Effects of Print Orientation on Mode-I Fracture Toughness of Additively Manufactured PLA: Simulation by XFEM

In engineering applications, considering the growing utilization of Polylactic acid (PLA) material manufactured through material extrusion (MEX) additive manufacturing techniques, it becomes imperative to predict its fracture behavior to assess damage thoroughly under various loading scenarios. As an initial step, this study focuses on determining the Mode-I fracture toughness of the PLA material manufactured by MEX in three different print orientations through a three-point (3P) bending fracture test. The raster angle utilized to fabricate the single-edge notch bending (SENB) specimens was chosen as ±45°. Three different print orientations were used to investigate the effects of printing direction (i.e., horizontal, lateral, and vertical) on the fracture properties. The fracture properties were extracted per the standard ASTM D5045-14 on the specimens fabricated in three different print orientations. The values of Mode-I fracture toughness of PLA were respectively obtained as 4.22, 4.18, and 3.56 MPa/m with horizontal, lateral, and vertical print orientation. Then, corresponding fracture energy values were calculated for numerical investigations. A commercial finite element package was utilized to employ the extracted values into the extended finite element method (XFEM) and investigate the crack propagation in the specimens. It was found that the numerical analyses well simulated the crack propagation and peak load (damage initiation point) experienced in the SENB specimens tested under 3P bending loading.