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Fibre metal laminates with integrated heater elements have a promising potential as de- or anti-icing systems in aircraft structures. The alternating metal and composite lay-up in fibre metal laminates seems ideal for the development of a multifunctional skin with embedded heater elements. However, the long term durability needs to be carefully examined. A unique thermal cycling setup has been designed and built to investigate the effects of thermal cycling on the material properties of GLARE (glass fibre reinforced aluminium). Peltier elements were used to provide external heating and external cooling by inverting the direction of the electrical current. With the same setup, heated GLARE samples can be internally heated using the integrated heater elements and externally cooled using the Peltier elements. Glass-fibre epoxy composite, GLARE, and heated GLARE samples have been thermal cycled for 4000, 8000 and 12,000 cycles with temperature differences of 120 °C. The interlaminar shear strength (ILSS) increased by 6.9% after 8000 cycles for the glass-fibre epoxy composite material compared to the non-cycled samples. The GLARE samples showed a maximum ILSS increase of 4.2% after 12,000 cycles. However, the heated GLARE samples showed a continuous decrease of the ILSS with a maximum decrease of 7.8% after 12,000 cycles. [ABSTRACT FROM AUTHOR]

This paper presents the effects of elevated in-service temperature on the flexural behavior of sandwich composites consisting of glass-fiber-reinforced-polymer (GFRP) skins and a phenolic core. The glass transition temperatures of the GFRP skin and phenolic core were obtained from dynamic mechanical analysis (DMA). Subsequently, the flexural behavior of the GFRP skin and the sandwich beams were assessed with a 3-point static bending test at temperatures ranging from room temperature up to 180 °C. The results show that the variation trend of the GFRP skin’s stiffness from 3-point static bending test is in general agreement with the corresponding storage modulus results from the DMA. The GFRP skin, phenolic core, and sandwich beams retained more than 80% of their mechanical properties at 80 °C. Moreover, the flexural behavior of the sandwich beams was governed by the GFRP skins up to 80 °C, while the phenolic core played a major part on overall behavior beyond this temperature. The full-composite action between the skin and core was lost due to the disintegration of the phenolic core at high temperature. [ABSTRACT FROM AUTHOR]

An innovative hybrid sandwich slab for the rehabilitation of floors in old masonry buildings was conceived, designed, and tested. This structural system is a lightweight composite floor consisting of bottom skin and shear ribs in Glass Fiber Reinforced Polymer (GFRP), a top layer of Deflection Hardening Cement Composites (DHCC), and Polyurethane foam core. In the first part of this study, the material/structural performance of the panel’s concept was assessed by experimental tests. The second part is now dedicated to the execution of advanced numerical simulations, including parametric studies, for assisting on the optimization of this composite slab system and investigating the influence of the relevant characteristics of GFRP and DHCC components. The influence of considering orthotropic behavior for the GFRP components and linear or nonlinear behavior for the DHCC are also investigated numerically in terms of accomplishing serviceability and ultimate limit state requisites for this structural system. The parametric studies show that the thickness of GFRP rib is the most important parameter to increase the load carrying capacity of this type of slabs. Based on the results of these parametric studies, two slabs are built and tested experimentally, and the obtained results are not only used to demonstrate the effectiveness of the developed structural system, but also to appraise the predictive performance of the constitutive models adopted in the FEM-based simulations. [ABSTRACT FROM AUTHOR]

This work is concerned with the use of infrared thermography (IRT) to investigate impact damaging of composite materials, which involve both a thermoset matrix and a thermoplastic one, reinforced with either carbon, or glass fibers. Several specimens are impacted at different energy values while the surface opposite to impact is monitored with a high frame rate infrared camera. Impact tests are carried out with a modified Charpy pendulum which allows for positioning of the infrared camera. The impact energy is varied within a certain range, owing to the different types of specimen material and thickness, to have different damaging levels, but mostly barely visible damage. The obtained results show that monitoring the thermal signatures induced by impact supplies information useful for the material characterization, specifically for identifying initiation and propagation of the impact damage. In particular, from the time evolution of thermo-elastic effects it is possible to get information useful to establish the time interval the impactor remains in contact with the specimen surface and to derive information about bending and deformation of the surface under the impactor pushing force. In addition, the maximum rise of temperature coupled with the time evolution of heating events supplies information about the damage severity. [ABSTRACT FROM AUTHOR]

Phenolic foam is a fire-retarding insulator that can endure temperatures of up to 300 °C, and it is carbonized when it is exposed to fire, which decreases its thermal conductivity and prevents the spread of fire. Therefore, phenolic foam has been used for many applications, such as in the architectural and aerospace fields. However, phenolic foam requires blowing agents during the fabrication process, which causes environmental pollution. Therefore, a new foaming method that is environmentally friendly is needed. In addition, due to the brittleness of phenol, a fiber reinforcement method is required to improve the mechanical properties of the phenolic foam. In this study, a new foaming method for fabricating low-density phenolic foam that uses microwaves is developed and optimized. The effect of the viscosity of the phenolic resin and the curing speed on the foam density and uniformity is investigated. To improve the mechanical properties of the phenolic foam, a reinforcement method using chopped glass fiber was optimized with respect to the fiber length and content. The mechanical properties of the fiber reinforced foam were evaluated by measuring the tensile strengths and fracture toughnesses. Finally, the thermal conductivity of the phenolic foam fabricated by the microwave foaming method is measured. [ABSTRACT FROM AUTHOR]

In this paper, results of flexure tests aimed at improving the structural behavior of softwood beams reinforced with unglued composite plates and at developing an effective alternative to the use of organic resins are presented. The addition of modest ratios of GFRP ( Glass Fiber Reinforced Polymer ) composite strengthening can prevent tension failure in timber beams. However the application of organic matrices presents problems of reversibility, compatibility and durability with timber and poor performance at high temperatures. The increment in capacity and stiffness and the analysis of the failure modes is the central focus of this paper. The experimental campaign is dealing with a significant number of un-reinforced and reinforced beams strengthened with unbonded GFRP plates. A 3-dimensional finite element model is also presented for simulating the non-linear behavior of GFRP-reinforced softwood beams. The ability of the numerical model to reproduce experimental results for the load–deflection curves is validated. [ABSTRACT FROM AUTHOR]

