Pultruded Glass Fiber-reinforced Polymer Research Articles

Statistical modeling of 3D fiber geometry in pultruded GFRP composite: A multi-scale approach

The fiber geometry is a crucial determinant of the fiber reinforced polymer composites’ mechanical properties. Specifically, the manufacturing process of stretching and gradual curving in pultruded composites invariably results in complex 3D fiber geometries. Despite its significance, there is still lacking a statistical method to accurately describe these spatially curved fiber shapes. This paper presents a novel multi-scale mathematical approach for modeling the complex 3D fiber geometry in pultruded glass fiber reinforced polymer (GFRP) composites, which includes the analysis of fiber misalignment and waviness at two scales. At the mesoscopic level, a modified elliptical symmetry angular Gaussian (ESAG) model effectively characterizes the fiber misalignment. Simultaneously, at the micro scale, a cosine series representation is employed for capturing local fiber waviness. The approach is verified with XCT scanning results of pultruded GFRP specimens. The current statistical modeling method provides a multi-scale approach for geometry analysis and further simulation of pultruded composite materials.

Strengthening of glass fiber sheets for multi-bolted pultruded GFRP connections: Effects of connection type and bolt-tightening force

This study investigated the effects of bolt-tightening forces on the connection strengths of non-strengthened and glass fiber sheet (GFS)-strengthened pultruded glass fiber reinforced polymer (PGFRP) connections through a series of experiments using double-lap and single-lap specimens. A total of 96 specimens (3 specimens for each parameter), half of which were non-strengthened, were tested under tensile loads and four bolt-tightening forces: 0, 5 N.m, 10 N.m, and 20 N.m. The (0°/90°)/chopped strand mat/(0°/90°) lamination was bonded to both PGFRP plates’ outside surfaces and improved the connection strengths. The results indicated that maximum failure loads increased with an increase in bolt-tightening forces. However, there were different trends in the maximum failure load changes, depending on the specimen type (non-strengthened or GFS-strengthened specimens; double-lap or single-lap specimens) and bolt-tightening forces. In addition, GFSs could effectively improve PGFRP’s connection strengths and ductility performances.

Experimental and finite element investigation on bolted connection in monolithic 3-dimensional cuff with pultruded box section

This article presents a concise and practical research study on the application of pultruded GFRP (Glass Fiber Reinforced Polymer) hollow sections in structural engineering. Experimental and computational investigations are conducted on the utilization of GFRP cuff components for joining tubular pultruded fiber-reinforced polymer (PFRP) beams and columns. Both adhesive bonding and bolted connections are explored for connecting PFRP box sections of beam-column interfaces. The study investigates twelve series of beam-to-column connections under monotonic loading conditions, varying cuff geometry. A finite element model is developed to represent the pultruded fiber-reinforced polymer box sections, columns, and cuff sections. The model’s accuracy in depicting frame stiffness and cuff damage patterns, considering different thicknesses and lengths of GFRP cuff connections, is validated against experimental test frame behavior. This research fills a gap in scientific inquiry regarding GFRP hollow profiles, providing valuable insights for structural engineering applications.

Mechanical Characterization of Pultruded GFRP Round Tube under Axial Loading

Abstract: Pultruded Fibre‐Reinforced Polymer profiles are widely used as structural elements in many civil infrastructure applications. However, the anisotropic elasticity and the application‐driven slenderness make these profiles prone to local buckling failure, well below their ultimate load capacity. In this paper, an experimental study was undertaken to characterise the tensile and compressive failure of GFRP round tube under axial loading. Based on the research focus of GFRP structures, this work will present a comprehensive study of the mechanical properties of GFRP tubes in terms of both tensile and compressive loads and investigate the mechanical parameters. This paper presents an investigation on the mechanical properties of pultruded Glass fiber reinforced polymer (GFRP) round tubes for structures subjected to tensile and compressive axial loading. The tensile and compressive strength of GFRP round tubes were first tested. For the stability under compression, the slenderness ratio 6 is adopted. The results show that the tensile strength of GFRP tube could reach 580 MPa, while the compressive strength has been around 72% of tensile strength. Also Experimental results showed that specimens exhibited linearly elastic up to failure. Compared with the single tensile failure mode of GFRP tubes, two types of compressive failure modes, including micro-buckling and local buckling were observed. Moreover, a finite element (FE) analysis was carried to simulate the tensile and compressive behaviours of round tube specimen. The comparison between the tensile and compressive peak load values obtained experiment and FE methods revealed that their difference is less than 5%. These indicated that FE analysis predicted reasonably the actual tensile and compressive behaviours of the pultruded GFRP round tube.

