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The purpose of this study is to examine the level of applicability of the four specifications of the serviceability in cracking for concrete beams reinforced with ribbed glass fiber-reinforced polymer (GFRP) bar. The four-point bending test was conducted with measuring the crack width at the bottom of the beams. For investigating the level of applicability of the four specifications of the serviceability in cracking, applied moment-maximum bar spacing was obtained by ACI 440 1R-15 for varying the bond coefficient, crack width, concrete cover depth, and the equivalent reinforcement ratio. Then, it compared with the relationships with the serviceability region specified by the four specifications. It was found that the evaluation of serviceability in cracking by the four specifications have provided quite different results according to the bond coefficient, allowable crack width as well as the equivalent reinforcement ratio. As a result, the four serviceability specifications should be seriously discussed for the cracking control of FRP reinforced concrete beams in case of considering some of influencing factor, especially for the equivalent reinforcement ratio. [ABSTRACT FROM AUTHOR]

In order to extend the use of pultruded glass fiber reinforced polymer (GFRP) composite materials in civil engineering, a systematic study on pultruded GFRP laminate is important and realistic for the design and construction of GFRP structures in bridge engineering. A practical method to evaluate the fiber volume fractions and the equivalent thickness of each lamina is proposed considering that a typical pultruded FRP profile is not truly laminated structure in rigorous sense. The elastic modulus and ultimate strength of each lamina were predicted based on micromechanics. In terms of the facts that lack of knowledge of the majority of bridge engineers on the behavior of composites, an innovative carpet plots with different fiber volume fraction are adopted to finish the laminate design procedure without much complicated calculation. In addition, a continuum damage model considering lamina shear nonlinearity, lamina damage along thickness direction, innovative damage evaluation methods, loading/unloading strategy and viscous methods to alleviate the convergence difficulties is proposed and implemented via user material subroutine. Three different types of pultruded GFRP laminate were fabricated, and material properties have been tested to validate the numerical and theoretical models. The Finite element simulation results agreed well with tests and could provide reference for the design and construction of GFRP structures. [ABSTRACT FROM AUTHOR]

Corrosion of steel rebars is known to cause deterioration of concrete structures that can lead to catastrophic failures. To mitigate this problem, steel rebars can be replaced with Glass Fiber-Reinforced Polymer (GFRP) rebars. However, the lack of ductility of GFRP-reinforced elements has prevented their use in many structural applications, especially in seismic areas. Stainless Steel (SS) rebars are corrosion resistant and have adequate energy absorption and ductility. However, they are much more expensive than steel rebars. This paper proposes the combined use of SS and GFRP rebars to achieve ductile and corrosion-free elements. The first challenge for such a proposal relates to designing SS-GFRP reinforced concrete frame with adequate lateral performance in terms of initial stiffness, ductility, and strength. Design equations, which are based on a comprehensive parametric study, are developed to allow designing such a frame. A six-storey concrete frame is then designed using the proposed equations and its lateral performance is examined using pushover analysis. [ABSTRACT FROM AUTHOR]

Multi-objective robust optimization of multi-directional carbon/glass fibre-reinforced epoxy hybrid composites has been presented in this study. Two conflicting objectives, namely minimizing the density and minimizing the cost under the constraint of a specified minimum flexural strength, were considered with the design variables being the fibre type, fibre orientation angle and fibre volume fraction of each lamina. A modified version of the non-dominated sorting genetic algorithm (NSGA-II) was used in order to find the Pareto optimal solutions. Furthermore, robust optimization problems were defined by including manufacturing related uncertainties in the thickness and orientation of each lamina. These uncertain variables were considered as uncertain-but-bounded with the worst case for the minimum flexural strength being determined through an internal anti-optimization solver. The optimization and anti-optimization problems were solved with Pareto optimal and robust solutions being presented for carbon/glass fibre hybrid composites with different levels of minimum flexural strength. The results showed that, in general, consideration of uncertainties in thickness and fibre orientation angle increased the material cost and/or density with this effect being more important for high strength composites. [ABSTRACT FROM AUTHOR]

The possibility of replacing the traditional steel reinforcement with glass fiber reinforced polymer (GFRP) cages in precast concrete tunnel segmental lining has been shown by the authors in previous papers. The use of GFRP rebars as structural reinforcement in precast tunnel segments, allows several advantages in terms of structural durability or in cases of temporary lining that will have to be demolished later. Furthermore, this reinforcement type can be a suitable solution to create dielectric joints, ensuring the interruption of possible stray currents, which often lead to corrosion problems. Nevertheless, this peculiar application requires curvilinear shape of the reinforcement, and then different production process and rebar geometries. In the present work, a suggestion for the optimization of the GFRP reinforcement for tunnel segment is given. Four different GFRP cage typologies are analysed and applied as a reinforcement in full-scale tunnel segments. Both bending and point load tests are developed and the structural performances of the specimens are compared and discussed. Finally, the best solution, in terms of cost-benefit analysis is proposed. [ABSTRACT FROM AUTHOR]

The in-plane compression and shear performance plays a significant role in achieving an optimum and reliable design of pultruded glass fiber-reinforced polymer (GFRP) bridge deck supported on steel girders that have been used in bridge decks retrofit application or new construction in the past decade. This paper presents a summary of several laboratory experiments that were performed on a pultruded GFRP bridge deck for pedestrian or light vehicular loading in order to evaluate both the deck’s in-plane compression and shear properties. The experimental results showed that the average web thickness has a relatively larger influence on the in-plane shear behavior than the in-plane compressive behavior. Three-dimensional finite element models utilizing the Hashin’s theory laminate failure, adhesive layers failure via cohesive element and initial geometry imperfections by using limited critical eigenmodes multiplied by empirical coefficient were employed to numerically simulate both the deck’s in-plane compression and shear ultimate capacity and stiffness based on elastic engineering constants obtained from micromechanics. The numerical results agreed well with experimental results that could provide a reference for the design and construction of such type of pultruded composite bridge decks. [ABSTRACT FROM AUTHOR]

