Carbon Fiber Reinforced Polymer Structures Research Articles

Quasi-static and dynamic behavior analysis of 3D CFRP woven laminated composite auxetic structures for load-bearing and energy absorption applications

This paper investigated the quasi-static and dynamic behavior of 3D auxetic metamaterial structures made from carbon fiber reinforced polymer (CFRP) laminated composite. The aim of the study was to enhance design methodologies for load-bearing and energy absorption applications of these 3D novel structures, filling the research gap in understanding their response to quasi-static and especially dynamic loadings. The two novel 3D structures were designed and fabricated by using an interlocking assembly method based on the 2D auxetic CFRP sheets, which were formed with hybrid double-arrow-head with re-entrant and star unit-cells and made with plain weave carbon epoxy prepregs. The finite element (FE) method was adopted to analyze the mechanical characteristics of the structures under the quasi-static and dynamic loading, and Hashin failure criteria were used to define damage in the structures. The study showed that the designed 3D auxetic CFRP structures simultaneously exhibit superior auxeticity, load-bearing, and energy absorption capacity.

Experimental Method to Determine the Draping Behavior of Auxiliary Materials for the Vacuum Bagging of CFRP Parts on Doubled-Curved Surfaces

AbstractThe production costs of aircraft primary structures made of carbon fibre reinforced polymer (CFRP) are significantly higher than for comparable metal-based structures. Today substantial effort is made to achieve a sufficient reproducibility and parts’ quality in manufacturing processes of CFRP structures. Especially the sub process vacuum bagging for infusion processes is still expensive. One of the reasons is the complex positioning of the flexible auxiliary materials which have to be stacked on the preform. During the positioning on doubled-curved surfaces these materials tend to form wrinkles, which can lead to defects of the composite part. Yet, a defined description of the wrinkling behavior of the auxiliary materials on doubled-curved surfaces does not exist. In this work a characterization of the wrinkling behavior on doubled-curved surfaces is investigated for the auxiliary materials of the Vacuum Assisted infusion Process (VAP®): release film, perforated peel ply, flow media, membrane and vacuum foil. Therefore, an experimental test method is derived similar to established hemisphere deformation test methods. The wrinkling behavior for the specific VAP auxiliary materials is empirically determined on differently curved surface geometries. It is shown that the draping behavior can be characterized by partial wrinkle-free surfaces between the wrinkles. A material specific threshold is derived to determine the appearance of wrinkles. The work shows that a characterization of the draping behavior of auxiliary materials on doubled-curved surfaces is possible. With the gained knowledge the potential for an increase of the vacuum bagging reproducibility is given.

Strip-based numerical analysis of CFRP-reinforced steel plates with multiple debonding defects using the Runge-Kutta method

In recent years, carbon fiber-reinforced polymers (CFRP) have earned extensive attention in the field of structural rehabilitation. Adhesive bonding, as a prevalent technique, plays a crucial role in utilizing CFRP for strengthening steel structures. Nevertheless, debonding defects, commonly arising within the bond region between CFRP and host structures, hold the potential to induce the premature debonding failure of adhesively bonded joints. As a result, this research attempts to propose a strip-based numerical method using the explicit 4th-order Runge-Kutta technique (strip-based RK4) to investigate the full-range bond behavior of CFRP-to-steel single-lap joints with multiple arbitrary debonding defects. Also, three-dimensional (3D) finite element models (FEMs) of fully bonded single-lap joints were established in conjunction with cohesive zone modeling (CZM) to simulate the single-lap shear test reported in literature, based on which joints containing debonding defects were further modeled. Predictions from the proposed methodology were subsequently compared with test results and FE analysis to confirm its accuracy. Thereafter, the parametric analysis was carried out to investigate the effects of parameters, including bond length and defect position, on the bond behavior of the single-lap joint. The results indicate that the proposed strip-based RK4 method is accurate, with errors within 2% compared to FE analysis, and computationally efficient, with runtime being less than 50% of FE analysis. The findings of this study can be used as a guide for the design or damage assessment of CFRP-repaired structures in the future.

