Directional spectral reflectivity measurements of a carbon fibre reinforced composite up to 450 °C

- The bi-directional reflectivity of carbon/PEEK composite is quantified as a function of temperature and incidence angle.
- A heating cell to measure normal reflectivity from 20 to 450 °C is developed.
- The reflectivity is maximum for grazing incidence and parallel fibres.
- The surface scattering profile of the composite is centred along the reflected specular directions.
- The fibres radiative behaviour is predominant in the composite material.

A quantitative study of the bi-directional reflectivity of a carbon/poly-ether-ether-ketone (PEEK) based composite is performed at room temperature using a Fourier Transform Infra-Red Bruker 80v spectrometer (0.6-25 µm) angles of incidence and collection ranging from 11 to 83° and by varying fibre orientation. Then, a home-made compact cell, based on a customized resistive heater, is adapted to the sample compartment of the spectrometer for measuring the temperature dependency of the normal reflectivity of the composite sample from 20 to 450 °C. A complete validation of the thermal performances of the cell is thus presented to support the interpretation of the previous reflectivity measurements. The respective contributions of the carbon fibrous reinforcement and of the PEEK matrix on the reflective behaviour up to 450 °C is finally discussed. Temperature is shown to play a minor role on the optical properties of the tested materials, thus indicating a predominant role of the carbon fibres. Conversely, the room temperature angular study shows the high importance of the beam incident angle with respect to fibres orientation and enables to characterize this strongly anisotropic reflective behaviour.