This paper presents a numerical study about the efficiency of implementing fracture toughness (Gc) as an input to the simulation of damage progression in pultruded glass fibre reinforced polymer (GFRP) materials. The Gc properties implemented in numerical modelling were determined through Compact Tension (CT) and Wide Compact Tension (WCT) fracture experiments conducted recently by the authors. The numerical models of those tests were developed in Abaqus software, using both built-in tools and user-defined material (UMAT) subroutines. The sensitivity of different damage parameters was assessed, taking into account the shape of the cohesive law (linear or exponential) and the ultimate transverse tensile stress, which ranged between the material strength, σu, determined through mechanical characterization tests, and the cohesive stress, σc, determined by assessing the initial slope in WCT fracture toughness results (with respect to the crack tip opening displacement). Validation of the numerical models was performed taking into account the experimental values of ultimate loads, softening slopes and crack growth rates. The experimentally based Gc results provided a good agreement between numerical and experimental results for all pultruded GFRP materials investigated. The best fit between numerical and experimental results was obtained for two sets of properties: (i) linear cohesive law and material strength; and (ii) exponential cohesive law and cohesive stress.
The local buckling behaviour and ultimate cross-sectional strength of tubular elliptical profiles in compression is examined in this study through numerical modelling. The numerical models were first validated against previous experimental data with good agreement observed, enabling an extensive parametric study to be performed. A total of 270 elliptical sections were simulated in order to examine the influence of cross-section aspect ratio, geometric imperfections and local slendernesses. The obtained ultimate capacities, load–deformation responses and failure modes are discussed. It was found that for lower cross-section aspect ratios the behaviour of the elliptical hollow sections (EHS) was similar to that of cylindrical shells across a number of metrics; however, as the aspect ratio increased, more plate-like stable postbuckling behaviour was observed. Imperfection sensitivity was found to decrease with increasing slenderness and aspect ratio. The influence of the shape of the initial imperfection on the strengths of the EHS columns was also assessed and was found to be generally limited. Finally, a design method has been proposed for Class 4 EHS members that reflects the reduction in capacity due to local buckling with increasing slenderness, but also recognises the improved postbuckling stability with increasing aspect ratio; the proposals were shown to provide safe and accurate predictions for the strengths of the EHS columns with nondimensional local slendernesses up to 2.5 and aspect ratios from 1.1 to 5.0.
This paper reports the results of an experimental and numerical investigation on the non-linear behaviour and load-carrying capacity of CFRP-strengthened cold-formed steel lipped channel columns, devoting special attention to their local-plate and/or distortional buckling behaviours. A preliminary GBT-based study concerning the column elastic buckling behaviour is performed, focusing on determining the (i) sheet location (web, flanges and/or lips) and (ii) carbon fibre orientation (longitudinal, transverse or inclined) that optimize the strengthening procedure (enhanced buckling behaviour vs. cost). Then, an experimental programme comprising a total of 19 short and long fixed-ended lipped channel columns is described. The columns were strengthened with carbon fibre sheets (CFS) bonded at different outer surface locations (web, flanges or lips) and having the fibres oriented either longitudinally or transversally — since the aim of the study is to assess the influence of the CFS on the column structural response, bare steel specimens were also tested. The experimental results, which consist of non-linear equilibrium paths (applied load vs. axial shortening) and ultimate strength values (most of them associated with local-plate and/or distortional failure mechanisms), are subsequently used to calibrate and validate geometrically and physically non-linear numerical analyses based on shell finite element models and carried out in the code Abaqus. Finally, on the basis of both the experimental and numerical results obtained, some relevant conclusions are drawn concerning the most effective CFS location and fibre orientation to strengthen lipped channel steel columns affected by local-plate and/or distortional buckling.
