Glass Fiber Reinforced Polymer Specimens Research Articles

Size effect on compressive behavior of GFRP bars

In the last three decades, studies investigating the use of Glass Fiber Reinforced Polymer (GFRP) bars as an alternative to conventional steel rebars have increased due to their corrosive resistance. In addition to corrosion resistance, GFRP bars utilize high specific tensile strength, which makes them highly desirable in civil engineering applications. However, major design guidelines for GFRP-reinforced concrete structures currently do not consider their compressive contribution. Nevertheless, there is a growing trend in utilizing GFRP bars as compressive elements, driven by various studies demonstrating their ability to bear compressive loads effectively. This increasing demand underscores the need to comprehend the mechanical properties of GFRP bars, particularly in terms of their compressive behavior. Furthermore, a standardized test method to evaluate their compressive properties has not yet been developed. Addressing these gaps, this research paper focuses on investigating the influence of specimen size on the compressive strength of GFRP bars, specifically emphasizing on the compressive properties of GFRP bars. Compressive tests were conducted on GFRP specimens with varying diameters while maintaining a constant slenderness ratio. The findings from these compression tests shed light on the critical role of size in the compressive behavior of GFRP. This research emphasizes the importance of considering size as a significant parameter in designing mechanical properties for GFRP reinforcements.

Flexural behavior of high strength concrete shallow wide beams reinforced by hybrid longitudinal reinforcement

ABSTRACT One of the most common statistical systems used in structures especially for wide span slabs are ribbed slabs with shallow wide beams (SWB). This experimental study aimed to investigate and enhance the flexural behavior of high-strength concrete SWB using hybrid longitudinal reinforcement from steel and advanced composite materials as a tensile main reinforcement in SWB. Longitudinal advanced composite bars locally manufactured from ribbed glass fiber reinforced polymer (GFRP) and the second type was ribbed basalt fiber reinforced polymer (BFRP). A group of six half scale SWB were examined in structures laboratory of American University in Cairo with dimensions 2.1 × 0.6 × 0.25 m for length (L), width (B) and depth (d) respectively with constant size effect (d/B). The first three specimens were completely reinforced at tension side with Steel, GFRP or BFRP ribbed bars to be considered a control specimen. Use of GFRP and BFRP bars enhanced the flexural capacity of SWB with 41% and 43% respectively compared to specimen completely reinforced with steel. But on the other hand, the crack propagation of specimens completely reinforced with GFRP and BFRP developed more quickly and had larger crack width compared to specimen completely reinforced with steel. Hybrid reinforcement from Steel with GFRP, Steel with BFRP and Steel with GFRP and BFRP specimens are used to enhance the crack pattern and mode of failure without a significant loss in flexural capacity of SWB. The flexural capacity of these three specimens was enhanced with 26%, 30% and 41% with a significant enhancement in crack pattern and ductility.

Experimental and analytical investigation on forced and free vibration of sandwich structures with reinforced composite faces in an acidic environment

The main objective of this study is to investigate the impact of nanoparticles as reinforcement material on the vibrational behavior of sandwich structures in an acidic medium. The glass fiber reinforced polymer (GFRP) faces were fabricated with and without the addition of 3 wt% nanoclay and nanosilica to determine the mechanical behaviors of the GFRP faces in the presence of an acidic medium. The obtained results showed adding 3 wt% of nanoclay caused better durability and less mass variation of composite specimens in sulfuric acid. The “Coefficient of acidic immersion expansion” (βacid) is determined by measuring the length and mass variation of GFRP specimens in the immersion, and applied to low order piecewise shear deformation theory (LOPSDT) for the first time; Also the frequency results of LOPSDT have been shown good agreement in validation with the ANSYS numerical solution. It is shown that acidic environment reduces the frequency of the first mode of sandwich plates with reinforced face by 3 wt% nanosilica, and nanoclay has increased by 6.81 % and 4.66 %, respectively. This study indicates after one month of immersion, the natural frequency of the sandwich with pure, and 3 wt% nanoclay reduces about 1 %, and the natural frequency of the sandwich with the faces reinforced with 3 wt% nanosilica reduces by more than 3 %; Moreover, the frequency of forced vibrations, caused by acidic immersion expansion, was improved significantly by 10.04 % and 6.54 % in the first mode by incorporating 3 wt% of nanoclay, and nanosilica into the faces of the sandwich in one month of immersion compared to the sandwich with pure faces.

