Carbon Fiber Epoxy Composites Research Articles

Interphase engineering in carbon fiber/epoxy composites: Rate sensitivity of interfacial shear strength and interfacial fracture toughness

AbstractDesigning the interface in polymer composites is fundamentally a challenging task. Here, we demonstrate a strategy to engineer the interphase microstructure in carbon fiber/epoxy composites (CFRPs) using carbon nanotubes (CNTs). The incorporation of CNT modifies the interfacial mechanics and interfacial chemistry in conventional CFRPs by creating concentrated, dispersed and mixed type interphase. Therefore, a detailed study is warranted to establish the interfacial microstructure‐property relationship in CNT modified CFRPs. Experimental results show that the relative improvement in interfacial shear strength (IFSS) and interfacial fracture toughness (Gic) depends on the microstructure of interphase. It is shown that simultaneous improvement in IFSS and Gic is possible with certain types of microstructural designs. Moreover, it is observed that IFSS and Gic are not constant material parameters but both of them show a power‐law type dependence on the applied loading rate. The range of rate sensitivity parameters as a function of interphase type suggests that while concentrated and mixed interphase is more suited to maintain the interfacial integrity, dispersed interphase is beneficial for energy dissipating applications of CFRPs. In addition, IFSS and Gic exhibit negative rate sensitivity for certain cases. Finally, it is shown that interphase designing using CNT is an excellent tool to accurately tailor the average interfacial properties of CFRP in a broad range of 16‐79 MPa and 100‐453 J m−2 for IFSS and Gic, respectively.

New approaches to bonding thermoplastic and thermoset polymer composites

The use of multi materials within a single composite structure provides many advantages, including component cost reduction, the ability to manufacture complex designs and greater potential for part recyclability. However, these multi materials can often have very different properties and surface chemistries, and can be challenging to join when using adhesives. This research explores a new processing concept of surface treatment that promotes adhesion between dissimilar composite materials by introducing covalent bonding between substrate and adhesive. An epoxy amine resin is dissolved in a solvent to functionalise the surface of a polyamide 66 glass fibre composite prior to adhesive bonding to a carbon fibre epoxy composite. The effect of surface treatment time, temperature and solvent polarity is investigated using Fourier Transform Infrared (FTIR) spectroscopy, lap shear adhesion and scanning electron microscopy (SEM). Lap shear strength of some solvent treated samples is more than 3 times higher than the untreated samples, while the extent of epoxide cure correlates strongly with adhesive strength. Solvent polarity had little or no effect on the bonding strength providing flexibility in solvent selection.

Fiber push-in failure in carbon fiber epoxy composites

Micromechanical quasi-static and cyclic fiber push-in tests performed with an indenter in-situ in a scanning electron microscope on polished slices (thickness around 300 μm) of carbon-fiber epoxy composites provide information on the effect of fiber density on the fiber-matrix debonding and the fiber failure. Specifically, "close-packed", i.e., fibers surrounded by six nearest neighbor fibers (called "hexagonal" hereafter) versus "isolated" fibers, defined as fibers at least one fiber diameter distant from the next nearest fiber, were compared. In spite of the more compliant behavior of isolated fibers under quasi-static and cyclic indentation loads, initiation of fiber-matrix debonding and push-in failure (fiber splitting into two or three parts) occurred at roughly comparable loads for both, "hexagonal" and "isolated" fibers. Earlier tests on thinner slices of such composites (thickness around 30 μm) had resulted in full debonding and fiber push-out without fiber failure. The fibers in the thicker slices showed first indenter imprints on the surface and an increasing hysteretic behavior in the load-displacement curves before debonding. The analysis of the cyclic load-displacement curves yields the elastic-plastic and the hysteretic (debonding) energy contributions.

