A changed free length or declining force at a fixed installed position is often described simply as a weak spring. Distinguishing the mechanism is necessary for an effective correction.
Permanent set often follows overstress
Compression beyond the safe range, excessive torsion angle or overextension can push local material past recoverable strain, leaving geometry changed after unloading.
Relaxation includes time and temperature
A spring held at fixed deflection may lose load over time even without cycling. Higher temperature commonly increases the effect.
Presetting needs a defined purpose
Production presetting can remove part of the unstable deformation in advance, but changes free dimensions and initial load and must match design intent.
Record a time curve
Capture load, temperature and deflection at multiple intervals rather than only start and finish to separate early change from long-term trend.
References
This article is informed by public standards catalogues and industry engineering resources. Project values should be confirmed by drawings, material certificates and sample validation.