A new generation of composite materials inspired by the structure of wood
Photo ©Sven Scheuermeier on Unsplash
Davide Ruffoni and Laura Zorzetto, researchers at the Aerospace and Mechanical engineering Research Unit (A&M - Faculty of Applied Sciences), drew inspiration from nature, and specifically from the design of the wood cell wall, in order to develop a new synthetic structure that could achieve superior collapse resistance. These results, applicable in many fields ranging from automotive to biomechanics, have just been published in the high impact journal Advanced Functional Materials (1).
iomimicry, the engineering process inspired by the properties, shapes, functions or materials of living organisms, is a constantly evolving discipline that draws its inspiration from the incredible abilities of nature. Engineers from the University of Liege, fascinated by the remarkable properties of the helix-reinforced structure of the wood material, have succeeded in modelling and manufacturing a new generation of composites showing enhanced strength and energy absorption. " Helices are versatile building elements used by nature to improve the mechanical performance and finely tune the local behavior of load-bearing materials," explains Davide Ruffoni, assistant professor at A&M research unit (Faculty of Applied Sciences). In biological materials (materials made by nature such as wood and bone), helical fibers are arranged in multiple layers with different fiber orientations resulting into a complex heterogeneous architecture, not matched in synthetic materials, that gives biological structures superior properties».
To test their concept, the researchers used 3D polyjet printing and computer simulations to manufacture and characterize multilayer wood-inspired helical composites. They were able to show how the mechanical functionalities of synthetic structures could be programmed by varying the orientation of the fibers and the compliance of the matrix. They were also able to demonstrate that the collapse resistance could be enhanced exploiting the design strategies observed in the wood cell wall.
This is the case of the multilayer tubular structure of the wood cell wall, where each layer has a soft elastic matrix reinforced by rigid helical fibers of cellulose having a diameter smaller than one micrometer. "In our research," says Laura Zorzetto, a doctoral student in the lab and first author of the article, "we combined 3D polyjet printing - a process for obtaining objects made of materials with different mechanical properties - with computer simulations to prototype cylindrical structures reinforced with helical fibers." Researchers first focused on composites with a main layer containing helical fibers, bordered by inner and outer layers composed of thinner fibrils. They showed how the mechanical functionalities of the synthetic structures could be fully programmed by varying the orientation of the fibers as well as the flexibility of the matrix. The researchers were able to demonstrate that the collapse resistance could be greatly improved by surrounding the main helical layer with a minimal amount of thin fibrils oriented perpendicular to the applied load, as observed in the wood structure.
"With this study, we were able to analyze a universal construction principle common to many biological and engineering materials," explains Davide Ruffoni. “We have succeeded in demonstrating that the biomechanical design principles of nature can be replicated in synthetic systems, at greater length scales and with completely different building blocks." These promising results should pave the way for the development of new generation composites characterized by locally adjustable deformations and heterogeneous energy absorption. This could offer new opportunities for the development of multifunctional materials for a variety of applications, ranging from aerospace to automotive and biomechanics.
(1) ZORZETTO L. & RUFFONI D., Wood-Inspired 3D- Printed Helical Composites with Tunable and Enhanced Mechanical Performance, in Advanced Functional Materials, 2018.