Carbon Fiber-reinforced Epoxy Research Articles

Characterization of hydrothermal aging induced voids in carbon fiber reinforced epoxy resin composites using micro-computed tomography

The main aim of this work is the voids characterization of carbon fiber reinforced epoxy resin (CFRP) composites after hydrothermal aging. The composites aged at varying time and temperature were investigated using micro-computed tomography, scanning electron microscope, fourier transform infrared spectroscopy, dynamic mechanical analysis as well as monitoring water uptake and inter-laminar shear strength. It is shown that the porosity increases rapidly in first 45 days while maintains stable in following 105 days. The equilibrium porosity at 35 °C, 55 °C, 75 °C and 95 °C are 0.52%, 0.54%, 0.67% and 0.72% respectively. The strip-like voids and fracture morphology indicate the destruction of interface and resin, but the former is more vulnerable. However, the resin matrix embrittlement is caused by network damage while chemical structure is almost unchanged. As a result, the water diffuses and inter-laminar shear strength deterioration. This study clarifies the influence of voids on structure and properties of CFRP composites and is expected to deepen the understanding of hydrothermal aging mechanism of CFRP composites.

Metric entropy and digital image correlation in deformation dynamics analysis of fibre glass reinforced composite under uniaxial tension

This paper proposes a combined method for the mechanical properties assessment of composite materials based on the analysis of the internal dynamics of raw data from uniaxial tensile tests. Determination of the Kolmogorov-Sinai (K-S) metric entropy from the recorded data enables to find the tensile strength of materials. The correctness of the methodology proposed was verified by the full filed DIC measurements. Therefore, the main aim of this research was to apply independent measurement tools in the analysis of the non-linear dynamics supported by their mutual validation. The experimental program carried out on the glass fibre-based thermoplastic Elium acrylic composite and E752 Carbon Fiber Reinforced Epoxy (CFRE) composite confirmed the high suitability of the presented methodology in ultimate tensile stress identification, and thus, its great applicability potential in many aspects of the contemporary engineering.

Thermal behaviour and fire and mechanical performance of carbon fibre-reinforced epoxy composites coated with flame-retardant epoxy gelcoats

We investigated the industrial applicability of multifunctional flame-retardant epoxy gelcoats based on flame retardants containing phosphorus (P), in particular ammonium polyphosphate (APP, which acts in the solid phase), resorcinol bis(diphenyl phosphate) (RDP, which mainly acts in the gas phase) and their combination. It was possible to apply most of the formulations via spraying with the use of a diluent, while gelcoats containing RDP were sprayable without a diluent. The presence of both flame retardants provided excellent fire performance, while the Shore D hardness of the gelcoats decreased significantly, which is favourable in terms of flexibility. We compared the effect of the composite (wet compression moulding and vacuum infusion) and gelcoat manufacturing (brushing and spraying) technologies on fire behaviour. Both vacuum infusion and spraying significantly decreased the peak heat release rate and the total heat release of the coated samples during the mass loss type cone calorimetry tests. The composites prepared by vacuum infusion and coated by spraying showed the best overall fire performance. Heat release rates, three-point bending test results and the dynamic mechanical analysis of the coated samples revealed that the flame retardancy of the composite base itself can be omitted.

Co-bonding of carbon fibre-reinforced epoxy and galvanised steel with laser structured interface for automotive applications

Materially bonded hybrid systems with precisely adjusted interfacial properties are of great scientific and industrial interest with regard to lightweight construction. In the present study, a material composite of carbon fiber reinforced plastic (CFRP) and galvanized steel is considered, where the metallic surface is laser structured in order to improve the adhesion properties. The resulting joining properties will be elicited by tensile shear tests in comparison to an alkaline cleaned surface condition and blind riveting. The potential of direct-joined hybrid systems with laser-structured substrate surfaces will also be considered using an automotive roof frame as an example. In the tensile shear test, the direct-joined hybrid joint with laser-structured metal substrate achieves significantly higher joint strengths than after alkaline cleaning. Compared to an aluminum/steel reference structure, the CFRP/steel roof frame exhibits a significant weight advantage with superior mechanical properties under flexural and compressive loading.

