The primary concern for elevated-temperature applications of helical springs is stress relaxation. Stress relaxation is the loss of load or available deflection that occurs when a spring is held or cycled under load. Temperature also affects modulus, tensile and fatigue strength. For a given spring, variables that affect stress relaxation are: stress, time and temperature, with increases in any parameter tending to increase the amount of relaxation. Stress and temperature are related exponentially to relaxation. Curves of relaxation vs. these parameters are concave upward. Other controllable factors affecting relaxation include:
It should be remembered that, if a material is used at its maximum temperature, a substantial reduction must be made in applied stress from that used at room temperature.
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