OK, three test samples are set up:
1. Elmers Glue-All Max, PU glue
2. Epoxy glue for Easton HIT connections for arrow points to shafts
3. Hysol 2-part PU, "FV"
These were just what was lying around, and have something to recommend them.
The PU expands while drying and is a little flexible after setting, and the Easton is for an application that receives a lot of pressure on the joint.
Tomorrow night, will put the rods in a vise, and see if the bent tubes will twist at the joints.
Could also try the epoxy putty, the 5 minute epoxy that dries a little flexible, and the Black Max suggested by Roger. BTW, the last is a rubberized glue, so Roger was perhaps thinking along the same lines as the most recent poster. Am running out of trash pieces to run tests on, though.
As suggested earlier, the Easton 340 tubes can't be messed with. They are ultra high temper, as noted by Roger, and would be weakened and more subject to breakage if 'folded, stapled or mutilated.' That includes crimping, etc.
Like the idea about boring small pits near the ends of the rod. May try that if all else fails.
BTW, these tubes are being used for side-arms on a 'Jackpack' suspension that folds a partial (no buckle) hip belt to cradle around the hips. Here's a photo of the first prototype sidearms next to the frame. It is called the 'ANT' frame because it has six legs:
The super glue was used on the sidearms in the photo, and failed. The position of the U-shaped ALU rod in the tubes controls the position of the sidearms next to the hips, and once set, must remain constant and unwavering.
This was easy when heavier 5/8" ALU tube was used in the past, and could be bolted to JanSport fittings at just the right angle. It's the use of much lighter materials that presents so many issues. The payoff, though, would be reducing a 6 lb. pack and frame to one weighing 2 to 2.5 lbs.
A possible last resort may be to find or make clamps that go over and around the sidearms, and lock them in the desired position. The rubber T fittings (cut to an 'L' shape) in the photo have been replaced with nylon PEX ones. Small screw hose clamps tightened around the tubes in those fittings might work, but would be uglier than he**.
Yet another solution might be to reinforce the tubes at their other ends, the ends that go into the fittings, with ALU rod, glue it, and drill a small dia. hole through the fitting and tube to hold a pin or bolt that would prevent the tubes from rotating in the fitting. Or maybe just drill and screw in a small sheet metal screw through the fitting and tube into the short piece of reinforcing rod in the center.
But as was noted, these approaches will weaken the tube. Maybe heavier L fittings at this location would compensate somewhat for that.
Thanks again for all your suggestions.