Tensile deformation behavior and phenomenological constitutive model of PEEK over a wide temperature range

• PEEK’s high-temperature tensile behavior modeled via glassy–rubbery phase competition. • Dual-parameter phase evolution improves constitutive prediction accuracy. • Strain-dependent piecewise model distinguishes elastic and plastic stages. This study investigated the tensile deformation behavior of polyetheretherketone (PEEK) over 30 °C–310 °C through experimental measurements and constitutive model development. Uniaxial tensile tests were conducted to obtain stress–strain response data at different temperatures, revealing the evolution of mechanical properties during the phase transition from the low-temperature glassy state to the high-temperature rubbery state. Experimental results demonstrated that PEEK exhibited linear elastic behavior with a high elastic modulus and yield strength at temperatures between 30 °C and 110 °C, reflecting the energy storage characteristics dominated by the glassy state. The material displayed significant nonlinear viscoelastic response and strain softening phenomena in the glass transition region (150 °C–190 °C). Above 230 °C, PEEK transitioned into the rubbery state, characterized by pronounced viscous flow behavior and a drastic reduction in elastic modulus and yield strength. Based on these observations, a phenomenological constitutive model incorporating contributions from both the glassy and rubbery states was proposed. By introducing a temperature-dependent volume fraction evolution function, the model couples the two-phase contributions to describe PEEK’s mechanical behavior across a wide temperature range. The proposed model provides a more comprehensive description of PEEK’s tensile response across the wide temperature range, particularly excelling in capturing phase competition mechanisms during glass transition.