Experimental study on the axial compression performance of pultruded GFRP tubes for emergency bridges

Glass fiber reinforced polymer (GFRP) tubes exhibit significant potential in the design and construction of emergency bridges owing to their high strength-to-weight ratio. Axial compression tests were conducted on 13 pultruded GFRP tubes with varying slenderness ratios (11.9, 14.3, 21.4, 28.6, and 35.7) and diameter-thickness ratios (37.2, 46.5, and 86.2). Furthermore, a nonlinear finite element model was applied to analyze the failure characteristics and load-bearing capacity of the GFRP tubes when subjected to axial loads. A modified Perry formula was proposed based on this analysis. The results indicate that the GFRP tubes are prone to experiencing brittle failure. With the slenderness ratio increases from 11.9 to 35.7, the failure mode tends to change from crushing to local buckling to global buckling. The modified Perry formula displays a high degree of agreement with experimental results, with an average error of 9.38%, and offers a more precise prediction of the capacity of composite tubes. The findings have practical implications for the design of composite truss bridges.

Flexural behaviour of bolted flange-plate with bonded sleeve splice connections for pultruded GFRP circular tubular hollow beams

The paper presents an experimental and finite element investigation of bolted flange-plate with bonded sleeve splice connections for joining pultruded glass fibre-reinforced polymer (GFRP) circular tubular beams. The moment-rotation behaviour was investigated in terms of initial rotational stiffness, moment capacity and rotation capacity for all the tested splice connections. The effect of the number of flange-plate bolts, flange-plate thickness and the length of the bonded sleeve were examined. Failure modes for the thinner flange-plates included opening, bending and yielding of the flange-plates in the tension zone. Thicker flange-plates and a higher number of bolts exhibited improved initial rotational stiffness with lower rotational capacity, which can be enhanced by higher bonded sleeve lengths. Available design codes for steel joints were used to classify the splice connections with regards to rigidity and strength. The failure modes from the finite element models were consistent with the experimental observations, which includes the plastic deformation of the flange-plate and the cohesive failure of the adhesive.

Experimental study on axial compression behavior of square pultruded GFRP tubular stub column

To investigate the influence of aspect ratio and width-to-thickness ratio on the axial compression behavior of square pultruded glass fiber-reinforced polymer (GFRP) tubular stub columns, axial compression tests were conducted on 12 GFRP tubular columns. The mechanical properties of the GFRP tubular columns, including load-bearing capacity, initial stiffness, compressive toughness, and ductility coefficient, were analyzed. The test results reveal that all GFRP tubular columns exhibit crushing failure, with specific failure modes, including mid-section fracture and longitudinal tearing along the corners of the columns. The load-bearing capacity is negatively correlated with the aspect ratio and width-to-thickness ratio. The initial stiffness negatively correlates with the aspect ratio, and the compressive toughness negatively correlates with the width-to-thickness ratio. The Hashin damage criteria for the C3D8R solid element was developed by utilizing the explicit finite element subroutine ABAQUS-VUMAT to analyze the axial compression behavior of GFRP tubular columns. Through parameter analysis, the relationship between the load-bearing capacity and fiber orientation was obtained, and an empirical equation for predicting the load-bearing capacity of the GFRP tubular column was proposed.

Behavior of functionally graded carbon nanotube reinforced composite sandwich beams with pultruded GFRP core under bending effect

A novel generation of composite sandwich beams with laminated carbon fiber-reinforced polymer skins and pultruded glass fiber-reinforced polymer core materials was examined for their flexural behavior. The strength and failure mechanisms of the composite sandwich beams in flatwise and edgewise configurations were investigated using three-point static bending tests. These sophisticated composite structures must be designed and used in a variety of sectors, and our research provides vital insights into their performance and failure patterns. In comparison to the reference specimens (FGM-1), the carbon nanotube-reinforced specimens’ bending capacity was affected and ranged from −2.5% to 7.75%. The amount of the carbon nanotube addition had a substantial impact on the beams’ application level and load-carrying capacity. Particularly, the application of 0.5 wt% additive in the outermost fiber region of the beams, such as in FGM-4, led to an increase in the bending capacity. However, the stiffness values at the maximum load were decreased by 0.3%–18.6% compared to FGM-1, with the minimum level of the decrease in FGM-4. The experimental results were compared with the theoretical calculations based on the high-order shear deformation theory, which yielded an approximation between 11.99% and 12.98% by applying the Navier’s solution.

