1,721,022 research outputs found
Buckling analysis of three-phase CNT/polymer/fiber functionally graded orthotropic plates: Influence of the non-uniform distribution of the oriented fibers on the critical load
No full textThe current paper aims to analyze the influence on the critical buckling loads of the non-uniform distribution of the oriented fibers along the thickness direction of three-phase CNT/polymer/fiber functionally graded orthotropic plates. The various plies of the laminated plates are reinforced by both carbon nanotube (CNT) particles and conventional oriented straight fibers. The orthotropic features of such layers are provided by the reinforcing fibers which are functionally graded (FG) along the thickness coordinate. In the literature, CNTs represent generally the sole reinforcing phase and are assumed aligned and graded in the thickness direction. Here, instead, CNTs are randomly oriented and uniformly scattered in the matrix, whose properties are further improved by aligned, graded, straight and oriented fibers. A general power-law function is introduced to define the non-uniform features instead of the usual patterns presented in the literature (such as FG-X and FG-O), which can be included in the proposed approach as particular cases. The current methodology is tested through the comparison with the results available in the literature. The validation procedure is carried out for two-phases composites, considering also CNTs as straight and aligned reinforcing fibers, characterized by both uniform and graded properties. Several boundary conditions are also analyzed and verified. As proven by the numerical results illustrated in the paper, the variation of the through-the-thickness distribution of the fiber volume fraction is able to change noticeably the value of both uniaxial and biaxial critical buckling loads of arbitrarily restrained thin and thick plates. This effect should be considered in the manufacturing process and in the mechanical analysis of these structures
Critical buckling load of honeycomb sandwich panels reinforced by three-phase orthotropic skins enhanced by carbon nanotubes
No full textThe buckling analyses illustrated in this research aim to provide useful results for the design and application of sandwich plates with a honeycomb core and three-phase orthotropic skins, which are reinforced by both carbon nanotubes (CNTs) and straight oriented fibers. A multiscale approach is developed to this aim, which is based on the Eshelby-Mori-Tanaka scheme and the Hahn homogenization technique. The outcomes are presented in terms of critical buckling loads for different boundary conditions, lamination schemes, fiber orientation and mass fraction of CNTs, in order to prove that all these elements represent fundamental design parameters in the analysis, manufacturing and behavior of these sandwich plates. The theoretical framework is based on the Reissner-Mindlin theory for laminated plates and on the von Kármán hypothesis as far as the nonlinear terms are concerned. The kinematic model includes the Murakami's function to deal with such peculiar mechanical configurations, which is required to capture the zig-zag effect due to the different mechanical properties of the core and the external skins. The numerical approach and the theoretical methodology are validated by means of the comparison with the experimental and the theoretical results available in the literature
Finite bending of hyperelastic beams with transverse isotropy generated by longitudinal porosity
No full textThe paper deals with the finite bending analysis of transversely isotropic hyperelastic slender beams made of a neo-Hookean material with longitudinal voids. The fully nonlinear behavior of the structures is presented in the framework of three-dimensional finite elasticity. A semi-inverse approach is used to describe the beam kinematics, which includes the anticlastic effect. The theoretical framework is developed in both Lagrangian and Eulerian reference systems. Explicit formulas are obtained for stretches and stresses, in a general framework valid for transversely isotropic beams. The effect of porosity on the Piola-Kirchhoff and Cauchy stress components is then discussed. The results are all obtained and validated analytically, and could be helpful to model structural systems in the fields of bioengineering and soft-robotics which exhibit both large displacements and deformations
Modeling and numerical investigation of the viscoelastic behavior of laminated concrete beams strengthened by CFRP strips and carbon nanotubes
No full textThe paper aims to prove that the application of innovative constituents and materials can noticeably affect the mechanical behavior of structures. The research is focused on the long-time behavior of concrete beams reinforced by Carbon Fiber Reinforced Polymer (CFRP) strips applied on their external surfaces. The concrete and the CFRP are both characterized by time-dependent mechanical features according to the theoretical framework provided by the linear viscoelasticity. Their properties are described through the introduction of the proper creep functions. The reinforcing strips are made of a polymer matrix reinforced by straight long Carbon fibers and randomly oriented Carbon nanotubes (CNTs). Due to the presence of two reinforcing phases at different levels (nano- and micro-scale), a multiscale model is introduced to compute the global mechanical properties of these innovative composites. Their characterization at the nano-scale is accomplished through the Eshelby-Mori-Tanaka scheme, whereas the Hanh approach provides the overall engineering constants of the CFRP strips. The Timoshenko beam theory for laminated beams is employed to describe the mechanical behavior of the structures. A numerical solution is developed to achieve the time dependency of central deflections and the redistribution of stresses along the thickness of the layered structures. Several responses are investigated to show also the effect of the mass fraction of CNTs, the thickness and the number of CFRP strips. The results presented in this paper could be taken into account to improve the structural response of concrete beams in contrasting the creep phenomenon due to the intrinsic nature of the material
