Correlation of microstructural damage to functional properties of irradiated carbon fibre based composites used in neutron chopper discs

Abstract: Understanding material behaviour has in the past enabled human development and will continue to characterize the various stages of our future development. The use of neutrons will greatly affect several research areas, such as sustainable energy production and cancer research, due to their interaction with nuclei. Neutrons will thus interact differently depending on the specific isotope, reveal information on crystal and magnetic structure and track dynamics of atoms. The European Spallation Source is currently under construction and can be compared to a giant powerful neutron microscope which is a huge step forward in everyday life science. To meet the need of each research area, numerous techniques and methodologies are required. To optimize performance, different energy spectra of the neutrons are needed depending on the research area. A neutron chopper is a type of mechanical neutron filter which filters out the wanted energy spectra. One of the most crucial components of the neutron chopper is the disc, made of carbon fibre reinforced epoxy, which will be in contact with the neutron beam. It is thus necessary to analyse the impact of radiation on the neutron chopper disc. To investigate whether the radiation damage is universal between different types of epoxy, two different epoxy resins were used. Each type of composite was then irradiated with 0, 3, 10 and 30 MGy. Using X-ray tomography in combination with a porosity analysis it was seen that the number of pores increased with radiation dose. However, this effect was only seen in one of the composites meaning that the radiation damage is not universal between different types of epoxy. It was seen that more elliptic medium sized pores are favourable. However, the mechanical properties, tested using three-point bending, showed no apparent change after exposures. Scanning electron microscopy revealed no evident changes of the fracture surfaces after irradiation. In totality, the results helped ESS to confidently select the type of epoxy that will ensure the longest neutron chopper disc lifetime and highest neutron instrument availability.