Carbon Fiber Reinforced Polymer Materials Research Articles

High-Temperature Effect on the Tensile Mechanical Properties of Unidirectional Carbon Fiber-Reinforced Polymer Plates.

Carbon fiber-reinforced polymer (CFRP) has the advantages of a high strength-weight ratio and excellent fatigue resistance and has been widely used in aerospace, automotive, civil infrastructure, and other fields. The properties of CFRP materials under high temperatures are a key design issue. This paper presents the quasi-static tensile mechanical properties of unidirectional CFRP plates at temperatures ranging from 20 to 600 °C experimentally. The laser displacement transducer was adopted to capture the in situ displacement of the tested specimen. The results showed that the tensile strength of the CFRP specimen was affected by the high-temperature effect significantly, which dropped 68% and 16% for the 200 and 600 °C, respectively, compared with that of the room temperature. The degradation measured by the laser transducer system was more intensive compared with previous studies. The elastic modulus decreased to about 29% of the room temperature value at 200 °C. With the evaporation of the resin, the failure modes of the CFRP experienced brittle fracture to pullout of the fiber tow. The study provides accurate tensile performance of the CFRP plate under high-temperature exposure, which is helpful for the engineering application.

Ultrasonic signal classification and porosity testing for CFRP materials via artificial neural network

Ultrasonic testing is one of the most commonly used non-destructive (NDT) methods to detect porosity in carbon fiber reinforced polymer (CFRP) material. However, the ultrasonic testing requires well-trained technicians and their high concentration during the testing process to avoid human errors. The artificial neural network (ANN) models provide an efficient and accurate way to reduce testing time and effort and reduce the human factor and uncertainty during ultrasonic testing. In this work, CFRP samples with 12 different kinds of porosity levels and thicknesses were prepared for the experiment. X-ray CT testing and through-transmission ultrasonic (TTU) testing are applied to measure the material porosity. Based on the porosity data obtained by these two testing methods, a backpropagation (BP) neural network was developed and trained to analyze and predict the sample porosity. In our experiment, the accuracy of our ANN-based method can reach up to 97.22%, and the average prediction result is 88.02%. Our experimental results demonstrate that our new method is quite promising to predict porosity testing results in CFRP materials.

Soft magnetic composites of carbon fibers decorated with magnetite in an epoxy matrix

ABSTRACT The chemical precipitation was used to obtain carbon fibers (CF) with surface modified by magnetite particles (Fe3O4). Processing was carried out by employing up to three subsequent coating stages of ultrasonic treatments. After each sonication stage, the coating was 17, 33, and 47 wt. % of the total weight of the modified fibers. Raman spectroscopy indicates the presence in the coating of a mixture of iron II and III states. As-decorated fibers were used to fabricate composites with an epoxy resin (ED-20) matrix cured with PEPA. The quantity of the carbon fiber filler was of 1, 3, and 6 wt %. At room temperature, the saturation magnetization of the soft magnetic samples was 0.37, 0.83, and 1.72 emu/g for the indicated compositions. Carbon fiber reinforced polymer materials with extra functions such as magnetic in this case, are expected to be useful in applications from the power and energy industries.

Experimental study on seismic performance of square RC columns strengthened with multi-layer prestressed CFRP fabric

In this study, a wedge tensioning anchorage device, which enables strengthening of square reinforced concrete (RC) columns with multi-layer prestressed carbon fiber reinforced polymer (CFRP) fabric, was designed and tested. Nine RC columns (three unstrengthened and six strengthened with prestressed CFRP fabric) were tested under combined constant axial loading and horizontal cyclic loading at different axial compression ratios, various prestress levels, different numbers of CFRP fabric layers, and variable area wrapped with prestressed CFRP fabric. The results showed that both the ductility and energy dissipation capacity of the strengthened columns significantly improved. The increase in the prestress level strongly affected the stiffness and horizontal load bearing capacity of the columns, and the increase in the number of CFRP layers had a larger effect on the enhancement of their energy dissipation capacity. For the RC columns fully wrapped with prestressed CFRP fabric, the energy dissipation capacity significantly increased, the ultimate drift ratio was 167% higher than that of the unstrengthened columns, and the energy dissipation capacity increased 6.5 times, respectively.

