In situ real-time 3D observation of porosity growth during composite part curing by ultra-fast synchrotron X-ray microtomography

The present study reports on an experimental development addressing 3D void growth in epoxy-based carbon fibre-reinforced composites during their curing process. For that purpose and to investigate autoclave condition effects, composites samples were cured according to different curing cycles by using a specially designed device, which was installed on a synchrotron beamline dedicated to ultra-fast X-ray microtomography. Thus, 3D in situ images of the voids evolution could be obtained as a function of time, temperature, pressure, initial water content and resin conversion degree, which are the driving factors of void size evolution during the polymerization cycles. Results confirm the combined roles of humidity and temperature on the porosity growth and highlight the complex shape of the generated bubbles. It is also emphasized that a sharp increase of the applied pressure during the curing cycle instantaneously reduces the pore size. Such results improve the understanding of the cure of composites parts and can finally be used as input data for modelling purpose or for validation of existing models.