Grade Epoxy Research Articles

Interlaminar fracture properties of UV and plasma‐treated glass fiber epoxy composites

AbstractDespite the low density and high specific strength properties, the fiber‐reinforced composites are characterized by a relatively low interlaminar fracture toughness and their ultimate properties are strongly affected by the fiber matrix adhesion. This study aims to investigate the influence of fiber surface treatments, such as UV and atmospheric plasma, and of the interfacial shear strength, on the flexural properties and Mode I interlaminar fracture toughness of glass fiber epoxy composites. The vacuum‐assisted resin infusion technique is used for the composite fabrication. Scanning Electron Microscopy analysis is used to observe and to explain the changes in the morphology of the fibers after surface treatment. Remarkably, the results showed an overall reduction in the mechanical properties. The interfacial shear strength values of the UV and plasma‐treated samples were reduced by 34.9% and 49.5% respectively. The flexural strength was reduced by 7.9% and 5.9% respectively. The Mode I fracture toughness values for the UV and plasma‐treated samples were also reduced by 49.8% and 62.2% respectively.Highlights UV and plasma treatments were performed on glass fibers to improve performance. Push‐out tests were carried out to evaluate fiber/matrix adhesion. An aerospace grade epoxy resin curing in thermal press‐clave was used. Mechanical tests related Interfacial Shear Strength to composites performance.

Enhanced mechanical and interfacial performances of carbon fiber reinforced composites with low percentage of amine functionalized graphene

AbstractThis paper reports improvement in the tensile, flexural and interlaminar shear strength (ILSS) properties of ADG‐NH2/Epoxy/CFRP composites at low filler content. Five symmetrical CFRP composite laminates were prepared through wet layup process assisted by vacuum bagging technique with varying wt% proportions (0.25, 0.5, 0.75 and 1) of ADG‐NH2/Epoxy. Tensile tests, short beam shear test and flexural tests were carried out as per ASTM D3039, ASTM D2344 and ASTM 790‐10 respectively to assess the effect of the ADG‐NH2 functionalized nano additives on their mechanical properties. The variation in ILSS were studied for varying temperatures (room temperature, 35, 50, 75, 85, & 100°C for each type of ADG‐NH2/Epoxy wt% (neat, 0.25, 0.5, 0.75 & 1)) of ADG‐NH2/Epoxy/CFRP composites. The ILSS was enhanced up to ∼27% for 0.5 wt% of ADG‐NH2 reinforced CFRP at room temperature but reduced with the higher concentrations (0.75 wt% & 1 wt%). It was observed that ILSS reduced with gradual temperature variations up to 100°C w.r.t room temperature. But an increment was observed up to 0.5 wt% for ADG‐NH2 for all temperature. Form the test results, it has been recorded an improvement in mechanical properties that is, the elastic modulus by ∼18%, ultimate tensile strength by ∼21%, % elongation at break by∼19% and toughness by∼28% for the 0.5 wt% of ADG‐NH2 graphene nano additive reinforced CFRP composite laminates as compared to neat epoxy CFRP laminates. Results also show the augmentation in the Max load by ∼24%, flexural strength by ∼33%, flexural modulus by ∼43%, and flexural strain by ∼26% were observed for the 0.5 wt% of ADG‐NH2 graphene nano additive reinforced CFRP composite laminates as compared to neat epoxy CFRP composite laminates. Fractographic studies of fractured surface using SEM analyses shows better adhesion mechanisms which supports the augmentation in mechanical properties with addition of amine functionalized graphene to CFRP laminate.Highlights Reinforcement of amine functionalized (ADG‐NH2) graphene in the epoxy matrix and incorporation with carbon fibers to enhance the interfacial and flexural properties. Evaluation of temperature effects on interlaminar shear strength properties of amine functionalized CFRP composites Improvements in tensile, ILSS and flexural properties observed for a low percentage (0.5 wt%) of ADG‐NH2 graphene reinforced CFRP composite laminates. Use of aerospace grade epoxy and resin with amine functionalized graphene for further use in aerospace industry applications.

