Fatigue performance of fused filament fabrication PLA specimens

This paper aims to analyze the fatigue response of PLA parts manufactured through fused filament fabrication (FFF). The influence of four factors (layer height, fill density, nozzle diameter and velocity) on the fatigue performance of cylindrical specimens is studied through an L27 Taguchi experimental design. This design is run for two different infills: linear and honeycomb. Specimens have been tested on a rotating fatigue bending machine. The optimal set of parameters and levels resulting in the highest number of cycles to failure have been determined, and implemented to manufacture a second set of specimens, which have been tested at different stress levels to represent the Wöhler curve. Fill density proves to be the most influential parameter on fatigue life, followed by layer height. The tests undertaken to represent the Wöhler curve revealed that 35.8 MPa can be considered as a lower threshold of the endurance limit for this kind of specimens. This value can be useful to use these devices to manufacture human implants, as PLA is a biocompatible material. The main novelty of this paper is that no previous fatigue life assessment of PLA parts manufactured through FFF has been developed.