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Graphene has been extensively studied as nanofiller to produce ultra‐strong and ductile metal nanocomposites but challenges such as poor adhesion at the metal–carbon interface have yet to be met. Carbon honeycombs (CHCs) are highly porous 3D graphene networks that possess a very large surface area‐to‐volume ratio, an outstanding physical absorption capacity and notable mechanical properties. Herein, these recently synthetized 3D CHCs are introduced in copper as nanofillers, and the mechanical properties of the nanocomposites, such as elastic modulus, tensile strength, failure strain, compressive strength, and critical strain, are obtained using molecular dynamics simulations. Three CHC lattice types are studied, and the metal–carbon interface is accurately modeled by using melting and recrystallization of the copper matrix around the nanofiller. Gains between 28% and 50% are obtained for the Young's modulus, while the tensile strength improved between 43% and 49%. Pullout tests reveal that the copper nanopillars that form by the filling of the honeycomb cells of CHC by copper atoms considerably increase the pullout force and are responsible for improvements in adhesion and in loading stress transfer.
This paper presents the formulation of a Generalised Beam Theory (GBT) developed to analyse the structural behaviour of composite thin-walled members made of laminated plates and displaying arbitrary orthotropy. The main concepts and procedures involved in the available isotropic first-order GBT are revisited and adapted/modified to account for the specific aspects related to the member orthotropy. In particular, the orthotropic GBT fundamental equilibrium equations and corresponding boundary conditions are derived and their terms are physically interpreted, i.e., associated with the member mechanical properties. Moreover, different laminated plate material behaviours are dealt with and their influence on the GBT equations is investigated. Finally, in order to clarify the concepts involved in the formulated GBT and illustrate its application and capabilities, a thin-walled orthotropic beam is analysed and the results obtained are thoroughly discussed.
No abstract is provided for this article.
General GBT-based fully analytical formulae have been derived in a companion paper, which provides distortional bifurcation stress estimates in cold-formed steel C- and Z-section members acted by arbitrary applied stress distributions and displaying four end support conditions. This paper (i) addresses the implementation of the above general formulae, (ii) illustrates their application in detail, (iii) validates them, by means of comparisons with exact results, and (iv) compares their estimates with values yielded by other formulae available in the literature. After considering a wide range of (i) cross-section geometries and lengths and (ii) applied stress distributions, it is concluded that the GBT-based formulae are both accurate and universal.
It is widely accepted that wrinkling of thin sheets under tension is due to the compressive stresses that emerge in central zone, orthogonally to the direction of applied tension, being caused by the variation of Poisson’s effect from the fixed supports to central zone of the sheet. By means of an analytical approach consisting of displacement fields (designated as “modes”) that kinematically enrich the solution of pre-wrinkling stress field, this paper shows that Poisson’s effect is not the sole cause of wrinkling. Starting from an extensional mode, other modes with physical meaning (associated to Poisson’s effect and warping shear) are consecutively added to the final displacement field. This modal approach unveils that transversal compressive stresses, which trigger the sheet wrinkling, are due not only to restrained Poisson’s effect (known factor) but also due to warping shear deformation. This identification is the main and original contribution of the present work. The reduction of warping shear in stretched sheets (e.g., via the addition of transversal fibers) could possibly avoid wrinkling phenomena of elastic thin sheets and membranes used in aerospace applications, such as inflatable antennas and solar sails. Additionally, the paper presents approximate analytical solutions of pre-wrinkling fields (displacements, strains, stresses) that are deemed useful to derive future fully analytical formulae for the prediction of critical wrinkling loads.
