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Abstract: The behaviour of structural fibre composite sandwich beams made up of glass fibre composite skins and phenolic core material was investigated under three-point short beam and asymmetrical beam shear tests. The effect of the shear span-to-depth ratio (a/D) on the strength and failure behaviour of the composite sandwich beams was examined. The results showed that with increasing a/D ratio, the failure load of the sandwich beam is decreasing. On the contrary, the coupling effect of flexural stresses increases with increasing a/D ratio. Noticeably, the fibre composite sandwich beams tested under asymmetrical beam shear exhibited higher failure load compared to beams tested under short beam shear. Analysis showed that the shear stress in the core is more dominant than flexural stress when the a/D ratio is 1 for the sandwich beams under short beam test and 1–3 for the sandwich beams tested under asymmetrical beams shear test. The proposed prediction equation which accounts for the combined effect of shear and flexural stresses due to the changing a/D ratio, presented a good agreement with the experimental results, showing that it can reasonably estimate the failure load of structural fibre composite sandwich beams. [Copyright &y& Elsevier]

Abstract: The fatigue behaviour of small scale composite unit cells consisting of seven fibres and surrounding matrix is developed for use in fatigue simulations. The predicted fatigue properties of these 7-fibre unit cells are compared with the fatigue properties of single glass fibres and of unidirectional composite dog–bone specimens. These predicted results provide stochastic fatigue characteristics that can be used as input for modelling the fatigue behaviour of larger composite structures. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental and analytical study about the mechanical response at elevated temperature of glass fibre reinforced polymer (GFRP) pultruded profiles. The paper first describes results of DMA and DSC tests that were used to evaluate the glass transition and decomposition processes of the GFRP pultruded material. The paper then describes an extensive study about the tensile, shear and compressive responses of the GFRP material at temperatures varying from 20°C to 250°C. In these tests the mechanical responses of the GFRP material as a function of temperature were assessed, namely the load–deflection curves, the stiffness, the failure modes and the ultimate strength. Results obtained in these experiments confirmed that the mechanical performance of GFRP is severely deteriorated at moderately high temperatures, particularly when loaded in shear and compression, owing to the glass transition of the resin. The final part of this paper assesses the accuracy of different empirical models and one phenomenological model to estimate the tensile, shear and compressive strengths of GFRP pultruded material as a function of temperature. All empirical models, including a function based on Gompertz statistical distribution suggested in the present paper, provided accurate estimates of tensile, shear and compressive strengths as a function of temperature. The phenomenological model was less accurate and in general provided non conservative estimates of material strength. [Copyright &y& Elsevier]

Abstract: This paper deals with the study of water diffusion in unidirectional composite associating experimental data, analytical and numerical models. A fibre/matrix interphase with a gradient of molecular mobility is characterized by microthermal analysis. The fibre dispersion observed by optical microscopy shows an important heterogeneity and many contacts between fibres. This particular fibre distribution as well as the interphase thickness have been considered to model our composite microstructure accurately. Diffusion kinetic parameters from water absorption measurements on both the resin and the UD composite were then used in the finite element analysis of the composite. The comparison between experimental data, analytical and numerical models show the influence of fibre distribution and interphase properties on water diffusion kinetic. An average water diffusion coefficient is then identified for the interphase. [Copyright &y& Elsevier]

Abstract: Glass fiber reinforced plastic (GFRP) composite material is often utilized in marine applications for the construction of boats and ships. In this application it is a usual procedure to protect the material with a layer of gel-coat, but if the gel-coat breaks the material would be in direct contact with a humid environment. The main objective of this study was to understand the degradation that sea-water causes on GFRP mechanical properties. The article deals with two common resin systems in marine applications, i.e. polyester and vinylester, and reports the results of quasi-static and vibration tests at different sea-water exposure times, and fatigue tests in dry and wet environments of unexposed specimens and specimens aged in sea water for 22-weeks. The results show degradation of the material in terms of ultimate stress in the case of quasi-static loading, and no appreciable degradation on the fatigue loading case. Vibration tests demonstrated a stable flexural modulus during the water exposure period. [Copyright &y& Elsevier]

Abstract: The performance of adhesively bonded joints composed of aluminum sheet and stainless steel foils was investigated at the cryogenic temperature for the secondary barrier LNG (Liquefied Natural Gas) containment system. Since the huge adhesive bonding area such as LNG carriers or floaters cannot be surface-treated economically by chemical treatment, new flame surface treatment method for the metal foils was evaluated and compared with other conventional surface treatments such as mechanical or chemical surface treatments at the cryogenic temperature. The surface wettability by contact angle measurement of the metal foil was investigated with respect to surface treatments and environmental aging conditions. The effects of adhesive thickness on the adhesive bond strength and fracture toughness have been also investigated at the cryogenic temperature. The experimental results showed that the bonding performances depended strongly on the surface treatment method, adhesive thickness and fiber reinforcement for the adhesive, such. It was also found that the thick adhesive joint had a reduced bonding strength at the cryogenic temperature, but the glass fiber reinforcement improved much the bonding strength and fracture toughness for thicker adhesive at the cryogenic temperature. [Copyright &y& Elsevier]