High Strain Rates Impact Performance of Glass Fiber-Reinforced Polymer Impregnated with Shear-Thickening Fluid

This paper examines the behavior at high strain rates of a shear-thickening fluid (STF) impregnated glass fiber-reinforced polymer (GFRP) fabric using a split Hopkinson pressure bar (SHPB). This study involved impact testing of 4 GFRP specimens and 20 GFRP-STF composite specimens at four different strain rates. The STF employed in this study was synthesized by incorporating 20.0 wt.% of 12 nm silica in polyethylene glycol. Rheological tests indicated that the STF exhibited a noticeable shear-thickening effect, with viscosity surging from 3.0 Pa·s to 79.9 Pa·s. The GFRP-STF specimen demonstrated greater energy absorption capacity, deformation ability, and toughness, bearing higher and faster impact loads than neat GFRP. Specifically, the GFRP-STF specimen showed a 21.8% increase in peak stress and a 92.9% rise in energy absorption capacity under high-strain-rate loading. Notably, the stress–strain curve of the GFRP-STF specimen exhibited a distinct yield stage, while the energy absorption curve displayed no significant descending stage features.

Transverse Shear Capacity Predictions of GFRP Bars Subjected to Accelerated Aging Using Artificial Neural Networks

This paper presents the results of three different types of glass fiber-reinforced polymer (GFRP) bars subjected to different harsh environmental conditions. Three types of pultruded GFRP bars, namely, Bar A (13.04 mm dia.), Bar B1 (13.02 mm dia.), Bar B2 (10.19 mm dia.), and Bar C (13.22 mm dia.) were subjected to accelerated aging. GFRP specimens were exposed to four conditionings (alkaline, alkaline with salt, acidic, and water), two temperature regimes (20°C and 60°C), and three time regimes (3, 6, and 12 months). The mechanical strength retention of the bars investigated based on the transverse shear strength (TSS) test, conforming to ASTM D7617M-11 revealed a decline in the shear strength characteristics of specimens proportionally with the exposure time. In general, Bar A, Bar B1, and Bar B2 performed well, but Bar C performed the worst since Bar C exhibited the least mechanical strength retention at elevated temperatures. Scanning electron microscopy (SEM) of the cross section of the conditioned specimens revealed the nature of the evolution of deterioration and the state of glass fibers, polymeric resin matrix, and fiber-matrix interface, validating the decrease in transverse shear capacity of the bars. SEM micrographs showed fiber damage, with debonding occurring at the fiber-matrix interface and cracking of the polymeric resin. Leaching out of glass fibers into the matrix of varying degrees upon conditioning was observed through the X-ray mapping of silicon. Furthermore, strength prediction models developed using multiple linear regression and artificial neural network (ANN) techniques were compared. Coefficients of correlation (R2) of 0.94 and 0.76 and root mean square errors (RMSE) of 7.43 and 12.00 were obtained with models developed using ANN and multiple linear regression, respectively, showing that ANN can be used as a robust tool for GFRP shear strength prediction.

Influence of a Flat Polyimide Inlay on the Propagation of Guided Ultrasonic Waves in a Narrow GFRP-Specimen.

Structural health monitoring systems for composite laminates using guided ultrasonic waves become more versatile with the structural integration of sensors. However, the data generated within these sensors have to be transmitted from the laminate to the outside, where polyimide-based printed circuit boards play a major role. This study investigates, to what extent integrated polyimide inlays with applied sensor bodies influence the guided ultrasonic wave propagation in glass fiber-reinforced polymer specimens. For reasons of resource efficiency, narrow specimens are used. Numerical simulations of a damping-free specimen indicate reflections of the -mode at the integrated inlay. This is validated experimentally with an air-coupled ultrasonic technique and a 3D laser Doppler vibrometry measurement. The experimental data are evaluated with a method including temporal and spatial continuous wavelet transformations to clearly identify periodically occurring wave packages as edge reflections and distinguish them from possible inlay reflections. However, even when separating in-plane and out-of-plane movements using the 3D measurement, no reflections at the inlays are detected. This leads to the conclusion that polyimide inlays are well suited as substrates for printed circuit boards integrated into fiber-reinforced polymer structures for structural health monitoring, since they do not significantly influence the wave propagation.

