Multi-step deformation lattice structures from the rotation of unit cell

A multi-step deformation lattice structure (MSLS) is introduced. MSLS can exhibit multiple deformation pathways under compression. It leads to multi-stress plateaus in the stress–strain relationship. The underlying mechanism is caused by the rotation of the unit cell that composes the structures. Analytical models of plateau stress is first established based on the plastic hinge dissipation principle and is validated by experiments. By studying the MSLS composed of different unit cells rotated with different angles, four stress–strain relationships are obtained. Furthermore, the Young's modulus and the yield strength of MSLS show a tendency of decreasing and then increasing with the increase of rotation angle. Moreover, the rotation angle can lead to a transition of the MSLS between bending-dominated behavior and stretching-dominated behavior. Finally, it is found that MSLS has a negative Poisson's ratio and a minimum value is −0.9, and Poisson's ratio tends to zero rapidly when strains is larger than 0.3. This work provides new insights into the use of rotating unit cell to create multi-step pathways and auxetic lattices that can be used to design engineering structures with multiple tasks and application for impact protection.