The economic efficiency of pultrusion can be significantly improved by operating the process at higher pulling speeds. This experimental study analyzed the relationships between the pulling speed, morphology, and mechanical properties of pultruded glass fiber/vinyl ester resin structural composites. Four batches of 150 mm × 3.5 mm flat laminates were produced at pulling speeds of 200, 600, 1000, and 1400 mm/min. Optical and scanning electron microscopy (SEM) were used to study the morphology of the produced flat laminates. The flexural and interlaminar shear properties were determined for both 0° and 90° fiber orientations. The observed difference in the mechanical characteristics of flat laminates can be explained by the presence of bubbles, longitudinal voids, and matrix cracks and by an increase in their density and dimensions with an increase in pulling speed. This study is the first one to demonstrate the possibility of high speed pultrusion of large cross-section profiles suitable for structural application. Authors were able to achieve the pulling speed of 1000 mm/min, increasing the output by as much as 1.7 times as compared to the regular speed pultrusion, without compromising significantly the mechanical performance of produced profiles. The results of this study would be of assistance for a better understanding of high-speed pultrusion. [ABSTRACT FROM AUTHOR]

• The long-term bond durability of GFRP-RC beam structure is investigated; • The mBPE model was modified to consider the splitting of concrete cover; • The effect of working crack on structural bond performance is re recognized; • The long-term bond behavior prediction model of GFRP-RC beam was proposed. This paper investigates the long-term bond-slip behavior of GFRP (glass fiber reinforced polymer)-RC (reinforced concrete) beams. The specimens used in the bond test have been exposed to alkaline accelerated corrosion solution for eight years. In order to more accurately explore the long-term degradation law of the GFRP-RC beam, the factors of sustained load, pre-crack, and specimen form are also considered in this test. The experimental results show that the long-term degradation efficiency of specimens with pre-cracks increases significantly. The interfacial fracture energy and maximum bond strength at fracture failure are reduced by 16% and 23%, respectively. Although the overall bond performance of GFRP-RC beams will deteriorate with service time, the structure usually enters the slow degradation stage. However, the pre-cracks inhibit the arrival of this stage so that the structure will suffer more damage. In order to more intuitively evaluate the safety level of the residual bond performance of the structure in the current state, the long-term degradation prediction model of the GFRP-RC beam is established. [ABSTRACT FROM AUTHOR]

In the paper, effect of quartz additions on the durability of a polymer composite was investigated. The tested material was based on a resin MC-DUR 1200VK with two layers of E-type glass fiber reinforcement of an area density 300 g/m2 with an emulsion binder. The quartz was added in form of powder of fraction 0.1–0.3 mm in different proportions. Durability was measured in terms of specific wear work obtained from the novel tribological tester TT-4. Its important feature was the application of friction belt instead of disc or plate, which made it possible to avoid undesirable impact of the used friction surface and wear debris on the measurement results. Apart from that, standard measurements of flexural strength, shear strength between the layers, tensile strength, proof resilience, and microhardness were performed. It was found that the examined polymer composite increased its wear resistance when it contained 1% of the quartz powder. Similarly, the best results were achieved for the composite with 1% addition of quartz for the shear strength and proof resilience. However, further increase of the addition content caused decrease of the wear resistance. On the other hand, in comparison to the composite with no quartz powder, all other properties worsened after the quartz powder was added in any proportion. Despite no clear trends in characteristics after quartz addition was present, important finding was that it was disadvantageous to increase above 1% addition of quartz powder in the composite of resin MC-DUR 1200VK reinforced with two layers of E-type glass fiber of a weight 300 g/m2 with an emulsion binder. Initial researches also demonstrated that quartz additions might have different effect on the similar composite with other sort of reinforcement. [ABSTRACT FROM AUTHOR]

In this investigation, full-scale reinforced-concrete (RC) circular-beams with glass fibre reinforcement polymer (GFRP) bars and spirals were modeled using nonlinear finite element (FE) program. All the specimens had 3000-mm length. The RC-beams were modeled in a three-dimension space, taking into account the material nonlinearity and the elastic plastic behavior of the concrete, in addition to the elastic characteristics of the GFRP materials. The results of the numerical analysis were verified by comparing them against experimental results of six similar previously tested specimens, that had 500-mm diameter. The analysis included tracing the load-deformation response of the RC circular-beams, load-strains behavior on the surface of the concrete as well as the strains in the GFRP bars. The outputs from the FE analysis showed that the program was able to foresee the experimental results with good precision. The, average, value for the experimental shear strength to the foreseen ones by the FE program, (V exp /V Model) for the six beams, is "1.00 ± 0.05″ with 2.5% COV. After ward, a parametric study was performed to expand and evaluate more parameters such as size effect (200, 300, and 400 mm), span-to-depth (a/d) ratio from 1.5 to 3.5, and spirals' reinforcement ratio between 0.32 and 1.27%. The numerical investigation confirmed the prominent effect of these parameters on the shear strength and behavior of the GFRP-RC circular-beams. [ABSTRACT FROM AUTHOR]

This work investigates the repair of corrosion damage in metallic pipes using glass fiber reinforced plastic (GFRP) patches. The main idea is to analysis of the effect of the thickness of the GFRP patch and the patch surface roughness on the effectiveness of the repair. Commonly, to perform such repair, a composite sleeve wrap is used according to international standards. The work shows that is not necessary a composite sleeve to repair low pressure leaking metallic pipes, only a bonded GFRP patch is sufficient. Burst tests were performed on API 5L gr.B steel hydrostatic specimens with a 10, 15 and 25 mm hole repaired with 100 mm X 100 mm GFRP patches with three different surface roughness. The effectiveness of the repair is strongly dependent on its thickness and surface roughness of GFRP patches. Experimental results show a relation with failure pressure GFRP patch thickness and surface roughness. Higher GFRP patch thickness, elevated failure pressures are presented. Also, high values of surface roughness produce increased failure pressures. A model based on the Linear Elastic Fracture Mechanics is used to obtain an estimate failure pressure using only one algebraic equation. [ABSTRACT FROM AUTHOR]

