AsianScientist (Jun. 9, 2015) – The secret to the surprising strength of mantis shrimp clubs is their nanostructure and size—just below a critical threshold where cracks would form. The study documenting these findings has been published in Nature Materials.
Mantis shrimps, with their googly eyes that have inspired DVD readers and cancer detectors, are famed for their punching ability, with some even able to destroy aquarium glass.
Although previous research has described the structural design and mechanical properties of mantis shrimp dactyl clubs, quantitative details such as stress-strain curves were not available.
In the present study, a team led by Assistant Professor Ali Miserez from the Nanyang Technological University used a combination of nanomechanical and spectroscopic methods to investigate the extraordinary properties of the mantis shrimp clubs.
“Ceramics—like the mantis shrimp club—are hard but usually brittle, so the club serves as a fascinating model structure to design impact-resistant bioceramics, which could be used in implant applications,” Miserez explained to Asian Scientist Magazine.
“What we sought to address here was to mechanistically elucidate how the club structure is able to withstand such high impact without cracking. We wanted to understand the mechanisms allowing the club to absorb impact energy.”
Using nano-mechanical testing, the team developed methods to continuously monitor the mechanical stresses and deformation on the club surface in response to contact forces with small diamond tips. At the same time, they used high-resolution electron microscopy studies to observe the impacted surfaces after testing.
“We also used confocal Raman microscopy, using a method that allows us to observe residual stresses on the surface of the club after testing. Finally, we also used dynamic finite element analysis (DFEA) simulations to simulate the impact of the club on a hard target,” Miserez said.
Previous work by the Miserez group showed that the outer surface of the club is made of highly oriented fluorapatite crystals (similar to shark teeth) and of a tiny amount of chitin and protein. In the present study, they found that although the club surface is as hard as ceramics, it can actually deform during impact in a fashion similar to metallic materials.
Metals are not as hard as ceramics but they can absorb more impact energy because they can be irreversibly mechanical deformed, a phenomenon called ‘plasticity’ which allows them to absorb mechanical energy instead of cracking. The researchers showed that the club was ‘quasi-plastic,’ a property which was key to its uniquely high impact resistance.
“We have also found that at the micro- and nano-scale, the mechanism responsible for absorbing the energy is the sliding and rotation of the fluorapatite crystals. As these nano-crystals move internally during an impact, they absorb the mechanical energy. This is where the small amount of chitin/protein is useful because they facilitates the movement of the crystals,” Miserez explained.
“In other words, the chitin or proteins act as solid ‘lubricants’ for the internal movement of the crystals during impact.”
Having thoroughly understood the structural principles for the extraordinary impact tolerance of mantis shrimp clubs, Mizerez and colleagues hope to mimic the structures synthetically.
“There are a wide range applications where such material could be useful, from bullet-proof vessels to wear-resistant implants with longer durability (current hip implants usually last 15 years) to ultra-scratch resistant cases for luxury watches!” Miserez enthused.
The article can be found at: Amini et al. (2015) The Role of Quasi-Plasticity in the Extreme Contact Damage Tolerance of the Stomatopod Dactyl Club.
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Copyright: Asian Scientist Magazine; Photo: Ali Miserez/NTU.
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