Official Answer
Answer
Fatigue failure in wave springs usually initiates at the inner or outer diameter of the crest or valley where the tensile stress is highest. Under a scanning electron microscope (SEM), the signature appears as 'striations' indicating incremental crack growth per cycle. Failure often occurs due to 'set' followed by cracking. If the spring is operated beyond its fatigue limit (e.g., $\sigma_{max} > 0.5 S_{ut}$ for carbon steel), the crack propagates until the remaining cross-section cannot support the load, leading to a final brittle fracture zone. Prevention involves reducing the wave height $h$ or increasing the number of waves $N$ to lower the stress per wave.