Femtosecond laser micromachining of carbon fiber-reinforced epoxy matrix composites

Unidirectional carbon fiber-reinforced epoxy matrix composites fabricated by compression die molding technique were exposed to femtosecond laser pulses of 1030 nm wavelength, 560 fs duration and a pulse repetition rate of 100 kHz. Laser tracks were engraved on the composite surface using pulse energy from 1 to 5 μJ both in the direction parallel and perpendicular to the fibers axis. The resulted morphology of the laser treated surface was investigated by field emission scanning electron microscopy (FESEM). The laser induced periodic surface structures (LIPSS) with an average periodicity of 195 ± 45 nm were observed on the carbon fiber surface while the epoxy matrix showed fine granular morphology. The surface topography of the laser tracks was quantitatively analyzed by 3D reconstruction of stereographic pairs of FESEM images recorded at two different inclinations of specimen with respect to the incident electron beam. The difference in ablation depth of fiber and epoxy was measured from stereographic images which showed a remarkable change in ablation depth of fiber and the matrix for pulse energy in the range 1–3 μJ and 4–5 μJ. The observations made in this study are expected to be useful for achieving improved bonding in composite structure repaired by adhesive joining.

Structural and modal analysis of small wind turbine blade using three different materials

The aim of the research is to investigate and compare the performance of small wind turbine blades made using three different materials by performing structural analysis. Also, it investigated the vibration characteristics of these blades. SOLIDWORKS software was used to create the three-dimensional model of the blade, which was then exported to ANSYS softwarein order to achieve the numerical simulation based on the Finite element method. In this work, three different materials Aluminum alloy (Al-2024), Glass fibre reinforced epoxy (GRFP), and Carbon fibre reinforced epoxy (CFRP) were selected to build the body of the blade parts. The structural analysis result shows that the CFRP gave the lowest deformation and highest stress whereas GRFP and AL-2024 gave almost similar results. Modal analysis results show that GFRP has lower modes of vibration than other materials.

Crashworthiness Assessment of Carbon/Glass Epoxy Hybrid Composite Tubes Subjected to Axial Loads.

The crashworthiness of composite tubes is widely examined for various types of FRP composites. However, the use of hybrid composites potentially enhances the material characteristics under impact loading. In this regard, this study used a combination of unidirectional glass–carbon fibre reinforced epoxy resin as the hybrid composite tube fabricated by the pultrusion method. Five tubes with different length aspect ratios were fabricated and tested, in which the results demonstrate “how structural energy absorption affects by increasing the length of tubes”. Crash force efficiency was used as the criterion to show that the selected L/D are acceptable of crash resistance with 95% efficiency. Different chamfering shapes as the trigger mechanism were applied to the tubes and the triggering effect was examined to understand the impact capacity of different tubes. A finite element model was developed to evaluate different crashworthiness indicators of the test. The results were validated through a good agreement between experimental and numerical simulations. The experimental and numerical results show that hybrid glass/carbon tubes accomplish an average 25.34 kJ/kg specific energy absorption, average 1.43 kJ energy absorption, average 32.43 kN maximum peak load, and average 96.67% crash force efficiency under quasi-static axial loading. The results show that selecting the optimum trigger mechanism causes progressive collapse and increases the specific energy absorption by more than 35%.

Novel Thermoplastic Composites Strengthened with Carbon Fiber-Reinforced Epoxy Composite Waste Rods: Development and Characterization

The increasing use of carbon fiber and epoxy resin composite materials yields an increase in the amount of waste. Therefore, we present a solution consisting of composites manufactured by hot pressing, employing polyamides (either PA11 or PA12) and a mechanically recycled carbon fiber-reinforced polymer (CFRP) as reinforcement. The main objectives are to study the manufacturing of those composites, to evaluate the fiber distribution, and to perform a mechanical, dynamical, and thermomechanical characterizations. The X-ray micro-computed tomography (μCT) shows that the fibers are well-distributed, maintaining a homogeneous fiber volume fraction across the material. The variability in the results is typical of discontinuous fiber composites in which the fibers, although oriented, are not as homogeneously distributed as in a continuous fiber composite. The mechanical and dynamic properties barely differ between the two sets of composites. A dynamic-mechanical analysis revealed that the glass transition temperature (Tg) increases slightly for both composites, compared to the polymers. These results illustrate the viability of the recycling and reuse route for preventing the deterioration of carbon fibers and promoting the subsequent reduction in the environmental impact by employing a thermoplastic matrix.