Graphyne and graphdiyne nanofillers (nanoplatelets and nanotubes), are embedded in Aluminum matrices originating graphyne and graphdiyne/Al nanocomposites. Pristine Al and the nanocomposites are melted and then recrystallized at a fixed colling rate, 1 K/ps. Al nanocomposites with planar nanofillers show a 46–53% increase in nucleation temperature and 78–88% recrystallization yield while Al nanocomposites with tubular nanofillers present a 16–32% increase in nucleation temperature and a 65–75% recrystallization yield. Al nanocomposites with planar nanofillers present a 26–36% increase in the Young's modulus, while Al nanocomposites with tubular nanofillers show a 23–31% increase in the Young's modulus. The improved mechanical properties of graphyne and graphdiyne/Al nanocomposites depend on i) the elasticity and shape (planar vs tubular) of the nanofillers ii) the level of recrystallization of the Al matrix and iii) the interfacial adhesion in the interface between the nanofillers and the Al matrix. Graphyne pore size positively affects interfacial adhesion.
No abstract is provided for this article.
This paper presents and discusses elastic geometrically non-linear Generalised Beam Theory (GBT) results on simply supported cylindrical steel panels under in-plane bending stresses, extending the knowledge on curved panels under uniform compression recently reported by the authors. Due to its inherent modal nature, GBT enables the acquisition of in-depth knowledge on the behaviour of these complex structural elements, which cannot be obtained with standard shell finite element analysis. In particular, a modal analysis investigation is conducted to assess the imperfection sensitivity of curved panels characterised by distinct curvatures and by considering (i) four distinct loading conditions (including the pure bending case), (ii) two distinct critical-mode initial geometrical imperfection shapes (first two bifurcation modes), and (iii) three distinct amplitudes – whenever relevant, three “positive” and “negative” amplitudes are considered. The work begins by the GBT buckling analysis of the selected panels followed by an in-depth investigation on the corresponding post-buckling behaviour. These results provide the evolution, along the equilibrium paths, of relevant modal displacement profiles, modal participation diagrams and deformed configurations. For comparison and validation purposes, ABAQUS shell finite element results are also reported.
This paper presents an analytical study on the elastic critical behaviour of cylindrically curved panels under pure compressive stresses, for which an energy formulation is developed. Firstly, this energy formulation is described, the general assumptions are stated, the degrees-of-freedom and the displacement functions are defined and, using strain-displacement relations, the strain energy and the potential energy are derived. Secondly, the resulting general energy formulation is used to obtain, whenever feasible, simple expressions or, otherwise, values of the elastic critical stress of simply supported cylindrically curved panels under pure compression. A discussion on the number of degrees-of-freedom necessary to obtain accurate results is also presented. The analytical results are compared to numerical (finite element) results obtained by the authors. Finally, a parametric study is made regarding the influence of constraining (or not) the panel longitudinal edges on the elastic critical stress.
The paper derives, validates and illustrates the application of GBT-based formulae to estimate distortional critical lengths and bifurcation stress resultants in cold-formed steel rack-section columns, beams and beam-columns with arbitrarily inclined mid-stiffeners and four support conditions. After a brief review of the Generalised Beam Theory (GBT) basics, the main concepts and procedures employed to obtain the formulae are addressed. Then, the GBT-based estimates are compared with exact results and, when possible, also with values yielded by formulae due to Lau and Hancock, Hancock and Teng et al. A few remarks on novel aspects of the rack-section beam-column distortional buckling behaviour, unveiled by the GBT-based approach, are also included.
We introduce a new specific hyperelastic/plastic model and porosity evolution law able to capture the deformation and damage of additively manufactured PLA-N polymers (Fused Filament Fabrication — FFF). Porosity growth is driven by projecting the right Cauchy–Green tensor in the normal to the deposition direction and by solving a local maximization problem. Fracture energy is introduced directly in the resulting law by means of a length scale. A full finite-strain plasticity model is adopted, based on the Hosford yield criterion. Strain softening is regularized with a gradient-enhanced technique, which is solved in tandem with the equilibrium equations. A comprehensive analysis of the hyperelastic transversely isotropic/porous constitutive law is performed, with physical insight on the directional strain softening behavior. A normalized CT test specimen is used to qualitatively assess the effect of deposition direction on the crack path and to investigate the effect of mesh density in the load/displacement curves. We then present a comparison with our experimental results for a cellular PLA-N beam composed of 3 × 13 cells, in terms of crack behavior and load/displacement results. Sequential collapse of the cells and strain localization match the experimental observations.