This study presents experimental investigation and formulation of a new anisotropic nonlinear thermo-viscoelastic constitutive model to understand the time-dependent multi-axial responses of polyamide composites subjected to various histories of mechanical loading at several isothermal temperatures: 20 °C-100 °C. The composites were tested under uniaxial tension along 0° and 90° injection molding directions and the axial and lateral responses of the specimens were recorded. Experimental results indicate that composites exhibit pronounced time-dependent responses, even at low temperatures, and mechanical loadings, even at relatively low strain levels, cause permanent deformations and hysteretic responses. A new constitutive model that accounts for continuous microstructural changes under thermo-mechanical stimuli was formulated to describe the macroscopic anisotropic responses of the composites. The model was derived based on a multi-network approach and the microstructural changes are governed by the deformations of the composites. Elevated temperatures soften the polymers, making it easier to deform the composites, and thus accelerate the microstructural changes. The model is shown capable of describing mechanical responses of polyamide composites under various loading conditions, loading histories, and temperatures. [ABSTRACT FROM AUTHOR]

In this study, the structural behavior of medium density fiber board (MDF) beams reinforced by unidirectional glass fiber reinforced thermoset polyurethane outer layers is investigated by conducting beam bending and vibration tests followed by a parametric study. First, the MDF material properties are determined by 3 point bending and cantilever beam vibration tests. Then the same tests are conducted on the composite sandwich beam specimens produced by hand layup technique and the level of increase in overall stiffness and the ultimate failure loads are determined. The experimental results obtained are found out to be in good agreement with the analytical results and the numerical results obtained using a 1D shear deformable beam model. Finally, a parametric study is conducted to determine the influence of FRP reinforcement for different span lengths and fiber volume ratios. The results obtained from this study show that reinforcing MDF beams by FRP outer layers may considerably increase the flexural stiffness for all span lengths but the ultimate failure load may not be increased for short span lengths due to core shear failure, especially when there is no constraint on maximum displacement. [ABSTRACT FROM AUTHOR]

The electromechanical impedance method (EMI) has shown its damage detection capacity under hazardous environments. Moreover, it is cost-effective, because it involves a bonded piezoelectric transducer (PZT). But the daunting task in the EMI method is the selection of robust and effective damage index, frequency ranges, and combining the information for damage quantification. In this paper, an innovative standard deviation approach is used for the selection of effective frequency ranges. The novice nature of frequency range selection is based on the difference between healthy and damaged state data. Further, a data fusion technique is introduced for damage detection and classification using analytical and experimental data in this effective frequency range. This paper presents four samples of metal and composite with different damage scenarios to demonstrate the applicability of the method. The paper investigates damage in thin aluminium (Al) plate with holes using the EMI method. Further, simulated mass damage and impact damage study to the glass fiber reinforced polymer (GFRP) composite plate. A combined C-index statistical data-driven damage matrices are calculated and further compared with the RMSD index approach. The method looks suitable for identifying the damage location and damage severity simultaneously and is more effective for the less severe damage cases. [ABSTRACT FROM AUTHOR]

Modern archery bows employ composite limbs of organic materials and fibre-reinforced plastics (FRP) to increase strength and durability in a lightweight structure. However, empirical methods are often employed for the manufacturing of the bows. We propose a systematic method for the design and fabrication of FRP bows based on an inverse modelling approach of the elastica theory, which significantly simplifies the analysis of the bow's limb deformation. The construction materials are analysed by the three-point bending test and by strain gauges. We manufacture three asymmetric FRP Japanese bows with a length of 1.6 m, a force of 5 kgf, and different unbraced curvatures by using wood and glass fibre laminates. The excellent matching between the manufactured bows and the design is confirmed by a small discrepancy in the measurements of bending stress (RMSE < 8 MPa), final force (< 5%), and deformation (RMSE < 2 mm) of the bows. The inverse model demonstrates the use of FRP in bows traditionally manufactured with organic materials, by posing constraints to preserve their long-established shape. Compared to the try-and-cut approach, our method provides the sufficient requirements and failure criteria for the construction of a bow's limb, without involving complex numerical simulations. [ABSTRACT FROM AUTHOR]

This study focuses on the axial crushing behavior of double hat-shaped composite tubes prepared using plain woven fabrics reinforced by carbon fibers, glass fibers and their intra-layer hybrids. A multi-scale modelling strategy was adopted to study the crushing response of composite structures. The Chamis model was used to calculate the effective properties of carbon and glass yarns at the micro-scale level. At the meso-scale level, representative volume element (RVE) models were constructed considering the real fabric pattern. Intra-layer hybridized lamina properties can be obtained using RVE models subjected to typical loading cases. The results were validated through tension, compression and in-plane shear tests. At the macro-scale level, we used a stacked-shell strategy to create the axial crushing finite element models. The effect of intra-layer hybrid on the crushing failure mechanisms of composite tubes was analyzed and compared to that of non-hybrid carbon fiber reinforced polymers (CFRP) or glass fiber reinforced polymers (GFRP) tubes. [ABSTRACT FROM AUTHOR]

Presented research aims to prove the appearance of lateral-distortional buckling mode by observing the beams' deflection characteristics. Eight-layer channel and lip-channel cross-section glass fibre reinforced polymer (GFRP) beams subjected to pure bending in the web plane were discussed. The Finite Element Method and the Semi-Analytical Method were used to perform all calculations. Deflection angles at the beams' ends show that the lateral deflection sharply increases from load close to critical one and in the post-buckling range. It was observed that for simply supported beams subjected to bending, the lateral-distortional global buckling mode is accompanied by rotation at support in the flange plane. In the FEM approach, the lowest buckling mode is usually considered in beams subjected to bending, and the angle of rotation in the load plane corresponding to the critical bending moment is only analysed. However, in the interactive buckling analysis, the horizontal rotation at the supports is accompanied by the global mode, and its impact is often neglected due to its high bifurcation value compared to the lowest mode. Moreover, in the paper, the influence of this mode on the equilibrium paths, the critical buckling load, the load-carrying capacity, distributions of internal membrane forces, and vertical and horizontal angle of rotation was investigated. [ABSTRACT FROM AUTHOR]

