Polyether ether ketone (PEEK) materials are increasingly used in industry, including seals in oil and gas equipment and as a bearing surface for orthopedic implants such as knee and hip joints. In many of these applications, the polymer is subjected to loading cycles at varying temperatures. Thus, accurate simulations of PEEK behavior require the constitutive model used for the material to capture time- and temperature-dependent behavior. Despite this need, there are few material models available in commercial software codes capable of capturing the combined effects of temperature, strain rate, and time.
Veryst developed an advanced constitutive model for PEEK to represent its time- and temperature-dependent behavior. First, Veryst designed an efficient test program that probed the temperature-dependent relaxation behavior of a representative PEEK formulation. The results of these tests were imported to the MCalibration® software, which was used to calibrate parameters for the Three Network (TN) model, available in the PolyUMod® library (both software programs developed by Veryst and now available through PolymerFEM.com). Figures 1 and 2 illustrate the final comparison of the calibrated model with experiment. The resulting model can simulate the behavior of PEEK components across a wide range of temperatures using commercial finite element codes such as Abaqus, ANSYS, COMSOL Multiphysics, LS-DYNA, and MSC.Marc.
Figure 1. Stress-strain behavior of a PEEK material subjected to load/unload cycles with intermediate relaxation steps. Solid lines indicate the experimentally measured response. Dashed lines show corresponding predictions given by the calibrated Three Network (TN) model from the PolyUMod library
Figure 2. Corresponding experimentally measured (solid lines) and predicted (dashed lines) relaxation behavior during the stress-strain cycles shown in Figure 1