Abstract: Due to the mechanical properties of fibre reinforced polymer (FRP) bars, deflections often drive the design of FRP reinforced concrete (RC) flexural members. This has led to an increasing number of studies focused on the analysis of short-term deflections of FRP RC beams. However, investigations and experimental data focused on long-term deflections are scarce. The time-dependent deflection in RC beams is a function of member geometry, material properties and loading characteristics. Maximum service loads, as well as repeated loading, affect the deflections under sustained loads. This paper presents the results and discussion of an experimental programme concerning eight glass FRP RC beams tested at service load, and subsequently subjected to sustained loading for 250days. Two reinforcement ratios and two levels of sustained load were considered. The experimental results revealed an effect of the loading–unloading processes and the reinforcement ratio on short and time-dependent deflections. No significant influence of the sustained load level was observed. Moreover, the theoretical predictions obtained with different models have been compared with the experimental results. The modified time-dependent factor presented in ACI 440.1R-06, together with the modified Bischoff’s equation to compute the immediate deflections due to sustained load, give the best agreement with experimental deflections. [Copyright &y& Elsevier]

Abstract: Glass fiber reinforced polymer (GFRP) composites are used extensively to strengthen and/or to rehabilitate infrastructures. The current study focuses on the use of GFRP for enhancing local buckling behaviour of wide flange steel beams. The study is conducted numerically using a nonlinear finite element model developed in-house. In the numerical model, consistent shell elements are used to simulate the flanges and web of the steel beams as well as the GFRP plates. The interface between the steel and GFRP plates is simulated using a set of continuous linear spring systems representing both the shear and peel stiffness of the adhesive based on values obtained from a previous experimental study. The numerical model is validated using test results and numerical predictions available in literature. Various failure modes, including GFRP rupture, adhesive shear failure, and local buckling of the flanges of beams are included in the model. The effect of geometric imperfection and residual stresses are also included. The model is then used to conduct a parametric study to assess the effect of bonding GFRP plates on enhancing the local buckling behaviour of wide flange steel beams. The results reveal that the effectiveness of this approach especially for the case of slender beams. [Copyright &y& Elsevier]

Abstract: In this work, unidirectional multi-scale, carbon nanostructure (CNS)–glass fiber–epoxy, composites were manufactured using a novel in-line continuous production scalable chemical vapor deposition based CNS manufacturing process. The processing parameters peculiar to the growth system, specifically growth chamber temperature, catalyst concentration and line speed, were varied to observe the effect on the CNS growth and parent filament degradation. Unidirectional tension and compression tests were conducted to measure the strength and modulus in the filament direction and failure mechanisms of the hybrid materials identified. Based on the results of tensile tests, gains in tensile strength and tensile modulus are achieved through a uniform coverage of short CNS. The greatest increases in CNS-enhanced composite compressive strength can be achieved through the combination of low weight percent CNS on the fiber and minimal parent filament environmental degradation. For stiffness governed applications, these CNS-enhanced composites may not provide the ideal solution. However, applications which demand significant deformation prior to failure or damage tolerance can benefit from the properties afforded by these CNS–fiber–epoxy composites. [Copyright &y& Elsevier]

Abstract: In the last decades, FRP composites have been widely used for constructing entire civil structures. One of the challenging issues for building with pultruded FRP composites is understanding the behaviour of bolted joints. In this paper, the results of a numerical analysis performed on different types of bolted composite joints with different geometry and subjected to tensile loads are reported. The aim of this study is to examine the distribution of shear stresses among the different bolts by varying the number of rows of bolts as well as the number of bolts per row. The study also considers the presence of variable diameter washers and their influence on the bearing stresses of composites with different fibre orientations. For verification of the validity of the analytical models, numerical results are compared to experimental results reported elsewhere. The results of this study showed that in multi-bolt joints, the load is not distributed equally due to varying bolt position, bolt-hole clearance, bolt-torque or tightening of the bolt, friction between member plates and at washer-plate interface. The results also indicated that in the presence of washers, the stress distributions in the fibre direction, varying fibre inclinations, are decreasing for each value of washer pressure. [Copyright &y& Elsevier]

Abstract: The faces of low-observable radomes constructed with sandwich structures are usually made of glass fiber or aramid fiber composites due to their high specific strength and compatibility of stealth characteristics. In this work, a hybrid composite face composed of both E-glass/epoxy and aramid/epoxy composites for low-observable radomes was designed to exploit the better characteristics of both composites. Three design methods, including the characteristic medium thickness, the wavenumber and the dielectric wavelength methods, were applied to satisfy the functional requirements of composite faces. The three design methods were evaluated via three-dimensional (3-D) electromagnetic wave transmission analysis and the free space measurement method. [Copyright &y& Elsevier]

Abstract: The bearing properties of recently developed hybrid fiber/metal laminates, or COmmingled Boron/glass fiber Reinforced Aluminum laminates (COBRA), are investigated in this study. The bolt-type bearing tests on GLass REinforced aluminum laminates (GLARE), non-commingled hybrid boron/glass/aluminum fiber/metal laminates (HFML) and COBRA were carried out as a function of e/D ratio, metal volume fraction, fiber volume fraction, and fiber orientation. Experimental results show that with the same joint geometry and metal volume fraction, the commingling of boron fibers improves the bearing strength of fiber/metal laminates. Observations show the boron/glass fiber prepreg, transverse to the loading direction, results in a bearing mechanism that effectively increases the bearing strength. The bearing strength of COBRA with longitudinal fibers is lower than that with transverse fibers due to the fact that shearout failure takes place before maximum bearing strength is reached. The experimental results show that, with only either transverse fiber orientation or longitudinal fiber orientation, COBRA with 18% boron fiber volume fraction possesses a higher bearing strength when compared to HFML with 6% boron fiber volume fraction. In addition to the properties in COBRA with parallel-plies commingled prepreg, the bearing properties of various COBRA with [0°/90°] and [0°/90°/90°/0°] cross-ply commingled prepregs are also discussed. [Copyright &y& Elsevier]

