The "spongy" bone found near joints is strong but light. Yong Mao of the University of Nottingham, UK and colleagues discovered that this fractal patterns that is self-similar on all length scales can be used to help in building highly efficient load-bearing structures.
(An example of the generation-2 structure that the researchers built in the lab, which could be used as a scaffold. Due to manufacturing limitations, the scaffolding here is made of solid rather than hollow beams. (Courtesy: Yong Mao, D Rayneau-Kirkhope et al.)
Engineers reduce the mass by using a hierarchical design, where the same sparse patterns appear at different length scales. One example is the Eiffel Tower which is a big metal rod made up of smaller metal rods.
To demonstrate the weight savings of higher generation structures, the team started with constructing a simple hollow frame on a 3D printer using polymeric resin. They then varied the diameter and thickness to obtain the strongest tube with the least amount of material. The process was repeated several times. They calculated the relationship between the volume of material making up the tube and the maximum load that the tube could support. It showed that through changing the hierarchical order of the structure, the scaling of material required for stability against loading can be manipulated.
The team found, for example, that a crane boom made from generation-1 structures would be 100 times lighter than one made from solid steel, and a steel generation-3 structure would be 10,000 times lighter than a solid beam.
A drawback from 3D printing is that imperfections could cause serious problems. "Even a small imperfection at a local scale could have a large impact as there is no extra material that could take the added stress and maybe that is why this kind of fabrication has not been practical to date," explains Mao to PhysicsWorld. Mao says that the team is also studying its models to better allow for such errors. But he is convinced that commercial techniques will improve over the coming year, providing the necessary precision tools. Mao also feels that the recently commercialized technique of 3D printing could really benefit the fabrication of these structures. "We could just upload our deferent designs to a program and people could download and print off the structures at home," he says.
Posted in 3D Printing Applications
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