Fiber Reinforced Polymer Materials Research Articles

An Ordinary State-Based Peridynamic Model of Unidirectional Carbon Fiber Reinforced Polymer Material in the Cutting Process

Due to the complexity of the composite structure, analyzing the material failure process of carbon fiber reinforced polymers (CFRP) is fairly difficult, particularly for the machining process. Peridynamic theory, a new branch of solid mechanics, is a useful tool for dealing with discontinuities. This study presents an ordinary state-based peridynamic (OSB-PD) model for unidirectional CFRP material in the cutting process. In this model, angle tolerance is used to overcome the fiber angle limitation in a classical OSB-PD laminate method, and the short-range force approach is utilized to simulate the contact of the cutting tool and workpiece. The effectiveness of the supplied models is validated by tension and cutting tests. Finally, it can be indicated that the OSB-PD model is capable of predicting machined surface damage and cutting force, based on the comparison of simulation and experimental data.

Retrofitting of Shear Compression Failure-Critic Short Columns with a New Technique

One of the reasons that cause the collapse of buildings is deficient short columns, which need to be retrofitted to prevent the collapse of the building in a potential earthquake. External reinforced concrete (RC), steel plates, and fiber-reinforced polymer (FRP) jacketing are standard retrofitting methods to retrofit columns to increase their shear capacity. However, in compression shear failure, the effectiveness of steel and FRP jacketing is quite limited due to the premature buckling of the FRP and steel material. On the other hand, RC jacketing is not practical because it requires more labor and covers more architectural places. Thus, the main motivation of this study is to present the effectiveness of a new method to retrofit short columns, including those with dominated shear compression failure. For this purpose, HSPRCC (high-performance steel plate-reinforced cementitious composite) was adapted to retrofit such short columns. This method is a combination of high-performance concrete and perforated steel plates. Short-column specimens representing existing RC buildings were retrofitted using the HSPRCC and tested. Perforated steel plates anchored to the specimen by steel bolts and repair mortar are used as a matrix. The retrofitted specimens were found to exhibit much better performance both in terms of shear strength and deformation capacity. It was also observed that the retrofitting method is effective in contributing to increasing the compression shear capacity.

Development of a unified design buckling curve for fibre reinforced polymer plates subjected to in-plane uniaxial and uniform compression

Presented are 24 non-dimensional buckling curves to estimate the strengths of Fibre-Reinforced Polymer (FRP) square plates having four simply supported edges and subjected to in-plane uniaxial and uniform in-plane compression. The curves are constructed by the authors from a parametric numerical analysis using ABAQUS® software with changing variables for: material properties; initial geometrical imperfections; laminate lay-ups; and plate thicknesses. These strength curves express relationships for the buckling reduction factor with plate slenderness, and account for post-buckling strength. We observe that regardless of the laminate lay-up (except for purely unidirectional), the choice of FRP material and the magnitude of the initial geometrical imperfection the predicted buckling reduction factors display a meaningful correlation with plate slenderness. Presented is a proposed unified buckling design curve, defined as the lower bound to 18 of the 24 ABAQUS®-generated buckling curves. This new curve is benchmarked by the authors against experimental test results extracted from the literature and it is found that there is a reasonable agreement. The authors recommend that the proposed buckling design curve has the potential to be introduced into structural design standards as a procedure to design the buckling strengths of FRP plates.

Parametric Study on Steel–Concrete Composite Beams Strengthened with Post-Tensioned CFRP Tendons

A sustainable environment can be achieved by strengthening the existing building to avoid new construction and by replacing the construction materials with long-lasting sustainable materials such as a fiber-reinforced polymer (FRP). Using post-tensioned (PT) FRP systems has proven to be an effective technique in strengthening the structure and decreasing cracks and deformability. In this study, a 3-D finite element model was built to investigate the flexural behavior of composite beams strengthened with external PT FRP tendons. Limited research studied the use of FRP tendons to enhance the structural behavior of composite beams. This paper represents a comprehensive study of the effect of several parameters that control the design of the FRP tendons. Parameters such as PT level, tendon material, tendon length, degree of shear connection (DOSC), and tendon profile shape were considered under loading. The 3-D model’s correctness is validated using published experimental data. It was observed that of all FRP materials, carbon FRP is the best type for upgrading the beam strength, and it was recommended to use a 30 to 40% PT level. In addition, applying external PT over the full length of the beam increases the ultimate load capacity significantly. However, due to the difficulty of construction, it was recommended to use 90% of the beam span length since the difference in beam capacity does not exceed 5%. Finally, adding PT tendons with a trapezoidal and parabola profile to composite beams significantly increases the yield load and the beam capacity.

