. A macroscopical and phenomenological model using a series approach with respect to the strain invariants will describe the material. Earlier investigations of the quasistatic behavior have shown, that a description with respect to uniaxial experiments is usually not able to display general biaxial loading states as well as a description which is only dependent on the first invariant. Multiaxial simulations do not match if a uniaxial modell development is used, even taking into account elastic behavior only. If a detailed look on real applications is taken, the assemblies complex geometries result in complex deformation states even if the macroscopical loading condition is quite simple, for example only uniaxial. This local variation of the strain conditions also results in a variation of the strain rates distributed over the whole geometry during the loading. As a fact, it has to be pointed out that the viscoelastic behavior for such multiaxial loading conditions plays an important role in this context. Filled rubber materials usually show a pronounced viscoelastic behavior strongly influencing the overall material behavior. An as general as possible material description with respect to multiaxial deformations requires a very broad experimental investigation as well. Hence, we will use the biaxial tensile test regarding both, quasistatical loading conditions as well as dynamical loadings. Hereby different loading paths have to be taken into account to represent the time dependency with respect to the material memory concerning the loading history. The number of necessary experiments and the characteristical long relaxation times yield in a complex experimental procedure. For that purpose, we will develop a new experimental process which allows as much information as possible for the material model, but also not too much information. Our goal is to do as less experiments as possible, but also as much as necessary, which also have to be taken into account in the further model and parameter identification. The resulting material model is supposed to be as general as possible in order to represent multiaxial deformations properly. The shape of the model approach has to be investigated including this generality with respect to time-dependent multiaxiality. The numerical realization will be implemented in an open-source FE-code.

• DFG Programme: Research Grants