Carbon Fiber Reinforced Polymer Laminates Research Articles

Prediction of pseudo‐ductility and structural optimization of nacre‐inspired carbon fiber‐reinforced polymer laminate

AbstractTo enhance the ductility of carbon fiber‐reinforced polymer (CFRP) composites, a variety of nacre‐inspired structures with discontinuities were constructed based on the ratio of overlapping length to CFRP laminate thickness. The damage mechanisms and tensile characteristics of discontinuous laminates were elucidated using finite element analysis and experimental investigation. To anticipate the mechanical behavior of the CFRP laminate, an improved Chang‐Chang failure criteria was devised. Moreover, a model adopts the Benzeggagh‐Kenane criterion on cohesive surfaces for delamination initiation and propagation. The predicted stress–strain values are validated using experimental data under tensile stress. Furthermore, a mathematical model accurately predicted the relationship between the tensile performance of nacre‐inspired laminate and overlapping length. According to the findings, the longer the overlapping length (more than 19.5 mm) is, the lower the pseudo‐ductility. Meanwhile, the shorter the overlapping length (less than 17.5 mm) is, the lower the tensile strength. Furthermore, the laminate exhibits some pseudo‐ductility as well as little decrease in tensile strength when the overlapping length is approximately 18.5 mm.Highlights A mathematical model for predicting the tensile properties of various nacre‐inspired laminates was established. The relationship between the discontinuous structure and the pseudo‐ductility of the nacre‐inspired laminate was revealed. Compared with other similar structural laminates, the laminate with an overlapping length of 17.5 mm has better overall performance. Proposed an improved Chang‐Chang progressive failure criterion that was utilized to simulate and analyze the mechanical response and damage of the nacre‐inspired laminates under tension.

Shear performance of lightweight SCC composite beam internally reinforced with CFRP laminate stirrups and GFRP bars: Experimental and analytical study

This research demonstrates the structure feasibility of using carbon fiber reinforced polymer (CFRP) laminate stirrups as a form of transverse reinforcement in shear deficient GFRP reinforced lightweight self-compacting concrete (LWSCC) beams. An experimental study performed on eight full-scale shear deficient beam specimens. One beam served as the reference specimen and remaining beam specimens were internally reinforced with impregnated CFRP laminate stirrups. The parameters investigated in this study were the stirrup configuration, number of layers, stirrup spacing and width. Specimen tested under two-point loading and all results in term of load-deflection response as well as their failure modes were reported. All tested specimens failed due to shear compression failure mode along with the rupture of CFRP laminate stirrups, and the inclusion of CFRP laminate stirrups has significantly enhanced the nominal capacity of LWSCC beams ranged from 91%− 200% over control specimen. Shear strengths of the tested specimens were also theoretically predicted using different design standards. Comparison between the experimental and predicted shear strength has shown that ACI 440.1R-15, CSA S806–12, and CSA S6–14 provided the closest prediction. Therefore, it has been concluded that CFRP laminate stirrups can be used as a transverse reinforcement in GFRP reinforced LWSCC beams.

Effect of Duty Cycle on Cutting Force for Ultrasonic Vibration-Assisted Milling Carbon Fiber-Reinforced Polymer Laminates

Cutting force is an important factor that affects the surface quality of machining carbon fiber-reinforced polymer (CFRP). High cutting force can lead to surface damage such as the burrs and the delamination in the machining process of CFRP. Ultrasonic vibration-assisted machining (UVAM) can reduce the cutting force in the machining process. This work is focused on the relationship between the duty cycle and the cutting force in UVAM of CFRP. Based on the kinematics of UVAM, the movement of the cutting tool edge and the tool–workpiece separation in UVAM were analyzed, and a calculation formula for the duty cycle was obtained. The milling experiment of CFRP was conducted to compare the cutting force between UVAM and conventional machining (CM), and the relationship between the reduction in the cutting force in UVAM and the duty cycle was determined. The experimental results showed that when the duty cycle was 0.2916, the cutting force of UVAM was reduced by 7.4% to 27% compared with that of CM. When the duty cycle was 1, the cutting force of UVAM was reduced by −4.5% to 7.5% compared with that of CM. Therefore, the effect of reducing the cutting force of UVAM can be enhanced by adjusting the process parameters to reduce the duty cycle of UVAM, and a lower cutting force can be obtained.

