Microstructured materials as strong as steel yet less dense than water
Researchers in Germany have developed a lightweight, high-strength material inspired by the framework structure of bones and wood and the shell structure of bees' honeycombs. Created using 3D laser polymer printing combined with a ceramic coating, the material is less dense than water but, relative to its size, boasts strength comparable to high-performance steel or aluminum.
Although inspired by nature, the polymer microarchitecture produced by a team at the Karlsruhe Institute of Technology (KIT) outperforms its natural counterparts in terms of strength/density ratio. The underlying structure was produced using a process of 3D laser lithography or polymer printing and hardening.
A number of structures were tested, including triangular, hexagonal and honeycomb. These were then coated by gas deposition to provide extra strength, with coatings of a ceramic material and alumina both tested. The polymer structure measured roughly 50 µm long, wide, and high, while various coating thicknesses were tested ranging from 10 nm to 200 nm.
It was found that a honeycomb polymer structure with an alumina coating of 50 nm yielded the highest stability to density ratio. This microarchitecture outperformed the triangular and hexagonal counterparts produced and tested, while no additional strength was achieved after a coating thickness of 50 nm of alumina was exceeded. This optimized honeycomb structure failed at a pressure of 28 kg/mm2, yet only had a density of 810 kg/m3, which the team says exceeds the stability/density ratio of bones, massive steel or aluminum.
"The novel lightweight construction materials resemble the framework structure of a half-timbered house with horizontal, vertical, and diagonal struts,” said study co-author Jens Bauer. "Our beams, however, are only 10 µm in size.”
The team says microstructured materials are often used for insulation or as shock absorbers, and that such open-pore materials can be used as filters in the chemical industry.
The team's results have been published in the journal Proceedings of the National Academy of Sciences.