Nitinol Strain 2

[voram]

What does Max.Strain in nitinol mean in
1. Bending (superelastic)
2. nitinol spring (shape memory)
3. tension (superelastic and shape memory
Advance thanks

 

[israelkk]

There is a vast and excelent information on Shape Memory Alloys on the net.

 

[voram]

Thanks man.but i'm able to come across detailed information on strain for nitinol components. for wire strain refers to change inlength. what does it mean in case of bent nitinol rod or a nitinol coupling where the original diameter is recovered by heating

 

[israelkk]

Nitinol can recover up to 8% strain for limited number of times and 3-5% for hundered thousands to millions cycles.

When you bend a wire or a rod the outer radius is stretched and the inner radius is comressed, the amount of stretch and compress can be calculated to fit the desired stretch.

The diameter also changes and it is usually very small if you use a bending tool. However, if you can calculate the change ad the result of the bending radius then you can design it not to go beyond the 8% or the 3-5% range.

 

[voram]

I came across that 8% strain in nitinol is applicable in tension, compression, and shear.

Is the 8% strain in tension of nitinol wire is same for all wire diameters? and how diameter of wire can affect its strain properties ?

Advance Thanks

 

[israelkk]

As far as I know yes, strain recovery is the material property.

 

[voram]

Actually i bought an educational kit which contains some SMA paper clamps, some Tension, compression springs, SMA wires , Superelastic tube , wires and rods. I want to do some experiments to determine the basic characteristics of the material. Please help me out regarding what experiments can be done and what properties can be found out...
Thanksin advance

 

[zer0signal667]

Just a note- strain recovery is a material property, so in tension each wire diameter should behave the same. But if you want the pieces to change shape in a bending fashion, size is an issue. A thicker wire will not be able to recover after deforming around the same bending radius as a thinner wire.

 

[voram]

Thanks for the reply. Then in larger diameter nitinol wire in bending, where can we consider the maximum strain

1. strain at the outer bending radius(tension) (or)
2. strain at the inner bending raius (compression)....
thanks in advance

 

[zer0signal667]

Tensile strain at the outer radius and compressive strain at the inner radius should be the same. Check out this link I found pertaining to NiTi wires:

http://www.sma-inc.com/html/surface_strains.html

 

[voram]

Thanks for the link. The information was indeed useful. If we fix the bending actuator strain as say 5%, how can we practically control the bend diameter. In other words, how can we measure practically during experiments the bend diameter?
Advance thanks

 

[voram]

whether all Shape Memory Alloys can be electrically heated. If not, may i know what are the limitations. \Thanks in advance