Enhancing fatigue life of steel plates with CFRP laminate: Effects of curing temperature, stress range, and adhesive thickness

Steel bridges often require rehabilitation and retrofitting to address cracks and deteriorations caused by age, environmental factors, and increased loads. Carbon fibre reinforced polymers (CFRP) strengthening is a reliable and efficient method used for strengthening steel structures, particularly in steel joints subjected to cyclic loading from traffic. This study explores the impact of adhesive curing temperature on the fatigue behaviour of CFRP-steel joints under various stress ratios and ranges, it also evaluates the effect of adhesive thickness on fatigue life of the joint. Results indicate that curing temperature has no effect on fatigue behaviour, and the stress range-fatigue limit is constant at 30 MPa. Strain readings were taken to monitor debonding initiation, and the failure mode was predominantly steel-adhesive debonding. Adhesive thickness <2 mm has no significant effect on fatigue life of steel joints strengthened with CFRP. This research provides valuable insights for improving durability of steel bridges and structures.

Cross-scale data-based damage identification of CFRP laminates using acoustic emission and deep learning

Damage characterization of laminated composites has undergone extensive research, leading to the development of several damage models that incorporate acoustic emission (AE). However, feature extraction from AE data will cause the loss of certain information in the construction of damage models, which manifestly falls short of feature analysis in the frequency domain. In this study, a novel cross-scale data-based damage identification methodology for carbon fiber-reinforced polymer (CFRP) laminates is proposed by combining the AE technique with deep learning approach. Elementary experiments involved with single damage mode are designed to avoid blind inference, and the cross-scale correlation of AE features between component materials and CFRP laminates is established by wavelet packet transform (WPT). The time–frequency spectrums of AE signals of CFRP laminates by continuous wavelet transform (CWT), which adequately preserve the frequency domain information, are adopted as inputs to the convolutional neural network (CNN) model. The proposed methodology achieves a high accuracy of 96.3% in detecting and classifying damage modes (i.e., matrix cracking, matrix/fiber debonding, and fiber breakage) in unidirectional CFRP laminates.

Uncovering the hidden structure: A study on the feasibility of induction thermography for fiber orientation analysis in CFRP composites using 2D-FFT

The induction heating process elicits a heating response in a carbon fiber reinforced polymer (CFRP) composite distinctly different from those in metal. Prior work in our lab and elsewhere has established that the intensity and spatial distribution of the heating patterns are governed by the fiber orientations in each layer and the degree of electrical contact between layers. Based on more extensive work on this non-conventional heating behavior, we show that the analysis of induction heating patterns enables the characterization of the fiber orientations and stacking order within the material. In the first step, 2D Fast Fourier Transform (2D-FFT) is used to extract the fiber orientations from the spatial characteristics of the heating pattern recorded with an infrared camera. In the next step, the extracted fiber orientation is used to design bandpass filters to carry out the inverse 2D-FFT and obtain the layer stacking order. Our findings demonstrate that this approach can accurately identify the layer orientations (maximum error of 6o) and the stacking sequence in quasi-isotropic CFRP laminates with up to 12 layers. We believe that the proposed approach has the potential as a valuable nondestructive, non-contact tool for large-area inspection and quality control in manufacturing fiber-reinforced composites.

Performance and failure analysis of perforated CFRP/aluminum alloy bonding and self-piercing riveting hybrid joints

This paper explores the new hybrid hole-drilled bonding and self-piercing riveting (HH-BR) connection technique to enhance the strength and overall performance of carbon fiber reinforced polymer (CFRP) and dissimilar metal materials at joint interfaces. The forming quality, mechanical performance, failure modes, and fracture characteristics of the CFRP and aluminum alloy joints utilizing the HH-BR procedure were analyzed in detail and compared with the joints of the hole-less adhesive-bonding self-piercing riveting (H-BR) and self-piercing riveting (SPR). At the same time, the effects of different rivet performance levels, overlap lengths, and various fiber orientation angles on joint performance were discussed. The results show that joints made by the HH-BR technique have a substantial advantage in terms of achieving superior mechanical performance and interlocking value. Firstly, HH-BR joints with bent rivets and torn fibers have connection strengths that are noticeably higher than those with CFRP laminate delamination or rivet pullout failure. The use of the HH-BR technique for joining CFRP/aluminum alloy culminated in reduced strength loss and higher energy absorption than H-BR and SPR joints, improving the joint's overall strength. Secondly, the interlock value between the rivet and the plate, is what essentially determines the strength of HH-BR joints, especially evident in connections with 0°/90° fiber orientation and more overlap lengths. The results also show that there is a strong relationship between the height of the rivet head and the joint's mode of failure, and the height of the rivet head is affected by the rivet force. Furthermore, the interlock value's magnitude, the joint's remaining bottom thickness, and the metal material's capacity for plastic deformation are all directly correlated.

