For educational purposes, I'm gonna cite this for extra negative points. You'd think automatically, a stress riser, and true. But the seat stays are loaded in compression, and their slenderness lends them to buckling failure, and thus stiffness is the key factor, and not strength per se, and, the failure may not be preceded by warning cracks, but instead causing sudden, total, catastrophic failure (an actual engineering term). Buckling failure and causes is one of the least intuitive mechanical failure modes, usually not grasped before a class in Mechanics of Materials.