Damage recovery after low-velocity impact has been assessed in woven E-glass fibre-reinforced polymer composites with an epoxy matrix and a blend of epoxy and 25 vol% of poly(ε-caprolactone) (PCL). Impact was carried out at three energy levels (8.5, 17, 34 J) and composites with epoxy-PCL blends demonstrated similar energy absorption capacity as compared to pure epoxy composites even though the extent of damage (quantified by C-scans and optical microscopy) was higher. Ultimate compressive residual strength of the modified composites was, for the different impact energy levels, 23–33% lower as compared to unmodified composites. Healing efficiency after a thermal mending cycle at 150 °C for 30 min has been quantified using three complementary characterization methods; impact damage could be recovered from 20% to 100% depending on the impact energy level. These modified matrix composites are thus able to fully recover low-velocity impact damage at energy levels often met in real structures. [ABSTRACT FROM AUTHOR]

Layered gypsum-based composites for S-band electromagnetic (EM) wave absorption were designed and fabricated by introducing carbon black (CB) coated glass fiber grids, and the EM wave absorption properties were measured by arching testing method. The results indicate that the EM wave absorption can be greatly improved by the glass fiber grids, and the absorption properties can be influenced by periodic size, sample thickness and CB content. The composites with double layer glass fiber grids exhibit wider bandwidth and lower reflection loss due to the formation of gradient impedance. Moreover, the design of double layer matrix can make the absorption peaks shift to lower frequency, which can be attributed to the multiple scattering and reflections of incident wave caused by expanded perlites. The reflection loss of the prepared composites can be less than −10 dB in 2.2–3.63 GHz. This gypsum-based composites can be a candidate to prevent S-band indoor EM radiation. [ABSTRACT FROM AUTHOR]

Characterization of the complicated failure behavior in fiber metal laminate (FML) depends on well understanding of the contributions from metal and composite layers. It seems to be very cumbersome to deal with this by conventionally collecting the stress, strain and damage patterns through experiments or numerical simulations, especially when complicated load (e.g., off-axis load) or a more hybrid degree is adopted. Since all mechanical responses in nature are governed by energy principles, in the present study an energy dissipation approach was introduced in FML. Analyses were carried out with employing the available history outputs in Abaqus, where four kinds of energy variables in terms of internal or total strain energy ( E int ), elastic or recoverable strain energy ( E elast ), energy dissipated by plastic deformation ( E plast ) and damage ( E dam ) were requested for both the constituents and the laminates. Two issues were clarified by this energy approach: off-axis dependence of mechanical response and damage behavior in notched glass fiber reinforced aluminum laminate (Glare), and the reinforced effect of titanium on notched Glare (a more hybrid case). Results have shown the potentiality of energy approach in straightforwardly and effectively characterizing the failure behavior of FMLs. [ABSTRACT FROM AUTHOR]

In situ SEM tensile tests are performed to shed more light on the onset and damage evolution in the shell layer of a short glass fibre reinforced polyamide 6.6 (SGFRP) composite obtained by injection moulding. Damage mechanisms are studied in three different loading directions including 0°, 45° and 90° with respect to the mould flow direction (MFD). The development of damage is monitored until total failure at different scales of observation. Qualitative results indicate that the orientation of tensile specimens with respect to the mould direction determines to a large extent the nature of involved damage mechanisms. Interfacial damage is by far the leading damage mechanism. Quantitative investigation further indicates multi-stage damage kinetics, which demonstrates an asymmetric behaviour with respect to sample orientation. One to two main directions of damage growth are identified as responsible for the failure properties of the studied composite depending on sample orientation. [ABSTRACT FROM AUTHOR]

This paper presents a novel methodology for predicting the dielectric constant of three-dimensional woven glass fibre-reinforced composites. A well-established approach of deriving the effective dielectric constant is the dielectric mixing formulae (rule of mixtures based), which either provide a single value or offer upper and lower bounds. For composites with three-dimensional fibre architecture, an accurate model considering the three-dimensional effect is needed. Here, the anisotropic effect is revealed using electromagnetic simulation to extract the effective dielectric constant of a model material with unidirectional fibres, which are aligned or orthogonal to the electric field. The rule of mixtures based formulae are evaluated. The most suitable formula selected for each case is then extended to a general case with arbitrary fibre orientation and is further used to characterise the capacitor element of an electromagnetic model for 3D woven composites. The proposed method is compared to measurements to demonstrate the improved accuracy. [ABSTRACT FROM AUTHOR]

In this study, a thin lightweight single- and double-slab with a nickel-coated glass-fabric design manufactured via the mass production electroless plating method is proposed for an enhanced echo radar cross section (RCS) for curved surfaces. The main objective of this research is to reduce the echo RCS from the C- band to the Ku-band (in GHz) for a wing airfoil model (NACA0012) radar-absorbing structure. For conventional microwave absorption performance, a high weight percentage of nano-conductive particles within a polymer matrix is crucial. However, certain difficulties are encountered in terms of high viscosity and thickness control in the polymer matrix for its application to the curved surface of the wing airfoil model. The proposed RCS absorber models reduce these difficulties associated with conventional RCS models. When the proposed absorbers are applied to the wing structures to cover the entire surface, the simulated results of the echo RCS level capacity demonstrate a 10-dB reduction from the C-Band to Ku-band for a wide-angle oblique incidence in both the horizontal and vertical polarizations. From a practical standpoint, these results show that nickel-coated-glass-fabric/epoxy composites have a tremendous potential for application to the wing airfoil model in a stealth aircraft. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation into the durability behaviour of textile-reinforced concrete (TRC) subjected to both tensile and bending loads to compare its macroscale characterization. Composites are produced as a laminate material using 2 and 6 layers of glass fibre mat as reinforcements. The instantaneous and long-term (durability) properties of composite TRC are identified by tensile and flexural testing with specimens made from the same fresh mortar. The long-term tests are conducted in two ageing environments: natural ageing, which was conducted under the laboratory atmosphere (20 °C and 50% RH), and accelerated ageing, which consisted of immersion of the specimens in hot water at 50 °C. The durability performance of TRC is evaluated by the reduced macroscale performance and damage mechanisms. The effects of the reinforcement ratio, testing conditions, and thermal conditions on the long-term response of TRC are investigated, and the microstructure of both matrix and fibre is observed and discussed after the tests with observations via scanning electron microscopy (SEM). The addition of layers of glass fibre (reinforcement ratio) increased the strength capacity and the first macro-crack strength of TRC in both tensile and bending tests. The ultimate strength value of the TRC composites obtained from the tensile test is lower than that from the bending test over the same tested days as a result of the different redistribution mechanisms; however, the difference between tensile and flexural stress remains approximately equal with similar deviations. An increase in the tensile and flexural strength capacity over the ageing time is observed before 90 days of ageing. However, after 90 days, the test results showed a loss of ductility of the accelerated aged specimens. [ABSTRACT FROM AUTHOR]

