Carbon Fiber Reinforced Epoxy Laminates Research Articles

Compression and hydrothermal ageing after impact of carbon fibre reinforced epoxy laminates

This paper proposes a new methodology for the assessment of seawater ageing effects on impact-damaged composite laminates. CF/Epoxy laminates which were unimpacted, and impacted at 30 J, 60 J, and 90 J by hemispherical and conical impactors were subject to 4 months hydrothermal ageing in renewed natural seawater at 60 +/-2 °C. The majority of water uptake by impacted laminates (0.05 wt% − 0.3 wt%) occurred in the first 24 h and is believed to be held in damage cavities by capillary mechanisms. The increase in diffusive water uptake rate by the matrix due to impact damage was only small, at less than 0.008 wt%.mm.hr−0,5, compared with the total diffusive water uptake rate of 0.1 wt%.mm.hr−0,5. Hydrothermal ageing reduced the residual compressive strength of pristine laminates by 25 % and impact-damaged laminates by 8 % to 16 % for impacts between 30 J and 90 J.

GO-tagged PEI sizing agent imparts self-healing and excellent mechanical properties to carbon fiber reinforced epoxy laminates.

Carbon fiber-reinforced epoxy (CFRE) laminates have attracted significant attention as a structural material specifically in the aerospace industry. In recent times, various strategies have been developed to modify the carbon fiber (CF) surface as the interface between the epoxy matrix and CFs plays a pivotal role in determining the overall performance of CFRE laminates. In the present work, graphene oxide (GO) was used to tag a polyetherimide (PEI, termed BA) containing exchangeable bonds and was employed as a sizing agent to improve the interfacial adhesion between CFs and epoxy. This unique GO-tagged-BA sizing agent termed BAGO significantly enhanced the mechanical properties of CFRE laminates by promoting stronger interactions between CFs and the epoxy matrix. The successful synthesis of BAGO was verified by Fourier-transform infrared spectroscopy. Additionally, the partial reduction of GO owing to this tagging with BA was further confirmed by X-ray diffraction and Raman spectroscopy, and the thermal stability of this unique sizing agent was evaluated using thermogravimetric analysis. The amount of GO in BAGO was optimized as 0.25 wt% of BA termed 0.25-BAGO. The 0.25-BAGO sizing agent resulted in a significant increase in surface roughness, from 15 nm to 140 nm, and surface energy, from 13.2 to 34.7 mN m-1 of CF. The laminates prepared from 0.25-BAGO exhibited a remarkable 40% increase in flexural strength (FS) and a 35% increase in interlaminar shear strength (ILSS) due to interfacial strengthening between epoxy and CFs. In addition, these laminates exhibited a self-healing efficiency of 51% in ILSS due to the presence of dynamic disulfide bonds in BAGO. Interestingly, the laminates with 0.25-BAGO exhibited enhanced Joule heating and enhanced deicing, though the EMI shielding efficiency slightly declined.

Experimental assessment of barely visible impact damage carbon fiber reinforced epoxy composite using ultrasound method

Background Carbon fiber reinforced epoxy (CFRP) is susceptible to impact damage which could resulted in reduction of the mechanical properties. This paper studies the architecture of barely visible impact damage (BVID) to comprehend the extent of damage on quasi-isotropic CFRP laminates of varying thickness (i.e. 16, 24 and 32-ply laminates of 3, 4 and 5 mm respectively). Methods Quasi-static indentation is chosen to produce BVID on CFRP laminates, followed by using non-destruction evaluation method, namely conventional contact-type ultrasonic testing (UT) and C-mode scanning acoustic microscopy (C-SAM) method. Results The findings revealed (1) the size and shapes of the BVID on CFRP laminates, (2) no damage was found at the center of the impact point, and (3) the bridging between the point of impact to the outer damaged diameter due to the consequence of diverse orientation of carbon fiber strips which exhibit excellent mechanical properties before structural failure. Conclusions The results concluded that the UT and C-SAM method can identify both the pristine region and the internal damaged structures in CFRP laminates.

