Lightweight construction materials of highest stability thanks to their microarchitecture

Mar 21, 2014
The framework construction made of a ceramic-polymer composite is highly stable, although the individual elements have a thickness of a few hundred nanometers only. Credit: J. Bauer/KIT

KIT researchers have developed microstructured lightweight construction materials of highest stability. Although their density is below that of water, their stability relative to their weight exceeds that of massive materials, such as high-performance steel or aluminum. The lightweight construction materials are inspired by the framework structure of bones and the shell structure of the bees' honeycombs. The results are now presented in the journal PNAS.

"The novel lightweight resemble the framework structure of a half-timbered house with horizontal, vertical, and diagonal struts," says Jens Bauer, Karlsruhe Institute of Technology (KIT). "Our beams, however, are only 10 µm in size." In total, the lightweight construction elements are about 50 µm long, wide, and high.

"Nature also uses open-pore, non-massive structures for carrying loads," Oliver Kraft, KIT, explains. Examples are wood and bones. At the same , however, the novel material produced in the laboratory can carry a much higher load. A very high stability was reached by a shell structure similar to the structure of honeycombs. It failed at a pressure of 28 kg/mm2 only and had a density of 810 kg/m3. This exceeds the stability / density ratio of bones, massive steel, or aluminum. The shell structure produced resembles a honeycomb with slightly curved walls to prevent buckling.

To produce the materials, 3D laser lithography was applied. Laser beams harden the desired microstructure in a photoresist. Then, this structure is coated with a ceramic material by gas deposition. The structures produced were subjected to compression via a die to test their stability.

Microstructured materials are often used for insulation or as shock absorbers. Open-pore materials may be applied as filters in chemical industry.

Explore further: Could future spaceships be built with artificial 'bone'?

More information: High-strength cellular ceramic composites with 3D microarchitecture, Jens Bauer, Stefan Hengsbach, Iwiza Tesari, Ruth Schwaiger, and Oliver Kraft, PNAS Early Edition, DOI: 10.1073/pnas.1315147111

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Eikka
5 / 5 (1) Mar 21, 2014
It failed at a pressure of 28 kg/mm2 only and had a density of 810 kg/m3.


kg/mm^2 is a nonsensical unit. It's not analogue to pounds per square inch (psi) if that's what the writers were after. If they wanted to use the kilogram-force they should have used kgf.

The article abstract states their highest compressive strength was 280 MPa which corresponds to 28.5 kgf/mm^2 but that conversion is unnecessary because MPa is already a unit of pressure: Newtons per square millimeter.

This exceeds the stability / density ratio of bones, massive steel, or aluminum.


Although aluminium can withstand 530 MPa so it's still twice as strong for the same size.
Sigh
not rated yet Mar 21, 2014
This exceeds the stability / density ratio of bones, massive steel, or aluminum.

Although aluminium can withstand 530 MPa so it's still twice as strong for the same size.

That's why it says "stability density ratio". It's about how much strength you get per weight, not per cross section area.
Eikka
not rated yet Mar 21, 2014
It's about how much strength you get per weight, not per cross section area.


Well, in this case they did not actually reference the strength per weight ratio but the absolute strength.

In relative terms it's about 40% stronger than aluminium per mass, for compressive stress.

Tension wasn't mentioned. My guess for the reason is that the structure is highly unstable or very springy for tension, which would make it poor for bending and twisting. That's usually what happens with these sorts of optimimized structures, like bone or metal foams. You can squeeze them but if you bend or stretch them they break.