Effects of silver nanowires and their surface modification on electromagnetic interference, transport and mechanical properties of an aerospace grade epoxy

The aerospace industry has progressively grown its use of composites. Electrically conductive nanocomposites are among important modern materials for this sector. We report on a bulk composite containing silver nanowires (AgNW) and an aerospace grade epoxy for use in carbon fiber reinforced polymers (CFRPs). AgNWs’ surfaces were also modified to enhance their ability to be dispersed in epoxy. Composites were obtained by use of three-roll milling which is of major interest for industrial applications, especially for the aerospace sector, since the process is scalable and works for aerospace grade resins with high curing temperatures. Our main objective is to improve the electromagnetic interference (EMI) shielding performance of CFRPs via improving the properties of the resin material. The addition of AgNWs did not considerably alter the flexural strength of the epoxy, however the composite with surface-modified AgNWs has a 46 % higher flexural strength. Adding AgNWs over a low threshold concentration of 0.05 wt% significantly enhanced the electrical conductivity. Conductivities above the percolation threshold lie around 102 S/m. At a concentration of 5 wt% AgNW, the EMI shielding efficiency (SE) of epoxy increased from 3.49 to 12.31 dB. Moreover, the thermal stability of the epoxy was unaffected by AgNWs. As a result, it was discovered that (surface modified) AgNWs improved the (multifunctional) capabilities of the aerospace grade epoxy resin which might be used in CFRPs to further enhance properties of composites parts, demonstrating suitability of AgNWs’ as a reinforcement material in aerospace applications.

Assessing sustainability and green chemistry in synthesis of a Vanillin-based vitrimer at scale: Enabling sustainable manufacturing of recyclable carbon fiber composites

Sustainable manufacturing of carbon fibre (CFs) reinforced polymer (CFRP) composites featured technically by low-cost and rapid manufacturing techniques, use of renewable materials, and non-destructive recycling process. By developing an inherently recyclable thermoset, this research bridges between these three components of sustainable manufacturing by focusing on a fast cured vanillin-based Schiff base polyimide network in all-solid state. In this study, a multifunctional vanillin-based monomer was synthesised at scale in water which can be cured using a diamine without requiring any organic solvent. A CFRP was fabricated using this newly developed Schiff base polymer using compression moulding technique, and its mechanical and thermal/fire performance were compared to a CFRP made of a commercially available automotive grade epoxy resin. The resulting Schiff base CFRP composite demonstrated exceptional fire retardancy, complemented by remarkable tensile strength and modulus values of 427 MPa and 45 GPa, respectively. These characteristics meet the criteria for a broad spectrum of high-performance applications. In contrast to conventional CF reclaiming processes, a novel and efficient chemical recycling approach was introduced, enabling the delamination of CF layers containing the Schiff base network without requiring the separation and purification of the polymer matrix. This approach facilitates the low-cost remanufacturing of new CFRP composites with mechanical performance comparable to the original composite. Finally, green chemistry matrices as well as simplified life cycle assessment (LCA)-like approaches, including the EcoScale and GREEN MOTION rates, were employed to evaluate the efficiency and environmental impact of the CFRP manufacturing process.

Physical and mechanical properties of graphene and h‐Boron nitride reinforced hybrid aerospace grade epoxy nanocomposites

AbstractVarying graphene nanoplatelet (GNP) and hexagonal boron nitride (h‐BN) based fillers were integrated to an aerospace grade epoxy resin typically used as matrix to obtain or repair structural parts of aerospace platforms. The three‐roll milling approach was used for this purpose. Five cycles were performed for the mixing while the gap between rollers was 50 μm. Microstructure and thermal properties of the nanocomposites were studied. Moreover, mechanical and transport (electrical as well as thermal) performances were investigated. Results show that certain fillers yield multifunctional properties, that is, enhanced flexural strength by up to 69% in combination with high electrical conductivities with orders of magnitude of approximately and improved thermal conductivities up to 9.3%. For instance, the hybrid nanocomposite sample produced with 0.5 wt% GNP and 0.5 wt% h‐BN added to the epoxy matrix exhibits an electrical conductivity which increased fold, a flexural strength increased by 69% and thermal conductivity increased by 7% in comparison the neat epoxy. Hence, in this study it was demonstrated that these properties can be engineered and tuned effectively for aerospace applications like lightweight avionic chassis which have specific requirements like thermal and electric conductivity which naturally leads to the possible usage of GNP and h‐BN in an epoxy. Correspondingly, presented results are of relevance for novel thermal interface materials with tailored electrical properties.