Bio-inspired helicoidal thin-ply carbon fiber reinforced epoxy laminates with nylon microparticles for improved toughness and healing

Bio-inspired helicoidal thin-ply carbon fiber reinforced epoxy laminates with nylon microparticles for improved toughness and healing

Impact performance on industrial scalable graphene reinforcement composites

Carbon fiber reinforced epoxy laminates are widely used in the design and manufacturing of aeronautical structures. Among different manufacturing procedures, resin transfer moulding (RTM) has emerged as a cost-effective alternative to prepregs manufactured in an autoclave. However, the laminate obtained by RTM exhibits approximately 20% lower mechanical properties. To address this limitation, the addition of nanoparticles has been suggested as a solution. In this study, graphene particles were obtained by in-situ mechanical exfoliation in the resin and directly injected into the mould. The major achievement of this study is that the entire manufacturing process was performed at an industrial scale using the same tooling used to produce aircraft structures. Laminates with varying concentrations and dispersion times were manufactured using RTM and subjected to compression after impact tests, resulting in a 7.6% improvement. Furthermore, analysis through SEM techniques revealed the role of graphene in the bear capacity of the laminates. Finally, to demonstrate the feasibility of the proposed methodology in an industrial environment, a real aircraft structure was manufactured with graphene, without any modifications to the actual industrial process.

Effect of Strain Rate on Tensile Properties of Carbon Fiber-Reinforced Epoxy Laminates with Different Stacking Sequences and Ply Orientations.

In practical application situations, a carbon fiber-reinforced polymer (CFRP) is often subjected to complex dynamic loadings. The effect of the strain rate on mechanical properties is very important for the CFRP design and product development. In this work, static and dynamic tensile properties of CFRP with different stacking sequences and ply orientations were investigated. The results showed that the tensile strengths of CFRP laminates were sensitive to the strain rate, while Young's modulus was independent of the strain rate. Moreover, the strain rate effect was related to the stacking sequences and ply orientations. The experimental results showed that the strain rate effects of the cross-ply laminates and quasi-isotropic-ply laminates were lower than that of the unidirectional-ply laminates. Finally, the failure modes of CFRP laminates were investigated. Failure morphology demonstrated that the differences in strain rate effects among cross-ply laminates, quasi-isotropic-ply laminates, and unidirectional-ply laminates were caused by the mismatch between the fiber and the matrix when the strain rate increased.

Experimental assessment of barely visible impact damage carbon fibre reinforced epoxy composite using ultrasound method

Background: Carbon fibre reinforced epoxy (CFRP) is susceptible to impact damage which could resulted in reduction of the mechanical properties. This paper studies the architecture of barely visible impact damage (BVID) to comprehend the extent of damage on quasi-isotropic CFRP laminates of varying thickness (i.e. 16, 24 and 32-ply laminates of 3, 4 and 5 mm respectively). Methods: Quasi-static indentation is chosen to produce BVID on CFRP laminates, followed by using non-destruction evaluation method, namely conventional contact-type ultrasonic testing (UT) and C-mode scanning acoustic microscopy (C-SAM) method. Results: The findings revealed (1) the size and shapes of the BVID on CFRP laminates, (2) no damage found at the point of damage, and (3) the bridging between the point of impact to the outer damaged diameter due to the consequence of diverse orientation of carbon fibre strips which exhibit excellent mechanical properties before structural failure. Conclusions: The results concluded that the UT and C-SAM method can identify both the pristine region and the internal damaged structures in CFRP laminates.

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.

Effect of Dispersing Multiwalled Carbon Nanotubes and Graphene Nanoplatelets Hybrids in the Matrix on the Flexural Fatigue Properties of Carbon/Epoxy Composites

