1,721,120 research outputs found
Multiscale DIC Applied to Pantographic Structures
No full textBackground: Since the mechanical behavior of pantographic metamaterials depends upon the properties of their microstructure, accurate descriptions of unit cells are needed. Objective: The present effort is motivated by this requirement to characterize the detailed deformation of unit cells formed of two orthogonal sets of 3 beams. Methods: Their deformations in a bias extension test were measured via digital image correlation performed at different scales. Results: Thanks to the gray level residuals, the microscale results were found in better agreement with the experiment than mesoscale and macroscale analyses. Fine analyses around the hinges showed that relative displacements occurred between the two beam layers. Conclusions: Such experimental analyses supply full-field data to validate models (e.g., as a starting point in homogenization procedures) for describing the mechanical behavior of pantographic metamaterials
Mesoscale modeling and experimental analyses for pantographic cells: effect of hinge deformation
Get PDFIn order to synthesize exotic metamaterials, it was proposed to use as elementary components of metamaterial microstructures so-called pantographic cells. The use of a mesomodel based on Euler–Bernoulli nonlinear beam theory is utilized for describing their behavior when their characteristic sizes are of the order of millimeters. With an in-house code, in which the connecting hinges were modeled as elastic extensional and torsional elements, simulations were performed and compared with experimental data. The comparison was carried out for compression and extension tests. It is proven, both numerically and experimentally, that the hinges undergo different deformation mechanisms. As a consequence, for compression and extension tests, the distribution and the total value of the strain energy vary significantly. The analysis is made possible in parts via Digital Image Correlation, which allows kinematic fields to be measured and the hypotheses employed for developing the proposed model to be probed experimentally
Large in-plane elastic deformations of bi-pantographic fabrics: asymptotic homogenization and experimental validation
No full textBi-pantographic fabrics are composed of two families of pantographic beams and correspond to a class of architectured materials that are described in plane as second-gradient 2D continua. On a discrete level, a pantographic beam is a periodic arrangement of cells and looks like an expanding barrier. The materialization of a bi-pantographic fabric made from polyamide was achieved by additive manufacturing techniques. Starting from a discrete spring system, the deformation energy of the corresponding continuum is derived for large strains by asymptotic homogenization. The obtained energy depends on the second gradient of the deformation through the rate of change in orientation and stretch of material lines directed along the pantographic beams. Displacement-controlled bias extension tests were performed on rectangular prototypes for total elastic extension up to 25%. Force–displacement measurements complemented by local digital image correlation analyses were used to fit the continuum model achieving excellent agreement
Identificazione di proprietà meccaniche di un giunto adesivo in laminati GLARE mediante Correlazione di Immagini Digitali
No full textMesoscale DVC analyses and parameter calibration for pantographic block in 3-point flexure
Get PDFIn the present work, the mechanical response of a fiber network metamaterial was studied when subjected to 3-point flexure. To account for the initial deformation of the sample due to the fabrication process, backtracking (i.e., the nominal mesh was accurately repositioned in the reference configuration) was implemented in the Digital Volume Correlation (DVC) procedure. Kinematic fields were then measured via DVC at two different scales. Finite element based DVC was validated thanks to a series of initialization steps. The displacement fields were successfully measured and a peculiar deformation mechanism was observed. These measurements were employed to calibrate the constitutive parameters of a second gradient continuum model introduced for modeling this type of metamaterial. Numerical simulations are shown to be in good agreement with experimental measurements at the macroscopic scale
Enhanced Piola–Hencky discrete models for pantographic sheets with pivots without deformation energy: Numerics and experiments
No full textThe problem of the synthesis of second gradient (meta)materials, via architectured microstructures made of micro-lattices, has been solved (Alibert et al., 2003; Seppecher et al., 2011) by choosing ideal pivots as preferred constraints. The obtained homogenized macro-equations (Boutin et al., 2017; Eremeyev et al., 2017) show some pathologies that reflect the exotic behavior of the considered metamaterials, even if they are of interest by themselves (Eremeyev et al., 2017). The theoretical issues that they raise not only represent an intellectual challenge but also means for disclosing potentially interesting new phenomena. To make such disclosure evident, the related technological demand arose, namely, to find an innovative design and production process to construct (Golaszewski et al., 2018), by using additive manufacturing, some pantographic sheets (made in this instance of polyamide but hopefully later also using metals or alloys) whose pivots do twist practically without deformation and with negligible dissipation. Remarkably the specimen could be printed as a monolith and required no post-assembly but only an easily standardized run-in procedure. In this paper, in order to introduce a mathematical description for pantographic sheets with perfect pivots and to avoid to face the aforementioned pathologies, a discrete, finite dimensional, Lagrangian model is formulated. Moreover, in order to include the case in which the beams interconnecting the pivots are long enough to store non negligible bending energy between the closest pairs of pivots, an enhanced Piola–Hencky discrete model is introduced. Two types of nodes are distinguished, the first one interconnects two pantographic fibers, the second one simply interconnects two different segments of the same fiber. The Vietnam long neck peculiar deformed shape experimentally observed in standard extension bias test is obtained with very short computing time, so that the innovative code that has been elaborated can be used as subroutine in more complex computation schemes. A preliminary digital image correlation analysis (Sutton et al., 2009; Hild and Roux, 2012b) is performed and shows that a remarkable agreement between theoretical predictions and experimental evidence can be obtained. This circumstance is easily explained by observing that the numerical code is based on a discrete model directly inspired by the mechanical properties of pantographic sheets and that, therefore, the passages to a continuum model via homogenization (dell'Isola et al., 2016) and then to the subsequent re-discretization, via the introduction of more or less suitable finite elements, are avoided. In our opinion a theory driven formulation of a directly discrete numerical model presents many advantages and it seems suitable for tackling future structural optimization problems
Rescaling and mesoshear deformations of lattice metamaterials
Get PDFExperimental results are presented for a lattice metamaterial with a complex mesostructure composed of parallel fibers aligned at different levels. The experimental evidence suggests that the fibers, in addition to their own deformations, such as elongation and bending, and to the relative rotation between two adjacent layers, may also slide relative to each other under certain conditions. This deformation mechanism is taken into account and used as a key hypothesis in the development of a new continuum model. A remarkable rescaling property possessed by the considered metamaterial is also discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
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