Optimal route to lighter, stronger carbon fiber composites

Carbon forms the basis of all organic molecules, which, in turn, form the basis of all living things. Recently, however, carbon has also found use in disciplines such as aerospace and civil engineering, through the development of carbon fibers that are stronger, stiffer and lighter than steel. Consequently, carbon fibers have taken over steel in high-performance products like aircrafts, racing cars and sports equipment.

Carbon fibers are usually combined with other materials to form a composite. One such composite material is carbon fiber reinforced plastic (CFRP), which is well-known for its tensile strength, rigidity and high strength-to-weight ratio. Nevertheless, researchers are still working to improve the strength of CFRPs, and one popular approach is known as 'fiber-steered design', which aims to enhance strength by optimizing the orientation of the fibers.

However, the fiber-steered design approach is not without its drawbacks. "Fiber-steered design only optimizes orientation and keeps the thickness of the fibers fixed, preventing full utilization of the mechanical properties of CFRP," explains Ryosuke Matsuzaki from Tokyo University of Science (TUS) in Japan, who researches composite materials. "A weight reduction approach, which allows optimization of fiber thickness as well, has been rarely considered."

Against this backdrop, Matsuzaki and his colleagues have proposed a new design method for simultaneously optimizing the orientation and thickness of the fibers, depending on their location in the composite structure. This has allowed them to reduce the weight of CFRP, compared to a constant thickness linear lamination model, without compromising strength. They report their findings in a paper in Composite Structures.

Their method consists of three separate processes: preparatory, iterative and modification. In the preparatory process, an initial analysis is performed using the finite element method (FEM) to determine the number of layers. This allows the researchers to conduct a qualitative weight evaluation with a linear lamination model and a fiber-steered design with a thickness variation model.

The iterative process is used to determine the fiber orientation by the principal stress direction and iteratively calculate the thickness using 'maximum stress theory'. Finally, the modification process makes modifications by first creating a reference 'base fiber bundle' in a region requiring strength improvement. The next step in this process is to determine the final orientation and thickness by arranging the fiber bundles such that they spread on both sides of the reference bundle.

This method of simultaneous optimization led to a weight reduction greater than 5%, while allowing a higher load transfer efficiency than could be achieved with fiber orientation alone.

The researchers 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," says Matsuzaki.

This story is adapted from material from Tokyo University of Science, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.