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Why the use of NCF is growing in complex structural components

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NCFs are a type of “engineered fabrics” to reinforce polimeric composites that are made up of multiple layers or fibers stitched together. The most used NCF’s are biaxial, triaxial and cuadriaxial fabrics, where the fiber tows are straight and with different orientations (0, 45, 90 degrees) to provide multidirectional properties.

Non  Crimp FabricImage: Non Crimp Fabric

The combination of multiple layers of fibers, stacked in just one fabric, leads to faster and cheaper preforms production processes than unilayer based processes. It also has advantages for LCM (Liquid Composite Moulding) methods as NCF present better drappability due to the good deformability of unidirectional plies versus vowen fabrics that are undulated (crimp). An additional advantage of the NCF reinforced composites is that they generally feature better mechanical properties as the tows are not crimped or woven. Furthermore the delamination resistance and impact strenght of the NCF reinforced composites is better.

One key advantage of the NCF’s is the ability to drap into relatively complex shapes without giving rise to wrinkles that normally appear with standard woven textiles and preimpregnated tapes. The excelent conformability of biaxial fabrics under “dome type” deformation conditions is caused by a slipage of the fiber tows as there is no joints that restrict this movement.
This is why the use of NCF is rapidly growing in aircraft, automotive, yatching , wind energy and complex structural components.

A lot of work is being done in NCF to push the boundaries of this materials:

Research is beeing developed to increase the limits of the deformability of NCFs through the determination of the best stitching conditions. These studies show that the deformation of the biaxial y triaxial NCF under load (bias extensión test), happens through rotation, sliding and compaction of the tows. The resistance of the NCF to biaxial deformation is dependant on the density, the tension and the position of the stitches. Higher tension on the stitches gives bigger resistance to deformation due to better sliding resistance.

The veils and binders used by the different suppliers play also an important role. A veil is a thin layer of polimeric material formed by fibers with random orientation. Binders are thermoplastic particles that act like an adhesive. Nowadays they are used to minimice fragility of the epoxi matrix on the composite.They also avoid fraying or wrong orientation and specially optimize the permeability, improving process times. Permeability of the material is a key feature. On one hand high permeability accelerates infusion processes, on the other hand too much space between the fibers can lead to a worse impregnation of the fibers worsening the fatigue behaviour. Many innovations are beeing lauched in these topics.

The manufacturing requires handling and depositing the NCF on the mouls with big precision, repeatability and productivity. Drappability modeling is also an important research area , predicting and improving the deformation of the fabrics depending on the tension applied is the basis for the good part design and process optimization.

In this line developments like Drapetest http://bit.ly/1wu2Sm4 allows to automatically characterize drapability and the formation of defects during draping and forming The tester combines the measurement of the force required for forming with an optical analysis of small-scale defects .

Video: Bombardier CSeries uses NCF

-We go dry

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Dry Composites is an initiative by Danobat Composites to share the latest advancements in automation using dry composite material. This online community aims to connect companies, research centers, academics and experts interested in the use of dry composite material to develop structural parts in aerospace.

What do we mean by Dry Composites? There are two distinct methods of making composite structures. The first involves impregnating the fibres in a dedicated off-line machine to make a pre-impregnated material, called pre-preg. This is then transported to a factory that makes structures where it is laid up by machines or manually.

The second, more direct route is to take dry fibres, usually in some textile format and after assembly into a pre-form, infuse them with liquid resin. The infusion process is known by a number of trade names and acronyms such as RTM, VARTM etc.

The pre-preg route involves an extra process and hence cost, but it does result in structures with good consistent properties. Recently, the performance of structures made by infusing Dry Preforms has improved and is now claimed by some, to match that of more conventional pre-preg materials. Working with dry fibers, fabrics and textiles enables thicker layers to be used, saving time and labour costs, plus aiding in the creation of more complex, one-piece structures.

However whereas the pre-preg manufacturing industry is well served by automation with dedicated machine tools, the lay-up of dry fabrics has not received the same attention. Danobat Composites has pioneered the development of Automatic Tape Laying using woven and NCF fabrics. This has improved laminate quality, repeatability and reduced the cost of composite structures by significantly cutting manufacturing labour and material costs. Moreover, it is worth mentioning that the use of dry materials can give rise to out of autoclave curing processes acquiring required properties in primary structural aerospace parts.

Today, manufacturers face the challenge of doing more with less, the aerospace industry needs to adapt quickly to new material and process developments to remain competitive. In doing so, the ultimate goal of a disruptive automation technology is to introduce new processes that may deliver better high efficiencies and control at less cost. This requires broad support from an ecosystem of R&D, manufacturing, engineering teams and material developers.

Dry Composites is an open space for those interested in learning more about how automation using dry composite material can be applied to the aerospace industry. From sharing industry news, information, data and technical solutions about dry composite solutions to interviews and perspectives from expert sources. Our target audience includes decision makers, R&D engineers, global suppliers of advanced materials, software and automation companies.

If you are interested in learning more about advancements in the use of dry material in the aerospace industry, follow us on Twitter @drycomposites and join the LinkedIn Group Dry Composites.

Stay tuned for more!