Biocomposites
Biocomposites Thin-walled composite structures with improved stiffness- and damping properties normalized specific flexural stiffness [-] 1.2 - 1.1 - 1.0 - 0.9 - 0.8 - 0.7 - carbon carbon + powerRibs flax + powerRibs 0.002 0.004 0.006 0.008 0.010 0.012 0.014 loss factor, ξ [-] Figure 2. Plot of normalized specific flexural stiffness vs. loss factor. Fig. 1: Dry Bcomp powerRibs lying on a biax flax fabric (left) and example of a part after impregnation and consolidation with an epoxy resin (right) Natural fibre composites have gained significant attention over the last couple of years. However, these novel materials struggle to establish themselves at a large scale in the composites industry, despite their outstanding specific mechanical properties. This is mostly due to the fact that natural fibre preform suppliers have been very much focusing on mimicking their glass fibre preform counterparts, at significantly higher price-performance ratios often beyond the acceptance of the market. Since its founding in 2011, Bcomp (Fribourg, Switzerland) has been focusing on understanding the specificity of natural fibers and their composites, and developing corresponding technologies bringing striking benefits – in addition to the lower ecological footprint – to the end product. Bcomp’s strong R&D focus has further been strengthened through nationally- and EU funded collaborations with leading academic partners, such as the Swiss Federal Institute of Technology Lausanne (EPFL), The University of Applied Sciences and Arts Northwestern Switzerland FHNW, or the Katholic University of Leuven (Belgium). In only three years, Bcomp managed to implement their product solutions in various industries such as Sports and Leisure, Consumer Electronics and Mobility, achieving thereby a significant market share and boosting the company’s sales. Bcomp’s powerRibs technology (pat. pend.) consists of a natural fibre grid fabric resulting in ribs in the millimeter thickness range on the surface of composite parts, leading to a significant increase of the bending stiffness of thin fibre composite shell elements by adding minimal weight. During the two past years, Bcomp developed the ideal flax yarn and textile process for the powerRibs technology with its partners, taking maximum advantage of the flax’ high stiffness-toweight ratio and low density. Recently, the product has attracted a lot of attention in the Composites industry, and was awarded the Swiss Excellence Product Award 2013 and the Certificate of Material Excellence 2013 by renowned US material consultant Material ConneXion. In parallel, Bcomp is currently working on the qualification of the material with global leaders of the Automotive industry. An example of dry powerRibs fabric and its integration into a composite part is shown in Fig. 1. 16 bioplastics MAGAZINE [04/14] Vol. 9
Biocomposites By Christian Fischer managing director, co-founder Bcomp Ltd., Fribourg, Switzerland www.bcomp.ch Prior Bcomp studies and market applications have shown that the company’s natural composite solutions offer a great potential for the use in thin-walled composite structures requiring a high level of damping. This is due to the flax fibres’ unique combination of high stiffness-to-weight ratio, their significantly lower density when compared to carbon fibres, and their very high damping properties. In the framework of the Swiss Space Center’s Call for Ideas 2013, Bcomp has proposed to develop a new hybrid composite solution. By mixing carbon- and flax fibres in a specific way, and using Bcomp’s powerRibs technology, the aim consisted of developing a composite material with a so far unparalleled combination of specific flexural stiffnessand damping properties. The resulting thin-walled material would offer a novel alternative for structural shell elements in lightweight satellite structures, where high stiffness- and strength, low weight, and high damping properties are of high importance. Using two different strategies, namely (i) carbon-flaxcarbon micro-sandwich structures for enhanced stiffness and constrained layer damping in the flax layers, and (ii) Bcomp’s powerRibs technology, using flax fibre grids for the highly efficient reinforcement of composite shell elements, eight different layups were defined. Their specific flexural stiffness and damping performance were measured and compared with each other, showing a potential increase of both parameters using approach (i) by approx. 15 %, respectively. Approach (ii) yielded very significant damping improvements, with a specimen outperforming the reference carbon sample by 250 % at an equivalent specific stiffness. The results are summarized in Figure 2. While this study has clearly demonstrated the great potential of such material systems in space applications requiring high stiffness and damping at low weight, some phenomena still need to be understood, and there is a great potential to further optimize the presented concepts. Additional tests would be needed to understand whether the surface damping approach – the powerRibs being an extreme example of it – would generally yield better results with these carbon-flax hybrid composite structures than the constrained layer damping approach studied within this project, and the powerRibs can be further optimized to increase the flexural stiffness of the samples using this method. Furthermore, further studies would need to analyse influence of temperature, different stress- or strain levels, and further specifications in the use for given space applications, to name only few. bioplastics MAGAZINE [04/14] Vol. 9 17
