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Nowadays, polymer parts made by additive manufacturing methods (AM) have multiple applications in various industries. Different parameters affect the print quality of the parts and subsequently their mechanical properties. In this study, the effect of the print direction in 3D-printing on the high-cycle bending fatigue properties of polymer parts made by the fused deposition modeling (FDM) method has been investigated. The standard samples of the fatigue test were printed in both horizontal and vertical directions and were made of two polymers, PLA and ABS. The thickness of each layer was 0.15 mm and the infill percentage of the parts was 50%. The rotary bending fatigue test was performed under conditions of fully-reversed stress-controlled loading at different stress levels. The results included the stress amplitude versus the fatigue lifetime of FDM 3D-printed PLA and ABS polymers. Besides, the scanning electron microscopy (SEM) image of the fracture surface was also depicted after fatigue testing. Results showed that PLA specimens had better fatigue lifetimes than ones of ABS samples. Moreover, the fatigue strength of 3D-printed samples in the horizontal direction was higher than that of 3D-printed specimens in the vertical direction. The print direction, the material and the stress level were found to be statistically significant factors from the analysis of variances. The SEM image demonstrated beach marks on the fracture surface of fibers (3D-printed filaments) in the PLA specimen, which proved cyclic loadings. Then, cleavage facets were the result of the brittle fracture.
Azadi et al. (Sat,) studied this question.