Search

This work aims to scrutinize the effect of the silanization of glass fibers (GF) on the mechanical properties and cathodic disbonding resistance of an epoxy composite coating. Successful silanization was approved based on different characterization techniques, including Fourier transform infrared spectra, field emission-scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy, and thermogravimetric analysis. Tensile strength measurement exhibited a significant effect of silanization on the mechanical performance of the fiber-reinforced polymer (FRP). FE-SEM cross-sectional images illustrated improved interfacial bonding between the epoxy matrix and GF upon silanization. Pull-off measurements revealed improved wet adhesion strength of the FRP to the mild steel surface after exposure to the salt spray chamber when the GF were silanized. In addition, silanization revealed enhanced resistance to cathodic delamination (CD). Electrochemical impedance spectroscopy and electrochemical noise assessments proved silanization's significant influence on the FRP's CD resistance. [ABSTRACT FROM AUTHOR]

The article presents the results of experimental studies on the effects of the electrophysical processing of a polymer binder directly in a mold on the mechanical characteristics of glass fiber-reinforced plastic. The results of the supramolecular structure studies and the polymer binder's thermophysical properties are presented. Finally, the physical interpretation of the results is also presented. [ABSTRACT FROM AUTHOR]

Nowadays, it is a big challenge to measure the accurate mechanical deformation of FRP composites experimentally at high temperature by using direct contact-type strain indicators. The premature failure or surface damage of the composite samples due to variation of temperature restricts the use of conventional direct strain measurement systems. Additionally, the theoretical models are still under development to determine the temperature-dependent mechanical deformations of the FRP composites. Therefore, in this research work, an attempt was taken to measure the temperature-dependent mechanical deformation of the manufactured GF/VE composites experimentally by using a noncontact-type laser extensometer. The experimental results were also validated with the Friend's model by emphasizing the matrix's strengthening mechanism. Moreover, the temperature-dependent static mechanical, dynamic mechanical and fracture toughness of the GF/VE and pure VE composites were studied experimentally to show the overall deformation mechanism of a short fiber-reinforced polymer composites. The degradation mechanism of the GF/VE composites was also examined by using a microscopic study (FE-SEM) of the fractured samples. [ABSTRACT FROM AUTHOR]

Fiber-reinforced composites have a wide range of industrial applications owing to their light weight, high modulus, and good specific strength. Trimming using a mechanical punching tool is the fastest way to post process fiber-reinforced composites. However, quantitative analyses of the defects and process parameters are required to analyze the damage mechanisms and achieve high-quality cut surfaces. In this study, we quantitively investigated the defects on the sheared edge of woven glass epoxy laminates subjected to mechanical punching and explored the correlations between these defects and key process parameters, including punch-die clearance, weave alignment angle, and laminate thickness. The results demonstrate the necessity of considering glass fiber burr length and the dimensions of the cracked area simultaneously to evaluate the quality of the sheared surface. This study provides qualitative data on the interfacial damage mechanisms that occur during mechanical punching, which will help to tailor the process parameters of mechanical punching for fiber-reinforced polymers to obtain smooth cut surfaces. [ABSTRACT FROM AUTHOR]

In this paper, numerous experimental tests were carried out to study the behavior of concrete containing glass fibers and confined with glass fiber-reinforced polymer (GFRP). Concrete specimens containing different fiber percentages (0.3 wt.%, 0.6 wt.%, 0.9 wt.% or 1.2 wt.%) and with different strengths of concrete (8.5 MPa, 16 MPa and 25 MPa) and different confinement levels (two, four and six layers of GFRP) were used as research parameters. The samples were tested to failure under pure axial compression. The results imply that the confinement effect with GFRP is relatively higher for concrete samples containing glass fiber (GFCC) with a percentage equal to 0.6 wt.%. The theoretical of stress ratios (fcc/fco) estimated by using existing ultimate strength models are found to be close to the experimental results for high strength of GFCC, but not close to the experimental results for low strength of GFCC. [ABSTRACT FROM AUTHOR]

