CFRP Plates Research Articles

Variable curvature waveform clamping anchor for CFRP plate: Experimental investigation and theoretical model

Variable curvature waveform clamping anchor for CFRP plate: Experimental investigation and theoretical model

Effects of electron beam and atomic oxygen irradiation on hypervelocity - Impact tested / polyimide coated carbon fiber-reinforced plates

In a low-Earth orbit, space debris orbit at approximately the first cosmic velocity. When space debris strike a spacecraft, ejecta (fragments) from the spacecraft are widely scattered. The reduction in the number of ejecta (fragments caused by impact) must also be considered when selecting spacecraft materials. The authors’ group has previously examined the size of ejecta (fragments) and reduction in the number of ejecta. In general, the mechanical properties of polymer materials and CFRP plates may be damaged by space environments, such as radiation (gamma rays and electron beams (EBs)), atomic oxygen (AO), ultraviolet rays, temperature, and thermal cycling. The authors suggested an anti-AO coating/polyimide CFRP as a material resistant to space environments. The effects of EB and AO irradiation on the fracture behavior and ejecta of anti-AO coating/polyimide CFRP were examined for hypervelocity impacts. The results of static three-point flexural tests were compared with the fracture behavior and ejecta. A two-stage light-gas gun was used for the impact tests. Spherical projectiles formed of aluminum alloy 2017-T4 with a diameter of 1.6 mm were used. Photographs of the ejecta scattered in front of each polyimide CFRP plate were captured from the side using a high-speed video camera. The number and weight of the ejecta on the front side and perforation holes were examined.

Evaluation of the Strengthening Effects on Prestressed Carbon-Fiber-Reinforced-Polymer-Strengthened Steel Beam Bridges Using Macro-Strain Influence Lines

Effectively evaluating the effectiveness of bridge strengthening is a necessary means to ensure the normal operation of existing strengthened bridges, especially when evaluating the effectiveness of bridge strengthening without interrupting normal traffic. Based on a distributed long-gauge Fiber Bragg Grating (FBG) sensor, this paper derived the macro-strain influence line (MSIL) formula for a simply supported beam bridge under a moving vehicle load, studied the changes in the MSIL at the bottom of the beam under the vehicle load before and after the prestressed CFRP plate strengthening, and proposed a rapid evaluation method for the strengthening effect based on the amplitude of the MSIL as the evaluation index for the strengthening effect. Finally, the prestressed CFRP-strengthened steel beam was tested under the moving vehicle load. The theoretical analysis and the experimental results confirm that under the load of moving vehicles, the macro-strain–time history amplitude of the strengthened steel beams under different prestressed tensioning conditions is different. The amplitude of the macro-strain time history of the strengthened bridge is reduced compared to before strengthening, and the local strengthening effect of the bridge can be monitored by the amplitude change in a single sensor. The change in global stiffness can be evaluated by monitoring the MSIL obtained from multiple long-gauge strain sensors.

Research on seismic performance of reinforced concrete structures reinforced with CFRP plates

In the modern construction industry, natural disasters such as earthquakes pose an increasingly prominent threat to reinforced concrete structures, which often lead to serious damage to the structures. Therefore, how to enhance the seismic performance of reinforced concrete structures has become an urgent problem to be solved in the field of construction. This study delves into the seismic performance of CFRP plates in strengthening reinforced concrete structures. Firstly, the material characteristics of CFRP panels were analyzed, including the mechanical and adhesive performance indicators of carbon fiber panels, and corresponding specimens were made. Subsequently, through specimen loading experiments, the performance of reinforced specimens and unreinforced specimens under load was compared. The experimental results show that prestressed CFRP plates can significantly increase the cracking load and enhance the seismic resistance of reinforced concrete structures. In addition, simulation tests were conducted using a finite element model. Through simulation testing, the load deflection curve of the specimen was obtained, revealing the influence of CFRP plates on beam stiffness. Especially in the critical stages of concrete cracking and yielding of tensile steel bars, carbon fiber board has a particularly significant effect on improving the stiffness of beams.

