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It is known that changes on the microscopic, structural level of materials exert changes on their macroscopic properties, in particular elastic ones. This approach can be used to alter the elastic properties of materials. However, it is not easy to predict the impact of a particular change in the structure of crystals. The recent studies show that depending on the size, shape, and orientation of inclusions used, the resulting elastic properties may differ. Inclusions may enhance, weaken, or eliminate the auxetic properties in a hard sphere model. This study is focused on the influence of the spatial distribution of planar inclusions within the hard sphere crystal and its impact on its elastic properties. Periodic systems containing two nanolayer inclusions in the representative volume element, oriented orthogonally to [001]$\left[\right. 001 \left]\right. $‐direction and in various spatial ordering, are considered. It has been shown that introducing layer inclusions causes the deterioration of auxetic properties in the [110][11¯0]$\left[\right. 110 \left]\right. \left[\right. 1 \bar{1} 0 \left]\right. $‐direction. However, the latter weakly depends on the spatial ordering of the inclusion layers. Moreover, changes in the size of the inclusion particles, combined with different ordering of the inclusion layers, can be used to coarsely and finely tune the elastic properties of the model crystal. [ABSTRACT FROM AUTHOR]

Herein, an improved mechanical metamaterial is proposed, which is derived from the decomposition, rotation, and reassembly of reentrant structures. The structure is parametric, allowing for rapid redesign. The study focuses on the variations in equivalent stiffness and Poisson's ratio of the structure within the linear elastic range when internal rib angle θ changes. First, based on homogenization simulation analyses, it has been verified that this design achieves the tailorable equivalent elastic modulus and Poisson's ratio over a wide range, meanwhile, maintaining equal elastic properties in the orthogonal direction at all times. Second, to reduce future repetitive experiments, an interpolation model is established to expand the design domain. The fitting formula indicates that by modifying θ and relative wall thickness t/L0, the elastic performance of the structures can be tailored. Additionally, the impact of boundary conditions is discussed to minimize experimental costs. Finally, the accuracy of the simulations is validated through uniaxial compression tests. [ABSTRACT FROM AUTHOR]

AbstractThis study introduces a reinforced star-shaped auxetic honeycomb (RSSAH) sandwich beam, enhanced with hollow thin-walled tubes to improve bending resistance and energy absorption performance. The bending performance of the RSSAH is systematically investigated through quasi-static three-point bending tests and finite element numerical simulations. The findings suggest that when subjected to mid-span stress, the RSSAH displays both localized indentation and overall bending deformation, accompanied by notable negative Poisson’s ratio (NPR) impact under bending loads. Parametric studies are undertaken by numerical simulations to investigate the impact of compression position, auxetic angle, and face sheet thickness on the bending mode of the auxetic honeycomb sandwich beam. The analysis shows that the RSSAH can exhibit excellent bending performance and, at one of the compression positions, displays double-plateau stress characteristics. It is also found that altering key geometric parameters, such as the auxetic angle and panel thickness ratio, can greatly improve the bending capabilities of the RSSAH, achieving stable plastic deformation and high energy absorption. Finally, compared to star-triangle honeycomb (STH) sandwich beam, traditional reentrant honeycomb (RH) sandwich beam and star-shaped auxetic honeycomb (SSAH) sandwich beam, the RSSAH demonstrates superior bending performance and energy absorption capacity. This study offers insights and references for the development of innovative reinforced auxetic honeycomb sandwich beams. [ABSTRACT FROM AUTHOR]

Traditional acoustic materials typically have fixed acoustic bandgaps (BGs), making them unsuitable for complex vibration environments. In recent years, prestress-controlled acoustic metamaterials have emerged as an effective solution. However, most existing studies fail to meet the requirements for achieving broadband acoustic control in the low-frequency range (below 600 Hz). Therefore, this study introduced a negative Poisson's ratio structure, utilizing the so-called "trampoline effect," building on previous research to design a low-frequency, broadband negative Poisson's ratio structure acoustic metamaterial (NPRS-SC). It utilizes compression, rather than tension, conditions to control BGs. Numerical results indicate that the first low-frequency BG of NPRS-SC ranges from 66.1 to 281.1 Hz, with a lower starting frequency and broader stopband compared to traditional structures. It also demonstrates superior vibration damping performance. Importantly, by introducing compressive prestress conditions, the BG range can be gradually expanded, enhancing vibration damping performance. Specifically, when the strain value λ is set to − 0.03, NPRS-SC's first low-frequency BG can cover 85% of the frequency range below 600 Hz. Lastly, this study analyzes the influence of NPRS-SC's geometric parameters on its first low-frequency BG and vibration transmission performance. This research provides essential references and guidance for designing tunable, low-frequency, broadband acoustic metamaterials, offering robust support for future developments in acoustic control technology. [ABSTRACT FROM AUTHOR]

Negative Poisson's ratio tubular fabric plays an important role in mechanical and medical fields. To explore the impact of different raw materials and different structures on the negative Poisson's ratio effect, flat knitting technology was used to characterize the negative Poisson's ratio of three different structures of sheet and tubular fabrics made from polyester, cotton, and nylon. The tensile test and static burst test were applied to compare the performance of various sheet-knitted fabrics. The results show that yarn with better elasticity and elongation have a better auxetic effect. Fabrics with good auxetic effects have greater deflection and better energy absorption capacity. When measuring the longitudinal length variation of tubular knitted fabrics using cylinders of different diameters, it was found that when the number of weave cycles in a circle of tubular knitted fabrics is few, the negative Poisson's ratio effect of tubular knitted fabrics is better than that of sheet knitted fabrics. [ABSTRACT FROM AUTHOR]

A novel cross tetrachiral honeycomb metamaterial is proposed, which not only possesses the negative Poisson's ratio property, but also has a wide-frequency bandgap. The effective elastic parameters of the cross tetrachiral honeycomb are first theoretically analyzed; then, its designable performances for negative Poisson's ratio and elastic modulus are studied by varying geometric parameters. The dynamic properties of the cross tetrachiral honeycomb metamaterial are investigated by analyzing the band structure. It is shown that without the addition of external mass to the structure, a designable wide bandgap can be generated to isolate the in-plane waves effectively by selecting the ligament angles and the radius of central cylinder. In addition, an effective approach is proposed for tuning the bandwidth without changing the geometric parameters of the structure. Compared to classical negative Poisson's ratio metamaterials, the proposed cross tetrachiral honeycomb metamaterial is designable and tunable for achieving a specific static or dynamic performance, and has potential applications in engineering practice. [ABSTRACT FROM AUTHOR]