Thermal Aspects in Edge Trimming of Bio-Filled GFRP: Influence of Fiber Orientation and Silica Sand Filler in Heat Generation.

The present work aims to determine the influence of Glass Fiber-Reinforced Polymer (GFRP) laminating configuration in heat generation during the dry edge trimming process. Temperature measurement experiments were conducted on pure epoxy matrix, 15% unidirectional glass fiber reinforced epoxy, and 28% silica sand-filled GFRP specimens through eight type-K thermocouples evenly distributed along the trim plans and connected to a data acquisition system. Infrared thermographic measurements were also conducted to investigate the tool temperature evolution while processing. It was found that perpendicular fiber edge milling induces a sharp increase with peak temperature measurements reaching 119 °C, while machining parallel to fiber leads to a maximum temperature history of 41 °C, which is very close to that obtained from the pure epoxy test. It was also found that the addition of silica sand grains in the GFRP matrix reduces both tool and specimen temperature magnitudes up to 67% for 90° plies and 14% for 0° plies compared to silica sand-free composite initial values. The heat partition was calculated from the measured (electric) and estimated energies for the tool, the workpiece, and chips, respectively. It appears from predictions that the addition of silica sand grains increases the heat conductivity of the GFRP materials (with rates of 20% for 0° fiber orientation and 10% for 90° fiber direction), while it reduces that conducted to the milling tool. Scanning Electron Microscopy (SEM) inspections helped detect the dominating machining defects relative to each GFRP configuration and explained the heat generation and dissipation effects in light of peak temperature measurements.

Influence of Loading Direction on Impact Strength and Small Span Length Variation on Flexural Strength in GFRP Laminate

Abstract This experimental work focuses on the two aspects of glass fiber–reinforced polymer (GFRP) laminate. The first is the effect of GFRP plate thickness and impact loading direction on impact strength, and the second is the effect of GFRP panel thickness and small span length variation on flexure strength. The GFRP laminate thicknesses considered for experimentation were 2, 3, and 4 mm. Both Izod and Charpy impact tests were conducted by considering edgewise (lateral impact) and flatwise (normal impact) impact loading directions. The quasistatic flexural tests were conducted using a three-point bend method for two small span length variations, viz., 50.8 and 56 mm. Impact strength of 2-mm-thick GFRP laminate under the edgewise loading condition showed 13 and 134.1 % more for Charpy and Izod, respectively, compared with 4-mm GFRP samples. In contrast, under the flatwise loading condition, 2-mm-thick specimens showed 14 and 54 % more impact strength when compared with 4-mm-thick GFRP specimens. GFRP samples with 2-mm thickness showed 59.85 and 59.6 % enhancement in flexural strength for span lengths of 56 and 50.8 mm, respectively, when compared with 4-mm-thick GFRP panels. Improvement in flexural strength between span lengths 50.8 and 56 mm for thicknesses 4 and 2 mm is 26 and 42 MPa, respectively, which is a 10 % improvement. Analysis of variance statistical analysis showed that the loading conditions and thickness of GFRP panels in the case of impact and small span length variation, and thicknesses in the case of flexural strength, is the significantly influencing parameters.

Multi-step buckling optimization analysis of stiffened and unstiffened polymer matrix composite shells: A new experimentally validated method

A new multi-step optimization method is developed to predict the optimal fiber orientation in glass fiber reinforced polymer (GFRP) composite shells. The method contains 1) a regenerated genetic algorithm (GA) optimization strategy coupled with, 2) an analytical approach regarding assessing the failure of the tubular structure. Two critical factors, namely “ultimate buckling load” and “weight of structure” are particularly taken into account, while other crucial limitations, including angle and number of layers, shell thickness, and size of stiffeners, are considered in this study. Some experiments are conducted to evaluate the critical buckling pressure in GFRP specimens, and the obtained analytical results are verified through comparison with experimental ones. The results suggest that the application of this novel optimization algorithm leads to a decrease of 21% and 28% in optimum local mass of stiffened unsymmetrical angle-ply and unstiffened symmetrical angle-ply laminated composite shells, respectively.

