Most people have had the experience of moving the tab of an [aluminum can][1] back and forth until it breaks off. It usually only takes a few complete back and forth motions before the tab breaks off.

![Aluminum can with stay tab][2]

**What is the root cause of the tab breaking off?**

The possible causes seem to be:

* A fatigue fracture.
* An overstressing the metal.
* A result of plastic deformation.

But which one is it?

  [1]: https://en.wikipedia.org/wiki/Beverage_can#Stay-on-tab
  [2]: https://i.sstatic.net/6PljV.jpg