Materials and structures with negative Poisson's ratio exhibit a counter-intuitive behaviour. Under uniaxial compression (tension), these materials and structures contract (expand) transversely. The materials and structures that possess this feature are also termed as 'auxetics'. Many desirable properties resulting from this uncommon behaviour are reported. These superior properties offer auxetics broad potential applications in the fields of smart filters, sensors, medical devices and protective equipment. However, there are still challenging problems which impede a wider application of auxetic materials. This review paper mainly focuses on the relationships among structures, materials, properties and applications of auxetic metamaterials and structures. The previous works of auxetics are extensively reviewed, including different auxetic cellular models, naturally observed auxetic behaviour, different desirable properties of auxetics, and potential applications. In particular, metallic auxetic materials and a methodology for generating 3D metallic auxetic materials are reviewed in details. Although most of the literature mentions that auxetic materials possess superior properties, very few types of auxetic materials have been fabricated and implemented for practical applications. Here, the challenges and future work on the topic of auxetics are also presented to inspire prospective research work. This review article covers the most recent progress of auxetic metamaterials and auxetic structures. More importantly, several drawbacks of auxetics are also presented to caution researchers in the future study.

Auxetic metamaterials and structures: a review

Over the past several decades, a noticeable amount of research efforts has been directed to minimising injuries and death to people inside a structure that is subjected to an impact loading. Thin-walled (TW) tubular components have been widely employed in energy absorbing structures to alleviate the detrimental effects of an impact loading during a collision event and thus enhance the crashworthiness performance of a structure. Comprehensive knowledge of the material properties and the structural behaviour of various TW components under various loading conditions is essential for designing an effective energy absorbing system. In this paper, based on a broad survey of the literature, a comprehensive overview of the recent developments in the area of crashworthiness performance of TW tubes is given with a special focus on the topics that emerged in the last ten years such as crashworthiness optimisation design and energy absorbing responses of unconventional TW components including multi-cells tubes, functionally graded thickness tubes and functionally graded foam filled tubes. Due to the huge number of studies that analysed and assessed the energy absorption behaviour of various TW components, this paper presents only a review of the crashworthiness behaviour of the components that can be used in vehicles structures including hollow and foam-filled TW tubes under lateral, axial, oblique and bending loading.

https://myresearchspace.uws.ac.uk/ws/files/1765038/Paper_2.pdf

On the crashworthiness performance of thin-walled energy absorbers: Recent advances and future developments

Optimization for structural crashworthiness and energy absorption has become an important topic of research attributable to its proven benefits to public safety and social economy. This paper provides a comprehensive review of the important studies on design optimization for structural crashworthiness and energy absorption. First, the design criteria used in crashworthiness and energy absorption are reviewed and the surrogate modeling to evaluate these criteria is discussed. Second, multiobjective optimization, optimization under uncertainties and topology optimization are reviewed from concepts, algorithms to applications in relation to crashworthiness. Third, the crashworthy structures are summarized, from generically novel structural configurations to industrial applications. Finally, some conclusions and recommendations are provided to enable academia and industry to become more aware of the available capabilities and recent developments in design optimization for structural crashworthiness and energy absorption.

On design optimization for structural crashworthiness and its state of the art

Blast resistance of auxetic and honeycomb sandwich panels: Comparisons and parametric designs

A Numerical Study of Auxetic Composite Panels under Blast Loadings

Impact and close-in blast response of auxetic honeycomb-cored sandwich panels: Experimental tests and numerical simulations