The influence of key processing parameters on thermoset laminate curing

The many uncertainties in thermoset composite laminate processing can have undesirable consequences. It is impractical to address the uncertainties individually. A methodology is introduced in this study that ranks parameters by an influence metric to give insights into how to reduce variability in cure time most effectively. The presented example considers a range of parameters from the material, geometry, and processing conditions within a thermochemical model of composite laminate curing. Due to the nonlinearities in the process, the influence metric must include representative parameter uncertainty. In the example considered here of a high-performance aerospace grade epoxy system, dwell temperature and diffusion terms in the cure kinetics model were most influential. This was a result of a long dwell period and a post-vitrification final degree of cure. Therefore, the best investment to reduce curing variability is processing equipment with repeatable and uniform temperature.

Tailored multifunctional nanocomposites obtained by integration of carbonaceous fillers in an aerospace grade epoxy resin curing at high temperatures

Tailored multifunctional nanocomposites obtained by integration of carbonaceous fillers in an aerospace grade epoxy resin curing at high temperatures

Effect of loading strain rate on nano-indentation response of an aerospace grade epoxy polymer

Effect of loading strain rate on nano-indentation response of an aerospace grade epoxy polymer

Aero Grade Epoxy Vitrimer towards Commercialization.

Traditional crosslinked aero grade epoxy resins have excellent thermal-mechanical properties and solvent resistance, but they cannot be remolded, recycled, or repaired. Vitrimers can be topologically rearranged via an associative exchange mechanism, endowing them with thermoplasticity. Introducing dynamic bonds into crosslinked networks to obtain more sustainable thermosets is currently an interesting research topic. While recent research into vitrimers has indicated many advantages over traditional thermosets, an important shortcoming has been identified: susceptibility to creep at service temperature due to the dynamic bonds present in the network. In addition, designing aero grade epoxy vitrimers (similar to RTM6 resin) still remains a challenge. Herein, low creep aero grade epoxy vitrimer with thermal and mechanical properties similar to those of aero grade epoxy resins and with the ability to be recyclable, repairable, and reprocessable, has been prepared. In this manuscript, we demonstrate that aero grade epoxy vitrimer with reduced creep can be easily designed by the introduction of a certain fraction of permanent crosslinks, without having a negative effect on the stress relaxation of the material. Subsequently, the mechanical and relaxation properties were investigated and compared with those of classical aero grade epoxy resin. A high Tg (175 °C) epoxy vitrimer was obtained which fulfilled all mechanical and thermal specifications of the aero sector. This work provides a simple network design to obtain aero grade epoxy resins with excellent creep resistance at elevated temperatures while being sustainable.

Numerical Analysis of Micro-Residual Stresses in a Carbon/Epoxy Polymer Matrix Composite during Curing Process.

The manufacturing process in thermoset-based carbon fiber-reinforced polymers (CFRPs) usually requires a curing stage where the material is transformed from a gel state to a monolithic solid state. During the curing process, micro-residual stresses are developed in the material due to the different chemical–thermal–mechanical properties of the fiber and of the polymer, reducing the mechanical performance of the composite material compared to the nominal performance. In this study, computational micromechanics is used to analyze the micro-residual stresses development and to predict its influence on the mechanical performance of a pre-impregnated unidirectional CFRP made of T700-fibers and an aeronautical grade epoxy. The numerical model of a representative volume element (RVE) was developed in the commercial software Abaqus® and user-subroutines are used to simulate the thermo-curing process coupled with the mechanical constitutive model. Experimental characterization of the bulk resin properties and curing behavior was made to setup the models. The higher micro-residual stresses occur at the thinner fiber gaps, acting as triggers to failure propagation during mechanical loading. These micro-residual stresses achieve peak values above the yield stress of the resin 55 MPa, but without achieving damage. These micro-residual stresses reduce the transverse strength by at least 10%, while the elastic properties remain almost unaffected. The numerical results of the effective properties show a good agreement with the macro-scale experimentally measured properties at coupon level, including transverse tensile, longitudinal shear and transverse shear moduli and strengths, and minor in-plane and transverse Poisson’s ratios. A sensitivity analysis was performed on the thermal expansion coefficient, chemical shrinkage, resin elastic modulus and cure temperature. All these parameters change the micro-residual stress levels and reduce the strength properties.