• A large database of FRP-NSC columns is constructed from the literature. • Previous models for axial strength of FRP-NSC columns are evaluated. • Empirical and ANN model are proposed for axial strength of FRP-NSC columns. • The proposed empirical and ANN models portrayed higher accuracy compared with previous models. Previous research is deficient in the theoretical estimation of the axial load-carrying strength (ALCS) of glass fiber reinforced polymer (GFRP) composite columns. This study aims to calculate the ALCS of GFRP normal strength concrete (NSC) columns (GFRP-NSC) using two different approaches; empirical modeling and artificial neural networks (ANNs). The geometric, material, and testing details of 250 GFRP-NSC columns were collected from the previous studies. An initial assessment of the previous strength models for the ALCS of GFRP-NSC columns was accomplished over the constructed database. General regression and curve-fitting were used for suggesting an improved empirical model. The various hidden layers and neurons were calibrated to find an improved ANN model. Both new empirical and ANN models showed higher accuracy than the previous model for capturing the ALCS with R2 = 0.740, and R2 = 0.882, individually. A comparison of the predictions through one-way analysis of variance (ANOVA) at a 5% significance level depicts that the proposed models presented a higher accuracy than the previous models for capturing the ALCS of GFRP-NSC columns. Additionally, a detailed parametric investigation of GFRP-NSC members was carried out using the suggested empirical model to explore the influence of different variables of studied members. [ABSTRACT FROM AUTHOR]

This study proposes a novel approach to determine the fibre volume fraction in composites using vibration based non-destructive technique with a neural network. Currently, the volume fraction of a glass fibre/matrix based composite material is assessed using destructive techniques. Instead of changing or destroying the structure, a new non-destructive approach based on vibration analysis is proposed. Complete experimental protocols were developed to capture the vibration pattern. An auto-regressive model was developed as a feature extraction tool to classify the fibre volume fractions and as a pole tracking algorithm. The classification performances were within the range of 90–98%. For NDT method to be efficient, the classification results were then compared with destructive burn-out technique. The results of non-destructive test showed good agreement with those obtained through destructive test suggesting that the proposed method is an alternative to ASTM D2584-11 for determining the volume fraction of a glass fibre/matrix composite. [ABSTRACT FROM AUTHOR]

High tolerance requirements during fibre placement bear specific challenges, such as long process times for the global process, caused by fibre preparation and matrix-curing. To ensure highest quality composites, a new production process for an economic production of large structures is proposed. Therefore, the bonding of unidirectional, pre-consolidated fibre tows to a load-specific global structure is investigated. With this approach, the fibre embedding is temporary decoupled from the fibre layup process. By producing a structure from optimally aligned fibres and with a hedged bonding process, an increase of the manufacturing-rate and quality is possible. To prove a general suitability of this approach, initial basic investigations are carried out. Those demonstrate if an adhesively fixed prepreg structure can compete with a pure prepreg structure. In a first sample series, reference samples of pure prepreg and adhesively fixed prepreg samples with different adhesives are investigated. For a second sample series, the prepreg-surfaces of the adhesively fixed samples have been pretreated with different methods before bonding. Finally, pressure-tests, 4-point-flexure tests and interlaminar-shear-strength test have been carried out with all samples. All test results have been compared with the reference sample. Investigations led to initial promising results and motivate to further pursue this approach. [ABSTRACT FROM AUTHOR]

Morphing technology is inspired by biological motion for implementation in missions in a variety of areas without shape-change device. This study investigates the aerodynamic performance of a self-contained morphing winglet for an unmanned aerial vehicle (UAV) that mimics the wing-tip feathers of gliding birds. A smart soft composite (SSC), formed of shape memory alloy (SMA) wires and glass fibers within a soft polymeric matrix, was used to fabricate morphing winglets. Experiments were conducted with various diameters and numbers of embedded SMA wires, and numbers of the glass-fiber fabric lamina, which were compared with an analytical model. Morphing winglets were implemented at both wing tips of a WASP 4/7-scale UAV, and the aerodynamic characteristics were investigated using a wind tunnel testing with various attack angles. As results, when the morphing winglet was actuated, the lift-to-drag ratio increased by 5.8% compared with the flat wing geometry for attack angle greater than 5°. [ABSTRACT FROM AUTHOR]

Fibre Metal Laminates have been manufactured by liquid moulding. Flow paths have been drilled to enable the impregnation through the aluminium sheets. The effect of these holes on the low velocity impact behaviour has been studied. Damage mechanisms, dissipated energy and peak force of drilled samples have been compared to those of reference samples without holes. Results show that the presence of the holes has no effect on the performance of the plate and that the internal damage is confined to the surrounding of the impact zone. When the holes are inside the impact contact zone cracks in aluminium sheets propagate through the holes, but their effect is mitigated by the fibre bridging mechanism. Holes located out of the impact contact zone have no effect in the damage mechanisms. [ABSTRACT FROM AUTHOR]

The design of glass fibre reinforced polymer (GFRP) pultruded members is often governed by deformability and buckling phenomena, preventing the full exploitation of the material potential. Hybridization – the partial replacement of the glass reinforcement with (stiffer) carbon fibres – is a possible approach to improve the performance of GFRP thin-walled profiles. This paper presents an experimental study on the structural behaviour of I-section hybrid fibre reinforced polymer (FRP) pultruded columns made of glass and carbon fibres (GF and CF) embedded in a polyester resin. A bare GFRP reference profile and four series of hybrid C-GFRP profiles, with different types and architectures of CF reinforcement, were designed, manufactured and tested under compression in three different lengths – short, intermediate and long. Particular attention was given to the buckling behaviour of the columns and to the delamination at the interface between GFRP and CFRP layers. In terms of serviceability performance, results obtained confirm the hybridization’s effectiveness in increasing the axial stiffness of GFRP compressive members. In terms of ultimate limit states behaviour, hybridization increased the load carrying capacity of the long columns, which exhibited global buckling. In opposition, for the short and intermediate columns, which failed respectively due to local buckling and a combination of global and local buckling, the load carrying capacity of the hybrid columns was lower than that of the reference profile; such worse performance seems to have been caused by the delamination of the CF layers, owing to the relatively high axial strains that developed in those columns. In a companion paper (Part 2), the experimental data presented and discussed herein is compared with predictions from numerical models and analytical formulae, which also provide further information about the delamination and progressive failure of the hybrid columns. [ABSTRACT FROM AUTHOR]

