Tag Archives: non-woven

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

-“Dark-on-dark”: a machine vision approach for dry carbon fiber inspection

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As automation of dry carbon fiber manufacturing gains more and more momentum across the board, inspection systems become a crucial factor when it comes to assuring the quality of final products and the efficient use of available resources. Due to their ability to detect mistakes and faults at an early stage, it is straightforward to infer the great impact inspection systems can have when suitably integrated in a production line.

The systems presented in this entry are focused mainly in machine vision technology and cover inspection for both dry composite fabrics and post-infusion manufactured pieces. One of the main drawbacks they will need to overcome is the fact that carbon fabric absorbs a wide spectrum of light and presents a black color. Therefore, the design of an adequate lighting system will play a critical role at the task of detecting faults on the material (holes, fuzzballs, foreign-object-debris,etc.) and at providing good performance in the so called “dark-on-dark” scenario where vision systems tend to struggle.

APODIUS VISION SYSTEM

The Apodius Vision System (AVS) is designed to measure the fiber orientation of composite fabrics and, based on the irregularities of the obtained pattern, also detect gaps or impurities that dry composite plies may exhibit. Specifically, it can take orientation angle measurements of 0.1º precision for every 50×50 mm² of both woven and non-woven fabrics thanks to its diffuse lighting technology that minimizes reflections on the fabric’s surface. Also, it is attachable to a robotic arm and, combined with an intuitive software interface the AVS, enables an easy integration of fabric inspection inside a production system.

Apodius inspection head

Apodius´ inspection head

PROFACTOR FSCAN

Another product worth mentioning and highly related to quality control of composite parts is the FScan, designed by the Austrian applied research company Profactor. Instead of using the above mentioned diffuse lighting technique, their machine vision system exploits the reflection model of carbon fiber material and allows to produce high-contrast images. The sensor has a field of view of 60×60 mm² and its capable of scanning a surface with a speed of 1 m/s while detecting in real time all sorts of defects suchs as gaps, inclusions or missing rovings.

Profactor´s high constract carbon fiber images

Profactor´s high constrast carbon fiber images

EDIXIA

This French company with worldwide presence has a very strong background on automation of processes in several industries and is now expanding into the composite market. Their vast experience with different technologies allows them not only to look for defects in several kinds of fabrics, but also to inspect cracks, surface roughness and even fiber orientation of manufactured pieces, after the infusion process is completed. Contrary to 2D systems that infer the presence of defects from irregularities in the observed patterns, Edixia also makes use of 3D technologies which allows them to take direct measurements of the height of a wrinkle, depth irregularities or the 3D location of a cut edge.

Edixia features

Edixia´s features

SURAGUS

Finally, although they do not integrate cameras in their solution, a very original alternative is provided by Suragus. Taking advantage of the conductive properties of carbon fiber, Suragus takes an eddy current approach for this problem, allowing them to successfully leap over the challenging “dark-on-dark” scenario of vision systems. Furthermore, since eddy currents have some penetration in the material, the obtained measurements are not limited to the properties of the surface but also cover a few layers below it. This enables fast inspection for mulitple-layer fabrics (up to 5-7) that otherwise could not be inspected with standard vision systems. Their current  products are able to inspect a square surface of up to 600×600 mm² with a resolution up to 100-200 microns.

Suragus´ Eddy Current Inspection system

Suragus´ Eddy Current Inspection system