Fiber-reinforced Polymer Composite Systems Research Articles

Electrochemical and structural performances of carbon and glass fiber-reinforced structural supercapacitor composite at elevated temperatures

The structural supercapacitor can store electrical energy and withstand structural loads while saving substantial weight in many structural applications. This study investigated the development of a structural supercapacitor with a fiber-reinforced polymer composite system and explored the operating temperature’s influence on its performance. The electrochemical and mechanical properties of structural supercapacitors beyond the ambient temperature have not yet been studied; hence, evaluating parameters such as specific capacitance, energy density, cycle life, and structural performance at elevated temperatures are highly desired. We have designed and manufactured single and parallelly connected multilayer structural supercapacitor composites in this research. Carbon fibers were used as a bifunctional component, acting both as a current collector while acting as a mechanical reinforcement. In addition, glass fibers were added as the separator which is also acting as an integral reinforcement. The electrochemical and mechanical behavior of structural supercapacitors at elevated temperatures up to 85 °C were experimentally investigated. The test results revealed that at room temperature, the developed double-cell structural supercapacitor, which demonstrated an area-specific capacitance of 1.16 mF cm−2 and energy density of 0.36 mWh cm−2 at 0.24 mA cm−2, which are comparable to current achievements in structural supercapacitor research. The structural supercapacitor’s tensile, flexural, and compression strengths were measured as 109.5 MPa, 47.0 MPa, and 50.4 MPa, respectively. The specific capacitance and energy density reached 2.58 mF cm−2 and 0.81 mWh cm−2, while tensile, flexural, and compression strengths were reduced to 70.9 MPa, 14.2 MPa, and 8.8 MPa, respectively, at 85 °C. These findings provide new comprehensive knowledge on structural supercapacitor devices suitable for applications operating within a temperature range from ambient conditions to 85 °C.

FRP Radome: A Short Review

The Radome is an expression derived from radar and dome. It is a cover or enclosure to defend radar antennas from environmental influences. The Radome must be capable to face up to various outside loads and conditions and is to be transparent to the Electro-Magnetic Waves. Essentially, the geometry and material selection of the radome is dictated by the Electromagnetic design and performance. Since the overall performance of a radome relies upon the materials used, the materials play a vital role in the design of the radome. Composites are gaining wider acceptance for use as Radome due to the number of advantages like high strength to weight ratio, ability to be molded into complex shapes, and better Electromagnetic performance. Modern radomes are manufactured using composite materials using textile fibers held together with polymer matrix. Using a hybrid system of fiber reinforcement offers the opportunity to optimize the Fiber Reinforced Polymer composite system based on mechanical, electrical, and cost criteria of the radome.

Atomistic to continuum scale investigations on mechanical properties of epoxy bonded fiber reinforced polymer composite systems under hygro-thermal exposures

Epoxy polymers are widely used as adhesives in bonded composite systems. In this study, multi-scale computational investigations from molecular dynamics (MD) to finite element (FE) simulations are carried out to understand the material behaviour at atomistic level and to evaluate the performance at macro level. MD investigations are carried out to understand the extent of degradation of mechanical (such as strength, modulus) and transport properties (such as moisture diffusion coefficient) due to different environmental conditions like moisture ingress and high temperature. The influence of degree of curing of epoxy (diglycidyl ether of bisphenol-A) and type of hardener (diethyltoluene diamine, diethylene triamine, trimethylene hexadiamine) on the mechanical performance of the cross-linked epoxy polymer systems is also investigated. In-depth investigations are also carried out to identify the factors contributing to the total potential energy of cross-linked epoxy polymers and their role during the process of curing. Diffusion coefficient (key transport property) of epoxy polymer under moisture exposure is also determined using MD simulations. It has been demonstrated that high temperature causes the increase in diffusion in epoxy polymer systems. The observations on the performance of the epoxy system under moisture exposure obtained from MD simulations are translated to the higher length scale. The moisture ingress (in turn, significant reduction in mechanical properties) in epoxy polymer used for bonded composite system is also investigated using FE simulations. It is found that the extent of moisture ingress in the epoxy adhesive increases rapidly when epoxy polymer is environmentally exposed (under high temperature), and thus, the whole system gradually loses its effectiveness due to mechanical degradation. The findings of this study will help in understanding crucial parameters and aid to better use/engineering of epoxy polymers.

Towards the Development of Novel Hybrid Composite Steel Pipes: Electrochemical Evaluation of Fiber-Reinforced Polymer Layered Steel against Corrosion.

