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3D-printed composite is lighter than wood and stiffer than concrete


June 27, 2014

A new 3D-printed composite surpasses the lightness and stiffness of balsa wood (Photo: Har...

A new 3D-printed composite surpasses the lightness and stiffness of balsa wood (Photo: Harvard University)

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Reseachers at Harvard University have developed a way to 3D-print a cellular composite with record lightness and stiffness using an epoxy resin. This marks the first time that epoxy is used for 3D-printing, and the advance could lead to the development of new lightweight architectures for more efficient wind turbines, faster cars, and lighter airplanes.

If you take all of the materials known to man, whether natural or man-made, and observe their relative properties, you'll soon find a very clear pattern: density and strength always seem to go hand-in-hand. The very light foams are generally extremely weak, and on the other end of the spectrum, the heavy materials like steels and other metals are among the strongest we know.

There are, however, a few outliers. One such example is balsa wood, which has a density as low as 40 kg per cubic meter (2.5 lb per cubic foot) but is still very strong, thanks to a microscopic structure that features a highly effective mix of cellulose and lignin fibers. Balsa wood is therefore used in applications where light but strong structures are critical, from the blades in wind turbines to the chassis of model airplanes and helicopters. There is however a serious supply problem, in that over 95 percent of the world reserves of balsa wood comes from a single country – Ecuador.

Scientists at Harvard have now come up with a way to manufacture a cellular composite that's even better than balsa wood, doing away with the occasional structural defects in the wood that can make it less reliable as a building material.

The researchers took inspiration from the microscopic structure of balsa, which is mostly hollow and in which only the cell walls are carrying the load. Their built their new composite using an epoxy-based resin containing nanoclay platelets to increase viscosity, as well as two types of fillers – silicon carbide "whiskers" and discrete carbon fibers.

Square, hexagonal and triangular honeycomb structures composed of the resin (Image: Harvar...
Square, hexagonal and triangular honeycomb structures composed of the resin (Image: Harvard University)

One very interesting feature is the fact that the researchers can control the exact stiffness of the material by changing the orientation of the fillers as needed. Orienting the silicon carbide whiskers perpendicularly to the direction which will face the most load makes the material stronger – for the same reason that it's easier to chop wood longitudinally and not perpendicularly to its fibers.

This tunable property means that designers can digitally integrate into the composition the stiffness and toughness of an object from the very beginning, and have it comply with the desired specifications.

According to principal investigator Prof. Jennifer A. Lewis, their research is a significant step because it paves the way for 3D-printing using materials, such as epoxies, which can be used for structural applications, as opposed to the thermoplastics that your standard 3D printer uses. Using this resin, Lewis and colleagues obtained composites that are as stiff as wood, up to 20 times stiffer than commercial 3D-printed polymers, and twice as strong as the strongest printed polymer composites up to that point.

Applications for this technology could include more efficient wind turbines and perhaps innovative architecture for building lighter but safe cars that increase mileage.

A paper describing the advance appears in the journal Advanced Materials.

Below, you can watch a short clip of the composite being printed.

Source: Harvard University

About the Author
Dario Borghino Dario studied software engineering at the Polytechnic University of Turin. When he isn't writing for Gizmag he is usually traveling the world on a whim, working on an AI-guided automated trading system, or chasing his dream to become the next European thumbwrestling champion.   All articles by Dario Borghino

I must have this now.

Mark A
27th June, 2014 @ 10:57 pm PDT

Interesting. How does the material stand up to jet fuel?

27th June, 2014 @ 11:32 pm PDT

3D printing just keeps getting smarter, amazing.

28th June, 2014 @ 12:09 pm PDT

Interesting that the illustrations shown depict only 2D patterns to provide structural strength - these boys need to start thinking in 3 dimensions! ☺

30th June, 2014 @ 05:53 am PDT

Looks good, but the demo doesn't seem to show the inclusion of carbon fibers...just epoxy.

For building materials, it would be interesting to research such materials that would retain strength, shape, and flexibility. Thus standing up to earthquakes cheaply.

I can see some applications for materials that have strength, but fold along axis and still retain strength along those axis.

How about exo-skeletons for broken limbs, armor, and robot bodies?

How about snake type bodies that have strength in "scales", but are flexible? And especially in 3 dimensions?

How about drill shafts that allow steered drilling?

How about pipes that follow any curve?

How about hydrogen storage tanks that are "solid", yet contain the gas?

How about combining the film solar PV with this material to make a stiff panel?

How about combining basalt fibers with it instead of carbon fibers. cheap material and 7 times the tensile strength of steel? Since I saw basalt fibers tested once 35 years ago, I've always wondered why they weren't used for bridge cables.

30th June, 2014 @ 07:09 am PDT

Stiffness relates only to rigidity. It does not take into account flexural strength not elasticity which are major concerns in any kind of construction. BTW concrete is good only under compression. No good for tensile loads without steel bar reinforcements.

30th June, 2014 @ 08:46 pm PDT

@notarichman the dark streaks in the epoxy are concentrations of carbon fibers it comes premixed.

Joseph Mertens
2nd July, 2014 @ 11:48 pm PDT

Technically speaking, I would say this is not 3D printing. it is really extrusion in layers, and is relatively slow in producing structures. Can it not be made using normal 3D printing by scanning, which is faster than having a nozzle tracing out the design, very much like a snail leaving its trail (a clever analogy, if I say so myself!)

I note the different structures: square; honeycomb, etc. Surely, one of these must be the best for strength? I reckon honeycomb must be the winner, so why not establish that and get on with it?

5th July, 2014 @ 04:59 am PDT

This is the future. The nest step would be to incorporate continuous filaments instead of chopped fibers into the composite, perhaps using prepregs.

7th January, 2015 @ 12:29 pm PST
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