FRP Composites Research Articles

Modeling Reinforced Concrete Beam with Reinforced Internal Failure by FRP and Comparing It with Laboratory Sample

Diagnosing type and amount of deficits in beams and structure is highly important in terms of performance and impact. Despite of paramount studies on CFRP application, its usage as Strips can be mentioned as one of the most important ways. Using Half Scale in building structure and lab beams would provide more adducible results. Considering type of breakdown and its progress, the growth cracks on the surface of beams is different. In all constructions, the manner of implementation and the quality of materials are two important principles in terms of performance and efficiency of the structure. In present study, type breakdown in the beam of reinforce concrete is addressed in a nondestructive manner. In this technique, by using finite element method in identifying beam breakdown without creating an unstable condition, one can achieve a nondestructive situation in experiments which is significantly cost – effective. Hence, 16 250mm × 250mm × 2100mm concrete beams were built and divided into two groups with and without FRP composite. Each group has a control beam and remained samples have breakdown in concrete and rebar. Prepared beams were put in a 4 – point experiment and, upon gathering and analyzing relevant data, beams prototyping was begun. By using finite element method, all beams were prototyped in lab. The findings from prototyping and lab analyses are compared in the format of load – location change graph. One can consider the results of prototyping as a proper approximation of lab samples.

Seismic vulnerability assessment and retrofitting of historic masonry building of Malek Timche in Tabriz Grand Bazaar

Tabriz Bazaar is the first Bazaar in the world that was registered in the world heritage list of the UNESCO in August 2010. Malek Timche is one of the important and beautiful parts of Tabriz Bazaar. The objective of this research is to assess the seismic vulnerability, structural behavior and failure mechanisms of this historic building, and to propose an appropriate method for retrofitting and improving the seismic performance. The subject is studied in four main steps. To determine the mechanical properties of constructional materials, three-point bending test and compression test are carried out initially. Then, a three-dimensional model of the Malek Timche is established using finite element method, and the static, modal, and dynamic analysis are performed. In the third step, 16 possible failure mechanisms are obtained based on the stress contours achieved from dynamic analyses using the simplified kinematic method based on the Italian code, OPCM 3431. Finally, by using the results of the structural analysis, walls and domes of the structure are strengthened by reinforcements and FRP composites, respectively.

Performance of damaged RC continuous beams strengthened by prestressed laminates plate: Impact of mechanical and thermal properties on interfacial stresses

Strengthening of reinforced concrete beams with externally bonded fiber reinforced polymer plates/sheets technique has become widespread in the last two decades. Although a great deal of research has been conducted on simply supported RC beams, a few studies have been carried out on continuous beams strengthened with FRP composites. This paper presents a simple uniaxial nonlinear analytical model that is able to accurately estimate the load carrying capacity and the behaviour of damaged RC continuous beams flexural strengthened with externally bonded prestressed composite plates on both of the upper and lower fibers, taking into account the thermal load. The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened beam, i.e., the damaged concrete beam, the FRP plate and the adhesive layer. The flexural analysis results and analytical predictions for the prestressed composite strengthened damaged RC continuous beams were compared and showed very good agreement in terms of the debonding load, yield load, and ultimate load. The use of composite materials increased the ultimate load capacity compared with the non strengthened beams. The major objective of the current model is to help engineers' model FRP strengthened RC continuous beams in a simple manner. Finally, this research is helpful for the understanding on mechanical behaviour of the interface and design of the FRP-damaged RC hybrid structures.

Study of hourglass-shaped specimens for the analysis of compression behaviour in fibre direction of FRP composites using compression and four-point bending tests

Flat hourglass specimens are proposed to assess the compressive behaviour of FRP utilizing two testing techniques. The hourglass shape helped to ensure failure at the centre of the specimen and to minimize in-plane stress concentration in this zone. Four-point bending tests are carried out and measures are performed via DIC. A procedure to calculate bending moment is proposed and validated in presence of large displacements. To evaluate the specimen and the method proposed, two different materials were tested, an E-glass/Epoxy unbalanced woven and a Carbon/PEEK balanced woven. In a second time ASTM D695 compression tests are carried out on the E-Glass/Epoxy composite to compare the hourglass specimens to the standardized dog-bone. The two testing techniques are analysed and compared.

