Deriving Temperature Derating Factors for Polymer Fatigue Characterization in Engineering Resins
Polymer fatigue temperature derating derives from isothermal S-N curves and viscoelastic shift equations adjusted for cyclic hysteretic heat buildup.
Cyclic Creep
Meaning
Progressive deformation occurs in materials subjected to repeating loads even when the peak stress remains below the static yield point. This phenomenon of cyclic creep involves the accumulation of plastic strain over thousands of cycles. It terminates when the material either stabilizes through hardening or fractures due to excessive strain.
The evaluation of this strain is necessary for structural components. Limits vary.
Accumulation Rate
Every load cycle adds a small increment of permanent displacement to the component. Engineers measure cyclic creep to understand how a part will change shape over months of continuous operation. Without this measurement, a precision assembly might lose its alignment.
Failure Prediction
Speed of application affects the rate at which the material flows under stress. High frequency loads might lead to thermal softening while low frequency loads allow more time for molecular rearrangement. Monitoring cyclic creep during the pilot phase reveals whether a design can withstand the rigors of full scale manufacturing.
Component Life
Material fatigue often interacts with the deformation to accelerate the end of the useful life of a component. Predicting the impact of cyclic creep allows for the creation of maintenance schedules that replace parts before they reach critical dimensions. This proactive approach saves the cost of unplanned downtime in a production facility.