Fiber Reinforced Polymer Materials Research Articles

Structural Materials: Identification of the Constitutive Models and Assessment of the Material Response in Structural Elements Strengthened with Externally-Bonded Composite Material.

This article investigates the material behavior within multiple-component systems. Specifically, a structural concrete element strengthened to flexure with externally-bonded fiber-reinforced polymer (FRP) material is considered. Enhancements of mechanical performances of the composite structural element resulting from synergies in the framework of the multiple-component system are studied. The research work comprises the determination of the constitutive relations for the materials considered separately as well as the investigation of materials’ response within a complex system such as the composite structural element. The definition of the material models involves a calibration of the model constants based on characterization tests. The constitutive relations are integrated into the finite element model to study the material behavior within the multiple-component system. Results obtained by finite element analysis are compared with experimental results from the literature. The finite element analysis provides valuable information about the evolution of some internal variables, such as mechanical damage accumulation. The material synergies find expression in the load-carrying capacity enhancement and the delay in the damage accumulation in concrete.

Bridge Case Study: What a Contractor Needs to Know on an FRP Reinforcement Project

AbstractCivil works construction is now facing a transformational change with the growing implementation of fiber-reinforced polymer (FRP) materials as rebars and tendons for concrete structures. T...

A comparative analysis of adhesive bonding and interference fitting as joining technologies for hybrid metal-composite gear manufacturing

The aim of this work is to compare two different joining technologies for steel and carbon fibre reinforced polymer materials in a hybrid gear in order to improve the dynamic behaviour in terms of natural frequencies and damping properties. A comprehensive approach for the design and prototyping of hybrid metal-composite gears with interference fitting and adhesive bonding is provided. In a following phase, an accurate description of the experimental impact tests is shown in order to investigate modal performances. Successively, in a finite element environment, modal analyses are conducted and frequency response functions of the gear model are analysed by means of complex stiffness matrix that accounts for structural damping. Impact tests and simulations indicate that the solution with interference fitting is stiffer than the one with adhesive, even if the damping capacity is lower. The results for both technologies show that it is possible to enhance noise and vibrations behaviour of gears through the application of composite materials in place of conventional full-metal solutions.

Comparative study of mechanical technologies over laser technology for drilling carbon fiber reinforced polymer materials

More researchers have been worked to increase the quality of the machined composite materials. In this paper, acomparative experimental study of mechanical techniques over the laser techniques has been performed in the drillingprocess by using the carbon fiber reinforced polymer (CFRP). In order to identify the best process among the mechanicaldrilling (MD) and laser drilling (LD) technology various analysis methods like normality analysis, control chart analysis,and process capability analysis have been performed. Process capability index analysis for case study 1 and interval plotanalysis for case study 2 have been employed to evaluate the best process comparatively. Experiments have been performedin a vertical machining center (VMC) and CO2 laser. The final results revealed that the MD process is the best technologyfor drilling CFRP. Therefore, this work has been important for small-scale industries.

Review of Experimental Studies on Application of FRP for Strengthening of Bridge Structures

In recent years, fiber‐reinforced polymer (FRP) composites have been widely used as a new type of high‐performance material in concrete structures. FRP composites have the advantages of high strength, light weight, and corrosion resistance. Based on existing studies in the literature, this paper reviews the development and applications of FRP materials for the strengthening and rehabilitation of bridge structures. The types and properties of FRP composites are summarized, and the applications and development of FRP sheets, FRP bars, FRP grids, and prestressed FRP tendons for bridge structures are discussed. Different types of FRP composites result in different failure characteristics and bearing capacities. Moreover, this paper covers the FRP strengthening methods and the response properties of the flexural performance, bonding performance, and ductility. Significant conclusions regarding the strengthening/repair of bridge structures with FRP composites are presented. The review details the current state of knowledge and research on strengthening bridge structures with FRP composites and is helpful for better understanding and establishing design criteria.

