Glass Fiber Reinforced Epoxy Composites Research Articles

Influence of air DBD plasma treatment on the shear and flexural strength of adhesively bonded glass fiber reinforced epoxy composite joints

In this study, air dielectric barrier discharge (DBD) plasma treatment was applied at various voltages and treatment durations to improve the bonding strength of glass fiber reinforced epoxy composites (GF/EP). In addition, single lap shear and three-point bending strengths of adhesively bonded joints were compared between untreated and surface-treated (sanding, peel ply, and plasma) samples. Surface properties of GF/EP composites were examined using contact angle, surface free energy, X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), and Atomic Force Microscopy (AFM). Then, mechanical tests (single lap shear and three point bending) were performed and the damage modes were determined. Surface analyses revealed that wettability and polar functional groups increased on the GF/EP surface after plasma treatment. From the mechanical test results, it was observed that the plasma treatment applied to GF/EP composites increased both single lap shear and flexural strength compared to untreated, sanding and peel ply surface treatments. After both single lap shear and 3-point bending tests, adhesive, and light fiber tear failure modes were observed.

A systematic investigation of the transfer of polyphosphate/inorganic silicate flame retardants from epoxy resins to layered glass fiber‐reinforced composites and their post‐furnace flexural properties

AbstractThe systematic transfer of solvent‐free, additive flame retardant (FR) formulations from epoxy resins to glass fiber‐reinforced epoxy composites (GFRECs) through prepregs is difficult. Additionally, obtaining data on their post‐fire mechanics is often challenging. Utilizing melamine polyphosphate (MPP), ammonium polyphosphate (APP), and silane‐coated ammonium polyphosphate (SiAPP) FRs with low‐melting inorganic silicates (InSi) in an 8:2 proportion and 10% loading by weight in a diglycidyl ether of bisphenol A (DGEBA) resin, a systematic investigation of the processing properties, room‐temperature mechanics, and temperature‐based mechanics of the systems was performed. The resin was cured with a dicyandiamide hardener (DICY) and a urone accelerator. The results revealed no substantial impact of these FRs at the current loading on the resin's glass transition temperature or processability. However, the fire residues from cone calorimetry tests of the composites containing FRs were found to be only 15‐20% of the thickness of the resins, implying a suppression of intumescence upon transfer. At room temperature, the decrease in the flexural modulus for the composites containing FRs was negligible. Exposure of the composites in a furnace at 400°C as a preliminary study before ignition tests was shown to cause significant flexural moduli reductions after 2.5 min of exposure and complete delamination after 3 min making further testing unviable. This study emphasizes the need for future research on recovering modes of action upon transfer of FR formulations from resins to composites. Based on the challenges outlined in this investigation, sample adaptation methods for post‐fire analysis will be developed in a future study.Highlights Processibility of resins for prepreg production unaffected by polyphosphate/inorganic silicate flame retardants (FRs). FR formulations had a negligible effect on the mechanics of the composites. 15%–25% increase in the fracture toughness of the DGEBA‐based resin matrix with FRs. Suppression of intumescent behavior in the composites verified quantitatively. Significant reduction in flexural moduli of the composites post‐400°C exposure in a furnace.

Effect of nanoclay on the mechanical and thermal properties of glass fiber-reinforced epoxy composites

The effects of nanoclay (NC) addition on the thermal and mechanical properties of glass fiber-reinforced epoxy composites were investigated experimentally in this study. Nanocomposite plates were produced for this purpose using three different NC ratios (0.5%, 1%, and 1.5% by weight). Thermal characteristics of nanocomposites were investigated using dynamic mechanical analysis, differential scanning calorimetry, and thermogravimetric analysis. The mechanical and thermal results obtained from composites with three different NC ratios were compared with the results obtained from pure composites. The structures of nanocomposites were investigated with the help of SEM–EDS analyses. Furthermore, the effect of nanoclay on the failure behavior of composites was also investigated. In this study, the highest values in all mechanical properties were obtained from samples with a 1% NC-added. Obtained from 1% NC-added samples: tensile, compressive, shear strengths, elasticity modulus, shear modulus, and Poisson's ratio values were 31.06%, 4.25%, 14.30%, 7.35%, 11.94%, and 12.5% higher, respectively, than the values obtained from pure samples. Maximum loss modulus and maximum storage modulus were obtained from samples with 1.5% and 0.5% NC-added, respectively. In samples with 1.5% NC-added, the highest Tan δ value was obtained. Glass transition temperatures increased with the added NC. It was observed that the fiber–matrix interfaces were more clearly separated in the samples with 1.5% NC-added.Graphical abstract