Designing a particular change in a system structure to achieve the desired elastic properties of materials for a given task is challenging. Recent studies of purely geometrical atomic models have shown that structural modifications on a molecular level can lead to interesting and desirable elastic properties. Still, the result of such changes is usually difficult to predict. The present work concerns the impact of nanolayer inclusion ordering in hard sphere crystals on their elastic properties, with special attention devoted to their auxetic properties. Two sets of representative models, based on cubic crystals consisting of 6 × 6 × 6 unit cells of hard spheres and containing either neighboring or separated layers of spheres of another diameter, oriented orthogonally to the [001] direction, have been studied by Monte Carlo simulations in the isothermal–isobaric (NpT) ensemble. Their elastic constants have been evaluated using the Parinello–Rahman approach. The Monte Carlo simulations showed that introducing the layer inclusions into a pure face-centered cubic (FCC) structure leads to the system's symmetry changes from cubic symmetry to tetragonal in both cases. Essential changes in the elastic properties of the systems due to layer ordering were found both for neighboring and separated inclusions. It has been found that the choice of a set of layer inclusions allows one to tune the auxetic properties in two crystallographic directions ( [ 110 ] [ 1 1 ¯ 0 ] and [ 101 ] [ 1 ¯ 01 ] ). In particular, this study revealed that the change in layer ordering (from six separated layers to six neighboring ones) allows for, respectively: (i) enhancing auxeticity of the system in the [ 101 ] [ 1 ¯ 01 ] direction with almost loss of auxetic properties in the [ 110 ] [ 1 1 ¯ 0 ] direction in the case of six separated layers, while (ii) in the case of six neighboring layers, keeping the auxetic properties in both auxetic directions independently of the size of spheres constituting inclusions. [ABSTRACT FROM AUTHOR]

Incorporating arc‐curved configuration into auxetic honeycomb can evenly distribute pressure, reduce stress concentration, and avoid fracture. In this work, a novel arc‐curved chiral star‐shaped honeycomb (ACSH) has been proposed by combining the chiral honeycomb (CH), the star‐shaped honeycomb (SSH), and arc‐curved configurations. The crushing response of the ACSH is studied experimentally and numerically. In order to verify the accuracy of simulation, quasi‐static compression experiment is carried out on the ACSH sample fabricated by 3D printing. Subsequently, the crashworthiness of the ACSH is compared with other honeycombs. Particularly, under the crushing velocity of 2 m s−1, the ACSH exhibits exceptional specific energy absorption, which is 179% higher than that of the conventional SSH. Additionally, it is also found that introducing arc‐curved configuration can effectively reduce initial peak stress. Moreover, the effect of functionally graded design on crashworthiness is systematically analyzed. The findings indicate that the initial peak stress decreases with the decrease of gradient rate. When crushing velocity increases to 80 m s−1, the SEA of the ACSH increases with the increase of gradient rate. This work investigates the crushing response of a novel honeycomb, which can provide a reference for designing and optimizing novel lightweight honeycombs with better crashworthiness. [ABSTRACT FROM AUTHOR]

The exceptional energy absorption, deformability, and tuneable Poisson's ratio properties of negative Poisson's ratio (NPR) honeycomb biomimetic structures make them highly suitable for applications in aerospace, medical, and acoustic stealth industries. The present study proposes a re-entrant hybrid honeycomb (REHH) structure comprising a re-entrant octagonal unit cell and a re-entrant hexagonal unit cell. Theoretical models of the in-plane elastic modulus and Poisson's ratio are established based on beam theory, and these models are validated through finite element (FE) simulations and tensile experiments conducted on the REHH samples. The influence of the cell geometry parameters on the in-plane elastic behaviours is investigated. The results indicate that the NPR performance of the REHH structure exhibits superior deformation capability compared with the four-point star hybrid honeycomb (FSHH) structure. The experimental REHH structure samples exhibit significant tensile displacement capabilities in the x-direction. [ABSTRACT FROM AUTHOR]

A hollow auxetic cylinder lattice structure (HCLS) is proposed with tapered three-dimensional reentrant cells (TRCs) and connecting plates. The compressive performance of HCLSs is studied by finite element analysis (FEA) and compression test. HCLSs show excellent energy absorption and negative Poisson's ratio properties as well as unique rotational deformation mode during compression. The influences of structural parameters on the compression performance of HCLS are further studied. The values of the maximum rotation angle of H-hs2.0 and minimum negative Poisson's ratio (MPR) of H-la.3 are 37.32 degree and −0.653, respectively. HCLSs exhibit various functional properties and have great potential for application. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) auxetic woven fabrics and associated composites pose great potential in various industrial sectors, mainly in aerospace and automotive applications. Auxetic effect induces unique properties for smart applications due to its negative Poisson ratio. To date, composites based on different multilayer 3D woven auxetic shapes are not reported for structural applications. Considering this, different auxetic geometries were fabricated via on-loom stitching, and the mechanical properties of their composites were studied. Cotton (warp) and jute (weft) yarns were used to fabricate multi-layer geometries of auxetic arrowhead, rotating square, re-entrant honeycomb, and connected parallelogram geometry on a sample weaving loom. These basic geometries were filled with auxetic molds for shaping, which were then infused with epoxy resin. Amongst all, square-shaped multilayered 3D auxetic fabric structures showed better auxeticity and mechanical stability. Compared to non-auxetic composites, significantly better energy absorption, tensile strength, and compression properties were observed for auxetic composites. Also, the smaller size of rotating square-shaped geometries showed higher auxeticity and slightly better mechanical properties. [ABSTRACT FROM AUTHOR]

Auxetic textiles are intriguing materials with unusual capabilities. These materials exhibit a negative Poisson's ratio with extraordinary performance in toughness, resilience, shear resistance, and acoustic properties mainly due to their special structure and associated deformation mechanics. Auxetic materials can also have applications around energy absorption and can effectively be used for vibration damping and shock absorbency. The exceptional behaviour of auxetic textiles can be obtained by utilising specific fibrous materials and introducing auxetic geometry and structures differently during weaving, knitting, and nonwoven manufacturing. This issue of Textile Progress highlights the fundamental aspects of various auxetic structures and their properties in general and a detailed analysis of auxetic textile structures and composites, their manufacturing processes, modelling, characterisation, and applications. These materials can potentially revolutionise their applications in sports, automotive, construction industry, biomedical engineering, aerospace, marine, and defence personal protective equipment. Fundamental understanding of auxetic geometry, followed by developing and analysing these geometries by analytical and computational modelling, translating the geometry into appropriate textile structures for actual fabric production, characterisation of auxetic fabrics and their composites, and finally, some innovative applications in technical textiles are some of the fascinating issues addressed in this review. [ABSTRACT FROM AUTHOR]

