Carbon-epoxy Composites Research Articles

Dynamic Mechanical Performance of Glass Microsphere-Loaded Carbon Fabric–Epoxy Composites Subjected to Accelerated UV Ageing

This study investigates the effects of incorporating glass microspheres (GMSs) as fillers in carbon fabric–epoxy composites (CFECs) on their degradation behavior under environmental conditions such as moisture and ultraviolet rays. The GMS-filled composites were subjected to accelerated ageing and evaluated using dynamic mechanical analysis (DMA), the Charpy impact test, and inter-laminar shear strength (ILSS) tests. The results indicate that the addition of GMS fillers significantly improves the stiffness and viscoelastic behavior of the composites. However, the impact strength of the composites decreases with the addition of GMS fillers and accelerated ageing. The ILSS results demonstrate that the addition of GMS fillers improved the interfacial bonding between the carbon–epoxy matrix and fillers. This study provides insights into the mechanical properties of GMS-filled carbon–epoxy composites.

Influence factors on stress measurements using LCR waves for unidirectional carbon-epoxy composites

Influence factors on stress measurements using LCR waves for unidirectional carbon-epoxy composites

Supported Ionic Liquid-Phase Materials (SILP) as a Multifunctional Group of Highly Stable Modifiers and Hardeners for Carbon and Flax Epoxy Composites.

This paper introduces a novel approach to enhance epoxy resin formulations by using SILP materials as multifunctional hardeners and fillers in composite structures reinforced with carbon and flax fibers. This study explores the integration of ionic liquids (ILs) onto a silica support structure, presenting various permutations involving silica selection, ionic liquid choice, and concentration. The focus of this study was to elucidate the influence of SILP on resin curing ability and the mechanical properties of the resulting composites. Detailed research was conducted, including Brunauer-Emmett-Teller analysis (BET) for SILP materials and curing characterization for epoxy resin formulations with different SILP materials. Furthermore, the mechanical properties of the obtained composites were determined by Scanning Electron Microscopy analysis (SEM) (the force at break, the maximum elongation at break, tensile strength, and modulus of elasticity). Through SILP incorporation, the mechanical properties of composites, including the modulus of elasticity and tensile strength, are substantially improved, a phenomenon akin to traditional filler effects. The findings highlight SILP materials as prospective candidates for concurrent hardening and filling roles within composites (through a single-step procedure, with prolonged storage stability and controlled processing conditions), particularly pertinent as the composite industry veers toward epoxy bioresins necessitating liquefaction via temperature application.

Stability and Failure of Thin-Walled Composite Plate Elements with Asymmetric Configurations.

In the present study, the stability and failure phenomena of thin-walled constructions subjected to axial compression, featuring a central cut-out, and constructed from composite materials were explored. These constructions were fabricated from a carbon-epoxy composite using the autoclave method. The research encompassed experimental assessments on actual specimens alongside numerical analyses employing the finite element approach within the ABAQUS® software. The investigation spanned the entire load spectrum up to the point of structural failure, incorporating both practical trials and simulation analysis. During the practical assessments, the study monitored the post-buckling response and captured acoustic emissions to thoroughly evaluate the composite's failure mechanisms. Additionally, the ARAMIS system's non-invasive three-dimensional scanning was employed to assess deformations. Theoretical simulations utilized a step-by-step failure analysis, initiating with failure onset as per Hashin's theory and proceeding to failure progression based on an energy criterion. The simulation outcomes, particularly concerning the critical and post-critical phases, were juxtaposed with empirical data to identify the composite's vulnerability zones. The comparison underscored a significant concordance between the simulation predictions and the empirical findings.

Fatigue behavior of adhesive joints under modes I and II fracture in carbon-epoxy composites, influence of exposure time in a saline environment

This work investigates the fatigue crack growth behavior of adhesive joints under pure modes I and II within epoxy matrix composites reinforced with unidirectional carbon fibers. Experimental tests are made using Double Cantilever Beam (DCB) and End-Notched Flexure (ENF) setups for modes I and II respectively, considering exposure periods of one week and twelve weeks in a salt spray chamber. Control specimens are also studied for comparison.Static tests were conducted to securely establish the levels of Energy Release Rate (ERR) that were subsequently used to obtain the fatigue initiation curves (G-N) and fatigue crack growth curves (G-da/dN). A probabilistic model based on a Weibull distribution is applied to analyze fatigue initiation data.The fatigue limit in mode I, for all aging periods, is around 25 % of the static strength, while in mode II, it is around 20 %. These results are very close at all aging levels (0, 1, and 12 weeks). From this, it is inferred that aging in a saline environment of the studied joints does not have a significant impact on the fatigue limit.In the crack growth zone, for mode I, the velocity is higher in the specimens aged in both periods than in the unaged specimens. The same cannot be said for mode II, where a clear trend cannot be appreciated.

