Glass Fiber Reinforced Polymer Laminates Research Articles

MatrixCraCS: Automated tracking of matrix crack development in GFRP laminates undergoing large tensile strains

A novel image processing method for tracking development of matrix cracks in glass-fibre reinforced polymer (GFRP) laminates is presented. Images are acquired in a quasi-static tension test using transillumination white light imaging. These images show changes occurring due to developing damage. The method, called MatrixCraCS, tracks and quantifies matrix cracks while compensating for large specimen deformation and stitching threads, which obscure crack development and seriously impact crack detection. Matrix cracks are tracked via a sequential image difference and morphological filtering is used to detect cracks. MatrixCraCS is verified against synthetic images and shows an error of less than 7% in the quantified length of cracks and 0% detection failures. MatrixCraCS is validated against experimental results for a [±452°902°]S GFRP laminate, where microscopic analysis shows 5.92% error in crack detection. Error relative to manual crack tracking are quantified for detection failures and false positives as 3.3% and 1.57%, respectively. It is found that the method accurately quantifies cracks in GFRP laminates subject to large deformation and is robust against noise.

Enhancing Flexural Strength of RC Beams with Different Steel–Glass Fiber-Reinforced Polymer Composite Laminate Configurations: Experimental and Analytical Approach

This study intended to measure the efficiency of different strengthening techniques to advance the flexural characteristics of reinforced concrete (RC) beams using glass fiber-reinforced polymer (GFRP) laminates, including externally bonded reinforcement (EBR), externally bonded reinforcement on grooves (EBROG), externally bonded reinforcement in grooves (EBRIG), and the near-surface mounted (NSM) system. A new NSM technique was also established using an anchorage rebar. Then, the effect of the NSM method with and without externally strengthening GFRP laminates was studied. Twelve RC beams (150 × 200 × 1500 mm) were manufactured and examined under a bending system. One specimen was designated as the control with no GFRP laminate. To perform the NSM method, both steel and GFRP rebars were used. In the experiments, capability, as well as the deformation and ductileness of specimens, were evaluated, and a comparison was made between the experimental consequences and existing standards. Finally, a new regression was generated to predict the final resistance of RC beams bound with various retrofitting techniques. The findings exhibited that the NSM technique, besides preserving the strengthening materials, could enhance the load-bearing capacity and ductileness of RC beams up to 42.3% more than the EBR, EBROG, and EBRIG performances.

Improving the impact performance of natural fiber reinforced laminate through hybridization and layup design

There is growing interest in Natural Fiber Reinforced Polymer (NFRP) composites for structural components despite their lower mechanical performance than synthetic composites such as Glass Fiber Reinforced Polymer (GFRP) composite. This study demonstrates significant improvement in impact resistance of NFRP-GFRP hybrid laminates can be achieved through the integration of laminate layup design with interlaminar hybridization. By placing more GFRP plies near the top and bottom of the hybrid laminate while reducing the occurrence of neighbouring GFRP-GFRP plies and neighbouring NFRP-NFRP plies around the centre of the laminate, the impact resistance of the hybrid laminate can be significantly improved and even surpass GFRP laminates. On top of stacking sequence of plies, the impact resistance of the hybrid laminates can be further improved by introducing a bio-inspired helicoidal layup. The result shows that with 30 wt% GFRP plies and 70 wt% NFRP plies, the perforation energy of NFRP-GFRP hybrid helicoidal laminate outperforms both the plain GFRP and plain NFRP laminates by 11.7% and 143.8%, respectively, whereas the peak load of the hybrid helicoidal laminate subjected to impact is also comparable to the plain GFRP laminate.