Abstract: The kinetics of moisture sorption under immersion in water at room and elevated temperatures and flexural characteristics of dry (conditionally initial) and wet (moistened up to saturation level) composite material were investigated on flat specimens of polyester based glass fiber-reinforced plastic, cut from I-beam pultruded profile. It was found that the coefficients of diffusion and swelling are different in three principal axis of the composite. The former have the largest value in fiber axis direction, but the latter – in transverse to fiber axis direction out of plane of the layers. The observed difference in kinetics of mass gain and change of volume strain for the specimens of various sizes allowed evaluate the volume of pores, filled with water. The large data spread for the specimens, cut from the flanges, was found. Edge specimens have lower density and showed lower elastic and strength characteristics. The material specimens moistened up to saturation level showed the decrease in flexural modulus and strength for 8% and 16.5%, respectively. No effect of sorbed moisture on tensile modulus and strength of the composite (tension along the fiber axis direction) was found. [Copyright &y& Elsevier]

Abstract: The seismic performance of a concrete filled fiber reinforced polymer (FRP) tube (CFFT) bridge column was studied through shake table testing and nonlinear dynamic analyses of a one-fifth scale two-column bridge pier that also incorporated a conventional RC column. The FRP tube in the CFFT column was a prefabricated composite pipe with glass fibers aligned in ±55° with respect to the tube axis to provide both hoop and longitudinal strengths. The columns had nearly the same flexural capacities. The accumulated dissipated hysteresis energy of the CFFT column normalized by steel ratio was 1.6 times larger than that of the RC column; yet, it remained visibly damage free up to a drift ratio of 7%. The CFFT column failed due to FRP tube rupture under 8.4% drift ratio. The equivalent plastic hinge length of CFFT column was found to be more than twice that of the RC column, which implies larger spread of plasticity and smaller local ductility demands. The nonlinear dynamic modeling of the pier response using OpenSees led to very good agreement with the measured response of the pier under moderate and large-amplitude motions. [Copyright &y& Elsevier]

Abstract: Basalt reinforced composites are recently developed materials. These mineral amorphous fibres are a valid alternative to carbon fibres for their lower cost, and to glass fibres for their strength. In order to use basalt reinforced composites for structural applications, it is necessary to perform a mechanical characterisation. With this aim in the present work experimental results of several static and fatigue tests are described. Two polymeric matrices are taken into account, vinylester and epoxy, to assess their influence on the evaluated parameters. In parallel to these mechanical tests, also the thermal answer of the specimens to mechanical loads is evaluated by means of thermography. This experimental technique allows defining the composite local heating during the application of mechanical loads and its behaviour in details. Final discussion on obtained results is proposed focussing the attention on basalt fibre composite behaviour, and comparing mechanical properties of BFRP with other composite materials in glass and carbon fibres. [Copyright &y& Elsevier]

Abstract: In this study, nano glass fibre-reinforced polymer (nano-GFRP) composite reinforcing bars (rebar) for concrete structures were fabricated, and their performance during prolonged exposure to water and alkaline solutions was evaluated. Nano-GFRP rebar was prepared using the pultrusion method by adding nanomaterials to vinyl ester resin. The nanomaterials, including silica (SiO2), alumina (Al2O3), and silicon nitride (Si3N4), were added to vinyl ester resin at 1, 3, and 5wt.%. After exposure to water and alkaline solutions for 50 and 115days, tensile strength tests were carried out, and the moisture diffusion coefficient was determined and compared with that of general GFRP rebar. The results indicated that the tensile residual strengths of nano-GFRP rebar and general GFRP rebar were almost the same after exposure to water, whereas the tensile residual strength of nano-GFRP rebar was higher than that of general GFRP rebar after exposure to alkaline solution. The moisture diffusion coefficient of the alumina and silicon nitride samples increased slightly after exposure to alkaline solution, but the silica sample had a higher moisture diffusion coefficient; however, the moisture diffusion coefficients of all nano-GFRP rebar samples were comparable to that of general GFRP rebar. [Copyright &y& Elsevier]

Abstract: The design of concrete structures reinforced with glass fibre reinforced polymer (GFRP) bars is influenced by their reduced stiffness and brittleness. In hyperstatic structures, the methodology used in force analysis depends on the ductility of the structural systems, which in this case, being essentially provided by the concrete, can be potentially increased by confining concrete in critical zones. This paper presents experimental and numerical investigations about the flexural behaviour of continuous beams reinforced with GFRP bars, namely of their service and failure responses, and the effect of increasing concrete confinement in critical cross-sections. A calculation procedure to quantify the confinement effect in beams due to the reduction of the spacing between shear stirrups is first presented. The experimental investigations comprised a comparative study in which two-span concrete beams reinforced with either GFRP or steel bars were tested in bending. In the former, the effect of reducing the shear stirrups spacing was analyzed together with the under- and over-reinforcement at the central support and midspan cross-sections, respectively. The development of a crack hinge in the continuity support zone highlighted the better performance of beams under-reinforced on the top layer with GFRP bars compared to “equivalent” beams reinforced with steel, namely at the resistance level. In addition, the confinement at critical zones increased significantly the strength and ductility. The numerical investigations included the development of non-linear finite element models for all beams tested – numerical results are in good agreement with test data and seem to confirm the confinement effect observed in the experiments. [Copyright &y& Elsevier]

