Cyclic Creep/Retraction of Short Fiber Reinforced PEEK

We needed material data and a material model for structural simulation of a highly loaded gearbox component. The component needed to endure loading-unloading cycles at elevated temperatures.

We carried out tensile tests with a variation of strain rates and temperatures. And, to closely mimic the most damaging loading situation in the component, we did creep-retraction tests. In these tests at first a load is applied and held constant for 30 minutes and the creep strain response is recorded. Then the stress is removed, and the retraction of strain is recorded for additional 30 minutes. As the materials creep resistance diminishes as temperature increases, we chose the highest application temperature for these tests. Then we chose a material model and calibrated the parameters using our tests (red curves). As we wanted to picture the cyclic ratcheting of creep strain, we focused on a good description of the remaining strain after retraction. The green curves show the behavior of our model. It is composed of linear viscoelasticity and Chaboche-type visco-plasticity with a Norton flow rule.