Modeling of tensile behavior of hybrid GFRP-steel reinforced concrete chords

Arranging a hybrid combination of longitudinal fiber reinforced polymer (FRP) bars and longitudinal steel bars in the tensile zone of a concrete beam is able to sufficiently exploit the superior properties of both FRP and steel materials to achieve a satisfactory ductility level. As the foundation of analysis and design of hybrid FRP-steel reinforced concrete (RC) members, study of tensile behavior of concrete chords with FRP-steel reinforcement is essential and necessary. In this paper, the average crack spacing of hybrid (Glass Fiber Reinforced Polymer-GFRP and steel) RC chords is analytically estimated. Subsequently, the Tension Chord Model (TCM) is extended to predict the tensile behavior of hybrid GFRP-steel RC chords. Finally, the presented models are effectively validated by experimental results of concrete chords reinforced with GFRP bars and steel bars in different combinations available in the literature, and detailed discussions about analytical and experimental results are also performed.

Dimensionally and environmentally ultra-stable polymer composites reinforced with carbon fibres.

The quest to develop materials that enable the manufacture of dimensionally ultra-stable structures for critical-dimension components in spacecraft has led to much research over many decades and the evolution of carbon fibre reinforced polymer materials. This has resulted in structural designs that feature a near-zero coefficient of thermal expansion. However, the dimensional instabilities that result from moisture ingression and release remain the fundamental vulnerability of the matrix, which restricts many applications. Here, we address this challenge by developing a space-qualifiable physical surface barrier that blends within the mechanical properties of the composite, thus becoming part of the composite itself. The resulting enhanced composite features mechanical integrity and a strength that is superior to the underlying composite, while remaining impervious to moisture and outgassing. We demonstrate production capability for a model-sized component for the Sentinel-5 mission and demonstrate such capability for future European Space Agency (ESA) and National Aeronautics and Space Administration (NASA) programmes such as Copernicus Extension, Earth Explorer and Science Cosmic Visions.

Optimal FRP Jacket Placement in RC Frame Structures Towards a Resilient Seismic Design

This paper proposes an optimal plan for seismically retrofitting reinforced concrete (RC) frame structures. In this method, the columns are wrapped by fiber-reinforced polymer (FRP) layers along their plastic hinges. This technique enhances their ductility and increases the resiliency of the structure. Two meta-heuristic algorithms (i.e., genetic algorithm and particle swarm optimization) are adopted for this purpose. The number of FRP layers is assumed to be the design variable. The objective of the optimization procedure was to provide a uniform usage of plastic hinge rotation capacity for all the columns, while minimizing the consumption of the FRP materials. Toward this aim, a single objective function containing penalty terms is introduced. The seismic performance of the case study RC frame was assessed by means of nonlinear pushover analyses, and the capacity of the plastic hinge rotation for FRP-confined columns was evaluated at the life safety performance level. The proposed framework was then applied to a non-ductile low-rise RC frame structure. The optimal retrofit scheme for the frame was determined, and the capacity curve, inter-story drift ratios, and fragility functions were computed and compared with alternative retrofit schemes. The proposed algorithm offers a unique technique for the design of more resilient structures.

Machining effects on delamination failure in milling MD-CFRPs with uncoated carbide tools

As one of the main failure mechanisms emerging in the milling of carbon (C)-fiber-reinforced polymer (CFRP) materials, delamination is primarily affected by cutting tool material and geometry, machining parameters and the dynamic loads arising during the machining process. In this study, machinability tests were performed without the use of coolants to examine the effect of machining parameters on multidirectional CFRP composite workpieces, which have a wide application in industries. The tests were applied on a computer numerically controlled vertical processing center at three different cutting speeds (100, 200 and 300 m/min), three different feed rates (0·05, 0·15 and 0·25 mm/tooth) and constant cutting depth (1 mm). Following the tests, the changes in the workpiece were examined in terms of surface roughness, cutting forces, tool wear and delamination failures. The average surface roughness increased with increasing feed rate. Cutting forces also increased with increasing cutting speed, which caused improvements on average surface roughness values. As a machining parameter, feed rate was found to be a determining factor in the machining of CFRP composite materials.