Flexible materials to achieve deformable wing technology requires high mechanical properties of flexible materials，the existing research on chiral structures as flexible materials to drive deformable wings is based on the case of linear small deformations. In order to investigate the mechanical properties of chiral structures under large deformation conditions，five common chiral system negative Poisson's ratio structures，such as tri-chiral，anti-trichiral，tetra-chiral，anti-tetra-chiral，and hex-chiral structures are taken as the object of study. Based on the theory of cellular structural mechanics，the effect of topological structure and cellular element geometrical parameter on the in-plane compression and energy absorption characteristics of chiral system negative Poisson's ratio structures of the intrinsic model of ideal plastic materials are compared and analysed. The results show that the elastic modulus，plateau stress and energy absorption capacity of the chiral structure are inversely proportional to the cell element parameter α and positively proportional to the cell element parameter β. The topology affects the energy-absorbing properties of chiral structures significantly，i.e.，the energy-absorbing capacity of chiral structures with the same single-cell geometrical parameter is significantly enhanced with the increase in the number of ligaments.

Men are particularly sensitive to penis size, especially those with a deformed or injured penis. This can lead to a strong desire for penis enlargement surgery. Given the ethical sensitivities of the penis, penile implants need to be developed with both efficacy and safety. In this study, a polyvinyl alcohol (PVA) patch for penile enlargement prepared via cyclic freeze‒thaw cycles and alkaline treatment. The PVA hydrogels treated with 5 M NaOH had the best mechanical properties and stability. A negative Poisson's ratio structure is incorporated into the design of the enlargement patch, which allows it to conform well to the deformation of the penis. In rabbit models, the enlarged patches can effectively enlarge the penis without degradation or fibrosis while maintaining long-term stability in vivo. This innovation not only provides a safe option for patients in need of penile enlargement but also promises to make a broader contribution to the field of dynamic tissue repair.

Bi-directional re-entrant anti-tetrachiral (BRATC) structure with negative Poisson's ratio is developed in this paper to meet the requirement in the variation of morphing wing area. Inherited from the anti-tetrachiral (ATC) structure, the BRATC has the potential of lightweight and out-of-plane stiffness properties, which is suitable for simultaneous deformation and load-bearing capability in the design of morphing wings. At the same time, inspired by the design idea used in re-entrant anti-tetrachiral (RATC), the BRATC structure has improved the potential of deformability by relaxing the rotation constraints of the ligaments. The effect of the geometric parameters on the equivalent mechanical properties of BRATC, such as elastic modulus and Poisson's ratio was investigated by using the finite element method. The relation between geometric parameters and the mechanical properties is then obtained. Finally, mechanical properties of the BRATC structure are tested with the aid of additive manufacturing technology in the tensile experiment. [ABSTRACT FROM AUTHOR]

Recently, anti-tetra-chiral-type bulking-induced auxetic meta-structure (generated by arraying periodic orthogonal elongated holes onto a sheet structure) was proved to exhibit superior aseismic performance. Anti-tetra-chiral-type auxetics, however, present strong anisotropic performance, which may limit their potential applications, as proper structural orientations are required during operations to utilize the beneficial auxetic effect. In analogy with anti-tetra-chiral-type bulking-induced auxetic meta-structure, an anti-tri-chiral-type bulking-induced auxetic meta-structure was therefore proposed by arraying periodic tri-dumbbell-shaped holes onto a sheet structure. Systematic finite element (FE) analyses were then conducted on a unit cell with periodic boundary conditions to elucidate the deformation mechanism and investigate the effective mechanical properties of the proposed auxetic meta-structure. Results show that the proposed design exhibits excellent auxeticity and planner isotropy. A novel auxetic buckling restrained brace (BRB) core brace was then designed based on the proposed auxetic meta-structure. Numerical calculations were then conducted to investigate the aseismic performance of the proposed auxetic BRB core. It is shown that the proposed auxetic BRB core brace demonstrates better energy dissipation capacity compared to a traditional BRB core brace with positive Poisson's ratio and a recently reported auxetic BRB core brace with orthogonal elliptical holes. Practically, the aseismic performance of the proposed BRB core brace is independent of the orientation of the perforated holes and hence can allow uncertain fairly big manufacturing errors. [ABSTRACT FROM AUTHOR]

This article performs the buckling and vibration studies of the sandwich plates with a negative Poisson's ratio honeycomb core. Based on the isogeometric analysis in conjunction with the refined shear deformation theory, the discrete equilibrium equations of the sandwich plate are established. Numerical results show that the plate with negative Poisson's ratios of the honeycomb core layer has a higher load-bearing capacity than that with positive Poisson's ratios. In addition, the optimal inclined angles of honeycomb core for negative Poisson's ratios subjected to different loading types are obtained. The normalized natural frequency of the plate almost decreases by 10% when the Poisson's ratio ν12 of honeycomb core decreases from −0.3 to −5.5. [ABSTRACT FROM AUTHOR]

Poisson's ratio in auxetic materials shifts from typically positive to negative, causing lateral expansion during axial tension. This scale‐independent characteristic, originating from tailored architectures, exhibits specific physical properties, including energy adsorption, shear resistance, and fracture resistance. These metamaterials demonstrate exotic mechanical properties with potential applications in several engineering fields, but biomedical applications seem to be one of the most relevant, with an increasing number of articles published in recent years, which present opportunities ranging from cellular repair to organ reconstruction with outstanding mechanical performance, mechanical conduction, and biological activity compared with traditional biomedical metamaterials. Therefore, focusing on understanding the potential of these structures and promoting theoretical and experimental investigations into the benefits of their unique mechanical properties is necessary for achieving high‐performance biomedical applications. Considering the demand for advanced biomaterial implants in surgical technology and the profound advancement of additive manufacturing technology that are particularly relevant to fabricating complex and customizable auxetic mechanical metamaterials, this review focuses on the fundamental geometric configuration and unique physical properties of negative Poisson's ratio materials, then categorizes and summarizes auxetic material applications across some surgical departments, revealing efficacy in joint surgery, spinal surgery, trauma surgery, and sports medicine contexts. Additionally, it emphasizes the substantial potential of auxetic materials as innovative biomedical solutions in orthopedics and demonstrates the significant potential for comprehensive surgical application in the future.

