On-demand auxeticity and co-existing pre-tension induced compression stage in a sandwich design with kinematically constrained 3D suture tiles.

By incorporating concepts from auxeticity, kinematic constraints, pre-tension induced compression (PIC), and suture tessellations, tiled sandwich composites are designed, demonstrating behaviors attributed to the synergy between auxeticity and pre-tension induced contact and compression, simultaneously triggered by a threshold strain. The designs can theoretically achieve on-demand Poisson's ratio in the widest range (-∞, +∞), and once triggered, the Poisson's ratio is stable under large deformation. Also, once the overall strain goes beyond the threshold, the designs enter into a PIC stage, ensuring the middle soft layer takes the tensile load, while the tiles are under compression via contact and the 3D articulation of the tooth-channel pairs. In this PIC stage, the tooth-channel pairs provide kinematic constraints via the contact and relative sliding between teeth and channels. The deformation mechanisms and mechanical properties of them are systematically explored via an integrated analytical, numerical, and experimental approach. Mechanical experiments are performed on 3D printed specimens. It is found that the length aspect ratio and the obliqueness of the teeth significantly influence the constraint angle and therefore the auxeticity and strength of the designs.

Direction-dependent bending resistance of 3D printed bio-inspired composites with asymmetric 3D articulated tiles.

Inspired by the protective armors in nature, composites with asymmetric 3D articulated tiles attached to a soft layer are designed and fabricated via a multi-material 3D printer. The bending resistance of the new designs are characterized via three-point bending experiments. Bending rigidity, strength, and final deflection of the designs are quantified and compared when loaded in two different in-plane and two different out-of-plane directions. It is found that in general, the designs with articulated tiles show direction-dependent bending behaviors with significantly increased bending rigidity, strength, and deflection to final failure in certain loading directions, as is attributed to the asymmetric tile articulation (asymmetric about the mid-plane of tiles) and an interesting sliding-induced auxetic effect. Analytical, numerical, and experimental analyses are conducted to unveil the underlying mechanisms.