Study of Water Absorption Properties of Annealed Nanodiamond/Epoxy Nanocomposites

Water absorption behavior of annealed Nanodiamond (ND) particle filled epoxy composite, has been studied. Removal of impurity present in the pristine ND and its surface modifications, were carried out by heat treatment. Different weight percent of ND (0.1, 0.3 and .05 wt. %) were incorporated in a commercial grade epoxy resin (L-12) in a controlled manner. A good and homogeneous distribution of ND in the composite, was observed. This resulted in reduction of mobility of the epoxy chain due to formation of highly immobile mono-layers around ND as well as formation of hydrogen bond between the ND and the epoxy. The water absorption and the contact angle properties of the resulting composites are measured. The results indicate that the water absorption as well as contact angle of the composite decrease with the increase of incorporated ND. It is observed that incorporation of ND into epoxy matrix, enhances the water resistance property of the composite.

Study on the impact of Nano-reinforcements on the fatigue strength of adhesive joints

Single overlap joints had been created by combining two AISI 302 stainless steel sheets with the help of 3 M DP270 grade epoxy and their fatigue characteristics were examined under shear stress condition. Further, the effect of adding three distinct proportions of nano-titania with epoxy, on the mechanical characteristics of the joint was analyzed. The overlap lengths was selected as 20 mm and nano-titania proportions were elected as 1.0%, 2.0% and 4.0%, respectively during shear load condition. When the experimental findings were analyzed, it was shown that the mean damaging load associated with the usage of nano-dispersed adhesives rose significantly in general. As a consequence of the trials, it was discovered that the most effective nanoparticles proportion for boosting the fracture strength of adhesive joints is 4.0 percent, and the enhancement in rate of failure strength increase was noted as 85.52 percent. Additionally, it was shown that strain of nanoparticle had a noteworthy role in the shear characteristics of the adhesive junctions. Additionally, it has been shown that incorporating nanoparticles into the glue enhances junction extension. When the adhesive interfaces of the specimens were inspected, impairment was detected as adhesion dissociation, but nanoparticle replenishment had been detected as a combination of cohesive as well as adhesive characteristics.

Mechanical Properties and Characterization of Epoxy Composites Containing Highly Entangled As-Received and Acid Treated Carbon Nanotubes.

Huntsman–Merrimack MIRALON® carbon nanotubes (CNTs) are a novel, highly entangled, commercially available, and scalable format of nanotubes. As-received and acid-treated CNTs were added to aerospace grade epoxy (CYCOM® 977-3), and the composites were characterized. The epoxy resin is expected to infiltrate the network of the CNTs and could improve mechanical properties. Epoxy composites were tested for flexural and viscoelastic properties and the as-received and acid treated CNTs were characterized using Field-Emission Scanning and Transmission Electron Microscopy, X-Ray Photoelectron Spectroscopy, and Thermogravimetric Analysis. Composites containing 0.4 wt% as-received CNTs showed an increase in flexural strength, from 136.9 MPa for neat epoxy to 147.5 MPa. In addition, the flexural modulus increased from 3.88 GPa for the neat epoxy to 4.24 GPa and 4.49 GPa for the 2.0 wt% and 3.0 wt% as-received CNT/epoxy composites, respectively. FE-SEM micrographs indicated good dispersion of the CNTs in the as-received CNT/epoxy composites and the 10 M nitric acid 6 h treatment at 120 °C CNT/epoxy composites. CNTs treated with 10 M nitric acid for 6 h at 120 °C added oxygen containing functional groups (C–O, C=O, and O=C–O) and removed iron catalyst present on the as-received CNTs, but the flexural properties were not improved compared to the as-received CNT/epoxy composites.

