PSI - Issue 17

Trevor Sabiston et al. / Procedia Structural Integrity 17 (2019) 666–673 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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SEM analysis the fracture surface of the sample from Fig. 6 is shown in Fig. 7. These SEM images demonstrate that the main failure mode experienced by the NCF composite is delamination in the resin rich regions between plies. The appearance of the fracture surface is consistent with the fracture surfaces reported by Charambous et al., 2015 for delamination of a carbon fibre epoxy system. Charambous et al., 2015 found that the fracture occurred along the interface between the fibres and matrix as is observed in Fig. 7. Carvelli at al., 2010 also show using x-ray analysis that inter ply delamination is present in the specimens cycled to 100,000 cycles. Fig. 7 a) and c) shows rotation of the fibres which could be due to kink banding which is the primary failure mode of composites in compression including NCF composites (Edgren et al., 2006). From our testing delamination appears as the primary failure mode; however, it is possible that kink bands do form towards final failure. Transverse matrix cracks along with fibre failure and pull out are also present within the plies post delamination due to bending of the plies. The SEM images do not show evidence of the stitching yarns near the fracture locations. It is possible that the failure locations occur in regions where the stitching yarns are not present as there is a reduced delamination resistance in these regions.

Fig. 7. SEM images of the fracture surfaces a) delamination of NCF composite with multiple plies, b) resin rich area between two layers showing interfacial failure between the fibre and matrix, c) transverse matrix crack showing fibre pull out and fibre breakage, d) fibre matrix interfacial failure, transverse matrix crack, and planar matrix crack in a resin rich area