Numerical and experimental investigation on creep response of 3D printed Polylactic acid (PLA) samples. Part I: The effect of building direction and unidirectional raster orientation.

The main aim of this research work is to investigate the effects of building directions and raster orientations on the creep behavior of 3D-printed plastic material and to develop rheological constitutive models to estimate the creep behavior of components. These components have been manufactured through the Fused Deposition Modeling (FDM) technique in which materials are heated and extruded through a nozzle to create 3D Polylactic acid (PLA) specimens. Since 3D-printed specimens exhibit anisotropic behavior, studying their building condition is necessary. Both building direction and raster orientation are among the fabrication conditions that play a major role in the mechanical behavior of the specimens. The tensile behavior of 3D-produced PLA specimens and their creep behavior were evaluated. To model the creep behavior of 3D printed PLA, three different types of rheological constitutive models, Zener, Burgers, and modified Burgers were used analytically and numerically. The finite element (FE) model of the 3D printed unnotched samples was developed to predict the creep behavior of notched samples. The results show that 3D FE models can predict the creep behavior of AM-notched specimens with high accuracy.