Implementation and precision of CFRP geometric configurations before adhesive bonding repair based on 1064 nm infrared pulsed fiber laser ablation

Before the adhesive bonding repair of the aircraft’s CFRP (Carbon Fiber Reinforced Polymer) structure, the common practice is to remove the damaged area material and form a predetermined repair geometric configuration using the grinding method according to the repair design shape. The geometric accuracy, dimensional accuracy, and surface characteristics of the geometric configuration have a significant impact on the adhesive bonding and repair effectiveness in CFRP structure repair. In the study, a 1064 nm infrared pulse laser was used to selectively and controllably remove the three layers of cured prepreg (fiber and resin) on the surface of the CFRP laminate structure. Based on the analysis of geometric accuracy and surface morphology, the effectiveness of CFRP adhesive bonding repair was verified. The results showed that, under the condition of undamaged CFRP fibers and thorough removal of the surface resin, the laser achieved a dimensional accuracy of ± 50 μm and a thickness accuracy of ± 20 μm for CFRP geometric configuration. The angular accuracy of rectangular configuration was less than ± 0.15°, and the roundness accuracy of circular configuration was greater than 0.995. The mechanical validation of the adhesive bonding repair indicated that the tensile strength recovery rate of CFRP repair structure after laser treatment was 84.7 %, and the failure mode was cohesive failure.

Fast VGG: An Advanced Pre-Trained Deep Learning Framework for Multi-Layered Composite NDE via Multifrequency Near-Field Microwave Imaging

ABSTRACT Microwave nondestructive testing (NDT) techniques show promise for composite inspection due to microwave signals’ ability to penetrate and interact with internal structures. However, current microwave imaging approaches have poor spatial resolution, struggling to distinguish defects from defect-free regions. This limits reliable subsurface analysis and widespread adoption. This paper introduces a novel multi-frequency microwave imaging fusion method using an open-ended waveguide and deep learning to enhance defect detection accuracy in carbon fiber-reinforced polymer (CFRP) composites. The proposed technique employs an optimized feature extraction strategy to improve differentiation between defective and sound areas for superior subsurface visualization. The method leverages VGG-19 for efficient feature extraction and parallel processing to merge information from multi-frequency images. Our method significantly improved detection accuracy and F1 score, surpassing non-deep learning image fusion techniques by at least 50%. The optimized fusion strategy enables clear visualization of various defect types across multiple subsurface layers. Our approach also reduces computation time versus standard VGG implementation by 3–4×, showing scalability. The results demonstrate the proposed method’s potential to overcome existing constraints and provide rapid, accurate subsurface analysis of complex CFRP structures through an optimized deep learning framework, holding significance for expanding microwave NDE applications.

On crashworthiness and energy-absorbing mechanisms of hygrothermal-aged CFRP structures subjected to quasi-static loads

Understanding the gradual performance degradation of carbon fiber reinforced polymers (CFRP) is critical for the design of engineering structures that are expected to be affected by hygrothermal environments. This study aims to investigate the effects of hygrothermal aging on the degradation mechanisms of the mechanical properties and energy absorption of CFRP structures. An experimental database comprising tensile, compressive, and shear tests for CFRP composite laminates (in this study) and axial crushing tests for energy-absorbing structures (from the literature) was constructed, in which all CFRP samples were immersed in deionized water to achieve a saturated water-absorption state. A material constitutive model considering the effects of water absorption and temperature was developed and implemented via the user subroutine VUMAT of the ABAQUS software. The simulated results correlated well with the experimental measurements. Simulation results of axial crushing indicated that the degradation of the inter-layer properties tends to worsen the mismatch between the intra-layer and inter-layer properties, thus significantly degrading the load-carrying capability. Owing to degradation in compressive fracture toughness, the simulated results showed reduced post-crushing integrity, thus indicating a favorable effect on the load-carrying capability.

