Anisotropic and hyperelastic mechanical response of 3D printed TPU parts

Abstract

Thermoplastic polyurethane (TPU) is usually considered isotropic and hyperelastic. Nevertheless, when 3D printing techniques as fused deposition modelling (FDM) are used, an anisotropic behaviour (inherent to the process) is expected. The aim of the present research is to analyse the isolated effect of the raster angle on the mechanical response of 3D printed TPU parts. To avoid other effects, several specimens were manufactured with 100% infill density and parallel straight lines infill pattern. Four different printing configurations were analysed, 0°, ±45°, 90° and concentric pattern. The specimens were subjected to tensile loading and obtained data was used as input to fit three hyperelastic behaviour models, specifically the neo-Hookean, Ogden and Mooney–Rivlin models are compared. The obtained results show that the raster angles have a cleareffect on the mechanical properties of the 3D printed parts, leading to an anisotropic behaviour of the obtained specimens and on the appearance of the different stages of the hyperelastic behaviour. In addition, the fitting models used allowed to conclude that the neo-Hookean model is the best fitting the initial linear-elastic zone, while for the whole stress–strain curve, both the Ogden and Mooney–Rivlin models produce very good approximations.