Strain rate dependent material model for polymer composites

Licentiate thesis, 2020

We propose a micromechanical model that is able to predict the nonlinear behaviour and failure of unidirectional fibre reinforced polymer composites subjected to dynamic loading conditions. This novel material model is heterogeneous on the micro level and homogeneous on the ply level.

The fibres are assumed to be hyperelastic transversely isotropic and the matrix obeys a hypoelastic viscoelastic/plastic constitutive model enhanced by a continuum damage model. To model the matrix, a Zener rheological model for the viscoelastic behaviour combined with a Bingham model for the viscoplastic behaviour is assumed.

The proposed model is formulated in a framework that separates the fibre and the matrix contributions. Typical applications are unidirectional composites manufactured, for example, from unidirectional fibres embedded in a polymer matrix. Generally, the quasi-brittle compressive failure behaviour of composites happens during fairly large strains in the matrix. Therefore, a geometrically nonlinear description
has been developed.

Finally, using this model, we characterize the shear induced post-failure behaviour in compression of the composite material. Finite element simulations are conducted to predict the rate dependent properties of unidirectional polymer composites. The predictions of the finite element simulations are compared to published experimental results of an IM7/8552 material system under compression loading at different strain rates. The results are in a reasonably good agreement with the experiments.