Experimental and theoretical study on the flexural behaviour of RC beams strengthened with externally bonded reinforcement on grooves CFRP laminates

This paper presents a study on the flexural capacity of Reinforced Concrete (RC) beams strengthened with Externally Bonded Reinforcement on Grooves (EBROG) Carbon Fibre Reinforced Polymer (CFRP) laminates. Thirteen single-shear tests and seven RC beams strengthened with CFRP are examined, comparing Externally Bonded Reinforcement (EBR) and EBROG techniques with different groove distributions. The results showed that EBROG improved the bond and flexural performance. Comparison with existing prediction models reveals that while the literature models accurately predict EBR results, they underestimated the bending capacity for EBROG due to calibration based on EBR bond parameters. Consequently, a numerical model is developed to simulate Intermediate Crack Debonding (ICD) for various bond-slip laws, applicable to the different strengthening techniques. The proposed model is validated using experimental flexural tests and calibrated bond-slip laws obtained from single-shear tests, demonstrating accurate prediction of ICD failure for both EBR and EBROG.

Fire behaviour of reinforced concrete slab strips strengthened with prestressed NSM-CFRP laminates

Carbon fibre reinforced polymer (CFRP) composites are now widely used to strengthen reinforced concrete (RC) structures. Among the strengthening systems available, near-surface mounted (NSM)-prestressed CFRP laminates offer several advantages, as they significantly increase the load carrying capacity and also the serviceability performance of RC structures. However, as for other CFRP systems, there is a concern about their behaviour at elevated temperature and under fire exposure due to the glass transition process undergone by their polymeric components. Nevertheless, the fire performance of NSM-prestressed-CFRP strengthening systems has not yet been investigated. This paper presents an experimental study about the fire resistance behaviour of RC slab strips strengthened with prestressed NSM-CFRP laminates; the slabs were simultaneously subjected to a mechanical (fire) load and the ISO 834 fire curve, and the influence of the following parameters on their fire resistance behaviour was assessed: (i) the prestress level (0 %, 25 % and 50 % of the CFRP tensile strength), and (ii) the presence of passive fire protection, comprising up to 48 mm thick calcium silicate (CS) boards. The results obtained showed that: (i) without fire protection, the strengthening system remained effective during a very low period of fire exposure, which significantly decreased with the prestress level, from 16 min (0 %) to less than 5 min (50 %); (ii) with fire protection, even with 50 % of prestress, the strengthening system remained effective for more than 120 min; and (iii) the “critical” temperatures in the anchorages of the strengthening systems were found to be about 2.5Tg, 2.0Tg and 1.5Tg, for the prestress levels of 0 %, 25 % and 50 %, respectively, with Tg being the glass transition temperature of the adhesive.

A progressive damage model for carbon fiber-reinforced polymer laminates subjected to fastener pull-through failure

Most studies on composite joints focus on in-plane bearing mode, while little attention to fastener pull-through failure mode from out-of-plane loads. This paper presents a 3D continuum damage mechanics (CDM) model to investigate and assess the mechanical behaviors of carbon fiber-reinforced polymer (CFRP) laminates subjected to pull-through failure. The proposed model based on the use of intralaminar and interlaminar damage models is established and implemented by means of a user-defined subroutine VUMAT for Abaqus/Explicit. The novelty lies in the material model integrating the thresholds preset by the semianalytical approximation approach, which largely eliminates unnecessary fracture angle enumerations in Puck’s IFF theory, coupled with the simple parabolic interpolation search (SPIS) technique for optimal fracture angle search, considerably reducing the computational burden. Moreover, the numerical results compare well with experiments, effectively replicating the load–displacement response, damage modes, failure behaviors and damaged areas. This study provides an accurate and efficient computational methodology to analyze pull-through failures, enhancing the damage modeling and predictive capabilities for composite joints under out-of-plane loads.