Investigation of the Laminating Characteristics of CFRP Plates with a Thin and Wide Configuration in Production for an Effective Inspection Process

Investigation of the Laminating Characteristics of CFRP Plates with a Thin and Wide Configuration in Production for an Effective Inspection Process

Influence of curing conditions on the interface bonding properties of CFRP plate–steel

To understand the influence of different curing conditions on the interface bonding performance of CFRP-reinforced steel plates, tensile tests were conducted on epoxy resin dog bone specimens and CFRP-reinforced steel plate double lap specimens. The study explored the tensile performance of dog bone specimens under different curing temperature/time conditions and the mechanical properties of double lap specimens under different curing pressures and curing temperature/time conditions. The results indicate that increasing the curing temperature can shorten the curing time of dog bone specimens and also improve their elastic modulus and tensile strength. Elevating the curing pressure, curing temperature, and extending the curing time cause a transition in the failure mode of the double lap specimens from surface fiber stripping of the CFRP plate to a mixed failure dominated by surface fiber stripping and adhesive–steel interface debonding, and the bearing capacity, interface ultimate slip, and peak shear stress of the specimens significantly increase, with the shear stress concentration zone gradually expanding from the loading end towards the free end, simultaneously, the ductility of the specimen increased, and the failure process was delayed. The ultimate load, interface peak shear stress, and ultimate slip of the specimens cured at 90 °C are significantly higher compared to the control group cured at 20 °C and 0.01 MPa. However, with increasing curing time, the rate of growth shows a decreasing trend.

Improving defect detection capability of pulse and pulse phase thermography method for CFRP plates by enhancing rear surface heat transfer coefficient

Infrared pulse thermography (PT) is a noncontact and convenient nondestructive inspection method, and its application to various objects has been reported in many papers. However, conventional PT is not suitable for detecting deep- or near-rear-surface defects. This study focuses on PT inspections of CFRP plates and improvements in their defect detection capabilities. To improve the capability of detecting near-rear-surface defects, a method for enhancing the heat transfer coefficient (HTC) of the rear surface during PT inspection was examined in this study; this would increase the temperature difference in the defective areas observed in thermal images. To investigate the effectiveness of the proposed method, experiments were conducted on CFRP specimens with artificial defects. The CFRP specimens were inspected using the PT method, during which water was brought into contact with the rear surfaces of the specimens to enhance the HTC. The experimental results showed that the capability of detecting near-rear-surface defects improved when the rear surfaces were in contact with water with forced convection. In addition, obtaining phase images by applying a Fourier transform to the experimentally obtained temperature data (that is, pulse phase thermography: PPT) was examined. Consequently, the combination of the enhancement of the rear-surface HTC and the use of phase images was significantly effective in improving the defect detection capability.

Finite Element Analysis of Reinforced Concrete Beams Strengthened with Prestressed CFRP Plates with High Ductility

Finite Element Analysis of Reinforced Concrete Beams Strengthened with Prestressed CFRP Plates with High Ductility

Hybrid strengthening of RC beams with externally bonded carbon fiber reinforced polymer laminate and engineered cementitious composites transition layer

This paper presents the experimental study on the reinforced concrete (RC) beam strengthened with externally bonded carbon fiber reinforced polymer (EB-CFRP) laminate and engineered cementitious composites (ECC) material. A total of six beams were tested under the four-point bending test to investigate the influence of strengthening scheme, type of CFRP laminate and the width of CFRP plate on the flexural response. The results revealed that hybrid strengthened beam with the technical of EB-CFRP and ECC transition layer significantly enhanced the crack load (29.0%–133.3%), yield load (50.9%–96.5%) and ultimate load (50.0%–81.9%) of the beams relative to the control beam. The employment of ECC material was an ideal transition layer for delaying the interfacial debonding of CFRP laminate, where the ultimate tensile strain of CFRP plate in hybrid strengthened beams was 13.2%–33.33% higher than that of beam merely strengthened with EB-CFRP plate. Beams strengthened with CFRP sheet had the greater flexural performance and higher utilization of CFRP than its counterparts strengthened with CFRP plate. Moreover, the predicted model associated with ultimate bearing capacity of the hybrid beams was provided based on ACI 440.2R-08, which was relatively conservative with a margin for the ultimate load of the hybrid strengthened beams.

