Characterization of the non-isotropic tensile and fracture behavior of unidirectional polylactic acid parts manufactured by material extrusion

This study presents a comprehensive characterization of the fracture and tensile behavior of unidirectional polylactic acid (PLA) parts manufactured by material extrusion (MEX). The effect of the crack tip to filament orientation angle on the fracture behavior was investigated through three-point bending on single-edge notch bending (SENB) specimens printed at seven different build angles. The fracture test results show a brittle behavior for inter-layer fracture and a more ductile behavior for cross-layer crack propagation. Specimens with a 20 degrees build angle required the most energy for the crack to extend completely, exhibiting mixed cross -and inter-layer crack propagation. The elastic properties and the ultimate strength distribution were measured through tensile tests on dogbone specimens printed at five different build angles. The experimental stiffness and strength distributions show good agreement with the orthotropic material model and the Tsai-Hill strength criterion, with a maximum model error of approximate to 10%. The printed mesostructures and the fracture surfaces were observed with scanning electron microscopy (SEM). Finally, differential scanning calorimetry (DSC) was used to evaluate the level of crystallinity in the printed structures. The resulting data allows the development of fracture models able to capture the complete failure behavior of MEX fabricated parts.

Automated summary

This study comprehensively characterizes the fracture and tensile behavior of unidirectional PLA parts manufactured by MEX. The effect of crack tip to filament orientation angle on fracture behavior was investigated through three-point bending tests on SENB specimens printed at different build angles. Tensile tests on dogbone specimens were also conducted to measure the elastic properties and ultimate strength distribution. SEM was used to observe the printed mesostructures and fracture surfaces, and DSC was used to evaluate the level of crystallinity in the printed structures. The resulting data allows the development of fracture models for MEX fabricated parts.