Enhancing the Tribological Characteristics of Epoxy Composites by the Use of Three-Dimensional Carbon Fibers and Cobalt Oxide Nanowires

In this paper, the results of our research were presented into the sliding wear behaviors of reinforced epoxy composites made with 3D networked carbon fibers ornamented with nanowires of cobalt oxides (NWRs@CFs). Composites are made using the cast-in-place method. Under different normal loads and sliding velocities, these composites' wear and friction coefficient performances are assessed. Tests were performed at 400 rpm spindle speed, 10, 20, and 30 N normal load, and a duration of 300 seconds. Pure epoxy exhibits wear rates of 0.449, 0.481, and 0.501 * 10-5 mm3/Nm at 10, 20, and 30N. Conversely, 3D CFs/epoxy composites exhibit lower wear rates (0.334, 0.360, and 0.390 * 10-5 mm3/Nm) at the same pressure. The epoxy composites of NWRs@CFs wear less, measuring 2.1, 3.5, and 0.4 * 10-5 mm3/Nm under applied loads. The effects of speed on the tribological characteristics were also studied, the friction coefficients for 400, 800, and 600 rpm at 10 N. Pure Epoxy has fraction coefficients of 0.449, 0.494, and 0.552µ at 400, 800, and 600 rpm. In comparison, three-dimensional carbon fibers and epoxy composites show reduced wear rates (0.334, 0.376, and 0.304 µ) under identical loads. Epoxy composites of NWRs@CFs have friction coefficients of 0.261, 0.304, and 0.332µ. Pure epoxy has high wear, indicating less friction resistance.

Effect of TiO2 Nanofillers on the Mechanical and Abrasive Wear Properties of Epoxy Reinforced with Carbon Fabric Hybrid Composites.

Recent studies show that nanofillers greatly contribute to the increase in the mechanical and abrasive behaviors of the polymer composite. In the current study, epoxy composites were made by hand lay-up with the reinforcement of carbon fabric and titanium dioxide (TiO2) nanoparticles as secondary reinforcement in weight percentages of 0.5, 1.0, and 2.0. Hardness, tensile, and abrasive wear tests have been carried out for the fabricated composites. The obtained results confirm that as the percentage of filler addition increases, hardness of the carbon epoxy (CE) composite increases, and significant enhancement of 10.25% hardness is confirmed in 2 wt % nano TiO2-added CE composite. The CE composite filled with 2 wt % of TiO2 nanofiller shows 15.77 and 9.15% improvement of tensile strength and modulus, respectively, compared to unfilled CE composites. The abrasive wear volume exhibits a nearly linear increasing trend as the abrading distance increases. In addition, it is discovered that the abrasive wear volume is greater for higher applied loads. The inclusion of nano TiO2 reduced the wear loss in the CE composite for all abrading distances, regardless of the load, low or high. The scanning electron microscopy analysis of worn surfaces was carried out to analyze the contribution of the filler to improve the wear resistance.

A comparative study on milling-induced surface roughness during milling of jute–epoxy and carbon–epoxy composites and optimization for better surface finish through Taguchi and RSM techniques

