Effect of crack tip geometry and in situ compression rolling on fracture failure mechanisms in poly-lactic acid (PLA) extrusion-based additive manufacturing

Improving the mechanical strength and fracture failure properties of polymer parts printed through material extrusion remains an ongoing challenge in polymer additive manufacturing. This work presents experimental investigation of fracture properties of poly-lactic acid (PLA) polymer parts printed using a material extrusion process with an in situ post-extrusion compression roller. Center cracked samples with three different crack tip geometries are printed with in situ compression rolling and tested to investigate the nature of fracture process. Samples with raster direction along and orthogonal to the loading direction are tested. The crack propagation process is studied using high-speed imaging and microscopy. Tensile strength of samples with in situ compression rolling and circular notch is found to be 20.7 MPa, compared to 6.0 MPa for the baseline part. The mechanism of sample failure is found to be either fracture-driven or filament–filament interface-failure driven, depending on the crack tip geometry and raster orientation. The modes of failure for baseline and rolled samples for different loading conditions are studied and interpreted. Results presented here contribute toward the understanding of fracture properties of 3D-printed PLA samples, as well as the general design of 3D-printed fracture test samples.