Damage characterisation of cryogenically cycled carbon fibre/PEEK laminates

A unique insight into damage formation in CF/PEEK laminates before, during and after cryogenic cycling, using optical microscopy and 3D X-ray computed tomography (CT), is presented. Thicker laminates were found to exhibit significantly greater microcrack density and delamination when compared to thinner laminates, with lay-up and material type also being important contributing factors. Thermal residual stress induced microcracking was also found in thicker laminates post-processing. 3D rendering software was used to prove the presence of through thickness crack networks within the laminates, as well as the extent of cracking through the specimen width. Crack opening in inner and off-axis ply groups was found to be significantly less than outer plies, implying the importance of these plies in limiting laminate permeability. The presence of voids was found to influence crack nucleation and growth paths within the laminates, with full void volume characterisation presented.