Computational and experimental study on the resistance welding process of a glass fiber‐reinforced epoxy‐based composite with thermoplastic interlayer adherent

AbstractIn this work, resistance welding of a glass fiber‐reinforced epoxy composite (GFRC) was studied with numerical optimization and experimental validation. A steel mesh and polymethyl methacrylate (PMMA) films were used as the heating element and adherent interlayers, respectively. A transient heat transfer module was implemented to conduct the parametric optimization study, with variables of electricity power, clamping distance and weld time. The optimal welding condition was then confirmed as 20 W, 0.4 mm and 30 s, with a melting degree of 95.2%. A thermal meter and a thermal camera validated the simulated temperature results. Welding quality was experimentally characterized by single lap shear tests and scanning electron microscopy (SEM). The highest lap shear strength of 3.8 ± 0.3 MPa was captured on the specimen welded with the optimized condition. This was 76% that of the benchmark made with the adhesive bonding method but it was over 200 times faster.Highlights Resistance welding of GFRC with PMMA films and a steel mesh is studied with FEA. Simulation results are quantitatively validated with experimental methods. Optimal welding conditions are confirmed in association with welding tests.

Experimental and numerical analysis of the Microstructure and mechanical properties of unidirectional glass fiber reinforced epoxy composites

This paper proposes a numerical model to predict the pattern and features of the fracture surface and to understand the mechanisms and cause of the failure. Various fiber orientations of 0°, 90°, 0°/90° and ± 45° were utilized in the production of unidirectional glass-fiber-reinforced epoxy composites via the vacuum bagging technique. The mechanical properties of the manufactured composites were evaluated by measuring parameters including tensile strength, compressive strength, flexural strength and interlaminar shear strength. High-resolution scanning electron microscopy was used to examine the mechanisms of fracture in laminates. The mechanical properties of the composite material were found to be considerably improved when a unidirectional 0° fiber orientation was used, as compared to other fiber orientations. This was true for tensile, compressive, flexural and interlaminar shear loading modes. The composite laminates demonstrated several modes of breaking, including fibers pulling away from the matrix, holes in the matrix and river flow lines, depending on the direction of the fibers. The outcomes of the numerical simulation demonstrate a high level of fidelity with experimental findings. This study provides a valuable reference for predicting numerical analysis of the microstructure and mechanical properties.

Effect of Thermomechanical Loading at Low Temperatures on Damage Development in Glass Fiber Epoxy Laminates.

Due to the high interest in the use of glass/epoxy laminates in aerospace applications, aviation, and as cryogenic tanks, it is crucial to understand the behavior of composites under challenging environmental conditions. Polymer composites are exposed to low temperatures, including cryogenic temperatures, which can lead to the initiation of microdamage. This paper investigates damage initiation/accumulation and its influence on the properties of cross-ply woven glass fiber epoxy composites at low temperatures compared to room temperature conditions. To evaluate the influence of a low-temperature environment on the mechanical performance of glass fiber reinforced epoxy composite (GFRP) laminates, three types of test campaigns were carried out: quasi-static tensile tests and stepwise increasing loading/unloading cyclic tensile tests at room temperature and in a low-temperature environment (-50 °C). We demonstrated that the initial stiffness of the laminates increased at low temperatures. On the other hand, there were no observed changes in the type or mechanism of developed damage in the two test conditions. However, the reduction in stiffness due to the accumulated damage was more significant for the laminates tested at low temperatures (~17% vs. ~11%). Exceptions were noted in a few formulations where the extent of damage at low temperatures was insignificant (<1%) compared to that at room temperature. Since some of the studied laminates exhibited a relatively minor decrease in stiffness (~2-3%), we can also conclude that the formulation of matrix material plays an important role in delaying the initiation and formation of damage.