Experimental investigation on damage mechanism of GFRP laminates embedded with/without steel wire mesh under low-velocity-impact and post-impact tensile loading

Abstract To investigate the impact behavior and residual strength of glass fiber-reinforced polymer (GFRP) laminates embedded with/without steel wire mesh, low-velocity-impact (LVI) and post-impact tensile tests are conducted carefully. According to the wire diameter and spacing of steel wire mesh, we manufactured two groups of specimens via conventional vacuum-assisted resin infusion. Further, the digital image correlation technique was applied to record the strain evolution. Based on the results, including impact response history, failure morphology, strain contour, the failure mechanism and effect of the parameters of steel wire mesh is revealed in detail. The results show that the embedding of wire mesh can improve the impact resistance and residual strength, with a more significant effect as both the increase of wire diameter and decrease of wire spacing. Compared with GFRP laminates, the peak force of specimens with the thickest and densest wire mesh increase by 105% and 141% under LVI tests and 254% and 141% in post-impact tensile tests, respectively.

Moisture Effects on Acoustic Emission Characteristics and Damage Mechanisms of Balsa Wood Core Composite Sandwich under 4-Point Bending.

To contribute to the development of sustainable composites, this work investigates the effects of moisture on the key AE characteristics related to the damage mechanisms of a bio-based balsa wood core sandwich in 4-point bending tests, including cumulative counts, amplitude, peak frequency, and duration. Novel triple dog-bone balsa wood core sandwich specimens with different MC (moisture content) were studied by comparing microscopic observations and a proposed two-step clustering approach in AE analysis. Three MC states, i.e., dry, 50% MC, and 120% MC, are discussed. GFRP (glass-fiber-reinforced polymer) laminate skin damages were found to be predominant in most GFRP-balsa sandwich specimens, but balsa wood core damages play a more important role as MC increases. The degradation of the bending stiffness of the sandwich was proven to be faster in the first linear stage of the moisture absorption curve, while the decrease in bending strength was more pronounced at the MC saturation level. Finally, for all of the dry and wet sandwich specimens, peak frequency and duration were proven to be more helpful in identifying damages associated with the lighter bio-based balsa wood core, such as balsa core damages and skin/core debonding.

Fatigue performance investigation of perforated and bolted pultruded glass fiber reinforced polymer laminates based on experiment and digital images

To investigate the fatigue performance of perforated and bolted pultruded Glass Fiber Reinforced Polymer (GFRP) laminates, a series of tests are conducted including static tensile and cyclic fatigue test, while Digital Image Correlation (DIC) and CT tests were implemented to monitor strains around the perforations and damage developed in the samples subjected to tensile and fatigue tests respectively. The stress concentrations of the cyclic loaded perforated GFRP laminates are discussed based on the experiment results. Due to the stress limitation of single bolted laminates, the diameter to width ratio is suggested to be less than 0.3. The GFRP laminates with double holes have a better fatigue performance than that of single hole, which is called the double-hole effect. This effect is also found in double bolted GFRP laminates. Considering the strength of the laminates between the holes and to unify the requirement, the critical distance to width ratio is suggested to be 1.6 and the diameter to width ratio should be less than 0.3.

An Anisotropic Damage-Plasticity Constitutive Model of Continuous Fiber-Reinforced Polymers.

Accurate structural analyses of continuous fiber-reinforced polymers (FRPs) are imperative for diverse engineering applications, demanding efficient material constitutive models. Nonetheless, the constitutive modeling of FRPs is complicated by the nonlinear behavior resulting from internal damages and the inherent plasticity. Consequently, this study presents an innovative anisotropic constitutive model for FRPs, designed to adeptly capture both the damage evolution and plasticity. All requisite parameters can be easily obtained through fundamental mechanical tests, rendering the model practical and user-friendly. The model utilizes the three-dimensional Puck criteria to determine damages, initiating the evolution process through a combination of continuum damage mechanics and linear stiffness attenuation methods. This evolution is coupled with a one-parameter plastic model. Subsequently, the numerical implementation method, integrated into ANSYS, is detailed. This emphasizes the Cauchy stress and consistent tangent stiffness solution strategy. Finally, the effectiveness of the developed model is demonstrated through comprehensive verification, encompassing existing biaxial tension and open-hole-tension tests conducted on carbon and glass FRP laminates. The simulation results exhibit a remarkable correspondence with the experimental data, validating the reliability and accuracy of the proposed model.

