BUILT LIKE A LOBSTER SHELL

RESEARCHERS AT THE Royal Melbourne Institute of Technology, Melbourne, Australia, have developed 3D printed concrete (3DPC) that mimics lobster shell in its strength, resiliency, and durability. Their findings will likely lead to increased use of printed concrete, a technology already employed around the world for reducing the construction costs of buildings and other structures. Here are tidbits gleaned from ScienceDaily, January 19, 2021, and my usual Internet sleuthing.

By the way, this isn’t the first time that following the patterns of Mother Nature (biomimicry) has appeared here at SimanaitisSays. “Sometimes Science Sucks” described mechanical mimicry of the remora suckerfish. And even closer to today’s topic, “Shrimp Wallop Inspires Composite Design” gave details about mimicking the glass-shattering clubs of peacock mantis shrimp.

Printed Concrete. Traditional concrete uses a mold to form its mixture of cement, sand, aggregate, and water. By contrast, 3D printed concrete deposits the material layer-by-layer. ScienceDaily offers examples: “The emerging industry is already supporting architectural and engineering innovation, such as a 3D printed office building in Dubai, a nature-mimicking concrete bridge in Madrid, and The Netherlands’ sail-shaped ‘Europe Building.’ ”

Mimicking the Lobster Shell. The research is described in “Influences of Printing Pattern on Mechanical Performance of Three-Dimensional-Printed Fiber-Reinforced Concrete,” by Luong Pham, Guoxing Lu, and Phuong Tran, RMIT, in 3D Printing and Additive Manufacturing, December 30, 2020. 

Researchers described there is an “Hierarchical microstructure of the cuticle of the lobster (Homarus americanus).” The lobster claw is formed of clustered protein planes, stacked and rotated to form a ‘bouligand structure’ forming the exoskeleton material….” 

According to Wikipedia, a bouligand structure “enhances the mechanical properties of materials, especially its fracture resistance….” The mantis shrimp’s club is cited as an example of a bouligand structure.

ScienceDaily quotes researcher Tran: “As lobster shells are naturally strong and naturally curved, we know this could help us deliver stronger concrete shapes like arches and flowing or twisted structures.” 

Investigating 3DPCs. Tran and his colleagues describe: “Specifically, unidirectional (0°), cross-ply (0°/90°), quasi-isotropic (0°/ ± 45°/90°), and helicoidal patterns (with pitch angles of 10°, 20°, and 30°) are used to create unidirectional, bidirectional, and multidirectional layers in printed objects without and with 0.75% by volume of 6 mm-long steel fibers.”

The researchers subjected these 3DPC samples to tests of compressive and flexural strength, together with X-ray micro-CT analyses.

Stronger 3DPCs. With regard to compressive strength, the researchers found, “For the same material mix, by changing the printing patterns from the unidirectional to cross-ply, quasi-isotropic, and helicoidal patterns, it is observed an increase of up to 26.5% in the compressive strengths of samples without fibers…. When compared with samples without fibers, those with steel fibers have higher compressive strengths in any direction of any architectural pattern with a few exceptions.”

With regard to flexural strengths: “It can be concluded that for samples without fibers, the quasi-isotropic can be considered an optimal print pattern in both the horizontal and vertical directions. Of all helicoidal architectures, the 10°-angle helicoidal pattern is the most beneficial to the flexural strengths of samples without fibers over the unidirectional control…. The addition of steel fibers generally increases the flexural strengths in any patterns in comparison with counterparts without fibers.”

The researchers summarize, “There are definite enhancements on the mechanical properties of printed concrete resulting from the unconventional printing patterns, which have a promising potential for being applied in highly complex or self-supporting concrete architectures.”

They also note, “Further studies will be supported through a new large-scale mobile concrete 3D printer recently acquired by RMIT — making it the first research institution in the southern hemisphere to commission a machine of this kind.”

All inspired by the lobster’s claw. ds 

© Dennis Simanaitis, SimanaitisSays.com, 2021