Hi Gerry - Peeling and cleavage need to be accounted for in the joint design. Toughened adhesives these days cope with these very well. If the connection is symmetric then these issues are minimised. Also many bonded connections use bondlines that are too thin which makes it easy to peel due to the stress concentration at the edge.. The supplier should be able to provide guidelines on ideal bondline thicknesses. A good connection design should have a thick edge. So the bondline maybe say 0.5-1.0mm but at the edge its 3mm thick via a chamfer or some edge feature. this allows the edge to stretch further.
Mactec - I think the plan would be to machine everything first so any of those effects could be accounted for. I agree that rolled sections have internal stress that does relieve during machining so this has to be accounted for. But transport and SR of a small object is easier then a full frame.
Lots of commentary is based on failure but a machine frame or component is stiffness dominant. Nowhere near failure!! So strains are small, loads are small. So things like 100% welding is not needed, bonding could be done with low strength economical material not high cost fancy extra toughened adhesive. There would be a few single component adhesives that would work at the local hardware. Just putting forward some ideas on the subject. Hobbyists and Makers need a better frame build method then welded steel or AL construction extrusions. They don't have cranes, access to stress relief, large milling machines for correcting frames etc. So we need to explore these options.
I've attached a doc on adhesive joints for those interested. It's a Hexcel doc so a bit technical but it covers many aspects of joints well. Peter