Mode-I analysis of glass fiber-reinforced polymer laminates toughened by interleaved polyamide 66 nanofibers and chopped carbon using acoustic emission

The fracture toughness of epoxy resins is weak, so enhancing its properties is essential. In this research it was found that interleaving chopped carbon fibers and polyamide 66 nano mats between fiberglass reinforced plastic laminates with 110 µm thickness, increased fracture toughness in Mode I by 35 and 112%, respectively. Acoustic emission technique showed that damage mechanisms begin at further displacements of load point in modified samples. A hierarchical clustering model was used to classify various failure types. It was observed that matrix cracking, fiber breakage, and matrix cracking were the major damage mechanisms for Reference, chopped carbon, and nanomodified samples, respectively. The cumulative energy released by nanomodified samples was 83% lower than that of Reference and chopped carbon samples. A scanning electron microscope was used to validate different types of damage mechanisms.

Fracture research of adhesive-bonded joints for GFRP laminates under mixed-mode loading condition

Abstract The mixed-mode fracture characterization of adhesively bonded glass fiber-reinforced polymer (GFRP) plate joints is studied based on theoretical and experimental techniques. An improved beam model is used to estimate the compliance and the mixed-mode energy release rate (ERR) for GFRP four-point mixed-mode bending specimens. In this model, the deformation of the upper and lower GFRP plates is mutually independent, and the deformable adhesive is considered to satisfy the displacement compatibility conditions on the bonding interface. The explicit theoretical solutions of the compliance and ERR using the compliance method are reduced. The present theoretical solutions fit well with the finite element solutions by comparison with the rigid joint model. From the critical loads in experiment, the variation in fracture toughness on mixed-mode I/II has been determined by modifying the stiffness of the composite GFRP/GFRP substrate.

Non-additive polymer matrix coated rGO/MXene inks for embedding sensors in prepreg enhancing smart FRP composites

Two-dimensional (2D) nanosheets are promising nanomaterials that can be used as sensing elements in numerous applications such as wearable devices, machine tools, and aircraft; however, challenges remain in achieving high sensitivity, wide frequency sensing range, and reliability after long cyclic loading. Suitable ink formulations and preparation parameters for embedded sensors while retaining the structural integrity of the host structure should be determined. In this work, we demonstrated a synergistic combination of l-cysteine-reduced graphene oxide and MXene (LGM) inks in the absence of an additional polymer matrix to establish noninvasive conditions for embedding sensors in prepreg fiberglass/epoxy for smart composites with sensing capabilities. This sensor offers a high gauge factor of 47–1400 in different tensile strain ranges, with unnoticeable changes in the outstanding mechanical properties of the host glass fiber-reinforced polymer (GFRP) laminate. Long-term fatigue three-point bending tests were performed at different frequencies and bending angles, demonstrating excellent durability and stability. The corresponding sensors can also capture vibration signals in the low-high-frequency ranges. The nonintrusive embedment of sensors in GFRP laminates using the new coated non-additive polymer matrix LGM ink successfully preserves the mechanical properties of the host, including its structural integrity, with outstanding sensing performance for low-to-high-frequency signals.

Effect of Graphene Nanoplatelets on Flexural Behavior of Glass Fiber Reinforced Polymer Composites Subjected to Different Temperatures

