Experimental and Theoretical Investigations of Auxetic Sheet Metal

This paper deals with the mechanical and thermal behavior of aluminium sheets with a rectangular perforation structure exhibiting an auxetic behaviour. The negative Poisson’s ratio is basically achieved by the rigid rotation mechanism of the squares between the perforations. In this work uniaxial quasistatic tensile tests are carried out to characterize the perforation pattern. During the mechanical tests, the samples are observed simultaneously with a optical camera, used for Digital Image Correlation (DIC) to determine the local deformation fields, and passive thermography to visualize the heat evolution in the sample due to plastic deformation process. This led to the in situ thermomechanical characterization of the component and moreover to the determination of the effective material parameters such as Young’s modulus, Poisson’s ratio and thermoelastic constant. The results were then compared and validated by means of FEM simulations. Furthermore, the thermographic images were optimized in this work by using optical images to segment the sample from the background. These improved images were used to extract the temperature change due to plastic deformation to determine the yield stress.