A coupled framework of variational asymptotic method based homogenization technique and Monte Carlo approach for the uncertainty and sensitivity analysis of unidirectional composites

This article describes a computational framework, based on the variational asymptotic method unit cell homogenization technique coupled with the Monte Carlo method, for carrying out uncertainty and sensitivity analysis of the effective properties of fiber reinforced plastic composites. As an application, univariate and multivariate analysis have been undertaken to investigate the influence of the constituent material properties on the effective properties of the FRP composites. Both bivariate and global sensitivity analysis results are presented to highlight the contribution of the uncertainty in the properties of the constituent materials on the uncertainty in the effective properties. Model predictions are validated by comparing the results with data reported in literature.

Experiences With Using of Loading Tests and the “design Assisted by Testing” Method for the Determination and Verification of Structural Members and Details

This paper describes experiences with use of different types of experiments (i.e. loading tests) as well as with use of socalled “Design assisted by testing” method given in the standard “Eurocode 1”. Both these mentioned ways are useful in case of a determination and verification of important design parameters, material properties and load-carrying capacities (in case of different types of stresses, used materials or geometric configurations of designed constructions or their elements and details). In this area, during recent years, large number of miscellaneous loading tests have been performed at the authors’ workplace. Therefore, all presented information and all described experiment results in this article are directly based on solved experimental (and theoretical) research programs carried out at Institute of Metal and Timber Structures at the Faculty of Civil Engineering at Brno University of Technology in cooperation with research institutes and companies in the Czech Republic. Most of all research projects were focused on the load-carrying capacity determination as well as on the knowledge about an actual behaviour and failure mechanisms of steel and steel-concrete structural members and details (recently of members made of FRP or GFRP composite, too), usually in case of verification of either existing or newly designed building or bridge structures.

Usage of antimony trioxide, aluminum hydroxide and zinc borate in GRP composite production as fire-retardant additives: An experimental research

In this study, it was aimed to investigate the usability of compounds in inorganic structure and the effect of these compounds used in composites on the mechanical properties of composites in order to give fire retardant properties to glass fiber reinforced polyester composites (CTP). Antimony trioxide (Sb2O3), aluminum hydroxide (Al(OH)3) and zinc borate (2ZnO3.BrO3.3H2O) were added by different proportions (5%, 10%, 15%, 20%, 25%, 30%) to resin blends to improve the non-flammability of the composites. In experimental study, the combustion behavior of the doped CTP composites produced using different inorganic compounds was determined by international combustion standards ASTM D-635, ASTM D-3801 and ASTM D-5048. In addition, thermogravimetric analysis (TGA) was applied in order to determine the thermal behavior of the produced GRP composites due to temperature increase and tensile test were applied according to ASTM 638-14.As a result, when the flame retardant additive ratio is 15% or more in the GRP composites, the hand lay production became difficult due to the increase in viscosity. According to ASTM D-3801, when 30% AH is used, non-combustible material in V1 class can be produced. All FRP composites containing flame retardants were included in the HB - slowly burning material class. Flame retardant use generally reduced the tensile strength of GRP composites, but it was found that 10% increase in AT-doped CTPs.

Comparison of Ultrasonic Methods for Detecting Defects in Unidirectional Composite Material

Non-destructive tests are of pivotal importance in the industry, as they contribute to the decreasing of maintenance costs, reducing downtime and accidents. Ultrasound is a non-destructive method that can be used with several arrangements to identify faults in engineering materials. This work evaluated the use of three ultrasonic methods applied in FRP composites to detect manufacturing defects. The critically refracted longitudinal wave (LCR), the B-Scan images, and the signal-to-noise ratio of TFM (Total Focusing Method) images were compared to detect the delamination and the fiber waviness in unidirectional composite of carbon/epoxy. Rectangular samples without defects and with defects were used in the tests. To obtain the delamination in the samples, pieces of Teflon were placed between layers and for the samples with waviness, a silica sphere was used. The results showed that LCR wave is not recommended to detect these kinds of defects, the B-Scan image is efficient in detecting delamination, and the SNR variation of TFM images allows to identify the waviness and delamination in unidirectional FRP composites.

