terfenol/magnetostrictive

[pedrof]

Does anyone have experience in the use of magnetostrictive properties to clamp mechanical parts?

We would like to clamp a 0.5" diameter shaft and ideally use the strain of the material to release the shaft when a magnetic field is applied. Effectively, it would act like an energise to release solenoid.

Any thoughts welcome.

 

[MagMike]

Check out the mechanical properties of the material to make sure it can handle the expected loads - Terfenol is somewhat brittle.

Terfenol needs to be partially magnetized before it reaches a region where the strain response is linear to the applied magnetic field. Hopefully that will not be a problem in your application.

There are a bunch of good people at Etrema, where one of their core products is Terfenol:

http://www.etrema-usa.com/

Mike

 

[pedrof]

Thanks for the response.
In our application, with reference to the brittle issue....I don't think think there will be many shock loads on the material itself.
My main question I suppose is whether a ring of the material can be used so it moves in the radial direction. In theory, without the field applied it would be holding the shaft and once the shaft needs to be removed the applied field would increases the internal diameter by enough to free it. At 1200ppm strain the clearances are mechanically feasible. However, most of the examples on the etrema site relate to expansion along the axis and contraction perpendicular so what we would like may not be possible although they do say the axis can be oriented based on the application(at a cost I'm sure).

I'm based in the UK and am in comms with etrema through the only uk distributor but it is a slow process, I just thought I'd pick some brains on the forums to get as much info as possible.

Thanks again.

 

[MagMike]

Wow! Interesting application!

Unfortunately, radial expansion would be challenging. Not only does the Terfenol need to be oriented radially, the applied magnetic field would also have to be radially oriented. Producing a radial magnetic field is possible, but a challenge unto itself.

Since you are in the UK, you might want to contact Dr. David Jiles at the Wolfson Centre of Magnetics at Cardiff University. He did quite a bit of modeling/development work with Terfenol in the early 1990's.

 

[israelkk]

Using Terfenol-D is not simple you need to compress the Terfenol using a spring and activate a coil around the Terfenol bar. To my understanding in case of a ring the coil will be a toroidal coil around the ring so the inside of the coil will be inside the ring and will not allow a contact between the ring and the shaft. Add to this that the compressing force should be inward to the center of the ring.

If the shaft movement is rotation I think you may use a coil wrapped spring clutch/brake wrapped around the shaft and released by a solenoid

 

[EdStainless]

Maybe you could use a system of rods along the axis of the shaft and small cams or dogs to actually engage. This would be less compact, but the geometries would be much more manageable.

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