Quasi-static modes I, II and mixed modes I/II fracture toughness of two laminate composites: Part II — micro-computerized tomography and numerical simulations

In Part I of this paper, quasi-static fracture toughness tests were reported which were carried out on two carbon fiber reinforced polymer materials. One laminate was unidirectional and the second was composed of plies fabricated from a twill fabric. In Part II, which is presented here, micro-computerized tomography was performed providing a relationship between the observed experimental behavior and the micromechanical structure of the materials. This was carried out for the double cantilever beam (DCB), mixed mode bending (MMB) and end-notched flexure (ENF) specimens. Load–displacement curves were simulated numerically by means of a cohesive zone model and the finite element method to obtain better insight into the failure mechanisms observed for DCB and ENF specimens.

Reliability-based design optimization of strengthened and reinforced glulam beams in bending

ABSTRACT Over the past 60 years, research has been carried out to provide glulam members with enhanced mechanical performance. Strengthening and reinforcing methods tested to improve the behavior of glulam beams have been predominantly focused on the use of Fiber-Reinforced Polymer (FRP) and steel products. Glulam beams with such modified cross-sections have been shown to be rational alternatives to steel and concrete counterparts in designing stiff and strong structural systems, attracting research interests for reliable long-span and heavy-loading applications. There is, however, no comprehensive study indicating which strengthening configuration is optimum. In this paper, glulam beams in bending are investigated through Reliability-Based Optimization (RBO) to propose a quantitative strengthening scheme. Seven strengthening and reinforcing configurations made in steel and FRP materials are accounted for glulam beams of lengths up to 30 m. RBO results indicate that glulam beams can be configured optimally with more sustainability. Additionally, it allows for the definition of specific safety levels for optimally reinforced and strengthened glulam beams at the lowest cost compared to non-strengthened glulam beams. Furthermore, prestressed material offers the most cost-effective way to create glulam beams that are more sustainable, strong, and safe.

Experimental Study on Compressive Behavior of Concrete Cylinders Confined by a Novel Hybrid Fiber-Reinforced Polymer Spiral.

Modern fiber-reinforced polymer (FRP)-reinforced concrete structures are excepted to achieve superior mechanical performances and long service lives, even in harsh service environments. Hybrid FRP material could potentially meet this goal with its relatively high strength-to-cost ratio. This paper presents an experimental study on the compressive behavior of concrete cylinders confined by a novel hybrid fiber-reinforced polymer (HFRP) spiral. Nine types, forming a total of 27 confined or non-confined concrete cylinders, were subjected to an axial compressive-loading test. Concrete cylinders confined either with different spiral types or different spiral spacings were comparatively studied in the experiment. The results showed that the compressive failure modes and the stress-strain relationships of the HFRP-spiral-confined cylinders were similar to those of basalt-fiber-reinforced polymer (BFRP)-spiral-confined cylinders. The actual fracture strain of the HFRP spiral (tested as a single rod) was larger than that of the corresponding carbon-fiber-reinforced polymer (CFRP) bar, indicating the advantageous composite effect of the HFRP spiral. The maximum strain of the HFRP spiral reached over 70% of its ultimate strain in the cylinders compared to the BFRP spiral, which only reached 50%. Most of the existing models overestimated the ultimate stress and strain of the HFRP-spiral-confined cylinders. Wu's model was proved to be the most accurate model, yet proper modification was required for predicting the peak strain of the HFRP-confined cylinders.

