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This paper proposes a micromechanical model based on the finite element method (FEM) to analyze the ratchetting deformation of short glass fiber-reinforced polymer composites (SFRPCs). To reasonably consider the complex mechanical characteristics of the polymeric matrix under asymmetrical stress-controlled cyclic loading, a damage-coupled nonlinear viscoelastic-viscoplastic (VE-VP) cyclic constitutive model was constructed. The cyclic constitutive model of the matrix was introduced into the FEM model utilizing a user-defined material, and the corresponding experimental validation of the matrix was conducted. Subsequently, the cyclic constitutive model was introduced into the analysis of the micro-FEM model of the composites. The random orientation was considered to generate fibers in the FEM. Based on the analysis of the microscale representative volume element (RVE) model, the effects of different fiber content and cyclic peak stress on the ratchetting of SFRPCs were studied in detail. After validation, the effects of the fiber length and fiber stiffness on the ratchetting deformation of SFRPCs are discussed based on the developed micro-FEM model. The results show that the increase in the fiber length and fiber stiffness reduced the ratchetting deformation of SFRPCs within a specific content range. The model can assess the ratchetting deformation and damage evolution within the composites to provide more accurate predictions of the ratchetting deformation of SFRPCs and guide the expanded application of SFRPCs in structures. [Display omitted] • A damage-coupled nonlinear viscoelastic-viscoplastic cyclic constitutive model of the polymer matrix was proposed. • The constitutive model was introduced into microscale finite element model through the user-defined material subroutine. • Ratchetting deformation of SFRPCs was analyzed based on the constructed microscale representative volume element model. • Effects of fiber length and fiber stiffness on ratchetting deformation and damage of SFRPCs were investigated. [ABSTRACT FROM AUTHOR]

Abstract In this paper, an innovative Foam-filled Lattice Composite Bumper System (FLCBS) with fiber-reinforced polymer (FRP) skins and a foam-web core is proposed as protective structures for bridge piers against ship collision. FLCBS consists of FRP face sheets, FRP lattice webs and polyurethane (PU) foam cores, which can be manufactured at the same time by vacuum assisted resin infusion process (VARIP). FLCBS exhibits good energy-absorbing and highly designable properties. The design, performance evaluation, manufacture and installation of FLCBS for a real prestressed concrete continuous girder bridge were introduced. A detailed numerical model for performance evaluation was developed with the explicit finite element (FE) software package ANSYS/LS-DYNA. An experimental study of two foam-filled lattice composite panels under low-velocity impact was conducted to verify the numerical model for FLCBS. The corresponding FE models of the composite panels generally showed good agreement, compared to the impact load history and mid-span deflection history of experimental results. Based on the validated numerical model, both head-on collision cases and lateral collision cases with and without FLCBS were investigated. Simulation of different impact angles, velocities and locations were carried out. Numerical results indicate the obvious advantages of FLCBS by comparing peak impact force and impact duration. Significantly decrement of the peak impact force and effectively prolonged impact process indicate the superior performance of FLCBS. The modular fabrication and replacement, easy and time-efficient installation and highly designable structure make FLCBS very attractive as bridge protection in ship collisions. [ABSTRACT FROM AUTHOR]

Abstract: Use of fiber reinforced polymer (FRP) bars or grids instead of traditional steel reinforcements is an interesting application, especially to improve structural durability and extend the actual service life. As proved elsewhere by experimental and numerical results, a key aspect of the structural behavior of concrete slabs reinforced with FRP bars is the large reduction in both resistance and stiffness due to high temperatures. Thereupon six concrete slabs reinforced with glass FRP bars characterized by different values of concrete cover and anchorage length were recently tested in the fire situation. A comprehensive description of the experimental program and some significant experimental results are reported in a companion paper; the resistance of concrete slabs reinforced was showed strongly influenced by temperatures in the bars in the area directly exposed to fire but also in the anchoring area (not exposed zone). In this paper, at first, a detailed discussion of the experimental thermal readings is reported to give as a support to the remarks on mechanical response of the slabs reported in the companion paper. In particular the influence of concrete cover on temperature in exposed area and the temperatures in the area not exposed are examined to investigate the effectiveness of the anchor. The influence on the temperature in the bars of different concrete thermal properties is investigated. Furthermore, the influence of the thermal properties of the bars on the temperature field is evaluated. Finally, a simplified method for predicting temperatures of FRP bars in concrete slabs, obtained by considering the ISO standard fire curves is provided in the form of analytical relationships .Its reliability is showed by means of comparisons with the experimental results. [Copyright &y& Elsevier]