Experiment and Research on Calculation Methods on Flexural Mechanical Behaviors of Non-Metallic Reinforced ECC Beams

Engineered cementitious composites (ECC) has high tenacity and the characteristics of strain hardening. In the bending test, ECC beams equipped with carbon fiber reinforced polymer (CFRP) in the tensile region show good deformation ability and bending ability. In this paper, the constitutive models of ECC and CFRP materials are established by uniaxial tensile compression test. Based on the plane section supposition, the analysis theory of bending capacity of cross section for ECC beams with non-metallic reinforcement is proposed. The calculation results are compared with the four-point bending test results. The results show that: (1) ECC beams with non-metallic reinforcement reflect the advantages of the two materials, and have strong deformation capacity before bending failure. (2) The calculation results based on the theory of flexural capacity of normal section are in good agreement with the experimental results, and the maximum error is less than 4%. The research results can provide the basis and reference for the calculation analysis and practical application of non-metallic reinforced high toughness material structure.

Effect of build orientation and raster pattern on the fracture behavior of carbon fiber reinforced polymer composites fabricated by additive manufacturing

Additive manufacturing (AM) process parameters highly affect the mechanical and fracture properties of additively manufactured carbon fiber reinforced polymer (CFRP) composites. In this work, we study the effect of two process parameters, including build orientation (XYZ, XZY, and ZXY) and raster pattern ( ± 45º and 0º/90º), on the fracture behavior of the CFRP composites fabricated by fused filament fabrication (FFF). The mode I fracture toughness and effective fracture energy of the CFRP composite materials are measured on compact tension samples. The crack growth direction in the FFF-fabricated CFRP composites is found to be controlled by both build orientation and raster pattern. The fracture toughness of the examined CFRP material is sensitive to build orientation, while the effective fracture energy reveals significant dependence on both build orientation and raster pattern. The samples fabricated with the XYZ and ZXY build orientations exhibit 5-fold greater effective fracture energy than the ones with the XZY build orientation. A wide range of fracture energy dissipation mechanisms, including fiber-bridging and fiber pull-out, are identified depending on the process parameters. The reported fracture trends in this study have the potential to provide guidelines for the development of FFF-fabricated CFRP composites with high fracture resistance.

Bond characteristics of CFRP strengthened concrete members bonded using Modified Engineered Cementitious Composite

This study focuses on the development of an insulating cementitious adhesive for bonding Carbon Fibre Reinforced Polymer (CFRP) fabrics to a concrete surface. The epoxy adhesive which is the generally used adhesive for CFRP shows a low thermal performance. As a potential solution, Engineered Cementitious Composite (ECC) mortar was modified as a cementitious adhesive with improved thermal insulation. The ECC adhesive was developed using locally available class F fly ash, silica sand and Polyethylene terephthalate (PET) fibres other than the generally used cement and water (PET-ECC). The selected mix proportion for PET-ECC achieved a low thermal conductivity of 0.145–0.180 W/mK which limited the heat transfer through the adhesive layer. The effective bond length of the developed PET-ECC adhesive was 125 mm and the corresponding bond strength was 224.9 MPa. The respective bond strength was further enhanced up to 570.28 MPa by sticking river sand on top of CFRP fabric using epoxy adhesive before bonding it to the concrete surface using the PET-ECC adhesive. The use of PET-ECC as the bonding agent to strengthen compression members with CFRP confinement yielded an average strength enhancement of 34%.