Durability of FRP bars and FRP bar reinforced seawater sea sand concrete structures in marine environments

• Combination of the alkaline and marine environments aggravates the degradation of mechanical properties of FRP bars. • The variability of mechanical properties of FRP bars shows an increasing trend. • Bearing capacities of FRP bar reinforced SSC components decrease and the failure mode changes. • Environmental reduction factors in current codes are conservative. Fiber reinforced polymer (FRP) is one of the alternatives to steel, and can be directly used in seawater sea sand concrete (SSC). But FRP material still has durability problems in corrosive environments, which is one of the hot and difficult issues of current research. Based on the existing literature, this paper combs the degradation of the long-term property of FRP bars and the durability of FRP bar reinforced SSC (FRP-SSC) structures in the marine environment. The combination of the alkaline environment of concrete and the salt ions in sea sand and seawater aggravates the dissolution of the resin and debonding of the fiber-resin interface of FRP bars (particularly for BFRP bars). Therefore, the mechanical properties of FRP bars degrade with high variability which leads to the reduction of bonding between SSC and FRP bars. Additionally, the bearing capacity of FRP bar/steel-FRP composite bar (SFCB) reinforced SSC components in marine environments decreases, and the failure mode of components changes. The current codes use environmental reduction factors in the durability design of FRP bar reinforced concrete structures. But the values of reduction factors are conservative. Finally, it is pointed out that the quantification of variability for the mechanical property of FRP bars after long-term service, and the time-dependent reliability-based design methods of components are needed for further studies.

Developing a hybrid FRP-concrete composite beam

Current materials engineering trends put forward the development of efficient structural solutions. The steel replacement with fiber-reinforced polymers (FRP) exemplifies the key to the corrosion problem. However, the relatively low deformation modulus of typical FRP materials raises the deformations of the structural components. Together with the self-weight reduction increasing the kinematic displacements, the latter issue makes developing hybrid structures comprising compression-resistant concrete and high-performance in tension FRP profiles important. Although such hybrid systems are applicable for bridge engineering, the uncertainty of the inter-component bonding properties complicates developing these innovative structures, including the design models. The typical solution focuses on the local bond improvement, e.g., employing FRP profile perforation and mechanical anchorage systems. However, this study introduces an alternative solution, using the stress-ribbon bridge structural system for creating the hybrid beam prototype, which combines the synthetic fiber-reinforced concrete slab and pultruded FRP profile fixed on the supports. This work exemplifies the structural development concept when the finite element (FE) modeling outcome defines the target reference of the design procedure. Thus, on the one hand, this innovative structure simplifies the corresponding numerical (FE) model, which assumes the perfect bond between the components of the hybrid beam system. On the other hand, the solution to the support problem (resulting from a low resistance of pultruded FRP profiles to transverse loads) improves the structural performance of the bridge prototype, doubling the structure’s flexural stiffness and load-bearing capacity regarding the weak concrete supports’ system. The bending tests proved the adequacy of this solution in describing the design reference for further development of the proposed structural concept.

Research progress of FRP in steel and masonry bridge structures reinforcement

Fiber reinforced polymer (FRP) has been widely used in the reinforcement of concrete bridge structures, and it still has a good application prospect in the reinforcement of steel and masonry bridge structures. In order to summarize the research results of FRP in the reinforcement of steel and masonry structures, broaden the ideas of FRP strengthening bridges in China and promote its wide application in the field of bridge structure reinforcement, it is summarized from the aspects of anti-fatigue reinforcement, anti-buckling reinforcement, bearing capacity reinforcement and seismic reinforcement according to the different reinforcement mechanisms. The shortcomings of the existing studies were analyzed, some problems and ideas that can be further studied were put forward. Analysis result shows that the prestressed FRP reinforcement technology has a good application prospect because of its high material strength utilization rate. Generally, the method of prestressing FRP is used to strengthen the bridge steel members with fatigue cracks, and FRP and filler materials are used to form an external reinforcement system to improve the buckling resistance of steel members. FRP reinforcement can improve the bearing capacity and seismic performance of masonry structures. Follow-up studies should be continued to develop standardized prestressed FRP reinforcement and anchorage system with long-term reliable performance, further promote the engineering application of prestressed FRP reinforced steel structures and establish the specification system of FRP reinforced masonry bridges. The durability of FRP reinforced bridges under complex environment and coupling of various factors should be deeply studied.