Abstract: As a continuation of previous paper on modeling vertical density profile (VDP) formation for wood strand composites, this paper presents typical prediction results from the VDP model and describes the experimental investigations. By taking into account the non-uniform mat structure, the model can predict not only the overall panel VDP but also the localized VDP of a given area within the panel. Thus it links the horizontal density distribution to the vertical density distribution within the panel. The proposed model was validated by comparing its predictions with experimental data. Also the model can predict the effects of some key pressing parameters on VDP formation. Longer press closing times or preheating of the mat is found to make the VDP of the panel more uniform. This study is valuable for improving the fundamental understanding of the relationship between pressing variables and panel properties for process optimization. [Copyright &y& Elsevier]

Abstract This paper reports on the energy absorption characteristics of four types of innovative foam-filled multi-cell composite panels (FMCPs) composed of glass fiber reinforced polymer (GFRP) face sheets, GFRP lattice webs, and polyurethane (PU) foam. Quasi-static compression experiments on the FMCPs manufactured by a vacuum assisted resin infusion process (VARIP) were performed to demonstrate the feasibility of the proposed panels. Compared with the traditional FMCP with double-layer orthogonal foam cells, a maximum decrease in the peak crushing force (PCF) of approximately 148% was obtained for the FMCP with trapezoidal cells. Moreover, the enormous decrease in bearing load has been overcome by the proposed FMCPs. Among the four proposed FMCPs, the FMCP with double-layer dislocation cells exhibited the greatest specific energy absorption (SEA) capacity and the highest mean crushing load (MCL). Several numerical simulations using ANSYS/LS-DYNA were conducted on the FMCP with double-layer dislocation cells to parametrically investigate the effects of the face-sheet and lattice-web thickness, the foam-cell height, the foam-cell width, and the foam density. The effectiveness and feasibility of the numerical model were verified by the experimental results. The numerical results demonstrated that thicker face sheets and lattice webs, higher foam densities, and narrower foam cells can significantly increase the PCF and bearing load decrease. Moreover, the PCF and bearing load decrease were hardly affected by the foam-cell height. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the lateral planar crushing and bending responses of carbon fiber reinforced plastic (CFRP) square tube filled with aluminum honeycomb. The various failure modes and mechanical characteristics of filled tube were experimentally captured and numerically predicted by commercial finite element (FE) package LS-DYNA, comparing to the hollow tubes. The filled aluminum honeycomb effectively improved the stability of progressive collapse during crushing, leading to both hinges symmetrically occurred along the vertical side. The experimental results showed that energy absorbed (EA) and specific energy absorption (SEA) of the filled CFRP tubes could be significantly increased to 6.56 and 4 times, respectively, of those measured for the hollow tubes without fillings under lateral crushing. Although an improvement of 32% of EA and 0.9% of SEA were obtained for the lateral bending, still the design using aluminum honeycomb as filling was remarkably capable to improve the mechanical characteristics of CFRP tube structure. A good agreement was obtained between experimentally measured and numerically predicted load-displacement histories. The FE prediction was also helpful in understanding the initiation and propagation of cracks within the filled CFRP structure. [ABSTRACT FROM AUTHOR]

