1,721,013 research outputs found
Non-porous grooved single-material auxetics
No full textOver the years, great advances have been made in the field of auxetic metamaterials where one of the main focuses was the production of systems which can be produced through simple and relatively inexpensive means. In this work, auxetic systems created through the introduction of elliptical grooves, meant to mimic the rotating units mechanism, are proposed and analyzed. These systems were found to have the potential to exhibit Poisson's ratios ranging from ca.-1 to the Poisson's ratio of the material of the system itself, with some systems also possessing the remarkable property of a zero Poisson's ratio. The final product is a non-porous metamaterial with potentially tailor-made Poisson's ratio properties
A rosette approach for the determination of the compliance matrix
No full textThe computation of the Young's moduli and Poisson's ratio using finite element analysis is comparatively straight forward in the case of systems with non-orthogonal lattice vectors. However, the corresponding calculation of the shear coupling coefficients and the shear modulus is more demanding and less readily attainable. Yet these are needed in order to determine the compliance matrix, which is essential in order to obtain a complete description of the mechanical properties of a structure in any direction. Based on these considerations, this work aims at providing a general methodology for the computation of the complete compliance matrix for systems with non-orthogonal lattice vectors from measurements of the Young's modulus and Poisson's ratio obtained using a suitable rosette of unit cells. The theoretical framework will be outlined and then applied on an accordion-like honeycomb that does not possess a rectangular unit cell and has potential applications in cellular scaffolding, particularly of heart muscle tissue. For the computation, the values of the Young's moduli and Poisson's ratio from three differently-orientated non-rectangular unit cells were obtained using finite element simulations allowing the determination of the complete compliance matrix. The results were validated by comparison with numerical simulations carried out on another unit cell having a different orientation from the other three
A force-field based analysis of the deformation mechanism in α-cristobalite
No full textα-cristobalite is a metastable polymorph of silica which has the remarkable property of exhibiting a negative Poisson's ratio (auxetic). In this study, the mechanical properties and deformation mechanisms of this system were investigated through a force-field based approach. Besides simulations on the actual structure of α-cristobalite, a number of simulations where the rigidity of SiO2 tetrahedra was increased, were also conducted. This was done in order to obtain a clearer picture of the role which these tetrahedra play in determining the mechanical properties of this system. These systems were loaded in an off-axis direction in a number of planes about the [001] direction and the deformations observed were compared with those of type II rotating rectangle systems. It was discovered that the mechanical properties of α-cristobalite can be accurately described through the semi-rigid version of this model, even for cases where the tetrahedra were fully rigid
Auxetic Perforated Mechanical Metamaterials with Randomly Oriented Cuts
No full textPerforated systems with quasi-disordered arrays of slits are found to exhibit auxetic characteristics almost as much as their traditional ordered "rotating-squares" counterparts. This provides a highly robust methodology for constructing auxetics that may be used for various practical applications such as skin grafting, where a high degree of precision may not always be achievable
Auxetic behavior obtained through the large deformations of variants of the rectangular grid
No full textThe deformation behavior of intersecting ligaments forming variants of the square and rectangular grids under mechanical compression was investigated. It was shown that such systems are able to exhibit a negative incremental Poisson’s ratio at relatively large axial compressive strains. Numerical simulations and experimental studies indicated that the extent of auxeticity depends on the relative offset of successive ligaments, the relative lengths of the ligaments as well as on their thickness. It was also shown that there are two distinct modes of deformation, one resembling that of the reentrant hexagonal honeycomb and the other that of the meta-tetrachiral system
Analysis of the Deformation Behavior and Mechanical Properties of Slit-Perforated Auxetic Metamaterials
No full textPerforated systems constitute one of the most important classes of mechanical metamaterials. In this work, two types of “I”-shaped slit perforation patterns are proposed which may be used to design perforated systems that mimic the deformation mechanisms of a variety of re-entrant and anti-tetrachiral honeycomb systems. Using finite element analysis, it is shown how these systems have the potential to exhibit a large spectrum of negative Poisson's ratios, ranging from extremely negative to zero, which are retained over a wide tensile strain range. A detailed analysis of the deformation behavior of these systems is also presented along with a comparison of the changes in overall expansion and Poisson's ratios of both systems observed upon loading with those predicted by previously formulated theoretical models of re-entrant and anti-tetrachiral systems. It is hoped that this work will be of considerable aid in the efforts of scientists to understand the underlying principles governing the production of auxetic mechanical metamaterials through the use of perforations and also stimulate further research on how these and similar mechanisms may be implemented in perforated systems to design other metamaterials with anomalous mechanical properties
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
