Carbon Fiber Reinforced Polymer Laminates Research Articles

Effect of EPD coated silanized graphene oxide on carbon fiber reinforced plastic: An emphasis on mechanical properties at cryogenic temperatures

The space industry is constantly exploring lightweight, high-strength materials, particularly carbon fiber reinforced polymer (CFRP) composites. Nonetheless, in some cryogenic space applications, neat CFRP fails miserably. Here, silane functionalized graphene oxide (SGO) was coated on the carbon fiber surface to modify its properties. SGO is deposited onto a PAN-based plain weave carbon fiber using the electrophoretic deposition (EPD) process. SGO coated carbon fiber, along with epoxy resin, was used to fabricate CFRP laminates. From mechanical studies of CFRP samples, tensile, flexural, and impact strength improved by 13.1 %, 26.6 %, and 3.9 %, respectively, at room temperature (RT). The improvements were 15.1 %, 35.3 %, and 13.5 %, respectively, at cryogenic temperatures (CT). FTIR studies confirmed the emergence of a flexible Si-O-Si bond, which is a key factor for improved strength. AFM and SEM analysis were conducted to investigate contact roughness improvement. Contact angle microscopy examined SGO-induced wettability of modified carbon fiber. Also, a fracture study showed that the failure mode of SGO-coated CFRP at CT had changed from interface failure to matrix failure.

Predicting Crack Width in CFRP-Strengthened RC One-Way Slabs Using Hybrid Grey Wolf Optimizer Neural Network Model

This study deploys a hybrid Grey Wolf Optimizer Neural Network Model for predicting the crack width in reinforced concrete slabs strengthened with carbon fiber-reinforced polymers (CFRP). Reinforced concrete (RC) one-way slabs (1800 × 400 × 120 mm in size) were strengthened with CFRP with various lengths (1800, 1100, and 700 mm) and subjected to four-point bending. The experimental results were compared to corresponding values for conventional RC slabs. The observed crack width results were recorded, and subsequently examined against the expression recommended by Eurocode 2. To estimate the crack width of CFRP-reinforced slabs, ANN combined with the Grey Wolf Optimizer algorithm was employed whereby the applied load, CFRP width/length, X/Y crack positions, and stress in steel reinforcement and concrete were defined as the input parameters. Experimental results showed that the larger the length and width of the carbon fiber, the smaller the maximum crack width in the tensile area of the slab at the final load step. On average, the crack width in slabs retrofitted with CFRP laminates increased by around 80% compared to a slab without CFRP. The results confirm that the equation provided by Eurocode 2 provides an unconservative estimation of crack widths for RC slabs strengthened with CFRP laminates. On the other hand, the results also confirm that the proposed informational model could be used as a reliable tool for estimating the crack width in RC slabs. The findings provide valuable insight into the design approaches for RC slabs and rehabilitation strategies for existing deficient RC slabs using CFRP.

Effects of Elastic Couplings in a Compressed Plate Element with Cut-Out.

Analytical calculations were performed on carbon fiber-reinforced polymer (CFRP) laminates in an asymmetrical configuration. The asymmetric configuration of composites was investigated, where extension-twisting and extension-bending couplings were used to obtain the elastic element. Analysis of the presence of elastic couplings was conducted according to Classical Laminate Theory (CLT). Components of matrices A, B, and D, as well as the parameters Dc and Bt, were obtained using the MATLAB software environment. The results show that couplings between the extension and bending, as well as between the extension and twisting, were strongly dependent on specimen plies' orientation. Moreover, additional analysis was performed on the influence of layer angle on the terms which are components of the Bt and Dc coefficients. The results indicate that the angle of laying fibers around 45-50° significantly amplifies the effects of elastic couplings.

