Undertensioned wheels will start to fail in about 1-2000k from fatigue in the j bend of the spokes. They're a lot easier to build, because spoke windup and nipple galling don't start to be an issue until you get to decent tensions.
There are three failure modes that I've seen for an over-tensioned wheel:
1) The wheel will buckle in a potato chip shape - This is generally something that will happen at build time, and can be recovered from.
2) The inner wall of the rim will pull away from the side wall. This was particularly bad with the old Mavic MA single eyelet rims, but I've seen it on at least one other rim as well, a lightweight MTB rim laced as a tandem rear. (Completely inappropriate choice of components)
3) Spokes can be improperly tightened without lubrication in the threads, causing windup which later (when unloaded under tire pressure and rolling loads) causes the pinging sound of the wheel going out of true. This is not a structural failure, but it does cause the wheel to require attention.
For the buckling limit case, the ultimate load depends on the torsional stiffness of the rim, and a few other minor factors. Box or closed section rims are much better, U shaped rims are bad. Paradoxically, thinner spokes are better, and you need to lubricate the nipple threads and the contact with the rim. I used to really like the Mavic Open4 rims with the double eyelets, but that's gone out of style now.
There are three failure modes that I've seen for an over-tensioned wheel:
1) The wheel will buckle in a potato chip shape - This is generally something that will happen at build time, and can be recovered from. 2) The inner wall of the rim will pull away from the side wall. This was particularly bad with the old Mavic MA single eyelet rims, but I've seen it on at least one other rim as well, a lightweight MTB rim laced as a tandem rear. (Completely inappropriate choice of components) 3) Spokes can be improperly tightened without lubrication in the threads, causing windup which later (when unloaded under tire pressure and rolling loads) causes the pinging sound of the wheel going out of true. This is not a structural failure, but it does cause the wheel to require attention.
For the buckling limit case, the ultimate load depends on the torsional stiffness of the rim, and a few other minor factors. Box or closed section rims are much better, U shaped rims are bad. Paradoxically, thinner spokes are better, and you need to lubricate the nipple threads and the contact with the rim. I used to really like the Mavic Open4 rims with the double eyelets, but that's gone out of style now.