The synergistic effect of applying hybrid nanoparticles in improving the fatigue property of fiber reinforced polymer composites has rarely been explored before. Hence the monotonic and fatigue flexure properties of the carbon fiber reinforced epoxy laminates with matrix modified by multiwalled carbon nanotubes and graphene nanoplatelets were experimentally studied herein. The nanofiller ratio applied in the matrix modification was considered as a variable in the experimental program to investigate the effect of nanofiller ratio on the studied mechanical properties. A synergistic index has been employed to evaluate the synergistic effect of hybrid nanoparticles on the studied properties successfully. Experimental results show that the laminates with matrix modified under a nanofiller ratio (multiwalled carbon nanotube: graphene nanoplatelet) of 9:1 have the higher monotonic and fatigue strengths than those modified under other nanofiller ratios. The monotonic flexural strength and fatigue limit of the specimens modified under a nanofiller ratio of 9:1 are higher than the neat laminate specimens by 9.3 and 11.0%, respectively. The fatigue limits of the studied nano-modified laminates increase with the static strengths. Adding hybrid nanoparticles under proper nanofiller ratios in the matrix can suppress the degradation of the stiffness, further increase the resistance to fatigue damage. Examining the fracture surfaces of fatigued specimens reveals that the pullout/bridging effects of carbon nanotubes and the crack deflection effect of graphene nanoplatelets are the main reinforcement mechanisms in enhancing the fatigue strength of the composites.

Low velocity impact resistance of thin and toughened carbon fibre reinforced epoxy

This study investigates the effect of core-shell rubber nanoparticle and block copolymer matrix modifications on the low velocity impact resistance of thin (∼1.6 mm), multi-axial carbon fibre reinforced epoxy laminates. The results demonstrate a strongly enhanced damage resistance predominantly to impact energies of 9 J and 13 J. Lower impact energies do not sufficiently activate the energy dissipating capabilities of the applied toughening agents. In the case of 9 J impacts, it is found that the damage resistance increases with increasing modifier concentration by a successive reduction of the indentation depth. Once the impact causes large-scale fibre fracture (13 J), the damage mode changes and an increasing matrix toughness leads to a strong reduction of the damage area. However, a proper bonding between matrix and the embedded fibres is a mandatory precondition to take advantage of a core-shell rubber and block copolymer toughened matrix.

Vol4 num4-13 Compression after impact test on woven CFRP laminates with graphene

Nowadays carbon fibre reinforced epoxy laminates represent the standard material in the designing and manufacturing of aeronautical composite structures. However, advantages related to metals manufacturing could represent an important menace for the role of composite materials in this industry. Therefore, new improvements in composite structures have to be seek in order to improve their competitiveness. Graphene is a nanomaterial that possess the higher stiffness and strength ever measured. Therefore, the use of Graphene Related Material (GRM) for enhancing composite laminate materials could represent an important advance in order to reduce their impact vulnerability and to improve the performance of Resin Transfer Molding (RTM) composites.   In this work epoxy resin doped with GRM were used to manufacture carbon fiber aeronautical composites by RTM. Low velocity impacts and Compression After Impact (CAI) tests were performed. Regarding experimental methodology, ASTM standard was followed, also new measuring techniques were used as 3D High Speed Digital Image Correlations. All tests were performed on GRM enhanced material and reference material to compare their results. Under impact loads, elastic behavior, peak force or damage results do not depend on the addition of graphenic particles. Whereas, a minor improvement enhanced with GRM in compression preserving the visible damage for an impact equivalent to the tool drop (30 J). Is important to keep this effect in order to detect damages in the composites structures.

Thermal ageing effect on the mechanical properties of carbon fibre-reinforced epoxy laminates

