3D Printing and Mechanical Performance of Silicone Elastomers

Abstract

3D printing of soft, elastomeric materials has potential to increase the accessibility while decreasing the cost of customizable soft robotics and biomedical devices. In this work, the steps to building a 3D printer capable of printing with an extrudable liquid are described. A moisture-cure room temperature vulcanizing (RTV) silicone elastomer was 3D printed. The relative density of printed specimens was determined as a function of infill density specified in the software and the relationship was found to be non-linear and dependent on the sample geometry. Printed test specimens with a range of infill densities and several infill geometries were characterized under uniaxial tension and compression. In tension, the stress-strain behavior is non-linear over the entire curve. Ultimate tensile strength was relatively unaffected by infill density over a range of relative densities from 0.35 to 1.0, while extension at break decreased with increasing infill density. The apparent Young’s modulus was determined in the small-strain limit and is tunable from 310-1150 kPa by adjusting the infill density. Tensile strength of fully-dense printed samples (1150±30 kPa) is comparable to that of the bulk cast samples (1150±40 kPa), indicating good performance of the printing process and few defects. In compression, three different infill patterns and a range of infill patterns were tested. The specimens exhibit stress-strain behavior typical of foams—a linear elastic region with a modulus dependent on infill density, followed by a buckling plateau region and densification at high strains. Negative stiffness due to snap-through buckling was observed in some cases. Results for both tension and compression tests show the tunability of mechanical response achievable through changing the software infill density.