Effect of Combining Nano- and Microfillers for the Assessment of Thermal Class of Glass Fiber-Reinforced Epoxy Composites for Outdoor Insulation

The present work was taken up with the objective to develop a compact and reliable hybrid composite insulation, investigate the thermal properties of the developed composites and correlate the experimental data with results of mathematical modelling. A composite material made of unidirectional glass fibers reinforced with epoxy resin, and containing silica, alumina, and aluminatrihydrate fillers, was fabricated using the pultrusion technique. Thermogravimetric analysis, thermal conductivity, and coefficient of thermal expansion were conducted on the developed composites. The energy of activation was estimated from the thermograms using mathematical models to assess the thermal class of the composites. Though G-E composite is typically classified under class F insulation, the study has established that due to the unique filler combination, has a higher temperature index ranging between 156 °C - 166 °C. The improvement in thermal performance was observed when each filler is present in a weight percentage of 10%. The hybrid composites have excellent thermal conductivity (0.43 W/mK), a low coefficient of thermal expansion (22.1 μm/m°C), and hence useful for high-temperature insulation applications like circuit breakers, vacuum interrupters, transformers, switching gear etc.

Experimental investigation on impact behavior of curved sandwich composites with chiral auxetic core

The purpose of this study is to evaluate and compare the capability of impact energy absorption of the sandwich panels with various chiral auxetic cores. To this end, flat and curved panels were subjected to impact testing at varying energy levels. Glass fiber-reinforced epoxy composites and PLA material were used as the skins and core of the examined sandwich panels, respectively. The face sheets were produced by the hand-layup method and the auxetic cores with tetrachiral, anti-tetrachiral, and hexachiral configurations were printed using a 3D printer. The wall thickness, node diameter, and ligament length of the cells, as well as the core thickness, were kept constant for all the studied core structures. Flat and curved sandwich panels were obtained by combining the skins and cores produced in flat, 100 mm, 125 mm, and 160 mm radii of curvature with the epoxy used in skin production. Drop weight tests were carried out at impact energies of 10, 25, and 80 J. The contribution of the auxetic core configuration and panel curvature to the impact behavior of the sandwich panel was evaluated by examining the relationships between contact forces and deflection and by the analysis of the energy absorption and failure mode. The comparative evaluations showed that the auxetic core structure and the curvature of the panel have a significant effect on the impact properties of the sandwich panels. It was also observed that the use of tetrachiral cores could be the ideal design option for flat panels loaded at the perforation energy level. For curved panels, it was determined that the use of a hexachiral core configuration was advantageous in terms of more energy absorption capability, while the use of an anti-tetrachiral core structure was more effective in terms of specific energy absorption.

Effect of nano‐silica on fatigue behavior of glass fiber‐reinforced epoxy composite laminates: A Weibull distribution approach

AbstractThe aim of this study is to assess the impact of nano‐silica in glass fiber‐reinforced epoxy composite (GFEC) subjected to static and fatigue loading. Laminates were prepared in compression molding machine followed by the tensile test and tension‐tension fatigue testing at five different stress levels (from 50% to 90% of ultimate tensile strength). The addition of 3 wt% of nano‐silica with epoxy improved the tensile and fatigue strength as compared to neat GFEC. Scanning electron microscope (SEM) images of the fractured specimen showed the damage pattern which indicates that neat GFEC laminate exhibited damage patterns characterized by fiber breakage and matrix cracking. On the other hand, the modified GFEC with nano‐silica showed damage patterns including fiber pullout accompanied by fiber breakage and matrix cracking. During cyclic loading, the stress–strain hysteresis loop shows a reduced slope, indicating a decrease in the dynamic modulus of the specimen. This reduction in slope signifies a loss of stiffness during cyclic loading, particularly at high‐stress levels. The highest dynamic modulus at high‐stress levels indicates a rapid progression of severe damage and a shorter fatigue life. On the other hand, at low‐stress levels, the lower magnitude of dynamic modulus suggests a moderate damage progression and a longer fatigue life.Highlights Effect of nano‐silica in GFEC under static and fatigue loading conditions. GFEC with 3 wt% of nano‐silica shows improved tensile and fatigue strength. Examination of damage patterns through SEM analysis of the fractured surface. Depiction of the failure modes using damage pattern under fatigue loading. Comparison of fatigue life and dynamic modulus for neat and modified GFEC.