Research progress of FRP in steel and masonry bridge structures reinforcement

Fiber reinforced polymer (FRP) has been widely used in the reinforcement of concrete bridge structures, and it still has a good application prospect in the reinforcement of steel and masonry bridge structures. In order to summarize the research results of FRP in the reinforcement of steel and masonry structures, broaden the ideas of FRP strengthening bridges in China and promote its wide application in the field of bridge structure reinforcement, it is summarized from the aspects of anti-fatigue reinforcement, anti-buckling reinforcement, bearing capacity reinforcement and seismic reinforcement according to the different reinforcement mechanisms. The shortcomings of the existing studies were analyzed, some problems and ideas that can be further studied were put forward. Analysis result shows that the prestressed FRP reinforcement technology has a good application prospect because of its high material strength utilization rate. Generally, the method of prestressing FRP is used to strengthen the bridge steel members with fatigue cracks, and FRP and filler materials are used to form an external reinforcement system to improve the buckling resistance of steel members. FRP reinforcement can improve the bearing capacity and seismic performance of masonry structures. Follow-up studies should be continued to develop standardized prestressed FRP reinforcement and anchorage system with long-term reliable performance, further promote the engineering application of prestressed FRP reinforced steel structures and establish the specification system of FRP reinforced masonry bridges. The durability of FRP reinforced bridges under complex environment and coupling of various factors should be deeply studied.

The behavior of alkali-silica reaction-damaged full-scale concrete bridge deck slabs reinforced with CFRP bars

Steel material is susceptible to corrosion after being in an aggressive environment and chemical attacks causing major deficiencies and failure; in some cases, maintenance or repair is necessary. Consequently, carbon fiber-reinforced polymers (CFRP) materials have been innovated to replace the usage of conventional steel reinforcement. In this study, the behavior of reinforced concrete bridge deck slab has been investigated under the effect of ASR damage and internal reinforcement with CFRP bars. However, the effect of the reinforcement type (CFRP and steel), reinforcement ratio (0.38, 0.46, and 0.57) %, and ASR damage stage (without, first, second, and third) has been carried out using the NLFEA technique after a well-calibration process against available experimental data. Generally, it has been noticed that the utilization of CFRP bars significantly improved the slab's strength in compression and tension, stiffness, and modulus of elasticity. Moreover, an innovative and cost-effective reinforcing technique, using CFRP bars with a 0.38% ratio or 0.46% reinforcement ratio, represents an ideal solution to improve the ultimate load-carrying capacity, serviceability, and durability. In addition, CFRP exhibited more strain values in concrete and steel materials and decreased under exposure to ASR damage action. Under exposure to ASR damage action, both the elastic and post-cracking stiffnesses are reduced regardless of the reinforcement type. Generally, it has been observed that the resulting degradation could be approximated by a parabolic shape having a slower decreasing rate at ASR levels of 2 and 3 where the material's losing most of its mechanical properties. Finally, a linearly decreasing relationship was found between the slab's energy capability and ASR level.

Compressive behavior and analysis-oriented model of FRP-confined engineered cementitious composite columns

A total of 18 specimens of fiber-reinforced polymer (FRP) confined engineered cementitious composite (ECC) were tested under axial compression in this study. Both monotonic loading and cyclic loading were considered. Effects of different FRP materials, glass FRP (GFRP) tube and carbon FRP (CFRP) jacket, as well as different FRP thicknesses were investigated. All the specimens exhibited the typical strain hardening behavior, indicating the effective enhancement of compressive strength and strain of ECC under FRP confinement. Failure modes, stress–strain behavior and dilation behavior were presented and analyzed. The FRP-confined ECC showed large ultimate axial strains, demonstrating the superior deformability and ductility performance. Design equations were developed to predict the ultimate compressive strength and strain. Based on the test results obtained from this study and other test results collected in the literature, an analysis-oriented model was proposed to predict the overall compressive stress–strain behavior of FRP-confined ECC columns.