Effect of graphene-based nanofillers addition on the interlaminar performance of CFRP composites: An assessment of cryo-conditioning

Carbon fiber reinforced polymer (CFRP) composites are extensively being used as materials in aerospace and aircraft applications. For cryogenic applications, which require materials having high dimensional stability and low thermal conductivity, CFRP composites are an exquisite alternative to metals. These materials have to sustain and retain their promising mechanical properties which include high strength to weight ratio and stiffness at extremely low temperatures. This work involves the decoration of carbon fiber (CF) surface of carbon fiber epoxy (CF/E) composites with two types of graphene-based nanofillers. Graphene oxide (GO) and Graphene hydroxyl (GOH) were implemented onto the CF by electrophoretic deposition (EPD) technique. A comparative study of the effect of nanofillers on the interlaminar behavior of 3 CFRP composites (neat, GO-CF/E, GOH-CF/E) for different times of cryogenic conditioning was carried out. Modified CFRP laminates have shown an improvement of 15.6% and 11.42% with GO and G-OH respectively in interlaminar shear strength (ILSS) in the unconditioned state with respect to neat. The effect of fiber modification becomes less prominent with increasing time of cryo conditioning. GO was proposed to be a better modifying nanofiller than GOH. A dip in ILSS at 1 h of aging may be attributed to thermal shock and development of internal stresses. Recovery of ILSS values at higher times of aging was observed. Scanning electron microscopy was carried out to identify various modes of failure.

Micromechanical analysis of fatigue and crack growth in carbon-fiber epoxy composites based on mechanical testing

The paper presents static and dynamic tests of carbon/epoxy composite materials with fiber orientation at 0?/90? and ?45?. The main tensile properties were determined as a basis for subsequent dynamic tests, in which permanent dynamic strength, crack growth, and crack growth rate in the material due to the action of fatigue load were assessed. Comparisons were made regarding the structure of the tested specimens. Samples were obtained from prepregs with a specific density of 1600 kg/m3. The tests were performed at room temperature. Scanning electron microscopy (SEM) was used to analyze the damage in the material during these tests, the mechanisms of their further damage progression and, the impact on the growth and growth rate of the initial crack in the material. The analysis of numerical results and micromechanical analysis confirmed the dominant role of the reinforcing structural element in the material in all performed tests. The obtained results are of great importance in the application of composite materials of such structures under different operating conditions and load regimes.

Performance assessment of a hybrid intermittent-progressive grinding strategy for bi-directional carbon fibre reinforced composites

In today’s era, fibre reinforced composites (FRCs) due to their superior mechanical properties are preferred over metals in various applications such as sports, automotive, aerospace, etc. Even though high-quality fabrication procedures for near-net FRC structures are reported, their employment in many of the functional applications demands machining operations to yield controlled geometric tolerances and surface finish. To meet surface integrity without severe damages, machining using abrasive grains may be a potential solution. However, owing to non-homogeneous and anisotropic nature of FRCs, continuous engagement of abrasive grains may lead to undesirable effects of grinding force such as fibre pull-out, fibre breakage, matrix failure etc. Intensity of these damages, which are sensitive to the type of fiber and fibre orientations, is observed to be proportional to the depth of cut maintained by the cutting edge. While grinding bi-directional and multi-directional carbon fibre laminate composites using conventional abrasive tools, the aforementioned surface defects become a serious concern. Present paper aims to investigate the performance of a hybrid grinding strategy for bi-directional carbon fibre-epoxy composites, introduced with a title “Eccentric Sleeve Grinding (ESG)”, combining the merits of both intermittent and progressive cutting, solely using a conventional surface grinding machine and non-super abrasive wheel. Cost-effective eccentric sleeves for grinding wheel assembly and associated control over cutting scheme have been adopted in the proposed technique to achieve minimal damage material removal. Eccentric sleeve grinding experiments on 0/90° bi-directional carbon fibre reinforced composite (CFRC) at a range of depth of cut has been carried out and assessed the machining performance using indices such as grinding force, grinding efficiency in terms of force ratio, grinding wheel wear and surface defects. Superior tribological behavior was observed in ESG through the enhancement of grinding force ratio, in addition to significant reduction in normal grinding force, grinding wheel wear and surface roughness. Microscopic analysis of composite surfaces after ESG could illustrate the effectiveness of progressive-intermittent cutting to yield a favorable surface topography, without severe damages as observed in conventional surface grinding at same depth of cut.