Thermal Stability and Tribological Behaviors of Tri-fillers Reinforced Epoxy Hybrid Composites

The present works investigates the thermal stability and wear behaviour of tri-fillers reinforced hybrid composites. The Silica (S), Coconut shell (C) and Graphite (G) fillers reinforced homogeneous and functional graded epoxy composites are prepared by vertical injection molding techniques. The effect of filler contents, design parameters and its interaction on wear and friction behavior of SCG composites has been investigated. With help of Taguchi’s techniques, L27 orthogonal array, a series of experiments are planned and conducted on pin-on-disc tribo machine with three different loading of 10, 20 and 30 N, three sliding velocities of 1, 1.5 and 2 m/s by varying the G filler content of 10, 20 and 30 wt.% with constant weight fraction of S and C fillers of 10 wt.%. The results shows that the increasing the Gr content was increased the wear resistance and rate. The optimization techniques used to pridicated the composites parameters.

Thermal and Electrical Behaviour of the Persistent Current Switch for a Whole-Body Superconducting MRI Magnet

A prototype persistent current switch is developed for an actively shielded whole-body 1.5 T MRI magnet having an operating current of ∼500 A. The switch is developed using a six-strand CuNi-NbTi conductor. The total length of the conductor used in the PCS is ∼40 m using a bifilar winding technique having a room temperature resistance of 15 Ω and an inductance of 6.6 μH. Two numbers of thermo-foil heaters having a resistance of 90 Ω each are placed between the layers of the winding pack of the switch. The wet-winding technique is followed for the switch using a cryogenic grade epoxy. The characteristics of the switch are performed using a 4 K test rig for its applicability in the 1.5 T MRI magnet. The normal resistance of the switch is measured to be 12.5 Ω at 15 K which is 15% less than the estimated value. The total energy loss onto the switch is estimated to be 0.24% of the ramping energy of the magnet at 6 V charging voltage. The thermal switching profile of the switch is studied and correlated with the total energy loss.

Experimental Studies of Resin Systems for Ablative Thermal Protection System

The present work was initiated to finalize resin for the development of thermal protection system (TPS) for the external surface of a polymeric composite rocket motor case made up of Carbon roving and Epoxy resin. The temperature on the outer surface of the composite case increases due to kinetic heating caused by aerodynamic drag and vehicle velocity. These rocket motor casings are functionally required only in the ascent phase of missile trajectory till motor action time and stage separation. Due to which the experienced heat flux is relatively less, and the temperature on the external composite case is in order of 250 °C - 300 °C depending on missile configuration & trajectory, unlike extreme thermal conditions on ablative nozzle liners exposed to rocket motor exhaust. The maximum allowable temperature in the present study for the Carbon-Epoxy case is 100 °C due to degradation in mechanical properties. The thermal protection system on the external surface will function as a heat-insulating layer based on the working mechanism of ablation. The resin of the thermal protection layer has a substantial impact on the manufacturing process and curing aspects, especially compatibility with the pre-cured carbon epoxy case layer. The generation of test results for thermal stability, cure characteristics and Tg for Epoxy resin has also been included in present studies as an additional objective that provides significant inputs for process development. The test results for Epoxy resin is also used as a basis for the finalization of resin for the thermal protection layer for processing aspects apart from its basic thermal stability characteristics. The ablative thermal protection working mechanism is based on the ablation phenomenon. In the case of ablation, resin plays a vital role due to pyrolysis and other thermal characteristics. In the present experimental studies, the Phenolic resin and Silicone resin are considered as candidate resin materials for ablative thermal protection system based on available literature and in house experience. The main objective of the present studies is to evaluate thermal stability, char yield after final decomposition through DSC and TGA techniques for both resins as these are fundamental characteristics needed for the present specific application. The test results for specific grades (formulation) of phenolic and Silicone resins are generated and compared. In the present work, the experimental studies to evaluate glass transition temperature (Tg), thermal stability, and cure characteristics for Epoxy resin is also carried through DSC. The test results of specific grade Epoxy resin provides a basis to assess thermal margins for resins selected for ablative thermal protection system and inputs for process development and design requirements. The scope of the present studies is aimed to finalize the resin system for external thermal protection of composite rocket motor case based on thermal characteristics test results and other compatibility aspects with the structural layer.

Mechanical Properties of the Carbon Nanotube Modified Epoxy-Carbon Fiber Unidirectional Prepreg Laminates.