The effects of zircon particles on the mechanical and morphological properties of glass fibre reinforced epoxy composite

Recent studies have focused on improving the mechanical properties of thermosetting composites that seem to include inorganic nanoparticles dispersed throughout the matrix material. This study investigates the mechanical properties, crystallographic and morphological study of epoxy composites when ball-milled zircon filler is incorporated into epoxy at weight percentages of 0, 5, 10, and 15(wt%). Zircon nanoparticles and epoxy resin are blended using an ultrasonic liquid technique, and then compression moulding is used to make the composite materials. Using theoretical and calculated densities (g/cm3), the volume fraction of voids (%) in the prepared composites is estimated. The Mechanical tests were done in accordance with ASTM requirements. The average zircon particle size was found to be 73.26 nm using field emission scanning electron microscopy. The chemical composition, crystalline structure and the crystalline size (2.1 nm) of zircon particle was determined using X-Ray diffraction. In comparison to pure glass fibre reinforced epoxy polymer, the 10 wt% zircon particle's tensile strength, tensile modulus, flexural strength, and flexural modulus are 33.33%, 12.56%, 32.88%, and 15.74% higher, respectively. Strain energy for tensile test is 82.96%, elongation at break is 53.52% higher and strain energy for flexural test is 52.38%, elongation at break is 14.67% higher than pristine composites. As a comparison to neat sample, Shore "D" hardness at 10 wt percent ZrSiO4 is 5.88% harder, and Izod average impact strength (J/mm) is 63.20% greater. Pullout of fibre, damaged interfaces, filler dispersion and voids are identified using field emission scanning electron microscopy. Zircon filler of 10 wt% inclusion on epoxy with E-glass fibre reinforcement reportedly improves characteristics than other proportions, especially better improvement than plain sample. Because of this, the mechanical and structural properties of developed composites are enhanced by this approach. This research proposal would lead to a special combination of ZrSiO4 inclusion and E-glass fibre reinforcement in epoxy composites for aircraft structural applications.

Mechanical, tribological, and surface morphological studies on the effects of hybrid ilmenite and silicon dioxide fillers on glass fibre reinforced epoxy composites

Recently, researchers have been attempting to enhance the mechanical and tribological characteristics of thermosetting epoxy composites by incorporating inorganic nanoparticles and ensuring their uniform distribution throughout the matrix. This study characterises ball-milled ilmenite (FeTiO3-size of 63 nm) and silicon dioxide (SiO2-size of 67.5 nm) fillers added to epoxy in proportions of 0:0, 2.5:2.5, 5:5, and 7.5:7.5% by weight. A liquid ultrasonic technique is used to blend the fillers with the epoxy, and compression moulding is used to fabricate the composite. Mechanical tests were performed based on ASTM standards. Tensile strength, tensile modulus, flexural strength, flexural modulus and elongations at break(tensile and flexural test) of 5:5 wt % are 30.54%, 12.2%, 32.22%, 28.98%,23.78% and 23.53% higher than neat sample respectively. Shore "D" hardness and Izod's impact strength are 4.65% and 98.93% higher at 5:5 wt % than neat sample respectively. Specific wear rate decreased from 2.6 × 10−11 m3/Nm (neat GFRP: 0 wt % glass fibre reinforced polymer composite) to 0.7 × 10−11 m3/Nm at 5:5 wt % filler. Nanoparticles lowered the coefficient of friction by around 16.66%, 60.42%, and 33.33% at sliding distances of 100 m for 2.5:2.5, 5:5, and 7.5:7.5 wt % respectively with the neat sample. A 5:5 wt percent resulted in 76.68% less wear volume loss than pure GFRP. Field emission scanning electron microscopy (FESEM) analysis revealed element distributions, particle size, pullout of fibers, damaged interfaces, filler dispersion, voids, wear debris, interfacial debonding, and cavities. Thus, this approach enhances GFRP composite's mechanical, tribological, and structural properties.