During the present experimentation, milling machining was performed on two different composites, namely carbon fiber-reinforced polymer composite and jute fiber-reinforced polymer composite, using a computer numerical control vertical machining center. The selected machining parameters were spindle speed (S), feed rate (FR), depth of cut (DOC), and flute number or cutting edge number (FN). The output parameter is the machined surface roughness (Ra). Analysis of variance was used to predict the percentage influence of each parameter on machining quality. The parameter feed rate exhibited a higher influence on the machined surface roughness, followed by spindle speed, flute number, and depth of cut in sequence. Similarly, while milling the carbon fiber composite, the feed rate had the highest influence, followed by the parameter flute number. As for the surface roughness, the feed rate had a greater effect, followed by the spindle speed. Under the same machining conditions, it was observed that the sequence of parameters influencing the jute composite and carbon composite changed in the case of cutting force generation, but the sequence of parameters was the same for both cases in terms of roughness. The outcome of the work confirmed that to achieve a smaller value of roughness in the milling of jute–epoxy composite, the optimum combination should be S = 3000 rpm, FR = 800 mm/min, DOC = 0.25 mm, and FN = 6. Similarly, to achieve the minimum surface roughness value in the milling of carbon–epoxy composite, the optimum combination of parameters should be S = 600 rpm, FR = 100 mm/min, DOC = 0.25, and FN = 6. The average roughness values obtained during the milling of jute–epoxy composite and carbon–epoxy composites are 6.685 and 3.08 μm, respectively. In this present work, it is proved that the optimum combination of parameters to get the minimum surface roughness and the amount of surface roughness produced during milling are highly influenced by the type of reinforced material. The graphs are prepared for the entire range of input parameters to identify the intermediate Ra value at any input value without the use of software.

Investigations on the Influence of Nylon-66 Interleaving on the Fiber Matrix Interactions of Quasi-Isotropic Carbon Epoxy Composites using DMA

This paper presents the results of dynamic mechanical analysis of carbon fiber reinforced nylon-66 nanofiber interleaved epoxy composites. The role of nylon-66 nanofiber has been investigated with specific reference to the percentage of interleaving with nylon-66 nanofibers. For a better understanding of the fiber matrix interactions, the composites were subjected to γ-irradiation, and the resulting changes in the dynamic mechanical properties due to nylon-66 interleaving and γ-irradiation are investigated and discussed. Nylon-66 interleaving and exposure of the composites to γ-irradiation are observed to influence the dynamic mechanical properties. The study has established that 1.15% of nylon-66 interleaving of the epoxy carbon fiber composite improves the Tg and it also leads to enhancement of the dynamic mechanical properties. Individually, the improvements in dynamic mechanical properties of the base were ll nylon-66 interleaved carbon epoxy composites due to γ-irradiation is observed to be minimal.

Analysis of Dielectric Properties of Carbon-Epoxy Composite Laminates

This study highlights the investigation of different dielectric properties of non-interleaved carbon-epoxy and interleaved carbon-epoxy-nylon 66 nanofiber composite laminates. Carbon-epoxy quasi-isotropic composite laminates were developed in an autoclave using A 24-ply AS4/3501-6. Nylon-66 solution of 12 wt.% was prepared in dissolving crystals of Nylon-66 in the 90% formic acid and chloroform mixture with the weight ratio of 75/25, respectively. The nano fabric was developed by electro-spinning technique using prepared Nylon-66 solution. The fabric of 0.7g/m2 average aerial density and composite ply (AS4/3501-6) of 260 g/m2 average aerial density were observed. The interleaved laminates were developed using a nylon-66 nanofiber layer between the adjacent laminate flies. Measurement of some of the dielectric properties like dielectric constant, tan δ, and ac conductivity of the interleaved composite laminates was done at the frequency of range from 20 Hz to 10 MHz. Improvement in the different dielectric properties of the interleaved composite laminates was observed with the addition of a small wt.% of Nylon-66 nano fabric between the alternate layers of carbon-epoxy composite. A possible mechanism involved in the improvement of dielectric properties in the nanocomposites was reported in this paper.

Stability and load carrying capacity of thin-walled composite columns with square cross-section under axial compression

The study aimed to analyse the stability and load-carrying capacity of compressed thin-walled composite columns subjected to axial compression. The subject of the survey was composite columns with closed square cross-sections made of carbon-epoxy composite. Different lay-ups of the composite material characterised the test specimens - several cases of lay-ups were considered. The application of the subject of the research is closely related to the use of these elements as load-carrying elements of aerospace and building structures. The requirements for such structures are closely related to the provision of a large reserve of load-carrying capacity after buckling. Experimental testing was carried out using a universal testing machine and other testing techniques, where acoustic emission, an optical deformation measurement system, and a digital microscope, among others, were used. Numerical simulations using the finite element method were carried out parallel to the experimental studies. In the case of FEA simulations, original numerical models were developed considering known failure models of the composite material. For both empirical studies and FEM simulations, an in-depth analysis of the buckling and post-buckling states was carried out, considering the failure phase of the composite material. The novelty of the present work was the development of original FEM models, allowing faithful reproduction of experimental studies conducted on physical models, as well as the use of research methods to determine the load-carrying capacity of composite structures.