The fire resistance of two concrete slabs reinforced completely with glass fibre reinforced polymer (GFRP) bars was experimentally investigated through a full-scale standard fire test. The Canadian standard on design of FRP reinforced buildings (CSA S806) currently requires 60 mm of clear concrete cover in a FRP reinforced concrete slab to ensure 2 h of fire resistance. The two concrete slabs, which were identical in every aspect except the types of GFRP reinforcing bars, were designed and fabricated with 60 mm concrete cover in this experiment to examine the fire resistance of the existing FRP reinforced concrete structures designed using CSA S806. The uniformly distributed loads were applied causing flexural moment of 45 kN·m, which was 55% of the ultimate moment resistance of the slabs at room temperatures, and sustained throughout the fire test. Both loaded slabs endured more than three hours of ASTM-E119 standard fire exposure. The results promised a more efficient and economic application of FRP reinforcing bars in concrete construction. The effects of concrete cover, unexposed length in providing adequate anchoring at the ends, and two different types of widely used GFRP reinforcing bar were studied in this research. [ABSTRACT FROM AUTHOR]

The tensile fatigue behavior of glass-fiber-reinforced epoxy (GF/epoxy) composites embedded with shape memory alloy (SMA) wires prepared by vacuum assisted resin infusion (VARI) processing was investigated. The experiments were performed under cyclic tensile load. The damage mechanism of SMA composites under different stress levels of cyclic loadings was revealed. The fracture surface and fatigue failure modes of the specimens were examined and analyzed according to the damage mechanism under different stress levels. The stress-number (S-N) curves, the residual strength and residual stiffness of specimens were calculated after the experiment. The results show that the fatigue life of SMA composites is more than twice higher than GF/epoxy composites. Microstructural analysis using the scanning electron microscopy (SEM) technique was conducted on fractured surfaces to fully understand the failure mechanism. The fatigue failure modes in SMA composite laminates were revealed. [ABSTRACT FROM AUTHOR]

A novel sandwich element design consisting of two facings made of carbon reinforced Textile Reinforced Concrete (TRC), a low density foamed concrete (FC) core and glass fibre reinforced polymer (GFRP) connecting devices was experimentally investigated according to quasi-static and cyclic quasi-static four-point bending. Optical measurements based on Digital Image Correlation (DIC) were taken during testing to enable a detailed analysis of the bending behaviour and level of composite action. A model, verified by the experiments, was developed based on non-linear finite element analysis (NLFEA) to gain further insight on the failure mechanisms. Under both loading conditions, the bending behaviour of the TRC-FC composite elements was characterized by favourable load bearing capacity, partial composite action, superior ductility and multiple fine cracking. The connecting devices were found to be the critical elements causing the initial failure mechanism in the form of localized pull-out within an element. [ABSTRACT FROM AUTHOR]

In this work, the static and dynamic mechanical properties of glass fiber reinforced polypropylene (GRPP) laminated self-reinforced polypropylene (SRPP) composite structure were studied, which includes the influences of the SG (SRPP/GRPP) internal and external positions (with two SG positions which are S/G/S, G/S/G) and the SG thickness ratios (with three SG ratios which are 1: 1, 1: 2, 1: 3). Results show that the tensile modulus improvement of laminates was obvious compared with SRPP. A hypothesis is constructed based on the elementary flexural beam theory. The flexural responses of S/G/S and G/S/G are highly similar to SRPP and GRPP respectively, the flexural strength and modulus of S/G/S are less than 50% of G/S/G. The flexural modulus of G/S/G- SG1: 3 is 111 % of GRPP. The impact responses of S/G/S and G/S/G are similar to GRPP and SRPP respectively, but more energy was absorbed in S/G/S. With the increase of SG ratio, less damage and deformation were shown in two structures, which their modes converge. [ABSTRACT FROM AUTHOR]

For fillers reinforced polymer composites, the material properties of the composites are affected by the dispersion and orientation of the inclusions. In particular, high aspect ratio inclusions such as glass fibers in the polymer matrix generate the mechanical or thermomechanical anisotropy of the composites that are critical to the dimensional stability, flowability, toughness, and strength of the final products. We investigate the microstructural anisotropy of multiphase polymer composites composed of talcs and glass fibers to characterize the anisotropic thermomechanical properties of the composites. The internal structure of the composites is observed by using an X-ray microtomography to characterize fiber length distributions. The fiber length distributions are fitted to the Weibull distribution statistical function to model the ultimate tensile strength of the composites. A fiber efficiency factor is coupled with the statistical function to understand the effect of the fiber length distributions on the mechanical strength of the composites. The thermomechanical anisotropy is evaluated by using linear thermal expansion coefficients. The flowability of molten polymer composites is evaluated experimentally and numerically to evaluate the role of inclusions on rheological properties and processability of the composites. [ABSTRACT FROM AUTHOR]

