Official Answer
Answer
Fracture at the wave peak is the most common failure mode, as this is the point of maximum bending moment $M = P \cdot \frac{D_m}{2N}$. Failure can be due to: 1) Fatigue: Look for 'beach marks' or striations under SEM (Scanning Electron Microscopy), indicating cyclic stress. 2) Brittle Fracture: If the surface is granular, it may be Hydrogen Embrittlement or Over-hardening. 3) Wear: If the peak is flattened/thinned, the sliding friction against the mating part caused a 'notch' that acted as a stress concentrator. In a Crest-to-Crest spring, check for 'misalignment' where the peaks of one turn did not align with the peaks of the next, causing unexpected shear loads.