Abstract In order to predict the damage behaviours of 3D-printed continuous carbon fibre (CCF) reinforced composites, when additional short carbon fibre (SCF) composite components are employed for continuous printing or special functionality, a novel path-dependent progressive failure (PDPF) numerical approach is developed. First, a progressive failure model using Hashin failure criteria with continuum damage mechanics to account for the damage initiation and evaluation of 3D-printed CCF reinforced polyamide (PA) composites is developed, based on actual fibre placement trajectories with physical measurements of 3D-printed CCF/PA constituents. Meanwhile, an elastic-plastic model is employed to predict the plastic damage behaviours of SCF/PA parts. Then, the accuracy of the PDPF model was validated so as to study 3D-printed CCF/PA composites with either negative Poisson’s ratio or high stiffness. The results demonstrate that the proposed PDPF model can achieve higher prediction accuracies in mechanical properties of these 3D-printed CCF/PA composites. Mechanism analyses show that the stress distribution is generally aggregated in the CCF areas along the fibre placement paths, and the shear damage and matrix tensile/compressive damage are the key damage modes. This study provides a new approach with valuable information for characterising complex 3D-printed continuous fibre-matrix composites with variable mechanical properties and multiple constituents.

The high variability of shock in terrorist attacks poses a threat to people's lives and properties, necessitating the development of more effective protective structures. This study focuses on the angle gradient and proposes four different configurations of concave hexagonal honeycomb structures. The structures' macroscopic deformation behavior, stress-strain relationship, and energy dissipation characteristics are evaluated through quasi-static compression and Hopkinson pressure bar impact experiments. The study reveals that, under varying strain rates, the structures deform starting from the weak layer and exhibit significant interlayer separation. Additionally, interlayer shear slip becomes more pronounced with increasing strain rate. In terms of quasi-static compression, symmetric gradient structures demonstrate superior energy absorption, particularly the symmetric negative gradient structure (SNG-SMS) with a specific energy absorption of 13.77 J/cm³. For dynamic impact, unidirectional gradient structures exhibit exceptional energy absorption, particularly the unidirectional positive gradient honeycomb structure (UPG-SML) with outstanding mechanical properties. The angle gradient design plays a crucial role in determining the structure's stability and deformation mode during impact. Fewer interlayer separations result in a more pronounced negative Poisson's ratio effect and enhance the structure's energy absorption capacity. These findings provide a foundation for the rational design and selection of seismic protection structures in different strain rate impact environments.

Flexible materials with negative Poisson's ratio exhibit unique mechanical properties, which combined with other excellent optoelectronic properties will facilitate the nanoscale applications with complex functionalities. Based on first-principles calculations, we uncover a transparent two-dimensional pentagonal material, penta-CdO 2 , exhibiting dynamic, thermal, thermodynamic and mechanical stability. Penta-CdO 2 possesses excellent mechanical flexibility with larger negative Poisson's ratio of −0.47 than that of penta-graphene and good mechanical ductile property with a large ultimate strength. On the other hand, penta-CdO 2 is an indirect band gap semiconductor with a band gap of 3.28 eV concomitant with band-convergence characteristics, and its band edges fully span the redox potentials of water with excellent robustness across wide pH conditions and strain ranges. Furthermore, penta-CdO 2 exhibits good solar light absorption performances, nearly 100% transmission to visible light, high carrier mobility and anisotropy ratio, as well as favorable hydrogen evolution reaction free energy (Δ G H * = −0.64 eV), indicating its potential application as a photocatalyst for water splitting. The present theoretical prediction not only enriches the family of two-dimensional pentagon-based materials, but also uncovers its potential application prospects in flexible mechanics, optoelectronics, and photocatalytic water splitting. • Uncover a transparent 2D pentagonal material penta-CdO 2 by structure searching. • Excellent mechanical flexibility with larger NPR (−0.47) than that of penta-graphene. • Indirect band gap semiconductor concomitants with band-convergence characteristics. • Good solar light absorption, nearly 100% transmission, anisotropic carrier mobility. • Favorable hydrogen evolution reaction free energy (−0.64 eV) for water splitting. [ABSTRACT FROM AUTHOR]

Metamaterials are artificially created materials or structures with properties not found in nature. They encompass electromagnetic, acoustic, and mechanical metamaterials, which are particularly significant in applied engineering. Mechanical metamaterials exhibit unique mechanical properties such as vanishing shear modulus, negative Poisson's ratio, negative compressibility, etc. This paper reviews the most commonly used mechanical metamaterials and discusses their applications in the field of applied engineering, specifically in vibration isolation, energy absorption, and vibration reduction. The prospects for future developments in this field are also presented. [ABSTRACT FROM AUTHOR]

Recently, the application of two–dimensional (2D) piezoelectric materials has been seriously hindered because most of them possess only in–plane piezoelectricity but lack out–of–plane piezoelectricity. In this work, using first–principles calculation, by atomic substitution of penta–graphene (PG) with tiny out–of–plane piezoelectricity, we design and predict stable 2D X–PG (X = Si or Ge) semiconductors with excellent in–plane and out–of–plane piezoelectricity and extremely high in–plane hole mobility. Among them, Ge–PG exhibits better performance in all aspects with an in–plane strain piezoelectric coefficient d11 = 8.43 pm/V, an out–of–plane strain piezoelectric coefficient d33 = −3.63 pm/V, and in–plane hole mobility μh = 57.33 × 103 cm2 V−1 s−1. By doping Si and Ge atoms, the negative Poisson's ratio of PG approaches zero and reaches a positive value, which is due to the gradual weakening of the structure's mechanical strength. The bandgaps of Si–PG (0.78 eV) and Ge–PG (0.89 eV) are much smaller than that of PG (2.20 eV), by 2.82 and 2.47 times, respectively. This indicates that the substitution of X atoms can regulate the bandgap of PG. Importantly, the physical mechanism of the out–of–plane piezoelectricity of these monolayers is revealed. The super–dipole–moment effect proposed in the previous work is proved to exist in PG and X–PG, i.e., it is proved that their out–of–plane piezoelectric stress coefficient e33 increases with the super–dipole–moment. The e33–induced polarization direction is also consistent with the super–dipole–moment direction. X–PG is predicted to have prominent potential for nanodevices applied as electromechanical coupling systems: wearable, ultra–thin devices; high–speed electronic transmission devices; and so on. [ABSTRACT FROM AUTHOR]

