Mapping of local fibre strain in carbon fibre-reinforced polymers using X-ray diffraction

Current fibre break models do not accurately predict the occurrence of diffuse versus coplanar fibre break clusters, suggesting gaps in our understanding of load sharing in composites. There is a pressing need for in-situ 3D strain measurements within fibres to address this issue. This research explores a novel analysis method specifically tailored to carbon fibres involving microscale 2D/3D strain mapping via X-ray diffraction (XRD), enhanced by computed tomography (CT). Experiments provided new insights into strain distributions in proximity to fibre breaks, supporting the validation of existing load-sharing models. Various samples were crafted, including micro model composite- and thin-ply composite specimens. The latter were tested to determine if strains within regular composites could be assessed using the same XRD technique, informed by data from the model composites. All specimens underwent in-situ tensile testing at the ID11 beamline, European Synchrotron Radiation Facility (ESRF). During loading, fibre breaks appeared, which were located, and the material was interrogated with XRD analysis. Our approach aims to quantify strain recovery lengths and strain concentrations in fibres post-break. The presented technique holds promise for advancing micromechanical model validation.