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Shape-morphing structures based on pressure actuation promise efficiency gains and performance improvements in aeronautics, but require complex three-dimensional geometries. The compliance of these morphing structures originates from local areas of reduced wall thickness. However, the required high wall thickness ratios are challenging for integral fabrication from high-performance fiber-reinforced plastics, which are demanded to achieve high load-bearing capacity. This study investigates different woven flexure hinges made from a hybrid yarn of glass fibers and the polyamide PA6 for application in pressure-actuated cellular structures. The flexure hinges are mechanically characterized under pure axial and pure bending loading in a tensile and a column bending test method specifically derived for flexure hinges. The specimen quality is further assessed by permeability testing, optical microscopy, and thermogravimetric analysis. This study shows that the stiffness of anisotropic flexure hinges can be determined in simple mechanical tests without the need for complex modeling of reinforcing fibers or consideration of manufacturing-specific effects. The mechanical properties of a double-layer hinge configuration are superior to those of a single-layer configuration, whereas integrating additively manufactured PA6 inlays into the woven preform offers an effective approach for achieving high wall thickness ratios. The most promising hinge configuration is selected for the integral fabrication of the aeronautical morphing structure, which consists of multiple pressurized cells. [ABSTRACT FROM AUTHOR]

Abstract This paper presents an experimental study to assess the effects of food chemicals and temperature on the mechanical performance of glass fiber reinforced bio-based polyamide. The diffusion of food chemicals was mainly driven by thermal energy, following Arrhenius law in all tested environments. Degradation of mechanical properties and decrease in reliability were assessed, due to the plasticization of polymer matrix. Secondary but not negligible effect on flexural strength degradation is given by the different chemical interaction between polymeric chains and molecules of food chemicals. Colour change was measured and resulted to be positively correlated to diffusion. [ABSTRACT FROM AUTHOR]

Abstract The aim of this study is to compare two different standardized testing procedures, tensile testing and Mode-I double cantilever beam (DCB) testing, to evaluate a possible correlation between the dominant failure in glass fibre-reinforced plastics and their according acoustic emissions (AE). AE is processed by using a burst collection of all recorded transient signals and is further analysed with the k-means clustering algorithm. To generate damage related AE, a series of experiments for tensile testing and Mode-I DCB testing is performed on 16-layer glass fibre/epoxy specimens with a cross-ply lay-up for tensile and an unidirectional lay-up for Mode-I DCB testing. Three sensors at tensile testing and one sensor at Mode-I DCB testing gather AE data. The results of clustered burst signals show a good accordance between both testing procedures, with a similar weighted peak frequency (WPF) range in each classified cluster. In total, three different clusters are determined. An assignment of these three clusters to the three dominant damage mechanisms, visually observed by microscopy, is suggested. [ABSTRACT FROM AUTHOR]

Coupon test data from five pultruded GFRP profiles is used to generate longitudinal/transverse, tensile/compressive ultimate stresses, elastic moduli, minor/major Poisson's ratios and ultimate strains (some of which are not in the pultruders' design manuals). Characteristic ultimate stresses/elastic moduli are compared to design manual minimum values. The former depend on profile size/shape, whereas the latter are shape-/size-independent. Limit state design stresses are shown to be larger than permissible stress design stresses. However, most of the limit state longitudinal design elastic moduli are smaller and all of the transverse design elastic moduli are larger than the permissible stress values. [ABSTRACT FROM AUTHOR]

The temperature-dependent off-axis tensile behavior of quasi-unidirectional E-glass fabric reinforced polypropylene composites has been investigated both experimentally and constitutively in this paper. The nonlinearity in composites under off-axis loading is shown to be a combination of damage and plasticity regardless of temperature. A nonlinear constitutive model is established to predict the temperature-dependent nonlinear stress-strain curves of composites, in which the accumulation of plastic strain and evolution of damage in composites are described by the plasticity and damage theories, respectively. A full suite of temperature-dependent plastic and damage parameters in the model are determined through cyclic loading-unloading tests. [ABSTRACT FROM AUTHOR]

Repair of structural elements with bonded fiber reinforced polymers (FRPs) is widely used in many engineering applications. Within the strengthening of civil structures, failure usually occurs due to FRP debonding by in-plane shear mode fracture. In this work, mode II fracture behavior of concrete specimens, reinforced with pultruded FRP, was investigated by the authors. Shear tests were performed by using both conventional equipment and a non-contact optical technique, Digital Image Correlation (DIC). Starting from the experimental data, the evaluation of the J-integral and of specimens' fracture toughness was carried out. Subsequently, a cohesive law was associated to the J-integral and thus identified by comparison with experimental data, by means of the theoretical approach proposed by Rice. The proposed cohesive zone (CZ) model can be adopted in a Finite Element (FE) code for simulating the debonding failure in composite structures. [ABSTRACT FROM AUTHOR]

