This research is investigating the mechanical response of high-performance athletic footwear through static and dynamic testing. The material at hand, an expanded thermoplastic polyurethane (E-TPU), has only recently been introduced to the midsole application which is responsible for damping and energy return in a running shoe. Findings reveal reasons and ways to avoid variance when testing a closed-cell foamed material like the E-TPU. The static test data is used to fit a hyperelastic model to predict the behavior of the rubberlike material through finite element analysis. Dynamic test data is used for investigating the nonlinear viscoelastic properties of the material.
To accurately describe nonlinear viscoelastic behavior present for large or rapid deformations, a new model is adapted as a variation of common Prony Series which only describes linear viscoelasticity. This new model is mathematically derived and verified on the simple load case of uniaxial compression. Future research will investigate possible applications of the model to other rubber or rubberlike materials which frequently express nonlinear-viscoelastic behavior which may allow for more accurate predictions.
Simulation of a three-point bending test as a verification of the hyperelastic model