Thermo-viscoelastic characterization and modeling of a high-temperature stretchable film for foldable electronics applications

Foldable electronics with high thermal stability, flexibility and stretchability enable emerging applications such as soft robotics, electronic skins, human–machine interfaces, and foldable displays. This study presents a detailed thermo-mechanical characterization and modeling of Beyolex™, a recently developed non-silicone-based thermoset polymeric substrate used in stretchable electronics. During operation, Beyolex™ undergoes diverse loading histories, motivating a comprehensive experimental program. We performed tensile tests at various loading rates, along with stress relaxation, creep, and cyclic loading tests. To replicate in-service thermal conditions, experiments were conducted at 25 °C, 75 °C, 90 °C, 125 °C, and 150 °C, covering the full operational temperature range of the material. A finite viscoelasticity-based integral model was developed, formulated from the material’s equilibrium (long-term stress) response. The model was further enhanced to capture thermal effects and stress softening behavior. An iterative root-finding algorithm was developed to simulate the model’s response to both displacement-controlled and force-controlled loading conditions. Finally, a calibration methodology was implemented to fit the model parameters and assess its performance. Simulated results under various loading histories showed reasonable agreement with experimental data, supporting the model’s capability to represent Beyolex™’s thermo-mechanical behavior.