GFRP erosion depth model under alkaline solution erosion

Based on the physical phenomenon of the fiber reinforced polymer material after the erosion of the liquid medium, the erosion law of the liquid medium on the FRP is analyzed. And considering the anisotropy of the FRP material, a FRP point source erosion depth model based on Fick’s law is proposed. Taking the glass fiber reinforced polymer (GFRP) in alkali solution as an example, we carried out GFRP corrosion and aging test in alkaline solution, and the erosion depth of GFRP specimens was measured at 30, 90, 180, 360 and 720 days, respectively. At the same time, the water absorption rate of GFRP was used to calculate the erosion diffusion coefficient of solution medium. Through the comparison between the experimental value of erosion depth and the calculated value of erosion depth model, the error between the experimental data and the calculated data is within 10%, and the overall regularity is consistent. It shows that the erosion depth model of liquid medium proposed in this paper is reasonable and has high accuracy.

Damage process in glass fiber reinforced polymer specimens using acoustic emission technique with low frequency acquisition

The damage process in fiber-reinforced polymers (FRP) has been the subject of continuous studies in recent decades using different approaches. In particular, the acoustic emission technique has been proved to be a powerful tool in the monitoring of structures of this type of material due to the large acoustic activity captured when this material is loaded to rupture. The present work explores several indexes that were calculated from the experimental recording of acoustic emission signals, and their efficiency in describing the failure process in structures. One of these indexes, called c value, is originally proposed, and its sensibility it is compared with other classical parameters that are usually employed in the Acoustic Emission analysis. A 3-point bending test has been performed on a glass fiber reinforced polymer plate. Our own methodology was proposed to identify AE signals in semi-automatic manner. This methodology also allowed a faster analysis of the global parameters during the process data of the AE test. The global parameter evolution obtained from the acoustic emission data during the damage process could be considered as precursors of the more meaningful event and as an aid to understand in which way the structure is going to the collapse.

Effects of parameters controlling the impact resistance behavior of the GFRP fabric impregnated with a shear thickening fluid

This study investigates the low-velocity impact behavior of the glass fiber-reinforced polymer (GFRP) fabric impregnated with a shear thickening fluid (STF). Low-velocity impact tests were conducted on eight GFRPs and eight GFRP-STF composite specimens. The results show that the STF could improve the maximum resistive force and energy absorption of the GFRP-STF composite for both penetration and non-penetration samples. The effectiveness of the STF in improving the impact behavior of the composite were differed significantly owing to various physical parameters such as the number of layers, constraint type, and laying angle. The maximum resistive force and energy dissipation of the four-layered GFRP-STF, considering the interaction of two-way fibers, increased by 105% and 113%, respectively. However, GFRP-STF composites under the “+” and “O” constraint types could only improve either the maximum resistive force or the energy dissipation. Under a laying angle of 45°, the energy dissipation of GFRP-STF was also improved by 58.5% of the increase in maximum resistive force. It can be inferred from the impact tests conducted on all the GFRP-STF specimens that the specimens fail because of filament fracture or tearing in the zonal fracture, which is different from the results obtained for the GFRP specimens.

Improving durability of glass fiber reinforced polymer composites by incorporation of ZnO/OMMT nanoparticles subjected to UV radiation and hygrothermal aging

Glass fiber reinforced polymer (GFRP) composites have high sensitivity to UV radiation, temperature, and moisture, and these factors lead to the decrease of mechanical properties. This study attempts to modify unsaturated polyester (UP) and vinylester (VE) resins with nano zinc oxide (ZnO) and organo-montmorillonite (OMMT), in order to improve UV radiation resistance and hygrothermal resistance. The nano ZnO/OMMT modified UP and VE based GFRP composites were subjected to UV radiation and hygrothermal aging at 30 °C, 50 °C and 60 °C (95% RH) for 90 days. Mass loss, moisture uptake, color change, flexural properties and short-beam-shear test were investigated. In comparison to unmodified GFRP specimens, ZnO/OMMT modifying decreased the mass loss, the color change, saturation moisture uptake, and the coefficient of diffusion. After exposure in UV radiation for 90 days, the flexural strength and interlaminar shear strength of nano modified GFRP composites increased by 23.5% and 27.8% compared with those of the unmodified GFRP composites. Nano ZnO/OMMT modifying also increased the flexural strength and interlaminar shear strength by 26.5% and 27.2% in hygrothermal condition at 60 °C. Furthermore, based on the change of mechanical properties and Arrhenius rate model, a prediction model was proposed to predict the life of nano modified FRP composites.