Quantitative assessment of delamination in composites using multiple local-defect-resonance modes

Accurately visualizing the geometry and dimensions of internal delamination in fiber-reinforced polymer (CFRP) composites is a challenging endeavor. In this paper, we develop a method to identify and characterize delamination in composites by the integration of multiple local defect resonance (LDR) modes. The proposed method was validated by using T300/M914 CFRP plates containing three distinct defect geometries, employing both numerical simulations and experimental measurements. The approach commences with the application of a frequency-domain finite element method for LDR frequency determination, emphasizing improved computational efficiency. This technique is further corroborated through the use of the defect-to-background ratio (DBR) method, which identifies LDR frequencies in both numerical simulations and experimental testing. The integration of multiple LDR modes (IMLDR) at various frequencies enables precise imaging of delamination defects of diverse geometries and sizes. Experimental results closely align with the numerical findings, confirming that the integrated imaging results accurately correspond to artificial defects. This method furnishes precise descriptions of damage location, geometry, and dimensions. The obtained results indicate that the proposed IMLDR-based technique significantly enhances the accuracy and reliability of delamination imaging in composites. Consequently, it offers an effective approach for quantitatively assessing delamination damage in composites.

Experimental study on large-scale compression members strengthened with circumferential prestressed CFRP plate

There have been many research reports on the reinforcement of small-sized square columns with a cross-section of 200mm–300mm using prestressed carbon fiber-reinforced polymer (CFRP) materials, while there are few studies on piers in bridge and tower columns in cable-stayed bridges with a cross-section of several meters or even tens of meters. The horizontal prestressed steel tendons in the anchorage zone of tower columns in cable-stayed bridge replaced by prestressed CFRP sheets can not only facilitate construction and maintenance, but also have good fatigue resistance. The prestressed CFRP plate is used to reinforce the large-sized tower columns by using a specific device to tension the CFRP plate wrapped around the surface of the members. The tensioning device and test pedestal based on WSGG (wave-shaped-gear-grip) anchor clamping of CFRP plate have been developed in this paper, and the CFRP plate circumferential tensioning tests on the pedestal have been conducted. The test results are as follows: (1) the developed device can achieve circumferential tensioning of single-layer CFRP plate to 0.5ftk of the material, reaching a tensile force of 60kN, and generate effective restraint pressure on a 2-m long composite compression component; (2)The calculation formula for the constraint pressure generated by the circumferential prestressed CFRP sheet on the component has been derived and verified, and the maximum error between the calculated value and the experimental value is within 5%; (3) When iron sheet serves as the interface medium between CFRP plate and compression components, the prestress loss of the CFRP plate tensioned at one end is about 84% and 58%–60% when tensioned at both ends. It can be seen that the effective prestress of the CFRP plate with iron sheet as the interface medium is relatively small. Meanwhile, based on the distribution of compressive stress in the components and the effective pre tension value of CFRP plate, it can be seen that two end tensioning is better than one end tensioning; (4) The tensile stress of CFRP plate along the member is a cubic function when the tension force is 60kN, so it is deduced that the constrained compressive stress generated by CFRP plate on the member is a quadratic function distribution.

Fatigue performance of carbon fiber‐reinforced polymer strengthened single‐edge cracked steel plates: Effects of adhesive property and CFRP arrangement

AbstractCarbon fiber‐reinforced polymer (CFRP) is increasingly used to improve the fatigue behavior of damaged steel structures due to its advantages, including high strength and convenient processing. However, several issues, such as the effects of the adhesive property and CFRP arrangement, still need to be studied. In this study, a total of 20 single‐cracked steel specimens were tested under fatigue load, including two unstrengthened specimens, six single‐sided strengthened specimens, and 12 double‐sided strengthened specimens. The failure mode, fatigue life, crack propagation pattern, and interface damage development were obtained from experiments. The results show that epoxy resin structural adhesives (adhesives Araldite 420 and J133C) have the best bonding properties with CFRP. For the conventional epoxy adhesives, Araldite 420 and J133C can considerably improve fatigue life, which increased by more than 44.84 times to unstrengthened specimens. CFRP plate strengthening can significantly improve the fatigue life of single‐edge cracked steel plates. For the double‐sided strengthened specimens, the fatigue life can be improved by 6.93–44.84 times that of unstrengthened specimens. For the single‐sided, the fatigue life can be improved by 2.24–2.77 times. Properties of epoxy adhesive have a more significant effect on fatigue life compared to the thickness of the CFRP plate due to debonding.Highlights Ductile epoxy adhesives are most conducive to improving the fatigue behavior of CFRP strengthened steel plates. The fatigue life of steel plates can be improved by increasing the thickness of CFRP plates and using double‐sided CFRP strengthening. Interface debonding is the main failure mode of CFRP plates strengthening single‐edge cracked steel plates under fatigue.