Corrosion remains one of the major and most costly challenges faced by the steel industry. Various fiber-reinforced polymer coating systems have been proposed to protect metallic piping distribution networks against corrosion. Despite increasing interest among scientific and industrial communities, there is only limited predictive capability for selecting the optimum composite system for a given corrosive condition. In this study, we present a comprehensive evaluation of the electrochemical behavior of two different fiber-reinforced polymer composite systems against the corrosion of carbon steel pipes under a wide range of acidic and corrosive solutions. The composites were made of glass and Kevlar fibers with an epoxy resin matrix and were subjected to corrosive solutions of 0.5 M NaCl, 0.5 M HCl, and 0.5 M H2SO4. The kinetics of the corrosion reactions were evaluated using potentiodynamic polarization (PDP) tests. In addition, electrochemical impedance spectroscopy (EIS) tests were carried out at open circuit potentials (OCPs). It was demonstrated that the glass fiber-reinforced polymer coating system offered the best protection against corrosion, with a high stability against deterioration when compared with epoxy and Kevlar fiber-reinforced polymer coating systems. Scanning electron microscopy images revealed cracks and deteriorated embedded fibers due to acid attack, sustained/assisted by the diffusion of the corrosion species.

Strengthening of Plain Concrete Cylinders with Natural FRP Composite Systems

This paper reports the performance of plain concrete cylinders confined externally with fiber-reinforced polymer (FRP) composites with natural sisal as the reinforcement. Strength tests are performed on plain concrete cylinders confined with different sisal FRP thicknesses such as 1, 2 and 3 layers. The results show that external confinement with sisal FRP enhanced the axial load-carrying capacity, ductility and energy absorption of concrete compared to control specimens. For predicting the ultimate strength of sisal FRP-confined concrete a new strength equation was developed based on the lateral confining pressure of sisal FRP which shows a good agreement with the experimental results. To assess the durability criteria, sisal FRP-filled concrete specimens are exposed to severe environmental factors such as variation in temperature, alternate wet and dry cycling and exposure to alkaline condition. The outcomes indicate that sisal FRP-confined specimen subjected to temperature variation has shown a remarkable increase in strength, whereas alkaline exposure has exhibited a decrease in strength.

Structural Damage Assessment of FRP Strengthened Reinforced Concrete Beams under Cyclic Loads

Worldwide, the need for structural retrofit is on the rise and the use of Fibre Reinforced Polymer (FRP) composite material systems is becoming an accepted method for repairs, rehabilitations, and strengthening of deficient structures. The great qualities of the FRP materials, certified in the laboratories and confirmed in the fields have all contributed to propel the material as a very promising one, though more works need to be done to certify the fatigue resistance and durability criteria. This research looked at the experimental investigations of Reinforced Concrete (RC) beams strengthened flexurally with externally-epoxy bonded FRP laminates under four point cyclic loads. Dynamic tests are used to assess damages in the FRP-strengthened RC beams under cyclic loads. 6 RC beams of 150 x 200 mm cross-section and length of 2.20m and were reinforced with four 12mm ribbed longitudinal steel bars. Three types of FRP laminates made of high modulus carbon fibre, high strength carbon fibre and glass fibre were adopted. The results confirm that dynamic-based method is an efficient way of assessing damage evolution in RC beams strengthened with FRP laminates under cyclic loads. The results offered a criterion that can be adopted for quick assessment of the efficiency of FRP composite systems before applying them to civil applications.

Limit state design criteria for FRP strengthening of RC bridge components

Fiber-reinforced polymer (FRP) composite materials provide novel, effective and potentially economical solutions for rehabilitating and strengthening existing reinforced and pre-stressed concrete bridges, buildings and other structures where deterioration has occurred or performance requirements have changed. FRP composites may be designed to act as external flexural, shear or confinement reinforcement to increase the load capacity of the strengthened structural components. This paper summarizes research to develop technical support for practical limit state (strength) design criteria for repair and strengthening of reinforced and pre-stressed concrete bridge elements for compression and/or flexure using externally bonded FRP composite systems. The limit state design criteria take uncertainties in structural strength and stiffness into account using structural reliability methods, and will support and enhance the use of FRP materials in civil construction by providing engineers with rational guidelines for repair and strengthening.

Short and Medium Term Durability Evaluation of FRP-Confined Circular Concrete

Evaluation of environmental durability of concrete circular specimens strengthened using externally applied fiber-reinforced-polymer (FRP) composites for confinement reinforcement was studied. FRP-confined concrete cylinder tests were carried out for various environmental exposure conditions including interior, exterior, and freeze–thaw cycling in saltwater. Two types of resin matrix-based FRP composite systems, including epoxy and urethane resin, utilizing either carbon or glass fibers were used. In addition, continuous single and double layer wrapping schemes were applied for confinement for each of the four FRP composite systems. The overall stress–strain behavior of FRP-confined concrete does not change fundamentally but different levels of exposure significantly affect its absolute stress–strain curve. The radial strain and corresponding axial strain at the point of zero volumetric strain is significantly affected by different levels of environmental exposure. It is proposed that the relative FRP com...