Analytical solutions for vibrations and buckling analysis of laminated composite nanoplates based on third-order theory and strain gradient approach
No full textA nonlocal model based on the strain gradient approach is developed within the framework of the Third-order Shear Deformation Theory (TSDT) for the investigation of the free vibrations and the critical buckling loads of laminated composite nanoplates. The theory is suitable to deal with thick and thin plates since it includes also the First-order Shear Deformation Theory (FSDT) and the Classical Laminated Plate Theory (CLPT). An analytical procedure based on the Navier approach is employed to obtain the solutions, which are discussed highlighting the effects of the strain gradient, as well as the influence of the geometric ratios and mechanical properties, on the results. The paper aims at providing reliable benchmarks for further developments of the topic to be used as references in future comparison tests
Third-order theory for the bending analysis of laminated thin and thick plates including the strain gradient effect
Full text linkThe aim of the paper is the development of a third-order theory for laminated composite plates that is able to accurately investigate their bending behavior in terms of displacements and stresses. The starting point is given by the corresponding Reddy’s Third-order Shear Deformation Theory (TSDT). This model is then generalized to consider simultaneously the Classical Laminated Plate Theory (CLPT), as well as the First-order Shear Deformation Theory (FSDT). The constitutive laws are modified according to the principles of the nonlocal strain gradient approach. The fundamental equations are solved analytically by means of the Navier methodology taking into account cross-ply and angle-ply lamination schemes. The numerical applications are presented to highlight the nonlocal effects on static behavior
Bending of hyperelastic beams made of transversely isotropic material in finite elasticity
No full textThe paper aims to investigate the finite bending of hyperelastic beams composed of transversely isotropic soft materials. The constitutive laws are obtained by including the transverse isotropy effects in the compressible Mooney-Rivlin model. A suitable expression for the stored energy function is introduced for this purpose, showing its dependency on five material invariants. A fully nonlinear three-dimensional beam model, including the anticlastic effect, is developed. The general analytical formulation allows to consider the influence of transverse isotropy on the Piola-Kirchhoff and Cauchy stress components, since it is presented in both Lagrangian and Eulerian frameworks. The validity of the current model is finally discussed. This study is justified by many innovative applications which require the use of transversely isotropic components, such as the finite bending of soft robots or biological systems
Finite anticlastic bending of hyperelastic laminated beams with a rubberlike core
No full textA novel analytical approach to investigate the finite bending of hyperelastic laminated beams is presented. Two different nonlinear material models are taken into account, which are the compressible Mooney-Rivlin for rubberlike mediums and the Saint Venant-Kirchhoff for less deformable materials. The anticlastic bending is included in the formulation and the analytical expression of the transverse radius of curvature is presented. The stress analysis is performed in each layer separately, by considering the actual stored energy function of the constituents, in both Lagrangian and Eulerian frameworks. The finite bending of a sandwich beam is investigated in terms of stresses and stretches
Higher-Order Weak Formulation for Arbitrarily Shaped Doubly-Curved Shells
No full textThe aim of this chapter is the development of an efficient and accurate higher-order formulation to solve the weak form of the governing equations that rule the mechanical behavior of doubly-curved shell structures made of composite materials, whose reference domain can be defined by arbitrary shapes. To this aim, a mapping procedure based on Non-Uniform Rational Basis Spline (NURBS) is introduced. It should be specified that the theoretical shell model is based on the Equivalent Single Layer (ESL) approach. In addition, the Generalized Integral Quadrature technique, that is a numerical tool which can guarantee high levels of accuracy with a low computational effort in the structural analysis of the considered shell elements, is introduced. The proposed technique is able to solve numerically the integrals by means of weighted sums of the values that a smooth function assumes in some discrete points placed within the reference domain
Conforming and nonconforming laminated finite element Kirchhoff nanoplates in bending using strain gradient theory
No full textThis paper presents a comprehensive numerical finite element implementation of the nonlocal strain gradient theory applied to thin laminated composite nanoplates using Kirchhoff theory (known as Classical Laminated Plate Theory or CLPT). Hermite interpolation functions are used to approximate membrane and bending degrees of freedom according to the conforming and nonconforming approaches. To the best of the authors’ knowledge, there is no finite element formulation in the literature able to deal with laminated Kirchhoff plates including the strain gradient theory, which allows to consider general stacking sequences and boundary conditions. A simple and effective matrix notation is employed to facilitate the computer implementation. Benchmarks reported prove the accuracy of the implementation. Novel applications are provided for further developments in the subject
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