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## Efeitos mecânicos causados pela variação da inclinação do parafuso excêntrico no orifício da placa de autocompressão; Mechanical effects caused by the variation of the load screw inclination in the orifice of the dynamic compression plate

FREITAS, Rafael Lara de; PACCOLA, Cleber Antonio Jansen; SHIMANO, Antônio Carlos; KFURI JÚNIOR, Maurício
Tipo: Revisão de Livro
POR
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OBJETIVO: Avaliar os efeitos mecânicos da inclinação do parafuso excêntrico sobre a compressão axial com placa. MÉTODOS: Corpos de prova artificiais simulando fragmentos de osso diafisário foram fixados com placa DCP® de 4,5mm de sete orifícios. Uma célula de carga registrou as forças de compressão axial no intervalo entre os fragmentos. Guias de perfuração excêntrica com inclinações em relação ao plano longitudinal e transversal da placa foram confeccionados para o experimento. A compressão foi medida em dois diferentes sítios do foco de fratura virtual. De acordo com a magnitude da inclinação e sua direção em relação ao orifício da placa, oito diferentes grupos foram constituídos. Os ensaios mecânicos registraram a força máxima e a força máxima efetiva. RESULTADOS: A inclinação do parafuso em direção contrária à da rampa de deslizamento do orifício da placa foi acompanhada de diminuição nos valores médios de força máxima e força máxima efetiva de compressão 0º > 10ºi (p < 0,001), 0º > 20ºi (p < 0,001), 0º > 25ºi (p < 0,001). CONCLUSÃO: Em modelo experimental, utilizando-se placas do tipo DCP® não pré-tensionadas, a inclinação na inserção de parafusos excêntricos promoveu alterações nos valores médios da força de compressão axial. Houve diferenças significativas (p < 0...

## Thermo-mechanical vibration analysis of annular and circular graphene sheet embedded in an elastic medium

Fonte: Associação Brasileira de Ciências Mecânicas Publicador: Associação Brasileira de Ciências Mecânicas
Tipo: Artigo de Revista Científica Formato: text/html
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In this study, the vibration behavior of annular and circular graphene sheet coupled with temperature change and under in-plane pre-stressed is studied. Influence of the surrounding elastic medium 011 the fundamental frequencies of the single-layered graphene sheets (SLGSs) is investigated. Both Winkler-type and Pasternak- type models are employed to simulate the interaction of the graphene sheets with a surrounding elastic medium. By using the nonlocal elasticity theory the governing equation is derived for SLGSs. The closed-form solution for frequency vibration of circular graphene sheets lias been obtained and nonlocal parameter, inplane pre-stressed, the parameters of elastic medium and temperature change appears into arguments of Bessel functions. The results are subsequently compared with valid result reported in the literature and the molecular dynamics (MD) results. The effects of the small scale, pre-stressed, mode number, temperature change, elastic medium and boundary conditions on natural frequencies are investigated. The non-dimensional frequency decreases at high temperature case with increasing the temperature change for all boundary conditions. The effect of temperature change 011 the frequency vibration becomes the opposite at high temperature case in compression with the low temperature case. The present research work thus reveals that the nonlocal parameter...

## Impact behaviour of preloaded glass/polyester woven plates

García-Castillo, Shirley K.; Sánchez-Sáez, Sonia; López-Puente, Jorge; Barbero, Enrique; Navarro Ugena, Carlos
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
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In this work, the effect of a biaxial preload in the behaviour of glass/polyester woven-laminate plates subjected to high-velocity transversal impact was studied. For this, an analytic model based on energy considerations that include the presence of an in-plane preload was used. The results of the analytic model for the biaxial preload state were compared with those found for a non-preload plate, the difference between them being minimal for the pre-stressed level reached in the tests (31% of the static UTS). Therefore, numerical simulations were made in order to study the effect of the preload in greater detail; furthermore, experimental tests were conducted, validating the analytic and numerical model. In general, the two methods revealed minimal differences between the values of the ballistic limit and those of the residual velocity.; The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2001-0735) for the financial support of this work.; 7 pages, 4 figures.-- Issue title: "16th International Conference on Composite Materials (ICCM-16) -- ONR (Office of Naval Research) sessions on Dynamic Failure and Durability" (Kyoto, Japan, Jul 6–11, 2007).

