Natural fiber fabric saves weight in composite structures

A technology based on the concept of leaf-veins can be applied to strengthen synthetic fiber-reinforced composites and reduce overall weight. Based on flax fibers, powerRib fabrics can be used to reinforce thin-walled structures, resulting in a "pseudo mini sandwich," since no core material is involved. The fabrics can readily be processed with standard vacuum molding techniques.

Supplied by Bcomp (Fribourg, Switzerland), for a given performance, the technology reportedly enables 50% weight reduction while simultaneously cutting costs due to the need for less costly synthetic fiber reinforcement, which is of particular interest for the automotive  sector. The reinforcement material can be combined with all types of structural materials, such as carbon-fiber composites, glass-fiber composites and non-woven  natural-fiber composites.

 

Flax fiber fabric is employed to back-reinforce a composite structure.

For a given flexural stiffness, the weight of a reference carbon fiber-reinforced composite plate can be reduced by 27% with a cost lowered by 40 % when the carbon fiber is partially replaced by powerRibs. When compared to a 100% glass fiber-reinforced composite plate, cost can still be reduced by approximately 30% while slashing over 40% of the weight for the same performance.

This unique combination of high flexural stiffness and damping is reportedly ideal for a wide range of applications in the sports and leisure industry (including kayak hulls and bicycle frames) but especially in the automotive industry with the current strong drive for light-weighting and high-performance bio-sourced materials according to Bcomp: powerRibs can be used for automotive interior semi-structural shell elements (door panels, seat backs, front panels) as well as exterior body parts (roofs, fenders, etc.).

In addition to its extensive collaboration with the European Space Agency (ESA), Bcomp has formed collaborations with several players in the automotive industry, including leading toolmaker Georg Kaufmann Formenbau AG (Remetschwil, Switzerland) and several Tier 1 suppliers and OEMs.

With its high stiffness, low density and limited length, flax fiber is ideal for use in powerRibs technology. Maximum fiber length of 60 cm - looking like a disadvantage at first sight - is a key factor for this technology, since the fibers need to be spun into a continuous yarn for further textile processing. Thanks to the resulting twist, the yarn has a good compression strength perpendicular to its direction, keeping its shape during composite processing, and leading to a 3D surface characteristic to the powerRibs technology. However, mechanical properties in yarn direction rapidly decrease when the twist is too high.

With this in mind, Bcomp engineers have been optimizing the yarn twist angle over several years. The findings have been further developed in the framework of several R&D projects, and have been applied to various customer projects within the mobility-, space- and sports & leisure industries. One example is the ESA, which is very interested in the unique combination of high stiffness and damping properties offered by this technology.

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