This study proposes a mixed-mode fracture criterion for glass fiber reinforced composite laminates based on numerical and experimental biaxial loading. An optimal cruciform geometry is introduced first based on finite element (FE) simulation. Characterization testing is performed successively on uniaxial and cruciform specimens to determine equivalent loaded area, notch sensitivity behavior and critical fracture toughness properties of cross-ply GFRP laminates. In experimental biaxial testing, two types of crack orientations (0°, 45°) are studied with varying crack lengths. The experimental failure points show that cross-ply GFRP laminates attain higher load bearing capability under biaxial tensile–tensile loading compared to uniaxial testing. Appropriate non-dimensional geometry factor relevant to cruciform shape is determined based on experimental data points and FE simulation. Eventually, a mixed-mode fracture criterion is proposed for cross-ply composite laminate based on the findings from biaxial experimental loading. [ABSTRACT FROM AUTHOR]

A multi-objective robust optimisation (MORO) of carbon and glass fibre-reinforced hybrid composites under flexural loading based on an a posteriori approach has been presented in this paper. The hybrid composite comprised of T700S carbon/epoxy laminate at the tensile side and E glass/epoxy laminate at the compressive side. The conflicting objectives for optimisation were to minimise the cost and weight of the composite subject to the constraint of a minimum specified flexural strength. Fibre angles and thicknesses of each lamina were considered as uncertain but bounded variables with the worst-case analyses being performed as a non-probabilistic method and the effect of uncertainties being determined. A hybrid multi-objective optimisation evolutionary algorithm (MOEA) was introduced through modification of an elitist non-dominated sorting genetic algorithm (NSGA-II) and combining it with the fractional factorial design method. The performance of the hybrid algorithm was found to be superior to that of the original version of NSGA-II. The multi-objective robust optimisation of the hybrid composite was solved by utilising the proposed algorithm for several levels of strength with the robust Pareto optimal sets being generated and compared. Three scenarios have been considered to illustrate the applicability of the obtained solutions in an a posteriori decision making process. [ABSTRACT FROM AUTHOR]

Similarly to the post-buckling behavior of steel girder webs, the post-wrinkling behavior of glass fiber-reinforced polymer (GFRP) cell-core sandwich webs can increase their ultimate shear strength. Post-wrinkling is, however, different from post-buckling since wrinkling is a local buckling instability mode that can occur in any part of the web. Furthermore, all the previously presented theories or models have been limited to isotropic web plates, while the fiber architecture of orthotropic plates can greatly influence post-wrinkling behavior. Based on biaxial compression–tension experiments on GFRP web-core sandwich panels, the redistribution of the strain field during post-wrinkling was examined for two different fiber architectures, [90/0] and [±45] stacking sequences. The results proved that fiber architecture greatly influences the wrinkling loads and wrinkling mode as well as post-wrinkling behavior. During post-wrinkling, the ultimate shear strength of the sandwich structure and the redundancy of the system can be increased, thus enhancing the safety, functionality and reliability level of this type of structure. [ABSTRACT FROM AUTHOR]

In the present study, low-temperature material characteristics of polyurethane foam, glass fiber-reinforced polyurethane foam, and polyisocyanurate foam were investigated. These foams are key candidate materials for use in membrane-type liquefied natural gas insulation systems. Liquefied natural gas insulation systems should be able to withstand severe environmental conditions, such as fluid induced impact loading under cryogenic temperatures. For the robust design of insulation system, both failure characteristics and deformation recovery capacity of the materials must be evaluated. Therefore, the failure characteristics and the deformation recovery ratio of the foams were investigated at various temperatures and strain rate levels. The present study revealed that the fracture behavior and the recovery ratio were significantly affected by decreases in temperature. As a newly obtained insight, it has been found that the recovery ratio for all tested materials significantly decreased at −163 °C. This finding is the opposite of the behavior that typically occurs at low temperatures. In particular, polyurethane foam specimen after experiment at the temperature of −163 °C was easily broken into pieces even under the application of small loads. In addition, it has been revealed that polyisocyanurate foam showed superior mechanical characteristics at cryogenic temperatures owing to the ring structure of isocyanurate. [ABSTRACT FROM AUTHOR]

Low velocity axial impact crush behaviours and energy absorption characteristics of thin-walled aluminium conical (AC) and E-glass/epoxy composite over-wrapped aluminium conical hybrid frustrated shells (CWAC) have been studied through experimental and numerical procedures. In this regard, 15°–24° semi-apical angled aluminium and hybrid conical test specimens of required thickness and fibre ply orientations were fabricated through hand layup method. The axial impact tests were performed at different strain rates on each AC and CWAC samples with the help of low velocity impact test setup in order to assess the energy absorption capacity of each specimen against impact loading. The influence of inertia, strain rate, addition of GFRP laminates over aluminium shell and GFRP fibre ply orientation towards the crashworthiness performances of various categories of conical frusta were analyzed. The low velocity impact tests were also simulated with the help of finite element analysis (FEA) techniques of ABAQUS® software in order to predict and compare the crashworthiness of each category of specimen model with experimental results. The obtained crashworthiness test results and collapse behaviours of FEA analysis are found in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

We report a new approach to measure orthotropic properties of short glass fibre reinforced thermoplastics at the macroscopic scale taking into account all microstructural details. 3D imaging technique based on X-ray micro-tomography is used to assess fibrous architecture of an injected part at different positions characterised by different fibre flow histories. Finite element computation is used as a multiscale process, firstly by computing orthotropic parameters at a micro-scale for hundreds of bi-phasic 3D domains composing the macrostructure of the composite at all studied positions. Results are implemented in a second finite element computation as a collection of orthotropic material models composing the heterogeneous structure of the composite. [ABSTRACT FROM AUTHOR]