Numerical buckling analysis of carbon fibre-epoxy composite plates with different cutouts number by finite element method

Composite materials are one of most important engineering structures due to their desirable structural properties like corrosion resistance, high specific strength, specific stiffness, and lightness compared to conventional materials. This article provides numerical study with linear and nonlinear analysis of the influence of thin carbon/epoxy composite plates with rectangular cutouts on the buckling behavior. The aim of current study is to examine the effect of central rectangular cut outs number of single, double, and triple cut outs of rectangular carbon–epoxy composite plates on the maximum buckling load and maximum deflection under natural and post buckling mode. This determination is to evaluate the possibility of employing elastic elements such as thin carbon–epoxy composite plate elements, whose stiffness affected by modifying the laminate cut-outs number at constant total area, where the area of the single cut out, total area of double cut outs, and total area of triple cut outs are equal. The finite element method was adopted to analyse the structure numerically. Furthermore, in order to maintain stable structure operation under post-buckling range, the laminated composite plates were arranged symmetrical lay-up with extension bending couplings. The finding demonstrates that the distribute of cut out area on the composite plate area with rectangular shape at constant total cut outs area lead to increase the maximum load and slightly reduces the maximum deflection, this can be attributed to the improvement of the compression load distribution on the composite plate model.

Synergetic effect of rubber on the tensile and flexural properties of graphene based epoxy-carbon fiber hybrid nanocomposite

The interaction effects of rubber addition on the tensile and flexural characteristics of hybrid composites of Epoxy-carbon fiber with Graphene as nanofiller were studied. Bisphenol resin was used as matrix. The epoxy-carbon fiber composite was modified with 0.1, 0.2 and 0.3 wt% of graphene. The specimens with 0.1% graphene exhibited significant rise in tensile and flexural strength whereas on further addition of graphene with 0.2 and 0.3% the strength improved marginally compared to epoxy-carbon fiber composite. 10, 20 and 30% by weight natural rubber in liquid form was added to epoxy-carbon fiber with 0.1% graphene, which further enhanced the tensile and flexural characteristics of the hybrid composite. The specimens with 10% rubber reinforcement exhibited a nominal improvement in the tensile and flexural strength of the hybrid composite whereas the specimens with 20% rubber showed acceptable rise in the tensile and flexural strength. Upon further addition of rubber by 30% the strength decreased marginally. The SEM results for different configurations were analyzed to study the morphological and interfacial interactions.

Multifunctional Carbon Nanotubes Enhanced Structural Composites with Improved Toughness and Damage Monitoring

The potential of carbon nanotubes (CNT) as multifunctional filler in poly(epoxy)-based structural composites has been investigated. In a first step the reinforcement effect of CNT has been studied by tensile and three points bending tests, which evidenced significant improvements of stress and strain at break (respectively +17% and +30% for tensile tests on unidirectional carbon fibre-epoxy composites). Moreover, fracture experiments have also revealed a positive effect of CNT on the toughness (G1c) of carbon fibres-epoxy composites (+105% of improvement at the initial stage). In a second step, the health monitoring capability quantum resistive strain sensors (sQRS) made of CNT filled epoxy nanocomposite, incorporated in the core of glass fibres-epoxy composites has been studied. It was shown that during cyclic tensile tests, following the evolution of the relative resistance amplitude (Ar) of sQRS with strain gives a pertinent information on non-reversible phenomena such as plastic deformation and cracks’ development within the composite. In particular, the evolution of the sQRS sensitivity (gauge factor GF) under and over the elastic limit, allows to track damage accumulation throughout the composite. These results suggest a possible use of sQRS for the structural health monitoring (SHM) of composites in fields such as boating, wind energy, aeronautics and automotive.

Failure characterisation of CF/epoxy V-shape components using digital image correlation and acoustic emission analyses

Testing of V-Shape demonstrator components formed from carbon fibre epoxy composites was undertaken to assess the failure mechanisms at the corner section (V-Shape) of a square beam structure under static and fatigue loading configurations. Digital image correlation and acoustic emission analyses were used to determine the time to failure, as well as the location of failure, providing additional insights for failure characterisation. Digital image correlation was used on the surface of the specimens’ side as it analysed the displacements and strains on the externally visible through-thickness region. Acoustic emission analyses identified the origin and location of stress waves generated within the sample which were related to damage events. These techniques have shown a higher sensitivity to determining the onset of damage and the time to failure, in comparison to load drops, crosshead displacement changes, and strain gauge measurements, providing a more conservative and accurate measurement of component failure. They have also proven successful at determining the location of failure initiation, highlighting the added benefits of incorporating these techniques into component analyses.