This paper begins by presenting a Generalized Beam Theory (GBT) formulation for analyzing the vibration behavior of loaded composite thin-walled members, which accounts for the effects of (i) cross-section in-plane deformation, (ii) shear deformation, (iii) geometric and material coupling, (iv) primary, secondary and non-linear warping, and (v) rotary inertia. This formulation is then used to investigate the local and global vibration behavior of lipped channel columns and beams displaying cross-ply orthotropy, focusing on issues dealing with the variation of the fundamental frequency and vibration mode nature with the member length and applied stress level. For validation purposes, some GBT-based results are also compared with values obtained by means of 4-node shell finite element analyses using ABAQUS. Some relevant conclusions are drawn concerning the dependence of the member vibration mode shape (wave number) on the compression/bending level (applied-to-critical ratio).
This paper presents and discusses numerical results on the (i) elastic post-buckling behaviour and (ii) imperfection sensitivity of simply supported cylindrical steel panels under uniform compression. The results presented are obtained by means of a geometrically non-linear Generalised Beam Theory (GBT) formulation previously reported by the authors, which can include arbitrary member initial geometrical imperfections. The modal decomposition features of GBT enables extending the knowledge on the mechanics underlying these structural elements, which cannot be obtained with standard shell finite element analysis. The work begins by describing the GBT buckling analysis of four curved panels with distinct curvatures. Then, post-buckling results are presented and discussed for each of the four panels geometries, by considering (i) two distinct critical-mode initial geometrical imperfections shapes and (ii) five distinct amplitudes to assess the imperfection sensitivity – if the “sign” of the initial geometrical imperfection is relevant, ten amplitudes are considered. These results provide the evolution, along the equilibrium paths, of relevant modal displacement profiles, modal participation diagrams and deformed configurations. For comparison and validation purposes, shell finite element results are also reported.
No abstract is provided for this article.
Glass fiber–reinforced polymer (GFRP) pultruded profiles are prone to web buckling and/or crushing when subjected to concentrated loads in the direction transverse to the pultrusion axis due to their low elastic and strength properties. Based on a recent work in which it was concluded that the Tsai-Hill criterion does not succeed in providing reasonable estimates of the web-crippling capacity of GFRP profiles, in the present work another progressive damage model is implemented into a finite-element (FE) model for web-crippling analysis. First, previous web crippling experiments on I-section GFRP profiles are summarized. Then the basis of the FE model is presented (element types, failure initiation criteria, and damage model) and results of preliminary analyses (mesh size and viscous regularization) are discussed. Subsequently, the load versus displacement curves, damage zones, and failure modes of GFRP profiles under different load configurations and bearing lengths are presented. Finally, the model sensitivity to different parameters (transverse compressive strength, in-plane shear strength, matrix compressive fracture energy, modeling of web-flange rounded corner) is analyzed. The proposed model is shown to be much more accurate than those based on Tsai-Hill criterion. It is also shown that the in-plane shear strength governs failure initiation, while the transverse compressive strength is more influential to the profiles' ultimate behavior. This study also highlights the major impact of fracture energy in the behavioral response of GFRP profiles subjected to transverse concentrated loads.
This paper presents an experimental study about the web-crippling behaviour of pultruded glass fibre reinforced polymer (GFRP) profiles, loaded under end two flange (ETF) and interior two flange (ITF) configurations, with varying bearing lengths. The study was performed to address two significant research needs: (i) to obtain a better understanding of the web-crippling phenomenon in GFRP profiles with different cross-sections and fibre layups; and (ii) to provide additional experimental data on web-crippling, necessary to validate advanced numerical models and to develop design formulae. The experimental programme included materials with different levels of transverse reinforcement, provided by a total of four suppliers. These significant differences in the fibre layups among the profiles tested did not seem to affect the stiffness and ultimate loads significantly. To the contrary, the bearing length was found to have a significant effect on the failure mode, stiffness and ultimate load of all I-section profiles. Moreover, and despite their significant differences in terms of geometrical and material properties, all I-section profiles presented similar transverse compressive strain distributions, when loaded in the same conditions, showing that changes in fibre layups had a negligible effect on the effective bearing length of the various specimens.
