Visco-hyperelastic computational model for injection-molded thermoplastic polyurethane

Accurate predictive modeling and simulation is crucial for designing and utilizing components in engineering, manufacturing, and other applications. To describe the complex mechanical response of injection-molded thermoplastic polyurethane (TPU), particularly its nonlinear elastic and viscous properties, we present a visco-hyperelastic computational model. The model is derived from a strain energy density function, formulated as a combination of elastic and viscous components. To account for compressibility of TPU, the elastic part of the strain energy function is further divided into isochoric and volumetric contributions. Mechanical characterization involved extracting standard specimens from an injection-molded slap of TPU and subjecting them to uniaxial loading at four distinct strain rates. The material parameters were identified through optimization using the Nelder-Mead algorithm. The presented model is then demonstrated to successfully capture TPU’s complex mechanical response with a unified set of parameters. Key advantages of the model include easy identification of material parameters, compliance with thermodynamic principles, ease of implementation in finite element analysis, and accurate description of large nonlinear elastic behavior and strain-rate dependency.