Official Answer
Answer
Wave springs are typically manufactured from flat wire produced by rolling round wire. This process creates a natural round edge or 'deburred' edge. Any micro-fissures or sharp 'burrs' on the edge of the wire act as stress risers (K_t). In a cyclic application, these risers facilitate crack initiation. For high-cycle fatigue ($>10^6$ cycles), wire must be inspected for surface decarburization (in carbon steels) and edge quality. Polishing or vibratory finishing the springs after coiling and heat treatment can increase fatigue life by 20-30% by removing surface defects and inducing a slight compressive residual stress on the material's exterior.
