Characterizing the feasibility of processing wet granular materials to improve rheology for 3D printing

Rheological measurements and extrusion tests are used to evaluate the viability of high mass fraction (80% solids content) wet granular materials for extrusion-based 3D printing. Such materials have diverse applications from making dense, strong ceramic custom parts to 3D printing uniquely shaped energetic materials. Traditionally, 3D-printed colloidal materials use much lower mass fraction inks, and hence, those technologies will not work for systems requiring higher mass fraction solids content. These wet granular materials are highly non-Newtonian presenting non-homogenous flows, shear thinning, yield stress, and high elasticity. Such behaviors improve some aspects of print quality, but make printing very difficult. In this work, the relationship between the rheological behavior of wet granular materials and the processing parameters that are necessary for successfully extruding these materials for printing is examined. In the future, such characterizations will provide key indicators on how to alter printer design/operating conditions and adjust material behavior in order to improve printability. This study is a fundamental first step to successfully developing 3D printing technology of wet granular materials.