1,721,406 research outputs found
In-plane mechanical behavior of novel auxetic hybrid metamaterials
Full text linkWe present in this paper two novel concepts of hybrid metamaterials that combine a core unit cell of re-entrant or cross-chiral shape and lateral missing ribs. The first topology is a hybrid between an anti-tetrachiral and a missing rib (cross-chiral) configuration; the second one has a variable cross-chiral layout compared to the classical missing rib square structure. Their in-plane mechanical properties have been investigated from a parametric point of view using finite element (FE) simulations. The two classes of metamaterials have been benchmarked to obtain optimized designs and specific effective properties. Nonlinear simulations and experimental tests of the new re-entrant missing rib metamaterials featuring optimized geometry parameters have been performed to understand the behavior of these architectures under large deformations
Tunable, multi-modal, and multi-directional vibration energy harvester based on three-dimensional architected metastructures
Full text linkConventional vibration energy harvesters based on two-dimensional planar layouts have limited harvesting capacities due to narrow frequency bandwidth and because their vibratory motion is mainly restricted to one plane. Three-dimensional architected structures and advanced materials with multifunctional properties are being developed in a broad range of technological fields. Structural topologies exploiting compressive buckling deformation mechanisms however provide a versatile route to transform planar structures into sophisticated three-dimensional architectures and functional devices. Designed geometries and Kirigami cut patterns defined on planar precursors contribute to the controlled formation of diverse threedimensional forms. In this work, we propose an energy harvesting system with tunable dynamic properties, where piezoelectric materials are integrated and strategically designed into three-dimensional compliant architected metastructures. This concept enables energy scavenging from vibrations not only in multiple directions but also across a broad frequency bandwidth, thus increasing the energy harvesting efficiency. The proposed system comprises a buckled ribbon with optional Kirigami cuts. This platform enables the induction of vibration modes across a wide range of resonance frequencies and in arbitrary directions, mechanically coupling with four cantilever piezoelectric beams to capture vibrations. The multi-modal and multi-directional harvesting performance of the proposed configurations has been demonstrated in comparison with planar systems. The results suggest this is a facile strategy for the realization of compliant and high-performance energy harvesting and advanced electronics systems based on mechanically assembled platforms
Two-dimensional graded metamaterials with auxetic rectangular perforations
Full text linkThis work describes the in-plane uniaxial tensile mechanical properties of two-dimensional graded rectangular perforations metamaterials using numerical homogenization finite element approaches benchmarked by experimental results. The metamaterial configuration is based on graded patterns of centre-symmetric perforated cells that can exhibit an auxetic (negative Poisson’s ratio) behavior. Global and local equivalent mechanical properties of the metamaterial are measured using digital image correlation techniques mapped over Finite Element models to identify strain patterns and related stress distributions at different scales. The samples and their numerical counterpart are parametrized against the spacing and aspect ratios of the cells. The overall stiffness behavior of the graded perforated metamaterial plates features a higher degree of compliance that depends both on the geometries of the cells of the graded areas, but also on the graded pattern used. Local Poisson’s ratio effects show a general constraint of the auxetic behavior compared to the case of uniform plates, but also interesting and controllable shape changes due to the uniaxial tensile loading applied
Assessing the mechanical and static aeroelastic performance of cellular Kirigami wingbox designs
No full textAdaptive wings configurations have been evaluated for morphing airframe applications during the last two decades. Constructions with flexible hinges can be in particular a solution for small top medium-scale air vehicles, while novel Kirigami technologies help to produce flexible and complex structures by enabling novel geometric paradigms. In this study, a cellular Kirigami wingbox with an adaptive hinge is designed and manufactured. The mechanical properties of the wingbox are numerically evaluated, considering the shear modulus of the cellular elements patterning the wingbox. Thus, the equivalent torsional, flexural stiffness, as well as the shear centre location of the whole wingbox structure arecalculated. The analysis is parametrised against various possible internal cell angles and cell thickness values that define the Kirigami cellular tessellation of the wingbox. The static divergence speed is also evaluated by means of the same parametrisation. This study shows the feasibility of using a Kirigami wingbox concept for morphing/adaptive small to medium-scale from a structural and aeroelastic perspective
AUXHEX – a Kirigami inspired zero Poisson's ratio cellular structure
Full text linkThis work describes the development, manufacturing and testing of a zero Poisson’s ratio PEEK cellular structure (AuxHex) made using Kirigami-inspired techniques. The AuxHex hybrid cell pattern is a combination of cells with different shapes that interlock with each other. This principle can lead to graded honeycombs possessing, in different areas, synclastic as well as anticlastic behavior. The AuxHex samples produced have been tested for flatwise compression according to ASTM standards and the results are compared with a unit-cell-based analytical model. Hexagonal-cell shaped honeycombs were also produced with the same technique and used for direct comparison. The mechanical flatwise properties have been benchmarked against the ones of other experimental PEEK-based cores and commercially available honeycombs. AuxHex samples are found to have higher stiffness compared to other experimental PEEK honeycombs, but lower compared with the commercially available honeycombs. The strength thought, while it is still higher compared to the other experimental PEEK cores, it is comparable with other honeycomb configurations
Nonlinear elasticity of auxetic open cell foams modeled as continuum solids
No full textStructure evolution during deformation of isotropic auxetic foams is investigated by simple compression experiments. It is shown that the main feature observed in the experimental data can be accurately described by an isotropic hyperelastic model with an Ogden-type strain energy function. The model can be easily implemented in a finite element code and, hence, can be used to simulate foams undergoing complex structural deformation
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
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