Convolutional neural network method for damage detection of CFRP in electrical impedance tomography

Damage detection is vitally important for carbon fiber reinforced polymer (CFRP) laminates. When CFRP laminates are damaged, its impedance property is changed. Based on the electrical properties of CFRP laminates, the changed conductivity distribution can be reconstructed with the electrical impedance tomography (EIT) method. The detection method is attractive due to its simple equipment, low cost, and easy operation. However, image reconstruction of EIT faces a serious ill-conditioned nonlinear inverse problem. In order to solve this problem, a feature fusion convolutional neural network based on the dense connection (FF-D) method is applied in EIT to establish the mapping relationship between voltage measurement and conductivity distribution in this paper. The optimization can extract and utilize features to a greater degree and improve reconstruction accuracy and robustness. For the purpose of simulating the electrical properties of CFRP better, the conductivity values measured by an impedance analyzer are used as the data set. The correlation coefficient (CC) and root mean square error (RMSE) are used as indicators to evaluate the quality of image reconstruction. The simulation and experimental results suggest that the FF-D method can reconstruct images better than typical algorithms based on deep learning and conventional algorithms of EIT.

Recovery of carbon fiber-reinforced polymer waste using dimethylacetamide base on the resin swelling principle.

The mechanical recycling method of the carbon fiber-reinforced polymer (CFRP) has the advantages of simple process, less pollution and low cost, but only low utilization value of carbon fibers in powder or short fibers form can be obtained. To reduce the length and strength loss of the recycled carbon fibers, a novel and cost-effective dimethylacetamide (DMAC) swelling technique was developed to achieve rapid delamination of the CFRP laminates under mild conditions (120°C-160°C, 1h). The corresponding swelling ratios and mass-loss rates of cured epoxy resin (CEP) were about 121.39%-157.39% and 0-0.69%, respectively. Excessive swelling of CEP in DMAC resulted in the cracking of the resin matrix between the adjacent carbon fiber layers. Thus the CFRP laminates were delaminated into soft single carbon fiber layers, which showed excellent cutting performance and reinforcing properties. The delamination products were cut into thin strips of different sizes and vacuum bag molded into new CFRP laminates. The flexural strength and tensile strength of the newly produced CFRP laminates were about 76.38%-90.98% and 94.61%-98.54% of the original CFRP laminates, respectively. More importantly, the chemical compositions of DMAC and CEP were unchanged during the physical swelling process. No organic pollutants (caused by resin degradation) were generated. And the used DMAC can be easily recycled by filtration. Therefore, this study provides a strategy for low-cost and high-valued recycling of CFRP waste.

Experimental analysis of three essential types of hole making strategies in aircraft assembly technology concerning delamination factor

Large-diameter hole drilling for Carbon-Fibre-Reinforced-Polymer (CFRP) is challenging because of its non-homogeneity and anisotropic features. This research will illustrate the hand-laminated and unidirectional CFRP based on three-hole making strategies for helical milling, large hole and pilot hole drilling. In this article, CFRP analyzes and optimizes axial cutting force and Delamination Factor (DF) based on experimental data collected at different FR (Feed Rate). CFRP's large diameter hole quality analysis includes cutting speed (Rotational Tool Speed) and scanning electron microscopy (SEM) analysis of helical milling, pilot hole and large hole drilling. A comparative study between large hole diameter, pilot hole drilling, and helical milling of CFRP was also conducted to discover the better technology for hole calibration quality by analyzing Machining Force (MF) and DF. According to experimental tests of CFRP laminates, the MF is proportional to the FR. Compared to helical milling, pilot hole drilling with proper cutting parameters can create superior quality holes. As a result, it is recommended that pilot hole drilling be done at a low feed rate and a high rotational tool speed for optimum hole quality. The hole calibration was analyzed to distinguish the cutting parameters (Cutting Speed, FR, and MF) to reduce DF and improve hole quality. Low FR was necessary for CFRP high-speed drilling because delamination at the hole exit was a concern.

Effect of Air Cooling on Tool Wear in Drilling CFRP

Carbon fiber reinforced polymer (CFRP) is commonly used in many industries such as sports equipment, aerospace and automotive industries because of its particular properties of low weight and high strength. When penetrating the plastic with a large amount of fiber, problems such as fiber pull-out, delamination and matrix smearing exist. Delamination is a major problem in drilling the components/parts and assembling composite materials. Cutting CFRP without cooling enhances cutting temperature, leading to an increase in delamination. This paper investigates the effect of the difference between with and without air cooling on the drilling of bidirectional CFRP laminates using carbide tools. The cutting parameters studied were cutting speed and feed rate, while tool wear was the response of this study.