Numerical simulation of a composite shell for underwater application using CFD and FEA

In the present investigation, an attempt has been made to use fiber-reinforced composite material in place of metal for a shell used for underwater applications which is majorly subjected to hydro-static pressure. The study comprises the use of popular numerical techniques such as finite volume and finite element methods. CFD tool ‘ANSYS fluent’ which works based on finite volume method is used for the fluid flow simulation to get the forces acting on the structure. Structural analysis is performed for the imported loads from CFD result onto the structure with one-way fluid-structure coupling. FEM tool ‘ANSYS static structural which works based on finite element method is used for obtaining deformations and stresses in the shell. A sufficient number of iterations are made to get convergence of the numerical solution. Alternatives such as increasing the shell thickness and/or providing stiffeners to the shell are suggested to replace the metallic structure with FRP composites.

Impact of thermal effects in FRP-RC hybrid cantilever beams

This paper presents a theoretical approach of the structures reinforced with bonded FRP composites, taking into account loading model, shear lag effect and the thermal effect. These composites are used, in particular, for rehabilitation of structures by stopping the propagation of the cracks. They improve rigidity and resistance, and prolong their lifespan. In this paper, an original model is presented to predict and to determine the stresses concentration at the FRP end, with the new theory analysis approach. The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened beam, i.e., the concrete beam, the FRP plate and the adhesive layer. The theoretical predictions are compared with other existing solutions. The numerical resolution was finalized by taking into account the physical and geometric properties of materials that may play an important role in reducing the stress values. This solution is general in nature and may be applicable to all kinds of materials.

New proposal for flexural strengthening of a continuous I-steel beam using FRP laminate under thermo-mechanical loading

Construction materials such as composites are used recently for the reinforcement and rehabilitation of structures subject to risks of partial or total degradation during their service, which are due to either poor design, overload or a charge assignment. The use of fibers is a new technique which gives additional rigidity and resistance to structures. In this research, we develop an approach which makes it possible to analyze the interfacial constraints which are the cause of the delamination phenomenon at the level of the structure, for a continuous steel beam bonded by a FRP laminate plate, under thermo-mechanical loading coupled with the shear lag model. In such plated beams, shear forces develop in the bonded beam and these will be transferred to the FRP plate via the adhesion technique. Thus, the interfacial shear stress and normal stress will develop consequently, and debonding may occur at the FRP plate ends due to high interfacial stress values in this area. This original research aims to study the debonding phenomenon using an analytical model, in order to identify the interfacial stresses of a continuous steel beam strengthened by the FRP plate with taper model, taking into account a new coupled approach of thermomechanical loading effect. Finally, numerical comparisons between the existing solutions and the present solution enable a clear appreciation of the effects of various parameters. This article explores the effects of various parameters related to the subject, such as the effect of thermal loading, geometrical and physical properties, on the stress behavior of FRP composites. This solution is intended for application to beams made of all kinds of materials bonded with a thin composite plate. For steel I-beam section, a geometrical coefficient q is determined to show the effect of the adherend shear deformations. This research is helpful for the understanding on mechanical behaviour of the interface and design of such structures.

A novel study of flexural behavior of short glass fibers as secondary reinforcements in GFRP composite

As the commercialization of fiber-reinforced polymer composites is gaining momentum, new strategies for improving their mechanical properties are constantly being investigated by researchers worldwide. The key to enhanced mechanical properties of FRP composites is improved load transfer capabilities and stronger interfacial bonding at the fiber/matrix interface. A novel idea to fabricate laminated composites with the short fiber modified epoxy can address both these conditions and strengthen the composite. In this study, short glass fibers (0.2–0.5 cm chopped from glass fiber sheets) of concentrations 0.1 wt%, 0.3 wt% and 0.5 wt% of epoxy were incorporated into epoxy matrix, which was then used for fabrication of laminated glass fiber reinforced, short glass fiber modified epoxy composites (SGF-GE). Samples from the prepared composite were put to flexural testing and compared. 0.1% SGF-GE, 0.3% SGF-GE, 0.5% SGF-GE showed higher flexural strength than neat glass/epoxy composites (GE) with 0.1% SGF-GE showing the highest among all. Only 0.1% SGF-GE showed higher flexural modulus than neat GE composites, others showed lower values. Good dispersion and minimal agglomeration shown by short fibers in 0.1% SGF-GE composite is the key to enhanced flexural properties. Fractographic analysis using Scanning Electron Microscope was done to observe the distribution of the short fibers and derive conclusions on their role in enhancing the flexural properties of the composite.

