Investigation of Tensile, Viscoelastic, and Viscoplastic Behavior of Polylactic Acid Manufactured by Fused Deposition Modeling

Uniaxial tensile and uniaxial loading-unloading experiments are performed to characterize the mechanical properties of polylactic acid (PLA) manufactured by fused deposition modeling (FDM). To investigate viscoelastic and viscoplastic properties of PLA manufactured with FDM, uniaxial loading-unloading tensile tests are conducted at different strain rates. In addition, the influences of layer orientation on the mechanical properties of PLA specimens manufactured by FDM are investigated. The specimens are manufactured with a vertical and horizontal orientation. The influence of strain rate on ductility is also investigated. Decreasing the strain rate leads to an increase in strain at break. This increase in ductility is interpreted as a result of the effect on secondary bonds. Viscoplastic deformation followed by fracture is seen at lower strain rate tests. As stress and stiffness increases, ductility decreases. More ductility is seen at the horizontally oriented specimens than the vertically oriented specimens. On the other hand, the influences of layer orientation on the mechanical properties of PLA specimens are also investigated. It could be said that the tensile behavior is strain rate and manufacturing orientation dependent. As expected, the higher strain rate values yield to more brittle behavior. More brittle behavior is also reported at vertically oriented specimens. To compare with FDM specimens, injection-molded specimens are produced, and more brittle behavior is observed. Uniaxial loading and unloading tensile tests are also performed for the same specimens. It is observed that elastic recovery increases with increasing strain rate. Results showed that printing orientation does not have a major effect on elastic recovery.