From designing better tandem wing airplanes and improved bomb detection equipment to making lighter weight electronics and helping paraplegics and amputees, people have turned to nature countless times to fix our own problems – with the help of 3D printing, of course.
Mimicking solutions already found in nature to develop sustainable human solutions is called biomimicry, and a problem researchers frequently try to solve with this practice – turning to hedgehogs, lobsters, and even conch shells and fish scales – is that of improved protective equipment.
Two years ago, a collaborative team of researchers from Purdue University and the University of California, Riverside published research covering their use of 3D printing to develop super-strong materials inspired by the rainbow-colored mantis shrimp, and have recently published two new papers on their work. Their work is funded by the US Air Force Office of Scientific Research, the Multi-University Research Initiative, and a CAREER award by the National Science Foundation.
Don’t be fooled by its size – this small creature can pack a big punch, thanks to its dactyl club. This fist-like appendage can unleash blows at speeds roughly the velocity of a .22 caliber bullet, which helps it defeat prey like mollusks and crabs.
The impact region of the impact-resistant club’s structure is made up of crystalline calcium phospate, which surrounds its chitin fibers in a unique herringbone structure that protects the club, as well as giving it more momentum on impact.
Back in 2016, the team was working to develop materials that would use both the dactyl club’s impact-resistant herringbone structure and its protective outer coating to possibly make stronger protective gear. At the time, the herringbone structure had never before been observed in nature…which isn’t the case anymore.
Pablo Zavattieri, a professor in Purdue’s Lyles School of Civil Engineering, said, “However, we are seeing this same sort of design strategy not just in the mantis shrimp, but also in many animals. Beetles use it in their shells, for example, and we also are seeing it in fish scales, lobsters and crabs.”
The team’s latest findings show that the unique herringbone design actually prevents failure by causing cracks to follow the twisting chitin fiber patterns. The club’s composite material stops cracks from twisting, as it actually grows tougher when this occurs. The material’s fibers, which are arranged in a helicoidal architecture similar to a spiral staircase, guide the twisting – that’s what makes the specific pattern so tough. When the cracks form, they follow the twisting pattern, instead of spreading out straight, which would result in failure.
Purdue doctoral student Nobphadon Suksangpanya, UC Riverside doctoral student Nicholas A. Yaraghi, UC Riverside professor of chemical and environmental engineering and materials science and engineering David Kisailus, and Zavattieri just published two papers in the Journal of the Mechanical Behavior of Biomedical Materials and the International Journal of Solids and Structures on their fascinating work.
“This mechanism has never been studied in detail before. What we are finding is that as a crack twists the driving force to grow the crack progressively decreases, promoting the formation of other similar mechanisms, which prevent the material from falling apart catastrophically,” Zavattieri explained. “I think we can finally explain why the material is so tough.
“The novelty of this work is that, on the theory side, we developed a new model, and on the experimental side we used established materials to create composites that validate this theory.”
Kisailus said, “This exciting new analytical, computational and experimental work, which follows up on our initial biocomposite characterization of the helicoid within the mantis shrimp’s club and biomimetic composite work, really provides a deeper insight to the mechanisms of toughening within this unique structure.”
Previous researchers found that the dactyl club’s helicoidal architecture was specifically designed to survive continuous high-velocity blows. Now, new images from UC Riverside’s electron microscope show that numerous cracks will form, which dissipates the energy the material absorbs on impact.
The Purdue-UC Riverside team created and tested 3D printed composites that were modeled after this behavior. They were even able to use cameras and digital image correlation techniques to capture this unique cracking behavior in order to study the material’s deformation.
Zavattieri said, “We are establishing new mechanisms that were not available to us before for composites. Traditionally, when we produce composites we put fibers together in ways that are not optimal, and nature is teaching us how we should do it.”
Purdue’s John L. Bray Distinguished Professor of Engineering, Byron Pipes, even helped create some glass fiber-reinforced composites that incorporated the behavior. This research can help in developing stronger, lighter weight materials for a number of applications, such as sports, automotive, and aerospace.
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