In picture frame testing, influences of the clamping and fiber misalignment have been already studied for dry fabrics. Due to the presence of solid regions near the clamps in picture frame tests of thermoplastic continuous fiber reinforced composites at processing conditions, the influences of the clamping are amplified. This study examines the effects of the presence of unmelted material regions near the clamps on picture frame tests both analytically and experimentally for a polypropylene glass fiber composite, using a custom built picture frame which allows for an inward and outward repositioning of the clamps. The results show the presence of major strains in the composite samples when unmelted material is present near the clamps which can lead to forces up to 6.5 times higher than for supposedly ideal kinematic conditions. An overadjustment of the clamps by an up to 0.5% of the joint distance of the picture frame to allow for a minor amount of compression in the composite has shown favorable results which are comparable to correctly corrected measurements. This setting is hence recommended to generate more reliable and comparable results for intra play shear properties of thermoplastic composites. Further research is necessary to additionally account for fiber misalignment. [ABSTRACT FROM AUTHOR]

The present paper aims at investigating the influence of the mortar joints on the FRP-masonry debonding process and providing some insights on the reliability of experimental tests carried out on single bricks and theoretical formulas available to predict the debonding force. Masonry panels were constructed using two types of bricks and two types of mortars with significantly different properties. The masonry specimens were strengthened using glass fiber reinforced polymers and the debonding force was evaluated by a single-lap push-pull set-up. The obtained debonding forces were compared to those obtained by applying the same reinforcements to single bricks and calculated by applying theoretical formulas. The results of the study point out that neglecting the presence of the mortar joints and taking into account only brick mechanical properties, thus neglecting their surface and microstructural properties, may lead to significant inaccuracies in the estimation of the debonding force. [ABSTRACT FROM AUTHOR]

Microstructural characteristics are crucial in understanding and predicting the behavior of glass fiber reinforced polymer (GFRP) bars used for concrete reinforcement. Considering the lack of extensive GFRP microstructural knowledge, the main purpose of this study is to provide a documentation of GFRP microstructure and demonstrate its contribution in the durability of GFRP bars. Scanning electron microscopy (SEM) imaging was performed at different magnification levels on the cross-section of four different commercially available pristine GFRP bars. As a result of differences in the production method by pultrusion, each pristine bar presented a unique microstructural pattern including voids, defects, and fiber distribution. Two of the bars which demonstrated the most different patterns were exposed to accelerated conditioning in alkaline solution. The horizontal shear test was performed and the results were compared with the pristine bars. The difference in microstructural patterns was found to significantly contribute to GFRP durability. These results can be used as a benchmark for the microstructure of commercially available pristine GFRP bars and serve as a base for monitoring possible changes after any conditioning or testing. [ABSTRACT FROM AUTHOR]

In this study, the effect of the density of a polyisocyanurate (PIR) foam core on the behavior of axially loaded sandwich panels with glass fibre reinforced polymer (GFRP) skins are examined, for different panel heights. Thirty-six test specimens with a cross-sectional foam core area of 100 × 50 mm 2 and symmetrical 100 mm wide GFRP skins were fabricated with heights of 750, 1000, 1250, and 1500 mm to examine various slenderness ratios (kL e /r). Three PIR foam core materials with densities of 32, 64 and 96 kg/m 3 were used. An out-of-straightness assessment was first conducted to ensure that eccentricities were within acceptable limits. All samples were tested to failure in axial compression with pinned end conditions. It was shown that doubling and tripling the core density led to increases in peak load of 71 and 170%, respectively, due to the enhanced composite action and reduced shear deformations. On the other hand, slenderness had insignificant impact on peak loads, contrary to what one would expect from Euler's theory. The reason being the variety of governing failure modes. Columns with low (kL e /r) of 22–25 failed largely due to localized single skin buckling, while those with high (kL e /r) of 51–61 failed primarily by global buckling followed by secondary core shear failure with skin debonding. Columns with intermediate (kL e /r) experienced a combination of localized and global failure modes. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of simultaneous mechanical and environmental loading on the degradation rate of pultruded Glass Fiber Reinforced Polymer (GFRP) composites. The experimental program included testing a large number of GFRP coupons, with vinylester or polyester matrices, conditioned for 1000 or 2000 h under a wide range of sustained stresses and exposed to freshwater or saltwater at an elevated temperature of 60 °C. Mechanical tests, including tensile strength and elastic modulus measurements were performed on the GFRP composites. In addition, glass transition measurements, moisture uptake measurements, scanning electron microscopy, and acoustic emission testing were performed to better understand the synergistic effect of mechanical loading and environmental conditions. [ABSTRACT FROM AUTHOR]