On‐water rowing is a sport where participants make extensive, powerful, and complex repetitive movements with their wrists to pull and feather (twist) the oar. Herein, the aim is to assess the frequency and perceived causes of wrist and forearm pain in rowers and, in particular, assess whether there are any possible mechanical issues that could be addressed through the use of auxetic technology. Through an online survey of 145 on‐water rowers, it is found that 33.8% of the rowers reported wrist or forearm pain arising from rowing. The majority (67.3%) consider over‐gripping to be the cause while one out of five associated it with periods of tension and anxiety, which also led them to over‐grip. This indicates that rowing handles could benefit from the use of mechanical metamaterials, auxetics in particular, owing to their anomalous manner in how they deform when subjected to mechanical deformations. Moreover, given the rise in popularity of coastal rowing, which will become an Olympic discipline alongside classic rowing as from the 2028 Los Angeles Olympic Games, the potential use of auxetics in the manufacture of protective gear for use in coastal rowing is also discussed. [ABSTRACT FROM AUTHOR]

For the proposed new negative Poisson's ratio vascular stent, the effects of stent parameters on radial resilience, axial shortening rate, and radial support stiffness were compared and analyzed based on finite element methods and orthogonal tests, considering the complete compression-grip expansion process of the stent. It was concluded that decreasing the wall width of the cell structure or increasing the length of the cell structure could improve the radial resilience performance of the stent; decreasing the number of axial cell structures, decreasing the pinch angle, and increasing the wall width of the cell structure could reduce the axial shortening rate and could improve the axial shortening performance of the stent; increasing the wall width of the cell structure, the wall thickness of the cell structure and the number of axial cell structure could improve the radial support stiffness of the stent. In Vitro tests were conducted to study the effects of compression rate, circumferential compression position, and number of axial cells on the radial support performance of the stent. The geometric parameters of vascular stents have a significant influence on the mechanical properties of stents and should be given significant consideration in the clinical selection and optimal design of stents. [ABSTRACT FROM AUTHOR]

Poisson's ratio in auxetic materials shifts from typically positive to negative, causing lateral expansion during axial tension. This scale‐independent characteristic, originating from tailored architectures, exhibits specific physical properties, including energy adsorption, shear resistance, and fracture resistance. These metamaterials demonstrate exotic mechanical properties with potential applications in several engineering fields, but biomedical applications seem to be one of the most relevant, with an increasing number of articles published in recent years, which present opportunities ranging from cellular repair to organ reconstruction with outstanding mechanical performance, mechanical conduction, and biological activity compared with traditional biomedical metamaterials. Therefore, focusing on understanding the potential of these structures and promoting theoretical and experimental investigations into the benefits of their unique mechanical properties is necessary for achieving high‐performance biomedical applications. Considering the demand for advanced biomaterial implants in surgical technology and the profound advancement of additive manufacturing technology that are particularly relevant to fabricating complex and customizable auxetic mechanical metamaterials, this review focuses on the fundamental geometric configuration and unique physical properties of negative Poisson's ratio materials, then categorizes and summarizes auxetic material applications across some surgical departments, revealing efficacy in joint surgery, spinal surgery, trauma surgery, and sports medicine contexts. Additionally, it emphasizes the substantial potential of auxetic materials as innovative biomedical solutions in orthopedics and demonstrates the significant potential for comprehensive surgical application in the future. [ABSTRACT FROM AUTHOR]

AbstractTo enhance the performance of the six-missing rib honeycomb (ASRH), two axisymmetric missing rib honeycombs, ASRH-1 and ASRH-2, are proposed in this study. First, the in-plane impact performance of ASRH, ASRH-1, and ASRH-2 is experimentally compared to verify the accuracy of the finite element model. Then, the deformation patterns, specific energy absorption (SEA), and negative Poisson’s ratio (NPR) effects of the three honeycombs under different parameters were parametrically investigated. The results indicate that ASRH-1 and ASRH-2 exhibit higher SEA than ASRH at an impact velocity of 10 m/s, but the NPR effect does not change significantly. The axisymmetric honeycomb demonstrates no advantage at 50 and 100 m/s high-speed impacts. The Poisson’s ratio effect of the three honeycombs varied greatly with the internal ligament r of the honeycomb. The axisymmetric design offers a new concept for a NPR honeycomb design. [ABSTRACT FROM AUTHOR]

In order to predict the damage behaviours of 3D-printed continuous carbon fibre (CCF) reinforced composites, when additional short carbon fibre (SCF) composite components are employed for continuous printing or special functionality, a novel path-dependent progressive failure (PDPF) numerical approach is developed. First, a progressive failure model using Hashin failure criteria with continuum damage mechanics to account for the damage initiation and evaluation of 3D-printed CCF reinforced polyamide (PA) composites is developed, based on actual fibre placement trajectories with physical measurements of 3D-printed CCF/PA constituents. Meanwhile, an elastic-plastic model is employed to predict the plastic damage behaviours of SCF/PA parts. Then, the accuracy of the PDPF model was validated so as to study 3D-printed CCF/PA composites with either negative Poisson's ratio or high stiffness. The results demonstrate that the proposed PDPF model can achieve higher prediction accuracies in mechanical properties of these 3D-printed CCF/PA composites. Mechanism analyses show that the stress distribution is generally aggregated in the CCF areas along the fibre placement paths, and the shear damage and matrix tensile/compressive damage are the key damage modes. This study provides a new approach with valuable information for characterising complex 3D-printed continuous fibre-matrix composites with variable mechanical properties and multiple constituents. [ABSTRACT FROM AUTHOR]

Materials exhibiting auxetic behavior have garnered significant interest due to their potential applications across various fields, with synthetic auxetic materials being one such group. Theoretical studies have demonstrated the potential for various organic polymeric systems to exhibit auxetic behavior. However, to date, only a few synthesized molecular systems have shown some degree of auxetic behavior. Among the theoretical classes of molecular systems that have attracted attention are calix[4]arene systems in the “egg‐rack” conformation. While the theoretical systems proposed in the literature have been deemed difficult to synthesize, calix[4]arene chemistry has advanced tremendously in recent years. In fact, a number of molecular systems with configurations similar to those predicted to exhibit a negative Poisson's ratio have been synthesized, albeit with different chemical moieties. Consequently, it is deemed valuable to study the potential of these synthesized systems to exhibit a negative Poisson's ratio through force‐field‐based simulations. This study is extended to include theoretical calix[4]arene systems linked by acetylene moieties, which are also potentially synthesizable through known methods. It is suggested that these materials can exhibit auxetic behavior when subjected to on‐axis loading in the [001] direction. A detailed mechanistic study of these systems is also conducted. [ABSTRACT FROM AUTHOR]