Performance-Based Material Evaluation of Fiber-Reinforced Polymer-Wood Interfaces in Reinforced Glulam Members

Abstract A performance-based material evaluation methodology is reviewed as part of a broader project on the development of fiber-reinforced polymer (FRP) composite reinforced glued-laminated (glulam) members. The glueline interface was examined under test conditions that included the presence of moisture and temperature fluctuations, and the effect of wood preservatives. The objectives of this study were: 1) to determine if the current test methods used to assess durability of wood-wood bonds for exterior use (ANSI/AITC and ASTM D 2559 protocols) can be adopted for testing FRP composite reinforcement of wood; 2) to research possible modifications to the standard procedures when necessary to accommodate specifics of the adhesive bonds in hybrid FRP-wood assemblies; and 3) to propose a unified interpretation approach for FRP-wood interface test results focusing on development of acceptance criteria. Four commercially available FRP composite systems exhibiting exterior durability potential for glulam reinforcement were selected to validate the material qualification protocol. Two wood species were considered in this study: southern yellow pine and Douglas-fir. The four FRP composite material systems represented a broad spectrum of fiber reinforcement, matrix, adhesives, and fabrication processes. Experimental studies using the composite systems were conducted to validate the proposed methodology.

Interfacial characteristics of a carbon nanotube–polystyrene composite system

The performance of a composite material system is critically controlled by the interfacial characteristics of the reinforcement and the matrix material. Here we report a study on the interfacial characteristics of a carbon nanotube (CNT)-reinforced polystyrene (PS) composite system through molecular mechanics simulations and elasticity calculations. In the absence of atomic bonding between the reinforcement and the matrix material, it is found that the nonbond interactions consists of electrostatic and van der Waals interaction, deformation induced by these forces, as well as stress/deformation arising from mismatch in the coefficients of thermal expansion. All of these contribute to the interfacial stress transfer ability, the critical parameter controlling material performance. Results of a CNT pullout simulation suggests that the interfacial shear stress of the CNT–PS system is about 160 MPa, significantly higher than most carbon fiber reinforced polymer composite systems.

Mesoscopic aspects of polymer composites: Processing, structure and properties

There can be little doubt that the morphology of the polymer matrix, the geometrical arrangement of the reinforcing elements and the existance of flaws, all on a mesoscopic scale between a few micrometers to several millimeters, have a strong influence on the performance of composite materials. Mesomechanics describes the properties of these mesostructures. Most of the latter are a result of the particular processing conditions used for the various types of composites. This is demonstrated (in form of examples of the author's own experience) for an unfilled semicrystalline polypropylene, a blend of epoxy resin with an elastomeric toughener, an injection moldable short fiber reinforced polyethyleneterephthalate, a discontinuous aligned fiber/polyethersulfone composite, and a high performance continuous fiber reinforced polymer composite system respectively. Mesostructural design is discussed with regard to some possibilities of how to optimize the various mesostructures of these materials, in order to achieve a particular property profile.

Computer simulation of crystallization kinetics in fiber‐reinforced composites

AbstractA computer simulation model was developed to investigate spherulitic growth in polymers of infinite and plate‐limited volume as well as in fibre‐reinforced polymer composite systems. Parameters like thermal nucleation rate and athermal nucleation density, plate distance, and fibre content were varied. The simulation crystallization process was evaluated following Avrami's method in the case of infinite volume and by stepwise approximation by Avrami functions in the case of limited volume. In addition, the simulation method allows the visualization of the growing entities at any phase of crystallization. Therefore the geometry of growing entities can be easily compared with the corresponding crystallization exponent. A good agreement between the crystallization exponent and the growth geometry was found.Depending on nucleation mode, “infinite” systems yield Avrami exponents of 3 and 4. In plate‐limited volume, a transcrystallization effect was observed in case of high athermal nucleation density on plate surface and large plate distances. This particular skin effect decreases the three‐dimensional growth to a one‐dimensional needle‐shaped one. Small plate distance changes the spherical to a disk‐like growth, resulting in crystallization exponents of 2 or 3, depending on nucleation mode. The crystallization behaviour of fibrereinforced composite systems is more complex. Low fibre content or large fibre distance and high athermal nucleation density on the fibre surface induce the formation of transcrystalline zones. The three‐dimensional growth of the spheres at the beginning is restricted by their neighbours, so that their geometry changes to a pyramidical one. They grow with a front normal to the fibre surface and the crystallization exponent is shifted in between 2.0 and 2.6 depending on nucleation density. High fibre content leads to a growth along the triangular channels between three adjacent fibres; the corresponding exponent amounts to 1.6. © 1994 John Wiley & Sons, Inc.

Critical crack tip opening displacement for polymer composites

Applicability of critical stress intensity factor ( K IC ) and/or critical crack up opening displacement (CTOD c for epoxy and polyester polymer composites (PC) in mode I Fracture are investigated. Both unreinforced and glass fiber reinforced polymer composite systems are studied using single edge notched beams in three-point and four-point bending at room temperature. Crack mouth opening displacement method (CMOD) is used in determining the crack extension during pre-peak loading. The critical stress intensity factor is calculated at the tip of the effective crack and the critical crack extension is represented by the elastic crack tip opening displacement. A simple model has been developed to determine the elastic CTOD from the measured elastic CMOD, and the performance of this model is compared to several other models proposed for metals and cement concrete. The test results indicate that the two Fracture parameters are independent of initial notch depth. The two Fracture parameters are used in predicting the notch sensitivity of epoxy PC and polyester PC. Resistance curves based on stress intensity factor ( V R- curve ) and crack tip opening displacement ( V R- curve ) have been developed for the 4% glass fiber reinforced polyester PC.