This work presents an assessment of the damage mechanisms occurring during tensile tests in hybrid flax-glass fibres reinforced epoxy composites. The samples were composed of twill flax and glass fibre laminate plies with different stacking sequences and subjected to water immersion at 55 °C. The Acoustic Emission (AE) technique combined with scanning electron microscopy observations was used to identify the typical damage mechanisms and to follow their evolution. This identification was made with a statistical multivariable analysis in which the number of parameters and classes was optimised. Finally, the participation of each damage mechanism to the global failure was evaluated from the hits number and AE energy. The AE results showed that, although the hits number associated with the fibre failure was the lowest, their contribution to the overall failure of composites became predominant regarding the cumulative of AE energy. Furthermore, an additional group of AE signals induced by the delamination between flax and glass fibre layers was detected for the aged hybrid laminates. [ABSTRACT FROM AUTHOR]

The present investigation deals with an experimental analysis of punching process of Glass Fiber Reinforced Plastics (GFRP) sheets. The process has the potential to dramatically reduce the cycle time; thus, it can be used for industrial applications where large numbers of holes are needed. However, the laminate damage represents the major concern for the employment of hole punching. Thus, a campaign of experimental tests was conducted on thin laminates with varying the punch-die clearance. In addition, drilled holes were performed in order to compare the quality and strength of the holes performed by drilling and punching processes. To assess the influence of the process parameters on the holes quality, mechanical characterization was performed by means of tensile test with central hole and bearing test. Moreover, morphological analysis was conducted to determine the quality of the punched hole and the extension of the delaminated region. According to the achieved results, the damage produced by punching process, especially when small clearances were used, is limited and comparable to that produced by drilling process. [ABSTRACT FROM AUTHOR]

Modular glass fibre reinforced polymer (GFRP) multicellular structures were formed using pultruded GFRP box sections incorporated between two GFRP flat panels by adhesive bonding. Three types of fire resistant panels, namely glass magnesium (GM) board, gypsum plaster (GP) board and lightweight calcium silicate (CS) board, were installed at the outer face of the lower GFRP flat panel using screws. The lower surfaces of the built-up specimens were then exposed to fire. The thermal responses of the GFRP multicellular specimens assembled with different fire resistant panels were measured and comparatively analysed, in association with the damage patterns observed. It was found that the fire resistant panels effectively mitigated the temperature progressions developed in the GFRP components, thereby improving the fire insulation performance of those structural assemblies. The GM board provided the best fire insulation performance, with the highest temperature at the outer face of the upper GFRP flat panel (the surface unexposed to fire) being less than 120 °C after 90 min of fire exposure. Further, the effects of cavities and end closure configurations of the multicellular assemblies on the heat transfer were evaluated and highlighted. [ABSTRACT FROM AUTHOR]

An experimental investigation is presented into the explosive blast response of fibre-reinforced polymer laminates used in naval ship structures. Blast tests using plastic explosive charges were performed in air on square target plates made of carbon-polyester, glass-polyester, carbon-vinyl ester or glass-vinyl ester laminates, which are composite materials used in naval ships. The laminates were dynamically loaded by shock waves of increasing pressure and impulse, and the deformation, damage and residual mechanical properties were determined. The amount of blast-induced damage and the post-blast mechanical properties depend on both the fibre reinforcement and polymer matrix. E-glass laminates have higher resistance to blast-induced delamination cracking and tow rupture than carbon fibre composites. Furthermore, glass or carbon fibre laminates with a vinyl ester matrix have superior blast damage resistance compared to composites with a polyester matrix. The higher damage resistance is attributed to the higher flexural strain energy capacity and interlaminar fracture toughness properties of laminates containing glass fibres or vinyl ester matrix. [ABSTRACT FROM AUTHOR]

An unstructured mesh Galerkin finite element method is used to obtain estimates of the viscoelastic moduli of short glass fiber reinforced polymer composites. Periodic Monte Carlo models with 125 identical inclusions are studied. Both spheroidal and spherocylindrical inclusions are considered. The estimates are compared against predictions of the dilute approximation, Mori-Tanaka (MT) and self-consistent (SC) models. It is shown that at small fiber fractions, the dilute approximation (Eshelby) model is exact. However, for the axial stiffness the dilute regime is limited to fiber volume loadings of a few tens of a percent while typical short glass fiber polymer composites have fiber loadings from 10 to 20 percent. It is found that in this concentrated regime, both MT and SC models give excellent predictions for all but the axial stiffness modulus. To assess the feasibility of reliable stiffness and vibration damping design of composite structures from short fiber reinforced polymers, Monte Carlo models with various fiber orientation distribution (FOD) states are studied. It is shown that the quick Voigt (constant strain) orientation averaging procedure gives excellent viscoelastic stiffness predictions provided that the finite element estimates are used for the required moduli of the basis FOD state with fully aligned fibers. [ABSTRACT FROM AUTHOR]

Despite the increasing use of pultruded glass fibre reinforced polymer (GFRP) profiles in civil engineering structural applications, most common beam-to-column connection systems still mimic those used in steel frame structures, not accounting for the inherent differences of mechanical properties between the GFRP and steel. Therefore, due to the low transverse modulus and strength of GFRP profiles, these connection systems have several limitations in terms of stiffness and load carrying capacity. This paper presents the development of an innovative beam-to-column bolted connection system for GFRP tubular profiles comprising tailor-made steel connection parts that are positioned inside the GFRP sections. The experimental investigations first included double-lap tests to characterize the behaviour of bolted connections between GFRP and steel plates. Next, tests were performed on full-scale beam-to-column connections using the novel connection system, in which the following configurations were assessed: (i) one bolt per web (W1), (ii) two bolts per flange and short edge distance (F2), (iii) two bolts per flange and long edge distance (F2S), and (iv) four bolts per flange (F4). Results showed that the stiffness of the connection system is mainly influenced by the number of bolt rows, while the strength depends on the bolt edge distance – the maximum stiffness and strength were provided by configurations F4 and F2S, respectively. Moreover, with these configurations it was possible to obtain a pseudo-ductile failure behaviour. The stiffness of each connection type was estimated with reasonable accuracy using the “component method”. On the other hand, estimates of the failure load using the same method and the available design guides were non-conservative and presented poor correlation with the test results, suggesting the occurrence of mechanisms more complex than those considered to estimate the loads. Therefore, numerical models were developed to estimate the stress resultants in the bolts, which allowed to predict the strength of the connection series. [ABSTRACT FROM AUTHOR]