Abstract: This paper presents three dimensional (3D) finite element (FE) models of the low-impulse localised blast loading response of fibre-metal laminates (FMLs) based on an 2024-O aluminium alloy and a woven glass-fibre/polypropylene composite (GFPP). A vectorized user material subroutine (VUMAT) is developed to define the mechanical constitutive behaviour and Hashin’s 3D failure criteria incorporating strain-rate effects in the GFPP. In order to apply localised blast loading, a user subroutine VDLOAD is used to model the pressure distribution over the exposed area of the plate. These subroutines are implemented into the commercial finite element code ABAQUS/Explicit to model the deformation and failure mechanisms in FMLs. The FE models consider FMLs based on various stacking configurations. Both the transient and permanent displacements of the laminates are investigated. Good correlation is obtained between the measured experimental and numerical displacements, the panel deformations and failure modes. By using the validated models, parametric studies can be carried out to optimise the blast resistance of FMLs based on a range of stacking sequences and layer thicknesses. [Copyright &y& Elsevier]

Abstract: An experimental study was carried out to investigate the seismic performance of post-heated circular reinforced concrete columns wrapped with glass or carbon fibre reinforced polymer jackets. Eight shear critical reinforced circular columns with a shear span-to-depth ratio of 2.5 were tested under a combined constant axial and cyclic lateral displacement history, simulating earthquake loading. The columns were tested in three groups, unheated, post-heated and post-heated repaired with either glass fibre reinforced polymer (GFRP) or carbon fibre reinforced polymer (CFRP). In terms of seismic performance the test results indicated that using GFRP or CFRP jackets significantly increased the shear capacity, ductility and energy dissipation of the post-heated damaged columns. However, the GFRP or CFRP did not increase the stiffness of the post-heated damaged columns. It was found that the unheated and post-heated damaged columns failed in a brittle shear mode while the mode of failure of posted-heated columns repaired with GFRP or CFRP was successfully shifted from a shear to a ductile flexural failure. [Copyright &y& Elsevier]

Abstract: Electromagnetic wave reflections from glass fiber reinforced epoxy matrix composites with 0°/90° and ±45° fiber oriented plain-woven glass fabric (PW-GFRP-0/90, PW-GFRP-±45) at incident angles of 30°, 40° and 50° were measured in the frequency range 50–75GHz using a free-space reflection measurement system. The complex dielectric constants of both composites were calculated using a simple transmission line theory. The complex dielectric constants of PW-GFRP-0/90 and PW-GFRP-±45 are similar and were measured to be ε′=4.61±0.01 and ε″=0.16±0.002, respectively. The damage stored in PW-GFRP-0/90 and PW-GFRP-±45 was also evaluated by dielectric constant changes using the same system at an incident angle of 30°. For both composites, ε′ decreased with increasing applied stress and damage parameter. The dielectric constant change is effective for detecting the damage stored in composites and can be used to quantitatively evaluate the damage. [Copyright &y& Elsevier]

Abstract: Since the stainless steel primary barriers of Cryogenic Containment System (CCS) for Liquefied Natural Gas (LNG) ship failed by impact loads due to LNG cavitation during operation, the stiffness and strength of the primary barrier was increased much to endure the impact pressure of LNG, which increased the transfer of impact load to foam insulation panels under the primary barrier. The increase of impact load to the foam insulation panels will induce crack propagation into the insulation foam panels due to the low toughness of insulation foams at cryogenic temperatures. In this work, an impact isolation system was developed using glass fiber composite mats to lower the impact load transmission into the foam insulation panels. An optimal design process for the vibration isolation system was conducted by a numerical method. For reliability of the impact isolation system, cryogenic fatigue tests of the glass fiber composite mats were performed. Also, an impact test equipment with low impact duration was developed to simulate the efficiency of the impact isolation system. [Copyright &y& Elsevier]

Abstract: In this paper effective medium theory based on Clausius–Mossoti relation was used to predict dielectric properties of multiphase composite system. The composite consisted of E-glass fibers (plain weave S-glass, J.B. Martin) embedded in bisphenol A diglycidylether epoxy matrix (D.E.R. 324, D.O.W. chemicals) with hollow ceramic spherical inclusions (SF 14, P.Q. Corp.) at different volume fractions. In many engineering applications, materials with designed dielectric properties are often sought. An important question in engineering design of a composite material is how the overall properties of the composite depend on those of the individual constituents. Mixing the epoxy resin with hollow ceramic inclusions can effectively reduce dielectric constant of the resin, which is often desirable, rendering composites as good candidates for many applications, especially in telecommunications. Compensation for degradation of mechanical properties of matrix (due to inclusion insertion) is obtained by embedding fibers into the mixture. Measurements of dielectric constant and loss tangent for this multiphase composite system were conducted in the region between 0.1 and 100kHz range using DEA 290 (T.A. Instruments) dielectric analyzer and experimental results are presented. Good correlation between analytical model and experimental results was observed throughout all frequency range of investigation. [Copyright &y& Elsevier]

Abstract: T-bolt joints are widely used in the wind turbine industry. This paper describes the constitution and function of the different components of the joint, showing the different parameters that affect its performance, and presents a parametric analysis, useful for joint design and optimization, relating laminate thickness, bolt and cylinder diameters to pitch distance, and pretension of the bolt with external load. In order to provide information on the influence of the T-bolt geometry on the strength of the laminate in the net tension and bearing zones, tests for two different glass fiber – epoxy laminates, under different pitch/diameter ratios have been performed, forcing either bearing or tension failure modes. Stress and strain concentrations in the laminate have been estimated trough a three-dimensional finite element model that takes into account pretension effects and contact nonlinearities. How experimental results correlate with simple and finite element model analysis is discussed. Stress Point Criteria may be applied for joint tension failure with a characteristic distance of d 0 =0.9mm. [Copyright &y& Elsevier]