Bond behavior between CFRP and steel structures with random corrosion defects

Steel structures in long-term service are difficult to avoid corrosion and can be reinforced by carbon fiber reinforced polymer (CFRP) bonding method. To investigate the corrosion effect on the bond behavior between CFRP and steel, a modified cohesive zone model was proposed and verified by experiment. Then, a series of random corrosion morphologies controlled by the size and the shape of corrosion pit were generated. Finally, by importing the random corrosion morphologies and the corresponding cohesive parameters distributions into the model, a parametric analysis was executed. Results showed that the ultimate load of CFRP-corroded steel bonding system was sensitive to the size of corrosion pit, while the stiffness had identical sensitivities to the pit size and pit shape. The ultimate load would reach the peak value when the average pit width Wp,avg was 1.0 mm and the average pit depth-to-width ratio (Dp/Wp)avg was between 0.12 and 0.14, whereas the stiffness would reach a high level when the Wp,avg was between 1.0 mm and 1.2 mm and the (Dp/Wp)avg was between 0.12 and 0.14. Moreover, the effective bond length would reach a high level when the Wp,avg was between 1.0 mm and 1.2 mm and the (Dp/Wp)avg was about 0.10.

Investigation on interference and damage behaviours of electromagnetic riveted double-sided countersunk 30CrMnSiA/CFRP joints

Carbon fibre reinforced polymer (CFRP) structures benefit from electromagnetic riveting (EMR). However, incorrect riveting parameters could result in damages in CFRP structures during the EMR process. Excessive interference size may introduce initial damages to the joints. As a result, in this paper, the damage behaviours and the interference characteristics of the 30CrMnSiA/CFRP double-sided countersunk electromagnetic riveted joints are investigated. The riveting damage experiment was conducted, with the regular pressing riveting (RPR) process as a comparison. Moreover, a progressive damage FE model considering multiple typical damage modes of CFRP was developed for EMR damage prediction. The results show that when the rivet-hole diameter increases by 5% (4.08mm to 4.28mm), the average interference size of the joint under EMR and RPR processes decreases by 41% and 53%, respectively. Double-sided countersunk riveted joint interference size along the rivet axial distribution is not uniform, the CFRP sheet side of the interference size is relatively small. The EMR achieves a tighter, more uniform interference fit, while causing more severe riveting damages to the CFRP structure. Initial riveting damage exhibits a variety of modes, with delamination damage showing most significant sensitivity to rivet hole clearance.

A novel damage detection method for carbon fibre reinforced polymer structures based on distributed strain measurements with fibre optical sensor

This paper presents a novel approach for damage detection in carbon fibre reinforced polymer (CFRP) structures based on local strain feature matching. The proposed approach utilizes distributed in-plane strain measurements for plate structures under load (in-service application) to define a local point autocorrelation coefficient based on Delaunay triangulation and Hausdorff distance. This coefficient effectively identifies the discontinuities in distributed in-plate strain, enabling accurate capture of damage information through the damage index which is defined as the integral of this coefficient. Notably, the proposed approach requires no prior knowledge of the non-damaged strain distribution and yields excellent detection results for both Barely Visible Impact Damage (BVID) and Visible Impact Damage (VID). Leveraging the advantages of distributed strain sensing, coupled with image processing technology for the purpose of in-service damage detection of CFRP structures, the proposed novel method is a promising technology. The efficacy of this technology has been demonstrated in this paper through theoretical analysis and experimental investigations, offering valuable insights and reference for future research in this domain.

