Tensile failure strength and separation angle of FDM 3D printing PLA material: Experimental and theoretical analyses

It is discovered in this investigation that there exist two different failure modes and a special separation angle which is the demarcation point of the two different failure modes when FDM (Fused Deposition Modelling) 3D printing materials fail under a tensile load. In order to further understand the mechanical properties of FDM 3D printing materials and promote the use of FDM 3D printing materials, their tensile failure strengths at different printing angles and separation angles are measured and analysed theoretically. A new separate-modes of transversely isotropic theoretical failure model is established to predict the tensile failure strength and separation angle of FDM 3D printing PLA (polylactic acid) material based on the hypothesis of transverse isotropy and the classical separate-modes failure criterion. During this research, the tensile specimens designed according to the current test standard ISO (527-2-2012) for plastic-multi-purpose specimens are fabricated in 7 different printing angles (0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, 90 degrees) and three levels of printing layer thickness (0.1 mm, 0.2 mm, 0.3 mm). Experimental results show that the tensile failure strength increases with the increase of the printing angle or the decrease of the layer thickness. Meanwhile, inter-layer failure tends to occur when the printing angle is small and in-layer failure tends to occur when the printing angle is big. In comparison with the results predicted by the established theoretical model, all values of the Generalized-Relative-Root-Mean-Square Error are close to zero and the experimental separation angles are also between 45 degrees and 60 degrees. So the predictive capacity of the theoretical model is affirmed by experimental results.