Memory alloy bounces back into shape 10 million times

[mercalia]

this as a good frame material?

Memory alloy bounces back into shape 10 million times

http://www.bbc.co.uk/news/science-environment-32886000

[beardy]

Which bit of the frame do we want to change shape 10 million times?

It could find a use in our indexed gear systems though. dérailleurs without wearing pivots is a rather tempting idea. How many times do I change gear, I wonder?

[Mark1978]

I would think it would find more uses in the likes of suspension, or anything else that has to survive constant vibration.

[Brucey]

anything related to pedalling (about 5000 cycles per hour) quite quickly gets into a million plus stress cycles on a bike, and so does anything related to a bumpy road. And 'changing shape' is not a useful property for most parts on a bike, in fact.

So IMHO beardy is right, something like gear shifting might be the place for this. You still need it to last millions of cycles, and you need to be able to manufacture the material, join it to other stuff, etc, all for pennies... and so honestly, I can't see it happening anytime soon...

cheers

[beardy]

Mark.
Such elastic materials already exist, they even have a cement that can be made into springs!

This material does something quite different, it can change from one shape to another (in a limited way) rather than just deflect.

[al_yrpal]

All well designed metal bike bits change shape within their elastic limit all the time. Can't see any particular advantages from this stuff. Highly stressed springs might benefit but such things arent used on bikes except possibly cheapo MTB suspension.

Al

[beardy]

I dont know exactly what this material is doing, the reporting is typically imprecise (poor quality).

However it is clearly not working within elastic limits. The material appears to have (at least) two different shapes that it can change betwen by application of either heat or force. This will, I am guessing, be a change in its length v its width (in a 3d way) as the crystal structure within changes shape.

Such a small change can be amplified over a long arm or sheet of material. Think of how you can make a creased metal sheet twang from being folded one way to another, the actual metal at any one point only changes a tiny bit. A bit like that but not quite!

[Brucey]

shape memory alloys have been around for a fair while; if you want to understand what they do there is a good Wikipedia article I think.

The 'new thing' here is that the number of reversals before failure has been increased dramatically. This makes it possible to envisage applications where many reversals are necessary.

For example, you can buy bimetal switches which change state at a predetermined temperature (and do work a bit like a jam jar lid in fact) but these switches commonly have a life of a few tens of thousands of cycles. This means they are OK to be used on (say) temperature controls on washing machines. If a shape change alloy could be used instead of the bimetal material, more precise changes could be made but so far this has not been practical because the stuff is expensive and fatigues too quickly. This new material may help overcome part of that.

cheers

[mercalia]

we are near the silly season? I was thinking a collapsable bike you could just bend up and put in a bag, then when u take it out it spring into shape again...

[mercalia]

we are near the silly season? I was thinking a collapsable bike you could just bend up and put in a bag, then when u take it out it spring into shape again... Clearly an an Acme Corporation product

[beardy]

That would be more like a use for these material properties*, I had not considered that option.

It does conjure up comedy images of the bike suddenly deciding to revert to its folded shape whilst being ridden.


*In a blue sky, distant Sci-Fi sort of way.

[Mick F]

How many times do I change gear, I wonder?

I once added them up during my commute. Can't remember the figure, but it was astounding. I was 6sp double back then and rode 17miles each way every day.