Porosity and Mechanical Properties of PLA Structures Printed by FFF-3D-Printing Process with Actual Case Study

This paper is focused on the characterization of PLA parts elaborated by additive manufacturing. Fused Filament Fabrication (FFF) 3D-printing process was used to obtain both tensile specimens and lifting-eye. The tensile specimen was used to identify the porosity and mechanical properties. The lifting-eye was taken as a case study. Although the specimens were prepared with 100% infill density, the actual cross sections and macrographic analysis revealed a non-negligible percentage of porosity varying from 7 to 9%. Engineering stress-strain curves were determined for different raster angles. Results revealed relatively a low dependence of the stress-strain curve on this parameter. In addition, a short region was observed from the yield point to the onset of diffuse necking. Nevertheless, a large region was relatively shown before necking. The case study was undertaken by the free-shape optimization procedure to find the best inner shape allowing high strength when the lifting-eye is under imposed load. The optimization was performed based on the mechanical characteristics already identified. A specific prototype associating two lifting-eyes was designed, fabricated by 3D-printing process and tested with pulling test. This showed the relevance of the characteristic determination from our own experiments and the validation of the developed optimization.