Mechanical behavior and failure mechanism of aerogel-reinforced carbon fibre/epoxy composites under quasi-static/impact loading

The improvement of the impact resistance of carbon fiber reinforced epoxy (CF/EP) composite is of great significance for its application in safety protection. Herein, an approach to improve the compressive mechanical properties of CF/EP composites by self-interlocking Ti3C2Tx/polyvinyl alcohol (PVA) aerogel (TPA) has been developed. Mechanical responses and strain rate effects of CF/EP and TPA/CF/EP composites in longitudinal, transverse and through-thickness directions under quasi-static/dynamic loading have been studied. The results show that the stitching effect of TPA leads to the fact that the fracture has been dominated by cohesive failure and fiber breakage. Compared with CF/EP composites, TPA/CF/EP composites exhibit higher compressive strength and Young's modulus in the strain rate range from 0.003 s−1 to 2369 s−1. TPA/CF/EP composites have different damage evolution under quasi-static and dynamic loading and exhibits obvious strain rate sensitivity. Moreover, high-speed camera photographs and micro-morphological characteristics show that TPA/CF/EP laminates have different failure modes and fracture mechanisms for different loading directions. The well understanding of fracture mechanism can strengthen people's capability of and offer insights into designing advanced energy-absorbing materials and structures.

Self-interlocked MXene/polyvinyl alcohol aerogel network to enhance interlaminar fracture toughness of carbon fibre/epoxy composites

Interlaminar delamination is the most prevalent failure mode for carbon fiber reinforced epoxy (CF/EP) composites, which limits its applications. In this work, the interlaminar fracture toughness of CF/EP composites has been enhanced by the self-interlocked network arisen from Ti3C2Tx/polyvinyl alcohol (PVA) aerogel (TPA). The failure mode and toughening mechanism of interlocked TPA/CF/EP laminates has been explored from crack path behaviour and fracture morphology. The results show that the surface-modified MXene effectively improved the mechanical properties of TPA aerogels. The optimized loading of Ti3C2TX (7.69 wt%) and TPA areal density (27 g/mm2) can significantly enhance the GIC Init, GIC Prop and GIIC by 76%, 40% and 32%, respectively, without appreciably reducing the in-plane mechanical properties. The enhanced fracture toughness can be ascribed to cohesive failure at the interface facilitated by stitching-like effect of TPA, deflection and twisting of the main crack, the generation of numerous microcracks and pull-out of TPA skeleton and Ti3C2Tx, etc. Compared with the traditional interleave toughening, interlocked TPA not only achieves a comprehensive balanced mechanical enhancement of CF/EP laminates, but also avoids the toxicity of organic solvents.

Structural Health Monitoring of the Carbon Fiber Reinforced Epoxy/MWCNTS Composites under Vibration Loading, Using Electrical Resistance Change Method

This work aims to investigate the structural deterioration of the Carbon Fiber Reinforced Epoxy (CFRE) composite under vibration loading by monitoring the variation of the electrical resistance of the composite. The vacuum assisted resin transfer moulding process is used to fabricate the CFRE composites. Multiwall Carbon Nanotubes (MWCNTs) (0.5% wt) are added to the non-conductive resin to increase its electrical conductivity before CFRE fabrication. The tests were carried out by monitoring the variation in electrical resistance of the CFRE composite at 90 Hz frequency vibration loading. The dispersion of MWCNTs into the matrix and the damage of CFRE composite are illustrated by the SEM images. The results show that the electrical resistance change can be considered as a good indication to detect damage in CFRE (modified with 0.5 wt % MWCNTs) under vibration loading.