The main objective of this paper is to investigate the mechanical behaviour (strength and stiffness) of carbon nanotubes (CNTs) under combinations of bending and twisting. In order to achieve this goal, molecular dynamics (MD) simulations of bended and twisted CNTs are performed. The LAMMPS code is used, the AIREBO potential is considered for CC bonds, the temperature is kept at 300K and incremental bending and twisting rotations are imposed to the CNT. Two types of CNTs are analyzed, including zig-zag (8,0) and armchair (5,5) CNTs with similar radius and length. The CNTs are also analyzed for pure bending and pure twisting. The main results are shown in the form of diagrams of energy and moment against imposed rotations. Some relevant conclusions are drawn concerning the influence of loading (bending and twisting) on the stiffness, strength and failure of CNTs: namely, it is concluded that armchair CNTs possess higher strength and fracture toughness under twisting–bending loading than zigzag CNTs; additionally, it is found that both CNTs (armchair and zigzag) still support moderate-to-high bending levels without failure after being extremely twisted and torsionally buckled, even for twisting angles four times those corresponding to torsional buckling; finally, the results prove that CNTs, mostly armchair ones, exhibit very high twisting–bending stiffness and strength and can be used with confidence as torsional spring elements in nanoelectromechanical systems (NEMS).
This paper aims to investigate the elasticity, strength and failure of aluminum (Al) nanocomposites with holey-graphene (hG), which were melted and recrystallized. Five nanocomposites (Al-graphene and four Al-hG - two of them doped, with nitrogen and boron) were studied by molecular dynamics simulations. They were melted and subsequently recrystallized at a fixed cooling rate of 0.25 K/ps. The nucleation temperature of nanocomposites was increased by 300–200 K compared to pure aluminum. The Al crystallization in the nanocomposites was about 85 % (97 % for pure Al). The nanocomposites with undoped nanofillers showed an increase in Young's modulus between 15 and 27 % relative to pure Al, while doped nanofillers showed no improvement. The mechanical properties of the nanocomposites depended on the characteristics of the nanofillers, namely (i) the porosity, (ii) the percentage of recrystallization of the Al matrix, and (iii) the interfacial adhesion in the interface Al-nanofillers. The results show that undoped nanofillers have much higher Young's modulus and lower porosity compared to the doped nanofillers (N-hG and B-hG). Finally, the application of the inverse rule of mixtures to extract the Young's modulus of the nanocomposite was successful.
No abstract is provided for this article.
In this paper, an original analytical model to study the nonlinear flange curling in wide double-flange panels is presented. Flange curling phenomenon is the tendency of wide thin flanges (in compression or tension) to move towards the neutral axis of thin-walled members under bending. Since the earlier work of Winter, there has been scarce investigation on the flange curling phenomena. Despite the simplicity of the formula developed by Winter to account for flange curling effect, which is used in current steel codes (e.g., EC3), recent works showed that this expression is rather restrictive and does not apply to all cases. The analytical formulae developed here is rather general since they (i) consider the restraining effect provided by the web, (ii) account for the shift of the neutral axis due to curling, (iii) incorporate the decrement of the second moment of area due to curling, and (iv) are fully analytical, thus avoiding iterative techniques. The analytical model is applied to study the curling behaviour of trapezoidal (double-flange) panels and is validated by means of comparisons with experimental results available in the literature. Since EC3 rules state that the tensioned wide flange in liner trays should be reduced if the curling displacement is higher than 5% of the web height, approximate expressions to evaluate the reduced width of wide flanges are presented.
No abstract is provided for this article.
No abstract is provided for this article.
This paper addresses the development and illustrates the application of a generalised beam theory (GBT) formulation intended to perform first-order elastic-plastic analyses of thin-walled members made of isotropic non-linear materials exhibiting strain-hardening. After presenting an overview of the main concepts and procedures involved in the above GBT formulation, its application is illustrated through the analysis of (i) simply supported Z-section beams and (ii) fixed-ended lipped channel beams. In both cases, a bilinear elastic-plastic material model is adopted, which exhibits three strain-hardening levels, namely Esh = 0 (perfectly plastic model), Esh = E/100 and Esh = E/50. The results presented and discussed consist of equilibrium paths, modal participation diagrams, displacement profiles, beam deformed configurations and stress diagrams and contours. For validation purposes, most of the GBT results are compared with values obtained from shell finite element analyses − with a few relatively minor exceptions, a very good correlation is always found. Finally, the paper closes with some remarks concerning the influence of the strain-hardening slope on the structural behaviour of thin-walled steel beams.
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