Basically an expandable and contractable 'foam' using millions of tiny memory metal pieces that change from straight to helix configuration with applied heat. The 'foam' would need to be contained within a flexible container.-- xaviergisz, Feb 10 2007 US 2014/0277057 https://patents.goo.../US20140277057A1/enShape-memory polymer foam device for treating aneurysms [xaviergisz, Jan 15 2022] Very slick. Even better would be something which contracts when heated, to allow for expansion of adjacent solid components.-- bungston, Feb 10 2007 [bungston]'s got the right idea. we could then use it in expansion joints on the freeways and bridges so that water wouldn't get in and freeze.-- tcarson, Feb 10 2007 I'm not yet against or for this - I'd like to know: why? What use did [xaviergiz] have in mind?-- TheLightsAreOnBut, Feb 10 2007 Good question [Lights]; to be honest I hadn't really thought about it. It'd be a novelty to be able to store objects compactly in the fridge/freezer and watch them grow when brought to room temperature. There's probably applications in minimally invasive surgery and medical devices.
Since memory metals are bistable, so too is the memory metal foam. To get a continuum of contraction with temperature suggested by bungston and tcarson, you'd need to have each piece to have different critical temperatures. On the other hand, you might be able to implement their idea with bimetallic strips.
A variation of my idea is to use pieces that transform shape from flat to cylindrical. Another variation would be to encapsulate each piece in a flexible bag so that the pieces wouldn't get tangled.-- xaviergisz, Feb 10 2007 fair enough, I'll bun that. As [bungsten] implies, most materials expand with heat. The difference here, of course, is that you want a huge thermal expansion at around room temperature.
[bungsten] and [tcarson]'s wish might be fulfilled by foam structures resembling auxetic materials (google auxetics).-- TheLightsAreOnBut, Feb 10 2007 Does it need a use?
One thing: I think memory alloy is able to change itself from, say, a straight length into a helix on application of heat, but I don't think it will change itself the other way when it gets cold. I.e. it can only remember one shape.
Perhaps two opposing shapes would solve the problem?-- Ling, Feb 10 2007 good point Ling. I think the 'bimetallic' memory metal idea is excellent (where each metal has a different critical/changing temperature) .-- xaviergisz, Feb 10 2007 /* What to do? */ You could make a self-popping fish lure.-- reensure, Feb 11 2007 (+) (#####) (-<XXXXXXXXXXXXXX>-)-- 2 fries shy of a happy meal, Feb 11 2007 mercury-elastomer hybrid foam.... Would silly putty with quicksilver dissolved inside work for whatever you need this for? mwahahahahahaha, I can't believe I asked that with a straight face [+]!
Note: Keep out of reach from children!-- quantum_flux, Feb 11 2007 I have been thinking about the helix. Is this shape the best for the purpose described? Would a spring coil work as well? Or a random tangle?-- bungston, Feb 12 2007 I suggested a helix because it is a well-known, easy-to-visualise shape. I think I prefer a flat to cylindrial configuration: it'd tangle less, and be easier to manufacture.-- xaviergisz, Feb 12 2007 /I prefer a flat to cylindrial configuration:/ -you want to greatest change in volume with shape change. A flat shape can pack in the same space as a straight wire. The wire needs to get 3D if it is topack less densely.-- bungston, Feb 12 2007 Score to [xaviergisz]! [+]-- pertinax, Jan 15 2022 //use?// Higher density to volume change. More room in the submarine?-- wjt, Jan 23 2022 One potential use would be as a micro-actuator. Fill a chamber with expanding material and a piston moves when heat is applied. There is an intumescent material you can buy called Expancel which has been experimented with in micro- actuators, but only as a one-time-use - it expands about 5 times its volume when heated to 90ºC but doesn't contract when cooled.-- xaviergisz, Jan 23 2022 random, halfbakery