An improved method of eddy current pulsed thermography to detect subsurface defects in glass fiber reinforced polymer composites

Due to its induction heating mechanisms, eddy current pulsed thermography (ECPT) is always used as Non-destructive testing (NDT) technique only for conductive materials. This work explores the feasibility of ECPT to detect subsurface defects in glass fiber-reinforced polymer (GFRP) composites, a typical non-conductive material. The proposed method introduces a metal part as the heat-generating component to generate the induction heat. Then the induction heat in the metal part can be transferred to GFRP, which makes it possible to detect subsurface defects in GFRP. The detection mechanism of the proposed method is firstly investigated, and the influence factor analysis is then performed to obtain the optimal test condition. Experiments were finally performed on GFRP specimens with various subsurface defects to verify the effectiveness of the method. The results demonstrate that the proposed method is effective in subsurface defects detection of GFRP, which provides a promising way to extend the application of ECPT to non-conductive materials.

Investigation of indentation damage resistance on normal and inclined plane of glass/epoxy composite laminates using acoustic emission monitoring

This work relates to the investigation of indentation induced damage resistance in glass fiber reinforced polymer composite laminates under normal and inclined planes. Uni-directional [0] and cross-ply [0/90] glass fiber reinforced polymer composite specimens were subjected to 0° and 20° indentation loading with acoustic emission monitoring. The specimens were loaded at the centre using a hemispherical steel indenter with 12.7 mm diameter. Mechanical responses such as force–displacement behavior, absorbed energy and resulting damage area were used for the quantification of the indentation damage. Acoustic responses such as normalized cumulative counts, energy, duration and peak frequency were considered for monitoring damage progression during 0° and 20° indentation loading. The residual compressive strength of the glass fiber reinforced polymer specimens following indentation was measured by testing them under in-plane loading, once again with acoustic emission monitoring. The correlation between mechanical and acoustic strain energy was used for the evaluation of the damage severity of the laminates. The result revealed indentation damage resistance in cross-ply laminates as 65.08% and 68.01% higher than uni-directional laminates for 0°, whereas for 20°, there was a reduction in the damage resistance in cross-ply laminates to 43.27% and 57.39%. These were higher than uni-directional laminates under the displacements of 2 mm and 3 mm, respectively. The conclusion from these results was that transverse shear load at 20° inclination of laminate leads to reduction in residual compressive strength. Moreover, uni-directional glass/epoxy laminates have better residual compressive strength than cross-ply laminates for both 2 mm and 3 mm indentation displacements.

Influence of Fuel Absorption on the Mechanical Properties of Glass-Fiber-Reinforced Epoxy Laminates

This study investigated the influence of fuel absorption on the mechanical properties of glass-fiber-reinforced polymer (GFRP) composite. Three types of fuel, namely, aviation fuel, biofuel, and a blended fuel mixture between kerosene and biofuel, were used to perform complete immersion on the GFRP specimens through immersion-bath technique. The degradation of the tension and compression properties of GFRP composite caused by fuel attack were experimentally investigated. Three types of aviation fuel were used to environmentally age the GFRP specimens through immersion-bath technique. The GFRP specimens were manufactured using vacuum-assisted resin-transfer molding to achieve a volume fraction of 0.55 with <1% void content. The mechanical performance of the specimens were then evaluated by immersing them to the saturation point before performing tensile and compression tests. Results showed that the immersed specimens for all fuel solutions had slightly decreased tensile and compressive strengths and modulus compared with an as-received (non-immersed) specimen. This indicated the ability of GFRP composites in resisting the corrosive nature of fuels.

