Characterization of 3D Printed Cementitious Auxetic Composites under flexural loadings

Auxetic materials inherently have high energy absorption properties due to Negative Poisson’s Ratio (NPR) characteristics, which enables them to contract (or expand) in all direction when compressed (or tensioned) along their longitudinal axis. Recent, advances in 3D printing allows rational designing and development of these materials for desired properties. In this research, 3D printed re-entrant chiral auxetic (RCA) geometries by combining the conventional re-entrant auxetic shape and chirality for high NPR and energy absorbing characteristics were developed. Polylactic Acid (PLA) filament which is a sustainable printing filament was used for 3D printing of these geometries. These geometries were then embedded in cementitious matrix as reinforcement to exploit their NPR characteristics to enhance their energy absorption capabilities of cementitious composites. Consequently, three different cell-sizes of RCA geometries were designed to investigate their influence on the overall behaviour of cementitious composites. In total, 36 prismatic composite samples with embedded 3D printed auxetic reinforcement were developed of 20 mm thickness and various widths and lengths. The samples were tested under subjected to bending through three-point loading. The loading rate was also varied from 1 mm/min, 75 mm/min, 150 m/min to 300 mm/min to study behaviour of composites for their application in building protection from high-speed impact loads. The results were analyzed in terms of failure modes, load-displacement curves and energy absorption levels. All RCA geometries exhibited equally to increase the flexural resistance, energy absorption and ductility of cementitious matrix, however, the RCA geometries with larger cell sizes provided enhanced benefit under relatively high-speed loading of 300mm/min.