Fiber Reinforced Polymer Materials Research Articles

Efficiency of flexural strengthening RC beams using fiber reinforced polymer materials

The purpose of this study is to evaluate the efficiency of the flexural strengthening of reinforced concrete (RC) beams using the fiber reinforced polymer (FRP). The calculation procedures according to design standards including ACI 440.2R-17 and FIB-2019 are employed to assess the flexural capacity of strengthened RC beams. Three types of FRP materials, which are glass FRP (GFRP), aramid FRP (AFRP), and carbon FRP (CFRP), are used. For CFRP, three kinds of tensile strengths consisting of low (CFRP-L), medium (CFRP-M), and high (CFRP-H) levels are also utilized in calculations and assessments. A numerical model of FRP strengthening beam is developed in ANSYS and then verified with the results of design standards. Comparative studies on the efficiency of flexural capacity and cost benefit between the use of FRP sheets and a conventional retrofitting method are conducted considering a specific area of FRP sheets and 50% flexural strengthening target. The results reveal that flexural strength after strengthening based on ACI and FIB is very similar. The optimal options considering the strength and cost effects are CFRP-L and CFRP-M when using a constant area of FRP. Additionally, we suggest using CFRP-H or CFRP-M for strengthening the RC beams with satisfying a target strength improvement of 50%. Comparing with the conventional method such as section increment, using FRP is more beneficial for both required strength and costs as well.

Evaluation of flexural strength of hybrid FRP composites having three distinct laminates

The high-performance fiber-reinforced polymer (FRP) composites have been extensively preferred as a replacement to the conventional materials. These composites have impressive mechanical properties. This study involves the fabrication and investigation of the flexural strength of the hybrid FRPs material made from three distinct laminates. The hybrid FRPs have been prepared using hand lay-up technique. The fabricated specimens have been tested under three-point bending following ASTM D790 standards. From the results, it has been observed that the specimen having Kevlar at the topmost has the highest value of flexural strength. This feature of hybrid FRP makes it a better alternative to conventional materials used for leaf springs.

Shear Performance of Damaged Concrete Beams Reinforced by Penetrating FRP

This experimental study examined the shear behavior of damaged concrete beams reinforced with fiber-reinforced polymer (FRP) using a penetration method (penetration FRP) to explore the failure modes of the reinforced beams. The load-displacement curves and load-strain curves of the samples were analyzed, and the development and distribution of the oblique cracks of the reinforced beams were discussed. The influences of the damage degree and the reinforcement angle on the shear bearing capacity were determined. The results showed that, prior to cracking, FRP reinforcement had no effect on the stiffness of the samples and the cracking load of the samples remained basically the same; however, after cracking, the samples reinforced with FRP exhibited a larger shear capacity. Moreover, the ultimate load was higher for the undamaged reinforced beam than the damaged reinforced beam. The penetration of the FRP material into the beam at an oblique angle inhibited the development of oblique cracks, resulting in a better reinforcement effect and optimal bearing capacity of the strengthened beam.

Development of rectangular hybrid-stiffened-plate structural system with fibre-reinforced polymer fabric composite in tension zone

Reinforced concrete plates stiffened by the beams in the orthogonal directions are widely used in bridges and buildings. Local failure occurs due to stiff beams whereas shallow beams cause global collapse failure in the plate. A theoretical model using inelastic analysis (yield line analysis) has been formulated to predict the behaviour of the rectangular hybrid-reinforced concrete-stiffened-plate system which recognized the benefits of different types of fibre-reinforced polymer fabric and ferrocement in tension side. Parametric study was also conducted to capture the influence of different parameters such as number of panels, plate aspect ratio and beam strength parameter on the flexural capacity of plate system. Designer can select the proportionate hybrid-stiffened-plate system which fails globally to avoid negative yield lines through design chart. In the experimental study, four rectangular hybrid-stiffened-plate structural systems were developed with two internal beams in each perpendicular direction incorporating ferrocement and unidirectional carbon fibre–reinforced polymer fabric, unidirectional basalt fibre–reinforced polymer fabric and bidirectional glass fibre–reinforced polymer fabric sheet on the bottom side. The experimental ultimate load was recorded maximum in unidirectional carbon hybrid–stiffened-plate system, however, unidirectional basalt hybrid–stiffened-plate system gave the best performance with respect to the cost analysis. The numerical analysis had a reasonable consistency with experimental and analytical results.