Glass Fiber Reinforced Polymer (GFRP) Composite are increasing rapidly in Aerospace Industry, Civil and Wind energy sectors, where they can frequently be exposed to different temperature conditions. As the constituent polymer matrix is highly affected by temperature, extreme temperature conditions are critical for GFRP composite structural design. Researchers have recently found nanofillers such as graphene and carbon nanotubes with excellent multifunctional mechanical properties. Graphene Nanoplatelets (GnP) consist of several layers of graphene. GnP is considering an attractive nanofillers as it has improved polymer matrix properties. In this study, the weight percentage of GnP added in GnP-GFRP laminate is 0.25% and 0.5%.GFRP and GnP-GFRP laminates are fabricated by using the hand lay-up method, and the specimens are subjected to a three-point bending test in a thermal chamber with varying the temperature, i.e., 30°C, 50°C, 75°C, and 100°C. This paper investigates the effect of graphene nanoplatelets on the flexural behavior of glass fiber-reinforced polymer composites subjected to different temperatures. Flexural strength and modulus are evaluated, and the appropriate conclusions are determined. GFRP with 0.25% GnP shows higher strength than the neat and 0.5% GnP-GFRP. Here, it has also been shown that flexural strength and modulus decrease significantly with increasing temperature.

Effect of strain rate on glass fiber reinforced polymer composite using split hopkinson pressure bar

The aim of this study is to examine the stress–strain behavior of Glass Fibre Reinforced Polymer (GFRP) composite with three different orientations, namely [0°/90°]s, [±45]s, [0°/+45°/−45°/90°]T. To achieve this, the GFRP was simulated using the Split Hopkinson Bar (SHPB) setup in ABAQUS/CAE. The striker bar was used at three different velocities (9.7 m s−1, 12.7 m s−1, and 14.3 m s−1) to produce strain rates ranging from 1000 s−1 to 2000 s−1. The dynamic response of the GFRP composite was studied by considering its stress–strain behavior. The effect of strain rate on the elastic modulus and energy absorption capacity of GFRP laminates was analyzed through complete stress versus strain curves. The results showed that the elastic modulus and energy absorption capacity of GFRP laminates were sensitive to strain rates, with an increase in strain rate leading to an increase in the elastic modulus and energy absorption capacity.

Monitoring of Allowable Bending Stress Overload in Glass‐Fiber‐Reinforced Polymer Composites Using Magnetostrictive Fe–Co Fibers

For the safe operation of glass‐fiber‐reinforced polymer (GFRP) laminates, evaluating the applied stress and the health of composite structures is crucial. Magnetostrictive materials are functional materials that can be applied to structural health monitoring as sensor materials. Herein, a method for detecting whether the maximum stress of GFRP laminates under bending exceeds the allowable stress using magnetostrictive fibers is proposed. First, magnetostrictive Fe–Co alloy fibers are embedded in GFRP laminates. Then, four‐point bending tests are conducted. Magnetomechanical coupled modeling based on the composite beam theory is then applied to the experimental results. The effects of the position of Fe–Co fibers on the magnetostrictive behavior and mechanical properties of the prepared composites are evaluated. A concept for monitoring the relationship between the maximum bending stress and the allowable stress of the composite materials is proposed.

Comparative study of carbon and glass fiber reinforced polymer composites for the confinement of concrete columns

This study deals with the comparison of unconfined concrete specimens with carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) confined concrete specimens using epoxy as matrix. Initially, CFRP, GFRP and epoxy laminates were prepared for the analysis of various mechanical properties like tensile strength, flexural strength and fracture toughness. From the test results, CFRP and GFRP laminates exhibit better properties than neat epoxy laminate. Axial compressive strength, energy absorption characteristics, failure modes of the confined specimens are analyzed. Comparing with unconfined specimens, it is noticed that the axial load carrying capacity of GFRP confined specimens increased by 23%. While the CFRP confined specimen is compared, a considerable enhancement of 57% was noticed with a confinement effectiveness of 1.57. It is observed that confinement by the FRPs can also increase the fracture energy and ductility index significantly, which can avert the catastrophic failure of the structures.

