Removing Auxetic Properties in f.c.c. Hard Sphere Crystals by Orthogonal Nanochannels with Hard Spheres of Another Diameter

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It is known that a face centered cubic (f.c.c.) crystal of identical hard spheres containing a periodic array of nanochannels, oriented along one of the principal crystallographic directions and filled by hard spheres of another diameter, shows a significant decrease of its Poisson's ratio with respect to pristine crystal. This indicates an essential enhancement of auxetic properties by such nanoinclusions. The present work describes studies of the f.c.c. hard‐sphere crystal containing four nanochannel arrays, oriented along the [ 111 ] direction and its images with respect to cubic symmetry group transformations and selected in such a way as to not affect the symmetry of the crystal. The elastic properties of the current model are analyzed under different thermodynamic conditions and for different sizes of inclusions. These studies reveal that the auxetic properties of the system vanish when the diameters of inclusion spheres are greater than the ones forming the matrix f.c.c. crystal and, in the case of the widest nanochannels, also when these diameters are smaller. The studies are performed by Monte Carlo computer simulations in the isothermal–isobaric (NpT) ensemble, using the Parrinello–Rahman approach.

8 %

, the system is considered amorphous, rather than crystalline.…”

Section: Computational Sectionmentioning

confidence: 99%

“…In the case of certain binary systems, studied in the present article, it has been reported that one can reach even

10 %

σ^{'} / σ

(the scaling factor ) to the range from

0.95

1.07

.…”

Section: Computational Sectionmentioning

confidence: 99%

“…The studies have been extended to the model containing three arrays of nanochannels oriented in main crystallographic directions (

[100]

[010]

, and

[001]

Section: Introductionmentioning

confidence: 99%

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Poisson's Ratio of f.c.c. Hard‐Sphere Crystals with Cubic Supercells Containing Four Nanochannels Filled by Hard Spheres of Another Diameter

Narojczyk

Tretiakov

Wojciechowski

2022

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“…Mechanical metamaterials [1,2,3,4,5,6,7,8,9,10,11,12,13] are rationally-designed structures capable of exhibiting a plethora of atypical mechanical properties that are rarely observed in the case of naturally-occurring materials. Some of the most commonly studied of such properties are negative Poisson's ratio [14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29] (auxetic behaviour), negative stiffness [30,31,32,33,34] and negative compressibility [35,36]. Over the last thirty years, it has been demonstrated that devices utilising materials exhibiting such characteristics can be used in the case of a variety of applications including protective devices [37,38], sports equipment [39] as well as biomedical [40,41] and vibration damping devices [42,43,44].…”

Section: Introductionmentioning

confidence: 99%

Variable Dual Auxeticity of the Hierarchical Mechanical Metamaterial Composed of Re‐Entrant Structural Motifs

Dudek

Martínez

Kadic

2022

In this work, a novel hierarchical mechanical metamaterial is proposed that is composed of re-entrant truss-lattice elements. It is shown that this system can deform very differently and can exhibit a versatile extent of the auxetic behaviour depending on a small change in the thickness of its hinges. In addition, depending on which hierarchical level is deforming, the whole structure can exhibit a different type of auxetic behaviour that corresponds to a unique deformation mechanism. This results in a dual auxetic structure where the interplay between the two auxetic mechanisms determines the evolution of the system. It is also shown that depending on the specific deformation pattern, it is possible to observe a very different behaviour of the structure in terms of frequencies of waves that can be transmitted through the system. In fact, it is demonstrated that even a very small change in the parametric design of the system may result in a significantly different band gap formation that can be useful in the design of tunable vibration dampers or sensors. The possibility of controlling the extent of the auxeticity also makes the proposed metamaterial to be very appealing from the point of view of protective and biomedical devices.

“…Auxetic systems, as these structures are called, [ 41 ] have attracted increasing attention since the late 1980s. [ 42–69 ] The reason for this stems from the fact that they have improved functionalities as compared to their conventional counterparts. These include, among others, enhanced indentation resistance, [ 44,70–72 ] increased shear stiffness, [ 44,73 ] and fracture toughness, [ 44,74 ] as well as vibration control.…”

Section: Introductionmentioning

confidence: 99%

An Investigation of Reconfigurable Magnetomechanical Metamaterials

Galea

Farrugia

Dudek

et al. 2022

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Herein, an experimental investigation of an accordion‐like system with embedded magnetic inclusion is carried out. It is shown that the way that this structure deforms when subjected to an external magnetic field depends on the magnetic moment of the embedded magnets and the length of the arms. Stacking of the accordion‐like system leads to the formation of hexagonal honeycombs that can have a negative, zero, and positive Poisson's ratio. Variation in the configuration attained depends on the relative positioning of the magnetic inclusion and the applied magnetic field. In particular, one of the hexagonal honeycomb arrangements is able to switch between a conventional and a re‐entrant configuration upon the reversal of the external magnetic field. For all structures considered, the dimensions can be controlled through the external magnetic field, allowing for a high degree of turnability. Furthermore, their behavior can be altered in real time. The practical implications of the results are of interest since they indicate that these structures can be adopted in numerous applications, such in the design of scaffoldings for deployable structures, actuators, variable pored sieves, and sound proofing systems.