Dynamic mechanical properties of multi-scale carbon fibre reinforced PEEK.

The goal of this research was to study the effects that adding carbon nanotubes (CNTs) have on the dynamic mechanical properties of a thermoplastic polymer, poly(ether ether ketone) (PEEK), and woven composite materials over a wide range of temperatures, frequencies and strain rates. For this purpose, numerical analysis by representative volume element (RVE) and experimental methods were used. This work includes a study considering the suitability of classical micromechanical theories of composite materials for predicting properties of nanocomposites.
To find a suitable numerical method, finite element analyses were carried out using different kinds of unit cells and RVE. The finite element models allowed both viscoelasticity of the matrix and special behaviour of the interface zone to be represented. The interface was modelled in two ways: allowing bond slip between the fibre and polymer and by considering the interface as a separate volume between the fibre and polymer. Validation of the models was achieved by comparison of the results with experimental results of short fibre composite and nanocomposites. Experiments were carried out on nanocomposites of aligned CNTs and randomly oriented, treated and untreated CNTs in PEEK.
For woven composite materials, a finite element method was employed to develop a suitable three-dimensional RVE to predict the Young's modulus and the effective loss factor. CNTs were added to study their effect on the dynamic mechanical prosperities of woven composite materials over a range of temperatures and amplitudes. Experiments on woven composite materials with and without CNTs showed that adding CNTs to woven composite enhanced the modulus at different temperatures and untreated CNTs improved the damping over a range of temperatures. The numerical results for woven composite materials with CNTs and without CNTs were compared with DMA experimental results. Similar trends for modulus and loss factor with temperature change were shown.