Nanodiamonds (NDs) are the potential fillers to provide excellent mechanical and multi-functional capabilities. The growing interest in using NDs in a variety of fields has prompted researchers to use NDs to prepare various structural composites. Proper dispersion and interfacial adhesion between the NDs and the polymer matrix are required to use NDs as effective reinforcement in polymer nanocomposites. In this study, the mechanical properties of the epoxy-based glass fiber (GF)- and carbon fiber (CF)-reinforced laminated composites with the incorporation of annealed nanodiamonds (NDs) in the epoxy matrix was analyzed. The epoxy resin was modified through the step-wise addition of annealed NDs from 0.1 to 0.5 wt.%. The surface-modified NDs were characterized by SEM, XRD, FTIR, and TEM. The test results predict that the tensile strength was increased by 25, 23%, and tensile modulus increases by 33, 135% for GF- and CF-reinforced hybrid composites corresponding to the addition of 0.3 wt.% NDs into the epoxy matrix. Also, the flexural strength increased by 36, 37%, and flexural modulus increased by 71, 37% for the GF- and the CF-reinforced hybrid composites corresponding to the addition of 0.3 wt.% NDs into the epoxy matrix. These improved properties of hybrid composites are mainly due to the enhanced mechanical interlocking and weak Van der Waals force between the NDs particles that caused the efficient dispersion of NDs in the epoxy matrix and it has been reported in this study. [ABSTRACT FROM AUTHOR]

The main objective of this study is to investigate the structural performance of reinforced concrete (RC) beam specimens strengthened with 3D-fiberglass as compared with fiber-reinforced polymers (FRP) sheets. For this purpose, six RC beams were fabricated, strengthened, and tested under a four-point bending machine. One of the beams served as the control beam (REF), while the others were strengthened with carbon FRP (RCFRP), glass FRP (RGFRP), 3D-fiberglass and epoxy resin (R3DTR), 3D-fiberglass and epoxy resin extended to the sides (R3DTRB), and 3D-fiberglass and concrete repair (R3DTG). Failure mode, crack development, flexural capacity, ductility, the effectiveness of wrapping configurations, and the performance of epoxy resin in comparison with concrete repairer were studied between various beams. The results attest to the better performance and effectiveness of 3D-fiberglass over FRP in terms of flexural capacity, crack pattern, and ductility. The R3DTR and RGFRP specimens, compared to the control specimen, had the highest and lowest flexural capacity growth, with 19% and 8.4%, respectively. In addition, the failure modes observed in this study were in good agreement with the failure modes present in ACI.440.2R-17. Moreover, finite element (FE) models were proposed to predict the residual capacity of the specimens strengthened with FRP, using Abaqus software. [ABSTRACT FROM AUTHOR]

The present study concentrates on optimization and the effect of machining parameters on delamination that occurs during drilling operation of pure glass fiber-reinforced polymer (GFRP) composites and added GFRP composites which were developed for resistance to erosion wear. Contribution of drilling parameters to delamination was investigated by using Taguchi method and analysis of variance (ANOVA). Relationship between machining parameters and delamination was modelled by using response surface methodology. Correlations were established between the machining parameters by quadratic regression using response surface methodology (RSM). Delamination factors in the hole entrance and exit were obtained in drilling of pure glass fiber epoxy, and SiO2- and Al2O3-added GFRP materials using the experimental plan. Delamination factors at the hole exits were found bigger than delamination factors at the hole entrances. The smallest delamination values were obtained in GFRP/epoxy composite compared to Al2O3/SiO2-added GFRP composites at the hole exit. In the investigation of machinability of composites, considering the material as a variable, it has been determined that the material has a greater effect on delamination than the cutting parameters. A new machinability index defined and the material having the best machinability of the three materials was Al2O3-added GFRP composite at the entrance. Good machinability was obtained in drilling of pure GFRP/epoxy composite at the hole exit. It has been found that the effect of feed rate on delamination is greater than the cutting speed and the cutting speed has a low effect. Optimization of the multi-objective function created for maximizing the material removal rate, minimizing the delamination, was performed, and the optimum drilling parameters were obtained. As a result of the experimental study, it was found that the amount of delamination increased although the low mechanical property-added GFRP composites with the high resistance to erosion wear in accordance with pure epoxy GFRP composites due to the lack of a strong bond between the epoxy and the fibers in Al2O3 and SiO2. It was observed that the delamination amounts of pure epoxy GFRP, Al2O3-added GFRP, and SiO2-added GFRP composites increased respectively, while the compressive and tensile strengths of these three materials decreased. [ABSTRACT FROM AUTHOR]

