Chiral topologies for composite morphing structures – Part II: Novel configurations and technological processes

Abstract

The article presents the advancements in the technological processes developed to produce chiral honeycombs made of thin composite laminates. An original technological process, which was applied to produce chiral components for aerospace morphing structures, is critically analysed and a new approach is proposed. The objective of such approach is the production of thin-walled chiral composite structures with enhanced strength properties by using a more feasible technology. According to the new methodology, chiral honeycombs with polygonal nodes are obtained by assembling thin-walled prismatic composite tubes. Numerical models are developed to investigate the behaviour of such topologies. A comparison with the performances of chiral honeycombs with cylindrical nodes is presented, showing that the new configuration can provide negative Poisson's ratios that tend to the theoretical limit of −1 as the stiffness of the polygonal nodes is increased. Thereafter, a method to fill partially the nodes is proposed and numerically assessed, to enhance at the same time the auxetic behaviour and the mechanical properties of the chiral honeycomb. Finally a complete manufacturing process is developed. Hexa-chiral structural units are manufactured and subsequently tested to assess the auxetic response. Results are in acceptable agreement with numerical predictions and indicate that the novel technological route provides a significant contribution for the application of composite chiral honeycomb to morphing structures

Mechanical metamaterials with star-shaped pores exhibiting negative and zero Poisson's ratio

“…Despite the vast potential of auxetic mechanical metamaterials, which are superior to naturally occurring auxetics due to their increased versatility, one of the main challenges faced by researchers in implementing these systems for real world applications and devices is optimization of the production method. The procedure of making an auxetic metamaterial typically involves a multi-step manufacturing process, which includes the attainment of a specific geometrical configuration to achieve the auxetic effect, ideally with a high degree of precision via production techniques such as 3D printing [22][23][24][25], laser lithography [26], molding [27] and perforation methods [12,20,21,[28][29][30][31]. The suitability of a manufacturing process relies heavily on the type of geometric features that need to be introduced, which could present a challenge, especially if the auxetic properties are required at the micro-or nano-level.…”

Tailoring Poisson's ratio by introducing auxetic layers

“…In particular, they can be used to increase the sensitivity of piezoelectric elements (), in textile design , vibration damping , reinforcement of seats (), sport equipment (), industrial applications , etc. Hence, an increasing interest in searching for auxetic materials and for mechanisms responsible for their properties is observed .…”

Response of Chiral Auxetic Composite Sandwich Panel to Fragment Simulating Projectile Impact

“…[7,8] A special kind of cellular structure is the auxetic structure, [9,10] exhibiting a negative Poisson's ratio and some unique and non-intuitive deformation behaviour. [11][12][13][14][15][16][17][18][19][20] One of the most interesting for ballistic protection is that under impact the material flows towards the impact zone due to internal structure deformation. [21] This causes material densification under the impacted area and offers better energy absorption in comparison to conventional (non-auxetic) cellular materials.…”