When reading this article on the debris they found from Flight MH370 they mention a lab in France that is supposed to be able to look at the debris (a flaperon), and figure out of the flight had exploded in mid-air or if it had broken up on impact.

This has left me wondering, how would they do that? How can you tell from an exterior control surface** that the plan had exploded or broken up on impact?

**Examples may include elevons, flaperons, ailerons, elevators, basically anything that helps the plane move and is far away from the main fuselage.