1,720,962 research outputs found
A Continuum Model for Circular Graphene Membranes Under Uniform Lateral Pressure
Full text linkDespite the numerous applications of pressurized graphene membranes in new technologies, there is still a lack of accurate mechanical models. In this work we develop a continuum model for circular graphene membranes subjected to uniform lateral pressure. We adopt a semi-inverse method by defining a simplified kinematics of deformation and we describe the material behavior with a stored energy function that takes into account both nonlinearity and anisotropy of graphene. An expression of the applied pressure as a function of the deflection of the membrane is obtained from an approximate solution of the equilibrium. The simplifying hypotheses of the analytical model are verified by a finite element (FE) analysis in nonlinear elasticity. In addition, a numerical solution of the differential equilibrium equations of the exact theory is presented. The pressure-deflection response from FE and numerical solutions agree well with the prediction of the analytical formula, demonstrating its accuracy. The analytical solution is then employed for the response of a two-layered composite membrane made of graphene deposited onto a soft substrate. This application is of great interest since new nanotechnologies make use of layered nanocomposites. Differently from our entirely nonlinear approach, most continuum models in the literature are based on the assumption of linear elastic material, which is suitable only when deformations are small. The present work gives a comprehensive description of the mechanics of pressurized graphene membranes
On the anticlastic bending of solids at finite strains
No full textThe present work deals with the problem of compressible isotropic hyperelastic solids under finite bending. The problem is fully nonlinear and, conversely to the classical Rivlin solution [1], it is formulated in the framework of three-dimensional kinematics involving both large displacements and strains according to the context of finite elasticity. The model entails three kinematic assumptions, which stand for the planarity of the cross sections (Bernoulli-Navier hypothesis), the invariance of the curvature along the longitudinal direction of the solid (uniform bending) and the curvature of the cross sections (anticlastic curvature), that is assumed constant along the width of the solid [2]. Based on the semi-inverse approach and according to the kinematic assumptions, the 3D displacement field is found, and, in turn, the deformation gradient is assessed. Then, the equilibrium conditions, specialized for a compressible Mooney-Rivlin material, provide proper relations among the unknown kinematic parameters, thus leading to the closure of the problem. Emphasis in placed on the “moment-curvature relation”, which is found to be governed by two independent dimensionless parameters: the Eulerian slenderness and the compactness index of the solid cross sections [3]. Similarity is observed with respect the previous works of Lamb (1890) regarding the mechanical response of bent plates and the experiments performed by Searle (1933) as well. Moreover, such an analysis allows broadening the “Elastica” to the more general context of finite elasticity.
In this work, the main results provided by the theoretical model are compared with those obtained by FE simulations and an experimental investigation based on a specifically designed mechanical apparatus, founding good agreement also for the case of extremely inflexed solids
Coactive stresses in MEMS and NEMS based on periodically bent crystals
No full textA variety of MEMS and NEMS are base on chemical film deposition onto a ceramic substrate. Generally, the substrate consists of a Si (silicon) or Ge (germanium) plate. One of the most used chemical processes is low-pressure chemical vapor deposition (LPCVD). Through such a technology a wide class of MEMS/NEMS can be realized, with particular reference to crystalline undulators (CU)s [1]. CUs (Figure 1) are devices to generate intense coherent and collimated electromagnetic radiation across the UV and X-ray ranges. Electrical charges are forced to oscillate in the electromagnetic field of the crystalline lattice thus emitting electromagnetic radiation.The present study concerns the effects induced by coactive stresses on displacement and stress fields induced in the system by thermal loading due to the LPCVD process. The aim of the study is to find the optimum geometrical parameters (a, p, hf) suitable to obtain a CU. By imposing equilibrium conditions and perfect adhesion between the thin films and the substrate, a singular integral equation is derived. A closed-form solution is achieved by expanding the unknown interfacial shear stress fields in Chebyshev series. This leads to an algebraic system which solution allows assessing the stress, strain and displacement fields in the CU.
REFERENCES:
[1] Guidi V, Lanzoni L, Mazzolari A, et al. Design of a crystalline undulator based on patterning by tensile Si3N4 strips on a Si crystal. Appl Phys Lett 2007; 90(11): 11410
A cohesive-based FE interface for concrete members retrofitted with ultra performance cementitious mortars
No full textFinite element solution of vibrations and buckling of laminated thin plates in hygro-thermal environment based on strain gradient theory
No full textThe paper aims to develop a finite element methodology to deal with vibrations and buckling of laminated thin plates subjected to thermal and hygroscopic effects, once a second-order strain gradient theory is included to overcome the limitations of conventional elasticity and to capture nonlocal phenomena. The numerical scheme takes advantage of Hermite approximation for both membrane and bending primary variables, since the strain gradient introduces higher-order derivatives of the nodal displacements. Its versatility is proven by dealing with general lamination schemes and arbitrary boundary conditions. The analyzed configurations cannot be solved analytically
Shot-earth for sustainable constructions
Full text linkEarth has been used worldwide as a building material for centuries and it is still one of the most used construction materials. In many countries the excavated soil is becoming one of the largest construction waste and its disposal is costly and problematic. For this reason, there is a rising interest in employing the excavated soil directly in field, possibly as an added value construction material. In this paper a new type of rammed earth is presented. This new material is based on the shotcrete technology and has been named shot-earth. A mix of stabilized soil, aggregates and water is consolidated by high speed projection rather than by mechanical compaction to obtain both structural and non-structural elements. The first characterization of the physical properties of this material has shown the great potential of this technolog
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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