Unbonded Pre-Tensioned CF-Laminates Mechanically Anchored to HSC Beams as a Sustainable Repair Solution for Detachment of Bonded CF-Laminates

The present article outlines a Finite Element Model (FEM) that was created and validated by comparing it to prior experimental investigations to estimate the flexural performance of HSC beams strengthened with exterior bonded, unbonded, and unbonded pre-tensioned Carbon Fibre Reinforced Polymer (CFRP) sheets in several patterns. Nonlinear analysis was performed on three-point-loaded beams using ANSYS software, incorporating the constitutive characteristics of various components (concrete, CFRP, and steel). The comparison of FE-models and experimental data, namely for load-deflection curves, crack patterns, and failure modes, revealed that the developed numerical FE-models and experimental outcomes are in good accord. There has been numerous prior research on the behavior of beams strengthened with externally bonded CFRP sheets, but few on those reinforced with externally unbonded CFRP laminates, and even fewer on HSC beams reinforced with externally unbonded pre-tensioned CFRP laminates. Therefore, the major contribution of this article is to investigate the flexural behavior of HSC beams strengthened utilizing externally unbonded pre-tensioned CFRP laminates. The analysis revealed that the bending performance of RC-beams strengthened using external unbonded pre-tensioned CFRP-laminates is quite similar to that of bonded CFRP-strengthened beams, indicating a high potential for tackling the durability issues caused by detachment of bonded CFRP-strips in such structural elements. The existence of a fully wrapped CF sheet forced the beam to develop diagonal shear cracks in the region between the wrapped CF sheet and beam supports while also enhancing the flexural cracked zone at mid-span to change from smeared to discrete fractures. The flexural fractures spread over a deeper and wider area of the beam as a result of the incorporation of a half-wrap CF laminate. Externally unbonded CFRP-sheets pre-tensioned with 45% of the CFRP ultimate strength utilizing various patterns (straight and U-wrap) performed similarly to bonded CFRP-sheets, with a slight boost in load capacity of around 4.5% and notable reduces in deflection ranging from 9.7% to 16.24%. Using exterior unbonded CFRP laminates to strengthen RC-beams resulted in a flexural capacity increase ranging from 22.3% for NC beams to 71.6% for HSC beams.

Numerical Analysis on the Propagation of Ultrasonic Guided Wave in Damaged Carbon Fiber Reinforced Polymer Laminate

AbstractIn recent years, the propagation of ultrasonic guided waves (UGW) along the structure to inspect has amply proven to be an excellent strategy for the health monitoring of isotropic and composite structures (SHM—structural health monitoring). For the proper development of the SHM system, the finite element method (FEM) must be mentioned, since the possibility to study the UGW in very complex structures, even characterized by different materials. Successfully locating any possible damage and identifying its severity are key factors in SHM, thus allowing to reduce the design costs. Numerically, the damage can be modeled with several approaches but it is still not clear which is the best solution to accurately reproduce the UGW mechanisms in a faulty structure. The objective of this paper is to study the various effects that different severities of damage can have on UGW propagation. For the scope, various numerical approaches are considered and the results are compared.

Flexural behaviour of hollow reinforced concrete T-beams strengthened or retrofitted with carbon-fibre-reinforced laminates: Experimental and numerical investigation

This study investigates the effect of longitudinal rectangular openings on the flexural behaviour of reinforced concrete (RC) T-beams strengthened or retrofitted with external carbon-fibre-reinforced polymer (CFRP) laminates. Eight RC T-beams, with one solid and one hollow beam in each of four groups, were analysed using a three-point bending test. The CFRP laminate used in each beam was similar, and the beams had an identical longitudinal reinforcement ratio. The ultimate load capacity of the strengthened hollow RC T-beams showed a 9% decrease compared to that of the strengthened solid RC T-beams, while retrofitted hollow RC T-beams with 100% preloading exhibited a 24% decrease in ultimate load capacity compared to that of retrofitted solid RC T-beams. In addition, the CFRP laminate had a positive effect on reducing strain in hollow RC T-beams as compared to that of solid RC T-beams. The flexural behaviour of the CFRP-strengthened hollow RC T-beams with a 5% cross-sectional hollow core area was similar to that of strengthened solid RC T-beams. However, after preloading, the retrofitted hollow RC T-beams exhibited a decrease in flexural efficiency compared to the retrofitted solid beams. A validated numerical model was developed using ABAQUS to accurately simulate the behaviour of the hollow RC T-beams. Subsequently, a parametric study was conducted using the validated model to investigate the effects of varying the position and size of the hollow section on the response of the RC T-beams.