The dynamic behavior of metal foams under impact crushing is of great interest for both fundamental research and engineering applications. This paper presents a systematical and thorough investigation on the dynamic response of a colliding mass impacting on metal foams that exhibit strain hardening. Experimental investigation, finite element (FE) simulation and analytical modelling are conducted in this study. In the experimental work, an instrumented projectile acting as a colliding mass was designed and implemented by using a novel in situ deceleration measurement unit embedded within a metal body. This projectile measures in situ rigid-body deceleration and provides a measure for net resistance on the projectile during the dynamic impact test. In each test, the impact velocity and crushing depth of the projectile were recorded. Based on the metal foams that exhibit strain hardening in this study, an exponential stress-strain relation is proposed to model the static strength of aluminium foam specimens, which is used for subsequent FE simulation and the analytical model. The predictions of the proposed analytical model are compared with an earlier analytical model based on Rigid Perfectly-Plastic-Locking (RPPL) idealization. RPPL can only well approximate the stress-strain characteristic of metal foams with low strain hardening. It is found that the proposed analytical model matches the experimental results much better than the earlier analytical model based on RPPL. The experimental results also agree well with the FE simulation results that are obtained based on the proposed exponential stress-strain model. [ABSTRACT FROM AUTHOR]

The paper concerns an analysis of four-point bending tests of C-shaped profile beam built of 8-ply GFRP. Six different arrangements of layers were taken into consideration: [0/-45/45/90] S , [90/-45/45/0] S , [90/0/90/0] S , [0/90/0/90] S , [45/-45/45/-45] S , [45/-45/90/0] S . To compare experimental results, numerical simulations of investigated columns in Ansys 16.2 software were carried out. In addition, tests of bending on samples were recorded using ARAMIS ® system. For assessing the failure in numerical simulations, the following criteria were used: Inverse of Tsai-Wu, Maximum Stress and Hashin's criterion. For the arrangement of layers [0/-45/45/90]S the damage assessment were performed with the use of macroscopic observations, non-destructive testing with the use of ultrasonic techniques, X-ray computed microtomography, and microscopic examination with the use of stereoscopic, optical and scanning electron microscopy. [ABSTRACT FROM AUTHOR]

The direct tensile test is one of the experimental procedures used for the characterization of Fiber Reinforced Cementitious Matrix (FRCM) materials. From this test generally emerge the main phenomena characterizing the tensile response of FRCM: cracking of the matrix and de-bonding at the reinforcement-matrix interface. These phenomena, that in some cases are quite difficult to experimentally monitor and understand, particularly influence the performance of FRCM as strengthening systems. In this paper the authors present a simple numerical modeling approach able to simulate the tensile response of FRCM by reproducing the occurrence of both the cracking of the matrix and the de-bonding at the reinforcement-matrix interface. The numerical analyses reported in the paper show the reliability of the proposed approach and, in particular, its role as support tool for understanding the influence of local failure phenomena on the global tensile response of FRCM systems. [ABSTRACT FROM AUTHOR]

As promising materials, the NS mechanical metamaterials bring new alternatives for energy-absorbing materials, but also research challenges in performance prediction considering their large, local deformation. In this paper, numerical and experimental methods were employed to investigate the mechanical properties of the truncated-conical shell element. Also, empirical formulas, which can well predicate the element's response, were developed based on the simulated data. Mechanical responses of the metamaterials, consisted of truncated-conical shells in a periodic arrangement, were investigated through the multilinear model. These prediction models were all verified through the simulations and experiments, and the comparison results indicated that the presented models were applicable in wide parameter range, attributed to a piecewise fitting method. Generally, a comprehensive approach, of general applicability, is presented in this paper to study the NS metamaterial's mechanical response from local to global, and it can be a reference to researches on novel NS metamaterials. [ABSTRACT FROM AUTHOR]

This paper is to develop a simple micromechanics-based model taking account of progressive damaging for carbon black (CB) filled rubbers. The present model constitutes of the instantaneous Young's modulus and Poisson's ratio characterizing rubber-like material, a double-inclusion (DI) configuration considering the absorption of rubber chains onto CB particles, and the incremental Mori-Tanaka formula to compute the effective stress–strain relations. The progressive damage in filled rubbers is described by the DI cracking, which is represented by the remaining load–carrying capacity. The present predictions are capable of embodying the well-known S -shaped response of filled rubbers, and also verified by the comparison with the experimental and analytical results. Moreover, strain localization effect is clearly demonstrated by finite element method (FEM) simulations, and reaches a decisive interpretation to the complicated synergic micro-mechanisms between hard fillers and soft phase in such flexible composites. [ABSTRACT FROM AUTHOR]

