Originally Posted by
WalksOn2Wheels
I was talking specifically about the plasticity of the metal. If you look at the linear stress/strain curve of a given material, a metal stretched to near it's breaking point, and then not properly stress relieved is going to be near it's breaking point. The point of stress relieving is to push the spoke further in the plastic deformation range. Once it is stretched and then relaxes back to the length required, it now has a wider range of load that it can take before snapping.
While this is true, it is not the mechanism through which spokes typically break.
Stress relieving the spokes is typically done by applying an extraordinary force to the spokes in such a way that they bend more tightly around eachother and the flange of the hub (plastic deformation). Doing this usually causes the spokes to loosen as they are now taking a shorter path from the hub to the rim. If this is properly done during wheel building, the builder can then reintroduce the tension and true the wheel vertically and laterally. If the builder does not do this properly, it happens over the first few miles or so of riding... faster under a heavier rider... and then the rider is possibly left with a wheel that has insufficient tension in the spokes, which leads to fatigue failure if not corrected.