Bifurcation and propagation of mixed mode fatigue crack in steel plates repaired with prestressed CFRP laminates

The mixed-mode crack propagation model was proposed to predict crack growth trajectory of a central cracked tensile steel plate with prestressed carbon fiber-reinforced polymer (CFRP) reinforcement through verification of previous experiments. A sensitivity analysis of different parameters including CFRP fiber orientation, initial crack geometry, and prestress level was conducted to investigate CFRP repairing efficiency by using a combination of the programs FRANC3D and ABAQUS. The results show that the applied loading direction primarily governs the bifurcation angle of crack propagation. Increasing prestress level of CFRP along the applied loading direction can achieve ten-fold repairing efficiency of damaged steel structures.

Experimental and analytical study on the effect of different repairing and strengthening strategies on flexural performance of corroded RC beams

This paper reports the results of a study conducted to investigate the flexural behavior of corroded reinforced concrete (RC) beams that were first repaired with different types of cover repairing materials and then strengthened with the carbon fiber-reinforced polymer (CFRP) laminates. Thirteen RC beam specimens were prepared. One specimen was used as a control beam (un-corroded, unrepaired, unstrengthened), and the reinforcing bars in twelve specimens were corroded using an accelerated corrosion setup. While five corroded specimens (two unrepaired and three repaired) were tested without strengthening using CFRP laminates, the other seven corroded specimens (two unrepaired and five repaired) were strengthened with one and two layers of CFRP laminates before testing under flexure. For the RC beams subjected to 10 and 20% corrosion of steel bars (by mass), strengthening using one layer of CFRP laminate enhanced the load-bearing capacities by 89 and 73%, respectively, while strengthening with two CFRP layers improved the load-carrying capacity by 162 and 154%, respectively. Repairing the damaged cover of the corroded RC beams using ultra-high-performance concrete (UHPC) was found to be most effective in enhancing the load-bearing capacity and stiffness, whether the corroded beams were strengthened with CFRP laminates or not. Repairing of the cover using commercial repair material also enhanced the load-carrying capacity and stiffness, with ductility more than that of UHPC. Strengthening of the corroded beams further improved the load-carrying capacity. An analytical model was developed that can predict the load-bearing capacity of the beams with a fair degree of accuracy.

Multi-Criteria Evaluation of the Failure of CFRP Laminates for Frames in the Automotive Industry.

Methods to predict the fracture of thin carbon fibre-reinforced polymers (CFRPs) under load are of great interest in the automotive industry. The manufacturing of composites involves a high risk of defect occurrence, and the identification of those that lead to failure increases the functional reliability and decreases costs. The performance of CFRPs can be significantly reduced in assembled structures containing stress concentrators. This paper presents a hybrid experimental-numerical method based on the Tsai-Hill criterion for behavior of thin CFRPs at complex loadings that can emphasize the threshold of stress by tracing the σ-τ envelope. Modified butterfly samples were made for shearing, traction, or shearing-with-traction tests in the weakened section by changing the angle of force application α. ANSYS simulations were used to determine the zones of maximum stress concentration. For thin CFRP samples tested with stacking sequences [0]8 and [(45/0)2]s, the main mechanical characteristics have been determined using a Dynamic Mechanical Analyzer (DMA) and ultrasound tests. A modified Arcan device (AD) was used to generate data in a biaxial stress state, leading to the characterization of the material as a whole. The generated failure envelope allows for the prediction of failure for other combinations of normal and shear stress, depending on the thickness of the laminations, the stacking order, the pretension of the fasteners, and the method used to produce the laminations. The experimental data using AD and the application of the Tsai-Hill criterion serve to the increase the safety of CFRP components.