Additive Manufacturing of Self‐Sensing Carbon Fiber Composites

Carbon fiber‐reinforced polymer (CFRP) composites have gained substantial attention across various industries owing to their exceptional mechanical properties and lightweight nature. The emergence of additive manufacturing technologies brings new opportunities to the industry, offering advantages such as design freedom, rapid prototyping, and customization. However, the fabrication of CFRP composites through 3D printing techniques poses challenges pertaining to low resolution and limitations in complex geometry realization. This work introduces digital light processing printing as a versatile, high‐resolution method ideal for CFRP composite fabrication. The development and characterization of CFRP are focused on and the manipulation of mechanical properties through variations in matrix resins and fiber loadings is investigated, showcasing the versatility of CFRP composites for tailored applications. Additionally, the integration of self‐sensing capabilities in CFRP structures is explored, which opens up opportunities for applications in smart components for automotive and structural health monitoring.

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.

Experimental and numerical analysis of low-velocity impact damage of CFRP laminates with negative Poisson ratio (NPR) rubber protective layer

Carbon fiber-reinforced polymer (CFRP) structures are widely used in aviation industry, which can sustain damage during assembly from low-velocity impact events, decreasing residual stress and bearing capacity. A method of negative Poisson ratio rubber protective layer placing on the CFRP structures has been proposed to address this. The influence of cell angle on the impact response and protection effect were first investigated in this study. The experimental results indicate that the negative Poisson ratio rubber protective layer enhanced the impact resistance of the CFRP laminates, which reduces 33.1% the impact peak force and 17.5% the absorbed energy. Moreover, the impact resistance of CFRP with increases with the increasement of the cell angle. A low-velocity impact finite element model was developed with mixed-mode damage criterion for laminates and the hyperelastic model for rubber. The simulation results were validated with the experiment results in impact response and delamination damage. Additionally, the impact response and resistance were analyzed by varying seven different structural parameters of the protective layer to reveal the influence of relative volume. The experiment and simulation results demonstrated that the impact resistance increased with increasing cell angle and relative volume of the negative Poisson ratio rubber protective layer.

Research on the Heating Process of CFRP Circular Tubes Based on Electromagnetic Induction Heating Method.

Based on the electromagnetic induction heating method, heating and curing of Carbon Fiber Reinforced Polymer (CFRP) have the advantages of high energy utilization and no pollution. However, in the heating process, both the material weaving structure and mold material can affect the temperature field. Therefore, in this study, an electromagnetic heating finite element analysis model for CFRP circular tubes was established based on the equivalent electromagnetic thermal characteristics of CFRP. The study investigated the temperature rise mechanism of the material weaving structure under the magnetic field, and explored in-depth the influence of molds made of 45# steel and glass fiber-reinforced plastic (FRP) on the heating process of CFRP. The CFRP circular tubes with weaving structures of 89-degree winding angle, 45-degree winding angle, and plain weave were studied. The study found that when the metal mold was heated, the CFRP structure had almost no effect on the temperature distribution. However, when the glass fiber-reinforced plastic mold was heated, the temperature field changed with the CFRP structure, and the more fiber cross points, the more uniform the temperature field. The accuracy of the finite element model was verified through experiments. The aim of this research is to provide theoretical guidance for actual industrial production.

Computer-aided feature recognition of CFRP plates based on real-time strain fields reflected from FBG measured signals

Condition monitoring of critical and expensive carbon fiber reinforced polymer (CFRP) composite infrastructures is extremely essential task for uninterrupted operation and the durability of structures. Therefore, accurate and robust monitoring techniques and correlated damage identification algorithms need to be developed to characterize the health status of the CFRP structures. However, the effectiveness of existing methods is highly dependent on the structural properties of the CFRP plates. To identify the random damages caused by static or dynamic forces, the concept to establish the real-time strain fields of the structures based on measured signals is proposed. A moving surface spline interpolation algorithm based on Green's function has been developed to map the real-time strain fields of the CFRP plate using strain measured by surface-attached FBG sensors. A few static and impact loadings have been applied to a sample CFRP plate and the strain-field prediction by the proposed algorithm has been evaluated by a finite element model. Time and frequency domain analysis has also been conducted to recognize the dynamic response of the CFRP plates. Results indicate that the proposed algorithm can establish real-time strain field predictions with high precision, which can be used to recognize the static and dynamic responses of CFRP plate. Most importantly, the method is independent on the structural properties of the plate and the sensor layout, which is particularly significant for constructing the smart health monitoring system of CFRP.