RETRACTED: Manufacturing and evaluation of elastic properties of glass fiber reinforced polymers material

VJMech’s Editors have decided to retract this article because it duplicates significant parts of papers that had previously published in other journals. The authors have misconduct concerning plagiarism of papers without citation.We really apologies to readers of the journal that this was not detected during the submission and review process.

Study of the flexural behaviour of FRP-strengthened steel-concrete composite beams

Flexural strengthening of steel-concrete composite beams with fiber-reinforced polymer (FRP) materials has recently become a topic of considerable interest, due to the many advantages it may offer in both enhancing the design prospects of new structures and restoring the functioning condition of deficient existing structures. During the past two decades, a substantial number of experimental, numerical and analytical studies has been concerned with this topic. Although these studies have provided significant insights into the problem, a lack of simplified methods for assessing the FRP-strengthening effects in a quantitative manner still exists. Motivated by this need, a study that seeks to establish a sound understanding of the mechanics of the problem – which is a fundamental component for the development of simple and reliable analysis approaches – is presented in this paper. The basis of the study is the development of a new analytical method for the prediction of the moment-curvature relationship and the overall flexural response of FRP-strengthened steel-concrete beams, by assuming perfect bond between the constitutive components. The method only requires accessible spreadsheet calculations, which makes it both suitable for routine use in design practice and particularly useful for the scientific study of the problem. The new method is first validated against available experimental results and it is then employed in conducting a systematic parametric study, from which several conclusions of essential practical significance for the optimum use of FRP composites in strengthening the flexural behaviour of steel-concrete composite beams are derived.

Parametric investigation on the tensile response of GFRP elements through a discrete lattice modeling approach

Fiber Reinforced Polymers (FRP) are a relatively new construction material. Their attractive features, such as lightness and durability, are currently paving an attractive way for structural engineering applications. However, since their mechanical properties are strongly influenced by the arrangement of the fibers (which is dictated by the production process), more research is still needed to fully characterize the material and to predict its behavior under different multi-axial actions.In this regard, the goal of the present manuscript is to shed light on these aspects by means of numerical analyses according to a lattice modeling approach proposed in (Fascetti et al., 2016) for FRP materials and herein modified to better capture the uniaxial alignment of pultruded elements. Novelty of the work and main contribution to the field is the definition of a numerical procedure for the saturation of the computational domain with different pointsets (i.e. a regular and a random one) in order to increase the accuracy of the method. The proposed approach is validated for tensile loadings, both in terms of mechanical properties and failure modes, through a parametric investigation carried out to simulate the results of the experimental campaign reported in Quadrino et al. (2018) which employed small-scale specimens directly extracted from pultruded glass fiber reinforced polymers (GFRP) beams.

Axial Compressive Performance of CFRP Confined Self-stressing High-strength Concrete Cylinders

Due to the advantages of FRP (fiber reinforced polymer), such as light weight, high strength and corrosion resistance, FRP-confined concrete columns are gradually applied in civil engineering structures and have drawn wide attention from the engineering community. In order to avoid the stress hysteresis of CFRP (carbon fiber reinforced polymer) and make full use of FRP materials, expansive agent was added to concrete to make self-stressing high-strength concrete. In this study, the axial compression performance of 18 CFRP-confined self-stressing high-strength concrete cylinders was examined. The parameters include the CFRP layers and the level of prestress (with or without prestress). Experimental results show that 3.53–5.34 MPa prestress in concrete and 799.3–1584.2 MPa prestress in CFRP are produced in the composite cylinder. The stress-strain curves obtained from the experiment shows that the intercept stress, inflection stress and peak stress of the self-stressing specimens are all higher than those of the non-prestressed specimens. With the application of prestress, the utilization ratio of CFRP increases as well. In the theoretical calculation of intercept and peak stress, by modifying the existing models, the experimental results are in good agreement with the calculated results.

