The importance of bonding in intralayer carbon fibre/self-reinforced polypropylene hybrid composites

The influence of the hybridisation configuration on the mechanical properties of hybrid self reinforced polyamide 12/carbon fibre composites

“…In this case, when the carbon fibre prepreg tape broke, at around 2% strain, the remaining SRPA12 fraction survived and then continued to be load bearing until 11% failure strain (which is typical for these pure SRPA12 materials). So if the carbon fibre tapes are located on the outside of the sample, and so the components can act independently, then the tensile behaviour is very similar to the SRPP/carbon fibre hybrids from the previous study [2]. In those SRPP/carbon fibre hybrids, delamination between the layers had the same effect of 'separating' the two components.…”

“…However, for the materials in this current study, where the bonding between the polyamide fraction and the carbon fibres is much better during tensile loading brittle behaviour occurs even at a carbon fibre fraction of 8%. Figure 11 shows a comparison of the tensile and bending properties of these two different intra-layer based hybrids (both with an 8% carbon fibre fraction) highlighting the different balance of properties that can be achieved with the two different base polymers (the PP hybrid results are taken from our previous work described in [2]). In tension, the PP based hybrid retains the high failure strain of the pure SRPP sheet (>20%) due to local debonding and delaminations at the point where the carbon fibre fraction fails, contrasting with the PA12 based hybrid which fails when the carbon fibres fail at less than 2% tensile strain.…”

“…Following on from this study, Swolfs et al [2,3,28] looked at the same material combination, oriented polypropylene tapes and carbon fibres, but in this case in an intra-layer configuration. Here, an oriented polypropylene tape was co-woven with a carbon fibre/polypropylene prepreg tape to produce a co-woven cloth, which was then processed using the hot compaction process to produce hybrid composite sheets.…”

“…This trade-off between modulus and toughness, often called the modulus/toughness dilemma [1][2][3][4], continues to be a major area of research interest, with the continuing objective of developing so called 'hybrid' materials that could combine these two important properties. One popular route to hybridisation is to combine two different fibre types in a composite, often a high modulus but brittle fibre (usually carbon) and a ductile, and often lower modulus, polymeric fibre.…”

“…In particular, a 'positive hybrid effect' is achieved when the experimentally measured property is found to be greater than predicted by the chosen model. For the results of the intra-layer carbon fibre/PP hybrids described by Swolfs et al [2], the tensile test results of these hybrids suggested a positive hybrid effect for the failure strain of the carbon fibres (observed as a stress drop in the stress-strain curve), with an increase in the composite tensile modulus in line with model predictions, but with a minimal decrease in the composite failure strain, up to a carbon fibre loading of around 7 volume percent . Swolfs et al proposed that this was mainly due to the beneficial effect of having intermediate bonding between the layers when using polypropylene, allowing delamination and additional energy absorption to take place.…”