Springs may experience tens of thousands to millions of cycles. When life is insufficient, switching to a more expensive material is rarely the complete solution. Design, manufacturing and assembly must be reviewed together.
Mean stress and stress range
Fatigue risk is closely related to the stress change between minimum and maximum working positions. More travel, fewer active coils or local geometry transitions can increase the stress range. Evaluate the real operating window, not only the maximum static load.
Surface condition sets the crack origin
Scratches, folds, decarburization, corrosion pits and unsuitable grinding marks can initiate cracks. For high-cycle parts, wire surface quality, forming, stress relief and corrosion protection should be controlled as one process.
Misalignment and lateral friction
Compression springs may bow and rub when guidance is insufficient, slenderness is excessive or ends are unstable. Torsion spring leg interference, installation-angle error or an unsuitable mandrel can create local loads beyond the design model.
Validate realistic conditions
Life testing should reproduce actual travel, frequency, temperature, lubrication and installation as closely as possible, while recording failure location. Passing prototypes must be followed by production controls for critical dimensions, load and material lots.