Abstract: Due to their different mechanical properties, cracking and deformability behaviour of FRP reinforced concrete (FRP RC) members is quite different from traditional steel reinforced concrete (SRC) having great incidence on their serviceability design. This paper presents and discusses the results of an experimental programme concerning concrete tension members reinforced with glass fibre reinforced polymer (GFRP) bars. The main aim of the study is to evaluate the response of GFRP reinforced concrete (GFRP RC) tension members in terms of cracking and deformations. The results show the dependence of load-deformation response and crack spacing on the reinforcement ratio. The experimental results are compared to prediction models from codes and guidelines (ACI and Eurocode 2) and the suitability of the different approaches for predicting the behaviour of tensile members is analysed and discussed. [Copyright &y& Elsevier]

Abstract: This paper studies the high-velocity impact response of sandwich plates, with E-glass fibre/polyester face-sheets and foam core, using finite-element models developed in ABAQUS/explicit code. The failure of the face-sheets was predicted by implementing Hou failure criteria and a procedure to degrade material properties in a user subroutine (VUMAT). The foam core was modelled as a crushable foam material. The numerical models were validated with experimental data obtained from scientific literature. The contribution of the foam core on the impact behaviour was evaluated by the analysis of the residual velocity, ballistic limit, and damaged area. [Copyright &y& Elsevier]

Abstract: This paper presents an analytical study about the viscoelastic time-dependent (creep) behavior of pultruded GFRP elements made of polyester and E-glass fibers. Experimental results reported in Part 1 are firstly used for material characterization by means of empirical and phenomenological formulations – a good general agreement is obtained using the following analytical models: (i) Findley’s power law, (ii) Bruger–Kelvin model and (iii) Prony–Dirichlet series. Based on accelerated characterization methodology –Time-Stress Superposition Principle (TSSP) coupled with Findley’s law, for a reference stress of 20% of the material ultimate stress, an elastic deformation increase of 30% is obtained after 50,000h. The creep parameters and deformation estimated by using the Findley’s model derivations indicate a consistent prediction of time-dependent deformation and viscoelastic properties of the two types of elements analysed – laminates and beam. A straightforward formulation to predict the time-dependent elastic modulus is applied, showing that the flexural stiffness should be reduced by 25% of its initial value after 1-year and as much as 50% after 50-years. Similarly, the power law coupled to Euler’s classical beam theory suggests a reasonable adaptability to the creep phenomenon in the linear regime and proved to provide accurate predictions for deflections under flexural loading up to 40% of the ultimate strength. After 50years, under normal service load level (1/3 of the failure load), the total creep deflection will attain almost twice the initial deflection. If taking into account the shear deformation (Timoshenko’s postulated) of the full-size element with “effective” stiffness properties such estimate is reduced nearly 25%. [Copyright &y& Elsevier]

Abstract: Glass fiber-reinforced polymer (GFRP) bridge decks possess inherently high strength-to-weight ratios, but relatively low effective elastic moduli. As a result, serviceability issues govern GFRP bridge deck design. Therefore, the objective of this study was to increase the stiffness of a commercial GFRP honeycomb sandwich panel through the inclusion of steel within the cross section. GFRP-steel hybrid parametric studies were conducted to evaluate improvements on the GFRP honeycomb deck panel stiffness. Possible configurations included the embedment of steel plates within the face sheets and the placement of steel tubes within the core. Core stiffness analyses were also performed, leading to the development of the steel hexagonal honeycomb core concept. An experimental study, including large-scale beam tests, was conducted. The large-scale tests were performed to assess the equivalent flexural and shear stiffness, comparing the hybrid steel core concept and the current GFRP core design. From the large-scale beam test results, an overall stiffness increase was observed. [Copyright &y& Elsevier]

Abstract: Critical strain energy release rate of glass/epoxy laminates using the virtual crack closure technique for mode I, mode II, mixed-mode I+II and mode III were determined. Mode I, mode II, mode III and mixed-mode I+II fracture toughness were obtained using the double cantilever beam test, the end notch flexure test, the edge crack torsion test and the mixed-mode bending test respectively. Results were analysed through the most widely used criteria to predict delamination propagation under mixed-mode loading: the Power Law and the Benzeggagh and Kenane criteria. Mixed-mode fracture toughness results seem to represent the data with reasonable accuracy. [Copyright &y& Elsevier]

Abstract: The tensile behavior of adhesively-bonded double-lap joints composed of pultruded glass fiber-reinforced adherends and an epoxy adhesive was investigated under temperatures ranging between −35°C and 60°C. The load–elongation response was influenced primarily by the thermomechanical behavior of the adhesive and much less so by that of the adherends. For temperatures above the adhesive glass transition temperature, strength and stiffness decreased with the former being less affected than the latter. The failure mechanism changed with increasing temperature from fiber-tear to adhesive failure. The crack initiation loads were unaffected as long as the temperature remained below the adhesive glass transition temperature. However, the crack propagation rate was higher at low temperatures. Critical strain energy release rates for crack initiation and propagation consistently rose as temperature increased. Modeling results obtained using existing empirical models and FEA compared well to the experimental data in the examined temperature range. [Copyright &y& Elsevier]

