has anyone ever attempted to create a machine that would trial semi-random material compositions with minimal human involvement?

Yes, someone did. It's actually an active field right now, from high-throughput simulations to try to limit the search space, to additive manufacturing of thousands of samples, to semi-automated characterisation and some testing (e.g. corrosion; for things like mechanics it's more difficult). The idea is te be more efficient than semi-random.

ok, so quasi-random. Would it be more useful to have such a machine to feed data back to models to better the simulations where we could do more in less time and prune down to more likely candidates?

That’s the active research area GP mentioned. In startup land there are a few large outfits, Lila Sciences, Period Labs, Radical AI are all doing a mix of simulations, AI, and autonomous laboratory infrastructure specifically for materials science. (Lila does a lot of biotech but the have materials researchers too)

Also lots of interest and activity in this space in the national labs and academic research scene

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