Material Characterization of 3D-printed Silicone Elastomers

Abstract

Silicone elastomers can be tailored to a broad range of mechanical properties and find application in damping, sealing, biomedicine, mold making, or prototyping. For additive manufacturing of silicone elastomers there are several approaches such as sub-surface catalysis, photo- or temperature-initiated polymerization feasible, which can further be divided in silicone extrusion, drop-on-demand, and vat photopolymerization. Many suppliers provide print services for silicone rubber components, nevertheless printing soft materials is still demanding and few printer component suppliers can be found. The processing (time-temperature history) of the cross-linked silicone rubber influences the properties of the 3D-printed part. Therefore, reliable material parameters are needed for product engineering and mechanical simulation. The objective of this work is to characterize and analyze the mechanical behavior of two 3D-printed silicone rubbers. Also, various infill amounts are examined to study the change of apparent hardness (structural macroscopic hardness) of the specimen. We developed an extrusion-based silicone 3D-printer with temperature-initiated polymerization using the print head vipro-HEAD 3/3 (ViscoTec Pumpen- u. Dosiertechnik GmbH, Germany). The print-parameters were optimized for SilasticTM 3D 3335 (Dow, Michigan), which is currently the only commercially available material for this purpose (Shore A 50). Uniaxial tensile as well as compression, biaxial tension, and pure shear tests were performed to characterize the mechanical behavior of the 3D-printed specimens at different loading rates. Hyperelastic material models were fitted and compared in terms of the accuracy to accommodate the material behavior at room temperature. For a second softer silicone rubber (Shore A 10), the print parameters were optimized, and cubes were tested in compression. It could be shown that the harder material can reach lower apparent hardness than the softer material, when the infill amount is adjusted accordingly.