Navy under-matching filler metal studies (multiple rounds)

Tom's "about every twenty-five years" lament. The Navy spent millions in the 1960s on near-full-scale under-matched test panels with explosive loading; spent millions again about 25 years later; reached the same conclusion both times. Used to make the fracture-mechanics point: severe undermatching concentrates strain in the weld metal.

So under-matching has been a holy grail, and people have tried. The Navy has spent on several different occasions millions of dollars making great big foundations and testing near full-scale things. When I say near full scale, something the size of a small car, and doing mechanical tests to see how it fractures. Because remember, in the submarine business you've got to set off an explosion next to it — that's what's going to happen if someone hits you with a depth charge. They've tried it and they've always found that it doesn't work. The reason has nothing to do with welding; it has to do with fracture mechanics. Think about it: if I have two very strong things held together by something very soft, and I now deform this in an underwater explosion or anything else, in the laboratory I'm going to concentrate all my strain in the weld metal. These other two things are like grips and they don't deform at all. If you're severely under-matching — by more than five percent — you'll concentrate all your strain in the weld metal, and if you've got fifty times as much base metal as weld metal, you now have fifty times as much strain concentrated in the weld, and you're just going to break it.