An improved wrapping scheme of axially loaded fiber-reinforced polymer confined concrete columns

Columns failed near the mid-zone were commonly found in practical engineering when subjected to an increasing compression load caused by the vertical ground motion during an earthquake, indicating that more confinement may be necessary at the mid-zone. Fiber-reinforced polymer (FRP) materials have been widely used to strengthen the columns. Different wrapping schemes, including full, partial, and nonuniform wrap, have been proposed. Generally, FRP-confined concrete stub columns using the existing wrapping schemes failed by the rupture of FRP at the middle zone, indicating the middle zone of the columns were not well confined by using the existing wrapping schemes. A new wrapping scheme with more FRP sheets applied in the middle zone is proposed. Experimental tests with a total of 28 specimens were conducted to evaluate the performance of different wrapping schemes, based on which an arrangement way that the applied FRP materials decrease from the middle zone to the end is recommended. The results suggest FRP materials along the height of a column can be more efficiently utilized by using the recommended wrapping scheme. Additionally, compared with the specimens using the existing wrapping schemes with the same amount of FRP materials, the recommended wrapping scheme significantly improves the strength and ductile behavior of columns.

Behavior of Cross Arms Inserted in Concrete-Filled Circular GFRP Tubular Columns.

Fiber-reinforced polymer (FRP) materials nowadays have attracted much attention in both retrofitting of aged infrastructure and developing of new structural systems attributed to the outstanding mechanical properties. Extensive studies have been performed on concrete-filled glass FRP (GFRP) tubes for the potential application in piling, poles, highways overhead sign structures and bridge components. The new hybrid member also provides an alternative solution for traditional transmission structures. However, the connection between concrete-filled GFRP tubes and cross arms has not been fully understood. In this paper, an experimental study and theoretical analysis were conducted on the behavior of cross arms inserted in concrete-filled circular GFRP tubular columns. Steel bars with a larger stiffness in comparison with GFRP tubes were selected here for the cross arm to simulate a more severe scenario. The structural responses of the system when the cross arms were subjected to concentrated loads were carefully recorded. Experimental results showed that the concrete-filled GFRP tubes could offer a sufficient restraint to the deformation of the cross arm. No visible cracks were found on the GFRP tube at the corner of the cross arm where the stress and strain concentrated. Theoretical solutions based on available theories and equations were adopted to predict the displacement of the cross arms and a good agreement was achieved between the prediction results and experimental findings.

An application of non-ordinary state-based peridynamics theory in cutting process modelling of unidirectional carbon fiber reinforced polymer material

The usage of carbon-fiber-reinforced polymer (CFRP) composite keeps increasing in modern industries. However, because of the complexity of CFRP structure, the analysis for CFRP failure process, especially for machining process, is quite difficult. This paper presents a non-ordinary state-based peridynamic approach that can be applied to CFRP machining analysis. In order to describe the composite’s anisotropy, fiber bond and matrix bond is first introduced in this approach. For describing the failure characteristic of composite, the Maximum stress failure criteria and Hashin failure criteria is then incorporated into the state-based peridynamic approach. Finally, the contact state between tool and workpiece is detected by utilizing the penalty method in modeling the machining process. To demonstrate the effectiveness of the present method, tension and cutting experiments are conducted as well.

Structural performance of a hybrid FRP composite – lightweight concrete bridge girder

A novel hybrid fibre-reinforced polymer (FRP) composite – lightweight concrete (LWC) girder was developed and implemented in a bridge superstructure as a result of the comprehensive R&D project. The new bridge system is intended to have durable, structurally sound, lightweight, and cost effective hybrid FRP/LWC girders that will take full advantage of inherent and complementary properties of composites and lightweight concrete. The proposed hybrid girder consists of a FRP shell with trapezoidal cross-section and a lightweight concrete slab, reinforced with glass fibre-reinforced polymer (GFRP) rebars and acting compositely with the shell. Before implementation, a test specimen fabricated as a full-scale model of prototype bridge girder was subjected to a series of quasi-static and fatigue loading tests. This paper presents the selected results of research on evaluation of stiffness, strength, ultimate capacity, and global factors of safety against failure. The test results were compared to the performance criteria formulated in the relevant bridge standards. The output of research confirmed that the proposed hybrid bridge girder has an excellent performance from the structural engineering point of view, and fulfils the appropriate standard conditions to be implemented in an actual bridge. Moreover, due to quite high safety factors it seems to be possible to optimize the hybrid girder design by reducing the amount of FRP material required.