Thermostable matrix are extensively used in structural components because of their good mechanical properties [1]. The region of stability of these polymers is defined by the glass transition temperature (Tg) [2]. The typical service temperature of these materials should be lower than Tg but in some cases operating temperatures can exceed Tg which causes a variation in the properties of the polymer and consequently, modifies the mechanical properties of the composite material [3]. Therefore, it is important to understand the effect of temperature on the failure mechanisms that occur in the material in order to ensure stability and durability [4,5]. The objective of this work was to evaluate the effect of temperature and time of exposure on the mechanical properties of carbon/epoxy composites. For that purpose, samples were aged at different temperatures and periods of time and then, impact and flexural tests have been performed. It was observed that thermal ageing caused notable variations in the glass transition temperature of the epoxy resin. In consequence, two different effects were observed: in most cases, thermal ageing causes a reduction on the mechanical properties of the composites due to the thermo-oxidation of the epoxy resin and the loss of adhesion in the matrix/fibre interface, especially at higher temperatures; however, at temperatures below the Tg, there is an increase of the maximum strength because of a post-curing effect. [1] E. Selver, P. Potluri, C. Soutis, Impact damage tolerance of thermoset composites reinforced with hybrid commingled yarns, Compos. Part B 91 (2016) 522-538. [2] E. Ernault, E. Richaud and B. Fayolle, Origin of epoxies embrittlement during oxidative ageing, Polymer Testing 63 (2017) 448-454 [3] A. Mlyniec, J. Korta, R. Kudelski and T. Uhl, The influence of the laminate thickness, stacking sequence and thermal ageing on the static and dynamic behaviour of carbon/epoxy composites, Composite Structures 118 (2018) 208-216 [4] A. P. C. Barbosa, A. P. P. Fulco, E. S. S. Guerra, F. k. Arakaki, M. Tosatto, M. C. B. Costa and J. D. D. Melo, Accelerated ageing effect son carbon fibre/epoxy composites, Composites Part B, 110 (2017) 298-306 [5] S. Marouani, L. Curtil and P. Hamelin, Ageing of carbon/epoxy and carbon/vinylester composites used in the reinforcement and/or the repair of civil engineering structures, Composites Part B, 43 (2012) 2020-2030

Improvement in Tensile Quasi-Static and Fatigue Properties of Carbon Fiber-Reinforced Epoxy Laminates with Matrices Modified by Carbon Nanotubes and Graphene Nanoplatelets Hybrid Nanofillers.

The monotonic and cyclic properties of carbon fiber-reinforced epoxy (CFEP) laminate specimens with matrices modified by multiwalled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) were experimentally studied. The laminate specimens were fabricated by the hand lay-up procedure and six MWCNT:GNP weight ratios, i.e., 0:0, 10:0, 0:10, 5:5, 9:1, and 1:9, were considered to prepare the nanoparticle-modified epoxy resin by using an ultrasonic homogenizer and a planetary centrifugal mixer. Then, these laminate specimens with their matrices modified under various nanofiller ratios were employed to investigate the influence of the number of nanofiller types and hybrid nanofiller ratios on the quasi-static strength, fatigue strength, and mode I fracture toughness. The experimental results show that adding individual types of nanoparticles has a slight influence on the quasi-static and fatigue strengths of the CFEP laminates. However, the remarkable synergistic effect of MWCNTs and GNPs on the studied mechanical properties of the CFEP laminates with matrices reinforced by hybrid nanoparticles has been observed. Examining the evolution of stiffness-based degradation indicates that adding hybrid nanoparticles to the matrix can reduce the degradation effectively. The high experimental data of the mode I fracture toughness of hybrid nano-CFEP laminates demonstrate that embedding hybrid nanoparticles in the matrix is beneficial to the interlaminar properties, further improving the fatigue strength. The pushout mechanism of the MWCNTs and the crack deflection effect of the GNPs suppress the growth and linkage of microcracks in the matrix. Furthermore, the bridging effect of the nanoparticles at the fiber/matrix interface retards the interfacial debonding, further improving the resistance to delamination propagation.

Cyclic Relaxation, Impact Properties and Fracture Toughness of Carbon and Glass Fiber Reinforced Composite Laminates.

In this paper, the mechanical properties of fiber-reinforced epoxy laminates are experimentally tested. The relaxation behavior of carbon and glass fiber composite laminates is investigated at room temperature. In addition, the impact strength under drop-weight loading is measured. The hand lay-up technique is used to fabricate composite laminates with woven 8-ply carbon and glass fiber reinforced epoxy. Tensile tests, cyclic relaxation tests and drop weight impacts are carried out on the carbon and glass fiber-reinforced epoxy laminates. The surface release energy GIC and the related fracture toughness KIC are important characteristic properties and are therefore measured experimentally using a standard test on centre-cracked specimens. The results show that carbon fiber-reinforced epoxy laminates with high tensile strength give high cyclic relaxation performance, better than the specimens with glass fiber composite laminates. This is due to the higher strength and stiffness of carbon fiber-reinforced epoxy with 600 MPa compared to glass fiber-reinforced epoxy with 200 MPa. While glass fibers show better impact behavior than carbon fibers at impact energies between 1.9 and 2.7 J, this is due to the large amount of epoxy resin in the case of glass fiber composite laminates, while the impact behavior is different at impact energies between 2.7 and 3.4 J. The fracture toughness KIC is measured to be 192 and 31 MPa √m and the surface energy GIC is measured to be 540.6 and 31.1 kJ/m2 for carbon and glass fiber-reinforced epoxy laminates, respectively.