Experimental Study on Loss of Prestressing by Friction in Annular Tension of CFRP Plates

Experimental Study on Loss of Prestressing by Friction in Annular Tension of CFRP Plates

Numerical study of steel–concrete composite beams strengthened by CFRP plates with prestressed unbonded reinforcement system

This work developed a three-dimension refined finite element (FE) model to study the flexural behavior of steel–concrete composite beams strengthened with CFRP plate by prestressed unbonded reinforcement (PUR) system. The numerical result has excellent agreements with the experimental results on the failure mode, overall load–deflection response and strain development at mid-span section as well as CFRP plates. The verified FE model was applied to carry out a comprehensive parametric study, evaluating the effects of sectional area, prestress level and profile of CFRP plate, to investigate the optimum parameter range of PUR system for beam reinforcement. It is found that the yielding load rises as the sectional area, prestress level, and pillar spacing of CFRP plates increase. Besides, the ultimate bearing capacity of beam can be efficiently improved by increasing the sectional area of CFRP plates, while the mid-span deflection and ductility were maintained at failure. Moreover, as the prestress level of CFFR plate increases, the bearing capacities of reinforced beams marginally rise but the ductility markedly decreases. The ideal prestress level for strengthening is considered as 10 %∼30 %. Furthermore, the profile of CFRP plate has significant impact on failure of reinforced beams, but has little effect on ultimate load. The results of parametric studies are of great significance for the practical reinforcement application of the PUR system with CFRP in bridge engineering.

Bending performance of steel beams with circular web openings strengthened with CFRP plates: a numerical study

Bending performance of steel beams with circular web openings strengthened with CFRP plates: a numerical study

Fatigue performance and parameter optimization of CFRP-reinforced steel plate considering elevated temperature

This article aims to investigate the effect of elevated temperature on the fatigue performance of CFRP-reinforced cracked steel plates and optimize the design parameters for their reinforcement. Based on the self-developed adhesive GY34, a finite element model of the CFRP-reinforced central cracked steel plate is established by the ABAQUS software. Parametric analysis is carried out on different bonding methods of CFRP plates and different thicknesses of adhesive layers for CFRP-reinforced cracked steel plates. The effect of elevated temperature on the reinforcement is also studied to verify the excellent performance of GY34 adhesive. Furthermore, the enhancement of fatigue life for cracked steel plates reinforced with CFRP plates at different temperatures is investigated using the Paris model and modified Newman model. The results show that double-sided reinforcement with CFRP is more effective than single-sided reinforcement. All of the different bonding methods could reduce effectively the stress intensity factor of cracked steel plates and improve significantly the bearing capacity of the steel plates. Among them, increasing the number of CFRP layers and their elastic modulus yield the most significant improvement on the reinforcing effect. Elevated temperatures effect greatly on the mechanical properties of adhesively bonded CFRP-reinforced steel plates. The effective bonding length and the stress intensity factor amplitude at the crack tip of the steel plate increases with temperature rises, which may accelerate the growth rate of fatigue crack and reduce the reinforcing effect on fatigue life.

In-situ stress measurement method for CFRP plates based on the Lyapunov exponent of air-coupled ultrasonic Lamb waves

The air-coupled ultrasonic technique is a reliable method for measuring the stress state of composite plates. This paper aims to address the requirement for efficient and accurate stress measurement of large component composite plates by proposing an air-coupled ultrasonic in-situ measurement method. Ultrasonic Lamb waves can propagate over long distances while maintaining sensitivity to slight changes and are suitable for in-situ stress measurement of CFRP plates. However, due to the serious mismatch in acoustic impedance, the air-coupled ultrasonic Lamb waves have a low signal-to-noise ratio, which can affect the accuracy of stress measurement. Focusing on this problem, the method employs the Lyapunov exponent with a moving window to accurately extract the acoustic-time characteristic instead of just judging the presence or absence of a weak signal compared with the traditional method of using the Lyapunov exponent. To evaluate the effectiveness of the proposed method in different fiber directions of CFRP plates, seven uniaxial tensile specimens are obtained along 0°, 15°, 30°, 45°, 60°, 75°, and 90° fiber directions, respectively. Utilize stress coefficient calibration results KL to realize the uniaxial stress measurement with a spatial resolution of 150 mm. The experimental results demonstrate that the stress measurement errors are within ±7.29 MPa in the range of 0–150 MPa, and the standard deviations of the repeatability measurement experiment are below 4.57 MPa. The proposed method exhibits significant advantages in terms of measurement accuracy and repeatability compared with traditional stress methods based on peak extraction or cross-correlation. It is a suitable technique for health monitoring and evaluation of composite plates.