The effectiveness of seismic retrofitting using three different fibers—carbon fiber (CF), glass fiber (GF), polyethylene terephthalate (PET) fiber—and a fiber combination of aramid fiber (AF) and PET fiber (called hybrid fiber reinforced polymer (HF)) wrapped on reinforced concrete (RC) circular columns was experimentally evaluated. A total of 11 RC circular columns were tested: three control columns and eight retrofitted columns in three different test groups. The purpose of fiber wrapping was flexural strength improvement as well as enhancement of rotational capacity in the plastic hinge region. Mechanical properties of CF, GF, AF, and PET were first defined; that is, CF, GF, and AF exhibited linear stress–strain behavior with limited ultimate strain capacity typically less than 3%, while ductile PET exhibited as much as 15% strain and non-linear stress–strain behavior with a very low elastic modulus. In the RC column tests, all three different fibers and the AF + PET fiber combination were effective in enhancing the strength and ductility but resulted in different structural behaviors and failure modes depending on the fiber type and the fiber amount used. The column sections were then analytically studied by section analysis using the behavior of confined concrete, the non-linear relationship of fiber-reinforced polymer (FRP), and the actual material properties of reinforcement. The analytical and experimental results revealed that ductile PET is beneficial, as it demonstrates more ductile behavior with a degree of strength enhancement similar to that of CF and GF. [ABSTRACT FROM AUTHOR]

The effect of Al2O3 and B4C nanoparticles on the quasi-static penetration test (QSPT) and Charpy impact test of glass-fiber-reinforced polymer composite plates has been studied with the aim to clear up whether there is a correlation between results of these two tests. Punch shear tests on the plates were carried out. The data for the absorbed energy obtained from the Charpy impact test were feasible to predict whether fiber-reinforced polymer nanocomposites will give positive results in the QSPT or ballistic tests. The predominant damage mechanisms were delamination and fiber break during the QSPT. Addition of 1 wt.% Al2O3 nanoparticles to the composite increased its punch shear strength by 8.97%, but the addition of B4C nanoparticles raised its hardness. It was also found that neither Al2O3 nor B4C increased the amount of absorbed energy. [ABSTRACT FROM AUTHOR]

Polymeric foams are extensively used as the core materials in sandwich structures and the core material is typically bonded between relatively thin fibre-composite skins. Such sandwich structures are widely used in the aerospace, marine and wind-energy industries. In the present work, various sandwich structures have been manufactured using glass-fibre-reinforced polymer (GFRP) skins with three layers of poly(vinyl chloride) foam to form the core, with the densities of the foam layers ranging from 60 to 100 kg/m3. This study has investigated the effects on the quasi-static flexural and high-velocity impact properties of the sandwich structures of: (a) the density of the polymeric-foam core used and (b) grading the density of the foam core through its thickness. The digital image correlation technique has been employed to quantitatively measure the values of the deformation, strain and onset of damage. Under quasi-static three-point and four-point bend flexural loading, the use of a low-density layer in a graded-density configuration reduced the likelihood of failure of the sandwich structure by a sudden force drop, when compared with the core configuration using a uniform (i.e. homogenous) density layer. The high-velocity impact tests were performed on the sandwich structures using a gas-gun facility with a compliant, high-density polyethylene projectile. From these impact experiments, the graded-density foam core with the relatively low-density layer located immediately behind the front (i.e. impacted) GFRP skin was found to absorb more impact energy and possess an increased penetration resistance than a homogeneous core structure. [ABSTRACT FROM AUTHOR]