Experimental Analysis on the Impact Behaviour of Graphite-Filled Glass Fibre Reinforced Epoxy Composites Subjected to Sea Water Ageing and Notch Depth

Experimental Analysis on the Impact Behaviour of Graphite-Filled Glass Fibre Reinforced Epoxy Composites Subjected to Sea Water Ageing and Notch Depth

Numerical and Experimental Investigations on the Low Velocity Impact Properties of Glass Fiber Reinforced Epoxy Composites: Effects of Radius of Curvature

Numerical and Experimental Investigations on the Low Velocity Impact Properties of Glass Fiber Reinforced Epoxy Composites: Effects of Radius of Curvature

Electrical degradation dynamics of glass fiber-reinforced epoxy composites considering different fiber orientation

Glass fiber-reinforced epoxy composites (GFREC) have been widely used in the mechanical components of electrical and electronic devices because of its lightweight, high mechanical strength, excellent electrical insulation properties and corrosion resistance. The research on the electrical degradation dynamics of GFREC is of great significance to avoid the failure of electrical insulation system. Herein the composite samples were prepared using vacuum impregnation technique. The electrical degradation morphology and statistical characteristics (electrical tree length, width, expansion coefficient, breakdown probability and breakdown time) were discussed. The results show that the electrical tree will develop towards the fiber side and grow rapidly along the interface in GFREC. The interfacial orientation will affect the growth characteristics of electrical tree. When the angle between the glass fiber and the needle electrode is 45°, the composite material has relatively superior tree propagation resistance performance, lower breakdown probability and higher breakdown time. The effects of electric field distribution on the tree initiation and electrical degradation are discussed, which reveals the relationship between the electrical degradation and the fiber orientations. The electric field-driven tree growth (FDTG) model is used to explain the growth of trees along interfaces with different orientations from the perspective of dynamic electric field distribution.

Low-velocity impact behavior of 3D woven structural honeycomb composite

This paper describes the in-plane impact behavior of 3D woven honeycomb sandwich composites comprising glass fiber reinforced epoxy composite. In this study, 3D woven honeycomb structures with similar cell shapes were developed with different cell geometry by varying the cell size, free wall length, bonded wall length, opening angle, and the number of honeycomb layers keeping the overall thickness of the composite constant. The variation of cell geometry was carried out by changing the number of picks in the honeycomb walls. Composite samples were made using VARIM (vacuum-assisted resin infusion method) process. The behavior of the force-displacement curve and the energy-time relationship under impact loading of 100 J were analyzed. The total energy absorption was determined for different cell geometry and the number of layers of the honeycomb composites. The results showed that structural changes in honeycomb composite significantly affect the specific energy absorption. The specific energy absorption increases with a large cell size, less opening angle, higher wall length, and a greater number of layers.

Evaluation of self-healing capability of a polycaprolactone interphase in epoxy/glass composites

Self-healing composites possess the ability to self-repair in response to damage, either autonomously (i.e., without human intervention), or when subjected to an external stimulus such as heat. This work was focused on the evaluation of the interfacial self-healing capability of glass fiber-reinforced epoxy composites in which polycaprolactone nanoparticles were deposited as a coating on the surface of the fibers. Polycaprolactone nanoparticles were synthesized following solvent displacement technique and deposited on the fibers (with and without the sizing agent) by electrophoretic deposition. Scanning electron microscopy revealed high-quality nanoparticles deposition, with good level of homogeneity and compactness. Epoxy microdroplets were cured on the fibers and microdebonding tests were performed to estimate the interfacial self-healing capability, calculated as the ratio of the interfacial shear stress measured before and after the thermal mending process. An interfacial adhesion recovery of about 50 % was obtained, thus indicating an interfacial self-healing capability induced by the polycaprolactone nanoparticles.