This paper presents the results of numerical studies carried out on concrete columns confined by Carbon Fiber Reinforced Polymer (CFRP) and loaded in uni-axial compression. A numerical simulation of confined columns experimentally tested by [1] is performed for relatively small concrete specimens of constant size but with different cross-section corner radius. The experimental results, reported in terms of axial stress–strain relationships and failure modes, constitute a useful database for the calibration of numerical models. These results clearly demonstrate that CFRP confinement is much less effective in square than in circular cross-sections. Therefore, the influence of the corner radius on the non-uniform stress distribution due to confinement, is numerically investigated using the proposed microplane-based model that takes into account the effect of multi-axial stress states in concrete. The experimental results are used to calibrate and verify the prediction capability of a three-dimensional finite element code (3D FE) that is based on the microplane constitutive law for concrete [2] . In the finite element model carbon fibers are modelled using nonlinear truss elements, while epoxy resin as well as concrete are modelled using microplane-based constitutive law and 3D finite elements. Given that experimental results for unconfined and confined configuration are available for each specimen, the 3D FE concrete model has been preliminarily calibrated on unconfined concrete specimens and then used in the analysis of a confined specimen. It is demonstrated that numerical models can predict behavior of confined concrete columns from the experimental investigations, confirming the predictability of the numerical microplane-based approach used. [ABSTRACT FROM AUTHOR]

Abstract: The introduction of tow-steered laminates in structural applications demands reliable design methodologies to predict and simulate their mechanical response. The full details about the mechanisms that lead to damage and failure of these novel panels are not yet known. In this work, a numerical analysis tool has been developed for structural simulations in a three-dimensional domain. This paper presents a comparison between different configurations and modeling approaches of these panels. Finite element analyses are carried out to simulate the first-ply failure of tow-steered panels under tensile load. The simulations show how matrix cracking is affected by discontinuities in the fiber angle between adjacent courses and fiber-free areas resultant from manufacturing effects; whereas fiber tensile failure is directly influenced by the orientation angles of the fiber, whose distribution depends on the chosen course cutting method: on one side, or on both sides. [Copyright &y& Elsevier]

Abstract: This paper presents a material model suitable for simulating the behavior of dry fabrics subjected to ballistic impact. The developed material model is implemented in a commercial explicit finite element (FE) software LS-DYNA through a user defined material subroutine (UMAT). The constitutive model is developed using data from uniaxial quasi-static and high strain rate tension tests, picture frame tests and friction tests. Different finite element modeling schemes using shell finite elements are used to study efficiency and accuracy issues. First, single FE layer (SL) and multiple FE layers (ML) were used to simulate the ballistic tests conducted at NASA Glenn Research Center (NASA-GRC). Second, in the multiple layer configuration, a new modeling approach called Spiral Modeling Scheme (SMS) was tried and compared to the existing Concentric Modeling Scheme (CMS). Regression analyses were used to fill missing experimental data – the shear properties of the fabric, damping coefficient and the parameters used in Cowper-Symonds (CS) model which account for strain rate effect on material properties, in order to achieve close match between FE simulations and experimental data. The difference in absorbed energy by the fabric after impact, displacement of fabric near point of impact, and extent of damage were used as metrics for evaluating the material model. In addition, the ballistic limits of the multi-layer fabrics for various configurations were also determined. [Copyright &y& Elsevier]

