CHIRAL AUXETICS AS A PROTECTIVE MATERIAL

Abstract

Auxetic materials have been theorised to exhibit superior impact resistance compared to conventional materials. With the rapid prototyping of auxetic structures for further study and validation, many studies have focused only on the quasi-static loading response of auxetic structures. There is thus a research gap on their dynamic behaviour. A good understanding of the latter is important to assess potential applications in a protective system against impact loading. This thesis first demonstrates the effectiveness of auxetic hexachiral sandwich panels under low-velocity impact with a 2D finite element analysis simulating a low velocity impacting load on sandwich structures with honeycomb, re-entrant and hexachiral lattices. The hexachiral structure showed significant improvement in terms of the reaction force and stress distribution. A hexachiral structure with wavy ligaments with better auxeticity and isotropy properties is next considered, which is shown to be more effective in impact resistance, by reducing the reaction force on the protected surface. A better performance of the wavy hexachiral structure persists with a phase shift in the underlying lattice structure, or with a directed impact loading at different angles. The results motivate using the wavy hexachiral structure as a sandwich panel core, for enhanced protection against low velocity impact loading.