Energetically weak points in thermally insulated building envelopes are formed by thermal breaks that are implemented to structurally connect external balconies to internal slabs. Current thermal breaks comprise stainless steel bars that penetrate the insulation layer and thus cause significant thermal losses. A new thermal break composed of highly insulating aramid and glass fiber-reinforced polymer (AFRP and GFRP) components and aerogel granulate insulation materials was developed and the first prototypes of the load-bearing components were experimentally investigated. The use of AFRP leads to an excellent thermal performance with linear thermal transmittance values of below 0.15 W/m K. The experimental prototype investigations confirmed the targeted ductile failure mode through concrete crushing in the component–concrete interfaces. The serviceability limit state conditions are met for a targeted balcony cantilever span of 4.0 m. The material-tailored components can be manufactured by fully automated processes such as filament and tape winding and pultrusion to economically produce large quantities within a short time. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to simulate long-term hydrostatic tests on Glass Fiber Reinforced Plastic (GFRP) pipes. An experimental procedure for obtaining pressure class of GFRP pipes on the basis of long-term behavior is very time consuming and costly that sometimes take about 2 years for collecting required data. Then, obtained results are extrapolated to 50 years. In this work, a theoretical modeling procedure is developed to obtain residual strength of pipes after 50 years taking into account creep phenomenon. Developed progressive modeling consists of creep modeling, stress analysis and failure evaluation. An integrated modeling procedure is developed reporting time-to-failure at any desired internal pressure. As a case study and also validation purpose, the developed modeling procedure is conducted for predicting long-term behavior of a specific GFRP pipe subjected to internal pressure. A comparison between real experimental data and theoretical modeling is presented. A very good agreement between predicted 50-year hydrostatic pressure and experimental data implies on the proficiency of the developed modeling. Since the developed modeling is just in need of short-term experimental data on pure resin, it could be used as an appropriate engineering tool for industrial centers. [ABSTRACT FROM AUTHOR]

In this paper, a new generation of composite sandwich slab is proposed as a solution for the rehabilitation of slabs in old masonry buildings. An innovative solution was developed during this research formed by four components: a Deflection Hardening Cement Composite (DHCC) layer on the top compression skin, a glass fiber reinforced polymer (GFRP) skin at the bottom tension surface, GFRP ribs to transfer shear from top to bottom layers, and foam core for thermal-insolation purposes. The DHCC layer contributes significantly for the load carrying and deflection capacity due to its stiffness, compressive strength and toughness, offers resistance to the occurrence of buckling phenomena in the GFRP ribs, improves the performance of this structural concept against impact and fire, and constitutes an excellent medium for the application of finishing materials, like ceramics or timber. Two different hybrid composite slabs were developed and tested, and their behavior was assessed under flexural loading. The results showed that the developed hybrid sandwich slabs accomplish all design requisites for serviceability and ultimate limit states, and assure a stiffness/dead-weight and load-capacity/dead-weight ratios much higher than conventional structural slab systems. [ABSTRACT FROM AUTHOR]

The kink behavior of non-slender glass fiber-reinforced epoxy prismatic specimens of variable length and fiber volume fraction at temperatures ranging from 25 °C to 125 °C was investigated. Splitting failure occurred at the glassy state while kinking failure was observed at the glass transition state and buckling with subsequent post-peak kinking at the rubbery state. Kink initiation was caused by the initial imperfections, i.e. the waviness of the unidirectional fibers. Initiation occurred through fiber microbuckling caused by combined compressive and shear stresses at the glass transition state and predominant shear stresses at the rubbery state due to the preceding buckling. The kink band width was narrow at the glass transition state due to the significant compressive stresses and corresponded to the wavelength of the initial fiber waviness. The kink band width at the rubbery state was much wider and corresponded to the band width of the maximum shear stresses at the inflexion points of the buckling shape. The kink band angle depended on the ratio of compressive to shear stresses. The different specimen slendernesses and fiber volume fractions did not influence the kink initiation and kink band formation mechanisms. [ABSTRACT FROM AUTHOR]

The geopolymer concrete internally reinforced with fibre-reinforced polymer (FRP) bars is anticipated to offer durable, sustainable, and cost-effective civil infrastructures. In this study, the effect of the anchor head on the pullout behaviour of the sand coated glass-fibre-reinforced polymer (GFRP) bars embedded in the geopolymer concrete was investigated using a direct pullout test. Straight and headed GFRP bars with different nominal diameters ∅ (12.7, 15.9, and 19.0 mm) and embedment lengths l d (0 ∅ + l ah , 5 ∅ + l ah , and 10 ∅ + l ah for headed bars, where l ah stands for the anchor head length, and 5 ∅ and 10 ∅ for straight bars) were considered. The results showed that the provision of anchor head is an efficient method to enhance the anchorage capacity of GFRP bars in geopolymer concrete. The anchor heads improved the anchorage of the sand coated GFRP bars by as much as 49–77%. Furthermore, the mechanical bearing resistance provided by the anchor head alone resulted in the development of approximately 45% of the GFRP bars’ nominal tensile strength. A comparison of the experimental results with the published studies showed that a much higher load is required to pullout the GFRP bars in geopolymer concrete than in Ordinary Portland Cement-based concrete. [ABSTRACT FROM AUTHOR]

Most wind turbine rotor blades comprise several adhesively connected sub-components typically made from glass fibre reinforced polymer composite materials. It is a well-known fact that wind turbine blades are prone to fail in their adhesive joints. However, owing to the complexity of their structural behaviour, little is known about the root causes of adhesive joint failure. This paper investigates the effects of geometrical non-linearity on energy release rates (ERRs) of transversely oriented cracks present in the adhesive joints of a wind turbine rotor blade. Utilising a computationally efficient numerical slice modelling approach, the Virtual Crack Closure Technique (VCCT) is used to compute Mode-I and Mode-II ERRs induced by bi-axial bending. Generic critical loading directions are identified; these may have far-reaching consequences for blade design, analysis and testing. [ABSTRACT FROM AUTHOR]

A physics-based model describing the thermal interaction between a lightning channel and a composite structure has been developed. The model includes: (i) spatial and temporal evolution of the lightning channel as a function of the electric current waveform; (ii) temporary and spatially non-uniform heat flux generated at the composite structure, where the heat flux is an explicit function of the electric current waveform and the instant lightning channel radius; (iii) nonlinear transient heat transfer problem formulation for layered anisotropic composites that accounts for temperature-dependent material properties, a moving boundary of the expanding lightning channel, and phase transition moving boundary associated with instantaneous material removal due to sublimation. The model is applied for evaluation of thermal damage of the tip glass fiber reinforced polymer matrix composite panel of the Sandia 100-meter All-glass Baseline Wind Turbine Blade (SNL 100-00) subjected to lightning strike. [ABSTRACT FROM AUTHOR]