Flexural behavior of reinforced concrete beams strengthened by carbon fiber reinforced polymer using different strengthening techniques

The externally bonded reinforcement on grooves (EBROG) method is increasingly recognized as an alternative strengthening method that can overcome the debonding problem. This study aims to experimentally investigate the effectiveness of EBROG as compared to the conventional externally bonded reinforcement (EBR) method in strengthening reinforced concrete (RC) beams. Twelve RC beams have been tested under four point load bending. One of these beams has been designated as a reference beam, seven beams have been strengthened with carbon fiber reinforced polymer (CFRP) sheets, and four beams have been strengthened with CFRP laminates using EBROG or EBR methods. The effect of CFRP type, number of layers, as well as the type of strengthening methods on the flexural performance have been also investigated. The load, deflection, stiffness, and failure modes were recorded and discussed intensively. Overall, test results indicated that the flexural strength and stiffness of the strengthened specimens using EBR or EBROG methods increased compared to the control beam, where the increase in the load carrying capacity of beams strengthened using the EBR method ranged between 24.8 and 48.2% and by the EBROG method ranged between 31.7 and 76.7% of the control beam. The most interesting result obtained is that the failure mode of beams has been changed from debonding of CFRP material to rupture of CFRP in some samples strengthened by EBROG, which demonstrates the superior behavior of this strengthening technique as compared to the traditional strengthening using EBR.

Performance of Reinforced Concrete Beams Strengthened with Carbon Fiber Reinforced Polymer Strips.

Carbon fiber reinforced polymers (CFRP) have shown considerable potential in the repair and rehabilitation of deficient reinforced concrete (RC) structures. To date, several CFRP strengthening schemes have been studied and employed practically. In particular, strengthening of shear damaged RC members with CFRP materials has received much attention as an effective repair and strengthening approach. Most existing studies on strengthening shear-deficient RC members have used unidirectional CFRP strips. Recent studies on strengthened T-beams demonstrated that a bidirectional CFRP layout was more effective than a unidirectional layout. As such studies are limited, in this study, the feasibility of bidirectional CFRP layouts for the shear strengthening of rectangular RC beams was experimentally evaluated. Bidirectional layout details with CFRP anchors as well as rehabilitation timing were considered and investigated. The test results showed that the members with a bidirectional CFRP layout carried less shear strength capacity than those with unidirectional layouts for the same quantity of CFRP material. Nevertheless, the bidirectional CFRP layout allowed for a uniformly distributed stirrup strain compared to the unidirectional CFRP layout at the same load level, which increased the efficiency of the transverse reinforcement. Additionally, the shear contribution of CFRP material according to the CFRP strengthening timing was verified.

Laser induced breakdown spectroscopy online monitoring of laser cleaning quality on carbon fiber reinforced plastic

Carbon fiber reinforced polymer (CFRP) has attracted extensive attention in the industrial field due to its advantages of light weight and high hardness. The use of laser to clean the epoxy resin film on the surface of the carbon fiber is beneficial to improve the bonding performance. Combined with laser-induced breakdown spectroscopy (LIBS) technology, an on-line monitoring system for laser cleaning is designed to monitor the quality of laser cleaning in real time. The laser used in the experiment is a fiber laser widely used in laser cleaning, which has high cleaning efficiency, flexible use, and can be processed in a multi-dimensional space. The system is coupled with the scanning galvanometer which can be cleaned dynamically in all directions. The function of fast, real-time and high-resolution on-line monitoring of cleaning quality is realized. In this paper, prior information such as element composition and LIBS spectrum of epoxy resin and substrate carbon fiber in CFRP materials were obtained, and the differences were compared and analyzed. The results shown that the LIBS technology was feasible to monitor the cleaning quality. Subsequently, the experiment tested the influence of the laser process parameters on the LIBS characteristic spectrum, and it was confirmed that the average spectral intensity value at the wavelength (588.819 nm) was positively correlated with the average laser power. After that, according to the measured LIBS characteristic strength value, three evaluation grades of cleaning quality were effectively delineated. The piecewise linear fitting method was used to solve the value range of LIBS mapped by different grades, and the key data such as the optimal cleaning parameter threshold were calculated. Finally, scanning electron microscope (SEM) was used to observe the morphological characteristics of samples after laser cleaning under different grades, confirming that the LIBS characteristic line could effectively characterize the quality of laser cleaning.