Fatigue damage monitoring of composite laminates based on acoustic emission and digital image correlation techniques

Timely and effective health evaluation of carbon fiber reinforced polymer (CFRP) structures under dynamic fatigue loading is one of the key issues of CFRP in practical engineering applications. This paper uses a combination of acoustic emission (AE) and digital image correlation (DIC) to study the fatigue behavior of CFRP open-hole laminated beams with different stacking sequences under pure tensile loading, and analyze the influence of different damage mechanisms on the ultimate fatigue failure of the specimens. Two parameters, AE hit rate and absolute AE energy, are used to characterize the stiffness degradation behavior of CFRP structures. The strain field distribution characteristics during the damage failure of specimens with different stacking sequences are discussed in association with DIC. Based on the data obtained by AE and DIC, the damage modes of two types of layered CFRP laminated beams are identified by combining principal component analysis (PCA) and the K-means++ algorithm. The clustering results are consistent with the microscopic image results of the fracture surface. The identified modes are employed to characterize the dynamic evolution of fatigue damage in CFRP, and the contribution of different damage modes to the ultimate fatigue failure of the specimens is analyzed using cumulative damage index (CDI) values.

On axial crushing behavior of double hat-shaped CFRP and GFRP structures

This study aimed to investigate the energy-absorbing mechanisms of composite structures subjected to quasi-static and dynamic axial crushing loads. Double hat-shaped composite tubes were prepared using carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) composite materials. The results indicated that these composite tubes exhibited a progressive end-crushing mode and had a comparable load-carrying capacity at a crushing velocity of 2 mm/min. When the loading rate was increased to 6.1 m/s, a 23.3% reduction in the energy absorption of the CFRP structures was observed; whereas the energy absorption of the GFRP structures remained relatively constant. A stacked-shell finite element model, which considered the effects of strain rate on intra-layer and inter-layer properties, was developed to simulate the axial crushing behavior of the CFRP and GFRP tubes. The predictions made by the finite element model were found to correlate well with the tested crushing process, force–displacement curves, and final failure mode. The mechanical properties of the composite materials were also observed to play a critical role in the energy-absorbing mechanisms, contributing to the distinct crushing responses of the CFRP and GFRP structures. The results of this study are expected to help clarify the differences in the energy-absorbing mechanisms between CFRP and GFRP tubes, thereby contributing to the crashworthiness design of composite energy-absorbing structures.

An experimental study on the drilling of CFRP sandwich structures with filled and unfilled aramid honeycomb cores

Lightweight carbon fibre-reinforced polymer (CFRP) sandwich structures with honeycomb cores have excellent specific bending stiffness and good dimensional stability; therefore, their future applications will extend extensively, despite their difficult-to-manufacture nature. Although the drilling of single CFRP structures has been widely investigated, the published experience of drilling honeycomb cored CFRP sandwich panels is strongly limited. Therefore, the main objective of the present paper is to experimentally analyse the machinability of CFRP sandwich panels with filled and unfilled aramid Cormaster honeycomb cores through the analysis of thrust force, drilling torque and drilling-induced burrs. A twist and a brad and spur drill were used in two sandwich structures at three feed levels for the drilling experiments. The thrust force and drilling torque were measured by a KISTLER dynamometer, and the burrs were processed through digital image processing of optically captured images. The experimental results show that the application of fillers in the honeycomb only slightly decreases the nominal specific stiffness of the CFRP/honeycomb sandwich structures and slightly increases the thrust force; however, a significant improvement is achievable by their application in the drilling-induced burr formation of the honeycomb core.