Propagation characteristics of electromagnetic field penetrated into laminated CFRPs using eddy current testing with pancake coil

Propagation characteristics of electromagnetic field (EMF) is crucial to identify and position the potential defects when using eddy current testing (ECT) method for conductive medium. Therefore, in this work, the EMF propagation characteristics in carbon fiber reinforced polymer (CFRP) composites are thoroughly investigated by using finite element (FE) method. Considering the layered structure, stacking sequence, and interlaminar interface, we utilize a contact impedance interior boundary condition to model CFRP laminates, and then discuss the calculation accuracy and mesh refinement. The numerically solved results are compared to the theoretically calculated ones, and clearly point out the significant discrepancy between the true skin depth and the standard one. The findings reveal that the electrical anisotropy is one of the important factors in affecting the EMF propagation. The strong anisotropy results in more power loss and a frequency-independent decay rate than the ones in the weak and isotropic cases, which is proved by introducing Poynting theorem. Additionally, the other critical factor affecting the EMF attenuation is the lay-up stacking sequence of CFRPs, which is quite different from that of the isotropic mterials. Besides, the driving coil geomerty is another factor in affecting the EMF propagation characteristics from the point of the incident field.

Strategies for strengthening of corroded reinforced concrete beams using CFRP laminates and UHPC jacketing

AbstractThis article aims to investigate the flexural behavior of strengthened corroded reinforced concrete (RC) beams using carbon fiber‐reinforced polymer (CFRP) laminates and using a hybrid system of CFRP laminates and ultrahigh‐performance concrete (UHPC) layers. A total of 15 RC beam specimens were prepared, out of which one specimen was uncorroded–unstrengthened, and 14 specimens were corroded using accelerated corrosion set up to cause a significant reduction in the load‐carrying capacity of the RC beams. The damaged covers of the corroded RC beam specimens were first repaired and then strengthened with different strengthening strategies involving CFRP laminates alone as well as the CFRP laminates and UHPC jacketing together. The experimental results obtained by testing the strengthened RC beam specimens in flexure showed a significant enhancement in the load‐carrying capacity and stiffness of the strengthened corroded RC beams. The number of CFRP laminates, hybridization of the CFRP laminates and UHPC layer, and the thickness of the UHPC layer all significantly improved the load‐carrying capacity and stiffness of the strengthened corroded RC beams indicating the possibility of selecting an optimal strategy out of different options for strengthening the corroded beams to achieve a targeted degree of the efficacy of the strengthening. The analytical model developed in this study to estimate the flexural capacity of the strengthened RC beams was found to predict the values of the load‐bearing capacity of the RC beams strengthened using different strategies very close to their respective experimental values.

Statistical fatigue failure life of unidirectional CFRP under bending load

Our developed accelerated testing methodology (ATM) based on the matrix resin viscoelasticity for the failure life prediction of carbon-fiber reinforced polymers (CFRP) was applied for statistical prediction of long-term fatigue failure life under bending load for the longitudinal direction of unidirectional CFRP laminates, which is an important basic aspect of design for the durability of CFRP structures used for aircraft and other applications. First, the formulations for fatigue life prediction of FRP under cyclic loading are introduced. Second, the time-dependent and temperature-dependent viscoelasticity of matrix resin and the statistical flexural static strengths of CFRP laminates at various temperatures are introduced as the basic data of failure life prediction of CFRP laminates. Third, fatigue bending tests for CFRP laminates are performed at various load levels with various frequencies and temperatures. A master curve of non-dimensional fatigue strength versus number of cycles to failure (S-N master curve) is constructed by substituting data of the second and third steps into the formulations. Finally, the long-term fatigue strength data obtained under cyclic bending load for unidirectional CFRP laminates are compared with the long-term creep strength obtained in the previous paper.

Effect of ply orientation and laminate thickness on carbon fibre reinforced polymers under low‐velocity impact

AbstractComposite materials, which have gained prominence in the aerospace industry due to their high strength‐to‐weight ratio, are vulnerable to delamination damage when struck by low‐speed projectiles due to their low through‐thickness strength. This paper presents the experimental evaluation of a composite plate subjected to low‐velocity impact. The plates under discussion were constructed using a carbon fibre reinforced polymer laminate with a quasi‐isotropic ply structure. Experiments were carried out using a conical‐shaped impactor on carbon/epoxy laminated plates with three different orientations ([0/0] 4 s, [0/90] 2 s, and [45/0–45/90] s) that were put through two distinct impact energies (7 J and 14 J). Impact response is determined using drop‐weight impact tests. The techniques of ultrasonic C‐scan, field emission scanning electron microscopy (FESEM), and surface micrographs were integrated to provide a new and in‐depth understanding of damage evolution and failure mechanisms in composite laminates. Damage resistance appears to decrease as impact energy increases. Furthermore, thicker laminates have lower absorbed energy but, on the other hand, more widespread delamination due to increased bending stiffness. Furthermore, quasi‐isotropic laminates outperform in terms of damage resistance and increased energy absorption rates by 8 % to 15 %. The efficacy and logic of the suggested model were shown by a strong connection between experimental results.