Multi-objective optimization of an intersecting elliptical pressure hull as a means of buckling pressure maximizing and weight minimization

AbstractPressure hulls are one of the keys in the design of submarines. In order to improve the accuracy and efficiency of pressure hull structure, methods of optimizing it were studied. In the present study, an overview of the multi-objective optimization of intersecting cross elliptical pressure hulls (ICEPH) with and without the core layer under hydrostatic pressure was investigated in order to maximize buckling load capacity (λ) and minimize the buoyancy factor (B.F) of the ICEPH according to the design requirements. Five models were built, four composite models constructed from boron/epoxy (B(4)/5505) and carbon/epoxy composite (USN-150) with and without core layer. The fifth is a reference metallic model constructed from HY100. Criteria regarding failure for both composite and metal shells are considered as indications of optimization. Both Tsai-Wu and maximum stress failure criteria were employed to check the composite failure. The modeling and the multi-objective optimization were performed using ANSYS parametric design language (APDL) in order to determine mass, critical buckling load, and failure criteria. The results illustrated that carbon fiber-epoxy composite (USN-150) with a core layer is preferred for obtaining minimum weight, with an improvement ratio (IR) 64.314 % superior to that of a metallic pressure hull. By contrast, (boron/epoxy B(4)/5505) without a core layer is preferred to obtain a maximum buckling load.

Study on thermal stability of typical carbon fiber epoxy composites after airworthiness fire protection test

SummaryThe thermal stability of the T700 carbon fiber epoxy composites, which had been tested under different conditions (nonvibration plus nonscrubbing airflow, vibration, scrubbing airflow, and vibration plus scrubbing airflow), were investigated according to the obtained weight loss behavior, integral program decomposition temperature (IPDF), and activation energies (E) by using thermogravietry‐differential thermal analyzer. The results indicate that the weight loss ratio, IPDF, and E of T700 carbon fiber epoxy and its residues in the third and fourth layers are similar under the nonvibration plus nonscrubbing airflow and vibration, and the thermal stability under the vibration condition is slightly stronger. In addition, the weight loss ratio, IPDF, and E of the epoxy and its residues in materials are also similar under scrubbing airflow and vibration plus scrubbing airflow, and the thermal stability under vibration plus scrubbing airflow is better. However, it is significantly less than the thermal stability of materials under nonvibration plus nonscrubbing airflow and vibration. Therefore, it can be found that the vibration exacerbates the flame severity and the scrubbing airflow has a significant cooling effect on the material during the airworthiness fire protection test, which have guiding significance on the airworthiness fire prevention items formulation of carbon fiber composite.

Finite element modelling and multi-objective optimization of composite submarine pressure hull subjected to hydrostatic pressure

The design of submarine pressure hull made of laminated composites depends on number of layers and fibre orientation of ply angle. In the present study an overview and comprehensive study about the multi-objective optimization of composite pressure hull under hydrostatic pressure to minimize the weight of the pressure hull and increase the buckling load capacity according to the design requirements. Three models were constructed, two models constructed from Carbon/Epoxy composite (USN-150) with and without core layer the third model is metallic submarine hull constructed from HY100. The low-density PVC foam material is used as a core material. The optimization process is carried out in ANSYS Parametric Design Language (APDL). The constraints on the optimization process are Tsai-Wu and maximum stress failure criteria. The results obtained emphasize that, the submarine constructed from Carbon/Epoxy composite (USN-150) is better than the submarine constructed from HY100. Furthermore, the submarine constructed from carbon fiber-epoxy composite (USN-150) with core layer is better than the submarine constructed from carbon fiber-epoxy composite (USN-150) without core layer. Finally, an optimized model with an optimum pattern of fiber orientations was presented. Hopefully, the results may provide a valuable insight for the future of designing composite underwater vehicles.

