Constructing a NiTi Flower Prototype

[Ayrity]

If anyone is familiar with NiTi metal, also known as Nitinol and muscle wire, I am trying to see if I can use it to create a complex shape, more specifically, I want to make a flower shape out of it. With a stem and petals, all made out of the metal. This is a part of a much larger project but is vital in its completion. Basicly I want to construct a flower shape out of NiTi tubing or thick wire for the stem and use thin sheets or foil for the petals. Then I want to be able to ball it all up into a rough sphere as small as possible, then I want to be able to run a current through it which will then in turn heat up the metal, allowing it to revert back to the flower shape. ANY help or information on NiTi metal and/or its properties or where I may be able to purcase it would be more than welcome. Anyone have experience with it at all? Thanks everyone for any help.

 

[Danger]

Tokai Industries markets a version of it called Biometal. While most NiTiNOL (that stands for Nickle Titanium -- Naval Ordnance Laboratories, by the way) requires a heat source such as a resistor, Biometal has a specific internal resistance that heats it past its hysterisis temperature when a current is sent through it. The electrical aspect is fairly precise, so they also sell the control circuitry. The drawback (which would screw it up for you) is that the last time I checked it was only available in 20 or 30 mil wires.

 

[Ayrity]

thanks for the acro break up haha. yeah the size would mess it up for me, but I don't need the wire with internal resistance exactly. I don't have a problem with using a control circuit that can include resistors as well. Also I am looking into heating it up with a magnetic field, what do you think about that? That way it wouldn't have to be plugged into anything. The speed of the reformation back to the flower shape is not important, so even a small field generating a small amount of heat inside the metal would be sufficiant. Any ideas on whether it is possible to construct the shape I am describing?

 

[Danger]

You'll need input from someone else regarding the effectiveness of induction heating with this stuff; I don't know much about it. I suppose that the material's permeability or permissivity or whatever the hell it's called determines that. Probably the shape too, since the field won't affect all parts of it identically.
As for shaping it... as far as I know, that's done while the material is being alloyed. It's the deformation that you impart during use, then it resumes its 'rest' form when heated. I don't think that you can alter the rest form to a new one, because it's based upon the crystal structure.

I believe that there are other shape-memory metals around, although not as efficient. A long time ago I heard of one called 'vitalium' that used a magnetic memory, but I can't remember anything about it.

 

[PerennialII]

If anyone is familiar with NiTi metal, also known as Nitinol and muscle wire, I am trying to see if I can use it to create a complex shape, more specifically, I want to make a flower shape out of it. With a stem and petals, all made out of the metal. This is a part of a much larger project but is vital in its completion. Basicly I want to construct a flower shape out of NiTi tubing or thick wire for the stem and use thin sheets or foil for the petals. Then I want to be able to ball it all up into a rough sphere as small as possible, then I want to be able to run a current through it which will then in turn heat up the metal, allowing it to revert back to the flower shape. ANY help or information on NiTi metal and/or its properties or where I may be able to purcase it would be more than welcome. Anyone have experience with it at all? Thanks everyone for any help.

Cool idea - I've been involved in developing material models for shape memory alloys & smart materials, can look you up some articles summarizing the properties, how large of a shape memory transformation can come up with etc (mostly modeling stuff, but think there are couple of review articles in there)?

 

[Danger]

Excellent! I'd like to see that myself.

 

[Astronuc]

Nitinol Devices and Components (NDC) Materials Group
http://www.nitinol.info/index2.html

An upcoming conference on Shape Memory and Superelastic Materials
http://www.asminternational.org/shape/committee.htm

I was looking for the website for Nitinol Technologies, Inc. but the don't appear to have one.

But - http://www.shape-memory-alloys.com/alloys.html?source=adword_nitinol

http://www.shape-memory-alloys.com/data_nitinol.htm

Good luck!

 

[Ayrity]

thank you everyone for all your help. Alot of these sites have tons of inforation, i can't seem to find anything on heating by way of magnetic induction though. And there isn't anything on how to make a complex shap, only a wire pattern or something. as far as re-shaping the metal to a rest state, I believe you could do this as long as you bring the metal above its transition temp, using like a buson burner or something. I was thinking (with or without the magnetic induction heating) that I would make the stem out of thin tubeing and run a small wire up through it to the petals, that way the circuit I design for it could make the stem grow all the way first, then make the petals expand.