Investigation of the Accelerated Ageing of Carbon-Epoxy Composites on their Mechanical Properties

Abstract In this work, carbon-epoxy composites obtained by an autoclave process were subjected to accelerated ageing in controlled conditions of temperature, water and UV radiation. Each composite was exposed to salt water at 60°C or UV radiation at 60°C over a period of 6 months. Changes within the composites were evaluated by mass and density variation, mechanical testing and also in terms of camouflage. Results did not show significant changes in mass loss or density, and it was found that mechanical properties had decreased slightly. The biggest change is in camouflage. It was observed that during accelerated ageing, the composites’ reemission coefficient becomes too high and composites lose camouflage properties.

Impact resistance of composite to aluminum single lap joints reinforced with graphene doped nylon 6.6 nanofibers

In this study, the low velocity impact resistance of pure and modified epoxy adhesives for single lap joints between aluminum and carbon epoxy composites was investigated. Epoxy resin was used as the adhesive, and pure epoxy resin was modified by adding graphene-doped nylon 6.6 nanofibers (1%, 3% and 5% by weight) and pure nylon 6.6 nanofibers produced by electrospinning. These nanofibers are reinforced to aluminum-composite single lap joints as a second interface according to ASTM D1002-10 standard. Thus, single lap joints were prepared using 5 different adhesives. To create the impact effect, some joints were subjected to impact at a low velocity (1.04 m/s). Then, all impacted and non-impacted samples were subjected to single lap shear testing at room temperature and constant load to determine the impact resistance. While the non-impact lap shear strength of the pure epoxy adhesive samples was 6.81 MPa, the non-impact shear strength of the samples using pure nanofiber reinforced epoxy adhesive increased by 71.3% to 11.67 MPa compared to the pure epoxy adhesive. When comparing the post-impact failure loads, it was determined that the addition of graphene increases the impact resistance. Furthermore, adhesive surfaces were examined by scanning electron microscopy (SEM) for damage analysis after the tensile tests and toughening mechanisms such as bridging, adhesive crack formation, nanofibers breakage was determined in epoxy adhesives reinforced nanofiber with graphene in different proportions by weight. In addition, the glass transition temperature, melting temperature, thermal decomposition temperature and mass loss of epoxy resin, and graphene doped/undoped N6.6 nanofiber-reinforced epoxy adhesives were analyzed by Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) and it was determined that the addition of 3% GNP to N6.6 nanofiber reinforcement increased the thermal stability by 12.4%, the addition of 1% GNP to N6.6 nanofiber reinforcement increased the thermal resistance (glass transition temperature) by 34.9% compared pure epoxy.

Experimental investigation of 3D printed infill structures for crash absorbing applications

In recent years additive manufacturing technologies have rapidly evolved and are now an effective tool adopted for final components production. 3D printing techniques allow to realize complex geometries that are difficult if not impossible to fabricate by means of conventional production methods. This peculiarity can be exploited to design and manufacture infill structures that can be used in various engineering applications. Combining lightweight 3D printed infill structures with conventional laminate carbon-epoxy composites can be an efficient way to realize light and stiff components that find their optimal use in crash absorbing applications. Plain polymers and fiber reinforced polymers composites represent an interesting solution for additive manufacturing, offering light weight and ductility of the polymeric matrix with the possible enhancement of mechanical properties with the addition of fibers. This work focuses on the study of commercially available 3D printed infill structures via compression tests on cubic samples, deepening understanding about different densities and different strain rates effects on material’s behavior.

Machine learning based inverse framework for predicting the transverse and shear modulus of carbon fiber

Evaluating the transverse and shear modulus of carbon fibers experimentally is challenging and are usually obtained by an inverse approach using a micromechanical model. This paper presents an inverse approach for predicting the fiber properties from experimentally evaluated properties of the unidirectional (UD) lamina, using a machine learning (ML) based surrogate model. The ML framework is based on Gaussian process regression (GPR), which also provides a measure of uncertainty in the predictions. The ML model is trained using synthetic data generated using Finite Element (FE) homogenization considering different fiber and matrix properties, volume fractions, and fiber distribution. The proposed inverse framework is demonstrated to predict the elastic properties of polyacrylonitrile (PAN)-based fibers used in carbon-epoxy composites that have significant variations (low to high modulus) in its properties (T300-M60J). The fiber properties predicted using the GPR surrogate shows good agreement with the values reported in the literature, with a difference of less than 1.5%. The computational framework is further extended to predict the elastic properties of the woven fabric laminate using multi-scale homogenization. In summary, the results show that the GPR-based surrogate model offers an accurate and computationally efficient alternative to FE-based forward model for predicting the properties of the fiber.