Behaviour Analysis of Strengthened-RC Beam with Natural Fiber Reinforced Polymer (NFRP) based on Abaca Fiber by Using Finite Element Method

The use of synthetic Fiber Reinforced Polymer (FRP) as a composite material is an alternative material that has been widely used for strengthening and repairing reinforced concrete structures. However, the high price is one of the obstacles in applying synthetic FRP materials in developing countries such as Indonesia. Utilization of natural fiber as a Natural Fiber Reinforced Polymer (NFRP) composite material is an alternative, especially in shear strengthening of reinforced concrete beams. Because it has good tensile strength and also is environmentally friendly. Technological developments in the field of computing make modelling various aspects easier. One of them is modelling reinforced concrete (RC) beams. ATENA V534 is a software that can be used for finite element-based modelling. Therefore, in this study, the ATENA V534 software was used to evaluate the results of research and testing behaviour of reinforced concrete beams from the previous studies about strengthened beam for shear by using NFRP. Behaviour that is evaluated in the form of load and deflection, the pattern of cracks and failure, and stress and strain of reinforcements. The numerical results obtained in ATENA V534 showed in a good agreement with experimental results.

Retrofitting of Beams using Fibre Reinforced Polymer

Retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion etc. Many of the existing reinforced concrete structures throughout the world are in urgent need of rehabilitation, repair or reconstruction because of deterioration due to various factors like corrosion, lack of detailing, failure of bonding between beam- column joints etc. Fibre Reinforced Polymer (FRP) composite has been accepted in the construction industry as a promising substitute for repairing and in incrementing the strength of RCC structures. It stabilizes the current structure of buildings and making them earthquake resistant. This paper presents a representative overview of the current state of using FRP materials as a retrofitting technique for the structures not designed to resist seismic action. It summarizes the scopes and uses of FRP materials in seismic strengthening of RCC structures and masonry retrofitting.

Simulation, Fabrication and Testing of UAV Composite Landing Gear

This study concerns the use of the fused filament fabrication technique to create models of the landing gear of an unmanned aircraft. These components are made of filament with short fibers (chopped fibers) of carbon fiber and fiberglass. In order to identify the material with the high mechanical strength, the designed models were subjected to a finite element analysis and to a three-point bending test, followed by a microscopic examination of the tested components. Following a comparative study, both the finite element analysis results and the three-point bending test results provided similar results, with a relative error of 2%, which is acceptable in the aviation field. After analyzing all the results, it was found that the carbon fiber-reinforced polymer material has the highest mechanical performance, with a bending strength of 1455 MPa. Among the fused filament fabricated landing gears, the one with the best mechanical performance was polyethylene terephthalate with short carbon fiber, which had a bending strength of 118 MPa. Microscopic analysis of the landing gear models, manufactured by the fused filament fabrication process, indicated the typical defects of composite filaments: voids and interlayer voids.

FRP Material for the Performance of Bridge Components Reinforcement and Improvement

Most bridges today suffer from ageing as a result of increased uses and the erosion of the natural environment. Engineers often need to focus on the actual strengthening needs in the projects they design, as each method has its own limitations and applicability, and there are gaps in the strengthening and improvement methods for various bridge elements. This paper provides a synthesis of some methods of strengthening bridge elements to facilitate comparison and discussion during construction. The application of Fiber Reinforced Polymer (FRP) materials in bridge engineering is then explored and the different types of FRP materials are compared. The results show that the strengthening methods are more suitable for each bridge member. For bridge decks, the analysis of various FRP reinforcement test results and crack extensions lead to the conclusion that the FRP reinforcement is closer to the modulus of elasticity of concrete and has better coordination of deformation, making it a splitting of concrete. However, when discussing the strengthening of bridge girders and pier members, the type of damage that occurs under different damage and loads is different. Therefore, there are different options and methods for different types of FRP materials.