The deep mining of coal resources is accompanied by severe environmental challenges and various potential engineering hazards. The implementation of NPR (negative Poisson's ratio) bolts are capable of controlling large deformations in the surrounding rock effectively. This paper focuses on studying the mechanical properties of the NPR bolt under static disturbance load. The deep nonlinear mechanical experimental system was used to study the mechanical behavior of rock samples with different anchored types (unanchored/PR anchored/2G NPR anchored) under static disturbance load. The whole process of rock samples was taken by high-speed camera to obtain the real-time failure characteristics under static disturbance load. At the same time, the acoustic emission signal was collected to obtain the key characteristic parameters of acoustic emission such as acoustic emission count, energy, and frequency. The deformation at the failure of the samples was calculated and analyzed by digital speckle software. The findings indicate that the failure mode of rock is influenced by different types of anchoring. The peak failure strength of 2G NPR bolt anchored rock samples exhibits an increase of 6.5% when compared to the unanchored rock samples. The cumulative count and cumulative energy of acoustic emission exhibit a decrease of 62.16% and 62.90%, respectively. The maximum deformation of bearing capacity exhibits an increase of 59.27%, while the failure time demonstrates a delay of 42.86%. The peak failure strength of the 2G NPR bolt anchored ones under static disturbance load exhibits an increase of 5.94% when compared to the rock anchored by PR (Poisson's ratio) bolt. The cumulative count and cumulative energy of acoustic emission exhibit a decrease of 47.16% and 43.86%, respectively. The maximum deformation of the bearing capacity exhibits an increase of 50.43%, and the failure time demonstrates a delay of 32%. After anchoring by 2G NPR bolt, anchoring support effectively reduces the risk of damage caused by static disturbance load. These results demonstrate that the support effect of 2G NPR bolt materials surpasses that of PR bolt. [ABSTRACT FROM AUTHOR]

AbstractOrigami metamaterials exhibit abnormal mechanical properties through artful structural design. To further explore the mechanical behavior of reentrant metamaterials, a multi-directional auxetic origami metamaterial (AOMM) was designed, and its negative Poisson’s ratio effect was analyzed through the diagram of load bearing and deformation. Theoretical models related to geometric parameters, relative density, folding rate, equivalent elasticity and load plateau were established to reveal the deformation transformation mechanism, and the influence of size parameters on the equivalent elastic constants was drawn. Using thermoplastic polyurethane (TPU) as the substrate, two types of multi-directional AOMMs were fabricated by 3D printing, and quasi-static compression experiments were performed. The results show that the TPU AOMMs has a reusable compressive capacity, whose compressive mechanical behaviors are mainly contributed by the buckling instability and large deformation of sidewall. There is a coupling effect between the cross connection boundaries, which results in the difference in mechanical properties of AOMM with different geometric sizes. The prediction results of relative density, load plateau and yield strain through equivalent theories approximate that of experimental results. Simultaneously, finite element analyses were conducted, which agrees well with the experiments. These foundings may provide reference for the design and application of novel auxetic or origami metamaterials. [ABSTRACT FROM AUTHOR]

Based on a novel multi-arc concave cell, four types of thickness gradient honeycomb structures with positive gradient, negative gradient, symmetric positive gradient, and symmetric negative gradient are constructed by changing cell wall thickness, and the relative density of the structure is deduced. The in-plane impact dynamics of gradient structure are revealed by numerical method. The deformation collapse mode, the dynamic response curve, the energy absorption effect, and the platform stress of different gradient arrangement and impact velocity are analyzed. It is found that gradient arrangement and impact velocity have significant effects on the impact properties of the thickness gradient honeycomb structures. When the impact velocity is low, the structure shows laminar shrinkage deformation, but this phenomenon will gradually disappear with the increase of impact velocity. The results show that the energy absorption capacity of the negative gradient structure is the best under different impact velocities. The platform stress is greatly affected by the impact velocity and less affected by the gradient arrangement. [ABSTRACT FROM AUTHOR]

Osteoblasts are mechanosensitive cells. Tensile stress with different conditions, including loading time, frequency, magnitude, etc. would cause varied responses in osteoblasts. However, it was not clarified that the effect of the loading types on the osteoblasts. In this study, we focused on the effect of varied tensile stress types on osteoblasts, including isotropic stretch, biaxial stretch, and uniaxial stretch with the negative ratio of transverse strain to axial strain (NR) −1, 0, and 0.2 respectively. Cell proliferation was determined to be most efficient when stimulated by 6% strain at a frequency of 1 Hz and a negative value of 0 for 1 h/day. The varied strain resulted in a thickening of the F-actin cytoskeleton and a thinning of the nucleus. Nuclear flattening caused Yes-associated protein (YAP) to be transported to the nucleus. It was suggested that the influence of loading types on the mechanobiology responses must be noticed. The mechanism of cell mechanical sensitivity under varied loading types was explored, which would provide good suggestions for designing microstructures to control deformation patterns in bone tissue engineering. [ABSTRACT FROM AUTHOR]

Background: Geometric parameter optimization, novel design, and mechanism modeling of auxetic materials have been widely studied. However, manipulating the topology of the 3d printed auxetic unit cells and its influence on the damage have yet to be explored. Objective: This study aims to characterize the energy absorption properties and damage mechanisms of the modified auxetic unit cells. Methods: In the current study, bending-dominated re-entrant auxetic unit cells (Cell0), torsion-dominated auxetic unit cells with cross elements (CellX), buckling-dominated auxetic unit cells with vertical elements (CellB), and bending-dominated auxetic unit cells with panels (CellW) have been fabricated by FDM (Fused deposition modeling). Uniaxial compression testing of the PLA (Polylactic acid) unit cells has been carried out, and a camera has observed their deformation behavior. SR- µCT (Synchrotron radiation microtomography) and an SEM (Secondary electron microscope) accomplished further damage analysis of the struts. Results: Adding additional struts hinders the lateral shrinking of the re-entrant auxetics, and re-entrant auxetic unit cells with cross elements have shown higher energy absorption capacity and efficiency than others. The struts' damage has been governed by building direction, printed material, and strut dimensions. Intra-layer and interlayer fracture of the layers and rupture in the circumferential direction of the PLA struts have been observed in the SR- µCT slices. Conclusions: By additional struts, it is possible to fabricate complex auxetic structures with enhanced energy absorption properties, but their inherent characteristics dominate the damage of the struts in the auxetic unit cells. [ABSTRACT FROM AUTHOR]

