Microstructures and failure in 3D printed viscous materials

Additive manufacturing using high-viscosity pastes containing a large fraction of solid particles offers advantages in terms of high part densities, reduced slumping during printing and less shrinkage during postprocessing. The challenges in extruding these mixtures through fine nozzles can be overcome by vibration assisted printing (VAP), which can rapidly 3D print extremely high viscosity materials. The mechanical properties of printed parts and their relation to microstructural features using viscous pastes is not well understood, which can be influ-enced by the large volume fraction of particles. This work aims to investigate the effect of printing of high viscosity materials on their morphology and mechanical behavior. A commercial polymer clay was used for 3D printing tensile test specimens, along with molding of reference samples. Mechanical properties and fracture morphology were characterized using a microtensile tester inside and outside of a scanning electron microscope (SEM) in-situ. Additionally, x-ray computed tomography was used to study the porosity and fracture morphology of the samples. The average strength of printed polymer clay was comparable to molded samples, though fracture locations were different, primarily due to weak spots and gaps arising from 3D printing tool paths generated by a commercial slicer. The intertrack strength in these parts appeared to be as strong as the bulk of the material as there was no discernable delamination within the gauge section of the samples that had alternating 45/- 45 degrees track orientations with some of the tensile load acting at interfaces. Optimal printing parameters and slicing paths could further reduce defects in the microstructure of the printed samples, producing comparable me-chanical properties between printed and cast or molded materials.

Automated summary

Additive manufacturing with high-viscosity pastes can improve part density, reduce slumping and shrinkage. Vibration assisted printing (VAP) is effective in extruding high viscosity materials. However, the mechanical properties and microstructural features of printed parts using viscous pastes are not well understood. This study aims to investigate the effect of printing high viscosity materials on morphology and mechanical behavior.