Whilst the presence of a hybrid effect for the flexural strength of hybrid polymer matrix composites has been noted by several researchers, the reasons behind such a phenomenon remain unclear. In this work the authors have investigated the effect of hybridisation on the flexural strength of carbon/glass fibre reinforced epoxy hybrid composites with the aim of elucidating the mechanisms behind the hybrid effect. Classical lamination theory (CLT) and finite element analysis (FEA) were employed to determine the stress distribution within the composites with the maximum allowable load at first ply failure (FPF) and apparent flexural strength being determined based on four commonly used failure theories, namely, maximum stress, maximum strain, Azzi-Tsai-Hill and Tsai-Wu. Using the results of this analysis, general rules for the improvement of flexural strength in hybrid composites were proposed. Through application of these rules it was shown that a positive hybrid effect could be achieved for the flexural strength in both unidirectional and bidirectional hybrid composites when an optimal stacking configuration was used. Furthermore, the flexural strength predicted by the different failure theories was compared with it being noted that the strength obtained using the Tsai-Wu failure theory was significantly different from the strength obtained by other theories under certain circumstances, in particular for situations when the laminas contained different angles and/or materials. Overall it is hoped that the explanation of the mechanisms behind the hybrid effect of flexural strength together with the general design rules outlined in this work will lead to the improved optimization of hybrid composites. [ABSTRACT FROM AUTHOR]

It is the first time to report the effects of graphene oxide (GO) coating on the mechanical properties of short glass fiber (SGF) reinforced polymer composites. GO-coated SGF reinforced polyethersulphone (PES) composites are manufactured using extrusion compounding and injection molding techniques. The micro-structures and morphologies of GO and GO-coated SGFs are investigated using scanning electron microscopy, small-angle X-ray scattering, atomic force microscope and Fourier transform infrared techniques. Then, the tensile and flexural properties of the GO-coated SGF/PES composites are systematically studied taking into account the effect of GO coating content. It is observed that both the tensile and flexural strengths are effectively enhanced by the GO coating on the SGF surfaces. This observation is mainly attributed to the enhanced interfacial adhesion between SGFs and PES due to the GO coating. Moreover, the tensile and flexural moduli are also improved by the addition of GO due to the fact that GO has a much higher modulus than the PES matrix. [ABSTRACT FROM AUTHOR]

In the present study, the effects on the microstructure and the impact behavior of thermoset polyurethane composite material, exposed to an accelerated aging environment, were assessed. A combined hygrothermal and ultraviolet (UV) chamber is used in an accelerated aging procedure to simulate temperate climate conditions. The samples were manufactured using a vacuum assisted resin transfer molding (VARTM) technique using a novel two-part polyurethane resin (Methylene diphenyl diisocyanate/Polyol) infused into plane weave E-glass fiber mats. Samples were exposed to the UV/moisture rich environment for 250, 500, 750 and 1000 h. Effect of UV exposure on color change of composite specimens was evaluated using colorimetry. The rate of color change and the total change in color for the fiber reinforced composite was shown to be much less than that of pure polyurethane. Optical microscopy observations revealed that the color change was limited to surface discoloration due to the fiber reinforcement limiting degradation to the surface polymer matrix microstructure even after extended UV-exposure. The accelerated aging effect on the glass fiber reinforced polyurethane was examined using low velocity impact tests to evaluate impact properties of the material throughout the aging process. The test showed that the bulk composite material was resistant to the UV aging by demonstrating no significant change in impact properties due to the accelerated aging process. [ABSTRACT FROM AUTHOR]

Micromechanical modelling of short fibre reinforced thermoplastics requires identification of damage mechanisms and their kinetics as a function of their microstructure. A compact tensile machine has been designed to observe damage mechanisms during in situ microtomography tensile tests. 3D pictures of the gage length are presented at different levels of damage, from the initial state to the failure of the specimen. Fibre failure, damage at fibre ends, debonding and damage growth in the matrix have been identified as damage mechanisms for these materials. Vicinity between crossing fibres has been pointed out as microstructural configurations driving the damage mechanisms. An analysis of the damage evolution (density, morphology and orientation) allows to establish a macroscopic failure scenario, consistent with microscopic observations. [ABSTRACT FROM AUTHOR]

The mechanical properties of injection moulded short glass fibre-reinforced polyamide composites was investigated using experimental techniques. The Digital Image Correlation technique was applied during the tensile tests in order to obtain the stress–strain curves and to identify the fracture location at the early stages of the tests. Moreover, the thermographic technique was used during the static tests in order to identify the fracture zone and also during the fatigue tests, carried out at different frequencies, to study the temperature evolution of the specimen. A theoretical model was developed to analyze the temperature evolution during the fatigue test and the effect of the test frequency. The aim of this study is the application of the Thermographic Method for the fatigue assessment of short glass fibre-reinforced polyamide composites. [ABSTRACT FROM AUTHOR]

Glass Fiber Reinforced Polymer (GFRP) composites have low permeability and high corrosion resistance. In recent years, as the use of GFRP in applications requiring high corrosion resistance has gradually expanded, its long-term performance in highly corrosive environments has caught public attention worldwide. Nevertheless, there is only limited theoretical research and accumulated test data on the corrosion resistance of GFRP. This paper analyses the long-term performance of GFRP in highly corrosive environments. Samples cut from pultruded GFRP profiles were exposed to alkaline, saline, and acidic solutions of different concentrations at 60 °C. Additionally, the effects of acidic solutions at high temperature (90 °C) were investigated. Flexural properties, changes in the flexural fracture mechanism, hardness, the rate of weight gain, changes in appearance, and scanning electron microscopy (SEM) images of fracture sections were analyzed over periods of 7, 15, 30 and 90 days. Results indicate that flexural strength decreases with increased exposure time to both acidic and alkaline solutions. Under conditions of high concentration acidity and high temperature acidity, respectively, flexural strength decreases even more drastically. Additionally, it was found that saturated NaCl solution has little effect on GFRP. [ABSTRACT FROM AUTHOR]

