Analysis of notch effect in the fracture behaviour of additively manufactured PLA and graphene reinforced PLA

The fracture assessment of additively manufactured PLA and graphene reinforced PLA (PLA-GR) has been performed in this paper. Tensile and fracture specimens were fabricated with three different raster orientations (0/ 90, 30/-60 and 45/-45) in order to analyse the effect of the printing strategy on the resulting mechanical properties. A total of 30 tensile tests and 120 fracture tests were performed, covering fracture samples with defects of different notch radii (0 mm, 0.25 mm, 0.5 mm, 1 mm and 2 mm). The Theory of Critical Distances was applied over the fracture results, obtaining estimations of the corresponding critical distances and the subsequent predictions of the apparent fracture toughness. Graphene addition has a different effect depending on the raster orientation. Graphene causes a significant improvement of tensile and fracture properties for specimens fabricated at 30/-60 and 45/-45. However, this phenomenon is not observed in raster orientation 0/90. SEM analysis shows a clear change in the fracture micromechanisms between PLA and PLA-GR. It can be also observed how graphene samples of 30/-60 and 45/-45 present a similar aspect of the fracture surfaces, which are different from those observed in raster orientation 0/90.