Full-scale evaluation of creep coefficients and viscoelastic moduli in honeycomb sandwich pultruded GFRP composite cross-arms: Experimental and numerical study

The utilization of pultruded glass fibre-reinforced polymer composites (PGFRPC) to replace traditional wooden cross-arms in high transmission towers is a relatively recent development. While there have been numerous investigations into enhancing cross-arm structures, there remains a notable absence of research focused on the elastic characteristics of a full-scale PGFRPC cross-arm, particularly one enhanced with a honeycomb sandwich structure. To full-fill the gap, this paper presents an experimental and numerical study through cantilever beam flexural tests on assembled cross-arm condition to examine deflection behavior and the flexural creep response. For deflection behavior, the load was applied up to actual working load. For creep behavior, the hanging load was applied for 1000 h in open area condition followed ASTM D2990 standards. By using Findley's power law, confirming the ability of this empirical approach to simulate the viscoelastic response of the cross-arm. The results obtained prove that the addition of a honeycomb sandwich structure reduced deflection and improved resilience against bending forces, enhancing specific points' elastic modulus slightly. Long-term creep tests revealed Point Y3 had the highest strain, but the enhanced cross-arm displayed superior resistance and a shorter viscoelastic transition period, indicating increased stability. Besides that, the Findley's Power Law Model effectively represented creep behavior for both cross-arm types, with low errors. Over 50 years, both versions showed a significant reduction in average elastic modulus, with the enhanced variant 20 % stronger due to the honeycomb structure. In conclusion, this study validates the superior creep properties of the enhanced PGFRPC cross-arm and demonstrates the honeycomb sandwich structure's substantial role in increasing strength and extending the cross-arm's lifespan, making it a valuable enhancement for such applications.

Flexural creep response of honeycomb sandwich pultruded GFRP composite cross-arm: Obtaining full-scale viscoelastic moduli and creep coefficients

The application of pultruded glass fibre-reinforced polymer composites (PGFRPC) as a replacement material for conventional wooden cross-arm in high transmission towers is relatively new. Although there are several studies on enhancement of the cross-arm structure, there is still a lack of study on the elastic properties of a full-scale PGFRPC cross-arm enhanced with honeycomb sandwich structure. To full-fill the gap, this paper describes an experimental methodology used to obtain the elastic properties of the cross-arm using a three-point bending (3-PB) flexural test by following ASTM D790 standard for deflection behaviour and flexural creep response. The investigation involved several cross-arm members subjected to loading across different span lengths by propose two methods in order to measure the effective cross-arm member section flexural modulus (Ec) and shear modulus (Gc). The creep behaviour of the panels was successfully modeled using Findley's power law, confirming the ability of this empirical approach to simulate the viscoelastic response of the cross-arm. Next predictions were made for up to 50 years of service and the results shows the elastic modulus reduction for the enhanced cross-arm with the honeycomb sandwich structure was approximately reduce to 70 % compare with existing cross-arm which reduce almost 75 % at 50 years of application. The enhanced cross-arm exhibited lower deflection and better creep resistance and increased the bending strength of the cross-arm as well as extended its potential lifespan. Predictions indicated that the enhanced cross-arm maintained better mechanical properties over time compared to the existing one.

Flexural Creep Behavior in Utilization of Woven Glass-Fibre as Reinforcement in Pultruded Glass Fibre-Reinforced Polymer Composite Cross-Arms: Experimental and Numerical Analysis

Pultruded glass fiber-reinforced polymer (PGFRP) composite is a relatively new material used to replace conventional wood in the fabrication of cross-arms for transmission towers. Much research has been undertaken on coupon-scale PGFRP composite cross-arms. However, a few have been completed on full-scale PGFRP composite cross-arms under actual operating load. Thus, this work investigates the effect of wrapping woven glass fiber fabric as an additional reinforcement on the creep reactions of PGFRP composite cross-arms installed in a 132 kV transmission tower. In the first stage of this research, the deflection of the original cross-arm under various loads ranging from 0 to 9 kN was evaluated and was followed by the actual working loads. This experiment was repeated on cross-arms wrapped with different numbers of glass fiber fabric layers around the weakest point of the beam. Then, the creep behaviors and responses of the woven glass fiber-reinforced cross-arms were evaluated and compared with the original cross-arms from the previous study. The actual operating load was applied to the PGFRP composite cross-arms for 1000 hours to study their capability to support the weight of electrical cables and insulators. In order to replicate the tropical climate, the cross-arm were mounted on a test rig in an open area. The findings of this study revealed that reinforcing the cross-arm by wrapping it with woven glass fiber fabric could extend its life and hence reduce the maintenance cost and effort for long-term usage. The finding of this study will also become essential knowledge on woven fabric wrapping applications on square profiles.