Analysis and optimization of junction between cylindrical part and end dome of filament wound pressure vessels using data driven evolutionary algorithms

The junction between cylindrical part and end dome is the most critical place of the filament wound composite pressure vessels because the shear forces and bending moments occur in this area. The strength analyses of junction between cylindrical part and different types of known end domes based on influence coefficients method were performed for filament wound composite pressure vessels manufactured using glass-epoxy and carbon-epoxy composites. Four known end domes were considered that is, a spherical shell, a geodesic-isotensoid shell, a shell based on minimizing of the Tsai-Hill’s strength criterion and shell designed in authors’ previous work (Hoffman 1 shell). Moreover, the study is also dealing with design of optimal end dome shape which takes account to the junction area. Finding of optimal end dome shape was based on data-driven evolutionary algorithms. Using input dataset from the analytical simulation surrogate models were created using Evolutionary Deep Neural Nets (EvoDN2) algorithm. The multicriterial optimization procedure was performed using Constrained Reference Vector Algorithm (cRVEA) optimization algorithm. Results indicates that the optimal end dome shape highly depend on material properties.

Flexural behavior of carbon/glass inter-ply hybrid FRP composites under elevated temperature environments

Abstract In this research work, the three-point flexural performance of carbon and/or glass inter-ply hybrid epoxy composite by altering the hybrid ratio and stacking position was studied. These materials were tested at various temperatures (30 °C, 50 °C, 70 °C and 110 °C). The test results of hybrid composites results were compared with neat glass/epoxy and carbon/epoxy composites. The stacking position of carbon fibers in hybrid composite plays a vital role while doing a flexural test. Incorporation of two stiffer carbon fibers in glass/epoxy composite i.e., C2G3 and C1G3C1, resulted in a remarkable increment in the case of flexural strength. All composites exhibited ductile behavior at 110 °C. The fractured surfaces revealed the failure mechanism of the composites.

In-situ X-ray computed tomography of mode I delamination in carbon-epoxy composites: The effect of the interface ply orientation

Test methods determining interlaminar fracture toughness of composites are typically performed in conjunction with in-situ surface imaging techniques to detect the crack initiation and monitor its propagation. However, these methods struggle to visualise the 3D evolution of the crack front. In such tests, initiation detection is based on force-displacement curve features, such as the non-linearity point, or edge observations. This paper reports the implementation of a methodology for in-situ 3D characterisation of the crack front in a double cantilever beam test using microfocus X-ray computed tomography. The crack initiation and propagation inside the bulk were determined through crack segmentation in the in-situ tomograms, allowing quantification of the fracture toughness without the need for artificially imposed initiation criteria such as the non-linearity. Two different delamination interfaces were investigated: 0°//0° and +45°//−45°. These two interfaces can be viewed as two extremes in terms of delamination behaviour. The results of the proposed methodology are compared against those measured via the “conventional” edge microscopy coupled with digital image correlation.

Effects of Low Temperature and Water Saturation on the Blast Response of Carbon and E-Glass Epoxy Composites

Effects of Low Temperature and Water Saturation on the Blast Response of Carbon and E-Glass Epoxy Composites

Failure Analysis of Beam Composite Elements Subjected to Three-Point Bending Using Advanced Numerical Damage Models

Abstract This paper deals with the experimental and numerical analysis of three-point bending phenomenon on beam composite profiles. Flat rectangular test specimens made of carbon–epoxy composite, characterised by symmetric [0/90/0/90]s laminate ply lay-up, were used in this study. Experimental testing was carried out with a COMETECH universal testing machine, using special three-point bending heads. In addition, macroscopic evaluation was performed experimentally using a KEYENCE Digital Microscope with a mobile head recording real-time images. Parallel to the experimental studies, numerical simulations were performed using the finite element method in ABAQUS software. The application of the above-mentioned interdisciplinary research techniques allowed for a thorough analysis of the phenomenon of failure of the composite material subjected to bending. The obtained research results provided a better understanding of the failure mechanism of the composite material.