The Push Drill Mechanism as a Novel Method to Create 3D Mechanical Metamaterial Structures

Two of the most prominent 2D auxetic mechanisms, namely, the rotating rigid unit and the chiral systems, work, at least partly, by converting linear to rotational motion. This property can be harnessed by introducing a system that can convert back the rotational motion to a linear displacement so as to induce an expansion or a compression in the out-of-plane direction. The push drill mechanism offers an effective way of providing this capability. It is, hence, possible to couple 2D rotating rigid unit or chiral structures to the push drill mechanism to create novel 3D auxetic structures. The resultant Poisson's ratio in the out-of-plane direction can be both negative and positive depending on the connectivity. Herein, the concept is illustrated with the use of rotating squares. An analytical model is derived to determine the parameters on which Poisson's ratio and Young's moduli depend. Subsequently, the analytical results are compared with those obtained from experimental testing of different sample structures with the two showing good agreement. Further considerations indicate that it is possible to design 2D and 3D auxetic systems with the push drill as the only deformation mechanism.