Investigating the role of synthesized reduced graphene oxide and graphite micro-fillers on mechanical and fretting wear performance of glass fiber epoxy-based composite

In the current study, graphite was exfoliated using a Hummer’s technique to produce graphene oxide (GO), which was then reduced with hydrazine hydrate (a reducing agent) to produce reduced graphene oxide (rGO) with high purity. The XRD, FT-IR, SEM, and TGA analysis confirmed the synthesis of rGO by stating its crystal phase, chemical functional group, morphology, and thermal stability. The objective of this study is twofold: firstly, to synthesize the reduced graphene oxide (rGO) cost-effectively, and secondly, to explore its potential as an additional filler in Glass Fiber Reinforced Polymer (GFRP) composites. Aiming to enhance their overall performance. The GFRP laminate composite was fabricated through the hand layup technique by varying the concentration of Gr (i.e., 0.5 wt% & 1 wt%) and rGO (i.e., 0.5 wt% & 1 wt%). The morphological study of the fracture surface revealed a proper dispersion of filler obtained at 0.5 wt% and by increasing the concentration to 1 wt% it reveals a clustering of fillers and formation of micro-voids. The result revealed that maximum improvement has been observed in the GFRP composite having 0.5 wt% rGO composite than neat GFRP composite. Incorporation of rGO micro-filler in GFRP laminate composite significantly improved the tensile strength, flexural strength, and in their modulus by 59.56%, 18.21%, 24.45%, and 22.75% respectively compared to neat GFRP laminate composite. In the case of 0.5 wt% graphite filler demonstrates an enhancement in tensile strength, flexural strength, and their modulus by 37.98%, ∼8%, 6.64%, and ∼5% respectively. In fretting wear test reveals that 1 wt% of graphite filler has better wear resistance than all other composites. The worn morphology revealed adhesive and abrasive wear as the predominant wear mechanism. The incorporation of rGO filler in GFRP makes it a promising material for industrial applications that demand high strength and superior wear resistance.

Towards safe shearography inspection of thick composites with controlled surface temperature heating

Thick glass fiber-reinforced polymer (GFRP) composites, e.g. thickness of more than 50 mm, are increasingly used in a wide variety of industries, particularly in the marine and wind energy sectors. Defect detection and characterisation in these composites remain appealing challenges due to the material complexity and the presence of various manufacturing and in-service defects. In this study, we propose a novel shearography method with controlled surface temperature (CST) heating for deep defect detection (i.e., 15 mm depth and more) in thick GFRP laminates. The proposed CST heating has been developed based on analytical solutions to control the maximum surface temperature of a test object during shearography inspection. Numerical and experimental studies have been performed to analyse the defect behaviour and defect detection under various heating scenarios, a topic which is rarely reported for thick composites with shearography. Compared with conventional shearography, the CST shearography method maximises heating energy input with a controlled and stable maximum surface temperature for deep defect detection. Results indicate an enhancement of about 27% in defect signal for the defect at 15 mm depth in comparison to conventional heating. The results also provide insight for implementing an efficient inspection in terms of the inspection duration and the number of datasets. This study makes a step towards safe, quantitative and predictable inspection of deep defects in thick composites.

Cyclic aging analysis of CFRP and GFRP composite laminates

When a composite laminate is subjected to humidity, moisture diffusion occurs depending on the number and thickness of the lamina. Water diffusion changes the mechanical response of laminates and usually causes a significant reduction of the mechanical properties of the composite specimens in ocean structures. One of the most important mechanical properties of laminates is flexural stiffness which should be considered in the design procedure. Despite the extensive research on single cycle aging of composites, cyclic aging of these materials is less explored. The aim of the current research is to investigate the variation of mechanical properties of carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) composites as a substrate in adhesive joints with the same initial flexural stiffness values subjected to cyclic wet/dry aging conditions for long-term structural applications. The matrix used in the CFRP and GFRP composites are based on epoxy and vinyl ester, respectively. Both unaged and cyclically aged samples were characterized by tensile and three-point bending tests. In order to simulate the moisture absorption condition of composites in adhesive joints, one side of the composite laminates was sealed with aluminum foils and three sides were exposed to humidity. The interaction between the composite thickness and the number of aging cycles was also investigated. The experimental results show that in cyclic aging condition, the reduction of flexural stiffness in CFRP is more than GFRP laminates and GFRP laminates is more suitable for ocean applications.

