Super elastic-plastic behavior of the surface grooves resulting in tensile anisotropy of 3D-printed elastomers

It is popularly acknowledged that additively manufactured polymer parts normally demonstrate mechanical anisotropy owing to their layer-wise characteristics with insufficient interface bonding. For 3D-printed rigid thermoplastic objects, such anisotropy has been largely reduced or even eliminated by accurately measuring the actual load-bearing area using microscopy technology. However, this method becomes not effective anymore when it comes to the 3D-printed elastomers, of which the origin of mechanical anisotropy is rarely regarded in literature. For this reason, we proposed a supplementary explanation of the tensile anisotropy based on an investigation of the mechanical dependence of 3D-printed thermoplastic polyurethane on the formed microscopic features. Seven categories of tensile specimens with varying microscopic features, including layer counts, layer height, surface groove angle, and bonding area, were fabricated by material-extrusion printing technology. The distinctive deformation process of these features during tensile testing process was analyzed, on which the dependence of both the stress-strain behavior of the as-printed elastomers and their failure mechanism were discussed with respect to the elastic-plastic behavior of elastomer. Ultimately, the tensile anisotropy was found to be primarily dependent on the surface grooves which contribute to a significant stress concentration effect during the tensile process.