This paper reveals the influence of arching action on the shear behaviour of glass fibre reinforced polymer (GFRP) reinforced laterally restrained concrete slabs in bridge decks. A total of seventeen full-size one-way concrete slabs were constructed and tested in this study. Those restrained test slabs represents typical full-scale dimensions of a real bridge deck slab 400 mm wide by 2400 mm long and 200 mm deep. The test variables were lateral restraint stiffness, reinforcement configuration and concrete strength. The behaviour of test slabs was discussed and the influence of those structural parameters on the amount of arching action was evaluated by comparing the results of different specimens. The test results showed that increasing the arching effect resulted in shear failure mode and larger shear strength. The experimental shear strengths of the restrained test slabs were compared with some theoretical predictions in the literatures. The results indicated that those theoretical methods yielded high conservative predictions. A theoretical model that takes into account the effect of arching action in the shear-strength prediction was proposed by the writers. This method provided accurate and slightly conservative predictions. [ABSTRACT FROM AUTHOR]

Thirty-six, four-point flexure tests on simply supported pultruded glass fibre reinforced polymer composite (GFRP) Wide Flange (WF) beams with mid-span bolted splice joints are described. The joints were fabricated with two and six pultruded GFRP splice plates. Three splice plate lengths were investigated and two bolt torques were used to tighten the bolts. Each of the twelve splice joint combinations was subjected to three repeat tests up to the serviceability deflection limit. Their load versus deformation responses were shown to be linear and repeatable. During each test loads, support rotations, splice joint end rotations and mid-span surface strains were recorded for each mid-span deflection increment. The beams’ transverse stiffnesses and splice joints’ rotational stiffnesses were derived from the test data. The variation of the stiffnesses with splice plate length, number of splice plates and bolt torque was also quantified. A simple analysis was developed for splice-jointed beams and was used to predict the transverse and rotational stiffnesses determined from the test data. It was shown that the transverse stiffnesses could be predicted to within 10%, provided a rigid-body rotational correction was applied. The correction also provided an estimate of the splice joint’s slip displacement. [ABSTRACT FROM AUTHOR]

This paper presents some experimental results dealing with the mechanical performance of composite beams obtained by bonding Glass Fibre Reinforced Polymer (GFRP) rectangular pultruded panels by means of an epoxy structural adhesive. The flexural response of these bonded beams was compared with those obtained by the pultrusion process with the same geometrical and material properties. As a matter of fact, no significant loss of performance emerged in terms of failure load; moreover, an increase of pre-failure stiffness was observed. This result may allow us to consider bonded GFRP beams as a viable simplification within the field of composite structures. [ABSTRACT FROM AUTHOR]

The failure mechanism of non-slender glass fiber-reinforced epoxy prismatic specimens subjected to axial compression and different temperatures was investigated. Digital image correlation was used to map and derive the failure modes. The failure mode changed from splitting failure at ambient temperature to kinking at the onset of the glass transition temperature. The kink initiation mechanism could be clearly observed. Based on the initial waviness of the fibers, the wave amplitude disproportionally increased at one specific location up to fiber microbuckling and surrounding matrix failure; the wavelength of the initial imperfection was thereby maintained. The kink band then rapidly propagated through alternating horizontal and inclined segments leading to an overall inclined kink band of 31° on average. The kink band width doubled from around three to six times the average wavelength of the initial imperfection. [ABSTRACT FROM AUTHOR]

The objective of this article was to experimentally evaluate timber–concrete composite beams in two different situations – with and without glass fiber reinforced polymer (GFRP). Four full-scale composite beams (5.4 m in length) were produced, two of which had reinforcement (nominal thickness of 10 mm) and two with no reinforcement. The fiberglass reinforcement was formed from the impregnation of unidirectional fiberglass cloth – effective thickness of 0.5 mm – with epoxy resin. The connection system consisted of steel hooks inclined at 45 degrees, bonded with epoxy adhesive to the holes previously drilled on the wood, whose apparent density at 12% moisture content was 0.79 g/cm 3 . The reinforced timber–concrete composite beams tested had performance efficiency of 79% and average rupture strength of 142.5 kN. Finally, the reinforced timber–concrete composite beams were analytically evaluated using the proposed method in Eurocode5, showing reasonable agreement with the experimental results. [ABSTRACT FROM AUTHOR]

A novel method using microwaves is proposed to detect and evaluate defects in glass fiber reinforced plastic (GFRP) laminates. A thin circular plastic film simulating delamination was inserted in GFRP laminates and was detected using microwave reflectometry. A focusing mirror sensor consisting of a horn antenna and two metal mirrors was used to improve the measurement resolution. In addition, the thickness of the film was calculated using a proposed model based on microwave propagation theory. Measuring the variation in the amplitude of the microwave reflectivity, a 7.5-μm-thick film was successfully detected in a 3-mm-thick GFRP laminate. Moreover, the calculated results of the inserted film thickness had a high degree of accuracy. [ABSTRACT FROM AUTHOR]

A study on the robustness of unidirectional S-2 glass and T700S carbon fibre reinforced epoxy hybrid composites under flexural loading is presented in this paper. The flexural strengths of various stacking configurations are computed using the Classic Lamination Theory (CLT), and the computed data are fitted to a regression model. With the aid of the developed regression model, robust indices are developed for both flexural strength and specific flexural strength. The concept of robust strength is introduced to address both the strength and robustness criteria, with which a design guideline for robust hybrid composites is given. Simulation studies are conducted to demonstrate the validity of the proposed method. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of nanoclay content on flexural, impact and water absorption properties of Fibre Reinforced Polymer (FRP) and FRP face sheet sandwich laminates with polystyrene foam core. Four different combinations of FRP composites (0, 2, 4 and 6 wt% of nano clay) have been prepared by hand lay-up manufacturing techniques (HL) and they have been investigated for the same to obtain the best combination. Further, based on the best combination obtained, two different (0 and 4 wt%) sandwich laminates are prepared to make relative comparison among various laminates. X-ray diffraction (XRD) results have been obtained from the FRP samples, where the nanoclay has indicated that, the mode of dispersion and intergallery spacing of the layered clay. Scanning electron microscopy (SEM) has given morphological picture of the FRP fracture samples. The results of the study show that, the flexural, impact and water absorption properties of the nano polyester sandwich laminate have been greatly increased at 4% of nanoclay loading. [ABSTRACT FROM AUTHOR]