Abstract: Researchers have developed several measures to improve shear resistance capacity of sandwich structures composed of thin composite face sheets of Eglass/epoxy and low density PVC foam core, but these methodologies are either costly or result in damage to the sandwich composites before being placed for production. A novel, innovative cost-effective methodology of introducing fiberglass shear keys attached to face skins to improve the stiffness and strength of the sandwich composite panel is being proposed in this manuscript. Manufacturing of the sandwich composite panels along with experimental and numerical investigations have been performed in this manuscript to demonstrate the potential of the proposed simple methodology which can be utilized for shear-sensitive design and analysis of sandwich composite structures and/or components. A parametric study has also been carried out to determine the effect of change in shape, size, spacing and material of the shear keys on the sandwich composite panel global response. [Copyright &y& Elsevier]

Abstract: The flexural behaviour of a new generation composite sandwich beams made up of glass fibre-reinforced polymer skins and modified phenolic core material was investigated. The composite sandwich beams were subjected to 4-point static bending test to determine their strength and failure mechanisms in the flatwise and the edgewise positions. The results of the experimental investigation showed that the composite sandwich beams tested in the edgewise position failed at a higher load with less deflection compared to specimens tested in the flatwise position. Under flexural loading, the composite sandwich beams in the edgewise position failed due to progressive failure of the skin while failure in the flatwise position is in a brittle manner due to either shear failure of the core or compressive failure of the skin followed by debonding between the skin and the core. The results of the analytical predictions and numerical simulations are in good agreement with the experimental results. [Copyright &y& Elsevier]

Abstract: This paper investigates the influence of exfoliated nano-structures on sandwich composites under impact loadings. A set of sandwich composites plates made of fiberglass/nano-modified epoxy face sheets and polystyrene foams was prepared. The core was 25mm thick and the face sheets were made of eight layers of woven fabric glass fibers and nano-modified epoxy (≈0.8mm of thickness). The epoxy system was bisphenol A resin and an amine hardener. The fiber volume fraction used was around 65%, while the nanoclay content varied from 0wt.% to 10wt.%. The nanoclay used was Cloisite 30B from Southern Clay. The sandwich panels were submitted to low-velocity impact tests with energies from 5J to 75J. Two sets of experiments were performed, i.e. high velocity+low mass and low velocity+high mass. Damage caused by the two groups of experiments and peak forces measured were dissimilar. The results show that the addition of 5wt.% of nanoclay lead to a more efficient energy absorption. The failure modes were also analyzed, and they seems to be affected by the nanoclay addition to face sheets. [Copyright &y& Elsevier]

Abstract: The low velocity impact behavior of three layer thermoplastic laminates consisting of woven glass fiber and polypropylene has been investigated for two different fiber volume configurations. Panels with configurations of 50/50 and 20/80 in the warp and fill directions were subjected to low velocity impact energies between 4 and 16J using an instrumented dropping weight impact tower. Load vs. displacement plots showed the excellent energy absorbing capabilities exhibited by the woven composites. Both configurations dissipated approximately 75% of the 16J incident impact energy. An energy-balance model was used to successfully predict the impact response of the woven thermoplastic composites. The impact damaged plates were tested under four point bend (4PB) loading conditions. Results showed a reduction in flexural strength and modulus as the impact energy increased. A simple compression molding damage repair process was applied to the 16J impacted composite plates. 4PB testing of the repaired samples revealed a significant recovery in the flexural strength and modulus of the thermoplastic woven composite with both fiber configurations. [Copyright &y& Elsevier]

Abstract: A multifunctional – hybrid – composite material that incorporates carbon and glass fibres embedded into an epoxy matrix was developed. This material can be made to undergo a shape change without inserting activators. This is accomplished by selective heating of the embedded carbon fibres through the application of an electric current (Joule effect). The resulting shape change was determined and the stresses generated during heating were measured via a 3-point bending device. The possibility of using the reinforcing fibres of a multi-directional composite as activators for inducing specific deformation modes is discussed. [Copyright &y& Elsevier]

Abstract: In this study, the impact behavior of laminated glass–epoxy composites at several temperatures (20°C, −20°C and −60°C) was studied experimentally. Impact tests were performed by using Fractovis Plus impact test machine with a constant impactor mass of 5.02kg. Composite specimens with stacking sequence [0/90/45/−45] S were impacted at varied impact energies ranging from 5J to 70J. Variation of the impact characteristics such as maximum contact load, maximum deflection, maximum contact time and absorbed energy versus impact energy are depicted in figures. Results indicated that the ambient temperature highly affects the impact response of composite materials. [Copyright &y& Elsevier]

Abstract: The present work aims to obtain failure modes and failure loads for multi-pin joints in uni-directional glass fibre/epoxy composite laminates by finite element analysis and validating the results with the experimental work. In multi-pin joints, the effect of variation in pitch-to-diameter ratio (P/D) is also important, in addition to side width-to-diameter (S/D) and edge-to-diameter (E/D) ratios. A two-dimensional finite element model is developed using ANSYS software. Tsai–Wu failure criteria associated with material property degradation is used in the analysis to predict failure load and to differentiate failure modes. The results from experimental and finite element analysis showed that it is very important to consider the affect of E/D, S/D and P/D ratios in designing multi-pin joints. [Copyright &y& Elsevier]

Abstract: This paper presents the design, analysis, and fabrication of a reusable pultruded GFRP (glass fiber-reinforced-polymer) deck panel that can be used to furnish the roadway surface of temporary structures. A five-cell GFRP deck panel is proposed here to overcome the steel corrosion and fatigue problems of conventional steel deck panels. A finite element analysis was carried out to design the cross-section and to evaluate the structural performance of the proposed GFRP deck panel within the design limits. The GFRP deck panels were successfully fabricated in accordance with the proposed cross-sectional profile and GFRP stacking patterns and have been installed in a construction site. The findings and recommendations for future study are also summarised. [Copyright &y& Elsevier]

