Glenn,
Shape memory materials are really neat stuff. When you see them work,
it's like magic. But they have always been way too expensive for most
everyday applications. The cost is not only due to the cost of materials, but the
elaborate process required to train them. Even steel alloy SMAs have been
too expensive, because they have always shown too small of a shape memory
effect to be effective on a cost/benefit basis. As with all smart
materials, you also have to rethink your mechatronic design process. However, it
might be worth the effort of a creative mind. It would be interesting if
someone has come up with a new alloy that has a large effect and low cost.
I have never worked directly with the material, although I have
periodically studied the commercial applications since I first visited some of the
manufacturers and wrote about it in 1986. Many alloys have long been shown
to exhibit the shape memory effect, including steel), but the effect has
generally been too small to produce enough work to make high-volume
applications worth the expense of producing the material. Without high
volumes... (chicken/egg).
The most popular material was actually copper and zinc (brass) alloys
that Raychem (now Teico) developed for clamps and pipe fittings. I believe
one of the bigger applications today is in orthodonture wire and also
specialized medical surgery tools. As I recall, shape memory alloys have to be
heated to one temperature and (austenitic) crystalline phase, (essentially)
trained, and then cooled to another working temperature and (martensitic)
phase. When the ambient temperature rises (from a blow torch, hot water,
or body heat), it remembers and returns to the austinitic phase and shape.
The temperature range of the effect varies for each alloy and is limited.
Anti-scald shower water cutoffs, fire damping, automated greenhouse
windows, artificial muscles for robots, wires for underwire bras, actuators for
moving wings on butterflies in greeting cards, and lots of other
applications have been thought up and commercialized, but with no lasting success.
If you need to work only once, and if you don't need it to have a large
or long-lasting effect, some of the known materials might be useful.
Other materials, including some ceramics and plastics, exhibit a kind of
shape memory effect, although I don't think the physics are quite the
same. I remember (sic) one Japanese company was producing a shape memory
plastic it was using for automatic chokes in lawn mowers and for toys and
novelty items. I think I have some samples in a box here somewhere. Perhaps
that is more in line with a material you would like to use.
Brock Hinzmann
Technology Navigator
SRI Consulting Business Intelligence
Menlo Park, California
bhinzmann@bic.sri.com
voice: +1 (650) 859-4350
SiderWhite wrote:
>Just read an interesting article on shape memory stainless steels (SMSS)
>(Advanced Materials & Processes, Feb 2001,
>http://www.asminternational.org/Template.cfm?Section=AdvancedMaterialsand
Pro
>cesses&NavMenuID=60). Unfortunately you need to be an ASM member to view
>this article.
>Very interesting material, it costs much less than the nickel-titanium
shape
>memory alloys (such as nitinol) but it has less fully reversible strain.
One
>of the biggest application areas for this alloy could be in pipe
couplings.
>To make a connection, two pipes with diameters slightly smaller than the
>shape memory alloy coupling are inserted into the coupling. The shape
memory
>alloy is then returned to its prior microstructure, thus gripping the
pipes
>tightly. Such couplings are already applied in piping systems on the
U.S.
>Navy F-14 Tomcat aircraft using the more expensive TiNi alloys (previous
>information was excerpted from the article).
>
>I can't help but think somehow there could be some fanatstic RP
applications
>for this material, perhaps a recyclable RP material where you could
>constrain it to the shape you wanted to create a layup tool or some
other
>use and then when you are done with it, return it to its prior
>microstructure for use agian on another project. Has anybody ever worked
>with this material?
>
>Best Regards,
>Glenn Whiteside
>
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