A large debate animates the community about the mechanical performance of complex parts obtained by injection moulding (IM) of short glass fibre reinforced polymer (SGFRP) composites. Difficulties to measure exact fibre length and orientation distributions in complex geometries are limiting in terms of basic understanding of damage mechanisms in industrial parts and fatigue design improvement. In this work, we are interested to shed more light on the mechanical performance of short glass fibre reinforced polyamide composites in correlation to local microstructural heterogeneities which are caused by inserts used during IM. For such purpose, we combine X-ray microtomography (μ-CT) and finite element computation to determine the elastic modulus in various positions in an open hole plate configuration with a dissymmetric fibre distribution. Our predictions show that effective properties do not vary significantly around the hole in all space directions. However, stress profiles (through the thickness) far enough from the hole reveal a five-layer quasi symmetric structure evolving to three-layer near the cylindrical insert. We believe that such alteration is responsible for the observed failure of the composite at precisely the positions of highly affected fibre distribution. [ABSTRACT FROM AUTHOR]

This paper describes the low velocity impact behavior of repeatedly impacted honeycomb sandwich structures which are used in aircraft interiors comprising of unidirectional glass fiber reinforced epoxy composite face sheets and aluminum honeycomb core. Impact energies, maximum loads and the permanent deflection of honeycomb sandwich structures were determined with instrumented drop weight impact test machine to evaluate the repeated impact performance and damage resistance. On the other hand, the preliminary single impact loading tests also performed in order to find the energy levels which were ranged fully elastic energy level to perforation energy level for sandwich composites. Impact test results obtained from repeatedly impacted honeycomb sandwich structures were correlated with a function of force–time, force–deflection and energy-number of impacts curves. This work is also focusing on the residual compressive properties of single and repeatedly impacted honeycomb sandwich structures. Shimadzu AG-X test machine with a load cell of 10 kN was used for compression after impact tests (CAI). The values of residual compressive strength of the single and repeatedly impacted honeycomb samples were compared with the undamaged honeycomb samples according to compressive load–displacement curves. [ABSTRACT FROM AUTHOR]

In recent years, natural fiber as a green and renewable resources have attracted much attention to be used as reinforcement in composites. The aim of this work is to assess mechanical properties and durability in harsh environments of epoxy-based flax and glass bio-hybrid fiber reinforced plastics (bio-HFRP) composites. With the same fiber mixing ratio, the flexural and dynamic mechanical properties of the bio-HFRP composites were studied by changing the stacking order. The pure flax FRP and bio-HFRP composites were exposed to hygrothermal at 20 °C, 40 °C, and 60 °C for 28 days, respectively. The water absorption and diffusion capacity, the bending and shear properties were analyzed. Compared with the pure flax FRP, the flexural strength of G 2 F 2 s group sample was increased by 2.2 times. When exposed to the hygrothermal environment, flexural strength loss rate of the G 2 F 2 s group sample is only reduced by 4.35%, 9.00% and 11.51%, and its flexural modulus decreases 15.48%, 15.90% and 23.89%. It shown that the addition of glass fiber effectively improves the water absorption of flax fiber composites. Hybridization of flax fibers with glass fibers was a practical approach to enhance FRP laminates in hygrothermal environmental conditions after synthesizing the stacking sequence, mechanical properties and aging resistance. [ABSTRACT FROM AUTHOR]

Three-dimensional woven spacer composites (3DWSCs) have a great potential to applied in aerospace or transportation fields due to their high strength-to-weight and stiffness-to-weight ratios, with excellent skin-core debonding resistance. Among these properties, the compressive strength of the 3DWSCs which is most critical, and still needs to be improved to meet the highly requirements in practical applications. In this study, we designed and manufactured 3DWSCs with highly enhanced compressive strength and energy absorption by adopting bulked glass fibers (BGFs) as pile yarns to weave its core layer to absorb more epoxy resin. Consequently, the specific compressive strength of 3DWSCs woven by BGFs as pile yarns with saturated epoxy resin absorption was 52.54 MPa g−1 cm3, 180% higher than that of the 3DWSCs woven by regular glass fiber (RGFs). Furthermore, the work of fracture of 3DWSCs woven by BGFs as pile yarns with saturated epoxy resin absorption was 14.82 N m, which enhanced 474% compared with that of 3DWSCs woven by RGFs. The failure cross sections depicted multiple brittle fractures of the pile yarns for both composites under compression, which caused multiple peaks in their stress–strain curves. [ABSTRACT FROM AUTHOR]

Pultruded glass fiber reinforced polymer (GFRP) sections are increasingly used as load bearing elements in civil construction. Their low elastic modulus and thin-walled nature make these sections prone to buckling phenomena when loaded in compression. This paper presents a study on the axial compression behavior of the pultruded GFRP channel sections. Two variables were considered including column slenderness ratio and wall width-to-thickness ratio. Therefore, four channel sections with different dimensions were selected. Seven column lengths ranging from 100 mm to 1400 mm were used for each channel section under axial compression. Three failure modes were observed including section crushing, local buckling and global buckling which were highly related to the column slenderness. Load-displacement curves and compression capacities were reported and compared. Finally, existing analytical design equations in the literature were validated using experimental results. Recommendations on compression design of pultruded GFRP channel sections were made based on the results in the current study. [ABSTRACT FROM AUTHOR]

In this study, low-velocity impact tests were applied to E-glass fiber (GFR) and basalt fiber reinforced (BFR) filament-wound hybrid composite pipes. The BFR/GFR hybrid pipes were subjected to low-velocity impact tests when they were oil-unfilled, oil-filled at 0 bar (unpressurized oil) and low oil pressure at 5 bar. Impact energies were applied as 15 J, 20 J and 25 J, respectively. After the experiments, the dynamic behaviors and damage formation within the samples were evaluated in terms of type and severity. [ABSTRACT FROM AUTHOR]