Fiber Reinforced Polymer (FRP) composites are widely used for strengthening and conservation of historic masonry, even if research problems are still open. The mechanical behavior of masonry columns having a circular cross section, confined with glass and basalt FRP systems was studied in this paper. An extended experimental investigation is presented in order to show the results of axial compression tests on circular masonry columns built with natural blocks (calcareous stone). Active confinement was also studied by using a novel technique that employs Shape Memory Alloys (SMA). Totally twenty-four masonry columns were built, instrumented and tested. Different fibers, strengthening schemes and matrix/adhesive were used for the confinement of the columns. Unstrengthened columns were tested as reference specimens. Axial strain of the columns and tensile strain of the fibers in the direction perpendicular to the primary axis of the columns were measured with the applied load. Experimental results revealed the effectiveness of the FRP-confinement for masonry columns. Active confinement was found to be effective at early loading stages since an increased stiffness of the SMA/GFRP-confined columns was measured. A prediction of the compressive strength was obtained by using the model of the Italian guidelines CNR DT 200 (National Research Council) in order to compare the experimental results with the design approach, also for new types of fiber like basalt which were not included in the technical codes. Finally, the experimental results were compared with theoretical values calculated according with to two existing analytical models in order to test their effectiveness for the analyzed configurations. [ABSTRACT FROM AUTHOR]

The dynamic fracture of S-2 glass fiber-reinforced polymer matrix composites (FRPMCs) was investigated in this study. The matrix ductility was improved by a recently developed network topology modification technique via mixing partially reacted substructures (mPRS). The composite material was manufactured and characterized by micro-CT scanning and scanning electron microscopy (SEM). Dynamic single-edge notched bending (d-SENB) experiments were performed on the composites by using a modified split-Hopkinson pressure bar. Each specimen's fracture process was visualized by ultrafast X-ray imaging. Such in-situ radiography enabled identifying the damage initiation below 50-μm scale and inspecting its propagation through the internal structures of opaque composites, thereby accurately quantifying the composites' mechanical properties. Furthermore, the identical d-SENB experiments were designed and the digital image correlation (DIC) was employed to monitor the stress wave propagation on the composite specimens. The force and deflection measurements were modified and correlated to the physical damage processes. Besides, quasi-static SENB experiments were conducted to identify the loading rate effects on the composites' fracture behaviors. The force and deflection history, bending stiffness, energy dissipation, and fracture toughness at different loading rates were quantified and compared. Finally, post-fracture analysis by micro-CT scanning and SEM provided physical observations on the variation of the fracture morphology at different loading rates. [ABSTRACT FROM AUTHOR]

Abstract: The span limits of two glass fiber-reinforced polymer (GFRP) bridge concepts involving GFRP-balsa sandwich plates are discussed. The sandwich plates were either used directly as slab bridges or as decks of a hybrid sandwich-steel girder bridges. In the latter case, the potential of the sandwich decks to replace reinforced concrete (RC) decks was also evaluated. Taking the limits of manufacturing into account (800mm slab thickness), maximum bridge spans of approximately 19m can be reached with FRP-balsa sandwich slab bridges, if a carbon-FRP (CFRP) arch is integrated into the balsa core. Above this limit, hybrid sandwich-steel girder bridges can be used up to spans of 30m. RC deck replacement requires timber and steel plate inserts into the balsa core above the steel girders. GFRP-balsa sandwich slabs or decks exhibit full composite action between lower and upper face sheets. Stress concentrations occur at the joints between balsa core and timber inserts which however can effectively be reduced by changing from butt to scarf joints. [Copyright &y& Elsevier]

Abstract: Monitoring of drop impact damage is necessary because it produces invisible damage in composite materials without any visible mark on the surface. Monitoring of drop impact damage was carried out on Woven Glass Fibre Reinforced Polymer (WGFRP) composite laminate through Acoustic Emission (AE) technique. The significant AE parameters like signal strength, root means square value, counts and counts to peak were determined for drop impact damage. Impact damage tolerance was predicted using Artificial Neural Network (ANN) trained with AE parameters as input and impact damage tolerance as output. The predicated impact damage tolerance was with average error tolerance of 3.35%. The proposed network finds very good agreement for prediction of impact damage tolerance of impact damaged WGFRP composite laminate in real time application. [Copyright &y& Elsevier]