This study provides a fuzzy-based model for predicting the shear contribution of FRP in RC beams strengthened by externally bonded FRP sheets. For this purpose, ultimate strain of FRP, effective depth of FRP, compressive strength of concrete, width and spacing and angle of FRP, shear span to depth ratio, the elastic modulus of FRP and thickness of FRP were considered as input parameters while shear strength of FRP is treated as the target one. After a comprehensive review in existing literature, 89 FRP-strengthened RC beams were selected which had experienced FRP rupture failure mode. The results indicate that the proposed fuzzy-based model could predict the shear contribution of FRP in RC beams strengthened by FRP sheets with a good degree of precision compared with the results obtained directly from the existing guideline equations such as fib-TG9.3, CIDAR, ACI 440.2R-08 and CSA-S806(12). Proposed model provide an accurate and reliable tool than the guidelines equations. [ABSTRACT FROM AUTHOR]

In this research, glass fibre reinforced composite laminate samples were manufactured with filament winding technique using four different vinyl ester resin systems to study ageing. The manufactured laminate samples were conditioned in an environmental cabinet (70 °C, 95 RH%), water immersion (95 °C), and in sulphuric acid solution immersion under pressure (5% H 2 SO 4 , 95 °C, 15 bar). After 6 and 12 months of conditioning, the samples were tensile tested and the results were compared with the initial values. Regardless of the matrix type, conditioning in the environmental cabinet resulted in the lowest weight gain and least decrease in tensile properties: the decrease in the tensile strength values was 10–25% after 12 months’ conditioning depending on the vinyl ester used. The water immersion was more detrimental to the samples than the 5% H 2 SO 4 immersion causing the highest weight gain and the greatest decrease in tensile strength (up to 65%). However, when comparing the tensile performance, it was noted that the highest weight gain did not inevitably correlate with the strongest ageing effect. In water immersion, the ultimate strength deteriorates faster than the proof stress level leading to a decreasing damage tolerance of the vinyl-ester composite laminates. [ABSTRACT FROM AUTHOR]

The fatigue lifetime of composite pipe subjected to cyclic internal hydrostatic pressure with variable amplitudes is considered. Progressive damage modeling technique is utilized on the basis of stiffness degradation for monitoring damage progress in composite structure. The modeling which consists of three different phases as stress analysis, damage estimation and mechanical properties degradation is implemented in parallel with the random generation of fatigue loading pattern. All involved parameters defining the fatigue loading scheme, including maximum stress amplitude, mean stress amplitude and number of cycles are treated as random variables resembling real conditions of pipes in the operational field. Therefore, instead of deterministic fatigue analysis as a normal practice regulated by normative standards for the experimental analysis, full stochastic fatigue modeling is conducted. Obtained results are statistically analyzed and the probability of each estimated fatigue lifetime is reported. [ABSTRACT FROM AUTHOR]

The collapse behavior of random, woven [0/90] and angle-ply [±60°] oriented Glass Fiber Reinforced Composite (GFRP) conical frusta under low velocity axial impact loading is reported in this work. The GFRP conical frusta having uniform wall thickness with semi-apical angle in the range of 15–24° were fabricated using chopped random, woven roving and uni-directional ply-oriented E-glass fiber mats through hand layup method. The low velocity drop weight impact test setup was utilized to study the load-deformation and energy-absorption characteristics of conical frusta at different strain rates. The finite element analysis (FEA) were also performed using ABAQUS® software to predict the collapse behavior and energy-absorption characteristics of the same categories of GFRP specimen models similar to the experimental conditions. The results from both the procedures were compared and the crashworthiness characteristics of GFRP conical frusta were studied. The energy-absorption characteristics of conical frusta during impact and quasi-static loading testing were also compared and reported. [ABSTRACT FROM AUTHOR]

The fracture toughness of laminated composite materials is a very important property for damage-tolerant design, but remains poorly understood under transverse mechanical loading conditions. In this study, the transverse intralaminar fracture in unidirectional laminates with ductile polymer matrices is investigated. The presence of a ductile matrix calls for the use of concepts of nonlinear fracture mechanics for the accurate determination of the resistance of the composite to crack propagation. Unidirectional glass fiber-reinforced polymers with a polyurethane (PU) matrix are studied and compared to a benchmark epoxy (EP). The fracture toughness of these composites was evaluated through the determination of R-curves using the J-integral method, whereas the underlying fracture mechanisms were investigated through in situ testing in a scanning electron microscope. The results suggest stronger adhesion of the polyurethane matrix onto the glass fibers as compared to the epoxy-based polymer. This enables full exploitation of the ductile behavior of the PU matrix, ultimately endowing the laminate with outstanding fracture toughness. The investigated PU matrix has thus the potential to generate laminated composite parts with significantly higher damage tolerance than its epoxy counterpart. [ABSTRACT FROM AUTHOR]

Joining of composite materials has been an issue ever since composites were introduced. Among various joining methods, adhesive joining has been widely adopted because the adhesive joining uniformly distributes stresses over larger area, while the mechanical joining of composites induces stress concentration and fiber breakout. However, adhesive joining requires the surface treatment of composite adherends to increase the bonding strength; this treatment is not only costly but also generates much environmental pollution. In this study, a composite adherend that does not require any surface treatment to constitute an adhesive joint is developed. The composite adherends are manufactured by a “soft layer method” to expose bare fibers on the surface during composite fabrication. The bonding strength was significantly improved due to the exposed bare fibers, which was comparable to that of the adhesive joint treated by the conventional peel ply method without generating waste materials. [ABSTRACT FROM AUTHOR]

