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Microstructured materials as strong as steel yet less dense than water

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April 14, 2014

The framework construction made of a ceramic-polymer composite created at KIT (Picture: J....

The framework construction made of a ceramic-polymer composite created at KIT (Picture: J. Bauer/KIT)

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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.

Source: Karlsruhe Institute of Technology

6 Comments

The article title is a misnomer...these structured plastics have an equal or greater *strength-to-weight* ratio than some steels and many aluminum alloys, not an equal or greater *strength*. That is a very important distinction, one that separates a revolutionary miracle of engineering from an interesting increment forward in nano-structured materials development.

Justin Chamberlin
15th April, 2014 @ 02:35 pm PDT

Just shows that 1B bees can't be wrong!

The Skud
15th April, 2014 @ 07:58 pm PDT

"A honeycomb polymer structure . . . outperformed the triangular and hexagonal counterparts. . ."

Poor choice of terminology, as an actual honeycomb structure IS hexagonal. What is shown in the photos is not honeycomb structure, but something along the lines of a modified FCC lattice---an orthogonal mesh stiffened with diagonal bracing, like a truss. So, "truss structure" perhaps?

And have they tried actual unmodified FCC, BCC or HCP? These could possibly offer still better performance. My bet is on FCC, unmodified.

Ref: http://en.wikipedia.org/wiki/Face_centered_cubic

Freederick
16th April, 2014 @ 01:26 am PDT

@Justin:

Arguably, it is more often important to have a minimum weight structural component, than it is to have a structural component of minimum cross-section. Thus "strength to weight" would seem to be a more critical parameter than "strength".

To put it another way, you have those technical structures where lightweight strength matters a lot (aircraft and spacecraft frames, mobile powerplants, tall structures, suspension cabling) and those where weight is of no concern (stationary powerplants, low structures, etc.). For the former, strength-to-weight is the critical parameter; for the latter, price-per-strength, and it is here that steel (and sometimes concrete) wins hands down.

The real reason metals are still used in aircraft frames etc. is not superior strength, but superior fatigue performance, graceful (plastic rather than brittle) failure, and thermal range.

Freederick
16th April, 2014 @ 01:40 am PDT

Well, I can see this being useful for body panels on airplanes.

The current technique is like five sheets of cardboard, made from aluminum.

This would be lighter and provide more... hey !

What if you built a Zeppelin using this print-to-order technique?

You could have a semi-rigid outer hull, built of honeycomb plastic, with a gasproof inner liner.

There was an Edgar Rice Burroughs novel about Zeppelins, when a new alloy was discovered as light as cork and as strong as steel.

It actually worked with vacuum tanks, because vacuum is lighter than Helium.

William Carr
21st April, 2014 @ 04:59 pm PDT

William, think of atmospheric pressure: 14.5 lbs per sq. inch. Therefore the pressure on 1 sq. foot of Zeppelin hull is 12 x 14.5 lbs. You calculate!

windykites1
18th June, 2014 @ 04:12 am PDT
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