Mechanical behavior of cylindrical GFRP chimney liners subjected to axial tension

The large diameter filament-wound glass fiber reinforced polymer (GFRP) tube as the chimney liner is a pivotal anti-corrosion structure in the wet flue gas desulfurization system. Fourteen GFRP specimens with a larger size (3000 mm × 1100 mm × 5.6 mm) and twenty GFRP specimens with a smaller size (350 mm × 25 mm × 5.6 mm) have been investigated by tensile tests. All specimens were cut from two GFRP chimney liner specimens, which were fabricated with the scaled-down ratio of 3:1 (practical to experimental) according to the standard guide for design of GFRP chimney liners for coal-fired units. Among the fourteen larger specimens, seven specimens were cut into two segments and then jointed by the hand-wound technique at the middle height of the specimens, while the other seven larger specimens and twenty smaller specimens were integrated. All specimens were subjected to axial tension at four different temperatures, including the ambient temperature (approximately 30 °C), 60 °C, 90 °C, and 120 °C. Based on the tests, the failure modes and tensile load-displacement relationships were determined. The temperature-dependency and size-dependency of the tensile strength, tensile strain, and elastic modulus were analyzed. Moreover, the comparisons between integrated and jointed specimens were examined. Finally, a modeling method for the tensile mechanical properties of composites under elevated temperatures was proposed for GFRP chimney liner design.

Enhancing the interface friction between glass fiber-reinforced polymer sheets and sandy soils through sand coating

ABSTRACT Soil-pile interface friction is an important geotechnical engineering factor to be considered in achieving a safe and cost-effective design. Conventional materials such as concrete, steel, and wood exhibit serious long-term soil substructure problems, particularly with regard to durability, deterioration, and corrosion. Fiber-reinforced polymer (FRP) composites are potential alternatives for addressing these long-term problems. This paper describes the results of an experimental study of the interface friction between sandy soil and glass FRP (GFRP) sheets coated with different ratios of sand per unit of surface area. A direct shear test was used to study 18 different groups of GFRP specimens. The test parameters were the amount of silica sand coating and normal stresses in the direct shear tests. The GFRP specimens were sheared against three types of soil: sand, silty sand, and sandy lean-clay, of which the first two were used in both dense and loose states. The experimental results showed that coating the GFRP sheets with silica sand was effective in enhancing the interface friction with sandy soils under different normal stresses. A pile implication analysis was also performed to compare the effect of sand coated GFRPs on the load capacity of friction piles with different length to diameter ratios.

Warpage Reduction of Glass Fiber Reinforced Plastic Using Microcellular Foaming Process Applied Injection Molding.

This study analyzes the fundamental principles and characteristics of the microcellular foaming process (MCP) to minimize warpage in glass fiber reinforced polymer (GFRP), which is typically worse than that of a solid polymer. In order to confirm the tendency for warpage and the improvement of this phenomenon according to the glass fiber content (GFC), two factors associated with the reduction of the shrinkage difference and the non-directionalized fiber orientation were set as variables. The shrinkage was measured in the flow direction and transverse direction, and it was confirmed that the shrinkage difference between these two directions is the cause of warpage of GFRP specimens. In addition, by applying the MCP to injection molding, it was confirmed that warpage was improved by reducing the shrinkage difference. To further confirm these results, the effects of cell formation on shrinkage and fiber orientation were investigated using scanning electron microscopy, micro-CT observation, and cell morphology analysis. The micro-CT observations revealed that the fiber orientation was non-directional for the MCP. Moreover, it was determined that the mechanical and thermal properties were improved, based on measurements of the impact strength, tensile strength, flexural strength, and deflection temperature for the MCP.

Tensile strength of GFRP and hybrid composites under various environmental conditions

Purpose The purpose of this paper is to study the mechanical behavior of glass fiber reinforced polymer (GFRP) and hybrid composites under various adverse environmental conditions. This mainly helps the researchers to overcome the obstacles that have been met when they use the materials individually and also to know the impacts of environment on them. Design/methodology/approach The GFRP and hybrid specimens are made according to the American Society for Testing and Materials standard. The specimens are then immersed in aviation turbine fuel, hydraulic fluid and concentrated sulfuric acid. The tensile strength of the specimens is then determined using the universal testing machine. Findings The tensile strengths of the normal specimens and the specimens subjected to various environmental conditions are determined. The results obtained for GFRP and hybrid specimens are then compared. Research limitations/implications The researchers can extend the time intervals further for a better understanding of the strength of the composites. Practical implications Once better combinations are found out with the highest strength to weight ratio and its resistance to various adverse environmental conditions, it can be used in real-time applications. Social implications The best hybrid combinations can be used in place of metals in future. Originality/value This is an original research and is clearly based on the experimental results, so it adds very much value to the aviation industry because strength to weight ratio is one of the major issues to be taken into consideration.