Enhancement of Mechanical Properties in Carbon Fibre Reinforced Epoxy Composite with and without graphite powder

The use of composite material in engineering field is increasing day by day. Composite materials are largely replacing conventional metals nowadays due to their mechanical behaviours. Among all composite materials carbon fibre reinforced composites are of greater interest due to their high strength. There are several new developments made in carbon fibre composites like carbon nanotubes, carbon black etc.. in order to increase the composite strength. In this research, we are going to analyse the strength of the carbon fibre reinforced epoxy composite by using graphite powder as an additive material because of its negligible weight and hardness nature. Generally, composites were prepared by hand layup process. Specifically the tensile, the flexural and the impact properties are taken into the consideration. Three different specimens are prepared and tested for the above strengths. The first specimen is carbon fibre epoxy composite without any addition of graphite powder (filler material). The second one is carbon composite with 5% addition of graphite powder as a filler material and the last specimen is of carbon fibre composite with 10% addition of graphite powder. The above mentioned strengths are calculated for each specimen with the help of a Universal Testing Machine and Impact Tester. Specimen 3 shows greater strengths whereas Specimen 1 shows least strength among all the three specimens. The inclusion of graphite powder in the carbon composite shows increase in the mechanical properties of the resulting specimens.

The effect of boron carbide on the mechanical properties of bidirectional carbon fiber/epoxy composites

This research work based on carbon fiber epoxy (CF/Ep) composites shows the effect of Boron carbide B4C filler on mechanical properties using a hand layup procedure followed by the vacuum bagging process method. The boron carbide fillers were uniformly dispersed in epoxy resin and used as matrix material. The weight percentage of (B4C) filler material in the composite was varied and mechanical properties were obtained with microfiller. The T800CF/Ep composites with 1%wt., 3%wt. and 5%wt. B4C fillers were taken for evaluating the mechanical properties. All composites were fabricated with an equal weight percentage of carbon fiber and a similar consolidation process. The mechanical properties like tensile properties, flexural properties, Interlaminar shear strength, impact strength and hardness are studied to know how the mechanical response of composite structures varies with filler addition. Testing followed the trend of 1%wt. > 3%wt. > 5%wt. of B4C in all mechanical properties of B4C filled CF/Ep composites. Tensile strength of 1%wt. B4C filled composites were better than basic CF/Ep composites whereas 3%wt. & 5%wt. B4C filled composite values were lower. The tensile modulus of all the B4C filled composites was better than basic CF/Ep composites. Flexural properties of 1%wt. and 3%wt. B4C filled composites were better than basic CF/Ep composites whereas 5%wt. B4C filled composite values were lower. Interlaminar shear strength (ILSS) of 1%wt. B4C composites gave better results whereas 3%wt. and 5%wt. B4C filled composites gave lower results. The impact energy of all composites gave lower values than basic CF/Ep composites. Hardness values of all B4C filled composites were better than basic CF/Ep composites. The most important developments in the mechanical properties of composites are further supported by scanning electron microscopy.

Flexural strength enhancement in carbon-fiber epoxy composites through graphene nano-platelets coating on fibers

Carbon-fiber epoxy composites show extremely high modulus and strength in the uniaxial direction. However, they fail relatively easily under flexural loading due to the weak nature of the interface between the carbon-fiber and epoxy. In the current study, the desizing and oxidation treatment of carbon fibers and the coating of graphene nano-platelets (GNPs) on the carbon-fibers has been done with an aim to strengthen the interface/interphase between the fiber and the matrix. GNPs were coated on the carbon fibers before making the final laminates through vacuum assisted resin transfer molding. The flexural strength of the laminates has been found to improve significantly with GNP addition. Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy have been used to examine the nature of interface/interphase between the fiber and the matrix as well as the mechanism of failure of the composite.

Utilizing vacuum bagging process to prepare carbon fiber/epoxy composites with improved mechanical properties