Abstract: Glass fibre reinforced polymer (GFRP) pultruded profiles have been increasingly used in civil engineering structural applications in the past few decades owing to their high strength, low weight and corrosion resistance. Nevertheless, the low material moduli, which makes design most often governed by deformability and instability phenomena, the brittle failure mechanisms and the high initial costs, have been delaying their widespread use. Hybrid GFRP–concrete structural solutions have been proposed to overcome the aforementioned limitations, namely the low material moduli. Furthermore, GFRP material creep models suggest that such hybrid structures may reduce the creep deformations when compared to full GFRP structures. In this context, this paper presents experimental and analytical investigations about the creep behaviour of a hybrid GFRP–concrete footbridge comprising two I-shaped GFRP pultruded profiles and a thin deck made of steel fibre reinforced self-compacting concrete (SFRSCC). The experiments comprised flexural creep tests on a 6.0m long footbridge prototype subjected to a uniformly distributed load for up to 2642h, during which deflections and axial deformations were monitored. In order to assess the influence of loading and environmental conditions on the creep behaviour of the structural system, the prototype was tested for three different combinations of load levels and seasons. Experimental results showed that (i) GFRP–concrete hybrid structures lead to a considerable decrease of the creep deformations of GFRP structures and that (ii) environmental conditions significantly influence the viscoelastic response of these hybrid structures. The models proposed, based on the creep response of the constituent materials, were able to predict the observed structural response for the different load levels and environmental conditions with very good accuracy. Therefore, they are proposed to predict the long-term response of GFRP–concrete structures instead of empirical models based on short-term experimental data. [Copyright &y& Elsevier]

Abstract: The aim of this work is to analyze the possibility to join aluminum alloy AA6086 and composite laminates reinforced with basalt fibers, an innovative material which use is growing in several applications as an alternative to glass fibers. To this goal, three joining techniques were investigated: mechanical by Self Piercing Riveting (in the next called SPR), adhesive by co-curing technique and mixed in which the joining techniques (i.e. adhesive and mechanical) were combined. Two manufacturing technologies (i.e. hand lay-up and vacuum bagging) were used both to produce composite substrates and to realize co-curing adhesion between the substrates to be joined. Mixed joints were realized by inserting the rivets in co-cured joints after 48h than the initial phase of the curing process (i.e. the phase of mixing the resin with own hardener). Overall, six lots of joints were realized (two for each joining technique). All joints were characterized by performing single lap joint tests. The mechanical results were analyzed through a two way analysis of variance. The experimental results show that adhesive joints, realized by vacuum bagging method, show average failure load 22.9% higher and standard deviation 70.6% lower than those realized by hand lay-up, respectively. This means that the vacuum bagging technology allows to increase the adhesion strength of the interface between metal sheet and Basalt Fiber Reinforced Polymer (in the next BFRP), allowing the above failure load growth. Furthermore the failure mechanisms change from adhesive mode to partially cohesive one for the adhesive joints realized by hand lay-up and vacuum bagging, respectively. By comparing mixed joints, different results are obtained: i.e. the hand lay-up joints show both higher average failure load (+42.9%) and standard deviation (+208.3%) than those realized by vacuum bagging. The poor performances of the mixed joints realized by vacuum bagging can be considered due to the excessive value of the chosen riveting load. Statistically, two variables were investigated: i.e. joining technology (i.e. mechanical, adhesive and mixed) and manufacturing process (i.e. hand lay-up and vacuum bagging). These can influence the properties of the joints. In particular, the joining technology results a significant factor. Moreover, an interaction between the two variables exists. [Copyright &y& Elsevier]

Abstract: The results of a numerical investigation into the efficiency of glass fibre reinforced polymers (GFRPs) in improving the seismic performance of an 8-storey moment resisting reinforced concrete building are presented. In order to assess the effect of the transverse reinforcement, the building is detailed with different levels of transverse reinforcement representing well-confined and poorly-confined conditions. Although GFRP wrapping of columns at critical regions is the main retrofitting technique considered in this study, the effect of increasing the beam ductility on the seismic performance of a structure is also evaluated for the code-compliant building. The retrofitting strategy aims to provide both columns and beams with more ductility and energy dissipation instead of increasing the lateral strength. The load–displacement curves obtained from pushover analysis of the frames are then used in the seismic assessment using a capacity spectrum approach (the N2 method). The results confirm that GFRP wraps is capable of improving the seismic performance and ductility of the poorly-confined structure substantially, compared to the original structure. However, it was found that using FRP composites in order to increase the ductility of code-compliant building only, was not that effective. [Copyright &y& Elsevier]

