Relaxation and Creep

Over time, all springs undergo a loss of elasticity. Depending on the type of load imposed on the spring, this loss of elasticity manifests itself as relaxation or creep.

Relaxation is the decrease in force, ΔF, seen over time if a spring is compressed to a constant length Creep. One speaks of creep when the spring to which a constant force has been applied in time further decreases in length by an amount ΔI so that its overall height l_o is reduced.

The relaxation or creep of the spring under working conditions is decisively influenced by the following factors:

1. Amount of load stress, which for practical purposes is expressed by ō_I
2. Residual stress condition result from the presetting process in production
3. Working temperature
4. Material strength, especially also at high temperatures (heat strength)
5. Duration of load application

Hot-preset springs have about the same surface residual stresses as cold-preset springs. However, they have a plastification zone extending deeper into the material and thus a less steep decline in residual stress. The result is a lower resetting tendency than on cold-preset springs.

The permissible relaxation values for cold-preset springs are shown in Fig. A and B. For working temperatures higher than 100 °C , please contact Mubea.