When you’re trying to fasten two things together, you’re basically trying to make them behave as though they are one. Nails, screws, glue, and other fasteners all exist to combine separate things, but always by keeping them as two entities. Welding, by contrast, actually does make them one — perhaps with a structural weak point at the old junction, but a single object nonetheless. By melting small portions of the metal together, welding can create air- and water-tight seals, and extremely strong connections. But one downside is that it can only be done with certain types of materials — or so we thought.
It turns out that a peculiar type of welding, one which might look foreign to those most familiar with the sparks and masks of arc-welding. A super-heated torch flame will certainly provide enough heat to melt two objects together, but so will plenty of other techniques. If you want to weld, say, wood, then you’ll have to find a way to provide enough heat to fuse two pieces of wood without actually making it burst into flame. Wood, after all, doesn’t melt.
Or perhaps it does. As you can see in the video below, the use of friction can cause two pieces of wood to fuse, literally welded together. One piece is held stationary while the other vibrates rapidly above it, moving less than two millimeters each way, but 200 times per second. It’s a technique usually used to combine two pieces of titanium, often in the form of rotational friction rather than the linear friction (back and forth movement) in this video.
The TWI researchers that are looking into this can’t totally explain the wood welding phenomenon, actually. They think the cellular structure melts and forms an unknown matrix which cools into a stable joint, now actually a feature of a single fused object. During the fusing process, charred wood is ejected in tight shavings, meaning that some portion of the wood is actually burned away as the friction process begins.
Assuming there was a way to actually implement something a finicky as 200-hertz vibration on a large scale, the ability to completely stop air flow between pieces of wood could fundamentally improve construction. The joint’s strength is not discussed, however. Though we could find uses for this in the future, right now it’s just an interesting question, and a very cool video.