Audio Files  Meera Senthilingam  This week, Neil Withers
explores an unusual phenomenon…  Neil Withers  Have you ever
seen those spectacles that can be screwed up, but then ‘rebound’
back to their original shape? If so, you’ve probably wondered,
like I have, how on earth they work. After all, it seems to go
completely against anything you’ve learnt or experienced about
how metals behave. Paperclips, for example, once bent out of
shape, are more likely to fall apart than resume their old
shape.  It might surprise you to discover that the shape memory
effect, as it is known, goes back quite a few years – to the
1930s. But products incorporating materials that make use of
this effect only came on the market a bit more recently, in the
past few decades.  Most of the materials known to have this
shape memory are alloys – mixtures of two or more metals – and
the most widely known one is a nickeltitanium alloy known as
nitinol. The name comes from the two metals and the place its
properties were discovered, the US N