Impact resistance and energy absorption of chiral lattice and aluminium foam

Abstract

Benefiting from the excellent energy absorption capacity and high strength-to-weight ratio, lightweight cellular solids have been widely used for structural protection against impact loading. Materials possessing negative Poisson's ratio properties have exhibited potential to offer enhanced impact resistance over conventional materials, due to their localised densification effect towards the point of impact. However, the shrinkage behaviour meanwhile leads to an increased impact force, which may cause damages to the protected structures. Chiral lattice exhibits Poisson's ratio of -1 even undergoing large deformations. Owing to the geometric topology, it is possible that some parts of the chiral lattice experience irreversible plastic deformation while other parts maintain intact in the wake of mild impact occasion. Firstly, the theoretical solution of the yield stress of chiral lattice was obtained in terms of quasi-static loading. Thereafter, the in-plane dynamic crushing and energy-absorption capacity of chiral lattice were studied numerically by means of finite element (FE) method. A comparative study between the chiral honeycomb and conventional hexagonal honeycomb was also performed to reveal the advantages and disadvantages of the two types of materials. In addition, a parametric study was conducted to investigate the effects of geometric topologies and impact scenarios on the response of chiral lattice. The numerical results show that the performance of plastic energy dissipation of chiral lattice is dependent not only on structural parameters but also on crushing velocities. The DI-HPB (Direct impact Hopkinson Pressure Bar) experiments have also been conducted to investigate the cushioning performance of chiral lattice. Secondly, a numerical study of the high-speed impact performance of the sandwich panel with chiral lattice cores was carried out following a mesh convergence analysis. The local impact characteristics of the sandwich panel were studied in association with the parametric study. It is observed that the impact force and the plastic strain energy absorption are independent of the layers composition and the number of the unit cells, but dependent on the relative density of the sandwich cores. The effects of key parameters (L/R, initial impact velocity, impact mass, impact angle and skin thickness) on the impact performance of the sandwich panels were investigated afterwards. Furthermore, a novel 3D chiral lattice structure was proposed by orthogonally placing 2D hexagonal nodes-based chiral lattices. The crashworthiness study of the 3D chiral lattice was performed numerically. It is demonstrated that the deformation behaviour of 3D chiral lattice highly depends on impact velocities, thus to the impact stress and energy absorption capacity. The other key design parameters such as initial impact mass, relative density and impact direction have also been taken into consideration in the study. Finally, the impact performance of cellular solid aluminium foam and its composites (aluminium foams covered by EPE foam layers) were investigated. Applying such foams for the protection of the incident bar from undergoing extreme impact stress was also investigated. Significant stress attenuation was observed when the aluminium foam was expanded onto the incident bar as a cushioning layer. Various configurations between aluminium foam and EPE foam have been considered in the experiments, the results show that the presence of EPE foam layers can affect the failure modes and damage locations of aluminium foams. This new finding shows the possibility of engaging damage controllable aluminium foam for the design of innovative composite structures.

Date of Award	2019
Original language	English