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Search: JS1 Revelation Structural Wing Test.
This is a glider wing snapping.
I was there, in fact, I welded the frame that is bolted to the floor, to hold the spar at the wing root. The designer of the wing predicted the spot where it would fail, within 50mm, and the load at which it would fail within 1%.
The digital readout shown is the safety factor, above designed loads. It failed at 1.74 times the 5.5g (total glider mass) load.