Experimental characterization of fibre-reinforced composites improved with nanofibres or nanotubes

A review is presented on the testing and mechanical properties of continuous fibre reinforced composites modified with nanotubes or nanofibres either dispersed in the resin or grown on the microfibres. The nano-level cross-links are shown to be able to (1) increase the fibre/matrix interfacial strength, (2) reduce the inter-fibre crack growth, and (3) improve the inter-ply delamination resistance. A positive influence on the thermal expansion is also detected. However, for unfavourable material constitutions, the strength properties can stay almost the same or even significantly deteriorate

Damage development around moulded-in holes in flat braided composites

Textile techniques like overbraiding offer the possibility to perform some function integration during the composite fabrication stage. As an example, it is possible to integrate axes or holes necessary to transfer loads to the composite structure. Moreover, this prevents drilling and therefore fracturing load-carrying fibres at a latter stage. However, this means a local reorientation of the fibre and therefore a change in properties. This paper proposes a model for the reorientation of the fibres around a moulded-in hole. A subsequent finite element analysis shows the influence of this reorientation on the stress situation around the hole. Validation on pressed glass-PPS specimens loaded under tension shows that the proposed model is able to predict damage initiation in the vicinity of the hole

Deformability of a textile reinforcement modified with nanofibres

Deformability of a textile fabric is studied experimentally using a) friction test, b) out-of-plane compression, and c) bending. These tests reveal that a grafting of the fabric with carbon nano-fibres can significantly deteriorate its deformability. Therefore an optimal CNF mass fraction should be chosen for a particular production case, to obtain a compromise between improved strength and decreased drapability

On the mechanical behaviour of a butt jointed thermoplastic composite under bending

In the present work, the mechanical behavior of a recently developed novel butt jointed thermoplastic composite was investigated under bending conditions. The laminated skin and the web were made of carbon fiber (AS4) and polyetherketoneketone (PEKK). The butt joint (filler) was injection molded from 20% short carbon fiber filled with PEKK thermoplastic. The skin and web were co-consolidated together with the butt joint in the form of a hybrid T-shaped structure. A three point bending (3 PB) set-up was used to investigate the mechanical response of the hybrid composite. The crack initiation and propagation mechanisms for the filler and the delamination at the skin-filler interface were captured using a high speed camera. It was found from the experimental observations that the crack initiated in the filler and then propagated towards the skin-filler interface. A numerical model was also developed using the finite element method in ABAQUS including the crack initiation and growth in the filler together with the delamination at the skin-filler interface. For this purpose the virtual crack closure technique (VCCT) was employed for the crack growth in the filler and the traction separation law was applied at the skin-filler interface using a cohesive surface. The residual stresses and deformations coming from the co-consolidation process were predicted by applying a thermal load and taken into account in the quasi-static analysis. A good agreement was found between the predicted and measured force-displacement curves. The developed numerical model was further employed to address the crack initiation and growth in the filler and delamination at the skin-filler interface using the mix mode effective fracture energies. A linear elastic behavior was found in the structure until the crack initiation in the filler

Friction measurements on carbon fibre tows

Friction plays an important role in the production of fibre reinforced\ud composite products. The fibrous tows deform during the forming phase. Friction is\ud regarded as a dominant phenomenon in tow deformation mechanisms. The coefficient\ud of friction is a material-interface characteristic which gives a relation between applied\ud deformation loads and frictional forces. A capstan experiment has been performed with\ud carbon fibre tows on a steel cylinder. This work aims to clarify friction related mechanisms\ud and identify dominant parameters. The applicability of the capstan experiment is\ud investigated with respect to the frictional behaviour of fibrous tows

Synthesis of Carbon Nanofibers on Large Woven Cloth

This experimental study aims at the in situ growth of carbon nano-fibers (CNFs) on relatively large (25 × 30 cm2) single-layer carbon-fiber fabrics. It is shown that CNFs can be grown with the distribution potentially suitable for a future use in polymer-matrix composite materials. Details of tuning the catalyst deposition method and the CNF growth process are presented and analyzed. In particular, the Ni catalyst deposition method and the type of solvent are shown to strongly influence the uniformity of a CNF growth on carbon fibers, and sometimes even processibility of the whole specimen