This paper presents a study on the bond characteristics of glass fiber reinforced polymer (GFRP) bars in engineered cementitious composite (ECC). Ninety beam specimens having variable parameters namely bar diameter, GFRP bar types (standard low modulus 'LM' and high modulus 'HM'), two concrete types (ECC and normal concrete 'NC') and embedded length (5, 7 and 10 times bar diameter) were tested as per RILEM specifications. Bond stress-slip characteristics and failure modes of specimens as well as influence of variable parameters on bond strength are described. The performance of various Codes and other existing equations in predicting bond strength of both low/high modulus GFRP bars embedded in ECC compared to NC is described based on experimental results. The bond strength decreased with the increase of embedment length--maximum bond strength reduction of 36% was observed. For both ECC and NC, bond strength reduced with the increase of bar size and ECC produced maximum 1.6 times higher bond strength compared to NC. Code based and other existing equations were found conservative in predicting bond strength of GFRP bars embedded in ECC. [ABSTRACT FROM AUTHOR]

Plain glass fibre-reinforced polymeric (GFRP) laminates and GFRP reinforced with randomly oriented short strips of shape memory alloy (SMA) were prepared by hand lay-up method. The SMA strip reinforcement was placed at 0.75 × thickness of the laminate with weight fractions of 2, 4 and 6%. The specimens were exposed to drop weight impact test and the experiments were conducted at a constant impact velocity of 2.80 m s with different test temperatures such as 303, 333 and 363 K. The impact damage area was evaluated using lighting technique and fracture response was analysed using scanning electron microscopic (SEM) images. Absorption of impact energy and damage area due to low velocity impact were calculated. It was observed that with the higher temperature, the SMA/GFRP laminates exhibit marginally-enhanced damage resistance compared to the plain GFRP laminates. Also, addition of SMA reinforcement was not contributing much to the impact resistance at higher temperature. [ABSTRACT FROM AUTHOR]

Nowadays, natural fibres are used as a reinforcing material in polymer composites, owing to severe environmental concerns. Among many different types of natural resources, kenaf plants have been extensively exploited over the past few years. In this experimental study, partially eco-friendly hybrid composites were fabricated by using kenaf and glass fibres with two different fibre orientations of 0° and 90°. The mechanical properties such as tensile, flexural and impact strengths of these composites have been evaluated. From the experiment, it was observed that the composites with the 0° fibre orientation can withstand the maximum tensile strength of 49.27 MPa, flexural strength of 164.35 MPa, and impact strength of 6 J. Whereas, the composites with the 90° fibre orientation hold the maximum tensile strength of 69.86 MPa, flexural strength of 162.566 MPa and impact strength of 6.66 J. The finite element analysis was carried out to analyse the elastic behaviour of the composites and to predict the mechanical properties by using NX Nastran 9.0 software. The experimental results were compared with the predicted values and a high correlation between the results was observed. The morphology of the fractured surfaces of the composites was analysed using a scanning electron microscopy analysis. The results indicated that the properties were in the increasing trend and comparable with pure synthetic fibre reinforced composites, which shows the potential for hybridization of kenaf fibre with glass fibre. [ABSTRACT FROM AUTHOR]

In injection molding process, the mold temperature can strongly affect the fiber orientation and distribution state in plastic parts. The fiber orientation behavior is discussed, and a model is used to describe the layered structure in injection parts. By studying the injected specimens, the fiber distribution and the layered structure in the part are illustrated and a variation of the fiber distribution along with the increasing of the mold temperatures is also demonstrated. The surface morphologies of the fiber-reinforced specimens at different mold temperatures are analyzed which are used to study the effect of the mold temperature on the fiber motion process of the resultant parts. Results show that in proper mold temperature, the fibers can be completely covered in polymer matrix and the mold temperature can greatly affect the part surface quality. [ABSTRACT FROM AUTHOR]

Glass fiber reinforced polymer (GFRP) due to its corrosion resistance is gaining popularity in the civil engineering community, as an alternative material to steel reinforcement. GFRP reinforced bar (rebar) has a high tensile strength with moderate elastic modulus and is elastic up to failure. However, it should not be treated in the same way as steel rebar because the interfacial bond behavior of GFRP bars to concrete is expected to vary from that of conventional steel bars, since various parameters that influence bond performance are different. This paper presents the results of an experimental and analytical studies on the bond strength of glass fiber reinforced polymer bars subjected to monotonic or reversed cyclic loads. The experimental program consisted of 30 test specimens. The test results indicated that the interfacial strength of the GFRP bars was quite different to that of the steel bars. In addition, the strength degradation of GFRP bars subjected to reversed cyclic load was more severe than that of the GFRP bars subjected to a monotonic load. [ABSTRACT FROM AUTHOR]