This research paper based on bidirectional carbon fiber/epoxy composites (CF/Ep) shows the effect of fiber architecture on mechanical properties using a hand layup procedure followed by the vacuum bagging process method. The three different fiber architectures T800CF/Ep, T700CF/Ep and T300CF/Ep were chosen for studying the mechanical properties. All composites were fabricated with an equal weight percentage of carbon fiber and a similar consolidation process. The tensile properties, flexural properties, interlaminar shear strength, impact strength and hardness are studied to know how the mechanical response of composite varies with fiber architecture. Testing results showed that the effect of fiber weave architecture is more obvious in CF/Ep composites than in neat epoxy with regard to mechanical properties. Both tensile and flexural properties showed that T800CF/Ep composites have a very good strengthening effect on both tensile load response and bending load response of CF/Ep composites. The fiber architecture has less effect on the density and serious effect on the strength and deformation of CF/Ep composites. Inherent properties and weaves structure of carbon fiber (CF) dictated the performance of composites. Compared to Hand layup method, the Vacuum bagging method showed (2–6)%, (11–15)%, (5–6)%, (15–20)% and (1–3)% improvement in tensile strength, tensile/flexural modulus, ILSS, impact strength and hardness respectively whereas the flexural strength values were almost near to the former values Grunenfelder et al. (2017). The most important developments in the mechanical properties are further assisted by scanning electron microscopy.

Investigation of the flexural and thermomechanical properties of nanoclay/graphene reinforced carbon fiber epoxy composites

Abstract

Caracterización de las propiedades tensiles de un material compuesto laminado Epoxi-Carbono empleado en la fabricación de un monoplaza tipo Fórmula SAE

El presente artículo analiza las propiedades tensiles de un material compuesto polimérico reforzado con fibras de carbono empleado en la fabricación del monoplaza para competición Fórmula SAE. Para ello se manufacturaron compuestos a partir de preimpregnados con diferentes orientaciones de fibra mediante un proceso de curado al vacío. Se evaluó el efecto de la orientación de las fibras sobre la resistencia y la rigidez de los compuestos formulados. Se instrumentaron las probetas de tracción con extensómetros biaxiales para obtener un registro real de la deformación y posterior determinación del módulo de Young. Los resultados experimentales fueron comparados con los resultados analíticos obtenidos a partir de la Teoría Clásica de Laminados mediante software especializado. Se desarrolló también un análisis microscópico de la región fracturada de las probetas para evaluar el efecto del proceso de manufactura. El conjunto de información generada a partir de los resultados experimentales y analíticos proporciona un entendimiento de la anisotropía de los materiales compuestos Epoxi-Carbono que permitirá tomar decisiones de diseño en futuros desarrollos dentro del proyecto Fórmula SAE.

Evaluation of the protective performance of hydrophobic coatings applied on carbon-fibre epoxy composites

Carbon–fibre epoxy composites are widely used for high-performance structural applications, where they are often exposed to harsh environments. The result of moisture ingress has been extensively studied, causing significant deterioration in the mechanical properties of these composites. This study evaluates the performance of five commercial hydrophobic coatings as protective layers, to inhibit moisture ingress into the composite. The coatings evaluated were NeverWet, HydroBead, SHC, Aculon and LiquidGlass. These coatings were characterised and compared in terms of hydrophobicity, surface energy, roughness and chemical composition. This study also evaluated two atmospheric plasma pre-treatments as a means of enhancing the adhesion performance of these coatings. The pre-treatments involved the use of an air plasma for the activation of the epoxy, as well as the plasma deposition of a nanometre thick SiOx interlayer coating. The durability and protective performance of the coatings, with and without the pre-treatments were then compared using an abrasion test as well as a water immersion study. The use of both plasma pre-treatments was found to enhance the adhesion and the abrasion performance of four out of the five coatings. Of the coatings and pre-treatments investigated, the LiquidGlass in conjunction with a SiOx-coating interlayer was found to exhibit the highest abrasion resistance. This was followed by the composite, which was plasma activated prior to the application of the Aculon coating. Only minor differences were observed when comparing the total moisture ingress (M%) of the epoxy, coated with the different hydrophobic layers. The composite coated with the Aculon and SiOx interlayer exhibited the least amount of moisture ingress, at 0.90%, compared to 1.08% of the uncoated specimen. The shear strength of epoxy composite, coated with the LiquidGlass, NeverWet and the activated Aculon combination, were within the range of the uncoated specimens, therefore the moisture ingress was reversible upon heating and no permanent damage to the epoxy–fibre interface was observed. It is concluded that, of the five coatings investigated, both the Aculon coating and LiquidGlass in combination with a SiOx interlayer coating, exhibit the greatest potential as protective layers for carbon fibre epoxy composites.