Strain rate-dependent failure modelling of impact damage in laminated CFRP structures

This work focuses on the development, implementation, and validation of a constitutive model for unidirectional composites, aiming to numerically simulate impact damage in laminated structures. The model incorporates a failure criterion that accounts for the influence of strain rate on failure initiation and distinguishes between four failure modes. Failure initiation criteria are 3D phenomenological-based criteria according to the previous work of Puck and Schürmann (1998) and Pinho (2006). Additionally, a mesh-objective damage propagation model is implemented to simulate the impact damage. The impact simulations are performed using Abaqus/Explicit, with the constitutive model implemented through the user subroutine VUMAT. Validation of the strain rate effects on failure initiation is performed using strain rate-dependent bi-axial failure curves for IM7/8552 and AS-4/3506. The analyses indicate that the properties governing the strain rate dependence of failure initiation are consistent. Therefore, the hypothesis was tested in which the same strain rate scaling approach could be used for CFRP materials for which only static properties are available. This hypothesis was tested in high and low-velocity impact simulations at laminated IMS60/977–2 CFRP plates. The results demonstrate that the model accurately replicates the experimentally observed impact-induced contact forces and effectively captures the damaged state in the impacted plate.

Detecting delamination defects in CFRP plates using nonlinear defect index of air-coupled Lamb waves and adaptively weighted imaging algorithm

The air-coupled ultrasonic technique is capable of detecting defects in in-service CFRP plates and ensuring their application safety. Traditional air-coupled ultrasonic methods often rely on the linear defect index, which is not effective in characterizing small-size defects. Additionally, the scanning step length completely limits their imaging spatial resolution, resulting in the contradiction between imaging spatial resolution and detection efficiency. To address the above problems, the nonlinear defect index and the adaptively weighted imaging algorithm are proposed. The nonlinear defect index uses the relatively nonlinear coefficient of the Lamb wave to enhance the ability to detect small-size defects. Considering the beam width, the adaptively weighted imaging algorithm constructs the relationship between any imaging point and all scanning paths. At this time, the imaging spatial resolution can be set arbitrarily, eliminating the dependence on the scanning step length. The experimental results demonstrate that the proposed nonlinear defect index can characterize the small-size defect more accurately than the linear defect index. When the scanning step length is increased to improve detection efficiency, the adaptively weighted imaging algorithm can achieve better imaging spatial resolution compared to the traditional defect probability imaging algorithm. For the small-size defect with a diameter of 10 mm, the proposed method has an area detection error of only 7.8 %, whereas the traditional method has an error of 22.4 %. The proposed method is promising to detect small-size defects of in-service CFRP plates in the aircraft skin.

Research on bond behavior of CFRP-concrete interface under quasi-static cyclic loading

In order to investigate the bond behavior of CFRP-concrete interface under quasi-static cyclic loading, static and quasi-static interface shear tests were conducted on three different adhesive layer thicknesses and two concrete strength grades. From these results, it can be seen that the load-slip envelope curves of the quasi-static cyclic loading specimen is similar to the quasi-static monotonic loading curves. As the adhesive thickness increases, the interface bearing capacity increases, the maximum strain of CFRP plate increases, and the effective bond length slightly increases. The interface failure mode is related to concrete strength. The failure mode of C30 concrete bonded with CFRP plate is cohesive failure of concrete surface layer, while the failure mode of C50 interface specimen is adhesive failure between CFRP and adhesive layer interface. As the thickness of the adhesive layer and the strength of the concrete increase, the interfacial bond strength and maximum strain of CFRP plate increase. It can be seen that the bond-slip envelope curves of the quasi-static cyclic loading specimen coincide well with the curves of the quasi-static monotonic loading specimen. As the magnitude of the cyclic loading increases, the unloading/reloading stiffness degradation, residual slip at zero load increases, and the dissipated energy increases. The fitting resulted in a degradation model of interfacial stiffness during quasi-static cyclic loading.