Laser selective ablated multistep interfacing for enhanced adhesive bonding joints of carbon fiber reinforced polymer materials

Carbon fiber reinforced polymer (CFRP) has been widely used in the aviation field, especially, in the skin structure of civil aircraft. However, the damage is inevitable in service time and the effective repair methods of CFRP are, especially, important. In this paper, a high-efficiency and high-strength multistep interface adhesive structure was designed and prepared by laser selective ablation for CFRP skin maintenance. The micromorphology and surface chemical composition were analyzed under different laser treatment parameters. The tensile shear strength test as well as impact strength test of CFRP multistepped adhesive bonding joints showed that the value of shear strength and impact strength were 86.29 Mpa and 9.43 kJ/m2, respectively, which increased about 11% and 15%, respectively, when compared with the conventional mechanical milling interface. The results showed that the resin matrix between carbon fibers was removed neatly by laser ablation treatment, which lead to the enlarged adhesive contact area and improved comprehensive mechanical properties of the CFRP joints.

A new high-frequency eddy current technique for detection and imaging of flaws in carbon fibre-reinforced polymer materials

Using a high-frequency (50 kHz-4 MHz) alternating current field measurement (ACFM)-style inspection, non-destructive imaging of carbon fibre-reinforced polymers (CFRPs) was performed for the detection and evaluation of flaws developed during their manufacture or in-service use. This was achieved using quantum well Hall-effect (QWHE) sensors, which have proven suitability for use in different non-destructive testing and evaluation (NDT&E) applications based on their high sensitivity (they require lower strength applied fields and can detect smaller perturbations in the magnetic field), high linearity (high contrast and imaging evaluation capabilities), wide dynamic range (making them less sensitive to offset and lift-off variations), wide frequency operating range (DC to MHz) and compact size (5-70 microns depending on the application). Their advanced III-V semiconductor materials and design enable these characteristics. Their low capacitance allows them to be operated at significantly higher frequencies than coils of comparable sensitivity or size. As such, the inherent advantages of QWHE sensors have been used in conjunction with a high-frequency ACFM-style magnetic imaging inspection technique, which is referred to as quantum well eddy current field measurement (QW-ECFM) in this paper. Here, the fundamentals of this new technique are outlined, as well as the outcomes of such a technique for evaluating CFRP materials, where individual fibre bundles have been resolved in high detail with high contrast. In addition, the ability to detect fibre misalignment has been shown, suggesting technique sensitivity to 3D orientations of fibre for better material qualification and the detection of delamination down to 2 mm in diameter. Therefore, this paper aims to provide an overview of this new QW-ECFM technique and summarise its performance for the detection and evaluation of various CFRP material flaws that are commonly found during manufacture and service.

Electromechanical-Mode Coupling Model and Failure Prediction of CFRP under Three-Point Bending

Carbon fiber reinforced polymer materials (CFRP) cause CFRP to bend or fail when subjected to external loads or impacts. In the case of static three-point bending, using the conductive properties of the carbon fiber inside the CFRP, the overall damage detection and failure prediction can be carried out by electromagnetic methods. The eddy current coil is used to realize real-time monitoring of damage, and the measured voltage value can be mapped to obtain the load of the sample. This paper conducts theoretical analysis and experimental verification, and obtains the relationship between CFRP stress damage and spatial conductivity change, and proposes a CFRP electromechanical coupling model under quasistatic three-point bending. Combined with the theory of electrically ineffective length, the CFRP three-point bending electromechanical coupling model was revised. Experimental results prove that the revised model can describe the load-conductivity change trend of three-dimensional braided CFRP more accurately, which provides a theoretical basis for monitoring the structural health of CFRP through electromagnetic methods.

