Homogenization and mechanical behavior under impact of auxetic metamaterials

Metamaterial is a class of materials with augmented properties compared to what one can usually find in nature. The properties of this class of materials rely principally on the microstructure that one designed rather than on the structural material itself from which the microstructure is made. In recent years, the progress in the techniques of ad- ditive manufacturing made possible the realization of very precise microstructures. The fabrication and testing of metamaterials have therefore become more accessible. In this work, the so-called auxetic metamaterials are studied. This category of meta- materials has the property to shrink in all the direction under the application of com- pression in one direction. This tendency to condensate confers an augmented capacity for impact absorption to such structures. The interest of using auxetic structure in protective design is investigated. Several tests of impact are realized on sandwich structures with a layer of auxetic structure. The several experiments will lead to pieces of evidence of a global augmented response in terms of transmitted force through the portion of the protective device. Furthermore, the possibility to evaluate the homogenized effective properties of such structures will be investigated. The equivalent stiffness matrices will be computed and the possibility to reduce the time of computation through the substitution of the real auxetic structure by the homogenized media is studied. The results of the experiments will lead to good adequation. However, no general proof will be established to quantify the reliability of the method as a function of the specific geometry or the number of cells.