Revolution Fibres have developed Xantu.Layr®, the world's first commercially available nanofiber interleaving veil. Xantu.Layr® has been shown to improve the fracture toughness (delamination resistance), compression after impact strength (damage tolerance) and fatigue resistance of composite laminates.
The Xantu.Layr® nanofiber veils act as nano-scale reinforcements of the brittle matrix resin, resulting in a tougher resin (even when used with already toughened resin systems) which is less prone to micro-cracking when stressed or impacted. Xantu.Layr® interleaved composites have shown improvements of 173% and 69% for Mode I and Mode II ILFT, respectively, improvements of 12% for ILSS, and improvements of up to 21% for CAI strength, all with negligible composite weight and thickness increases.
Xantu.Layr® has also been shown to be particularly effective in reducing the effects of fatigue (repetitive loadings), and improvements in fatigue life of up to 400% have been seen in some composites. The ability to improve the inherent weaknesses of composite materials using Xantu.Layr® presents an opportunity for composite components to be used in applications that were previously not possible.
Improving toughness in composite materials
Composite materials, especially carbon fiber reinforced polymers (CFRP's), are increasingly becoming the materials of choice in weight-critical structural components due to their high specific strength and stiffness. Despite these attributes, composites generally suffer from poor impact resistance, poor fracture toughness and poor delamination strength, particularly when brittle thermosetting epoxy resins are used. Currently, these problems are addressed by adding thermoplastic toughening particles to the bulk resin or by inserting tough polymer films or microfiber interleaving veils into the interlayers between the plies of the laminate. However, these toughening methods are not without their drawbacks.
Toughening particles added to resins often suffer from poor dispersion, and can form regions of high and low particle concentrations which can lead to reductions in composite performance. In addition to this, toughening particles are also free to flow with the resin during the curing process resulting in further uneven particle distributions. Toughening particles are also known to increase resin viscosity, making them particularly unsuitable for laminates fabricated using out of autoclave processing methods, and can increase laminate thickness, decrease in-plane stiffness and strength and potentially lower the glass transition temperature (Tg) of composite laminates.
This article appeared in the September–October 2017 issue of Reinforced Plastics.