Describing the Material Behavior of Steel and Carbon Fiber Reinforced Composites Using a Combined Damage-Plasticity Approach

Metal fiber hybrids (MFH) exhibit outstanding mechanical properties. They combine the advantages of ductile metallic materials with the well-known advantages of classical glass or carbon fibers in polymer matrices. Previous research has shown that these hybrid material concepts can improve structural integrity and energy absorption while maintaining their excellent weight-specific mechanical properties as well as allowing a wider range of multifunctional applications. In today’s component design process, simulation is a powerful tool for engineers to exploit the full mechanical potential of the material used. However, describing the material behavior including its multifunctional usability in numerically aided design processes of components is currently one of the major challenges for MFH. Against this background, this work focuses on the development and evaluation of a description method for MFH in the finite element analysis (FEA). A steel and carbon fiber reinforced epoxy resin (SCFRP) with hybridization at the laminate level is chosen as the reference material. To describe the behavior of unidirectional steel fiber reinforced plastic (SFRP) layers, a material model combining an orthotropic damage model and a 1D-plasticity model is proposed and implemented as a user-defined subroutine for LS-Dyna. In addition, SCFRP laminates are manufactured, tested under tensile loading, and used to parameterize the material models and to validate the description method for SCFRP. In this study, it is shown that the description method in combination with the newly developed material model is able to describe the complex failure mechanism of SCFRP. In particular, with respect to the material behavior up to the failure of the carbon fibers, a very good mapping accuracy can be achieved. Strain localization effects occur in both numerically predicted and experimentally measured post-failure behavior. Therefore, it could be concluded that the accuracy of the numerical predictions strongly depends on the geometric resolution of the discretization.

Strain-Field Modifications in the Surroundings of Impact Damage of Carbon/Epoxy Laminate.

The relationship between deformation and stress is crucial for any elasto-plastic body. This paper deals with the experimental identification of the basic parameters of the composite laminate model in relation to the finite element model. Standardized tensile, impact, and post-impact tests on a carbon fiber-reinforced epoxy laminate were used. The method by which the elasticity and failure parameters were obtained from the initial components is described. In the article, the modes of initiation and complete failure of samples in tensile tests, which are compared with the simulation, are presented. Furthermore, the article deals with the issue of the generation and detection of damage by low-speed impact, which can be caused by contact with moving objects, due to improper handling or maintenance. The results of impact analysis simulations are shown in the context of strain-field distribution changes obtained with the help of digital image correlation. The results showed high agreement between the calculations and the experiments. Based on this agreement, simulations of impact damage for various energies were performed. These simulations were used to determine the approximate sizes of the affected zones in relation to the impact energy. The results are finally discussed in the context of the possible use of structural health monitoring based on strain modifications.

Weibull reliability plots to study the strain rate effect on interfacial strengths of carbon fiber reinforced epoxy composites

AbstractTwo‐parameter Weibull reliability plots are utilized to determine the effects of strain rate on the interfacial strengths of unidirectional carbon fiber reinforced epoxy (CFRE) composites. Laminate specimens with two different fiber orientations are tested to failure under flexural loading. Type 1 laminates with fibers running parallel to specimen length (fiber orientation of 0° with respect to specimen span length) enable measuring inter‐laminar shear strength (ILSS) of the interface (between adjacent lamina) with locus of failure along beam mid ply. Seventy‐two type 1 laminates are tested at five levels of flexural strain rates: 1.89 * 10−5 to 9.37 * 10−2 s−1. Type 2 laminates with fibers running perpendicular to specimen length (fiber orientation of 90° with respect to specimen span length) enable measuring intra‐laminar (matrix/fiber) peel strength (ILPS) for tensile (mode I) strength of the matrix/fiber interface with locus of failure at beam bottom ply. Thirty‐six type 2 laminates are tested at three levels of flexural strain rates: 2.09 * 10−5 to 3.49 * 10−3 s−1. For each level of strain rate, Weibull plots are constructed. Stress values at failure probability (Pf) of 63.1% are assigned as strength values. The results show a slight decrease of the Weibull modulus, m, with increasing strain rates. The modulus decreases from 12.37 to 10.49 and from 11.11 to 9.68, for laminates type 1 and 2, respectively. For laminates type 1, ILSS increases with increasing strain rates rising 16.1% over the range of the tested strain rates. For laminates type 2, ILPS increases with increasing strain rates rising 38.1% over the range.