Drilling in woven fiber-reinforced plastics is a well-known practice in modern-day manufacturing. The high fracture toughness of woven fiber-based composites over unidirectional counterparts is increasing demand in aviation and electronics industries. Hence, failure of these materials at harsh environments is a matter of concern. Very few numerical studies on drilling of these composites have been carried out; hence, the present scope may be considered as a trial de novo. Delamination was studied in the present work at different feed-speed combinations. Drilling responses were estimated using finite element as a numerical simulation tool. An equivalent elastic macromechanical model was assumed for the woven composite workpiece. A 3D drill bit was modeled using commercial CAD package Pro-Engineer and Ansys Autodyn was used as the solver environment. The simulation and validation experiments were carried out at planned feed-speed combinations. The effect of process parameters on exit and entry delamination is also documented. The thrust determined by finite element techniques showed good prediction with the experimental results. [ABSTRACT FROM AUTHOR]

In this article, an advanced laminated composite is developed, combining the high damping properties of shape memory alloy (SMA) with mechanical properties and light weight of a glass-fiber reinforced polymer. The composite is formed by stacking a glass-fiber reinforced epoxy core between two thin patterned strips of SMA alloy, and two further layers of fiber-glass reinforced epoxy. The bars of the laminated composite were assembled and cured in autoclave. The patterning was designed to enhance the interface adhesion between matrix and SMA inserts and optimally exploit the damping capacity of the SMA thin ribbons. The patterned ribbons of the SMA alloy were cut by means of a pulsed fiber laser source. Damping properties at different amplitudes on full scale samples were investigated at room temperature with a universal testing machine through dynamic tension tests, while temperature dependence was investigated by dynamic mechanical analyses (DMA) on smaller samples. Experimental results were used in conjunction with FEM analysis to optimize the geometry of the inserts. Experimental decay tests on the laminated composite have been carried out to identify the adimensional damping value related to their first flexural mode. [ABSTRACT FROM AUTHOR]

The interest in fibre-reinforced polymer composites is growing rapidly due to its high performance in terms of mechanical properties, significant processing advantages, excellent chemical resistance, low cost, and low density. The development of composite materials based on the reinforcement of two or more fibre types in a matrix leads to the production of hybrid composites. In the present work, woven coir-glass hybrid polyester composites were developed and their mechanical properties were evaluated for different stacking sequences. Scanning electron micrographs of fractured surfaces were used for a qualitative evaluation of interfacial properties of woven coir-glass hybrid polyester composites. These results indicated that coir-glass hybrid composites offered the merits of both natural and synthetic fibres. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer-matrix composites are known to exhibit loading rate- and time-dependent mechanical response. Their fatigue strength is determined by a complex interaction of damage processes governed by loading duration and cycle number. Apart from mechanistic approaches, a number of empirical models of various sophistication have been proposed to predict the durability of composites, differing in the amount of experimental data needed for their application. The accuracy of several such models is evaluated by comparing the prediction to the experimentally determined stress ratio effect on fatigue life of glass fiber-reinforced polyester-matrix composite. It is found that the accuracy of prediction generally improves with increasing the amount of test data needed for model calibration. However, the most accurate method of fatigue life estimation, among the selected ones, is by the modified Goodman diagram. [ABSTRACT FROM AUTHOR]

A letter about a study on unidirectional glass fiber-reinforced polymer (GFRP) composites is presented. The study utilized glass fibers that were modeled as a doubly periodic face-centered hexagonal array. It hypothesized that the polymeric fibrils of matrix stretched between the crack surfaces behave based on the Barenblatt cohesive force model.