Performance of FRP confined and unconfined engineered cementitious composite exposed to seawater

Conventional concrete suffers from brittle failures under mechanical behaviour, and lack of ductility results in the loss of human life and property in earthquake zones. Therefore, the degree of ductility becomes significant in seismic regions. This paper investigates the influence of poly-vinyl alcohol fibers, basalt fiber-reinforced polymer (BFRP) and carbon fiber-reinforced polymer (CFRP) fabrics on the ductility and mechanical performance of low (LCFA) and high (HCFA) calcium fly ash-based engineered cementitious composite concrete. The study also focuses on the mechanical behaviour of the CFRP and BFRP materials using different matrix types exposed to 3.5% seawater environment. Cyclic loading and scanning electron microscopy observations were also performed to see the effect of chloride attack on mechanical performance and ductility of the specimens. In addition, utilization of CFRP and BFRP fabrics as a retrofit material is also evaluated. Results indicated that the degree of ductility and mechanical performance were found to be superior for the CFRP-engineered cementitious composite hybrid specimens under ambient environment, while LCFA-CFRP hybrid specimens showed better performance under seawater environment. The effect of matrix type was also found significant when engineered cementitious composite is used together with fiber-reinforced polymer materials. In addition, both fiber-reinforced polymer materials can be used as a retrofit material under seawater environment.

Reinforced concrete columns of square and rectangular section, confined with FRP – Prediction of stress and strain at failure

Fiber-reinforced polymer (FRP) confined concrete columns under axial compression reveal significantly enhanced axial strength and ductility compared to unconfined columns. Adequate FRP confinement provide hardening stress – strain behavior up to failure especially in columns of circular section. However, it is difficult to model and predict accurately the maximum stress and ultimate strain of the noncircular confined concrete columns in the presence of internal steel reinforcement, which is the real case for the majority of existing structures. Numerous experimental investigations have been carried out for axially loaded circular section concrete columns with or without internal steel reinforcement confined with FRP materials and other techniques. Also, a lot of predictive expressions of peak axial strength and strain and ultimate stress and strain, suitable for similar concrete sections, have been proposed. On the other hand, fewer studies concern reinforced concrete columns of square and rectangular section. The presented investigation gathers all the newest available test results on square and rectangular reinforced or plain concrete columns confined with composite reinforcements and assesses the performance of significant predictive expressions published in literature. The developed database includes these columns confined with FRP materials and other techniques and assesses the performance of 24 existing models proposed for the peak and ultimate conditions.

TEST STUDY ON THE BEST PASTING LAYER OF FRP REINFORCED CONCRETE

To optimize the strengthening method using the fiber reinforced polymer (FRP) for the reinforcement of the concrete structure with cracks, the three-point bending test was conducted on the concrete beams wrapped with different layers of FRP materials. The strain gauges were pasted on the surface of the specimens to measure the initial cracking load. The crack mouth opening displacement (CMOD) was utilized to test the load–crack mouth opening displacement curve. According to the improved calculation formula of the fracture toughness, the critical effect crack length [Formula: see text], initiation fracture toughness [Formula: see text] and instability fracture toughness [Formula: see text] of specimens were calculated. The test results showed that, under the same initial crack depth, the peak load of FRP reinforced concrete decreases with the increase of FRP pasting layer. When there was one layer wrapped over the specimen, the instability toughness of the specimen reached the maximum value and the crack resistance was the best. Based on acoustic emission testing method, the acoustic emission parameters of the above-mentioned concrete during fracture process were identified and collected. The optimal layer of the FRP reinforced concrete with cracks was analyzed from the acoustic emission method.