Studies on Chiral Auxetic Structures for Energy Absorption and Harvesting Applications

Abstract

This thesis investigates the deformation characteristics, energy absorption, and vibration newlineenergy harvesting potential of auxetic chiral structures. The research spans from studying the impact mitigation under high-velocity projectile impacts to exploring low-frequency energy harvesting applications using auxetic chiral designs. The work also presents a finite element (FE) based homogenization approach for analyzing cellular structures with reduced computational effort. newline newlineFirst, the energy absorption and impact response of sandwich structures with tetrachiral auxetic core is examined under projectile impacts with velocities ranging between 150-450 m/s. The FE model is based on the Johnson-Cook material model and validated through experimental studies using 3D-printed PLA samples and simulation results reported in literature. Further, a semi-analytical model is developed to estimate the residual velocities and energy absorption under blunt projectile impacts that shows good agreement with FE results with an error of less than 8%. The performance of tetrachiral cores is also compared with re-entrant and double arrowhead cores, revealing that the energy absorption is highest for blunt projectiles and remains nearly constant above the ballistic limit. The results of the study additionally demonstrate that structures with auxetic cores exhibit superior energy absorption than sandwich structures with conventional hexagonal honeycomb cores. As an extension of this study, the crashworthiness of 3D sandwich structures with graded hexachiral cores was investigated under dynamic compression. The influence of core gradient and compression velocity on energy absorption was studied. The results show that auxetic hexachiral structures exhibit enhanced crashworthiness and superior energy absorption compared to conventional honeycomb-core structures. These findings highlight the potential of auxetic cores for impact-resistant designs under static and dynamic loading. newlineLater in the study, the hexachiral structure was used to develo