Investigation on shear behavior of reinforced concrete deep beams without shear reinforcement strengthened with fiber reinforced polymers

Shear failure is an undesirable type of failure in terms of structural safety. Particularly, reinforced concrete (RC) deep beams without shear reinforcement are vulnurable to shear failure. In order to improve the shear behavior of such beams, externally bonded (EB) fiber reinforced polymer (FRP) as a strengthening technique is being applied to the outer part of the beams. However, investigations on the shear behavior of deep beams without shear reinforcement strengthened with FRP materials are insufficient in the literature. Therefore, a comprehensive experimental study was carried out on RC deep beams without shear reinforcements strengthened with fully wrapped FRP strips. The experimental parameters were chosen as the shear span-to-effective depth ratio (av/d), the number of carbon layers, the span length between carbon strips, and the type of FRP. A total of sixteen deep beams, four of which were reference beams, were fabricated and tested under three point bending load until failure. According to the experimental results, the gain percentage both in the shear and deflection capacities of strengthened deep beams increased with the av/d. Additionally, the failure modes and crack patterns of strengthened deep beams were different from those of the reference beams. Moreover, all test parameters affected the ductility behavior of deep beams having av/d of 1.5 and 2 positively. A comparative study was also conducted employing the methods commonly used in the literature and the methods based on the strut and tie model. It was observed that the methods based on strut and tie model provided superior estimates over the models commonly used in the literature.

Influence of elevated temperatures on the mechanical properties of glass fibre reinforced polymer laminates produced by vacuum infusion

One of the main concerns about the use of fibre reinforced polymer (FRP) materials in civil engineering is their behaviour when subjected to elevated temperatures and under fire exposure. In fact, considerable reductions in the mechanical properties of FRP materials have been reported even at moderately elevated temperatures (e.g. 50–150 °C), due to the glass transition of their polymeric matrices. Most previous studies on this topic have focused on the mechanical characterization at elevated temperatures of quasi-unidirectional pultruded FRP composites, namely profiles, rebars and strips; much less data is available about FRP materials produced with different methods with more balanced fibre architectures. This paper aims at contributing to fulfil this knowledge gap by presenting experimental and analytical investigations about the effects of elevated temperatures on the mechanical properties of glass-FRP (GFRP) laminates produced by vacuum infusion, with a balanced fibre architecture, representative of typical GFRP face sheets of sandwich panels used in civil engineering structures. The experimental programme included (i) tensile tests up to 300 °C, (ii) compressive tests up to 250 °C, and (iii) shear tests up to 200 °C, all under steady state conditions, as well as dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). The results obtained confirm that the mechanical properties of the GFRP laminates are severely affected by the temperature increase, especially those that are matrix-dependent: compared to room temperature, at 200 °C, the shear modulus was reduced by 88%, whereas the compressive strength and modulus were reduced by 96% and 67%, respectively. The tensile properties (fibre-dominated) were much less affected - at 200 °C, the tensile strength and modulus were reduced by 40% and 48%, respectively. Finally, the suitability of four empirical models and of a design-oriented temperature conversion factor to take into account the variation of the GFRP mechanical properties with temperature was assessed. Overall, the empirical models presented good agreement with the test data, and the temperature conversion factor provided conservative estimates of the material properties, attesting its suitability for design purposes.

Study on the Shear Capacity of Concrete Beam Reinforced with Glass Fiber Reinforced Polymers Grid Reinforcement

Abstract: Fiber Reinforced Polymer (FRP) composites have been widely used as a high-performance material in concrete structures as replacement of commonly using materials Corrosion of the internal reinforcing steel is the main cause of deterioration in reinforced concrete structures. This steel in reinforced concrete structures has cost a significant amount of resources globally over the past, also expensive as compared to FRP. Glass fiber reinforced polymer (GFRP) bars have been introduced as a light-weight, corrosion resistant FRP material which can be used as replacement for traditional steel reinforcing bars and stirrups in concrete structures. Glass fiber reinforcement polymer (GFRP) bars are also feasible and cost effective FRP products commercially available with significant cost advantage over stainless steel. The aim of this paper is to let engineers gain a better knowledge of the overall behaviour of GFRP as internal reinforcement so that they have more confidence using it as a sustainable material. In this study GFRP is used as longitudinal reinforcement and GFRP grid is used as stirrups A Finite Element (FEM) model has been developed using ANSYS 21 to analyses beams. For these six concrete beams, including one steel reinforced concrete (RC) beam and five beams with GFRP grids laid parallel to longitudinal axis was tested until failure. Parametric study on shear span ratio is conducted in four specimens. Load deflection curve are noted in each specimen analytically by using ANSYS software.