Temperature Effects on Failure of Rotating Beam of Hybrid Composite

Fiber-reinforced polymer materials are widely used in the design and manufacture of rotating structures like robot arms, wind turbine blades and helicopter blades. This is due to their high specific strength and stiffness, lightweight and ease to manufacture the complex parts of structures such as airfoils. In the present study, thermal effects on the failure of a rotating hybrid beam are studied. The beam is modeled as a composite laminate with the top and bottom layers made of carbon fiber-reinforced plastic and the middle layer glass fiber-reinforced plastic. The cost of carbon fiber is about ten times more than glass fiber and the hybrid arrangement of fiber reinforcements leads to a cost-effective design. Four different stacking sequences are investigated, namely [0/30/0]S, [0/45/0]S, [0/60/0]S and [0/0/0]S. To determine the failure limits of non-hybrid and hybrid rotating beams under thermal loads, Tsai–Wu failure criterion is implemented. Numerical results indicate that the failure index increases with increasing angular speed and temperature as expected. As the thicknesses of the carbon fiber layers increase, the failure index decreases which can lead to a longer service life. By using the minimum amount of the more expensive carbon fibers in the outer layers and less expensive glass fibers in the middle layer, the cost of the hybrid beam can be reduced and a cost-effective beam design under thermal loading can be achieved.

Integrated Prediction of Mechanical Behavior for the Non-Aligned Fiber Composites With Experimental Validation

Abstract This paper aims to present an integrated multi-scale method for predicting the anisotropic and nonlinear elasto-plastic behavior of short glass fiber-reinforced polymer (GFRP) materials typically produced by injection molding. The proposed method combines injection molding and microstructure together, with considering the nonaligned fibers and their corresponding anisotropy, to semi-analytically estimate the local effective mechanical properties at every point of GFRP. Micro-computed tomography measurement and injection molding simulation are used to obtain the fiber orientation tensor. The two-step mean-field homogenization method is applied to calculate the mechanical behaviors of the PA66GF30 GFRP with distributed-orientation fibers based on the fiber orientation tensor. Reverse engineering is used to obtain the optimized parameters of J2-plasticity and Tsai-Hill three-dimensional transversely isotropic stain-based failure criterion. Moreover, the integral mapping method can complete the transformation of the fiber orientation tensor from injection simulation to structure simulation model. The proposed integrated approach with the optimized parameters is verified by predicting the ring samples’ behavior from injection plates. The results from this investigation are expected to provide some design guidelines for GFRP composites.

Rubberized concrete properties and its structural engineering applications – An overview

This paper presents a review on rubberized concrete mixes and their properties such as strength, ductility, sound and water absorption, in addition to acid and sulphate resistance. Moreover, it discusses a review about using rubberized concrete in structural elements and its effect on ultimate compressive strength and ductility. Rubberized concrete mixes exhibit lower strength than ordinary concrete mixes. On the other hand, rubberized concrete has higher ductility and energy dissipation behaviour. Rubberized concrete with its lightweight showed a high resistance to freeze-thaw and sulphate and acid attacks in comparison with ordinary concrete. The most common structural member is Rubberized Concrete Filled Steel Tubes (RuCFST). In addition to the aforementioned merits of rubberized concrete, the confining effect of the steel tube recoups the reduction in concrete compressive strength caused by rubber inclusion. Limited researches concerned in strengthening and repairing of deficient Concrete Filled Steel Tubes (CFST) with different types of Fibre Reinforced Polymers (FRP). There is noticeable effect of using these FRP materials on RuCFST sections, ultimate strength and ductility

Materials for lightweight electric motors – a review

Electric motors are widely used in automobiles and large electric vehicles would be introduced in market in the near future to reduce global warming. Reduction in electric motor weight also reduces the overall weight of automobiles. The use of fiber-reinforced polymer materials reduces the weight of electric motors. Lightweight electric motors promote energy savings owing to the reduction of self-weight. Researchers all over the World are trying to make all parts of electric motors using lightweight materials. This review paper presents the outcome of research carried out by researchers from Germany and UK. Fiber reinforced plastics (FRP) reduce weight and increase mechanical and electrical properties. Phenolic composite materials gave promising results due to its electrical insulation properties and corrosion resistance. Thermosets do not swell when they are exposed to chemicals unlike thermoplastics. Aluminium matrix composites (AMC) are used to improve the motor efficiency resulting in a considerable weight reduction. Electric motors have 90 percent or above, which means that a high mechanical energy is derived from electrical energy. The remaining electrical energy is converted into heat. To prevent overheating, the heat is conducted through housing to a cooling jacket having cold water. Researchers have replaced the circular wire by rectangular flat wire that can be coiled tightly on the stator. Newer cooling concepts are developed for making housings using polymer materials. Carbon fiber reinforced materials with metal pins are used for reducing weight and to increase thermal conductivity. Use of high modulus fibers increase damping properties and reduce noise produced by electric motors. Comparisons between electric motors made of lightweight materials and traditional metals in terms of weight, efficiency, cooling rate are presented.

