Monotonic torsion behaviour of printed polylactic acid -preliminary insight into printing parameters

Additive manufacturing with polymer materials has been extensively studied for various load; however, limited research exists on characterization under torsional loads. Torsional stress often occurs in power transmission systems, gears, axles, aircraft wings, and biomedical devices such as bones. This study focuses on the monotonic characterization of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>P</mml:mi> <mml:mi>L</mml:mi> <mml:mi>A</mml:mi> </mml:math> under torsional load to determine the effect of printing parameters. Specimens with square, rectangular and cylindrical cross-sections were 3D-printed in three different orientations using an extrusion technique with full infill percentage. These specimens were then tested under tensile and torsional loads until failure to experimentally analyze their behavior. Torsional test results for three geometric cross-sections were compared to provide insights into the development of torsion-subjected components, based on their cross-section and printing angles. This exploratory study offers valuable insights into the mechanical characterization of 3D-printed components under torsion. The results indicate that the orientation during the extrusion process significantly influences the mechanical strength of the component. Although the prediction of torsion behavior using analytical tools shows an error of less than 20% with a printing orientation of 90°, the prediction accuracy decreases significantly at a printing orientation of 45°, with an error exceeding 32%. The mean error at this orientation varies depending on the geometry. Conversely, at a 0° orientation, the prediction error averages around 25%. Optimal performance was observed at a 0° orientation for both ultimate resistance and the angle reached before failure. Regarding cross-sectional geometry, cylindrical geometry provided the best resistance under torsional loads, followed by square, and finally rectangular.