In this paper, a class of axisymmetric thin-walled square (ATS) tubes with two types of geometries (straight and tapered) and two kinds of cross-sections (single-cell and multi-cell) are considered as energy absorbing components under oblique impact loading. The crash behavior of the four types of ATS tubes, namely single-cell straight (SCS), single-cell tapered (SCT), multi-cell straight (MCS) and multi-cell tapered (MCT), are first investigated by nonlinear finite element analysis through LS-DYNA. It is found that the MCT tube has the best crashworthiness performance under oblique impact regarding both specific energy absorption (SEA) and peak crushing force (PCF). Sampling designs of the MCT tube are created based on a four-level full factorial design of experiments (DoE) method. Parametric studies are performed using the DoE results to investigate the influences of the geometric parameters on the crash performance of such MCT tubes under oblique impact loading. In addition, multiobjective optimization design (MOD) of the MCT tube is performed by adopting multiobjective particle swarm optimization (MOPSO) algorithm to achieve maximum SEA capacity and minimum PCF with and without considering load angle uncertainty effect. During the MOD process, accurate surrogate models, more specifically, response surface (RS) models of SEA and PCF of the MCT tubes are established to reduce the computational cost of crash simulations by finite element method. It is found that the optimal designs of the MCT tubes are different under different load angles. It is also found that the weighting factors for different load angles are critical in the MOD of the MCT tubes with load angle uncertainty.

Crushing analysis and multiobjective crashworthiness optimization of tapered square tubes under oblique impact loading

Multiobjective optimization for empty and foam-filled square columns under oblique impact loading

Honeycombs are ultra-light materials with outstanding mechanical properties, which mainly originate from their unit cell configurations rather than the properties of matrix materials. Honeycombs are triggering in numerous promising applications in the fields of architecture, automotive, railway vehicle, marine, aerospace, satellite, packaging and medical implants, etc. Here we provide an in-depth overview of some important advances in basic structural design to obtain novel honeycombs with various improved mechanical properties. Firstly, the review introduces the classical honeycomb configurations. Then, a clear classification of advanced designs is established and discussed according to the design scale. The designs on the macro scale are divided into hierarchical, graded and disordered, while the designs on the meso scale are grouped as hybrid, curved ligament and reinforced strut. Moreover, the effects of different designs on the mechanical properties of honeycomb are discussed quantitatively. Finally, we summarize the important potential designs to improve the mechanical properties of honeycombs and the challenges in further research.

Advanced honeycomb designs for improving mechanical properties: A review

Honeycombs with re-entrant (RE) unit cells were found to have negative Poisson's ratios (NPRs) and enhanced energy absorption capabilities than regular hexagon honeycombs. For further improved energy absorption capacity, a novel re-entrant circular (REC) honeycomb configuration is proposed in this work by replacing the sloped cell wall of the regular re-entrant honeycomb with double circular arc cell walls, which can dissipate extra energy due to more formed plastic angles during the crushing process. The in-plane quasi-static crushing response of the REC honeycomb with large deformation was investigated theoretically and numerically. The numerical modeling methods in LS-DYNA software were validated by using the quasi-static crush test data of 3D-printed REC honeycomb specimens. Experiment and numerical simulations both revealed that quasi-static load can result in an “X” mode deformation of the REC honeycomb. Based on the simulated deformation profiles of the representative unit, theoretical models were derived to predict the REC honeycomb's crushing strength, i.e. plateau stress. Good agreements were found between the theoretical and the numerical results within a relative error about 9%. Parametric analyses further showed that the unit cell configuration has a great effect on the crushing strength of the REC honeycomb. The REC honeycomb presents a varied Poisson's ratio with the global strain of the honeycomb; smaller radius to height ratio and length to height ratio were found to yield more pronounced NPR effect. Moreover, compared with the regular RE honeycomb, the specific energy absorption of the REC honeycomb is much higher due to the introduction of the double circular arc cell walls.

Chang Qi

Papers

Impact and close-in blast response of auxetic honeycomb-cored sandwich panels: Experimental tests and numerical simulations

Crushing analysis and multiobjective crashworthiness optimization of tapered square tubes under oblique impact loading

Multiobjective optimization for empty and foam-filled square columns under oblique impact loading

Advanced honeycomb designs for improving mechanical properties: A review

Quasi-static crushing behavior of novel re-entrant circular auxetic honeycombs