Nitinol A SHAPE MEMORY ALLOY

ENG 45

SRJC FALL 2012

Paul Fein Allen Volpe Eric Baldwin

Shape Memory Alloys: What are they?

An Alloy that Exhibits Shape Memory Shape Memory – the ability to undergo elastic deformation at one temperature

and recover its original shape upon heating above its transformation temperature.

Nitinol - Metal alloy of nickel and titanium Roughly equal atomic percentages Very useful but very expensive.

Other Alloys Include: CuAlNi Others can be made with Zn, Cu, Au, Fe Ferromagnetics – memory alloys that recovers shape in magnetic field.

Uses for Nitinol Today (and tomorrow?)

Practical Present Day Uses Heart Valves Stents Eyeglass frames Novelty items Prosthetics Orthodontistry Robots Perpetual Motion Machines More Robots Aeronautics

Training SMA’s

“Quick and Dirty” Resistance Heating Oven Heating Work Training • Apply a large enough

current over time while restricting shape.

• Consistent and controlled heat throughout sample at/above training temperature.

• For the best effect quench immediately.

• For Nitinol heat to 500 degrees C or a faint red color.

• During extrusion the permanent shape is established.

• This is why our sample came in a straight line.

How it Works

Martensitic transformation Metal cools to twinned martensite

orientation which has the unique quality of being deformable without breaking atomic bonds.

Applied strain pushes it to deformed martensite.

Heat above transformation temperature reverts to Austenite which returns to and holds original shape.

Cools back to twinned martensite condition and is deformable again.

How it Works

Temp induced phase transformation no loading

After applied stress, unloaded, temp induced phase transformation

Temp induced phase transformation with continually applied load. The slopes of start and finish points explains why we could not calculate K.

Pictures from Lagoudas, D., pp 6-9.

Our Plan CURRENT DRIVEN SPRING LIFTER

What we did: 1. Followed the directions:

• Used a lighter to “train” the shape memory alloy.

• Failed. Hard.

2. Talked to Younes: • Used oven set to 500 degrees C

• Succeeded. Awesomely.

3. Moral of the Story: Talk to Younes First

4. Alternate Moral of the Story: the internet Lies!

The Story Begins…

Prepping the copper pipe

Wrapped Nitinol to make Spring Shape Heat and Quench

Drilled holes to run Nitinol wire through. Please Note: Special thanks to the tweakers of Paul’s neighborhood for not stealing this before we could scavenge it.

This is the shape it will attempt to resume after temporary plastic deformation.

Heat treated at 500 degrees C for 10 min then quenched in water.

And then there was testing, and it was good.

Initial Setup Initial Testing Behold, the magic of Nitinol!

Our initial plan involved the nitinol spring completing a circuit and contracting due to its own internal resistance.

We experimented with different weights and voltages in an effort to calculate the spring constant.

The spring looses rigidity as it cools, dropping the weight slowly.

Finished Product!

References

http://www.nitinol.com/nitinol-university/nitinol-facts/

Ashley, S. (1998, Jan). Metals that remember. Popular Science, pg 79-81,115

Lagoudas, D.C. (editor) (2008). Shape memory alloys: Modeling and engineering applications. Springer Science and Business Media. New York, NY.