 

[Danger]

Thanks for the links, Astro. Great stuff. I don't have time to read through them now, but they'll sure come in handy for future design work.
Ayrity, best of luck (okay, we don't believe in luck, but you know what I mean) with your project. Any time someone can combine technology and art, it's good. Dare I presume that you're ambidextrous? Such folks tend to be good at that sort of thing.

 

[Ayrity]

haha, how did you know? thanks for the encouragement though, I was kind of afraid I would be laughed at, ha. thanks though. if anyone has any more information it would be welcome thanks all

 

[PerennialII]

thank you everyone for all your help. Alot of these sites have tons of inforation, i can't seem to find anything on heating by way of magnetic induction though. And there isn't anything on how to make a complex shap, only a wire pattern or something. as far as re-shaping the metal to a rest state, I believe you could do this as long as you bring the metal above its transition temp, using like a buson burner or something. I was thinking (with or without the magnetic induction heating) that I would make the stem out of thin tubeing and run a small wire up through it to the petals, that way the circuit I design for it could make the stem grow all the way first, then make the petals expand.

Yeah, the typical shape is wire ... easy to make, handle, and since many of the applications are composite-type serves them pretty good. Some sort of a composite structure using the wires may be necessary in order to get the required displacement (or using the wires to excite displacement via some "mechanism"), whether the strain range can get out of the transformation suffices will be interesting to see (I'll PM you & Danger a link to some 'hosted' papers which may find interesting).

 

[Ayrity]

thank you for the response, I was worried about that as well, but I figured that not all of the growth would have to come out of the reaction, but rather it could just be bent back and forth net to itself, or coiled up to take up a smaller amount of space from the petals to the tip of the stem.

 

[Danger]

Since I haven't had a chance to look through the links, I don't know if this is a constant or not, but the Biometal at least works by contraction rather than expansion (ie: you stretch it and it returns). If they're all like that, you'd need some sort of leverage to reverse the motion for the design you mentioned. Another approach, which might require more constant energization, would be to have the petals spring-loaded open, and use the wire to close them.

 

[Ayrity]

hmm, that is an interesting notion. I know it is made to contract when powered, but the memory ability is the important part to me, like if I roll a sheet of the metal up then energize it (heat it up) it will roll back out, remebering its shape. I believe I can do the same thing with the petals. Right now my bigest problem is finding a place that sells the type of material I need. I can only find bits of the wire for sale, I need tubeing and foil or thin sheets...

 

[Danger]

Astro's first link provides wires, bars, tubes, strips, and sheets (the latter 2 either rolled or flat). You should be able to make just about anything you desire to from some combination of those.
One thing that I've always wanted to do was just have a square strip of the stuff with a transition temperature somewhere in the 80 degree C. range. I figured that it would be fun to crumple it up into a wad and drop it into someone's coffee cup.

 

[PerennialII]

One resource have found good in the past & yet not mentioned is the resource library of Johnson-Matthey (and well the site overall):

http://www.jmmedical.com/html/resource_library.html

Since I haven't had a chance to look through the links, I don't know if this is a constant or not, but the Biometal at least works by contraction rather than expansion (ie: you stretch it and it returns). If they're all like that, you'd need some sort of leverage to reverse the motion for the design you mentioned. Another approach, which might require more constant energization, would be to have the petals spring-loaded open, and use the wire to close them.

Sounds like you're talking about one-way and two-way memory effects, some variants of NiTi at least have it two-way, i.e. the shape memory change occurs both in heating and cooling.

 

[Danger]

Neat. This is the first time that I've heard of bi-acting material. That will be immensely useful for some of the stuff that I do.
Thanks again for the PM'd links. I haven't had a chance to go through them yet, but they're definitely getting stashed in my 'documents' folder under 'cool stuff'.

 

[PerennialII]

The site above has actually a pretty good intro and links to some papers of this "bi-"material property. The 'problem' of this property is then the decrease in recoverable strain .
http://www.jmmedical.com/html/2_way_memory.html