Tokyo researchers hit on new design method to reduce weight in reinforced plastics

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In a development that could lead to lighter aircrafts and automobiles, researchers from Tokyo University of Science have adopted a new design method that optimizes both fibre thickness and orientation, achieving weight reduction in reinforced plastic.

The backstory is that carbon fibres are popular in aerospace, racecars, and sports equipment applications due to their superior strength and lightness. But while a lot of effort goes into improving the strength of carbon fibre composites, such as fibre-reinforced plastic, only fibre orientation optimization is considered. But the Tokyo researchers have adopted a new design method that optimizes both fibre thickness and orientation.

Carbon fibres are usually combined with other materials to form a composite. One such composite material is the carbon fibre reinforced plastic (CFRP), which is well-known for its tensile strength, rigidity, and high strength-to-weight ratio. Owing to its high demand, researchers have carried out several studies to improve the strength of CFRPs, and most of these have focused on a particular technique called “fibre-steered design,” which optimizes fibre orientation to enhance strength.

Problem is, the fibre-steered design approach has its drawbacks. “Fibre-steered design only optimizes orientation and keeps the thickness of the fibres fixed, preventing full utilization of the mechanical properties of CFRP,” said research team member Dr. Ryosuke Matsuzaki. “A weight reduction approach, which allows optimization of fibre thickness as well, has been rarely considered.”

Against this backdrop, Dr. Matsuzaki and his colleagues Yuto Mori and Naoya Kumekawa proposed a new design method for optimizing the fibre orientation and thickness simultaneously depending on the location in the composite structure, which allowed them to reduce the weight of the CFRP compared to that of a constant thickness linear lamination model without compromising its strength.

Their method consisted of three steps: the preparatory, iterative, and modification processes. In the preparatory process, an initial analysis was performed using the finite element method (FEM) 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. The iterative process was used to determine the fibre orientation by the principal stress direction and iteratively calculate the thickness using “maximum stress theory”. Finally, the modification process was used to make modifications accounting for manufacturability by first creating a reference “base fibre bundle” in a region requiring 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 of simultaneous optimization led to a weight reduction greater than five per cent while enabling higher load transfer efficiency than that achieved with fibre orientation alone.

The researchers say they are excited by these results and look forward to the future implementation of their method for further weight reduction of conventional CFRP parts. “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 CO₂ emissions,” Dr. Matsuzaki said.

Source: Tokyo University of Science