The Material Heterogeneity Effect on the Local Resistance of Pultruded GFRP Columns.

Pultruded GFRP (glass fiber-reinforced polymer) materials are widely used in structural engineering because of their lightweight, corrosion immunity, and electromagnetic transparency. However, the design of load-bearing components facing substantial compressive stresses, e.g., columns, must be more stringent than steel structures due to excessive deformability, material heterogeneity, and vulnerability to stress concentration. This manuscript investigates the failure performance of locally produced GFRP materials, focusing on the material heterogeneity effect on the mechanical resistance of a support joint of a pultruded tubular GFRP column. This experimental campaign employs relatively short rectangular profile fragments to isolate the support behavior and verify a simplified numerical finite element model, which neglects the nonlinearity of GFRP material. This work determines the material failure mechanisms behind the mechanical performance of pultruded profiles subjected to longitudinal compression for various column lengths.

Load-carrying capacities of pultruded GFRP I-section columns under eccentric load

Pultruded fiber-reinforced polymers have been increasingly applied in engineering structures, and previous studies have focused on their axial behaviors. However, the axial load borne by the components of engineering structures is not ideal. This study presents an investigation of the behavior of I-section pultruded glass fiber-reinforced polymer (GFRP) columns subjected to eccentric loads via experiments and finite element analysis. The effects of load eccentricity around the major axis, as well as the slenderness ratio on the load-carrying capacity, were investigated. The results show that the load-carrying capacity of the GFRP column is dominated by column buckling followed by material crushing, and an increase in the eccentricity and slenderness ratio causes a decrease in the load-carrying capacity, with a progressive rate of decrease. The load-carrying capacity reduction coefficient was fitted considering the slenderness ratio and eccentricity within the scope of this study. The coefficient of determination (R2) for the fitted formula was 0.86. This study provides valuable references for designers in this field.

Experimental and numerical investigation of tensile-loaded staggered bolted and hybrid pultruded composite double lap joints

On-site construction projects typically employ staggered fastener patterns. This article describes the application of Hollo Bolts (HB). It also highlights the effectiveness of using flexible epoxy adhesive to increase the load-carrying capacity of staggered connections fastened with HB. The distribution of loads between connecting elements largely determines joint performance. Pultruded glass fiber reinforced polymer (PGFRP), bolted (B), and hybrid bolted/bonded (BB) double lap joints were subjected to a typical pulling load and numerically validated in this investigation. To simulate delamination effects, a Cohesive Zone Model with a 3D progressive damage analysis was developed. In addition, a parametric study capturing the influence of various geometrical variables such as e/d, overlap length, bolt size, adherend thickness, and the number of bolts was used to compare both categories of joints in detail. The results indicate that for staggered connections fastened with HB, an efficient load transfer can be obtained in conjunction with flexible epoxy adhesive. It is anticipated that this interaction will be even more effective as the overlap length, adherend thickness, and fastener diameter increase. The present study proves that BB connections are 43.56% stronger than B connections.

Formation of non-uniform fibre distribution and its effect on the flexural performance of pultruded GFRP box beams

This study investigates the effect of non-uniform fibre distribution (NUFD) as a defect in the pull-winding manufacturing process on the mechanical properties of pultruded glass fibre-reinforced polymer (GFRP) box section profiles. These profiles exhibit balanced mechanical properties but are susceptible to NUFD during production, negatively affecting local buckling capacity. Experimental and numerical analyses were conducted on pultruded GFRP profiles manufactured under three winding tension configurations, resulting in a 5% variance in load capacity during bending. Results show that corner NUFD influences local buckling capacity more than flange NUFD. Specifically, corner NUFD decreases load capacity by up to 20%, while flange NUFD increases it by up to 3%. Conversely, the effect of NUFD location is insignificant to the failure determined by the material strength without buckling instability. Moreover, a linear relationship between the rotational restraint coefficient and corner fibre volume fraction provides insight into the impact of material imperfections on load capacity.

Effect of drilling parameters on hole quality in drilling of pultruded GFRP composite material: Surface roughness, thrust force and delamination factor

Fiber reinforced polymer (FRP) composites are being used in a variety of areas. These materials need to be processed with some machining methods according to their usage areas, but their machinability is difficult. In this study, drilling is performed on glass fiber reinforced polymer (GFRP) composite produced by pultrusion with coated and uncoated drill. Then, surface roughness (SR), delamination factor (Fd) and thrust forces were investigated. Microstructures of chips formed during drilling were investigated and their effects on surface roughness were determined. Three distinct feed rates and cutting speeds were selected as machining parameters. Investigations showed that feed rate had a more significant effect on surface roughness, delamination factor and thrust force. It was understood that when the cutting speed increased, the surface roughness, thrust force and delamination factor decreased. Better results were obtained with TiN coated drills compared to uncoated drills.