The effect of plasma treatment of the multi-walled carbon nanotube (MWCNT) surface on the fracture toughness of an aerospace grade epoxy resin and its unidirectional (UD) carbon fiber prepreg laminates has attracted scientific interest. A prepreg route eliminates the possible risk of carbon nanotube filtration by unidirectional carbon fibers. X-ray photoelectron spectroscopy results suggested that oxygen atom concentration at the nanotube surface was increased from 0.9% to 3.7% after plasma modification of the carbon nanotubes. A low number (up to 0.5 wt.%) of MWCNTs was added to epoxy resin and their carbon fiber prepreg laminates. Transmission electron micrographs revealed that the plasma treatment resulted in a better dispersion and distribution of MWCNTs in the epoxy resin. Plasma-treated MWCNTs resulted in a more pronounced resistance to the crack propagation of epoxy resin. During the production of the reference and nanotube-modified prepregs, a comparable prepreg quality was achieved. Neat nanotubes agglomerated strongly in the resin-rich regions of laminates lowering the interlaminar fracture toughness under mode I and mode II loading. However, plasma-treated nanotubes were found mostly as single particles in the resin-rich regions of laminates promoting higher energy dissipation during crack propagation via a CNT pull-out mechanism.

Tailoring the thermomechanical behaviour of epoxy with the incorporation of bamboo and graphite filler

The present study is committed to overcome the problem associated with fiber orientation, delamination in composite material. Micro-sized bamboo particulate and graphite is selected as potential filler incorporation material in view of its potential application in thermal management in electronic, automobile parts, electronic packaging and consumer goods. Chemical treatment of natural micro filler is conducted to improve the binding strength among graphite and epoxy matrix. To develop the hybrid composite with varied bamboo filler 2.5 wt% to 12.5 wt% and graphite is incorporated in matrix material. Composite is developed by using NaOH treated micro bamboo particulate almost of 75 µm and graphite filler incorporated in the polymer matrix. The characteristics of specific ‘grade epoxy’ matrix are investigated through uniaxial tensile test, flexural test, dynamic mechanical analysis (DMA), thermal conductivity and wear performance. Results exhibited that with the addition of 0.2 wt% graphite filler (GF) in hybrid composite material enhanced the thermomechanical properties. The developed bamboo filler and graphite based hybrid composite will help to boost the utilization of waste natural filler for greener environment.

Численная оценка кинетических параметров докритического роста трещин в конструкционных клеевых соединениях при длительном статическом нагружении с использованием модели когезионной зоны и экспериментальных данных

The article proposes a numerical method for modeling and calculating the kinetics of subcritical crack growth and creating kinetic G-V diagrams for structural adhesive joints under prolonged static loading. The load was set by the global subcritical crack opening according to mode I. Modeling and calculations were carried out using a cohesive zone model implanted into the finite element method in the ANSYS software package. The parameters of the cohesive zone law and the kinetics of subcritical crack growth were experimentally determined for samples in the form of a double cantilever beam made of aluminum alloy plates glued with industrial grade epoxy glue. Comparison of the calculated and experimental data showed a good correlation.

Thermal and Mechanical Characterization of an Aeronautical Graded Epoxy Resin Loaded with Hybrid Nanoparticles.

Synthesized silica nanoparticles (SiO2) were coated with a thin polydopamine (PDA) shell by a modified one-step procedure leading to PDA coated silica nanoparticles (SiO2@PDA). Core-shell (CSNPs) characterization revealed 15 nm thickness of PDA shell surrounding the SiO2 core (~270 nm in diameter). Different weight percentages of CSNPs were employed as filler to enhance the final properties of an aeronautical epoxy resin (RTM6) commonly used as matrix to manufacture structural composites. RTM6/SiO2@PDA nanocomposites were experimentally characterized in terms of thermal stability and mechanical performances to assess the induced effects by the synthesized CSNPs on pristine matrix. Thermal stability was investigated by thermogravimetry and data were modelled by the Doyle model and Kissinger methods. An overall enhancement in thermal stability was achieved and clearly highlighted by modelling results. Dynamic Mechanical Analysis has revealed an improvement in the nanocomposite performances compared to the neat matrix, with an increase in the glassy (+9.5%) and rubbery moduli (+32%) as well as glass transition temperature (+10 °C). Fracture Toughness tests confirmed the positive effect in damage resistance compared to unloaded resin with an impressive variation in critical stress intensity factor (KIC) and critical strain energy (GIC) of about 60% and 138%, respectively, with the highest SiO2@PDA content.