Detection and quantification of artificial delaminations in CFRP composites using ultrasonic thermography

Delamination is inevitable during either fabrication or service of a carbon fiber reinforced polymer (CFRP) component. These flaws are major degradation phenomena that are difficult to be detected by nondestructive testing techniques, especially for closed delamination. This study performed an experimental investigation on delamination detection in CFRP plates using ultrasonic thermography with an ultrasonic transducer. In this work, a CFRP composite plate with delaminations was manufactured by a compression molding process. The ultrasonic was excited in the specimen and the heat was activated at the delaminations. Temperature distribution on the specimen surface was recorded by an infrared camera. The effects of wave propagation distance, delamination size, and depth were analyzed. Furthermore, the three most established signal processing techniques of thermography, namely thermal signal reconstruction (TSR), principal component analysis (PCA), and fast Fourier transform (FFT) were employed to deal with the subtracted-background thermal data. The performance of each algorithm was evaluated by temperature contrast, and global signal-to-noise ratio (SNR). Finally, the delamination area was quantitatively measured by Otsu’s thresholding method. The results indicate that the first and second principal components (PC1 and PC2) of PCA provide the highest SNR and the largest number of delaminations detected, respectively. The delamination of ϕ5 and a depth of 1.5 mm can be detected with excellent image quality. Hence, ultrasonic thermography can provide an efficient and cost-effective thermographic method for delamination detection in CFRP structures.

Developments in Laminate Modification of Adhesively Bonded Composite Joints.

The use of carbon fibre reinforced polymer (CFRP) materials is increasing in many different industries, such as those operating in the aviation, marine, and automotive sectors. In these applications, composite parts are often joined with other composite or metallic parts, where adhesive bonding plays a key role. Unlike conventional joining methods, adhesive bonding does not add weight or require the drilling of holes, both of which are major sources of stress concentration. The performance of a composite joint is dependent on multiple factors and can be improved by modifying the adhesive layer or the composite layup of the adherend. Moreover, joint geometry, surface preparation, and the manufacturing methods used for production are also important factors. The present work reviews recent developments on the design and manufacture of adhesively bonded joints with composite substrates, with particular interest in adherend modification techniques. The effects of stacking sequence, use of thin-plies, composite metal laminates and its specific surface preparations, and the use of toughened surface layers in the composite adherends are described for adhesively bonded CFRP structures.

On Crashworthiness and Energy-Absorbing Mechanisms of Thick CFRP Structures for Railway Vehicles.

This study aims to provide important guidelines for the crashworthiness design of composite energy-absorbing structures, especially railway vehicles. An experimental and numerical investigation was carried out to explore the crushing response of circular composite tubes reinforced with plain woven carbon fiber-reinforced polymers (CFRP). Quasi-static and dynamic axial crushing tests were performed on CFRP tubes with an inner diameter of 100 mm and a nominal wall thickness of 12 mm. Experimental results showed that increasing loading velocity led to a 21.8% reduction in specific energy absorption (from 99.7 kJ/kg to 78.7 kJ/kg) but had negligible influence on failure modes. Finite element models were also established and validated against the experimental results using ABAQUS/Explicit software. The effects of several different parameters such as the number of shell layers, friction coefficient, and interface properties on the simulated results, were also investigated and analyzed. A small variation in these parameters could change the total energy absorption of CFRP tubes. The comparisons between the predicted and experimental results indicated that a finite element model with 10 shell layers could effectively replicate the crushing response. In addition, the simulated results indicated that the damage of tubal wall materials dominated the major energy-absorbing mechanisms of CFRP tubes under quasi-static loads, which was 69.1% of the total energy. The energy dissipated by friction effects between the loading platen and the crushed fronds was 24.1% of the total energy. The increase in the loading velocity led to a decrease in the composite damage energy except for friction energy, resulting in a decrease in the total energy absorption.