Abstract: This paper presents some significant research results about velocity sensitivity of aluminum honeycomb under high-speed axial impact in a velocity range from 20 to 80m/s. Series experiments were carried out with the help of self-developed high-speed impact system. Afterwards, corresponding numerical simulation works as well as some parametric studies were conducted. The resultant comparison told out that the plateau stress increases markedly when impact below 30m/s, but slowly when impact at a velocity various from 30 to 80m/s. Before the parametric studies, inertial effect in various impact masses was investigated. Comparison between parametric results showed that the promotion on Specific Load and energy-absorbing capability increases with the impact velocity for various honeycombs. Density also has a great influence on Specific Load. The higher honeycomb density is, the greater amplitude performs. The energy absorption diagram for honeycomb with different geometric configurations reveals the relationship between dynamic plane stress and energy per unit volume, and also proves the promotion with increasing of impact velocity. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental study on the flexural behavior of three full scaled non-prestressed and prestressed composite beams with corrugated web, which had been developed by authors in their previous study. Also, the performance of the proposed flexural behavior model considering the accordion effect was examined, comparing to the test results. The test result showed that, due to the accordion effect before composite with the concrete, the introduced prestress in the top and bottom flanges of the steel beam has drastically increased, and that after composite with concrete, the flexural strength and stiffness of the prestressed specimens were superior to those of the non-prestressed specimen. It was verified that the proposed flexural behavior model accurately estimated the flexural behavior, before and after the composite with concrete, of the prestressed composite beams with corrugated web. Also, the horizontal shear strengths of the composite members, summing the average shear bond strength between steel plate and concrete and the direct shear strength of concrete, were evaluated considering the horizontal shear failure observed in the test specimens. [Copyright &y& Elsevier]

Abstract: In this study, the prestressed composite beam with corrugated web has been developed, which is suitable for the long-span structure that enables a reduction in story height as well. Utilizing the corrugated steel web improves the efficiency of prestress introduced into the top and bottom flanges due to the accordion effect, which also provides better deflection control and greater resistance against local and out-of-plane buckling. Additionally, when the corrugated steel web becomes composite with concrete, the slanting plate of the corrugated web induces bearing stress that can improve composite action between the steel beam and the surrounding concrete. In this study, a parametric study on the accordion effect has been performed by a total of 24 corrugated webbed steel beams utilizing the finite element analysis. Based on the analysis result, a simple approach for the estimation of the accordion effect has been proposed. In addition, this study introduces a flexural behavior model for the prestressed composite beams with corrugated web. The verification of the proposed methods in this study is presented in a separated paper. [Copyright &y& Elsevier]

Abstract: During the manufacturing of wood composites, mats of resinated fibers, particles or strands are consolidated under heat and pressure to produce panels with the necessary strength and stiffness properties. As the mat consolidates a vertical density profile (VDP) is established and it has a significant impact on panel properties. In order to tailor the VDP of the panel to various end-use applications, a means of describing of the effect of pressing variables on the development of the VDP is needed. In this paper, a comprehensive model is established to simulate the formation of VDP for strand-based wood composites. Based on the strand compression properties during hot pressing, this model can predict the in situ formation of density profile in combination with an existing heat and mass transfer model. As a structural model, it can predict the density distributions in both horizontal and vertical directions of the panel. Also it can help clarify the importance of pressing parameters and predict the effects of these parameters on VDP formation. [Copyright &y& Elsevier]

Abstract: The application of a multiscale method, called the multiscale aggregating discontinuities (MAD) method, to the failure analysis of composites is described. Two distinct features of the MAD method are the use of perforated unit cells, and the extraction of coarse-grained failure information. In the perforated unit cell, all subdomains of the unit cell that are not strictly elliptic are excluded, which enables the decomposition of its stable and unstable material. By means of these concepts, it is possible to compute an equivalent discontinuity at the macroscale, including both the direction and the magnitude of the discontinuity. This equivalent discontinuity is then passed to the macroscale along with the computed stress from the unit cell. The macroscale discontinuity is injected into the macro model by the extended finite element method (XFEM) procedure. In this paper, the method is improved by adding hourglass modes to the unit cell deformations, which better model growing cracks. Several examples comparing the MAD method with direct numerical simulations are presented. [Copyright &y& Elsevier]

