3D composite metamaterial with magnetic inclusions exhibiting negative stiffness and auxetic behaviour

In this work, through the use of a theoretical model and experimental testing, we investigate a novel three-dimensional mechanical metamaterial composed of structural units consisting of two arrowhead-like elements with magnetic inclusions. We show that such system has a capability to exhibit negative Poisson's ratio and negative incremental stiffness at the same time. We also show that both the type of the stiffness exhibited by the system and its magnitude can be solely controlled via the orientation of magnetic inclusions within the structure and the magnitude of the magnetic moment associated with magnetic inclusions respectively. More specifically, for a particular example of magnetic inclusions used in the experiment, the stiffness could assume an arbitrary value from the range approximately between -5 kN/m and 5 kN/m depending on the stage of the mechanical deformation and aforementioned factors. This range can be also conveniently adjusted depending on the size and properties of magnetic inclusions. This in turn allows to adjust mechanical response of the considered structure in accordance to a particular application without a need of reconstructing the system which would not normally be possible for conventional nonmagnetic systems attributing negative stiffness to their elastic properties. (C) 2019 The Authors. Published by Elsevier Ltd.