Fiber Reinforced Mortars (FRM) represents a promising technique for the in-plane and out-of-plane reinforcement of existing masonry buildings, coupling effectiveness with compatibility needs. The paper focuses on a technique consisting in the application on the masonry surface of a 30 mm thick mortar coating with Glass Fiber-Reinforced Polymers (GFRP) meshes embedded, presenting and discussing the results of several characterization tests (pull-out, lap-splice, bond and tensile tests) performed so to investigate on the tensile properties and bond performances of the strengthening system, useful for correct design procedures and suitable also for numerical modeling. The main aspects that has to be taken into account in the design of characterization tests are evidenced and the influence of some fundamental parameters (as the clamping system, the anchorage length, the boundary conditions and the sample dimensions) is discussed. Moreover, proper characterization tests permitted the estimation of the anchorage length to make effective the reinforcement and the definition of the stress-strain curve of the reinforced material subjected to tensile force. [ABSTRACT FROM AUTHOR]

In this experimental work, the behaviour of unidirectional glass fibre-epoxy composites under a cutting force was studied, in order to better understand the cutting mechanisms of processes involving but not limited to composite materials. Starting from composite panels manufactured by resin infusion process, dedicated specimens were obtained and subjected to a quasi-static punch-shear test. Eight different fibre orientation angles with respect to the direction of the cutting force were considered. For each case, different stress-strain behaviours were observed and discussed. The differences were also investigated, in terms of damage propagation, by means of microscopic observations of the cutting zone. [ABSTRACT FROM AUTHOR]

In this study, a low-velocity impact test of glass fiber-reinforced polypropylene (GFPP) composites was simulated considering interlaminar fracture toughness. In the simulation, intralaminar and interlaminar damage were modeled using the continuum damage mechanics (CDM) and cohesive zone method (CZM) models, respectively. The B-K criterion was used for the interlaminar damage model along with experimental results, which were obtained from fracture toughness tests of modes I and II and the mixed mode. Low-velocity impact tests were performed to verify the developed damage model, and various characteristics such as delamination and the force–displacement were evaluated. Finally, it was found that the developed damage model with interlaminar fracture toughness can be used to accurately predict the impact behavior of GF/PP composites, including interlaminar delamination. [ABSTRACT FROM AUTHOR]

A scalable technique was introduced to produce high volume lightweight composites using sheet molding compound (SMC) manufacturing method by replacing 10 wt% glass fibers (GF) with a small amount of cellulose nanocrystals (CNC). The incorporation of 1 and 1.5 wt% CNC by dispersing in the epoxy matrix of short GF/epoxy SMC composites with 25 wt% GF content (25GF/CNC-epoxy) produced 7.5% lighter composites with the same tensile and flexural properties of 35GF/epoxy composites with no CNC. The addition of 1 wt% CNC in 25GF/CNC-epoxy SMC composites resulted in increases of 15% in elastic modulus, 11% in flexural modulus and 14% in flexural strength, reaching the corresponding properties of 35GF/epoxy SMC composites. Moreover, it was found that although addition of CNC did not alter the impact energy, removing 10 wt% GF resulted in reduction of impact energy. [ABSTRACT FROM AUTHOR]

In this paper, the Generalised Probabilistic Approach (GPA) recently proposed by some of the present authors is applied in order to analyse the short fibre-reinforced materials behaviour at failure. Firstly, an experimental campaign consisting of tension tests, three- and four-point bending tests is carried out on a commercial Fibreglass composite. Then, the Primary Cumulative Distribution Function of Failure (PCDFF) is determined by employing both experimental and numerical results. In particular, the PCDFF is derived in two cases: (a) by considering the specimens subjected to the above three loading conditions separately (GPA single application); (b) by collecting both the specimens subjected to tension and those subjected to three-point bending in order to constitute a unique set (GPA joint application). Finally, a comparison between experimental failure probability values and PCDFF, being the latter obtained from both single and joint application of GPA, is provided for each loading condition. [ABSTRACT FROM AUTHOR]

This attempt proposes a Finite Element Approach (FEA) to investigate the tribological behavior of glass fiber reinforced polyester composite. The 3D finite element model was developed upon ABAQUS/Explicit. The Johnson-Cook criteria were considered for describing the material behavior and damage of both fiber and matrix phases. The fiber/matrix interface behavior was, however, modeled using a thin cohesive zone (CZ). A mixed-mode loading concept was specially adopted to predict delamination propagation within the interface. The prevailing wear mechanisms owing to Multi-Scratch Test (MST) were inspected at variable load and attack angle, using scanning electron microscope (SEM). Wear maps were built to highlight the correlation between friction coefficient and wear mechanisms. Predictions of both elementary and interacting mechanisms showed excellent correlation with observations. It was revealed that material removal process varies sensitively with the dominating failure mode. The proposed approach exhibits good ability not only in predicting active mechanisms but also in detecting damage sequences governing the surface integrity during scratching. [ABSTRACT FROM AUTHOR]

In this work an approach to predict the strength of notched structures made of quasi unidirectional glass fibre epoxy is presented. It takes into account the fabric specific behaviour in terms of hardening and softening. Four macroscopic ply failure modes are considered according to the Hashin criterion, depending on the direction of loading. Material hardening and softening is implemented according to Continuum Damage Mechanics. The hardening mechanism is modelled separately for matrix tension and shear. The softening mechanism is modelled by the incorporation of fracture toughness according to the failure mode (fibre/matrix failure in tension/compression). A new technique is proposed to determine the fracture toughness from uniaxial tension/compression tests of unidirectional notched laminate specimens. Special interest is given to the temperature impact on the material properties (elastic parameters, strengths and fracture energy) in a wide range (−40 °C to 160 °C). Since the interval covers the rubber temperature of epoxy the approach’s reliability under such conditions is examined as well. [ABSTRACT FROM AUTHOR]