Modelling and Validation of the Composite Shell of a Train Seat

The subject of the modelling work and the conducted experiments is the composite shell of a train seat. The activities carried out involved designing the geometry, planning the material structure, and selecting the materials to be used. The shell was built using polymer matrix fibrous composites (i.e. FRP – Fibre Reinforced Polymer – composites), which are lighter than steel and comply with the relevant standards for strength and safety at the same time. This was followed by creating a computational model for the shell and conducting a strength analysis in accordance with the guidelines of the relevant industry standard and strength hypotheses adopted for FRP composites. The calculations were conducted using ANSYS Composite PrepPost software based on the finite element method. The article offers a strength analysis of an optimised composite shell of a train seat. Based on the guidelines obtained as a result of the conducted modelling work, a physical prototype (validation model) of the seat was created. Hot vacuum lamination technology was applied in the production process. The experimental validation of the model, producing a positive result, was conducted using a test stand owned by S.Z.T.K. TAPS – Maciej Kowalski. Keywords: train seat structure, FRP composite, FEM modelling, experimental validation

A neuro-fuzzy approach to predict the shear contribution of end-anchored FRP U-jackets

The current study targets to estimate the contribution of the end-anchored FRP composites in resisting shear force using a soft computing tool i.e., adaptive neuro-fuzzy inference system (ANFIS). A total of 107 sets of data accumulated from literature was utilized for the development and evaluation of the current ANFIS model. A comparative analysis between the ANFIS predictions and the acquired experimental results has shown that the ANFIS predictions are in very good agreement with that of experimental ones. Additionally, the accuracy of the current ANFIS model has been weighed up against the estimates of nine widely adopted design guidelines. Based on various statistical parameters, it has been deduced that the effectiveness of the current ANFIS model is better than the considered design guidelines. Besides this, a parametric study was carried out to explore the combined effect of different parameters as well as the impact of individual parameters.

Analytical modeling of FRP hubbed flanges

In spite of the increasing use of FRP composites in bolted flange joints and the good knowledge of these structures and their material behavior the procedure used for their design is that of metallic flanges. There is a major concern to appropriately address the anisotropic behavior of composite materials in FRP flange design. Therefore, it is necessary to revisit this procedure by implementing a more suitable model to analyse the stresses and strains of FRP bolted flange joints.This paper presents an analytical model that treats FRP bolted flange joints integrity and tightness based on anisotropy and a flexibility analysis of all joint elements including the gasket, bolts and flanges. The theories that treats all parts of the flange are described in details. Finally, the developed analytical model is validated with experimental testing and numerical modeling of different size FRP flanges.

Compressive behavior of extremely low strength concrete confined with low-cost glass FRP composites

In this study, a total of 24 cylindrical concrete specimens were constructed and strengthened using locally available and Low-Cost Glass Fiber Reinforced Polymer (LC-GFRPs) composites. The considered research parameters were the strength of un-confined concrete (5 MPa and 15 MPa) and the confinement level (one, two, and three layers of LC-GFRP). The specimens were tested to failure under pure axial compression. The results indicate that LC-GFRPs are very beneficial to modify the ultimate load-carrying capacity and ductility of the confined concrete. In the end, the existing expressions, developed mainly for special purpose traditional FRPs to estimate the ultimate strength and strain of the confined concrete, were utilized to assess their application to the LC-GFRP confined concrete. It was found that all considered models are well capable to estimate the ultimate strength of LC-GFRP confined concrete but those models were not able to accurately predict the ultimate strain of the LC-GFRP confined concrete.

