Development of a tensile test procedure for unit lattice structures produced by material extrusion additive manufacturing

Abstract

With advancing technology, additive manufacturing (AM) has revolutionized various fields, from engineering to medicine. Lattice structures additively manufactured with polylactic acid (PLA) material stand out for their innovative designs and versatile applications. Upon reviewing the literature, it is noted that a test setup needs to be developed to investigate the impact of geometric variations due to AM on the fracture behavior of unit lattice structures. The aim of this study is to develop a tensile test procedure to characterize the mechanical properties of individual lattice cells fabricated by material extrusion AM technique from PLA. Variations of the mechanical properties are also determined by a high number of samples. Given the large number of identical samples, successful and reproducible holding and alignment of the lattice cells on the tensile test machine are essential. For this purpose, various holding fixture alternatives were investigated to effectively bond the lattice cells on the fixtures by a high strength adhesive. The tensile testing process was recorded with a camera, and deformation and fracture behaviors were examined from the camera footage. When the tensile test results were analyzed in graphs, various plateaus were observed in the section identified as the elastic region. Upon examining these plateau formations in video recordings and the test system, they could be due to two factors. First, the formation of this plateau could be related to the curing time and cross-link formation of the epoxy adhesive used. Second, it could be due to the linearity between the bonding surface and the sample. Based on the results, it was shown that the developed tensile testing procedure can be used to characterize the mechanical properties of lattice cells.