An anisotropic hyperelastic-plastic material model for the process-related material response of TPV

Due to their multiphase structure, thermoplastic vulcanizates (TPV) combine the outstanding rubber-elastic properties of elastomers with the efficient processability and recyclability of thermoplastics. As a result, an increasing number of elastomer components are being replaced by TPV. New challenges arise in the design of structural components made of TPV, such as the process-related anisotropy of the material. Under quasi-static uniaxial loading, the anisotropy can result in a reduction of stress response of up to 40 % in dependence on the testing direction with respect to the flow direction. This is due to the high shear velocities within the injection molding process and the resulting orientation and distortion processes of the elastomer particles. Hence, an integrative simulation routine is necessary to optimize the prediction of the mechanical response of injection molded TPV-components. This, however, needs further development in both the injection molding simulation predicting the local configuration of the material and the mechanical models. Existing mechanical models for TPV cannot consider the process-related anisotropy. In this work, an analytical anisotropic, quasi-static material model is presented, that gives an accurate prediction of the component behavior based on the local phase configuration.

Within the framework of the presented research, the morphological structure-property-relation of the material was investigated based on microscopic investigations of the phase morphology using atomic force microscopy (AFM) and uniaxial tensile tests of specimens with varying extraction orientations. Statistically representative volume elements (RVE) are used to investigate the deformation mechanisms with respect to the degree of distortion and the homogenized mechanical stress-stretching response under quasi-static loading.

Based on these findings, an analytical, structure-dependent hyperelastic-plastic model is developed, which describes the process-dependent quasi-static mechanical response of TPV. The model is based on a semi-physical homogenization approach on the molecular level. By implementing an interconnection of mechanical surrogate-models to represent the thermoplastic and elastomer phases as well as the introduction of a statistical molecular orientation distribution, the characteristic anisotropic elastic-plastic material behavior of TPV can be considered in the model.

In the long term, this model can be applied in an integrative modelling approach for TPV. This enables the potential of applying TPV in components with higher technical requirements using more sophisticated modelling techniques.