Restoration of Compressive Strength of CFRP Plates with Edge Delamination through CNT Crack-bridging Deposited by Resin Pre-coating Solution

Edge delamination, with only micro-scale crack openings, in carbon-fiber-reinforced-polymer (CFRP) composites due to light impact, machining and structural assembly is challenging to repair. This study presents a simple pressureless method to repair edge delamination in CFRP laminates. The compressive strength of CFRP panels with around 5–10 mm deep edge delamination cracks have been fully restored without utilizing any special equipment. Acetone-diluted resin pre-coating (RPC) solution, consisting of 95 m/m% acetone and 5 m/m% resin (without hardener), is utilized to penetrate deeply into sharp delamination cracks through capillary action, and 1 m/m% CNT dispersed into the RPC solution (RPC + CNT) is deposited inside the delamination cracks forming CNT-toughened adhesive joints. The compressive strengths of long cure time (3 month) are compared with 2-week results, showing 2-weeks are not sufficient for complete curing. With the 3-month curing period, the compressive strength of CFRP with edge delamination is 100 % restored by the RPC + CNT technique.

Damage mechanisms and analytical model of CFRP laminate under low-velocity normal and oblique impacts

The present work investigates the energy absorption performance of carbon fibre-reinforced polymer (CFRP) laminates subjected to low-velocity normal and oblique impacts. Experimental tests are conducted on laminates exposed to varying impact energies at both normal and oblique angles. The numerical model is developed to simulate the dynamic response of the CFRP. The research employs a combination of experimental and numerical methods to reveal the underlying damage mechanisms. The changes observed in the oblique impact response are explained through an analysis of the damage mechanisms. Analytical models for each energy absorption mechanism are proposed based on the principles of energy conservation and the theory of large bending deformation of anisotropic materials. The energy absorption performance of the laminates under oblique impacts, considering rebound and penetration conditions, is discussed. It is found that the delamination is the primary energy absorption mechanism of CFRP laminate under rebound conditions, while elastic deformation of fibres is the primary energy absorption mechanism under penetration conditions. Furthermore, the energy absorption performance of the laminate is found to be affected by the peak force and effective thickness of the plate, which change with the oblique angle. This paper makes a significant contribution by utilising experimental, numerical, and theoretical approaches to gain insights into the damage mechanisms of laminates subjected to oblique impacts.

Dynamic Feature Identification of Carbon-Fiber-Reinforced Polymer Laminates Based on Fiber Bragg Grating Sensing Technology

Carbon-fiber-reinforced polymer (CFRP) composites have many advantages, and have been widely used in aerospace structures, buildings, bridges, etc. The analysis of dynamic response characteristics of CFRP composite structures is of great significance for promoting the development of smart composite structures. For this reason, vibration experiments of CFRP laminates with surface-attached fiber Bragg grating (FBG) sensors under various dynamic loading conditions were carried out. Time- and frequency-domain analyses were conducted on the FBG testing signals to check the dynamic characteristics of the CFRP structure and the sensing performance of the installed sensors. The results show that the FBG sensors attached to the surface of the CFRP laminates can accurately measure the dynamic response and determine the excited position of the CFRP laminates, as well as invert the strain distribution of the CFRP laminates through the FBG sensors at different positions. By performing Fourier transform, short-time Fourier transform, and frequency domain decomposition (FDD) on the FBG sensing signals, the time–frequency information and the first eight modal frequencies of the excited CFRP structure can be obtained. The modal frequencies obtained by different excitation types are similar, which can be used for structural damage identification. The research in this paper clarifies the effectiveness and accuracy of FBG sensors in sensing the dynamic characteristics of CFRP structures, which can be used for performance evaluation of CFRP structures and will effectively promote the design and development of intelligent composite material structures.