Thermoreversible Bonds and Graphene Oxide Additives Enhance the Flexural and Interlaminar Shear Strength of Self-Healing Epoxy/Carbon Fiber Laminates

In the current era of high-strength, lightweight, and durable aircraft components, the need for carbon fiber-reinforced epoxy (CFRP) laminates is highly desired owing to their high specific strength and modulus, low coefficient of thermal expansion, and tunable properties that are unmatched by other materials. However, such components’ catastrophic failure occurs due to the interfacial defects and debonding, thereby reducing service life and economic viability. Therefore, there is a pressing need to enhance the mechanical properties of CFRPs through matrix and fiber modifications and introduce the components’ self-healing ability under a natural trigger. This study assessed the crucial role of “thermoreversible bonds” and graphene oxide (GO) “interconnects”, which worked in tandem toward significantly improving the mechanical properties and imparting self-healing properties in CFRP laminates. The laminates were fabricated with varying percentages of GO-modified epoxy matrix via vacuum-assisted resin transfer molding (VARTM) method. The carbon fibers were covalently modified with bis-maleimide (BMI) to establish a thermoreversible bond with GO at the fiber matrix interface to make interconnects. Flexural strength and interlaminar shear strength (ILSS) values for the optimized GO-modified epoxy laminates with BMI-deposited carbon fibers exhibited a significant increase of 30 and 47%, respectively. After a self-healing cycle triggered at 60 °C, they exhibited a recovery in their ILSS values up to 70%. These improvements are particularly useful for aircraft wings made up of CFRP laminates.

On the effects of temperature on tensile behavior of carbon fiber reinforced epoxy laminates

As a highly promising lightweight material, carbon fiber reinforced plastics (CFRP) composites have been widely used in aerospace, marine and automotive industries, which could expose to low or high thermal environments with varying material properties. This study investigated the effects of temperature variation ranging from −30 °C to 160 °C on tensile properties of CFRP experimentally and theoretically. The specimens were prepared using thermo-forming technology; and the glass transition temperatures of epoxy resins were measured by dynamic mechanical analysis (DMA). Digital image correlation (DIC) technique was used to capture the variation in strain and damage fields. By means of scanning electron microscopy (SEM), the failure mechanisms, delamination and resin softening, were identified by scrutinizing the images of fracture areas subject to different temperatures. The two-parameter Weibull analysis was conducted to evaluate the theoretical tensile strengths from relatively discrete data. The obtained Weibull parameters are considered useful for the reliability analysis of CFRP structures. It is found that the tensile strength decreases with the increase of temperature in a nonlinear fashion, which can be modeled in terms of a tanh function by correlating with the temperature-dependent experimental data. The study is anticipated to provide fundamental understanding and a predictive tool for mechanical strength of composite structures operating under different thermal conditions.

Layered self‐resistance electric heating to cure thick carbon fiber reinforced epoxy laminates

AbstractCuring of thick carbon fiber reinforced thermosetting composite laminates has been a major challenge due to the undesired through‐thickness temperature gradient. In this paper, a novel layered self‐resistance electric heating (L‐SRE) method to cure thick laminates was proposed. The thick laminate was divided into multiple independent sub‐layers, and the temperature of each sub‐layer was controlled individually. The experiment's results revealed that L‐SRE was able to achieve highly homogeneous temperature distribution filed through‐thickness both in rapid heating and exothermic reaction stages. The maximum temperature difference of dwell stage for L‐SRE process was less than 4.0°C, and the L‐SRE process that had an optimized thickness of each sub‐layer achieved the minimum mean temperature deviation of 2.1°C, which was 88.46% lower than that of the oven process. By using the optimized L‐SRE method, the maximum value of crosslink thermal overshoot was 12.2°C (32.5°C for oven curing). Different layered temperature control strategies were explored, and the lowest energy consumption of 309.7 Wh (19.82% of oven process) was achieved by using the single‐power pulsed heating. The method proposed in this paper provided a new solution for high‐quality and energy‐efficient curing of thick laminates.

