I would like to know if I build a 2'2'96" box out of 1" plywood sheathing (think diy altitude test chamber) would it be able to withstand a 4psi differential. I am looking at testing products at no greater than a simulated 9000 ft.
Dig out your old Strength of Materials text and do a little reading and math. 4psi is 576 lbs./sq.ft. on a 2' span from side to side. What bending stress in 1" thick mat’l.? Then, each sheet also has a 576 lb./ft. of length compressive (column) loading on it. 1" plywd. probably won’t work. You might be better off seeing if you can find a piece of 2 or 2.5' dia. thick walled pipe, 8' long, and putting appropriate ends on that for your test chamber.
A long time ago I was making some vacuum form tooling from plywood. Ended painting the whole thing with a couple of coats of laminating resin. The plywood wouldn't HOLD a vacuum