Tuning the mechanical properties of architectured materials: from sandwich beams to triply periodic minimal surface composite lattices

The continuous improvement of additive manufacturing techniques is enabling the fabrication of an emerging class of materials, named architectured materials, where individual constituents with different mechanical properties are combined at the mesoscale into a rich variety of spatial arrangements, engineered for enhancing mechanical performance. The design of such architectured materials can profit from the construction principles found in biological materials, which are finely tuned by evolution and often results in mechanical properties higher than expected from the individual constituents [1]. In this work, we exploit multimaterial PolyJet 3D printing to fabricate cellular solids with individual beams featuring a hybrid sandwich-like design, with the final goal of tuning and improving mechanical efficiency. Firstly, the flexural behavior of sandwich beams having a compliant core reinforce by two stiff faces is investigated for different core-to-face ratios using 3-point bending tests combined with Digital Image Correlation (DIC). The core is fabricated with a rubbery material (commercial name Shore95, Young’s modulus of about 100 MPa) while for the faces a rigid glassy material is used (commercial name Vero White, Young’s modulus of about 2 GPa). Our results reveal that distinct failure modes can be obtained not only depending on the core-to-face ratio but also on the interface gluing the faces to the core. Indeed, as a function of printing orientation, interfaces between face and core materials can either be sharp (i.e. < 20 µm) or blurred (i.e. > 150 µm) [2]. For the same core-to-face ration, blurred interfaces reduce delamination and improved flexural strength. We also highlight that for small core-to-face ratios, an increase in energy absorption (+30%) can be obtained with respect to a monolithic beam. Current research focuses on characterizing energy absorption capacity of composite honeycombs and triply periodic minimal surface (TPMS) lattices featuring sandwich-like walls. [1] Zorzetto and Ruffoni, Advanced Functional Materials (2018), 1805888 [2] Zorzetto et al., Scientific Reports (2020), 10:22285