Rate-related study on the ply orientation of carbon fiber reinforced epoxy composite laminates

In many practical situations, composite structures are often subjected to complex impact loadings ranging from low to high strain rates. Therefore, it is necessary to characterize the mechanical performance of composite materials at different strain rate. In this paper, carbon fiber-reinforced epoxy laminates with different stacking sequences and ply orientations under dynamic impact loadings were investigated by split Hopkinson pressure bar (SHPB) apparatus. Dynamic results were compared with quasi-static compression results. The experimental results show that the strength of specimens increased with the increase of strain rate. Specifically, the stacking sequence and ply orientation of composite laminates have great impacts on their strain rate sensitivities. Moreover, the failure modes of specimens under quasi-static and dynamic impact loadings were compared and analyzed from both macroscopic and microscopic scales. The fracture surface morphology show that the interface between fiber and matrix tends to be a ductile failure mode under higher strain rates. Finally, through optimization design, the balance point between strength and toughness of the composite laminate was investigated and suggested.

Study on mode-I fracture toughness of composite laminates with curved plies applied by automated fiber placement

Interlaminar fracture toughness is an important parameter to characterize the delamination performance of carbon fiber-reinforced epoxy laminates. In this study, the mode-I fracture toughness of interlaminar interfaces with different local ply angles were studied by experiments and numerical simulations. A set of double cantilever beam specimens of T800 carbon fiber/EH104 epoxy were prepared according to the ASTM-D5528–01 standard, where four specimens had straight ply interfaces (0°//0°, 15°//−15°, 30°//−30°, and 45°//−45°) and two specimens had curved ply interfaces (curvature radius: 300 and 500 mm). The mode-I fracture toughness was characterized using a data reduction scheme based on the modified beam theory. The results revealed that the mode-I fracture toughness values for the specimens with a curved ply interface were significantly higher than those for specimens with a straight ply interface.

Epoxy-functionalized polysiloxane/Nano-SiO2 synergistic reinforcement in cryogenic mechanical properties of epoxy and carbon fiber reinforced epoxy laminate

Resin matrix of carbon fiber (CF) reinforced resin laminates play a key role in transferring the external stress to carbon fibers. Especially in cryogenic environment, the mechanical properties of CF reinforced resin laminates depend largely on the mechanical properties of resin matrix. In this work, an epoxy-functional polysiloxane/Nano-SiO2 (EFPS/Nano-SiO2) was prepared to enhance the mechanical properties of epoxy resin and carbon fiber reinforced epoxy laminate at RT and cryogenic environment. The TEM images indicate that the grafting of flexible macromolecule EFPS on the surface of Nano-SiO2 can improve the dispersion of Nano-SiO2 in epoxy resin. The tensile strength of epoxy resin with 5 wt% content of EFPS/Nano-SiO2 increases by 7.95% at RT and 17.07% at 90K, fracture strain by 54.55% at RT and 26.91% at 90K, fracture toughness (KIC) by 48.82% at RT and 33.33% at 77K compared with the neat epoxy resin. The enhancement mechanism should mainly be attributed to the fact that the Nano-SiO2 particles debonding enhance the energy dissipation at crack front and the flexible EFPS significantly improves the movability of epoxy curing networks. The tensile strength of CF reinforced EFPS/Nano-SiO2 epoxy laminate shows an increase of 16.64% at RT and 25.01% at 90K, confirming that the effect of EFPS/Nano-SiO2 epoxy resin transferring the external stress from resin matrix to CF is better than that of neat epoxy resin. In addition, the mechanism of thermal cycling affecting the tensile properties of CF reinforced epoxy laminates are analyzed in detail.