## Impact Behavior of In-plane Pre-stressed Pannels

García-Castillo, Shirley K.; Sánchez-Sáez, Sonia; Barbero, Enrique; Navarro, Carlos
Tipo: info:eu-repo/semantics/conferenceObject; info:eu-repo/semantics/article Formato: application/pdf
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In this paper the behaviour of plates when they are subjected to normal impact under in-plane pre-stressed conditions was studied. Two kinds of lightweight materials were considered: aluminium alloy 7075 and quasi-isotropic glass fibre-reinforced vinylester resin. The residual velocity, the ballistic limit and, in the case of the composite material, the delaminated area, were measured in each test. Unstable cracks, that generate the catastrophic failure of the panel, were observed in the case of the aluminium at pre-stressed load levels lower than those inducing material yielding.; The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2001-0735) for the financial support of this work.; The 3rd International Conference on Structural Stability and Dynamics,, June 19-22, 2005, Kissimmee, Florida

## Strain dependent elastic modulus of graphene

López-Polín, Guillermo; Jaafar, Miriam; Guinea, Francisco; Roldán, Rafael; Gómez-Navarro, Cristina; Gómez-Herrero, Julio
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Indentation experiments on graphene membranes pre-stressed by hydrostatic pressure show an increase in effective elastic modulus from 300 N/m in non pressurized membranes to 700 N/m for pre-strains above 0.5 %. This pronounced dependence of the stiffness of graphene with strain is attributed to its high anharmonicity and the great influence of out of plane corrugations of this atomic thick membrane in its mechanical properties. Our experimental findings imply that graphene measured stiffness is highly influenced by the presence of corrugations and that the in plane elastic modulus corresponding to atomic bond stretching is more akin to 700 N/m, instead of the commonly accepted 340 N/m.; Comment: 17 pages and 4 figures

## In-Plane Bistable Nanowire For Memory Devices

Charlot, B.; Sun, W.; Yamashita, K.; Fujita, H.; Toshiyoshi, H.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We present a nanomechanical device design to be used in a non-volatile mechanical memory point. The structure is composed of a suspended slender nanowire (width : 100nm, thickness 430nm length : 8 to 30$\mu$m) clamped at its both ends. Electrodes are placed on each sides of the nanowire and are used to actuate the structure (writing, erasing) and to measure the position through a capactive bridge (reading). The structure is patterned by electron beam lithography on a pre-stressed thermally grown silicon dioxide layer. When later released, the stressed material relaxes and the beam buckles in a position of lower energy. Such symmetric beams, called Euler beams, show two stable deformed positions thus form a bistable structure. This paper will present the fabrication, simulation and mechanical and electrical actuation of an in plane bistable nanowire. Final paper will include a section on FEM simulations.; Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838)

## Initial stresses in elastic solids: Constitutive laws and acoustoelasticity

Shams, Moniba; Destrade, Michel; Ogden, Ray W.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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On the basis of the nonlinear theory of elasticity, the general constitutive equation for an isotropic hyperelastic solid in the presence of initial stress is derived. This derivation involves invariants that couple the deformation with the initial stress and in general, for a compressible material, it requires 10 invariants, reducing to 9 for an incompressible material. Expressions for the Cauchy and nominal stress tensors in a finitely deformed configuration are given along with the elasticity tensor and its specialization to the initially stressed undeformed configuration. The equations governing infinitesimal motions superimposed on a finite deformation are then used to study the combined effects of initial stress and finite deformation on the propagation of homogeneous plane waves in a homogeneously deformed and initially stressed solid of infinite extent. This general framework allows for various different specializations, which make contact with earlier works. In particular, connections with results derived within Biot's classical theory are highlighted. The general results are also specialized to the case of a small initial stress and a small pre-deformation, i.e. to the evaluation of the acoustoelastic effect. Here the formulas derived for the wave speeds cover the case of a second-order elastic solid without initial stress and subject to a uniaxial tension [Hughes and Kelly...

