The Space Shuttle Columbia disintegrated on reentry because a block of foam fell from the External Tank onto the reinforced carbon-carbon wing-leading edge of the Space Shuttle.  After the disintegration, engineers demonstrated the damage that could be wrought by a small block of foam, and the panels ruined during the demonstrations, along with a block of foam, are on display at the U.S. Space and Rocket Center.
<a href="//commons.wikimedia.org/wiki/User:Ke4roh" title="User:Ke4roh">James E. Scarborough</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>