Nitinol Situation

[BMccarthy81]

I'm grinding an 18 inch (45.72 cm) long, .048" (.122)diameter nitnionl wire with a thru-feed grinder. We're taking off .0006" (.0015 cm) and we're finding that the length grows .005" (.0127 cm). I would like to know the actual force needed to cause this elongation effect of Nitinol, or at least a decent spec sheet about the metal. It's hard to believe that a relatively low amount of pressure could cause this material to change in length, but the proof is right in front of my eyese.

 

[Goahead]

It seems that the length increase is less than 0.03%.
Possibly the amount of pressure is not so low.
Assuming that the original material is fully annealed,
if you could examine metallographically longitudinal sections of the ground wire you would probably see superficially deformed grains. Chemical milling would reduce the section without probably affecting the length.

http://www.welding-advisers.com/

 

[diamondjim]

Are you measuring the wire immediately
after grind? Is the temperature of the
wire the same after grind?

 

[rd400guy]

Who is your supplier of this NiTi? Did you contact them regarding what you're seeing?

I find it very hard to believe that you're mechanically deforming, and therefore elongating the wire. More likely the heat generated by grinding is inducing one of the phase transformations NiTi is known for. Do you know what the As temperature of your wire is? What condition is it in, annealed or cold worked? If cold worked, what percentage?