Abstract: This paper presents the test results of an experimental study carried out to investigate the residual tensile properties of new generation of GFRP bars after being subjected to several harsh environmental conditions for different periods. The bars were exposed to ten different environmental conditions for 6, 12, and 18months. In addition to a control laboratory condition, the environments included exposure to ordinary tap water and sea water at two temperatures (room and 50°C), sea water dry/wet, alkaline solution, and hot-dry condition at 50°C. Furthermore, the environments included two typical harsh field conditions of the Kingdom of Saudi Arabia. The performance of the GFRP bars was evaluated by conducting tensile tests on the bars after different exposure periods. Scanning electron microscope was used to investigate the degradation mechanism of the bars. After 18months of exposure, the test results showed that at 50°C the tap water and alkaline solution had the maximum harmful effect on the tensile strength of the tested GFRP bars. The two field conditions considered in the present study did not show any significant effect on the tensile properties of the bars. The test results also showed that the GFRP bars tested in this study had better resistance to alkalinity and water compared to most of the GFRP bars in the literature. [Copyright &y& Elsevier]

Abstract: In this study a total of 63 cubic specimens were prepared to investigate the pullout behaviors of the sand-coated and helically-wrapped GFRP bars as well as steel bars in concretes reinforced with structural fibers (steel, PP and PVA fibers). The results of direct pull-out testing were presented and analyzed with the aim of elucidating the effect of surface treatment of bar, fiber type, and fiber volume fraction in interface and suggesting the effective evaluation method for the improved ductility. The structural fibers in the interface changed the interfacial bond behaviors before and after the maximum stress and resulted in significant improvement of the relative bond strength, but bond failure modes largely depended on the interfacial property with the rebar. The fiber’s crack closing resistance, determined by evaluating both the residual bond strength and toughness indices, was used to determine optimum amount and type of fibers in the composites. The closing pressures due to PVA and hook end steel fibers had a good effect on resisting and controlling the interfacial crack initiation, growth, and propagation. [Copyright &y& Elsevier]

Abstract: This paper describes a detailed assessment of the structural safety, serviceability, capacity rating and long-term durability of a fiber-reinforced polymer (FRP) vehicular slab bridge superstructure. This first all-FRP slab bridge was installed in Korea on May the 22nd, 2002. The FRP slab bridge superstructure is a simply supported, its length is 10.0m, and is designed to carry two-lane traffic and has an overall width of 8.0m. The FRP slab bridge is a sandwich structure with a corrugated core, fabricated by a hand lay-up process with E-glass fibers and vinyl ester resins. The assessment includes a visual inspection, field load test identical to that performed in 2002. The field load test under actual service conditions was conducted as specified by the Korean Highway Bridge Design Code. In this first part, the field load test results performed in 2002, 2004 and 2011 are presented and the capacity-ratings of FRP slab bridge was evaluated. The assessment indicates that the FRP slab bridge has no structural problems and is structurally performing well in-service as expected. The assessment may provide a baseline data for the FRP slab bridge capacity rating assessment and also serve as part of a long-term performance of all-FRP bridge superstructure. [Copyright &y& Elsevier]

Abstract: This paper reports tests to failure of hybrid members comprising cellular GFRP decking connected to RC beams via an epoxy adhesive. RC beams of low crack widths under service loads are useful with GFRP decking owing to the economy of and modest expertise needed to install such beams. Key novelties of this investigation include the RC beams (steel, FRP and prestressed concrete beams have been used previously) with the GFRP decking, use of the epoxy-bonded (so chemical, an alternative to mechanical) connection between the GFRP decking and the concrete beams, and study of the positive and negative moment responses (for application to continuous bridges) of this hybrid form. The test results show the adhesive to be a significant deck-to-beam shear connector under positive and negative moments. Whether the deck was a tensile or compressive top chord, the primary failure mode, which occurred at high loads, was delamination within the GFRP at the deck’s flange-to-web joints, and was neither failure of the GFRP-adhesive interface nor of the adhesive between deck units. For the positive moment specimen there was also fracture of the concrete near the deck as observed for FRP-plated RC beams, despite the absence of flexural cracks from this near-deck concrete. [Copyright &y& Elsevier]

Abstract: This paper analyzes the flexural behavior of high strength concrete beams reinforced with hybrid glass fiber reinforced polymer (GFRP) and steel reinforcements. To verify the influence of the arrangement of rebar layers and support design of concrete structures with hybrid reinforcement, we have experimentally investigated the flexural strength, load–deflection and crack behaviors of hybrid reinforced concrete beams. Four beams, including one control beam reinforced with only GFRP bars, are tested. The arrangement of reinforcement layers is the main parameters considered. Theoretical models are proposed for the prediction of ultimate capacity and modes of failure. [Copyright &y& Elsevier]

Abstract: This paper investigates the residual tensile properties of newly developed glass fiber reinforced polymer (GFRP) bars after being subjected to elevated temperatures for different periods. A total of 120 GFRP specimens were tested in this study. Half of the samples were covered with concrete while the other half were bare bars. The specimens were subjected to three different controlled temperatures (100, 200 and 300°C) for three different periods (1, 2, and 3h). Test results showed that almost no losses were observed in the tensile modulus after all exposure periods and temperatures. Losses in the tensile strength, proportional to the level of temperature and exposure period, were recorded. The bars with concrete cover showed higher residual tensile strength compared to their counterparts without coating. The concrete cover was more effective at the lowest temperature level (100°C) and at the shortest time period (1h). Scanning Electronic Microscopy (SEM) technique was also used to investigate the effect of elevated temperature on the degradation mechanism of the GFRP bars. The results showed that increasing the temperature level affected the resin matrix surrounding the glass fibers and consequently affected the bond between the fibers and the matrix. [Copyright &y& Elsevier]