Effect of Silane Coupling Treatment on the Adhesion between Polyamide and Epoxy Based Composites Reinforced with Carbon Fibers

The increasing efforts aimed to design structures with reduced weight and better mechanical performances has led in recent years to a growing use of fiber reinforced polymer materials in several fields such as marine. However, these materials can be composed of chemically very different elements and, hence, may be difficult to joint. This research aims to improve the adhesion between a thermoplastic matrix of polyamide reinforced with short carbon fibers (PA12-CR) and a carbon fiber reinforced epoxy matrix (CFRP). Two different silane coupling agents, (3-Aminopropyl)trimethoxysilane (AM) and (3-Glycidyloxypropyl)trimethoxysilane (EP), were applied, through the spray deposition method, on the PA12-CR substrate to create a reactive layer between the adherents. Different deposition methods and coupling agents curing conditions were also investigated. The wettability of the PA12-CR surface as well as the chemical modifications induced by silane treatments were investigated through contact angle and Fourier Transform Infrared spectroscopy (FTIR) analyses. Furthermore, the interfacial adhesion between PA12-CR and CFRP substrates was evaluated through Mode I delamination tests (DCB). The effectiveness of the most promising treatment was finally verified on sandwich structures, having PA12-CR printed as internal core and CFRP laminates as external skins, through quasi-static three-point bending mechanical tests. Overall, the epoxy-based silane (EP) allowed significantly better resistance to the delamination up until the tensile failure of the CFRP substrate.

Depth resolved pulse compression favourable frequency modulated thermal wave imaging for quantitative characterization of glass fibre reinforced polymer

InfraRed Thermography is an expeditiously growing non-destructive testing and evaluation technique widely used to estimate the subsurface defect details in fibre reinforced polymer materials due to its remote, fast, easy, safe and wide area monitoring abilities. In order to explore the details of subsurface anomalies in active infrared thermography, a modulated heat flux with a predefined intensity and bandwidth is employed to excite the test sample. Among various widely used active infrared thermographic techniques for non-destructive testing and evaluation applications, pulse based and modulated lock-in thermography are predominantly in use. However, these conventional techniques limits their applicability due to high peak power heat source requirements (pulse based techniques) and poor resolution (modulated lock-in thermography) for detecting the defects located at various depths of different lateral dimensions. The present paper highlights a pulse compression favourable frequency modulated thermal wave imaging which can be carried out with moderate peak power heat sources in a limited span of time with improved test resolution and sensitivity. Further the proposed experimentation is validated with the analytical as well as numerical simulations on glass fibre reinforced polymer samples having flat bottom hole defects.

Material-structure integrated design optimization of GFRP bridge deck on steel girder

Design optimization of fiber-reinforced polymeric (FRP) composite products is essential to facilitate their applications in engineering structures. For bridge structures, the main design optimization goals are the reduction of FRP material consumption and the structure weight, which aim to reduce the initial construction cost and achieve a longer bridge span. Compared with conventional steel–concrete composite bridges, FRP-steel composite bridges possess more design variables and more complex design process, which necessitate the simplified optimization models. This paper aims to propose a two-scale design optimation method for FRP bridge deck on the steel girder. The macro behavior of the pultruded FRP composite bridge deck is analyzed. Regarding the micro level, the equivalent properties of pultruded GFRP lamination are calculated by combining micromechanics and classical lamination theory (CLT). The above-mentioned macro pultruded GFRP bridge level and the micro fiber/resin level were bridged based on the assumption that the micro-component effective homogenized strain equals to the corresponding macro strain. The two-scale lamination optimization of pultruded GFRP bridge deck is finally achieved by finding optimized two-scale design variables that can achieve the minimum bridge weight or the lowest initial construction cost with all listed constraint requirements satisfied. A pultruded FRP deck supported on equally-spaced steel girders was selected as a case study to show how to obtain the optimized two-scale parameters by using this proposed optimization method. The optimized results of the top flange thickness, tu, the bottom flange thickness, tl, the web height, hw, and the web thickness per meter, tw, are 46.02 mm, 45.86 mm, 300.0 mm and 37.42 mm, respectively. Results also showed that the optimized ratio of the 0°-lamina, 45°-lamina, and the 90°-lamina are77.9%, 17.1%, 5.0%. The optimized fiber volume fraction is 65.2%.