Non-pneumatic tires have the advantages of high safety and high load-carrying capacity, and have a broad potential for engineering applications. In this paper, the effects of different gradient angles on the static and dynamic performance of honeycomb spoke structure are studied. First of all, according to different gradient and gradient-free Non-Pneumatic Tires (NPTs) are designed and the corresponding finite element models of non-pneumatic tires are established respectively. Then, the static mechanical properties of NPTs are analyzed, including the bearing capacity of NPTs and the stress distribution of NPT components. Finally, the dynamic mechanical properties of gradient-free and gradient NPTs are simulated. The stress characteristics and rolling characteristics of the gradient to the key components of NPTs under dynamic load are analyzed. The results show that different gradients have effects on the radial stiffness of the tire, the maximum stress distribution position of spokes, tire rolling characteristics, and the stress characteristics of other parts of NPTs. The research results provide guidance for the structure design and optimization of non-pneumatic tires.

In the dynamic interaction between the runner and the ground, the running shoe is the only medium that bears the impact force of body weight and plays a crucial role in athletic performance. Traditional designs do not adequately consider the different shapes of the foot, which often leads to discomfort and aggravation of foot disorders. This study presents an innovative approach to running shoe midsole design using 3D-printed chiral negative poisson’s ratio (NPR) structures to enhance shock absorption and support, thereby optimizing biomechanical performance and comfort. Using computer-aided design (CAD) and computer-aided engineering (CAE), the biomechanical effects of different midsole structures has been explored through finite element analysis (FEA). The study focuses on optimizing the cushioning, propulsion and stability of the midsole to mitigate the impact on the ankle and knee. Static compression and dynamic impact simulations were utilized to comprehensively select optimized design of midsole structure and the selected structures was 3D printed to validate the biomechanical benefits in a wear trial. The results of the study highlight the superior performance of chiral NPR structures in reducing forefoot stress during standing and movement and advance the design and functionality of 3D printed materials in running shoes.

Auxetic structures, characterized by showing negative Poisson's ratio (ʋ) when loaded, are cellular metamaterials consisting of connected struts in repeating unit cells. The mechanical behavior of auxetics depends on dimensions of the unit cell such as height and length of the unit cell, strut thickness (St), and orientation angle (θ) of the struts. The present study investigates effects of variations in St and θ on ʋ and stiffness (E) of additively manufactured 316L stainless steel with re-entrant honeycomb auxetics fabricated by laser powder bed fusion technique. Poisson's ratio was acquired through linear elastic simulations via finite element analysis (FEA) and verified experimentally through digital image correlation (DIC) facility attached to tensile tests. The design of the auxetic patterns entailed a simulation of thirty-five distinct models, incorporating St values of 0.4–1.6 mm, as well as θ values of 70–90°. In comparison, experimental validation was conducted on nine specimens, featuring St values of 0.6–1.4 mm, and θ values of 70–80°. FEA and experimental results obtained by DIC exhibited ʋ values of −5.23 to −0.3 (for St 0.6-1.4 mm and θ 70–80°), displaying increased ʋ with reductions in both St and/or θ. Meanwhile, E increased with St increase or θ decrease, exhibiting values of 18.9–72 GPa, which could be optimized to fit with human bones stiffness as potential orthopedics implantation in future.

Osteoblasts are mechanosensitive cells. Tensile stress with different conditions, including loading time, frequency, magnitude, etc. would cause varied responses in osteoblasts. However, it was not clarified that the effect of the loading types on the osteoblasts. In this study, we focused on the effect of varied tensile stress types on osteoblasts, including isotropic stretch, biaxial stretch, and uniaxial stretch with the negative ratio of transverse strain to axial strain (NR) −1, 0, and 0.2 respectively. Cell proliferation was determined to be most efficient when stimulated by 6% strain at a frequency of 1 Hz and a negative value of 0 for 1 h/day. The varied strain resulted in a thickening of the F-actin cytoskeleton and a thinning of the nucleus. Nuclear flattening caused Yes-associated protein (YAP) to be transported to the nucleus. It was suggested that the influence of loading types on the mechanobiology responses must be noticed. The mechanism of cell mechanical sensitivity under varied loading types was explored, which would provide good suggestions for designing microstructures to control deformation patterns in bone tissue engineering.

Design of mechanical metamaterials with a negative Poisson's ratio (NPR), known as auxetics, is of great importance in the development of flexible electronics and tissue engineering. However, the mechanical performance of conventional auxetic metamaterials is largely hindered by the high porosity and lack of tunability, which restricts their practical engineering applications. Here, this study presents a programmable approach for designing integrated two‐phase auxetic composite metamaterials with pore‐free structure, robust interfaces, and customized mechanical properties by substituting the vacancy of the auxetic lattices (frame phase) with hydrogel‐based soft fillers (matrix phase). Manipulated by two‐phase stiffness contrast, integrated composite metamaterials exhibit a functional transition between auxetic and non‐auxetic behaviors. Rationally designing Young's modulus ratios in spatial domains endows the programming of composite metamaterials with the desired spatial heterogeneity. Furthermore, the incorporation of temperature‐responsive hydrogels to auxetic frames also enbles the development of dynamic programmable composites with the thermo‐driven adaptability. As a practical application demonstration, designed programmable composites are used to dynamically tune the phononic bandgaps. The design strategy of integrated two‐phase composite metamaterials paves the way for the development of advanced auxetic engineering materials with programmable mechanical properties, providing opportunity for conformal electronic patches, bio‐scaffolds, and smart functionality applications. [ABSTRACT FROM AUTHOR]

