Compressive behaviour of chiral auxetic cellular structures at different strain rates

The quasi-static and high strain rate response of chiral auxetic cellular structures were evaluated in this work. Samples of the chiral auxetic structures were fabricated with the Selective Electron Beam Melting (SEBM) technique from copper powder. Uniaxial quasi-static and low-speed dynamic compression tests were performed on a universal testing machine, while high strain rate tests up to 5000 s(-1) were performed using the one-stage powder gun. The experimental measurements together with infrared thermography and high-speed camera images were used to study the deformation mechanism of chiral auxetic structures. A significant effect of the shock enhancement observed in experiments at higher loading velocities was characterised by evaluating the specific energy absorption and specific strength. This phenomenon was further analysed in more detail by using parametric computational simulations, which offered more detailed analysis of mechanical behaviour at different strain rates. The computational results indicate that the plateau stress of chiral auxetic structure increases exponentially with increasing loading velocity. An empirical polynomial approximation was extracted from the computational results, which enables estimation of the plateau stress of auxetic cellular structures at arbitrary loading velocity in between the analyses velocity limits.