Nanofibre Technology: Composite Toughening Veils
Despite a list of impressive properties, carbon-fibre composite materials are generally poor performers when it comes to fracture toughness, impact resistance and delamination strength. This is a dangerous weakness, given that the failure propagates under the material surface giving an appearance of being visibly unchanged. These routes to failure result in micro-cracks which tend to propagate within the composites resin along the interlaminar-plane. However, this vulnerability can be significantly reduced through interlaminar toughening, boosting the resistance to crack propagation between the layers of carbon-fibres.
Interlaminar toughening has been well researched and has proven to be best achieved by inserting a nanofibre veil in-between carbon-fibre layers; the nanofibres of the veil can also be engineered to give the composite self-healing abilities. Nanofibres veils possess the high porosity required to allow suitable resin flow during infusion, as well as a high surface-to-volume ratio which is crucial for resin-fibre interfacing. Numerous polymers have been explored, with polyamide outperforming all others, achieving composite performance increases as high as 180% (Mode I crack opening), 70% (Mode II crack sliding) and 400% (fatigue resistance) (published DOI: 10.1016/j.compositesa.2015.01.028). This places it as an ideal material for use in aerospace and sporting industries.
A roll of composite toughening nanofibre, with the nanofibres observable in the magnified area.
At Radical Fibres, one of our fundamental advantages is the ability to include functional materials within the final veil. This could be in the form of embedded nanomaterials within the nanofibres, such as carbon nanotubes, or much larger particles entangled amongst the nanofibres, such as graphene platelets. Unlike traditional resin infusion methods, nanofibres offer an easier and safer route to uniform material delivery. This replaces the current industry approach to mix these materials directly into the resin, which has severe complications and drawbacks. It enables us to significantly enhance the composite performance levels whilst adding functionality, such as thermal/electrical conduction, anti-static, anti-warping and self-healing.
A graphene loaded nanofibre veil, with the graphene safely locked into the fibres, with the graphene platelets being well distributed. (B) Results from our own independent testing of graphene loaded veils within a carbon fibre composite.