This paper proposes a modeling methodology to predict the 3D and internal geometry of biaxial braids. Inspired by the digital element approach, braided yarns are modeled as a bundle of virtual fibers. Here we adopt truss elements to a virtual fiber with actual material properties instead of beam elements that have limitations due to the beam flexural rigidity. The mesoscopic morphology prediction of two common braid patterns of the diamond (1/1) and regular (2/2) are validated by a comprehensive quantitative comparison with X-ray micro-computed tomography (CT) scans of braided carbon fibers. We find that the fiber-level frictional behavior is able to explain the jammed state of braids wherein the frictional dissipation energy quickly grows, while the braid has a stable elongation, diameter, and braid angle. Parametric studies illustrate how the increase in the coefficient of friction affects the yarn cross-sectional shape, whereas it has an insignificant effect on the crimp and jammed state of braids. Models also reveal that changing a wide range of the fiber modulus of elasticity hardly impacts the mesoscopic morphology and crimp of the braids. [Display omitted] • Fiber-level modeling methodology is proposed to predict the mesoscopic morphology of 1/1 and 2/2 biaxial braids. • Braid diameter and yarn cross-section area are predicted with an average accuracy over 98%. • Varying the fiber-to-fiber coefficient of friction has negligible impact on the braid jammed state angle. • Low fiber-to-fiber coefficient of friction produces lenticular shaped yarn, while a high one produces an oval shaped yarn. • Increasing the fibers' Young modulus neither impacts jammed state nor the yarn shape. [ABSTRACT FROM AUTHOR]

The trailing edge is a critical part of blade because of monolithic bonding, which may lead to separation of edges while wind-turbine is in service. It is easily perceptible that the maintenance is (under harsh environmental conditions) extremely expensive and time consuming for wind turbine blades with excessive length (100 m). From technological point of view, o shore wind generation maintenance teams are targeting zero-maintenance and/or least maintenance in a well-chosen timing. As a matter of fact, the two halves (top and bottom skins) of a wind blade should hold together as long as possible to allow enough time for maintenance in the event of onset of damage. Accordingly, we are suggesting a strategy, which consist the joints with 'carbon-fiber cord composite stitching'. In order to implement this technique in industrial application, one should take care of lowering stress concentration as much as possible around drilled holes and should prevent indentation to carbon-fiber cords. This paper is addressing the mentioned technologies in detail, using numerical simulation. [ABSTRACT FROM AUTHOR]

The present work deals with the analysis of unreinforced and FRCM reinforced masonry walls subjected to out-of-plane loading. In particular, numerical simulations of full scale experimental clay brick walls, previously tested, are developed. The out of plane behaviour is relevant not only for flat walls, but also for curved structures, like as domes and vaults, for which FRCM demonstrated to be highly effective in improving their structural behaviour. In this paper, two tested walls are numerically analysed. The first wall has been tested in an unreinforced configuration inducing a significant damage distribution; then, it has been retrofitted by FRCM and tested again. The second wall has been reinforced without pre-damage and tested applying the same loading history adopted for the first wall. This allowed to remark the effect of retrofitting to damaged and undamaged walls. Both the walls were constrained on two consecutive sides and loaded by a pointwise force orthogonal to the wall mid-plane, applied at the top free corner inducing a biaxial behaviour. The numerical simulations are developed performing nonlinear three-dimensional (3D) FE analyses to clearly remark the potential benefits of the strengthening technique involving FRCM systems on the out of plane behaviour. On the basis of a micro-modelling approach, bricks and equivalent interfaces were modelled separately assigning the nonlinearity only to equivalent interface. In fact, experimental testes demonstrated that the cracking and failure localize in the mortar joints. The FRCM system was modelled by means of an equivalent layer bonded on one side of the wall through interfaces. A parametric analysis is performed on the mechanical properties of the interface to investigate on the influence of these parameters on the wall response. This allowed to discuss the main parameters governing the out-of-plane behaviour of such masonry walls. [ABSTRACT FROM AUTHOR]