Cyclic Fatigue Failure of Perforated 3D-Printed Polylactide (PLA) Specimens by Inserted Pin Loading

The failure of 3D-printed Polylactide (PLA) specimens with circular holes was studied under tensile and cyclic loading, respectively, by an inserted pin. Experiments were conducted for the perforated PLA specimens with various print angles from 0° to 90°, as well as [0°/90°]s and [0°/±45°/90°]s. The hole locations varied along the specimens. The PLA specimens showed two different failure modes: one through the print lines and the other between the print lines. Different print angles resulted in different tensile failure stresses under pin loading. The cyclic tests of different print angles showed very similar S-N data as the applied stresses were normalized to their tensile failure stresses if the failure mode was through the print lines. On the other hand, cyclic failure between print lines showed distinctly separated S-N data, even with the normalized applied stresses. The tensile failure stresses, failure locations, and orientations were successfully predicted using the failure criterion that is based on both stress and stress gradient conditions. A proposed mathematical interpolation equation provided good estimations of the tensile failure stresses and S-N curves of specimens with different print angles once the failure stresses were known for the 0° to 90° specimens.