Investigation of Wooden Beam Behaviors Reinforced with Fiber Reinforced Polymers

Wood material can be demolished over time due to different environmental factors. Structural elements may need to be strengthened over time as a result of possible natural disasters or during use. Beams are elements under load in the direction perpendicular to their axes. Therefore, they are basically under the effect of bending. When the studies on the behavior of beams against bending test are examined, it is known that the bottom surface of the material generally breaks. For this reason, fiber reinforced polymers (FRP) materials have been used in recent years to reinforce beam members. It is a scientific fact that it is necessary to prefer FRPs for the solution of this problem, as well as their properties such as lightness, corrosion and flexibility, their application without disrupting the appearance of wood.In this study, it was aimed to investigate the effect of reinforcing wooden beams with fiber reinforced polymer materials with different properties on different bending behaviors such as load bearing capacity, ductility, modulus of elasticity. It was observed that the ductility and bearing capacity of wooden beams reinforced with fiber reinforced polymer materials increased significantly compared to non-reinforced beams.

Energy dissipation in adhesive and bolted pultruded GFRP double-lap joints under cyclic loading

Fiber-reinforced polymer (FRP) structures, due to their low mass, are valuable alternatives to traditional steel or concrete structures in seismic areas. However, to resist seismic actions, FRP structures must be able to dissipate a significant amount of inelastic energy. Since FRP materials are brittle, this dissipation must occur in the joints. Monotonic tension and cyclic tension–compression experiments were thus performed on adhesive and bolted double-lap joints composed of pultruded glass fiber-reinforced polymer (GFRP) profiles; a flexible adhesive was used in the adhesive joints. A significant amount of energy was dissipated in the adhesive joints at lower and medium displacement rates through viscoelastic friction and damage in the adhesive, while almost no energy dissipation occurred at the highest rate. The energy in the bolted joints was dissipated by progressive crushing and shear-out failures in the inner laminates. Although the dimensions and monotonic strength of the adhesive and the bolted joints were similar, the former dissipated significantly more energy at the two lower applied displacement rates. The obtained results can contribute to the seismic design of inelastic joints in FRP structures.

Flexural Behavior of Concrete Beams Strengthened with Polyurethane-Matrix Carbon-Fiber Composites

Abstract Fiber-reinforced polymer (FRP) materials have been increasingly used for external strengthening of reinforced concrete (RC) infrastructure. However, the focus has been almost exclusively o...

Environmental Durability of FRP Bar-to-Concrete Bond: Critical Review

Abstract Although fiber-reinforced polymer (FRP) materials are considered noncorrosive, the FRP bar surface resin has been shown to deteriorate when exposed to aggressive environments and this can ...

Transverse Fracture Behavior of Pultruded GFRP Materials in Tension: Effect of Fiber Layup

This paper presents an experimental study about the transverse tensile fracture properties of several off-the-shelf pultruded glass fiber-reinforced polymer (GFRP) materials, with different fiber layups and geometries and significant variations of elastic and strength properties. Determining these fracture properties should enable more-accurate advanced numerical simulation of the failure behavior of pultruded GFRP materials and members used in civil engineering applications, namely in the analysis of structural connections or members subjected to concentrated loads (web-crippling phenomenon). For the different GFRP materials, based on compact tension (CT) and wide compact tension (WCT) tests, both the critical energy release rate (Gc) and the cohesive law were determined at the laminate level, applying the following four data reduction methods: standardized analytical expressions, J-integral, Compliance Calibration (CC), and Modified Compliance Calibration (MCC). The CT tests were unsuccessful in reaching a stable propagation stage and provided overestimations of Gc. Conversely, the WCT tests were able to achieve a stable propagation stage and thus provided more-consistent estimates of Gc and cohesive laws. Among the various data reduction methods, a good agreement was found between visually based methods. On the contrary, the MCC method was found to provide significantly lower estimates of Gc when compared with the remainder. Different reasons for this variation are identified and discussed. The sample of GFRP materials presented a significant variation of Gc, which was found to be highly dependent on the fiber architecture: (i) for the material with weaker transverse reinforcement layers, consisting only of continuous filament mats, Gc ranged between 6.6 and 10.7 N/mm; (ii) materials presenting cross-ply layers presented intermediate Gc values, ranging from 13.1 and 21.3 N/mm; and (iii) materials comprising quasi-isotropic layups presented the highest overall Gc estimates, ranging from 19.3 N/mm (similar to cross-ply materials) to above 150 N/mm.

