We introduce you to the devilish armored beetle ( Phloeodes diabolicus ), one of the toughest creatures that nature has given. It is like a small six-legged tank. It is so tough that it can survive being hit by a vehicle, so it is not a bad place to seek inspiration that will serve us human beings. Now, engineers at Purdue University in Indiana (USA) have managed to unravel the secrets of its design and incredible toughness, paving the way for a new generation of materials with similar characteristics that we could use in bulletproof vests, airplanes, vehicles in general and buildings.
How is it possible for this creature to absorb such a tremendous shock? Its exoskeleton withstands bird bites and attempts to be eaten by other predators, run over by a vehicle or stepped on by a brown bear. The species, which inhabits the desert regions of western North America, owes its power to unusual armor that is layered and assembled like a puzzle on its body, according to the study published in the journal Nature.
“Unlike other beetles like the Namibian beetle, which is more rounded, it is close to the ground and is flat on top,” says David Kisailus, a materials scientist at the University of California, Irvine.
The experts conducted several compression experiments (using compressive steel plates) on this beetle, finding that it could support around 39,000 times its own body weight (149 Newtons), compared to the approximately 68 Newtons that similar beetles could support. Extrapolating to humans, it would be as if a person were shouldering a stack of about 40 M1 Abrams battle tanks. Or what is the same: 3.5 million kilos. Inconceivable.
An engineering challenge
Analysis of microscope images, spectroscopy, CT scans, 3-D printed models and computer simulations of the scarab’s armor revealed the secrets of its strength. It is the tightly interlocking, shock-absorbing structures that connect pieces of the beetle’s exoskeleton that help it survive these enormous crushing forces; that is, the microstructures in the beetle’s armor, called elytra, make it nearly impossible to smash. They compose a protective shield of Herculean hardness. In flying beetles, these elytra protect the wings and facilitate flight. But this beetle doesn’t fly, so its microstructures help distribute applied force more evenly throughout the body.
“The suture acts like a puzzle. It connects several exoskeletal leaves, puzzle pieces, in the abdomen below the elytra ”, clarify the authors.
Does not break, only loses protective layers
When hit and, depending on the amount of force applied, the exoskeleton does not break, it only loses layers; fractures slowly. The exoskeleton blades snap together like puzzle pieces, preventing them from slipping out of place with great force.
The exoskeleton is composed of chitin, a fibrous material derived from glucose, and a protein matrix. When they compared the exoskeleton of the diabolical armored beetle with that of a similar beetle, they found that the battleship had significantly more protein, about 10% more by weight. But it is the suture line along which the beetle’s elytra coalesce that is vitally responsible for its final toughness.
“This work shows that we can go from using strong and brittle materials to materials that can be strong and hard by dissipating energy as they break,” concludes Pablo Zavattieri, co-author of the study. “That is what nature has allowed the armored devil beetle to do.”
“This study really ties the fields of biology, physics, mechanics, and materials science into engineering applications, which you don’t normally see in research,” says Kisailus.
Referencia: Toughening mechanisms of the elytra of the diabolical ironclad beetle, Nature (2020). DOI: 10.1038/s41586-020-2813-8 , www.nature.com/articles/s41586-020-2813-8