Behavior of eccentrically loaded rectangular RC columns wrapped with CFRP jackets under different preloading levels

Due to service loads during the FRP strengthening procedure in practical engineering, existing RC columns are subjected to a critical compression stress, which indicates that the effect of preload on the confinement provided by FRP composites should be considered. Against this background, an experimental investigation was performed to explore the performance of eccentrically loaded rectangular RC columns with different CFRP strengthening schemes and preloading levels. The results show that the load-bearing capacity and ultimate deformations of the specimens can be significantly enhanced after CFRP strengthening. In specific, the full wrapping strategy was more effective than CFRP strips for columns under a small eccentricity, while increasing the number of longitudinal CFRP layers on the tensile side of the specimens can achieve better strengthening effect for specimens under a large eccentricity. Moreover, the preload was found to have a detrimental effect on the load-bearing capacity and ductility of the specimens. Finally, a new stress-strain model of FRP-confined concrete considering the preload effect was proposed based on a collected database from the relevant literature. The axial load and bending moment capacity of the selected columns were calculated by using different stress-strain models; comparisons between the experimental observations and theoretical calculations revealed that better performance can be achieved by the proposed model.

Study on mechanical and thermomechanical properties of flax/glass fiber hybrid‐reinforced epoxy composites

AbstractA hybrid fiber‐reinforced plastic (HFRP) composite is defined as a composite material that is reinforced by two or more continuous fiber materials in the same resin matrix. This article used the hand layup method to prepare epoxy‐based flax and glass HFRP composites. Under the same fiber hybrid ratio, the interlayer and sandwich hybrid lamination methods were used for mechanical properties testing of the composite. The tensile and bending properties of the HFRP composites were obtained by tensile and three‐point bending tests, and the cross‐sectional morphology of the material was observed by a scanning electron microscopy. The thermomechanical properties of the HFRP composite were analyzed by the dynamic mechanical thermomechanical analysis (DMTA). The results showed that the effect of the different layup methods on the tensile properties of the HFRP composite material was less than the effect of the bending properties, and the bending properties showed a significant positive effect for the hybrid composites. When the glass fiber sheet was used as the core layer and the flax fiber sheet was used as the surface layer, the hybrid composites had improved bending properties, and their bending strength and flexural modulus were approximately 3.22 times and 3.81 times that of flax FRP composites, respectively. The storage modulus and glass transition temperature of the HFRP composites were higher than those of flax FRP composites as they increased by 84.1% and 8.01°C, respectively.

A novel optimization approach for bonded tubular gap K-joints made of FRP composites

Composite structures have wide applications in mechanical and civil-structures due to low weight-to-strength ratio. Such structures consist of several joints, which may run a risk of eventually weakening a structure around the joint region, particularly in case of excessive weight. It is, therefore, necessary to design the structures and optimize their geometric parameters to limit the chances of failures. The present study focuses on the laminated FRP composite made bonded tubular gap K-joint (α = 30°) with triangular adhesive fillet under axial compressive loading. The modeling and analysis were conducted by using the Finite Element (FE) based software ANSYS. The aim of this study is to optimize the different joint parameters, based on a failure criteria and ply-stacking sequence. The modeling procedure was validated with available experiment records and Finite Element Method (FEM) results. The geometric parameter tc = 6.0 mm tb = 4.4 mm and fr = 24.49 were taken with the help of the failure criteria, and also an empirical equation was suggested to predict the failure index. These parameters were further optimized using the Genetic Algorithm (GA) and reduce the failure index up to 20.0% and 23.8% for Bottom Toe Line (BTL) and Top Toe line (TTL) respectively. Finally the minimum value of the failure index was obtained by using the different ply stacking sequence and cross-ply stacking sequence gives the minimum value of failure index at BTL as well as TTL.

Opportunities for Recycling of Fiber-Reinforced Plastics Under Technical, Economic and Social Aspects

Fiber-reinforced composite plastics have been in extensive use across various industries. Owing to their properties of being lightweight materials with high strength to weight ratio; durability; stiffness; resistance to corrosion, wear, impact and fire, makes them suitable for applications in mechanical, construction, automobile, aerospace, marine and many other manufacturing industries. But this growing application of has also led to a research into the recycling and reuse of FRP composites and its recyclates. FRP recyclates have been found to be useful in various industries and also lower environmental pressure. This paper draws upon this opportunity of FRP recycling and studies its technical, economic and social aspects. The paper aims to develop an understanding to the dearth of recycling procedures available and thus highlights the importance of focused research in this area.