Moisture absorption characterization of carbon fiber‐reinforced polymer using Fickian and non‐Fickian models

AbstractThree classic moisture absorption models including the Fickian model, the Langmuir and the time‐variable diffusion model were adopted to describe the absorption behavior of carbon fiber‐reinforced polymer (CFRP) laminates in this work. A new non‐Fickian model based on the two‐phase absorption rule was proposed by introducing the equivalent absorption time into the Langmuir model. Experiments of accelerated moisture absorption were conducted for CFRP laminates with different lay‐ups under three temperatures. Moisture uptaking performance of the CFRP laminates was discussed. Preliminary data analysis of the moisture absorption content showed the existence of non‐Fickian diffusion behavior. Four numerical models were implemented into Matlab by combining the Gauss‐Newton algorithm with minimum mean square error. Effects of the environment temperature and the lay‐ups of the laminates on the diffusion process of water molecules in CFRP. The results demonstrated that the modified time‐variable Langmuir model shows the best fitting performance. The diffusion coefficient and equilibrium moisture uptake increased with the environment temperature. Water diffusion coefficients in monotonous ply‐structure is larger than that in multi‐angle plys.

Stochastic multiscale multimode interlaminar fracture toughness of buckypaper nanocomposites

Delamination is one of the primary damage mechanisms in laminated composites that affects the lifetime integrity of the composite systems. The present study examines the effects of Buckypaper (BP) nano-reinforcement on the multimodal interlaminar fracture properties of the carbon fiber reinforced polymer (CFRP) composites reinforced with BP membranes. The novelty and the focus of this study is the effects of multi-wall carbon nanotube (MWCNT) network size and interphase in the interlaminar fracture toughness of BP nanocomposites. Dry and pre-infused non-functionalized MWCNT BP were integrated at the mid layer of the composite before laminate curing. The Atomic Force Microscopy Peak Force Quantitative Nanomechanics Mapping (AFM PFQNM) technique and the Weibull model were applied to study the effects of random CNT network size and interphase on mode I, II, and mixed-mode I-II fracture properties. Weibull analysis of 150 dry and pre-infused BP data confirms a high scatter of CNT network size in dry BP compared to pre-infused BP. Weibull modulus of CNT network size (2.33 for large size and 5.18 for small size) and interphase thickness (3.46) show a robust, consistent entangled structure of CNTs in pre-infused BP. Dry BP improves the propagation energy release rate of the CFRP laminates up to 54%. However, it does not provide additional toughening in the initiation crack energy for modes I, II, and I-II. Mode I initiation and propagation, mode II initiation and mixed-mode I/II fracture energy of pre-infused BP nanocomposites are ∼33%, ∼52.5%, ∼14%, and ∼28% higher than the reference. The interlaminar crack either moves exclusively through the BP layer by circumventing the rigid CNT networks or moves forward through the interface of the carbon fiber monofilament above and below the reinforcing BP layer. This saw-like interlaminar crack path triggers numerous toughening mechanisms such as nano-toughened epoxy, nanoscale CNT bridging and pullout, and crack deflection, and it increases the total crack propagation path.