The use of 3D printers is expanding across various industries. The incorporation of reinforcing fibers and structures, such as negative Poisson, has the potential to enhance the mechanical properties of three-dimensional products. In this study, a specialized nozzle is developed for 3D Fused Deposition Modeling (FDM) printers dedicated to the production of continuous fiber-reinforced thermoplastic (CFRT) composites. The primary objective is to enhance the tensile strength and impact resistance of 3D-printed samples. It is achieved through the investigation of strategies such as fiber reinforcement, variation in the number of fibers within the reinforcing yarn, and the creation of samples featuring an internal structure with a negative Poisson's ratio (NPRS). In this regard, four types of 3D samples are prepared including polymer only, polymer with a negative Poisson's ratio structure, polymer reinforced with continuous fibers (glass and carbon fibers), and polymer reinforced with continuous fibers featuring a negative Poisson's ratio structure. The mechanical properties of these samples, including tensile strength and impact resistance, are also compared. The results indicate that incorporating fibers as reinforcement can enhance the mechanical properties of 3D-printed products. Moreover, continuous fibers with more fibers within the same yarn count have an increased strengthening effect. The use of negative Poisson structures significantly improves impact resistance but adversely affects tensile strength. [ABSTRACT FROM AUTHOR]

This study aimed to improve the energy absorption capabilities of auxetic structures, which are used in sandwich structures in engineering. To achieve this, the study used a combination of CFRP and aluminum materials in a hybrid double arrow-head auxetic (DAHA) structure. This paper conducted experiments and simulations to analyze the mechanical properties of the hybrid DAHA structures and found that the mixture ratio of hybrid material, ply angles of CFRP laminates, and inclination angles of beams significantly influenced the energy absorption performance of the structures. Additionally, the proposed hybrid DAHA structures outperformed other control groups when the thickness ratio of CFRP was 75%. The inclination angles of beams also affected the energy absorption capacity by changing the structural void of DAHA structures. These findings offer new insights into enhancing the energy absorption capacity of hybrid auxetic structures. The proposed hybrid structures can absorb more energy by 56.4% with a lower peak crushing force comparing with the traditional metal auxetic structure. Therefore, the CFRP/Aluminum hybrid auxetic structure has a bright future in the energy absorption fields. [ABSTRACT FROM AUTHOR]

Aiming to address the multi-objective cooperative optimization problem of ship structure lightweight and crashed-resistance, this study proposed a concave reentrant honeycomb-based negative Poisson's ratio (NPR) sandwich structure to replace the stiffened plate. The feasibility of using the sandwich structure to improve ship crashworthiness is demonstrated through finite element analysis. An intelligent optimization method is established to address the issues of multiple parameters and complex effects associated with composite structures and optimize the crashworthiness of the sandwich structure. The effectiveness of the optimization method and the feasibility of the NPR sandwich structure in ship crashworthiness have been validated, providing a reference for the design of new multi-functional ship structures. [ABSTRACT FROM AUTHOR]

Negative Poisson's ratio (NPR) metamaterials are attractive for their unique mechanical behaviors and potential applications in deformation control and energy absorption. However, when subjected to significant stretching, NPR metamaterials designed under small strain assumption may experience a rapid degradation in NPR performance. To address this issue, this study aims to design metamaterials maintaining a targeted NPR under large deformation by taking advantage of the geometry nonlinearity mechanism. A representative periodic unit cell is modeled considering geometry nonlinearity, and its topology is designed using a gradient-free method. The unit cell microstructural topologies are described with the material-field series-expansion (MFSE) method. The MFSE method assumes spatial correlation of the material distribution, which greatly reduces the number of required design variables. To conveniently design metamaterials with desired NPR under large deformation, we propose a two-stage gradient-free metamaterial topology optimization method, which fully takes advantage of the dimension reduction benefits of the MFSE method and the Kriging surrogate model technique. Initially, we use homogenization to find a preliminary NPR design under a small deformation assumption. In the second stage, we begin with this preliminary design and minimize deviations in NPR from a targeted value under large deformation. Using this strategy and solution technique, we successfully obtain a group of NPR metamaterials that can sustain different desired NPRs in the range of [-0.8, -0.1] under uniaxial stretching up to 20% strain. Furthermore, typical microstructure designs are fabricated and tested through experiments. The experimental results show good consistency with our numerical results, demonstrating the effectiveness of the present gradient-free NPR metamaterial design strategy. [ABSTRACT FROM AUTHOR]

Auxetic materials have attracted significant interest due to their exceptional mechanical characteristics and distinctive deformation modes. Nevertheless, the practical use of these materials in engineering is constrained by their limited ability to absorb energy. Thus, enhancing the energy absorption (EA) capabilities of auxetic materials is crucial to expand their range of potential applications. In this study, the EA capabilities of auxetic tubular structures with rotating deformation mechanisms are examined, with a specific emphasis on three different perforation shapes: elliptic, peanut, and square, along with their modified versions incorporating stiffeners. The study employs a combination of experimental testing and numerical modelling, utilising ANSYS/LS-DYNA to evaluate various crashworthiness parameters. These parameters include total EA, specific EA, maximum crushing force, and crushing force efficiency, all of which are assessed under quasi-static compression conditions. The research highlights the importance of perforation shape and stiffener incorporation in enhancing crashworthiness. Results show that elliptic perforations exhibit superior EA and stiffened auxetic models outperform conventional ones in terms of crash absorber performance. The presence of stiffeners significantly improves the ability of tubular structures to withstand crushing forces. Furthermore, the study validates the numerical model against experimental findings, demonstrating a high level of agreement in terms of crushing force–displacement, EA, and failure modes. The research provides valuable insights into the design and performance of crashworthy structures and offers potential applications in various fields where impact resistance and EA are critical. [ABSTRACT FROM AUTHOR]

A novel methodology is introduced for designing auxetic (negative Poisson's ratio) structures based on topological principles and is demonstrated by investigating a new class of auxetics based on two‐dimensional (2D) textile weave patterns. Conventional methodology for designing auxetic materials typically involves determining a single deformable block (a unit cell) of material whose shape results in auxetic behavior. Consequently, patterning such a unit cell in a 2D (or 3D) domain results in a larger structure that exhibits overall auxetic behavior. Such an approach naturally relies on some prior intuition and experience regarding which unit cells may be auxetic. Second, tuning the properties of the resulting structures is typically limited to parametric variations of the geometry of a specific type of unit cell. Thus, most of the currently known auxetic structures belong to a selected few classes of unit cell geometries that are explicitly defined in accordance with a specified topological (i.e., grid structure). Herein, a new class of auxetic structures is demonstrated that, while periodic, can be generated implicitly, i.e., without reference to a specific unit cell design. The approach leverages weave‐based parameters (A–B–C), resulting in a rich design space for auxetics that is previously unexplored. [ABSTRACT FROM AUTHOR]