Mechanical Properties of Thermoplastic Polyurethane-Based Three-Dimensional-Printed Lattice Structures: Role of Build Orientation, Loading Direction, and Filler.

This study addresses the influence of build orientation and loading direction on the static and dynamic mechanical properties of three-dimensional-printed thermoplastic polyurethane-based lattice structures (with different cell shape). Specimens were printed in horizontal, 45° angle, and vertical orientations. Three-point bending tests showed that the investigated specimens are characterized by a strong anisotropy of the mechanical properties, which depends on the loading direction. In this regard, the influence of the loading direction is much stronger for the specimens printed vertically or at an angle of 45°, whereas the properties of the lattice structures printed horizontally are almost isotropic. The best set of mechanical properties (regardless of the loading direction) is shown by the samples of lattice materials, with square cells obtained by horizontal orientation of the polymer layers. The possibility of significant (one order of magnitude) increase in strength properties with satisfactory ductility is shown by using an epoxy polymer as a filler. A mathematical model of the bending of a mesostructured beam was established, which made it possible to describe qualitatively the various mechanisms of its destruction, such as: the breaking of the bonds between the polymer layers due to their mutual sliding and flaking, and the rapture of the layers themselves. The findings presented here provide new insights into the development of lattice structures with unique mechanical properties for a wide range of applications.