Design and material selection of optomechanical systems for the extreme environment on Mars

Mars surface composition detector (MarSCoDe) is a scientific instrument suite onboard the Mars rover of the “Tianwen-1” mission, which uses laser-induced breakdown spectroscopy and shortwave infrared spectroscopy to detect the composition of soils and rocks at the surface of Mars. The optical head unit (OHU) is the core hardware of MarSCoDe, containing a Cassegrain telescope and other optical modules for lasers generation and signals transmission. The unit lacks thermal control resources and is located outside the rover’s cabin, which will directly face the Martian surface drastic temperature changes. We introduce the optomechanical designs that realize the lightweight and high thermal stability of the OHU optical system, especially the designs and implementations of the semiopen primary mirror based on silicon carbide and the fully closed optical bench based on carbon fiber-reinforced polymer. Meanwhile, the advantages and difficulties of silicon carbide, long carbon fiber-reinforced silicon carbide composites, and carbon fiber-reinforced polymer materials used for small and compact optomechanical systems are discussed. Subsequently, the environmental adaptability of the telescope system of OHU was studied through analytical and experimental methods, which show that it can achieve the required optical performance over a temperature range of approximately 100°C.

A prediction model of drilling force in CFRP internal chip removal hole drilling based on support vector regression

Drilling force is the main factor affecting the quality of carbon fiber-reinforced polymer (CFRP) holes and tool wear. Choosing appropriate process parameters can effectively control the drilling force and improve the quality of hole making and tool life. This study aimed to accurately predict and effectively control the drilling force during the chip removal hole drilling process in CFRP. First, a CFRP internal chip removal machining drilling force prediction model was derived based on the support vector regression (SVR) theory, and a suitable kernel function and loss function were introduced into the model to improve the prediction accuracy of the model. Second, a drilling experiment of the given type of CFRP material with internal chip removal was designed, and sequential minimal optimization was applied to solve the unknown parameters in the prediction model. The drilling force and tool parameters, suction parameters, and cutting parameter prediction models were constructed for processing a given type of CFRP material. Finally, using the constructed prediction model, the relationship between cutting parameters (speed and feed), tool parameters (drill diameter, peak angle, and relief angle), and suction parameters (negative pressure) and axial force during CFRP internal chip removal hole drilling was predicted and studied. The relationship between the aforementioned parameters and the axial force was in line with the research results of existing studies, and the selection range of tool parameters, cutting parameters, and suction parameters when processing a given CFRP material using an internal chip removal process was also given.

Fire behavior and design of steel columns reinforced by prestressed CFRP strips

This study analyzes the behavior of steel columns reinforced by prestressed (PS) carbon fiber reinforced polymer (CFRP) strips exposed to fire. First, tests are performed to study the CFRP material degradation under high temperatures. The elastic modulus and strength of the CFRP decrease with increasing temperature. Second, a thermal–mechanical coupling analysis is conducted with finite element method (FEM) to study the behavior of composite members exposed to fire. Under compressive preloading, the columns are exposed to the ISO 834 standard fire curve. The fire exposure time of columns with different initial CFRP prestressing forces is obtained. All the specimens fail because of global buckling either due to the slacking of the concave side of the CFRP or the plastic deformation of the steel. Subsequently, parametric studies are performed considering different initial CFRP prestressing forces, preloadings and column slenderness values. Finally, a design method is proposed for steel columns with PS CFRP that are exposed to fire, followed by a design example. Columns with protections can achieve high buckling capacities at room temperature and long fire exposure time.