Shape evolution and characteristics of carbon fiber reinforced polymer surface in laser ablation

Carbon fiber reinforced polymer (CFRP) has been far-ranging used for structural components in structural engineering. Laser paint removal is promising in the repair and maintenance of CFRP structural components. However, there are still many unknowns relating to laser paint removal, and the existing theory and practice are insufficient to guide the industrial application of laser paint removal from CFRP laminate. This paper uses nanosecond laser cleaning experiments on the paint of CFRP laminate surface to study the cleaning mechanism and cleaning effect of different process parameters for removing the paint. The surface morphology and three-dimension morphology of laser-cleaned samples are observed to reveal the cleaning quality. In addition, after laser paint removal, the nanostructures are generated on the carbon fibers (CFs) surface. The thermodynamic behavior of CFRP laminate during laser paint removal is discussed by the combination of experimental results and theoretical analysis. The contact angle measurements and single lap joints experiments demonstrate laser-cleaned surfaces present better wettability and higher tensile shear strength than other cleaning methods. This study provides a theoretical and experimental basis for the application of laser paint removal from CFRP laminate.

Comparative study of carbon and glass fiber reinforced polymer composites for the confinement of concrete columns

This study deals with the comparison of unconfined concrete specimens with carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) confined concrete specimens using epoxy as matrix. Initially, CFRP, GFRP and epoxy laminates were prepared for the analysis of various mechanical properties like tensile strength, flexural strength and fracture toughness. From the test results, CFRP and GFRP laminates exhibit better properties than neat epoxy laminate. Axial compressive strength, energy absorption characteristics, failure modes of the confined specimens are analyzed. Comparing with unconfined specimens, it is noticed that the axial load carrying capacity of GFRP confined specimens increased by 23%. While the CFRP confined specimen is compared, a considerable enhancement of 57% was noticed with a confinement effectiveness of 1.57. It is observed that confinement by the FRPs can also increase the fracture energy and ductility index significantly, which can avert the catastrophic failure of the structures.

Enhancement of vibrational characteristics of rotating CFRP composite tapered plates reinforced by graphene nanoparticles

AbstractIn the present study, the dynamic behavior of rotating carbon fiber reinforced polymer (CFRP) composite tapered plates reinforced with graphene nanoparticles has been investigated using a finite element (FE) formulation. The mechanical properties of CFRP laminates containing 0–0.5 wt% graphene nanoparticles were assessed using ASTM standard tests. The experimental dynamic analysis was conducted on CFRP and graphene reinforced CFRP composites under cantilever end conditions. The first‐order shear deformation theory (FSDT)‐based FE model was developed using MATLAB software to obtain the natural frequencies of the graphene reinforced CFRP plates. The validity of the FE results is compared with literature, and it shows excellent agreement for composite structures. Furthermore, parametric analysis is performed to explore the influence of wt% of graphene, rotating speed, setting angle, and ply thickness on the dynamic responses of graphene reinforced CFRP tapered plates.Highlights Effects of graphene reinforcement in CFRP composites are investigated. The mechanical characteristics were evaluated using ASTM standards. FSDT is employed to model the rotating tapered graphene‐CFRP plates. Vibration behavior of graphene‐CFRP composites is studied experimentally. Effects of various factors on the vibrations of the CFRP plates are studied.

Influence of distributed out-of-plane waviness defects on the mechanical behavior of CFRP laminates

One of the most common defects induced during manufacturing of laminates is out-of-plane fibre waviness. This defect significantly affects the mechanical behavior of the laminate and reduces fatigue life and the load capacity of the material. Therefore, it is important to understand the impact of fibre waviness on the performance of composite laminates. In this work, multiple out-of-plane waves have been introduced throughout a Carbon Fibre Reinforced Polymer (CFRP) laminate at different thickness positions. The specimens were tested under tensile loading and an analysis of the surface of the laminate has been carried out by means of Digital Image Correlation (DIC). The results obtained by DIC were able to predict the apparent strain of the laminate quite accurately, as well as locate up to seven undulations at different depths. It was proved that a laminate with multiple wrinkles has 16% less tensile load strength. The results were used to validate different Finite Element (FE) models of the laminate showing a good agreement. These simple models were able to predict the initiation and propagation of failure in both the matrix and the fibre.