Fire resistance has become a key property for structural lightweight sandwich components in aviation, shipping, railway vehicles, and construction. The development of future composite materials and components demands adequate test procedures for simultaneous application of compression and fully developed fire. Therefore an intermediate-scale approach (specimen size = 500 mm × 500 mm) is applied with compressive loads (up to 1 MN) and direct application of a burner to one side of the specimens, as established in aviation for severe burn-through tests. The influence of different core structures (polyvinylchloride foam, polyisocyanorate foam reinforced by stitched glass bridges, and balsa wood) was investigated for glass-fibre-reinforced sandwich specimens with and without flame retardants applied on the fabrics, in the matrix, and on surface for each specimen at the same time. Times to failure were increased up to a factor of 4. The intumescent coating prolongs the time to failure significantly. What is more, using the intrinsic potential of the front skin together with the core to protect a load bearing back skin in sandwich panels, the design of the core – here using the wood core – is the most promising approach. [ABSTRACT FROM AUTHOR]

Advances in new applications for composite materials create a difficult environment for an effective nondestructive evaluation as the complexity of the components increases with time. For the first time in this study, a nondestructive testing technique known as the electromechanical impedance (EMI) method is used to identify two different damage types in a composite structure. Since the EMI method is a non-model method that relies on the variations in the impedance signature that is quantified using a statistical method, data alone is insufficient to distinguish between different damage types as any changes in the structure cause the signature to change. A different method of attaching the piezoelectric transducer is combined with an averaging technique to differentiate the crack damage case from a debonding case. The study is concluded by conducting an experiment involving both damage types where the threshold values were defined for a successful damage identification process. [ABSTRACT FROM AUTHOR]

Combined with GFRP composites stress corrosion experiments, the traditional virtual crack closure technique (VCCT) is improved, and a new WDN-VCCT method is proposed to calculate the stress intensity factor (SIF) at the crack tip of GFRP composites. Its calculation formula makes up for the deficiency of the traditional VCCT method. The calculation results of the WDN-VCCT method and the calculation results of the stress extrapolation method (SEM) are compared and analyzed, and the actual accuracy of the two methods is fully evaluated. The results show that the calculation accuracy of the WDN-VCCT method is higher than that of the SEM method, the calculation efficiency is faster, and the calculation results are closer to the real value. [ABSTRACT FROM AUTHOR]

A novel experimental method for in-situ damage detection in symmetrical and balanced glass/epoxy laminates composed of unidirectional layers is introduced in this paper. A 3D finite-element micromechanical model accompanies this method to predict stiffness degradation in a cross-ply fiber-metal laminate caused by transverse cracks and metal damage. The model is developed in Abaqus. Two user-defined subroutines, UMAT and UHARD, are coded in FORTRAN and linked to the model. Using a Python script, periodic boundary conditions are applied to the model. The predictions are validated against conventional loading–unloading experimental tests. Validation shows excellent agreement between the proposed model and the experiment. [ABSTRACT FROM AUTHOR]

Structural damage identification has been researched for a long time and continues to be an active research topic. This paper proposes the use of the natural frequencies of a novel composite structures made of glass fibre reinforced polymer (GFRP). The proposed methodology consists of an improved Artificial Neural Network (ANN) using optimization algorithms to detect the exact crack length. In the first step, the characterization of fabricated material is provided to determine Young's modulus using an experimental static bending test, tensile test and modal analysis test. Next, numerical validation is performed using commercial software ABAQUS to extract more data for different crack locations in the structure. The comparison between experimental and numerical results shows a good agreement. ANN has been improved using recent optimization techniques such as Jaya, enhanced Jaya (E-Jaya), Whale Optimization Algorithm (WOA) and Arithmetic Optimization Algorithm (AOA) to calibrate the influential parameters during training. After considering several scenarios, the results show that the accuracy of E-Jaya is better than other optimization techniques. This study on crack identification using improved ANN can be used to investigate the safety and soundness of composite structures. [ABSTRACT FROM AUTHOR]

• Increase in ultimate load up to 55 %. • Effective stiffness increased up to 51 %. • Optimum strength increase is obtained with pre-stressed implants. • Reinforcing with GFRP resulted in an up to 32 % increase in ductility. This paper brings results of the bending testing of oak-wood laminated elements for structural use. The bi-directional laminations were reinforced with six types of implants made of glass fibre reinforced polymer (GFRP), some of which were pre-stressed before embedding in epoxy resin. Previously we reported on improving the mechanical properties of oak-wood laminated elements using carbon fibre implants (CFRP). Although it proved as an efficient improvement of the mechanical properties, it also raised the question of the cost effect to the final product. Therefore, within the larger study on investigating effects of different reinforcement systems, we tested glass fibres reinforced polymer (GFRP) as an alternative. Results showed that the introduction of implants improved the effective stiffness between 4 and 51 % and the ultimate load to failure up to 55 %. Furthermore, not only that insertion of the GFRP layers significantly contributed to the strength and stiffness improvement, but the ductility of the elements increased up to 32 %. Pre-stressing of the glass fibres reinforced polymer implants in tension before their installation contributed to the strength increase to a much greater extent than the increase in the number of layers. The best reinforcement effect is obtained if two layers of pre-stressed GFRP are used. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of pultruded glass fibre reinforced polymer (GFRP) circular hollow section (CHS) columns under concentric and eccentric compression. The member slenderness of the selected columns was in the short, intermediate, and long range, and two different eccentricities were chosen within the column's cross section. Predominant failure modes observed in the experiment include longitudinal splitting and localized delamination buckling. The load-carrying capacities of the concentric column under different slenderness values were quantified and compared with existing design rules. Under eccentric loading, the ultimate loads of the columns decrease with increasing eccentricity and slenderness, and the load–strain behaviour displayed non–linear characteristics due to geometric non-linearity. Failure modes of all the tested columns were well predicted by the FE models, and it was found that splitting material failure was due to hoop matrix tensile rupture. [ABSTRACT FROM AUTHOR]

