Eli5 Why there are so many rivets on fighter jets and why not use welding instead?
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For complex reasons, welds on aluminum are not as strong as the base metal. With steel the opposite is usually the case. Welds on high strength aluminum grades (which have been carefully heat treated to maximize strength) may suffer from a 30%-60% loss of strength in the heat-affected zone around the welds.
This effect can be remedied in some cases by heat treating a welded assembly a second time, but that tends to cause thermal distortion. It wouldn’t be practical to heat treat an entire assembled airframe. The typical proceedure is to heat the aluminum to about 50- 100 degrees below it’s melting point, then rapid cool by quenching in water or with a water spray. Then aging- tempering at about modest temperatures of about 220° C. At such high temperatures aluminum becomes quite soft and the entire airframe might sag and buckle like wet cardboard.
Very high strength, high performance aluminum alloys used in aerospace tend to have very poor weldability, and almost invariably have tiny weld cracks that are hard to detect.
Rivets are reliable. Quality of installation doesn’t tend to have a major effect on joint strength, as long as the holes are drilled and countersunk with appropriate tools.
Rivets are fairly easy to inspect.
A rivet failure or two in most case won’t result in catastrophic joint failure. Cracks in a single rivet have a hard time propagating to nearby rivets. Very small cracks in aluminum welds could easily grow larger due to heavy vibration.
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