## Buckling and wrinkling from geometric and energetic viewpoints

Nechaev, Sergei; Polovnikov, Kirill
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We discuss shape profiles emerging in inhomogeneous growth of squeezed tissues. Two approaches are used simultaneously: i) conformal embedding of two-dimensional domain with hyperbolic metrics into the plane, and ii) a pure energetic consideration based on the minimization of the total energy functional. In the latter case the non-uniformly pre-stressed plate, which models the inhomogeneous two-dimensional growth, is analyzed in linear regime under small stochastic perturbations. It is explicitly demonstrated that both approaches give consistent results for buckling profiles and reveal self-similar behavior. We speculate that fractal-like organization of growing squeezed structure has a far-reaching impact on understanding cell proliferation in various biological tissues.; Comment: 13 pages, 8 figures

## On interface waves in misoriented pre-stressed incompressible elastic solids

Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Some relationships, fundamental to the resolution of interface wave problems, are presented. These equations allow for the derivation of explicit secular equations for problems involving waves localized near the plane boundary of anisotropic elastic half-spaces, such as Rayleigh, Sholte, or Stoneley waves. They are obtained rapidly, without recourse to the Stroh formalism. As an application, the problems of Stoneley wave propagation and of interface stability for misaligned predeformed incompressible half-spaces are treated. The upper and lower half-spaces are made of the same material, subject to the same prestress, and are rigidly bonded along a common principal plane. The principal axes in this plane do not however coincide, and the wave propagation is studied in the direction of the bisectrix of the angle between a principal axis of the upper half-space and a principal axis of the lower half-space.

## Hyperelastic cloaking theory: Transformation elasticity with pre-stressed solids

Norris, A. N.; Parnell, W. J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Transformation elasticity, by analogy with transformation acoustics and optics, converts material domains without altering wave properties, thereby enabling cloaking and related effects. By noting the similarity between transformation elasticity and the theory of incremental motion superimposed on finite pre-strain it is shown that the constitutive parameters of transformation elasticity correspond to the density and moduli of small-on-large theory. The formal equivalence indicates that transformation elasticity can be achieved by selecting a particular finite (hyperelastic) strain energy function, which for isotropic elasticity is semilinear strain energy. The associated elastic transformation is restricted by the requirement of statically equilibrated pre-stress. This constraint can be cast as $\tr {\mathbf F} =$ constant, where $\mathbf{F}$ is the deformation gradient, subject to symmetry constraints, and its consequences are explored both analytically and through numerical examples of cloaking of anti-plane and in-plane wave motion.; Comment: 20 pages, 5 figures

## Acoustic waves at the interface of a pre-stressed incompressible elastic solid and a viscous fluid

Otténio, Mélanie; Destrade, Michel; Ogden, Raymond W.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We analyse the influence of pre-stress on the propagation of interfacial waves along the boundary of an incompressible hyperelastic half-space that is in contact with a viscous fluid extending to infinity in the adjoining half-space. One aim is to derive rigorously the incremental boundary conditions at the interface; this derivation is delicate because of the interplay between the Lagrangian and the Eulerian descriptions but is crucial for numerous problems concerned with the interaction between a compliant wall and a viscous fluid. A second aim of this work is to model the ultrasonic waves used in the assessment of aortic aneurysms, and here we find that for this purpose the half-space idealization is justified at high frequencies. A third goal is to shed some light on the stability behaviour in compression of the solid half-space, as compared with the situation in the absence of fluid; we find that the usual technique of seeking standing waves solutions is not appropriate when the half-space is in contact with a fluid; in fact, a correct analysis reveals that the presence of a viscous fluid makes a compressed neo-Hookean half-space slightly more stable. For a wave travelling in a direction of principal strain, we obtain results for the case of a general (incompressible isotropic) strain-energy function. For a wave travelling parallel to the interface and in an arbitrary direction in a plane of principal strain...

## Interface waves in pre-stressed incompressible solids

Tipo: Artigo de Revista Científica