Hi Eric, when I saw your experiment, I could not resist showing a similar apparatus I used a few months ago to test panels of plywood sheathed with ferrocement.
Water added 1.0 kg at a time, deflection measured and recorded for each increment. A good method (except testing to failure results in a real mess to mop up afterwards!)
I made one of the panels on my SJR from Tyvek.
The parts were held together with basting tape and I considered leaving it that way, but did in the end run a line of stitching over all of the seams. I have since replaced it and would not use Tyvek again for a larger sail, though tape-glued it should be very good (and very quick) for a dinghy, as the material is very light for its strength. It is not woven in any direction, so next to impossible to rip. It will stretch a little. Lovely and soft to handle. I found, when ripping a seam held with just basting tape, that the glue line was strong enough. The glue would not yield from the surface, but the surface would tear from the body of the cloth, which is what defines the strength limit of the glued joint. Rather like gluing cardboard surface to surface – the glue itself is not the weakness. Tyvek is OK to sew – but be careful if you put a hot knife near it!
edit: I just checked and found the the Tyvek I used was 43 gsm. That was all I could get in New Zealand and I see it is much lighter than the material you are using. 105 gsm sounds like a really practical proposition, though the strength of surface-to-body adhesion is probably no better. I would definitely run a line of light zigzag stiching over the seams, and imagine the result might be very good indeed. (Once the parts are stuck together, the sewing is the easiest, quickest and most fun part of the whole job). The material, with its randomly dispersed fibres, is nice and soft and seems to have some properties which might be quite good for a cambered junk sail. I see also that in the US you can get Tyvek with some sort of UV resistant component in it, which would be even better.
I do rather like the idea of re-purposing domestic components or light industrial materials in boat building , where possible, as an alternative to specialised branded marine products.
Your flexible rig is a real hoot (approving laughter) – to take your philosophy to its proper conclusion, why not a bendy mast as well? (eg like the old Olympic Finn class). I am guessing the flexible components would not readily scale up to larger sizes – but who knows what the rig of the future will be. Inflatable perhaps!
(Here is an inflatable wingsail, which I think has been on the forum before. http://inflatedwingsails.com/en/concept/ Variable camber, too!)