Status prawny Kościoła sui iuris

Chiral systems are a class of structures, which may exhibit the anomalous property of a negative Poisson's ratio. Proposed by Wojciechowski and implemented later by Lakes, these structures have aroused interest due to their remarkable mechanical properties and numerous potential applications. In view of this, this paper investigates the on-axis mechanical properties of the general forms of the flexing anti-tetrachiral system through analytical and finite element models. The results suggest that these are highly dependent on the geometry (the ratio of ligament lengths, thicknesses, and radius of nodes) and material properties of the constituent materials. We also show that the rigidity of an anti-tetrachiral system can be changed without altering the Poisson's ratio.The anti-tetrachiral system, with the unit cell shown in red.

Section: Introductionmentioning

confidence: 99%

A realistic generic model for anti‐tetrachiral systems

Gatt

Attard

Farrugia

et al. 2013

“…In (two‐dimensional) honeycomb with hexagonal cells, Poisson's ratio can be tuned to negative values including −1 by proper choice of cell dimensions and angles ; isotropic in‐plane behavior is possible. Related two‐dimensional paradigms include rotating hexamers and hinged squares and other polygons . In chiral honeycomb containing nodes that rotate, Poisson's ratio is −1, independent of strain and isotropic in‐plane.…”

Section: Resultsmentioning

confidence: 99%

The properties of copper foams with negative Poisson's ratio via resonant ultrasound spectroscopy

Liu

Lakes

2013

The Poisson's ratios of re‐entrant Cu foams with different initial relative densities were studied by resonant ultrasound spectroscopy (RUS). Slight anisotropy in foam was detected by RUS and removed by a small unidirectional compression. The transformation into the re‐entrant foam was accomplished by applying a sequence of permanent triaxial compression deformations. The Poisson's ratio first decreases and then increases with increasing compression strain. A minimum in Poisson's ratio of approximately −0.7 for all initial densities was achieved with an appropriate permanent compression strain, compared with −0.6 at similar density determined earlier via optical methods. Foams with higher values of initial density attained minima in Poisson's ratio at lower permanent volumetric compression. The shear modulus increased with increasing volumetric compression ratio, and showed a small hump near the point corresponding to Poisson's ratio minimum.

“…Negative value of Poisson's ratio does not contradict the classical elasticity, although it sounds incredible. A worldwide upsurge of research on those materials with negative Poisson's ratio (NPR) started from 1980s, after the pioneering work by Wojciechowski et al and Lakes . The terminology of “auxetics,” which is commonly used today, was introduced by Evans et al in 1991 to name the NPR materials.…”

Section: Introductionmentioning

confidence: 99%

Auxeticity from the Folded Geometry: A Numerical Study

Chen

Zulifqar

2019

The folded geometry has successfully been transformed into auxetic woven fabric in the literature. However, the influences of the microgeometric parameters on the macroscopic behavior have not been addressed yet. Herein, several key microgeometric parameters for the folded geometry are identified and the mechanical behaviors of the folded structure are preliminarily studied using the finite element method. The results show that the folded structure can be unfolded in both longitudinal and transverse directions when stretched and thus achieve a negative Poisson's ratio. More interestingly, another fantastic property of tension–bending coupling effect is found in the folded structure and a competition exists between the auxeticity and the tension–bending coupling effect. This is the first time to report a structure that can stimulatingly have the auxeticity and the tension–bending coupling effect. Due to the unique properties, the folded geometry is very promising in some important fields; for example, the textiles, civil engineering, and auto industry. The present work may provide a good guide for the design and application of the folded structure.