Wavelet packet energy-based damage detection using guided ultrasonic waves and support vector machine

Substantial work has shown that the modulation of structural damage on probing guided ultrasonic waves can result in wave components corresponding to different frequencies, causing wave energy transfer from central frequency to other frequency bands. To make use of the damage-induced wave energy transfer in different frequency bands, a data-driven method which combines wavelet packet decomposition (WPD), principal component analysis (PCA) and support vector machine (SVM), is proposed in this study for structural damage identification in both metallic and composite materials. Firstly, WPD is employed to decompose the original signal into different frequency bands, based on which the wave energy at each frequency band can be determined. A wave energy distribution vector is constructed according to the energy proportion of each frequency band. Then, PCA is recalled conducting dimensionality reduction for the energy distribution vectors, in order to improve the computational efficiency for subsequent SVM classification. The compressed energy distribution vectors are used as the input to train an SVM-based classifier for identifying structural damage. To validate the proposed WPD-PCA-SVM method, experiments are performed on both aluminum plate and glass fiber reinforced polymer (GFRP) laminate. According to the experimental results, the embryonic fatigue crack in the (aluminum) plate and the anomaly in the GFRP laminate can be identified by the proposed method, with a detection accuracy of 92.86% for aluminum plate and 95.45% for GFRP laminate, respectively, demonstrating the effectiveness of the proposed method for damage detection in both metallic and composite materials.

Effect of stress level on creep-fatigue interaction of woven angle ply GFRP laminates

In this study, effect of stress level on creep-fatigue interaction of woven angle ply glass fiber reinforced polymer (GFRP) has been studied. The rectangular test specimens were manufactured using bidirectional woven ply (45˚/-45˚) E-glass fiber of eight layers with 300 GSM and layer thickness to be 0.25 mm used as fibre reinforcement and LY556 epoxy Araldite based on Bisphenol A and HY951 hardener mixed as matrix material in the ratio of 10:1. Rectangular specimens were made from the prepared laminates and tested under tensile cyclic loading of constant amplitude at stress ratio 0.1 for three stress levels 80%, 70% and 60% of ultimate tensile strength (UTS) as per ASTM standard D3479. The results showed that cyclic creep strain depends on the stress level and rapid increase in strain happens after 75% of lifecycle at all stress level.

Transverse fatigue behavior analysis of symmetric and asymmetric glass fiber‐reinforced laminates

AbstractThis study examined the effect of interchanging the position of (0°/90°) and (±45°) angle ply around the midplane of an eight‐layer symmetric [(0°/90°)/(±45°)2/(0°/90°)]s and asymmetric woven glass fiber reinforced composite laminate having [(0°/90°)/(±45°)2/(0°/90°)//(±45°)/(0°/90°)2/(±45°)] and (±45°)/(0°/90°)2/(±45°)//(0°/90°)/(±45°)2/(0°/90°) stacking sequence by means of flexure and fatigue test. The flexural and fatigue behavior of glass fiber–reinforced polymer (GFRP) laminates was analyzed as well. The GFRP laminates in varying stacking sequence having a volume fraction of 55 ± 0.9% were subjected to fatigue and damage analysis under stress levels ranging from 90% to 50% of their ultimate flexural strength at f = 1 Hz, R = 0.1. Flexure and fatigue testing was done in accordance with ASTM D790/D790‐17. The experiment results showed that the symmetric laminate with (0°/90°) ply at the compression and tension sides exhibited greater flexural strength (458.09 MPa) and fatigue lives as compared to the asymmetric A (352.70 MPa) and asymmetric B (272.89 MPa) laminates with (0°/90°) and (±45°) ply at the compression sides respectively. Microscopy and transmission light photography techniques were used to detect the damage behavior and capture the debond zone images. The correlation between the load‐deflection curve, Wohler‐curve, hysteresis loops, dynamic stiffness and debond zones was also examined with regard to different stacked laminates.