Abstract: An expression of Young’s modulus of short inorganic fiber reinforced polymer composites was derived based on the tensile strength equation proposed in the previous paper, and the factor affecting the Young’s modulus was analyzed. This equation was applied to estimate the Young’s modulus of short inorganic fiber reinforced polymer composites. The results showed that the relative Young’s modulus increased nonlinearly with increasing fiber volume fraction, while increased linearly with an increase of fiber length-diameter ratio. Finally, the equation was verified preliminarily by using the measured Young’s modulus of the short glass fiber (SGF) reinforced polycarbonate/acrylnitrile–butadiene–styrene copolymer composites and the polypropylene reinforced respectively with SGF and short carbon fiber reported from literature, good agreement was found between the predictions and the experimental data. [Copyright &y& Elsevier]

Abstract: Interlaminar shear properties of fibre reinforced polymer composites are important in many structural applications. Matrix modification is an effective way to improve the composite interlaminar shear properties. In this paper, diglycidyl ether of bisphenol-F/diethyl toluene diamine system is used as the starting epoxy matrix. Multi-walled carbon nanotubes (MWCNTs) and reactive aliphatic diluent named n-butyl glycidyl ether (BGE) are employed to modify the epoxy matrix. Unmodified and modified epoxy resins are used for fabricating glass fibre reinforced composites by a hot-press process. The interlaminar shear strength (ILSS) of the glass fibre reinforced composites is investigated and the results indicate that introduction of MWCNT and BGE obviously enhances the ILSS. In particular, the simultaneous addition of 0.5wt.% MWCNTs and 10phr BGE leads to the 25.4% increase in the ILSS for the glass fibre reinforced composite. The fracture surfaces of the fibre reinforced composites are examined by scanning electron microscopy and the micrographs are employed to explain the ILSS results. [Copyright &y& Elsevier]

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: Fibre-reinforced polymers (FRPs) are an accepted material by structural engineers for the strengthening of structural elements. With increasing environmental concerns, further emphasis is being placed on the use of sustainable construction materials such as timber. This paper describes an experimental programme which examines the reinforcement in flexure of low-grade glued laminated timber (glulam) with a commercially attractive recyclable FRP. Unreinforced glulam beams, FRP plate reinforced glulam beams, unreinforced glulam beams incorporating an additional sacrificial lamination and FRP plate reinforced glulam beams, which had a sacrificial lamination bonded beneath the FRP plate, were fabricated and tested in flexure. The unreinforced glulam demonstrated linear elastic behaviour and exhibited brittle tensile-flexural failures in comparison to the pseudo-ductile behaviour of the reinforced beams. The addition of reasonable reinforcement percentages strategically located in the tension zone resulted in moderate enhancements in the stiffness while more significant improvements in the ultimate moment capacity were obtained. Strain profiles illustrated that increased utilisation of the compression strength of the timber is obtained when FRP reinforcement is included. [Copyright &y& Elsevier]

Abstract: New perspectives have arisen on basalt fibre applications due to the potential low cost of this material together with its good mechanical performance, in particular at high temperature. The idea to fill these fibres into a polymer matrix is relatively recent and could offer very interesting perspectives that have not yet been sufficiently investigated. In this work, with the principal aim of evaluating the possibility to replace glass fibres in most of their applications, mechanical tests were carried out on comparable E-glass and basalt fibre reinforced plastic laminates. The latter were cut by square plates fabricated through vacuum bag technology. The results obtained on the two laminates were compared showing a high performance of the basalt material in terms of young modulus, compressive and bending strength, impact force and energy. These good properties suggest possible applications of basalt fibres in fields where glass composites are nowadays largely applied. The short-beam strength tests confirmed what above said by denoting an interfacial adhesion similar to that between E-glass and epoxy matrix. [Copyright &y& Elsevier]

Abstract: The present paper deals with the mechanical behaviour of masonry columns confined by using fibre-reinforced polymer (FRP) composites. In particular, it presents the key results of a wide experimental program jointly carried out at the Laboratories of the Universities of Salerno and Salento (Italy). Several kinds of masonry, made out of either natural or artificial bricks having different dimensions, have been tested in this experimental programme. A total number of 54 column specimens have been built and tested in pure compression. Moreover, several composite systems (mainly based on glass fibres) have been utilised as confining device by applying a variable number of layers that allow to develop different levels of lateral pressure. The present paper reports the complete information about the geometric and mechanical parameters related to the tested specimens as well as the key aspects of the structural behaviour observed during the compression tests. In particular, the maximum load levels and the corresponding axial stresses and (average) strains are clearly reported. Finally, the main differences in terms of structural response due to the behaviour of the various materials utilised for both masonry and external wrapping are highlighted. Moreover, the same experimental results, along with further experimental data already available in the scientific literature, will be quantitatively analysed in a companion paper with the aim of calibrating a design formula for determining the axial strength of masonry columns confined by FRP. [Copyright &y& Elsevier]

