University of Twente
Faculty of Engineering Technology
Chair of Production Technology
De Horst, N131
P.O. Box 217
7500 AE Enschede
P +31 (0)53 489 2569
TRANSFORCE (Transverse Reinforcement of Carbon Fibre Composites with Carbon Nano Fibres)
Start / End:
June 2009 to June 2012
Prof. Dr. Ir. Remko Akkerman
Daily supervisor in PT group - Dr. Ir. Laurent Warnet
This project is primary funded by STW.
carbon fibre reinforced polymers, carbon nanofibres, catalytic preparation, transverse strength
PROBLEM: Increasing application of lightweight structures requires advanced composite materials. Continuous carbon fibre reinforced plastics (CFRPs) are characterised by high strength and stiffness at low weight. These advantages are predominantly obtained in the direction of the carbon fibre reinforcement. The mechanical properties in the direction perpendicular to the fibres, also denoted as the transverse properties, are governed by the polymer matrix and fibre/matrix interface. The transverse properties are generally an order of magnitude lower than the properties in the fibre direction; hence, they are the weaker links in a composite structure. Improving these properties extends the applicability of CFRP materials.
GOALS & OBJECTIVES: The project aims for the improvement of the transverse properties. The backbone is a modification of the surface of the reinforcing carbon fibres by the growth of carbon nanofibres (CNFs). The CNFs are grown onto the carbon ‘micro’-fibres (CMFs) by catalytic decomposition of hydrocarbon gas over metal particles. This is a most promising technique for the increase of the fibre/matrix interfacial strength and intra- and inter-bundle transverse mechanical behaviour. The effect of the modification is expected to take place on different levels.
Firstly, the fibre/matrix interface improves significantly by ‘whiskerisation’ (growing a coating of whiskers on a substrate) of CNFs as demonstrated already in the early 1990s. The improvement of the interfacial strength results in increased compressive strength, better fatigue performance, durability and impact resistance. Secondly, CNF crosslinks between the CMFs are expected to increase the transverse strength, reducing the ability of interfibre cracks to initiate and grow. Thirdly, crosslinks can be formed between subsequent plies in a laminate, which enhance the resistance against delamination.
The objectives of the current project are (1) to control the growth of CNFs onto CMFs with respect to CNF length, thickness (diameter), density (number of fibres per surface area unit) and distribution, (2) to establish the best reinforcement/resin combination, (3) to qualify and quantify the improvement of carbon fibre reinforced polymers by the incorporation of CNFs on the different levels, (4) to develop predictive models for the material properties to be used as engineering tools, and (5) to scale up from laboratory level to demonstration level, such that carbon fibre preforms can be enhanced with CNFs, resulting in a demonstration of the concept with an appropriate composite component.
Specific tests, which address the transverse properties of the composite, have to be explored also. These tests include stiffness tests, such as tensile and shear tests, as well as impact, hardness and fatigue experiments.
UTILISATION: Guidelines for optimal processing will be formulated, as well as design rules, which promote and facilitate the practical implementation of the CNF modified carbon/polymer composite.
A composite component will be developed with CNF modification to demonstrate the technology. Based on the findings, the fabric and laminate production will be evaluated with respect to performance of the processes (in rate and quality) and cost. The component production will be evaluated with respect to processing windows, part performance and cost. Further industrialisation of the technology is left to the industrial partners as a follow up development of this research project.
Three high tech companies and one research institute (NLR) support this programme and will participate in the user group. The industrial partners will evaluate the economic perspective of this technology in their specific setting, and implement it where it is cost effective. The NLR will assist in the knowledge transfer to industry.
1.In collaboration with CMG group in K.U.Leuven, a theoretical model is developed for compressibility of a nanotube/nanofibre forest with randomly oriented nanotubes. The model is applied to compressibility of a fibrous reinforcement with CNT-grafted fibres.
2.In collaboration with CMG group in K.U.Leuven, a mechanical model is developed for a hollow cylindrical beam representing a CNT.
3.Literature review is performed on the testing and mechanical properties of CNT/CNF-grafted textile composites. It is shown that the matrix, weight content and type of grafting should be well-adjusted to get a positive result for the strength improvement.
4.Permeability measurements are done in collaboration with K.U.Leuven. This property is shown to be weakly affected by the grafting, probably due to low nesting of the used woven fabric (5-harness carbon-fibre satin weave).
5.Deformability measurements for a dry textile (base or nano-grafted). The tool-ply or ply-ply friction depends on the grafting slightly, while the bending rigidity (Pierce cantilever test), in-pane shear (biaxial tension), and out-of-plane compressibility are strongly affected.
6.DCB tests on composite specimens (manufactured by vacuum infusion of an epoxy resin) show that the grafting increases GIc by about 50%.
7.Micromechanical analysis (FE modelling and evaluation of different theoretical estimations for the strength and stiffness) is in progress...