Scientists at Tokyo University of Science (TUS) have developed a new optimisation approach that will aid in the design of lighter carbon-fibre-composite materials.
Carbon fibres are stronger, stiffer and lighter than steel and have consequently largely replaced steel in high-performance products such as aircraft, race cars and sporting equipment.
They are typically combined with other materials to form a composite, such as carbon fibre reinforced plastic (CFRP), which is renowned for its tensile strength, rigidity and high strength-to-weight ratio.Research aimed at improving the strength of CFRPs has mostly focused on a technique known as ‘fibre-steered design’, which optimises the orientation of the carbon fibres.
However, as Ryosuke Matsuzaki, a member of the research team, points out, this approach has drawbacks. ‘Fibre-steered design only optimises orientation and keeps the thickness of the fibres fixed, preventing full utilisation of the mechanical properties of CFRP. A weight-reduction approach, which allows optimisation of fibre thickness as well, has rarely been considered.’
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In a new study published in the journal Composite Structures, Matsuzaki and his colleagues at TUS, Yuto Mori and Naoya Kumekawa, proposed a new design method that simultaneously optimises both the fibre orientation and thickness depending on the location in the composite structure. The new technique allowed them to reduce the weight of the CFRP compared to that of a constant-thickness-linear-lamination model without compromising its strength.
The method consists of three sets of processes: preparatory, iterative and modification.The preparatory process involves an initial analysis using the finite element method to determine the number of layers, enabling a qualitative weight evaluation by a linear lamination model and a fibre-steered design with a thickness variation model.In the iterative process, the fibre orientation is determined using the principal stress direction and the thickness iteratively calculated using maximum stress theory.Finally, in the modification process, modifications are made to account for manufacturability by first creating a reference ‘base fibre bundle’ in a region that requires strength improvement and then determining the final orientation and thickness by arranging the fibre bundles such that they spread on both sides of the reference bundle.
The method led to a weight reduction of more than five per cent while also enabling higher load-transfer efficiency than that achieved with fibre orientation alone.
‘Our design method goes beyond the conventional wisdom of composite design, making for lighter aircraft and automobiles, which can contribute to energy conservation and reduction of carbon dioxide emissions,’ said Matsuzaki.