Abstract: This paper investigates the performance of a glass fiber-reinforced polymer (GFRP) bridge deck under static and fatigue load cycles. The bridge deck has a sandwich panel configuration, consisting of two stiff face shells separated by a light-weight honeycomb core. The deck was manufactured using a hand lay-up technique. In this study, a full-size panel that had the same design as an actual bridge deck was tested. The experimental data are analyzed and compared to the results of finite element analysis. The data obtained have indicated that the failure of the system is governed by the delamination of the face shells from the honeycomb core, and the failure behavior is pseudo-ductile even though the material itself is brittle. Hence, the design of such a deck panel should be based on the shear strength of the face–core interface. However, the shear strength can depend significantly on the workmanship in the fabrication process. For design, if the interface shear strength can be reliably identified, the maximum shear stress should be no greater than 15% of the shear strength to avoid fatigue damage under the service load condition. [Copyright &y& Elsevier]

Abstract: Fiber-reinforced polymer (FRP) systems that have a strong resistance against long-term deformation must provide improved serviceability to reinforced concrete (RC) members under sustained loads. Consequently, there is a need to develop a method for accurately predicting the time-dependent behavior of RC beams that are externally bonded with FRPs. However, there are very few previous studies that have been carried out or experimental results available, on the time-dependent behavior of RC beams externally bonded with FRP. In order to enable a reasonable prediction, correlations should first be clarified between the stress–strain relationship of the concrete, the reinforcement and the FRP that changes over time. By using these correlations, deflections under sustained loads should then be forecast. In this study, RC beams were fabricated for this purpose. Carbon reinforced polymer (CFRP) and glass reinforced polymer (GFRP) materials were bonded to the tension face of the two respective RC beams. The beams were then placed under sustained loads for 300 days. For the specimens that were externally bonded with FRPs and for the conventional specimen, the strain of the compression and tension reinforcement and the strain of FRP and deflection were measured respectively for comparison. In order to theoretically predict the time-dependent behavior of the RC Beam externally bonded with FRPs, creep coefficients for concrete and shrinkage strains were calculated by using the CEB-FIP and the ACI-209 Codes. For the method used to forecast the stress–strain relationships of the concrete, reinforcement and FRPs that change over time were theoretically clarified and were then compared with the experimental results. The deflection of the RC Beams externally bonded with FRP was predicted by using the ACI 318 Standard, EMM, AEMM, Branson’s method, and Mayer’s method. They were also compared to the experimental results. Subsequently, in the case of RC Beams externally bonded with FRPs under sustained loads, the proposed method proved that it is possible to accurately predict long-term deformations. [Copyright &y& Elsevier]

In this paper, properties of glass fiber-reinforced thermoplastic polymers (GFRTP) were evaluated using recycled polyester (rPET) for injection molding bicycle frame. The effect on thermal and mechanical properties of rPET reinforced glass chop fiber according to fiber cross section and fiber content ratio were studied. The crystallization temperature of glass fiber (GF)/rPET, a glass fiber added thermoplastic composite, was higher than the crystallization temperature of rPET pellet without a glass fiber, and the shape of the exothermic curve was sharper. Mechanical characteristics of a GF/rPET thermoplastic composites has been increased by increasing fiber contents, than above a certain level did not longer increased. And mechanical properties of flat glass fiber reinforced rPET with low void volume were most excellent. In order to prove the validity of the experimental results, finite element analysis of thermoplastic composite was performed by Digimat and Abaqus to compare the experimental values according to the cross sectional shape and volume fraction of glass fiber. The results of finite element analysis showed a similar tendency between the experimental results and the analysis results. • The thermoplastic composite material was manufactured by injection molding using a recycled polyester chip and glass fiber. • Properties of the composite material addied with the glass fiber of a flat cross section were excellent. • The validity of the experimental results was verified through finite element analysis by Digimat and Abaqus. [ABSTRACT FROM AUTHOR]

This paper aims to present an experimental investigation on the behavior of web-flange junctions (WFJs) rotational stiffness of pultruded fiber-reinforced polymer composites (FRP). Channels and I-sections were tested using a simple set-up, which was developed in order to experimentally characterize the junctions in a direct manner. The Digital Image Correlation (DIC) technique was used, allowing overall deflections and relative rotations between web and flange to be monitored. The WFJs' imperfections were analyzed through an optical microscope and correlated with the cracks' formation. Further, damage thresholds are identified using available stress equations for curved composite members and lower bound functions are proposed to simulate the junction stiffness retention. Finally, two Equations are developed in order to analytically predict pultruded junctions' rotational stiffness per unit of width. In general, the theoretical and experimental results agreed fairly well, with a maximum difference of 24% for I-sections and 38% for channels. [ABSTRACT FROM AUTHOR]