Characterize the high-temperature steady-state rheological behavior and Arrhenius activation of PEEK via strain rate jump tensile tests

Polyetheretherketone (PEEK) is a high-performance thermoplastic polymer with diverse industrial applications, such as aerospace, automotive, electronics, and medical devices. However, systematic research on its high-temperature rheological characteristics is inadequate. In this study, strain rate jump tensile tests were introduced to examine the steady-state rheology phenomena and strain rate sensitivity of PEEK at four different temperatures and nine different strain rates. Theoretical analysis based on the free volume theory and the Arrhenius law was also carried out to further analyze the transition of PEEK from Newtonian flow to non-Newtonian flow. Results indicate that PEEK materials exhibit a transition from Newtonian flow to non-Newtonian flow similar to metal materials at high temperatures. The transition point from Newtonian flow to non-Newtonian flow is marked by the emergence of steady-state rheology and its characteristic stress. Theoretical analysis demonstrates that the transition of PEEK is in accordance with the Arrhenius low. Moreover, its apparent activation energy (1.42 eV) is significantly lower than that of metal materials (5.28 eV), indicating a lower energy barrier and an easier transition. The strain rate sensitivity index correlates negatively with rising temperatures, especially at lower rates. This study enhances understanding of PEEK's rheological characteristics at high temperatures, aiding the development and application of high-performance thermoplastic materials.