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aostling
10-17-2007, 06:01 AM
On my afternoon walk in the foothills near my house I came across this cactus skeleton. It is the woody framework of a cholla cactus, a common (and painful) plant of the Sonoran Desert. The skeleton is feather-light, and no good for anything structural.

http://i168.photobucket.com/albums/u183/aostling/chollaskeleton.jpg

But the look of it triggered a memory, of some open-cell aluminum foam I'd had on my desk, twenty years ago when I worked at Lockheed's cryogenic lab in Palo Alto. That product was used as the core of a storage dewar for solid hydrogen at about 14 kelvins. The open cell matrix provided plenty of room for the hydrogen ice, and its high thermal conductivity evened out temperature gradients throughout the dewar during the inevitable boil-off from heat leakage. I believe the product was made by Erg http://www.ergaerospace.com/duocel/aluminum.htm . Of course I wondered how it was made, but nobody I talked to knew; it was a proprietary process.

That application need not concern us here. But looking at the cactus skeleton, I thought it could probably be simulated in aluminum foam. A hollow metal pipe with porous walls might be the ultimate structural member for certain lightweight designs.

If anybody knows how the stuff is made, I'd like to know it.

Mcgyver
10-17-2007, 07:22 AM
a friend of mine (smart cookie with a PhD in physics from Cambridge) worked for a start up company that was trying to commercialize AL foam. last i heard, she'd left and they still weren't any closer to producing revenue...it was just too expensive a process. its a bubble blowing process :) , not sure how proprietary beyond that. she described the result as being the equivalent of an aluminum aero bar

jero100
10-17-2007, 07:40 AM
The link dosn't seem to work for me.

PTSideshow
10-17-2007, 08:56 AM
There is an outfit in Canada that has the process down to make sheets of the stuff. By the bubbling process. they showed some of it on one of those, How it's made or how'd they make that type programs a while ago. They to were searching for a way to make it cheaper and a wider market.I can't remember what the name of the program was.
By the way the cholla cactus wood is used in the making of parrot toy parts and toys as it gives them a delight to make tooth pick out of it. Is a pain to cut some times as some of it is rock hard other cuts like butter. As it is not native to Michigan it was what ever the guy collecting it would send me. So after a while I quite using it.:D

gld
10-17-2007, 09:42 AM
I saw aluminum foam being made a few nights ago on tv. Can't remember what chanel. (History or Discovery maybe Sience )Maybe someone else saw it.

Rusty Marlin
10-17-2007, 09:52 AM
Austrian company makes Al foam with controlled size and uniform cell size.
http://www.technologyreview.com/Biztech/17077/?a=f

Neat stuff, but I wonder how one attaches it to anything. It would be like running bolt through a sponge. Must be useing adhesive mounting or some form of TIG

A.K. Boomer
10-17-2007, 10:21 AM
Nature is amazing, like i posted before about Bee engineering,

We have those or a related species of cactus out here in colo.
I beg to differ with it not being good for anything structual --- I fixed a glider planes leading wing edge in the field with one cut halfways --- but I have to add that while the shapes and pattern of yours resembles something like "scrub oak" the stuff we have is more like lodgepole pine, very straight and all the webbing almost perfect, its extremely strong (for its weight) in many directions including torsionally, There is no disputing that round exoskeleton with proper web patterns (two opposing spirals interlocked) is as strong a structure as one can get pound for pound and for certain aplications... It does Extremely well torsionally --- just look at some steering drives on cars and trucks,,, If power steering is lost it will still transfer an ungodly amount of torsion before failure yet linear will allow for a total steering wheel collapse in case of a collision ---- :)

Evan
10-17-2007, 10:27 AM
Neat stuff, but I wonder how one attaches it to anything.
Adhesives. Adhesives have been used in aircraft to make laminated aluminum structures for at least 40 years. When I worked at Northwest Industries (CAE) in the 70s they had a huge vacuum chamber/oven for curing wing sections that had been glued together. A related product that has been around for many years is aluminum honeycomb. It is often laminated with a solid sheet on either side to make a honeycomb reenforced sandwich. It's glued.

gzig5
10-17-2007, 11:02 AM
I saw aluminum foam being made a few nights ago on tv. Can't remember what chanel. (History or Discovery maybe Sience )Maybe someone else saw it.


The show was on the History channel last week. I think it was Modern Marvels.

dp
10-17-2007, 12:34 PM
The piece of cactus can be 3D scanned and recreated with a 3D printer. I've wondered how useful the product of a 3D printer is for use in casting. 3D printers recreate solid forms that can exist only as CAD images or as output from computer generated solids. MRI scans would work, too. Artificial geodes, for example, and be formed and completely sealed up when finished, or you could print a ship in a bottle. Now if someone could come up with a way of printing directly to metal (crystal growth?) it would be a pretty fun tool to play with. Printed robots become possible at that point.

Swarf&Sparks
10-17-2007, 01:04 PM
Is this stuff light enough to encase in plaster then burn out with molten ali? Sorta "lost cactus" casting :D

I know that's a bit OT, but it's a fascinating form.