Mechanism of matrix influencing the cryogenic mechanical property of carbon fibre reinforced epoxy resin composite

This study focuses on the cryogenic mechanical property of carbon fibre reinforced epoxy resin composite (CFRP) unidirectional laminate, and the cryogenic evolution mechanism is discussed from the microstructural perspective of resin free volume and intermolecular forces. The primary transition temperature (147 °C) and the secondary transition temperature (−25 °C) is identified through dynamic mechanical analysis. As the cryogenic condition (−196 °C) is significantly lower than the temperature of main-chain segmental and micro-structure unit motion, the resin molecular segments are frozen, free volume fraction and resin toughness are reduced, thus the brittleness increases. These effects reduce the cryogenic failure strain of CFRP at break by 43.7% compared to room temperature, resulting in a smoother fracture surface morphology. Resin molecules under cryogenic condition have higher packing density, stronger intermolecular forces, which increase the strength and modulus of both resin and CFRP.

Mechanical Properties of Carbon Fiber Reinforced Composites Filled with Carbon Microparticles

The aim of this work is to investigate the effect of carbon micro particles used as epoxy resin fillers, for the mechanical properties of reinforced composites unidirectionally oriented carbon fibers. The motivation for this work was expansion knowledge of the possibilities of improving the user properties of these materials at maintaining their weight, thus finding new areas for application recycled carbon fibers from composite waste, which would also contribute to the solution issues of recycling and subsequent use of today's mostly landfilled composites. This work deals with the influence of carbon fillers embedded in epoxy resin on tensile and flexural properties of carbon fiber reinforced epoxy (CFRE) composites. Samples were made from unidirectional carbon multifilaments, and epoxy resin modified with selected carbon fillers in 2.5weight% concentrations. Composites were subsequently examined using flexural and tensile tests. All specimen filled with carbon particles showed increase of both, flexural and tensile properties, if compared to neat epoxy composites.

An additional hole to compensate for mechanical property of thermoset composite and aluminum alloy joint during resistance welding

A hole in the center of the aluminum (Al) alloy was processed to compensate for the mechanical properties of resistance welded joints of the carbon fiber reinforced epoxy resin matrix (CF/Epoxy) laminate and Al alloy for solving the problem of poor bonding quality in the center of the joint due to uneven temperature distribution in the resistance welding process. The resistance welded lap configuration of the upper Al and the lower laminate was employed, and through holes with a different diameter (d h) were prefabricated on the upper Al alloy plates. The molten polyetherimide (PEI) resin was bonded to the surfaces of the samples on both sides under the action of Joule heat, and the excess PEI resin filled the prefabricated through-hole of the Al alloy plate under pressure and realized the jointing of the 6063Al alloy plate and the CF/Epoxy laminate. The micro-morphology of the welded interface was characterized by scanning electron microscopy (SEM), and the heat distribution of the sample was simulated using COMSOL. The tensile shear force of the joint was tested, which rises with an increase of d h. The failure interface was analyzed in detail, which showed a strong correlation with d h.

Effect of CNTs deposition on carbon fiber followed by amination on the interfacial properties of epoxy composites

To enhance the interfacial properties of carbon fiber/epoxy composites, a layer of carbon nanotubes (CNTs) about 25–30 nm thickness was deposited on carbon fiber surface at low temperature by chemical vapor deposition (CVD), and then the CNTs were aminated to increase the surface wettability. Microbond test was conducted to characterize the interfacial shear strength (IFSS) of carbon fiber reinforced epoxy resin composites and the interlaminar shear strength (ILSS) and modeⅠfracture toughness (GIC) of carbon fiber composite laminates were also measured to characterize the interlaminar properties. The results showed that this surface treatment method significantly increased the fiber surface energy, effectively improving the interfacial bonding of the composites. The IFSS, ILSS and GIC of composites reinforced by the final treated carbon fiber were 39.42%, 32.21% and 95.33% higher than that of composites reinforced by the raw carbon fiber. The fracture surfaces also indicated a great interphase appeared in the composites, which was formed by the mechanical interlocking of CNTs and the chemical reaction between surface functional groups and resin.