Determining fiber length distribution in fiber reinforced polymer components is a crucial step in quality assurance, since fiber length has a strong influence on overall strength, stiffness, and stability of the material. The approximate fiber length distribution is usually determined early in the development process, as conventional methods require a destruction of the sample component. In this paper, a novel, automatic, and nondestructive approach for the determination of fiber length distribution in fiber reinforced polymers is presented. For this purpose, high-resolution computed tomography is used as imaging method together with subsequent image analysis for evaluation. The image analysis consists of an iterative process where single fibers are detected automatically in each iteration step after having applied image enhancement algorithms. Subsequently, a model-based approach is used together with a priori information in order to guide a fiber tracing and segmentation process. Thereby, the length of the segmented fibers can be calculated and a length distribution can be deduced. The performance and the robustness of the segmentation method is demonstrated by applying it to artificially generated test data and selected real components. [ABSTRACT FROM AUTHOR]

Glass fiber reinforced plastic (GFRP) composites are finding their way into high technology applications. The machining of GFRP composites is needed to produce near nett-shaped components. Damage free machining is necessitated for the longer inservice life of composites. The present study attempts a newer technique of the oscillatory vibration assisted drilling of GFRP composites in order to minimise the damages. For comparison, conventional drilling also has been carried out. The cutting performance is analysed through online studies such as the measurement of force, power and A.E. monitoring and through the measurement of tool wear as an offline technique. [ABSTRACT FROM AUTHOR]

Fiber reinforced plastics (FRPs), reinforced with carbon fiber, SiC fiber and glass fiber, were prepared by using a new thermosetting silicon-containing polymer, poly[(phenylsilylene) ethynylene-1,3-phenyleneethynylene](MSP), as a matrix resin. In MSP composite processing, no solvent is needed, no by-products are generated, and the curing temperature is low (150–210°C). The FRPs (MSP composite) showed high heat-, burn- and radiation-resistant properties. Bending strengths (110–140 MPa) and modulus (30 GPa) at 200°C and 400°C were almost equal with those at room temperature, and were not affected by 100 MGy of irradiation. Dynamic viscoelasticity and creep properties of MSP composite were also determined and compared with those of a polyimide composite. [ABSTRACT FROM AUTHOR]

In this paper, truncated-correlation photothermal coherence tomography (TC-PCT) was used as a nondestructive inspection technique to evaluate glass-fiber reinforced polymer (GFRP) composite surface cracks. Chirped-pulsed signal that combines linear frequency modulation and pulse excitation was proposed as an excitation signal to detect GFRP composite surface cracks. The basic principle of TC-PCT and extraction algorithm of the thermal wave signal feature was described. The comparison experiments between lock-in thermography, thermal wave radar imaging and chirped-pulsed photothermal radar for detecting GFRP artificial surface cracks were carried out. Experimental results illustrated that chirped-pulsed photothermal radar has the merits of high signal-to-noise ratio in detecting GFRP composite surface cracks. TC-PCT as a depth-resolved photothermal imaging modality was employed to enable three-dimensional visualization of GFRP composite surface cracks. The results showed that TC-PCT can effectively evaluate the cracks depth of GFRP composite. [ABSTRACT FROM AUTHOR]

Pulse thermography (PT) has proven to be a valuable non-destructive testing method to identify and quantify defects in fiber-reinforced polymers. To perform a quantitative defect characterization, the heat diffusion within the material as well as the material parameters must be known. The heterogeneous material structure of glass fiber-reinforced polymers (GFRP) as well as the semitransparency of the material for optical excitation sources of PT is still challenging. For homogeneous semitransparent materials, 1D analytical models describing the temperature distribution are available. Here, we present an analytical approach to model PT for laterally inhomogeneous semitransparent materials. We show the validity of the model by considering different configurations of the optical heating source, the IR camera, and the differently coated GFRP sample. The model considers the lateral inhomogeneity of the semitransparency by an additional absorption coefficient. It includes additional effects such as thermal losses at the samples surfaces, multilayer systems with thermal contact resistance, and a finite duration of the heating pulse. By using a sufficient complexity of the analytical model, similar values of the material parameters were found for all six investigated configurations by numerical fitting. [ABSTRACT FROM AUTHOR]