Experimental research on anti-seismic reinforcement of fabricated concrete pier connected by grouting sleeve based on CFRP and PET materials

To establish an anti-seismic reinforcement method (ASRM) for fabricated concrete piers based on carbon fibre reinforced polymer (CFRP) and polyethylene terephthalate (PET) materials, two 1/6-scale prefabricated piers with grouted sleeve connections (SFPs) and grouted sleeve prestressing tendon composite connections (SSFPs) were designed and manufactured. Shaking table tests were carried out for the model piers. Then, an ASRM using CFRP/PET with anti-sway external metallic dissipaters (AS-EMD) was proposed. The design and implementation methods of the CFRP–AS-EMD and PET–AS-EMD were established. Under the same excitation, shaking table tests of the SFPs repaired with the CFRP–AS-EMD and the SSFPs repaired with PET–AS-EMD were conducted. And finite element analysis (FEA) verification of the reinforcement effect was also carried out. The results showed that the initial seismic damage of the SFPs and SSFPs included pier body cracking, concrete spalling or crushing, and seam cracking at the bottom of the pier. The CFRP-AS-EMD and PET-AS-EMD can evidently decrease the horizontal displacement of the specimens, demonstrate good anti-sway capacity, provide a certain energy consumption capacity, and effectively improve the ductility of the reinforced pier specimens.

PARAMETRIC STUDY ON COMPOSITE BEAMS STRENGTHENED WITH PRESTRESSED CFRP PLATES AND TENDONS

Advanced carbon fiber reinforced polymer material (CFRP) has been widely used for strengthening structures. This paper aims to improve the ultimate capacity and stiffness of the composite beam externally strengthened with pre-stressed carbon fiber reinforced polymer plate by using CFRP tendons. The models were presented by 3-D FEM (finite element model) using ANSYS program to investigate the performance of composite beam which validated with experimental results presented. Various parametric studies achieved as degree of pre-stress level of CFRP tendons, tendon profile, degree of shear connection, the most effective beam load level to add CFRP tendons. Finally, the optimum strengthening conditions for the composite beam were studied.

A novel approach to modelling the bond characteristics between CFRP fabrics and steel plate joints under quasi-static tensile loads

Carbon fiber-reinforced polymer (CFRP) materials have been effectively used as externally bonded sheets to repair damaged steel structures such as airplanes and ships. In this study, a series of double strap joints with different bonding lengths are considered and examined to experimentally and theoretically assess the effective bond length. Various models exist in the literature which are used to predict the strength of steel and CFRP joints under various loading conditions. Non-linear Lagrange stress method (NLS) which is a novel stress-based method for predicting the failure load values is presented for the first time. This approach is based on 2D and 3D linear elastic finite element analysis. Relying only on two experimental tests, the new approach proposed here can quickly and easily predict the failure load in steel/CFRP samples. In this methodology, it is assumed that the adhesive joint will fail as the normal stress along the adhesive mid-line reaches a predetermined value at a critical distance. In addition, experimental data on steel/CFRP joints gathered from the literature are compared to predictions using the NLS method. It was found that results from the theoretical predictions (NLS) were in good agreement with experimental tests conducted on double strap joints. It was also revealed that the average accuracy of the NLS method is superior to other methods such as cohesive zone model and Hart-Smith. The results revealed that under the best conditions, the NLS model is 5 times more accurate than existing models.

UNDERSTANDING TEMPERATURE EFFECTS ON FRICTION AT TOOL – CFRP WORKPIECE INTERFACE USING OPEN-LOOP FRICTION TESTING

Cutting processes of carbon fibre reinforced polymer (CFRP) material generate significant energy in the form of heat which can be detrimental to final surface and sub-surface quality. By artificially changing the temperature of the workpiece to simulate cutting temperatures, thermal effects on friction metrics can be understood. Feed rate and CFRP pre-heating for macro and nanoscale open loop pin on plate friction testing has been completed for two aerospace grade CFRP materials with steel, carbide and coated carbide pins to give an insight to fundamental tool wear that occurs in CFRP machining.