The next time you are about to board an airplane cast an eye around the outside of the cabin door and notice the hundreds little dots visible under the paint of the fuselage. These are solid aluminum rivets and many thousand more of them are what hold the entire plane together. They are also a great example of how certain material properties can be used to your advantage.
As fasteners go, rivets are not all that visible in our daily lives and the image I usually conjure is of the dramatic and beautiful coordinated dance of steel workers setting big, white hot steel rivets in bridge structures or, famously, on the Empire State Building. The rivets were simple cylindrical pins with a head on one end and they were heated so they’d be soft enough to “upset” with a good-sized and well-swung hammer. In practice, after you’ve lined up the holes in the girders or plates that you’re joining, you called for a rivet to be pulled from the fire and tossed with great care to a guy waiting to catch it in a bucket. Next you grab the thing with tongs, still hot, push it through the plates and have your partner back it up with a sledge hammer while, from the other side you hammer/form the free end into a second head. Speed, of course, is critical to the whole operation. If the rivet is allowed to cool before it’s fully set, the game is over and you probably are left with a stone cold, mangled thing stuck in the hole. But at this point, when properly executed, the real beauty of the system comes into play. As the newly installed rivet cools, it shrinks! This draws the structure together even tighter and maintains an ideal tension on the joint. Perfect!
In principal, this riveting works the same way on a Boeing 737 though there are differences. The rivets are comparatively tiny, they aren’t steel and they are set cold. What really makes the process work on the plane is that the type of aluminum used for the rivets strengthens as it is formed. This is called work hardening. It happens with many metals and is usually seen as a problem to be dealt with, but in the aluminum rivet case it’s a nice perk if you’re aware of it and can exploit it.
We like our materials and fasteners and are always happy to advise on both.