Abstract: This paper presents results of the feasibility of carbon/epoxy composites (CFRP) as a future helicopter flexbeam material. Torsional behaviors of unidirectional CFRP and glass/epoxy composites (GFRP) with the same resin matrix were investigated. The initial torsional rigidity of CFRP was almost identical to that of GFRP. The torsional rigidities calculated using finite element analyses (FEA) agreed with the experimental results: the torsional rigidities are governed mainly by the material’s shear stiffness. Torsion fatigue tests were also conducted by controlling the angle of twist of the sinusoidal wave under a constant tensile axial load. No catastrophic failure occurred with either GFRP or CFRP, although decreased amplitudes of torque and torsional rigidities were observed according to the number of cycles. Results of X-ray CT inspections and numerical calculation by FEA revealed that degradation of a torsional rigidity is caused mainly by splitting crack propagation along the fiber direction. The torsion fatigue life of CFRP was superior to that of GFRP. Consequently, results confirmed that CFRP exhibits excellent properties as a torsional element of a helicopter flexbeam in terms of torsional rigidity and tension–torsion fatigue behaviors. [Copyright &y& Elsevier]

Abstract: The aim of this paper is the fabrication and mechanical testing of entangled sandwich beam specimens and the comparison of their results with standard sandwich specimens with honeycomb and foam as core materials. The entangled sandwich specimens have glass fiber cores and glass woven fabric as skin materials. The tested glass fiber entangled sandwich beams possess low compressive and shear modulus as compared to honeycomb and foam sandwich beams of the same specifications. Although the entangled sandwich beams are heavier than the honeycomb and foam sandwich beams, the vibration tests show that the entangled sandwich beams possess higher damping ratios and low vibratory levels as compared to honeycomb and foam sandwich beams, making them suitable for vibro-acoustic applications where structural strength is of secondary importance, e.g., internal paneling of a helicopter. [Copyright &y& Elsevier]

Abstract: In this study the effect of different woven linear densities on the bearing strength behaviour of glass fiber reinforced epoxy composites pinned joints is investigated experimentally. Woven fabrics with different linear densities of 200, 270, and 300g/m2 are used as reinforcements in epoxy resin. Single-hole pin-loaded specimens of each material were tested in tension. In order to evaluate the effect of joint geometry, the ratio of the edge distance to the pin diameter (E/D), and the ratio of the specimen width to the pin diameter (W/D) were systematically varied during experiments. Failure propagation and failure type were observed on the specimens. The results show that the bearing strength of glass fiber reinforced epoxy composites pinned joints is associated with the linear densities of woven fabric, fiber volume fraction, void content, and geometric parameters. [Copyright &y& Elsevier]

Abstract: There are various ways to connect a GFRP deck and girder which have been adopted as systems worldwide such as connection systems that use shear connectors and mechanical connection systems that use bolts or clamps, and recently there has been a study on a system to connect GFRP deck and steel girder using a bonding agent. In this study, an attempt was made to review and analyze the composite level of GFRP decking and a girder bolt connection system using the already proposed GFRP deck shape. In addition, an attempt was made to estimate the decreased rate of the composite level at various bolt connection intervals using the calculated strain and deflection, and also the analytical values of the composite level were compared with prior test results. [Copyright &y& Elsevier]

Abstract: The mechanical performance of the composites which are reinforced with glass knitted fabrics composed of tuck stitches have been investigated. Tensile, compression, impact and compression-after-impact (CAI) tests were performed and the results of the composites reinforced with full cardigan derivative knitted fabrics and 1×1 rib knitted fabrics of glass fibers have been compared. As for a composite material, performance depends not only on the strength of the constituent materials but also on the internal structural geometry of the constituents, it is interesting to study the effects of the tuck stitch which is one of three different types of loops that can be used to build the knitted fabrics and has a different geometry than the other loop types. [Copyright &y& Elsevier]

Abstract: In this study, edge-cracked aluminum plates repaired with one-sided composite patches were investigated experimentally for their response to Charpy impact test. Two different materials were used for composite patches, in one the reinforcement was woven glass–fibres while the other had woven carbon fibres as the reinforcement. Further, in each case, two lay-ups were used, viz. 3-ply and 5-ply. Also, the aluminum specimens had edge-cracks of three different lengths. In each case, the energy absorbed during the impact test, when the specimen had a crack of known length and reinforced with patches, was determined and compared with the energy absorbed during impact of the corresponding specimen without crack. It was observed that for a given crack length, the 5-ply patch of carbon fibres performed better than all other patches. For example, when the ratio of the crack length to the specimen width, i.e. l/w is 0.5, the percentage of the absorbed energy for the specimen repaired with 5-ply carbon fibre patch is 2-times as compared to the specimen repaired with 5-ply glass–fibre reinforced patch. [Copyright &y& Elsevier]

Abstract: This paper focus on the design of a GFRP truss-like structure for dismountable bridges with maximum span of 30m. The bridge structure is composed of a deck supported by prestressed trussed beams which are mounted by assembling GFRP tubular profiles and steel joints with bearing type connections. Experimental tests were carried out on short profiles to determine their compressive strength at the connections and on two 1:2.3 reduced models of the trussed beam structure: a short 1.3m span cantilever beam and a 13.0m span simple supported beam. The main results obtained from the performed experimental tests on short profiles and on the cantilever beam are presented herein. It is shown that a non-linear behaviour can be generated on the trussed cantilever beam by decompression of tubular members and that collapses are induced by buckling of diagonal members. [Copyright &y& Elsevier]

