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

Recent advances in lithography technology and the spread of 3D printers allow us a facile fabrication of special materials with complicated microstructures. The materials are called "designed materials" or "architectured materials" and provide new opportunities for material development. These materials, which owing to their rationally designed architectures exhibit unusual properties at the micro- and nano-scales, are being widely exploited in the development of modern materials with customized and improved performance. Meta-materials are found to possess superior and unusual properties as regards static modulus (axial stress divided by axial strain), density, energy absorption, smart functionality, and negative Poisson's ratio (NPR). However, in spite of recent developments, it has only been feasible to fabricate a few such meta-materials and to implement them in practical applications. Against such a backdrop, a broad review of the wide range of cellular auxetic structures for mechanical metamaterials available at our disposal and their potential application areas is important. Classified according to their geometrical configuration, this paper provides a review of cellular auxetic structures. The structures are presented with a view to tap into their potential abilities and leverage multidimensional fabrication advances to facilitate their application in industry. In this review, there is a special emphasis on state-of-the-art applications of these structures in important domains such as sensors and actuators, the medical industry, and defense while touching upon ways to accelerate the material development process.

Cellular Auxetic Structures for Mechanical Metamaterials: 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.

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

Deformation behaviors and energy absorption of auxetic lattice cylindrical structures under axial crushing load

On the low-velocity impact responses of auxetic double arrowed honeycomb

A comparative study of blast resistance of cylindrical sandwich panels with aluminum foam and auxetic honeycomb cores

Optimal design of a novel cylindrical sandwich panel with double arrow auxetic core under air blast loading

Computational investigation of wind tunnel wall effects on buffeting flow and lock-in for an airfoil at high angle of attack

In subsonic flow, buffeting refers to a fluid instability caused by flow separation in the flow around a bluff body or an airfoil at high angle of attack Typically, there is a dominant frequency o

Buffeting and Lock in of an Airfoil at High Angle of Attack

The initial velocity of fragment from cylindrical casing, which detonates at one end along the central of the casing, is the key issue in the field of explosion technology and its protecting. Most of the formula available can predict the initial velocity or the velocity of fragments at middle part of the cylindrical casing with greater length-dimeter ratio (L/d>2). However, when the length-diameter ratio is less than two, the initial velocity of the cylindrical casing filled with explosives will have a big difference. In the present work, a numerical simulation model acknowledged by X-ray radiography experiments was used to determine the influence of the length-diameter ratio. The formula was built on top of the Gurney formula and made use of a correctional function to account for the effect of the length-dimeter ratio. The formula was further acknowledged with the established numerical simulation model. The results indicate that the calculation formula can accurately predict the initial fragment velocity with different length-diameter ratio (L/d≤ 2).

Tong Zhou

Papers

A comparative study of blast resistance of cylindrical sandwich panels with aluminum foam and auxetic honeycomb cores

Optimal design of a novel cylindrical sandwich panel with double arrow auxetic core under air blast loading

Computational investigation of wind tunnel wall effects on buffeting flow and lock-in for an airfoil at high angle of attack

Buffeting and Lock in of an Airfoil at High Angle of Attack

Effect of the length-diameter ratio on the initial fragment velocity of cylindrical casing