Experimental and numerical investigation of bolted steel endplate with bonded sleeve end connections for pultruded GFRP circular tubular hollow beams

The paper presents an experimental and numerical investigation of bolted steel endplates with bonded sleeve connections developed for connecting pultruded glass fibre-reinforced polymer (GFRP) circular tubular beams. The moment-rotational responses were investigated in detail in terms of initial rotational stiffness, moment capacity, and rotation capacity for all the connections. The effect of endplate thickness and bonded sleeve length was also investigated. Predominant failure modes include bending and yielding of thinner endplates, while thicker endplates with low bonded sleeve lengths exhibit splitting failure in the bonded GFRP beam region. Available design codes for steel joints were used to classify the developed connections in terms of rigidity and strength. The failure modes from the finite element models were well matched by the experimental observations, which include the deformation of the endplate and the cohesive failure within the bonded sleeve region with the GFRP beam.

Sustainable Pultruded Sandwich Profiles with Mycelium Core.

This research focuses on exploring the potential of mycelium as a sustainable alternative to wood or solid foam in pultruded glass fiber-reinforced plastic (GFRP) sandwich profiles. The study evaluates the performance and the environmental sustainability potential of this composite by mechanical tests and life cycle assessment (LCA). Analysis and comparison of pultruded sandwich profiles with mycelium, polyurethane (PUR) foam and chipboard demonstrate that mycelium is competitive in terms of its performance and environmental impact. The LCA indicates that 88% of greenhouse gas emissions are attributed to mycelium production, with the heat pressing (laboratory scale) being the main culprit. When pultruded profiles with mycelium cores of densities 350 and 550 kg/m³ are produced using an oil-heated lab press, a global warming potential (GWP) of 5.74 and 9.10 kg CO2-eq. per functional unit was calculated, respectively. When using an electrically heated press, the GWP decreases to 1.50 and 1.78 kg CO2-eq. Compared to PUR foam, a reduction of 23% in GWP is possible. In order to leverage this potential, the material performance and the reproducibility of the properties must be further increased. Additionally, an adjustment of the manufacturing process with in situ mycelium deactivation during pultrusion could further reduce the energy consumption.

The effects of glass fiber sheet lamination on the connection strength of single-bolted pultruded glass fiber reinforced polymer profiles

In this study, a series of experiments and finite element analyses were conducted to investigate the effects of glass fiber sheet (GFS) lamination on the strength of pin-bearing single-bolted pultruded glass-fiber-reinforced polymer (PGFRP) connections. In the experiments, nine types of GFS lamination were molded using the vacuum-assisted resin transfer molding method (VaRTM) and bonded onto the surfaces of PGFRP members. Then, four different end distances of PGFRP plates to bolt diameters ( e/ d) were surveyed, ranging from 3 to 6. The results indicated that all types of GFS lamination offered excellent improvement effects for the ultimate loads of the PGFRP connections. The strengthening effects were better when the connections had smaller e/ d values. In addition, external 0°/90° GFSs provided the best performance for GFS-strengthened PGFRP connections with medium e/ d values. Finally, it was demonstrated that finite element analysis (FEA) could be a useful method for predicting the failure loads of GFS-strengthened PGFRP connections.

Web crippling performance of pultruded GFRP C sections strengthened by fibre-reinforced epoxy composite

This study aims to improve the web crippling performance of pultruded glass fibre-reinforced polymer (GFRP) C sections using fibre-reinforced epoxy composite (FEC). The strengthened GFRP C sections were subjected to two loading conditions: interior-two-flange (ITF) and exterior two-flange (ETF). The parameters considered were bearing lengths, FEC strengthening length and thicknesses. Two failure modes, namely web-flange junction failure and web buckling failure were observed for the pultruded GFRP C sections under ETF loading conditions as the bearing length changed. While the combination of the web-flange junction and FEC crushing failures were observed under ITF loading conditions at 20 mm and 50 mm bearing lengths. Furthermore, the average web crippling capacity of strengthened GFRP C sections improved by up to 426 % and 488 %, in comparison to control samples under ETF and ITF loading conditions, respectively. The average web crippling capacity of pultruded GFRP C sections increased up to 45 % when the bearing length increased from 20 mm to 50 mm. The finite element (FE) outcomes showed an agreement with experimental results in the context of failure patterns, load-displacement profiles and web crippling capacities. Finally, equations were proposed to estimate the web crippling capacity of pultruded GFRP C sections strengthened with FEC.