Effect of Water Absorption on Graphene Nanoplatelet and Multiwalled Carbon Nanotubes-impregnated Glass Fibre-Reinforced Epoxy Composites

Effect of Water Absorption on Graphene Nanoplatelet and Multiwalled Carbon Nanotubes-impregnated Glass Fibre-Reinforced Epoxy Composites

Waste Iron Filings to Improve the Mechanical and Electrical Properties of Glass Fiber-Reinforced Epoxy (GFRE) Composites

Several studies have been conducted to improve the mechanical and other value-added properties of glass fiber-reinforced epoxy (GFRE) composites by the addition of different fillers. In this work, waste iron filings (WIFs) obtained from the steel industry were incorporated into GFRE composite samples in varying amounts of up to 50% (%w) to improve their mechanical and electrical properties. The results showed that, with increasing WIF loading from 0 w% to 50 w%, the resultant composite density gradually increased from 1.4 to 2.1 g/cm3. Surface hardness, Young’s modulus, and tensile strength also increased significantly with the addition of up to 9 w% of WIF followed by a significant drop with more WIF addition due to agglomeration. Overall, Young’s modulus of the GFRE samples with any WIF content was higher than that of the GFRE composite with no WIF. The elongation at break results showed that the GFRE samples were less ductile upon WIF addition, which decreased from 2% to 0.6% upon loading the composite with 50% WIF. In terms of electrical conductivity, the GFRE samples with WIF content of 15% or more were electrically conductive and their electrical conductivity increased with WIF content. It was clear that more WIF was needed to establish a percolated network in the GFRE composites to render them conductive. The electrical conductivity of the GFRE samples containing 15% WIFs was around 2.9 kS/m and increased to 35 kS/m upon the addition of 50% WIFs. These novel electrically conductive GFRE composites could be promising for structural dynamic monitoring systems in the construction industry. They also support the efforts for the utilization of waste materials towards a circular economy.

New designs of sandwich panels to mitigate high-frequency noise inside space vehicles

Radiation of noise to the interior of a space vehicle during liftoff and transonic climb is a long-standing problem. To attenuate noise inside the crew compartment during launch and in-space operation, sandwich panels have been employed in the pressurized outer shell to passively reduce the exterior noise transmission. However, the layouts and the sound transmission loss of the implemented sandwich panels have not been made available for public release. Against this idiosyncratic practice, this study envisioned disseminating the know-how on the sound attenuation ability of dissimilar sandwich panels. To efficiently absorb and dampen the acoustic energy, the sandwich panels were specifically configured using a honeycomb core, felts and a closed cell aluminum-foam in the material lay-up. The face sheets of the sandwich panels consisted of either glass fiber-reinforced epoxy or carbon fiber-reinforced epoxy composites. The sandwich panels were tested as acoustic barriers to a diffuse sound field in a sound transmission suite. As found, an increase in the panel thickness brought a decrease in the anti-symmetric coincidence frequency of sandwich panels. A rubber damping layer in the material lay-up added limp mass to a sandwich panel and reduced the panel vibration at excitation frequencies beyond 500 Hz. Multiple felts reinforced the sound transmission loss of a sandwich panel by dissipating the acoustic energy into thermal energy at the felt interstices in the frequency regime beyond 315 Hz. In conclusion, this study proposed optimized sandwich configurations considering the constitutive materials, number of material layers, material layer thickness and stacking sequence. The optimized sandwich configurations could fairly deliver the demanded sound transmission loss in the high-frequency regime.

Effect of cellulose nanofibers on the fracture toughness mode II of glass fiber/epoxy composite laminates

Cellulose nanofibers (CNFs) were used to improve the fracture toughness of glass fiber reinforced epoxy composites (GFRPs). Different CNF suspensions were prepared and sprayed onto the surface of woven glass fiber laminates. The vacuum resin transfer molding (VaRTM) process was used to manufacture the GFRP composites. End notch flexure tests were conducted to evaluate the effect of CNFs on the critical energy release rate in mode II fracture toughness GIIC. The results revealed that 0.05 wt% was the optimum concentration. The interlaminar fracture toughness GIIC was improved by 28% with the addition of 0.05 wt% of CNFs to GF/epoxy composites. Whereas 0.1 wt% of CNFs resulted in decreasing GIIC due to the uncomplete impregnation of GF with epoxy resin caused by the thicker CNF layer at the interfacial laminates. The toughening mechanisms were investigated using a field-emission electron microscope. Large epoxy deformations and shear hackles were predominant for improving the interlaminar fracture toughness of GFRP composites.