Abstract: Interlaminar fracture toughness of composite materials plays an important role in the specific energy absorption (SEA) characteristics of crushing composite materials. In this regard the effect of fibre orientation and stacking sequence on the composite crash box design is sought by studying their effects on the interlaminar fracture toughness. In order to achieve this, glass fibre/epoxy orientations of [±60]10, [02/±45]5, [0/90]10 and [0/90]5S were studied experimentally. Tensile, shear, double cantilever beam (DCB) and axial crush box specimens from different lay-ups were made and tested under quasi-static conditions to determine the mechanical properties, interlaminar fracture toughness (G IC) and SEA. It was shown that the interlaminar fracture toughness of glass fibre/epoxy affects the frond bending resistance due to the main central interwall crack in a progressive crushing failure and consequently SEA. A higher interlaminar fracture toughness between laminates will enhance the SEA in the axial crushing of the composite box. [Copyright &y& Elsevier]

Computational micromechanics analysis of short fiber reinforced polymer (SFRP) composites is of great significance to provide an understanding of the relationship between microstructures and complex mechanical behaviors of the materials. In this study, an innovative computational framework is proposed for the analysis of SFRP composites considering multiple constituents and different failure modes. Firstly, a unit cell model composed of fiber, matrix and interface is built up to analyze the nonuniform stress distribution around a fiber. Secondly, a reconstruction algorithm is proposed to provide geometrical information of fiber distributions with arbitrary orientation state and a wide range of fiber length and fiber volume fraction. With the help of embedded element method (EEM) and MATLAB script, RVE models embedded with numerous unit cells are established. The predicted properties of the RVE models of short glass fiber reinforced polypropylene (SGFRPP) are verified by an orientation average method and a modified rule of mixture, respectively. The progressive damage procedure of the material is predicted and the damage initiation and evolution are for the first time quantitatively characterized by the extent variables of different failure modes. An in situ microtomography tensile test are performed to prove the feasibility and accuracy of the proposed framework. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced composites have been used as a secondary barrier structure in LNG cargo containment systems (CCS) for their excellent strength and corrosion resistance. However, during LNG transport, the tanks experience periodic thermal and bending stress because of the cryogenic environment. These conditions degrade the mechanical properties of the composites in the CCS. In this study, finite element analysis was conducted using the mechanical properties of each composite. A quasi-static tensile test was carried out, and the coefficients of thermal expansion were used to obtain the mechanical properties. To verify the reliability of the numerical analysis, modeled structural unit specimens were manufactured, and 3-axis strain gauges were attached to measure thermal strain under cryogenic conditions. Validation of the strain between experiments and computation was performed, and the finite element analysis was conducted based on the observed mechanical properties and their reliability. [ABSTRACT FROM AUTHOR]

Glass-fiber-reinforced aluminum layers (GLARE) are one of the excellent impact resistant materials, benefited from both the metal and glass fibers properties. Owing to their high impact damping properties, the shape memory alloys have been also considered as useful materials for arming the conventional impact-exposed materials. In the present paper, the shape memory wires were integrated with GLARE laminate and its response to the Charpy low-velocity impact was experimentally studied. The current study is aimed to determine the effects of three parameters (pre-strain percentage of shape memory alloy (SMA), glass fibers angle and the location of SMA wires within the novel fiber metal laminate) for the first time. Hybrid GLARE specimens of this study were planned by Taguchi design of experiments (DOE) method and contained Nitinol shape memory alloy wires. The results showed that the pre-strain and the angle of glass fibers are the most effective parameters on the impact energy absorption at accepted levels of confidence. Regarding the innovations in the construction of this type of impact-resistant hybrid composites, this study could be used in design of aerospace bodies. [ABSTRACT FROM AUTHOR]

Fiber-reinforced composites (FRCs) are valued for their high specific properties. However, FRCs are vulnerable to difficult-to-predict damage growth and complex failure modes thereby motivating the need for robust structural health monitoring (SHM). Self-sensing via nanofiller-induced piezoresistivity has much potential for this. Research in piezoresistivity to date has overwhelmingly focused on the direct current (DC) response. This is important because alternating current (AC) has important benefits such as improved data density, potential for greater sensitivity, and reduced power requirements. In light of the potential of AC-based methods, this work explores AC transport responsiveness to high-cycle fatigue loading in carbon nanofiber (CNF)-modified glass fiber/epoxy laminates via equivalent circuit analyses. These results show that equivalent circuit behavior is significantly affected by fatigue-induced damage accumulation suggesting a mechanism for monitoring fatigue. However, clear circuit parameter evolution-load cycle trends were not observed suggesting further work is needed to fully realize the potential of AC-based monitoring. [ABSTRACT FROM AUTHOR]

The fiber-reinforced composite (FRP) shaft need to consider vibration performance of the transmission system to improve work efficiency, comfort, service life and safety. The fiber materials and tubes containing metal connectors are important parts of the FRP shaft so that the study on the vibration performance of these two key components is of great significance for an in-depth understanding of the vibration performance of shafts. The finite element analysis (FEA), pulse vibration excitation technique (PVET) and formula computing were used to study the effect of the vibration characteristics of shafts. This study revealed that increasing the modulus of the fiber is one of the effective methods to increase the natural frequency of the FRP tube and the damping ratio of the carbon FRP tubes were slightly smaller compared with basalt and glass fiber. The FEA of FRP tube results were not distinct from the measured and calculated results so that these FEA results were relatively reliable. The damping of the tube with metal flanges at both ends were weaken compared the FRP tube. This work will be of great significance to the optimization design of the vibration performance of FRP shafts. [ABSTRACT FROM AUTHOR]