RE: Sailplane Wing Design Round II
Just a suggestion.
You mentioned the outer wing rods fractured. That doesn't show in the pictures so that might be why we've not been talking about anything but what looks broken in the pictures. They actually were the instruments of destruction that failed the center section. Look at where your fracture line zig-zags in the pictures. The center section failure on that side is basically where those two rods seem to end inside that side. They aided the major failure and still failed, possibly as the wing folded and got some extra aero forces thrown at their joint. They probably did go on impact, but that makes you wonder what they'd do if it caught a wing on landing.
I'd think about increasing the diameter of the primary rod one step up. No need to increase the smaller aft rod.
If you've not done that area of the center section yet, you might also consider combining the rod holding tubes with the main spar out in that area. Combining structures often allows you to make each part of the combination lighter.