Effect of the interplay between fiber surface chemistry and sizing reactivity on fiber matrix interaction in carbon fiber reinforced epoxy resin

ABSTRACT A comprehensive picture of the interaction between fibers and matrix in carbon fiber–reinforced epoxy resin is given. We present new data on fiber wetting by a resin, interphase formation, and fiber matrix adhesion and develop a model for fiber matrix interaction, considering earlier studies on fiber surface chemistry and interaction with sizings. The effect of surface chemistry is investigated by oxygen functionalization of carbon fibers by anodic oxidation utilizing two electrolytes. To address the influence of sizing reactivity, two epoxy-based sizings are applied with different number of epoxide groups per molecule. The fiber matrix adhesion is investigated by single fiber push-out tests. The resulting interfacial fracture toughness of functionalized fibers in epoxy resins depends on the fiber surface chemistry. Based on quantitative measurements, an influence of surface topography on the fiber matrix adhesion can be ruled out. Application of a standard sizing does not change the composite’s interfacial fracture toughness compared to the unsized case. In contrast, use of a reactive sizing generally increases fiber matrix adhesion. The systematic variation of interfacial fracture toughness is discussed based on the number of bonds formed between fiber and resin. Bonding between hydroxyl surface functionalities and epoxy groups of resin or sizing is assumed to dominate.

Static and fatigue tensile properties of carbon/glass hybrid fiber-reinforced epoxy composites

The static and fatigue tensile properties of high-strength polyacrylonitrile (PAN)-based carbon (IMS60) and electronic (E)-class glass (E-glass) hybrid fiber-reinforced epoxy matrix composites (HFRPs) were investigated. The fiber orientations of the HFRP specimens were set to unidirectional with [(0(IMS60))/(0(E-glass))]S (subscript S means symmetry and [(0(IMS60))/(0(E-glass))/(0(E-glass))/(0(IMS60))]), [(0(E-glass))/(0(IMS60))]S, [(0(E-glass))/(0(IMS60))2]S, [(0(E-glass))/(0(IMS60))3]S, [(0(E-glass))/(0(IMS60))5]S, [(0(E-glass))2/(0(IMS60))]S, [(0(E-glass))3/(0(IMS60))]S, and [(0(E-glass))5/(0(IMS60))]S. Under static loading for the [(0(IMS60))/(0(E-glass))]S, [(0(E-glass))/(0(IMS60))]S, [(0(E-glass))/(0(IMS60))2]S, [(0(E-glass))/(0(IMS60))3]S, and [(0(E-glass))/(0(IMS60))5]S HFRP specimens, the stress applied to the specimen was almost linearly proportional to the strain until failure. However, the tensile stress–strain curves of the [(0(E-glass))2/(0(IMS60))]S, [(0(E-glass))3/(0(IMS60))]S, and [(0(E-glass))5/(0(IMS60))]S HFRP specimens had a complicated shape (jagged trace). The Weibull statistical distributions of the tensile strength values were also examined. The Weibull moduli for the [(0(E-glass))/(0(IMS60))]S, [(0(E-glass))/(0(IMS60))2]S, [(0(E-glass))/(0(IMS60))3]S, [(0(E-glass))/(0(IMS60))5]S, [(0(E-glass))2/(0(IMS60))]S, [(0(E-glass))3/(0(IMS60))]S, and [(0(E-glass))5/(0(IMS60))]S HFRP specimens were higher than those for the mono carbon fiber-reinforced epoxy (CFRP) and glass fiber-reinforced epoxy (GFRP) specimens. Under fatigue loading, the fatigue properties of the HFRP specimens showed CFRP-dominant behaviour at high stress levels and GFRP-dominant behaviour at low stress levels. The fatigue properties of the HFRP specimens increased with increasing volume fraction of CFRP in the following order: ([(0(E-glass))/(0(IMS60))5]S > [(0(E-glass))/(0(IMS60))3]S > [(0(E-glass))/(0(IMS60))2]S > [(0(IMS60))/(0(E-glass))]S > [(0(E-glass))/(0(IMS60))]S > [(0(E-glass))2/(0(IMS60))]S > [(0(E-glass))3/(0(IMS60))]S > [(0(E-glass))5/(0(IMS60))]S).