Abstract
The layered architecture, and lack of through-thickness reinforcement, has led to delamination being the most common failure mode in fibre reinforced polymer composites. A variety of strategies have been developed to suppress delamination, however the majority also cause degradations to the in-plane mechanical properties. Suppressing delamination requires the interlaminar fracture toughness (ILFT) of the composite system to be enhanced, so as to demand more energy for cracks to initiate, coalesce and propagate. Vertically aligned carbon nanotube (VACNT) interleaves have shown promising qualities as delamination suppressors, due to their extremely high localised areal densities, and desirable alignment, which results in bridging of the resin-rich interlaminar region.The aim of this research is to understand how geometric characteristics of VACNTs, such as length and areal distribution, influence the ILFT enhancement, and hence, their delamination suppressive capabilities. Within the research, focus is placed on assessing the capabilities of VACNT interleaves as delamination suppressors in delamination-prone composite structures.
Mode I and Mode II ILFT tests are conducted on HexTow® IM7/HexPly® 8552, interleaved with VACNTs, with a selection of CNT lengths, areal densities, and areal distributions. Tensile tests are performed on VACNT interleaved, delamination-prone, tapered and notched specimens. All interleaved specimens are compared to an equivalent unmodified baseline. Fractography analysis, high speed camera footage, and computed tomography scans are performed on damaged specimens to determine their failure mechanisms and allow comparisons with an equivalent unmodified composite system.
Overall, VACNTs are found to suppress delamination, however their maximum toughening capabilities are limited to the secondary mode of failure of the host composite system, which, in this case, is intralaminar delamination. Distinguishing between an inter- or intra-laminar delamination dominated composite system is vital, before interleaves are selected as a delamination suppression technique. Cohesive elements with enhanced properties are shown to be a simple and effective method to model composite structures with VACNT interleaves.
| Date of Award | 24 Mar 2020 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Luiz F Kawashita (Supervisor), Ian Hamerton (Supervisor) & Stephen R Hallett (Supervisor) |