Question

What useful effect is created when a shape-memory ally is prevented from returning to its original shape when heated above the recovery temperature?

O The residual strain creates a stress.
O None of the other choices given.
O It will experience plastic deformation instead of twinning / de-twinning.
O The new shape becomes the shape to which it will return in the future.

Answer 1

Preventing a shape-memory alloy from returning to its original shape induces residual strain and creates thermal stress, which can be harnessed in practical applications for tightly joining components together or could lead to structural failure in other scenarios.

Step-by-step explanation:

When a shape-memory alloy (SMA) is prevented from returning to its original shape upon being heated above the recovery temperature, the resulting useful effect is the creation of residual strain that induces thermal stress. This stress can be exploited in various applications such as tightly fitting components together. SMAs can return to their pre-deformed shape when heated, but if they are constrained while above the recovery temperature, they develop internal stresses as they try to revert to their pre-deformed shape. The elastic limit of a material represents the threshold beyond which it undergoes plastic deformation, leading to a permanent change in shape. SMAs are unique in that they react to temperature changes to return to a shape set by previous mechanical deformation, but when restricted, they produce thermal stress, which can be useful or destructive depending on the application.