Axial compressive behavior of partially CFRP confined seawater sea-sand concrete in circular columns – Part I: Experimental study

Due to the extraordinary corrosion resistance of fiber-reinforced polymer (FRP), the use of seawater sea-sand concrete (SSC) combined with FRP materials becomes highly attractive in the constructions of coastal and marine infrastructures. To this end, a total of 40 CFRP confined seawater sea-sand concrete cylinders are constructed and tested under axial compressive load in this study. The main variables of the test include the concrete type, CFRP strengthening schemes and the number of CFRP layers. The failure modes, axial stress-strain curves, lateral strain-axial strain relationships and CFRP hoop strain distributions of the specimens are analyzed systematically. It can be detected from the test results that both unconfined and CFRP confined SSC exhibited similar mechanical properties compared with the corresponding specimens cast with normal concrete. Moreover, the clear spacing ratio and the confinement stiffness of CFRP were found to be the two most important factors in accounting for the axial compressive behaviors and the dilation properties. Finally, a new stress-strain model proposed in this paper and several existing models were used to predict the ultimate conditions of CFRP partially wrapped columns in this test. The accuracy and reliability of each model were verified and discussed by comparing the test observations and theoretical predictions.

Mitigation of IC debonding in FRP-plated concrete slabs using patch anchors

Reinforced concrete (RC) slabs can be strengthened using fiber reinforced polymers (FRPs) to enhance their flexural and shear resistance. However, premature debonding of the FRP material limits the level of strengthening achievable and represents an under-utilization of the FRP material. As a result, a variety of anchorage systems have been explored by researchers in an attempt to prevent or delay this type of failure. This paper presents a new FRP patch anchorage system which can be used to mitigate the commonly-observed failure mode of intermediate crack-induced (IC) debonding. This is the first experimental application where patch anchors are investigated in flexurally-strengthened RC slabs. Seven slabs 2700 mm × 400 mm × 150 mm in size were tested. Of these, two were unstrengthened, three were strengthened with 100 mm wide × 1.4 mm thick FRP sheet and two were strengthened in the same manner and anchored with four patch anchors. The use of patch anchors showed significant enhancement of both the strength and ductility of RC slabs compared with unanchored specimens.

Light FRP Strengthening of Poorly Detailed Reinforced Concrete Exterior Beam–Column Joints

Abstract Experiments have demonstrated the effectiveness of fiber-reinforced polymer (FRP) materials for the seismic strengthening of deficient reinforced concrete (RC) beam–column joints. However,...

Reliability Analysis of FRP-Confined Concrete at Ultimate using Conjugate Search Direction Method.

In this paper compressive strength and ultimate strain results in the current database of fiber-reinforced polymer (FRP)-confined concrete are used to determine the reliability of their design space. The Lognormal, Normal, Frechet, Gumbel, and Weibull distributions are selected to evaluate the probabilistic characteristics of six FRP material categories. Following this, safety levels of the database are determined based on a probabilistic model. An iterative reliability method is developed with conjugate search direction for evaluating the reliability. The results show that Lognormal and Gumbel distributions provide best probability distribution for model errors of strength and strain enhancement ratios. The developed conjugate reliability method provides improved robustness over the existing reliability methods owing to its faster convergence to stable results. The results reveal that the part of the database containing normal strength concrete (NSC) heavily confined (i.e., actual confinement ratio (flu,a/f’co) > 0.5) by low and normal modulus carbon fibers (i.e., fiber elastic modulus (Ef) ≤ 260 GPa) and moderately confined (i.e., 0.3 ≤ flu,a/f’co ≤ 0.5) by aramid fibers exhibits a very high safety level. The segments of the database with a low and moderate safety level have been identified as i) NSC moderately and heavily confined by higher modulus glass fibers (i.e., Ef > 60 GPa), ii) high strength concrete (HSC) moderately and heavily confined (i.e., flu,a/f’co > 0.3) by glass fibers, iii) HSC lightly confined (i.e., flu,a/f’co ≤ 0.2) by carbon fibers, and iv) HSC lightly confined by aramid fibers. Additional experimental studies are required on these segments of the database before they can be used reliably for design and modeling purposes.