Modeling of Polymer Seals at High Cryogenic Temperatures Across the Glass Transition

Abstract

Abstract. The design of polymer valve seals is challenging especially for cryogenic applications due to a significant stiffening of the polymer material when the temperature falls below its glass transition temperature. This can result in poor sealing and therefore leakage. This study numerically investigates the behavior of a polymer sealing ring used in a pressure control valve in a temperature range from room temperature to cryogenic temperatures at 173 K. To capture the significant change in the material behavior across the glass transition region as well as its characteristics at temperatures below and above, a new thermomechanically coupled model is developed. The model incorporates viscoelasticity to account for the rate-dependent material behavior by extending an existing finite strain thermo-viscoelasticity model with a generalized Zener model. Thermal aspects, such as temperature-dependent material parameters and thermal expansion, and internal heating due to viscous effects, are also taken into account. A key feature of the model is its split of the free energy into an entropic and an energy-dominated part, allowing to incorporate the transition from rubbery to glassy behavior by a temperature-dependent sigmoidal function. Mechanical and thermal material parameters, such as loss and storage moduli, thermal expansion, heat capacity, heat transfer coefficient, and glass transition temperature, are determined experimentally through dynamical mechanical analysis (DMA), differential scanning calorimetry (DSC), and thermomechanical analysis (TMA). Numerical simulations of a pressure control valve demonstrate the model’s applicability for industrial applications. This research contributes to the understanding of the mechanical and kinematic behavior of valves, in particular their polymer seal seats, at cryogenic temperatures.