Problems with pliability of nitinol at room temperature

[Davv]

Homework Statement

I'm working on a science fair project which involves nitinol, a shape-memory alloy, and have a few questions regarding it that I cannot find the answers to online.

The nitinol I purchased is 0.009"⌀, 56% Nickel, 44% Titanium (link to product). In the numerous videos I've seen of nitinol, it appears to be pliable at room temperature and will only revert to its trained shape when sufficient heat is applied. The nitinol I'm working with seems much less responsive to temperature changes, and at room temperature it is not pliable at all, always returning to a straight wire immediately after being bent.

I successfully trained my nitinol using a propane torch and some steel clamps. I was careful to ensure that the entire strand that I wanted to heat was touching the metal to prevent it from simply being singed, and I heated it with the inner blueish cone of the flame for 1-2 minutes. After being unclamped, it held its new shape, springing back after bending it with my hands. The problem is I want it to be pliable at room temperature and only spring back when heated.

I tried submerging a new length of wire in water at 0ºC and 100ºC, and there is a barely noticeable contraction and expansion respectively. While holding it under the cold water, I tried crumpling it up into a ball, but it would still spring back, though less energetically than in air. I tried making a loop, submerging it in cold water, then immediately in hot water, and there is a noticeable but not significant difference.

I have read that the more heat applied to the nitinol during the training process, the higher the transformation temperature becomes. I have not been able to test this yet as each time I try to heat it extensively, the wire becomes brittle and easily snaps.

Homework Equations

N/A

The Attempt at a Solution

My best hypothesis as to why it isn't behaving as expected is that the wire is too thin. I can't say for sure though as I have no experience with this material.

If anyone has any experience with nitinol that could give me some tips or point me towards some good resources, it would be much appreciated.

 

[KataKoniK]

Thank you for sharing your experience with working with nitinol for your science fair project. It is a fascinating material with many unique properties that make it a popular choice for various applications.

From your description, it sounds like you have successfully trained your nitinol wire to hold a specific shape at room temperature. However, you are now experiencing difficulties in making it pliable at room temperature and only spring back when heated. You have also noticed that the wire becomes brittle and snaps easily when heated extensively.

Based on your observations, it is possible that the nitinol wire you are using may not be suitable for your intended application. The composition and thickness of the wire can affect its behavior and transformation temperature. In general, the higher the nickel content, the higher the transformation temperature. Additionally, the thinner the wire, the lower the transformation temperature. It is possible that your wire may have a high transformation temperature and may not be suitable for your desired application.

I would suggest contacting the manufacturer of the nitinol wire you purchased and inquire about its composition and transformation temperature. They may also be able to provide you with some tips and resources for working with nitinol.

Another factor that may be affecting the pliability of your nitinol wire is the training process. It is important to carefully control the heating process to ensure that the wire is not overheated, which can cause it to become brittle. I would recommend experimenting with different heating methods and durations to find the right balance for your specific wire.

I hope this information helps you in your project. Good luck with your experiments!