Auxetic cellular materials are modern materials with unique mechanical properties. They exhibit a negative Poisson’s ratio due to their internal structure deformation, i.e. they get wider when stretched and thinner when compressed. Their complex internal structure necessitates that they can be fabricated only by additive manufacturing technologies. This work is concerned with analysis of 3D auxetic cellular structure build from inverted tetrapods. The analysed samples were fabricated from Ti-6Al-4V powder using the selective electron-beam melting (SEBM) method at the Institute of Materials Science and Technology (WTM), University of Erlangen-Nürnberg, Germany.
The mechanical behaviour of analysed auxetic samples with three different porosities was determined in two different orthogonal directions by quasi-static and dynamic (including high strain rate) compressive testing. The effects of fabrication procedure on compressive mechanical response of auxetic cellular structures were studied by means of micro computed tomography scanning and microscopy. The deformation patterns occurring during the dynamic testing were additionally observed with infrared tomography. The high strain rate compression testing up was performed by using powder a powder gun experimental device, where strain rates up to 10000 s-1 were achieved.
The results show that the strain rate effect on analysed auxetic samples is significant when the shock deformation mode is achieved, i.e. when most of deformation occurs at the impact front. The change in the loading orientation changes also the deformation mode of the auxetic structure from crushing in shear planes to layer-by-layer crushing both under quasi-static and dynamic loading conditions.