## 1 Introduction
If the crash velocity is too high, the crushing stroke can be insufficient and a high peak load can arise. In this case, either the crush tube length needs to be extended or a filler material must be used, such as foam and lattice structures. Auxetic materials are classified as mechanical metamaterials because of their artificial and highly tailorable properties, which also include negative stiffness (exhibiting increasing displacement under decreasing load) or a negative coefficient of thermal expansion. The auxetic properties may be obtained using a wide selection of geometries, each may be customized to provide a specific performance (such as improved vibration damping or acoustic insulation). More information about the classification of auxetic structures (such as woven, foam or lattice structures) can be found in literature [23; 24; 25]. Recently, metamaterials with auxetic properties have gained attention because of their superior energy-absorbing characteristics and vibration-damping capabilities [26; 27; 28; 29; 30]. [PERSON] et al. [29; 31] observed in quasi-static and vibration tests that anti-tetra chiral lattices could constitute excellent design platforms for energy dampers. Recently, auxetic lattice geometries were found to provide significant crush resistance and energy damping under compression in its in-plane direction, in which auxeticity is experienced. [PERSON] et al. [32; 33] studied experimental and numerical crushing analysis of re-entrant and anti-tetrachiral auxetic lattices. [PERSON] et al. [34] numerically evaluated the dynamic crushing behavior of auxetic honeycombs with various cell-wall angles under different levels of crush loading. [PERSON] et al. [7] compared the in-plane compressive properties of honeycomb, re-entrant auxetic, auxetic-strut and two different auxetic-strut/honeycomb hybrid cell structures. As these studies are confined to only-auxetic behavior, few experimental studies investigated the relationship of auxetic structures with composite tubes [35; 36]. Recently, [PERSON] and [PERSON] [37] investigated the crush response of auxetic lattices filled metal tube under the uniaxial compressive load. This research proposes an innovative concept for the energy absorption improvement of composite crashboxes in the case of lateral loading. The concept is based on the contraction of the cellular structures in the composite tube with negative Poisson's ratio under lateral compressing loads to potentially increase the crush performance of composite tubes. To demonstrate the concept experimentally, the chiral lattices were manufactured using a 3D printing facility; the carbon fiber composite tubes were supplied from a manufacturer. Chiral lattices, composite tubes (hollow) and chiral lattices filled composite tubes were axially and laterally compressed between two rigid plates during the quasi-static test process. There crush experiments were conducted for each group at least three times to show repeatability. The specific energy absorption, peak load, average (mean) crushing load, crushing efficiency and stroke efficiency were then calculated for each group. Finally, the results then compared to understand whether auxetic structures could be beneficial as a filler in designing efficient composite crushing tubes.