Unit 4 Shape Memory Alloys

Date: 2015-10-07; view: 487.

Shape memory alloys have many applications, but before I give some examples, what exactly is a shape memory alloy?

Essentially it's a metal which can be deformed when cold and will remember its original shape when heated. The particular alloy we are using here in the lab is nickel titanium.

We can see one application here in a conventional piston. When the piston is cold, the SMA coil or spring contracts and so the piston doesn't move. Heat causes it to expand and consequently the piston moves up. The advantage is that the device can work without any mechanical power, just from the heat which is supplied by the engine itself.

Let's look at some other applications. Over here, we have a domestic coffee machine. We've fitted a valve controlled by an SMA actuator. When the coffee machine reaches a certain temperature; the SMA actuator opens the valve and so the water is dumped onto the coffee. Again the system works without any additional power — electrical or mechanical — just the heat of the steam given off as the water heats up.

One more application — this time for the motor industry. We're experimenting with a spring device which expands when it cools. This device will be fitted to the cooling fan. In cold weather, the spring expands and this makes the fan close down, and thus helps to warm up the car. In warm weather, the spring contracts and therefore causes the fan to operate and, as a result, helps to cool down the car. Again a system using no external or additional power source. Right, are there any questions?