Steel plate connection is popular in modern timber structures. However, the steel plate may be subjected to corrosion issue due to the presence of moisture in timbers. This paper proposes to replace steel plate with glass fiber reinforced polymer (GFRP) plate for connecting timber elements, so that the durability of the timber structure is expected to be improved. An experimental study is presented on the static and fatigue performances of the proposed GFRP-timber bolted connections. Variables including bolt diameter, number of bolt rows, number of bolt columns were selected to understand their effects on the static and fatigue behaviours of the connections. Failure modes, load–displacement curves, static bearing capacities, fatigue lives, stiffness degradations of the GFRP-timber bolted connections were reported. The residue bearing capacities of the connections were tested after the fatigue loading tests to assess the fatigue effect on the connection static behaviour. This study contributes to the understanding of the mechanical behaviour of GFRP-timber bolted connections. [ABSTRACT FROM AUTHOR]

• Precast high HPC sheet piles prestressed with GFRP bars prototypes are presented. • Three Full scale experimental tests on HPC sheet piles prestressed with GFRP bars are carried out; • The flexural behaviour is analysed, up to failure; • One more than three years aged specimen is tested for analysing the influence of the time on the global behaviour. • Effectiveness of simplified analytical sectional models. Since decades, the prestressed reinforced concrete technique, with steel strands, has been widely used in structural and infrastructural fields. The paper deals with the possibility to replace the traditional steel strands with new composite Glass Fiber Reinforced Polymer (GFRP) bars for the prestressing of precast High Performance Concrete (HPC) sheet piles. The use of prestressing combined with composite reinforcing bars could be a good solution in all those cases where the attention of the design is focus on durability, structural lightness, speed of execution, sustainability, economic savings due to the reduction of the structure maintenance. In order to evaluate the potentiality and feasibility of the proposed technique, full-scale experimental tests on sheet piles are carried out at the Laboratory of the University of Rome Tor Vergata. A suitable design and check procedure is also applied and discussed. [ABSTRACT FROM AUTHOR]

In this paper, a multiscale approach is presented for strength and tensile modulus prediction of carbon nanotube (CNT) reinforced glass–epoxy composite. At the micro-scale, the three-dimensional representative volume element is obtained by randomly orienting the carbon nanotube in the resin according to the weight percentage. The interphase of the nanotube and resin is modeled using a cohesive element method. The behavior of the resin is accounted with a quasi-brittle non-local damage model. At the Mesoscale, the representative volume element is estimated by using the weight percentage of glass fiber and resin generalized with nanotubes. Finite element analyses were conducted to estimate the effective mechanical properties through numerical homogenization. The effect of different percentages of carbon nanotubes on tensile behavior was investigated experimentally and numerically. The results show that adding carbon nanotubes improves the tensile modulus by about 25% and the tensile strength by about 53%. In the numerical study, the strength of the composite is predicted with good accuracy by modeling the damage of resin, glass fibers, and fracture toughness mechanisms of carbon nanotubes such as bridging and pull-out of carbon nanotubes. A good agreement was observed between the simulation results and the experimental results at different percentages of carbon nanotubes. [ABSTRACT FROM AUTHOR]

This work presents an experimental and a numerical studies on the effect of the phenomenon of porosity on the mechanical properties of Glass Fiber Reinforced Polymer (GFRP). In a first part, material elaboration, as well as its characterization using a three-point bending test to extract the basic mechanical properties of the material, is considered. In a second part, a finite element model is created to simulate the problem of air bubbles broadly. Several cases of different shapes and sizes are simulated. The results show a significant effect on the reduction of load in both tensile and bending cases as the size of the bubbles increases. Furthermore, the second part includes the application of the Artificial Neural Network-Enhanced Jaya Algorithm (ANN-E JAYA) to predict the reduction of the tensile load as a function of different crack lengths obtained from an Extended Finite Element Method (XFEM) model. Next, to verify the accuracy of provided application , a comparison is made with two other applications such as Artificial Neural Network-Jaya Algorithm (ANN-JAYA) and Artificial Neural Network-Particle Swarm Optimization (ANN-PSO). The results of the three algorithms show good convergence, with a slight increase in accuracy for ANN-E JAYA. MATLAB code and data used in this article can be found at https://github.com/Samir-Khatir/GFRP-ANN-E-JAYA.git. [ABSTRACT FROM AUTHOR]

Local stress concentration occurs when faults are present in pipelines under pressure. An example of such defects is the problem of corrosion caused by the environment in the field of pipeline installation. In the first part of this paper, we attempt to model the corrosion in the hemi-ellipsoidal form in order to study the locations of stress concentration in the specimens by several experimental cases and their influence on the stress resistance. The Gurson-Tvergaard-Needleman (GTN) mesoscopic damage model is used to simulate the specimens with good accuracy. In the second part, the investigation is extended to a pipe under static pressure with and without the presence of a glass fibre reinforced polymer (GFRP) composite patch. The maximum stress and percent stress reduction in a defected pipe with a hemi-ellipsoidal defect are determined using a 3D finite element model. This part examines the impact of the geometry of the composite patches on the percentage reduction of the maximum stresses in a section of pipeline subjected to static pressure. In the third part, the stresses and the percentage reduction in the maximum stresses are predicted using an artificial neural network (ANN). An inverse problem using ANN and Jaya algorithm is proposed to predict the group level of different sizes of defects under composite patches based on the maximum stress and percentage reduction of stress that the pipe withstands. The new method relates directly to real-world pipeline construction and repair applications. It could be also used for structural safety monitoring. [ABSTRACT FROM AUTHOR]

In this study, a terahertz time-domain spectroscopy (THz-TDS) imaging system was devised to detect hidden multi-delamination in a glass-fiber-reinforced plastic (GFRP) composite laminates. Shapes, thicknesses and locations in the z -direction of each delamination among the overlapped multi-delamination were analyzed considering the interaction between the pulsed THz wave and the GFRP composite. THz wave power and phase were discussed by the analytical calculations and the experimental results with the evaluation of hidden multi-delamination. Then, the THz image results were compared with those of the ultrasound wave inspection method. Finally, hidden multi-delamination in the GFRP composite laminate was successfully detected and imaged using the THz-TDS imaging system, showing that this system can be widely utilized to evaluate the reliability of composite structures as a nondestructive evaluation method. [ABSTRACT FROM AUTHOR]