MODELING OF A THERMOPLASTIC-POLYURETHANE AND ITS POTENTIAL FOR ENERGY DISSIPATION DEVICES

This paper presents the testing and constitutive model calibration of a Thermoplastic Polyurethane (TPU) compound utilized in commercial TPU components, and explores the potential of this material to be used in response modification devices. Testing specimens were obtained from a TPU sphere used for check valves, acquired through water-jet cutting. Various tests, including tensile and compression tests under complex uniaxial loadings, were conducted to capture nonlinear phenomena such as stress softening, hysteresis, relaxation, creep, and rate dependence. The material is modeled with a nonlinear elastic equilibrium path incorporating stress softening (Mullins effect) and a hysteretic viscoplastic response exhibiting rate dependence at three different time scales. The Parallel Rheological Framework is employed to achieve this constitutive behavior. The Generalized Yeoh hyperelastic model represents the nonlinear elastic equilibrium path, while the Ogden-Roxburgh damage model is employed to model stress softening. The hysteretic viscous response is decoupled into three viscoplastic chains, each modeled using the Bergstrom-Boyce model with standard creep strain evolution laws. Model parameters were determined using a stochastic optimization scheme to fit all the considered tests simultaneously, demonstrating an outstanding agreement with experimental data across a wide range of loading scenarios. The optimal parameters were used to perform finite element simulations and obtain the hysteretic force-deformation relationship of a response modification device that may use the material in compression (e.g., dampers in chevron configuration) to illustrate the material potential for earthquake engineering applications.