In this paper, a plane stress finite element model was developed to study the behaviour of a rubberized concrete (RuC) cubic specimen subjected to uniaxial compressive loading. To obtain the geometry of the given RuC section, specifically the heterogeneous distribution of rubber aggregates within the concrete matrix, MATLAB Image Processing is used. Then, to allow the initiation, opening and propagation of cracks in the concrete matrix upon loading, which ultimately lead to the failure of the RuC cube cross-section, a numerical model based on the eXtended Finite Element Method (XFEM) is implemented. The study motivation and the research significance are first presented. Then, the experimental programme conducted to characterize RuC’s main mechanical properties is described. Both the image-processing and the numerical analysis of the proposed mechanical model are described, with emphasis on the implementation and calibration of XFEM to allow for multiple cracks to develop in the RuC section. The numerical results are validated based on the experimental data and a detailed study on the post-cracked behaviour of the RuC section is presented and lastly, some conclusions are drawn.
Fire Resistance of pultruded profiles of glass fiber reinforced polymer (GFRP) for rehabilitation applications: Experimental, numeric, and analytical study ABSTRACT This article presents a study on the fire resistance of beams manufactured with pultruded profiles of glass fiber reinforced polymer (GFRP). Fire resistance tests were done on beams with a span of 1.3 m, exposed to the action of fire and according to the standard ISO 834. In these tests, the effect of different types of exposure to fire and the degrees of loads applied, as well as the efficiency of different protection systems were evaluated. A numeric model in the ANSYS FLUENT software was developed to simulate the evolution of the ranges of temperatures in the cross-section, as well as an analytical model to determine the evolution of deformation on the beams. Keywords: composite materials; resistance to fire; experimental campaign; numeric simulation; analytical model. Resistencia al fuego de perfiles pultruidos de polimero reforzado con fibras de vidrio (GFRP) para aplicaciones en rehabilitacion: Estudio experimental, numerico y analitico RESUMEN El presente articulo presenta un estudio sobre la resistencia al fuego de vigas fabricadas con perfiles pultrusionados de polimero reforzado con fibra de vidrio (GFRP). Se realizaron ensayos de resistencia al fuego en vigas con un vano de 1.3 m, expuestas a la accion del fuego segun la norma ISO 834. En estos ensayos, se evaluo el efecto de diferentes tipos de exposicion al fuego y los niveles de carga aplicados, asi como la eficacia de diferentes sistemas de proteccion. Se desarrollo un modelo numerico en el software ANSYS FLUENT para simular la evolucion del campo de temperaturas en la seccion transversal y un modelo analitico para determinar la evolucion de la deformacion de las vigas. Palabras clave: materiales compuestos, resistencia al fuego, campana experimental, simulacion numerica, modelo analitico. Resistencia ao fogo de perfis pultrudidos de polimero reforcado com fibras de vidro (GFRP) para aplicacoes em reabilitacao: Estudo experimental, numerico e analitico RESUMO Neste artigo e apresentado um estudo sobre a resistencia ao fogo de vigas em perfis pultrudidos de polimero reforcado com fibras de vidro (GFRP). Foram realizados ensaios de resistencia ao fogo em vigas com um vao de 1.3 m, expostas ao fogo de acordo com a curva temperatura-tempo da norma ISO 834. Nestes ensaios, avaliou-se o efeito de diferentes tipos de exposicao ao fogo (em uma e tres faces) e niveis de carga aplicados, bem como a eficacia de diferentes sistemas de protecao. Foi desenvolvido um modelo numerico termico bidimensional no software ANSYS FLUENT para simular a evolucao das distribuicoes de temperatura na seccao transversal. Foi ainda desenvolvido um modelo analitico para determinar a evolucao das deformacoes das vigas. Palavras-chave: Materiais compositos, resistencia ao fogo, campanha experimental, simulacao numerica, modelo analitico.