Damage identification of CFRP laminate based on finite element analysis and FBG sensor network

Carbon fiber reinforced polymer (CFRP) is broadly used in the defense and aerospace industries due to its superior performance, and the real-time monitoring of its structural damage can enhance the reliability and safety of utilization. This paper is aimed at collecting the surface strain of CFRP laminates in real-time using FBG sensor network and constructing a structural damage identification model based on strain characteristics to identify the location of hole damage and the length and direction of crack damage. To investigate the impact of damage on the surface strain of CFRP laminates, this research conducted an extensive finite element analysis of laminates without damage and with various degrees of damage, combined with the genetic algorithm and linear regression to identify and optimize the parameters in the damage identification model. Then two CFRP laminates with comparable properties were fabricated, and the FBG sensor network was arranged on the surface to verify the efficiency of the damage identification model through experiments. Results of experiments show that the damage identification model proposed in this paper can accomplish accurate identification of hole damage location and crack damage length and direction within the error range, also proving the feasibility and effectiveness of combining finite element analysis, FBG sensor network, and intelligent algorithm to establish CFRP structural damage identification system proposed in this paper.

Behavior of artificially corroded RC beams strengthened with CFRP and hybrid CFRP-GFRP laminates

Steel corrosion is a major degradation factor for the reinforced concrete (RC) infrastructure and necessitates a costly repair after short service life. Predicting the strength of corroded and retrofitted structural elements while under service is a challenging task. For this purpose, the impressed current technique is frequently used to achieve the desired degree of corrosion in RC members in the laboratories. This study investigates the effectiveness of this technique on laboratory-scale RC beams and evaluates the behavior of severely corroded beams rehabilitated with carbon fiber-reinforced polymers (CFRP) and the hybrid of CFRP and glass-FRP (GFRP) laminates. Extensive literature is available on the behavior of sound RC members strengthened with FRPs, however, data are scarce on the behavior of corroded-strengthened RC beams. The RC beams were deteriorated by applying an impressed current of 750 µA/cm2 for 15 days. All the beams were tested under four-point bending till failure. The reinforcement mesh was non-uniformly corroded; the flexural bar facing the external cathode experienced a higher degree of corrosion than the opposite bar and the actual applied impressed current reached as high as 2388 µA/cm2. The flexural strength of the degraded beams, with 37 % weight loss on the main rebars, was 41 % less than counter-part sound beams. On the other hand, the CFRP strengthening regained the strength of degraded beams by 45 % compared to the unstrengthened-degraded beams. Whereas the CFRP-GFRP hybrid laminates regained strength up to 60 % compared to the counterpart-degraded beams and 12 % higher than the sound beams. This study demonstrated that a desired degree of corrosion could be achieved on a particular reinforcement portion with the impressed current technique. In addition, CFRP and CFRP-GFRP laminates are effective external strengthening techniques for rehabilitating degraded concrete infrastructure.

Meso/macroscale study on the shear failure of CFRP laminates considering fibre rotation

The shear failure mechanisms of ±45° braided and unidirectional carbon fibre reinforced polymer (CFRP) laminates are investigated. Off-axis tensile tests were carried out to determine the performance and failure modes of laminates with different numbers of layers. A mesoscale unit cell finite element model was established, and the simulation was validated. The results show that braided laminates and unidirectional laminates have different failure cracks. With the increase in the number of layers, the failure mode of laminates changes. For laminates with 8 or more layers, the necking effect appears at the fracture, and there is a fibre rotation strengthening stage in the stress–strain curve. The stress–strain response functions of laminates in the fibre rotation strengthening stage fitted according to test data can effectively reflect the properties of ±45° braided and unidirectional CFRP laminates.

A criterion for predicting delamination growth in composite laminates

To develop a simplified and physically sound delamination-failure criterion, this paper reports a joint experimental and numerical study in which out-of-plane quasi-static indentations with different indentation forces were applied to the centre of fully clamped rectangular carbon fibre-reinforced polymer (CFRP) laminates. The results show that two basic micro-delamination growth modes, which are separately dominated by opening and sliding microcracks, can be distinguished according to the fracture morphologies of the delaminations along the 0° fibre direction. Both are driven by the out-of-plane shear stress σ13, and the corresponding delamination failure threshold is the out-of-plane shear strength S13. Based on these results, a concise Hashin-type delamination-propagation criterion containing only a single stress component and single strength parameter is proposed, which, by incorporating it into the finite element model, the delamination growth along the fibre directions of multidirectional CFRP laminates can be precisely predicted; the prediction error is less than 10 %.