Answer
Stress relaxation is the time-dependent loss of load when a spring is held at a constant compressed height at elevated temperatures. It is a form of creep. For a wave spring, the relaxation rate depends on the material's metallurgical stability and the initial stress level. For example, SAE 1070 carbon steel begins to relax significantly above $250^\circ F$ ($121^\circ C$), losing 5-10% of its load. In contrast, Inconel X-750 can operate at $1100^\circ F$ with minimal relaxation. The failure is typically identified when an assembly (like a mechanical seal) begins to leak because the spring is no longer providing sufficient seating force. Designers use the 'Larson-Miller Parameter' to predict the long-term relaxation and compensate by over-designing the initial load or selecting a more stable superalloy.
