Reversibly Assembled Cellular Composite – Coming to a bridge near you #Sappers

Well, perhaps not soon but it is coming.

Lighter, stronger, cheaper and faster are the drivers behind military bridging, since an army of men needed to cross a gap many hundreds of years ago until the sophisticated military bridging systems in service today these factors have been both limiting and influencers of design.

From wood to iron and steel to sophisticated aluminium alloys materials have always influenced the length of gap that can be crossed with the required durability and load carrying capacity.

Military bridging equipment manufacturers have looked at composites but none have entered service in numbers because they don’t offer a leap in capabilities unlike for example, metal alloys, but a new discovery by MiT might just have the possibility to be the next big thing in materials for use in military bridging, amongst many other things of course.

The researchers at MiT’s Center for Bits and Atoms have published a paper that describes a revolutionary new material

Ensuring the light-weight and high-strength properties of carbon-fiber composite materials is costly. Cheung and Gershenfeld (p. 1219, published online 15 August; see the Perspective by Schaedler et al.) have mass-produced cross-sectional parts that can be assembled into strong, ultralight lattices. Carbon-fiber composites are sliced into cross-shaped pieces that can be independently tested and reliably assembled into rigid and reversible cuboctahedral lattices.

Read the paper at the link below

The work was of course sponsored by DARPA

Another article at MiT describes the advantages

A new lightweight structure that snaps together in tiny blocks like the bricks of a has been developed by researchers at MIT. Researchers are saying the new material may revolutionize the assembly of large structures such as aircraft, spacecraft, and dikes and levees. Neil Gershenfeld, director of MIT’s Center for Bits and Atoms, compares the structure, made from tiny, identical, interlocking parts, to chainmail.

The parts, based on a novel geometry that study co-author Kenneth Cheung developed with Gershenfeld, form a structure that is 10 times stiffer for a given weight than existing ultralight materials. But this new structure can also be taken apart and reassembled easily, in order to repair damage, or to recycle the parts into a different configuration, something that cannot be done readily with current composite materials.

Read more here

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The research investigates novel fabrication methods, small building blocks being assembled to make larger structures instead of the large monolithic composite structures in use today.

It is the construction geometry that is the main subject of the research and one that yields the most striking test results, 10 times the stiffness of other lightweight composite materials.

Reversibly Assembled Cellular Composite under load testing
Reversibly Assembled Cellular Composite under load testing
Reversibly Assembled Cellular Composite
Reversibly Assembled Cellular Composite

One of the most interesting features of this new method is the resulting structure fails progressively under load rather than catastrophically like conventional composites. They can also be easily repaired, again, unlike existing composites. 3D printing is used to fabricate the structures which is the final cherry on the cake, no more huge jigs for composite panels and structures, instead, a very sophisticated lego.

Gizmag has a good write up here

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September 23, 2013 9:21 am

Fascinating. It’s interesting particularly to me because my final year Mech Eng project involved spaceframes, which I was surprised to find were a lot easier to work out the stresses for than unitary material. This is effectively saying everything becomes a spaceframe :-)

Deja Vu
Deja Vu
September 24, 2013 12:06 am

The MiT paper has quite low values for yield stress and whilst it is stiffer than other composites, the Young’s Modulus (E) appears very low for a bridge material. I would have thought outer space or a use where the applied load was negligible but dimensional stability was required. Carrying a MBT or CLP would be a big ask.

As a MInstRE and a MIStructE I would like nothing better than to play Fantasy Bridging, but I suspect there can be few prospects of any serious bridge equipment procurement in the foreseeable future. However, maybe some of those surplus Challenger hulls could be used with ramps instead of turrets like the Churchill Ark to provide additional gap crossing and obstacle climbing capability. Of course, as this is Fantasy Bridging, we could give the Challenger Ark some offensive capability beyond swatting the enemy with the ramp. Are there any vertical launch ATk missile that could travel through holes in the folded ramps.

Another fantasy bridge of mine would be some sort of bulk raw material that could be extruded or shaped to form the bridge girders on site for whatever length required. Aluminium gutters for industrial sheds are formed on site from coiled aluminium strip. So possibly a tube could be cold formed from steel or aluminium strip to form an infantry bridge or ladder of considerable length.

Chris Werb
Chris Werb
September 24, 2013 3:47 pm

How about a floating bridge made out of that amazing expanding foam that we use to draught proof old cottages up here? Quick, but probably not very environmentally friendly though. :)

Deja Vu
Deja Vu
September 27, 2013 9:14 am

Werb Plastic tubes on a roll filled with an expanding foam and sealed at the ends. Yes good idea. Would need to be closed cell foam.