Carbon Fiber Reinforced Plastic Research Articles

Manufacturing Autoclave-Grade Thermoset Carbon Fiber-Reinforced Polymer Aerospace Composites without an Autoclave Using Nanoporous Materials.

Composite laminates utilizing autoclave-grade carbon fiber-reinforced plastic (CFRP) prepreg were manufactured using a polymer nanoporous network (NPN) interlayer that generates capillary pressure in lieu of pressure from an autoclave. The polymer nanofiber NPN film is integrated into the interlaminar region and is shown to eliminate voids in a vacuum-bag-only (VBO) curing process. After a preliminary investigation of the effect of NPN thickness on the interlaminar region and performance, an 8 μm thick polymer NPN was selected for a scaled manufacturing demonstration. Combining the polymer NPN with "out-of-oven" (OoO) electrothermal heating of a carbon nanotube (CNT)-heated tool, a 0.6 × 0.6 m void-free plate is successfully manufactured. OoO cure enables an accelerated cure cycle, which reduces the cure time by 35% compared to the manufacturer-recommended cure cycle (MRCC). X-ray microcomputed tomography (μ-CT) reveals that the laminates are void-free and of identical quality to autoclave-cured specimens. An array of mechanical tests including tension, compression, open-hole compression (OHC), tension-bearing (bolt-bearing), and compression after impact, reveal that the accelerated NPN-cured composites were broadly equivalent, with some instances of improved properties, relative to the autoclave-cured parts, e.g., OHC strength increased by 5%. With reduced capital costs, energy consumption, and increased throughput, the facile polymer NPN-enabled out-of-autoclave (OoA) fabrication method is shown to be a practical and attractive alternative to conventional autoclave fabrication.

Biomimetic papilla texture by femtosecond laser for high-strength CFRTP/A6061-T6 FSSW hybrid structures

The lightweight design concept in structural applications has generated interest in hybrid structures of carbon-fiber-reinforced thermoplastics (CFRTP) and metals as attractive structure components. However, these hybrid structures face challenges due to the significant differences in physical and chemical properties between CFRTP and metals, resulting in limited strength and rendering them unsuitable for advanced transportation. To address these limitations, the current research focuses on creating a biomimetic texture on A6061-T6 (6061) surfaces using femtosecond laser to manufacture high-strength hybrid structures, inspired by organismal body surfaces. The CFRTP and 6061 were joined by friction stir spot welding (FSSW). The femtosecond laser treatment produces double-scale roughness on 6061 surfaces and causes carbon to absorb into alumina. These changes in physical and chemical structures enhance the compatibility between 6061 and CFRTP. The biomimetic rough aluminum surface creates effective mechanical interlock at the interface with CFRTP, preventing the initiation and propagation of fracture cracks. The presence of absorbed carbon enhances the Al-O covalency, which influences the bonding behavior at CFRTP/6061 interfaces. The improved compatibility, mechanical interlock, and enhanced bonding behavior synergistically strengthen the joint strength of CFRTP/6061 hybrid structure modified by the biomimetic papilla structure. Current biomimetic design strategy inherits the remarkable natural wisdom and is expected to provide valuable insights for the development and application of CFRTP/metal hybrid structures.

Underwater dissimilar friction stir lap welding of aluminum alloy and CFRTP

With the rapid development of the transportation and electronic equipment industries, the demand for robust joining technology for metal/polymer has become imperative, especially in the pursuit of lightweight solutions. Underwater welding is one of the methods to reduce the formation of holes and other welding defects, which is conducive to improve the quality and strength of joints. In this study, the underwater friction stir lap welding (UFSLW) of 6061-T6 Al alloy and carbon fiber reinforced thermoplastic (CFRTP) joints is investigated. The welds are evaluated by optical microscope (OM) image, scanning electron microscope (SEM), and energy dispersive X-ray spectrometer (EDS) of the fracture, tensile, and hardness analysis. Research reveals that the presence of cracks and tunnel defects similar to those in air FSLW (AFSLW) is reduced in the underwater welding process. From the microscopic result analysis, the rapid dissipation of frictional heat and substrate viscosity in the cooling medium of circulating water in the stirring zone reduces the interaction between Al alloy and molten CFRTP, which leads to the rapid transformation of the plasticized material into a solid state and reduces the formation of thick stacked layer. In addition, finer Al alloy fragments are obtained in the welding zone due to the fast cooling rate. Ultimately, the maximum tensile strength of 32.12 MPa is achieved, which is 10.76% higher than that of the same welding parameters in air. Based on UFSLW technology, the joint strength of this study is 69% higher than that of Al alloy and polymer joints, which demonstrates enormous application potential and opens up new prospects for the joining technology of dissimilar materials.

Linear friction welding of light metals and carbon fiber-reinforced plastics

Linear friction welding of light metals and carbon fiber-reinforced plastics

Electrical Discharge-Assisted Turning for UD CFRP Under Low Voltage Condition

The demand for carbon fiber reinforced plastics (CFRP), classified as functional resins, has increased for micromachined products that are manufactured using lathes and used in the medical field. However, the problems with machining CFRP include the occurrence of burrs and deterioration of the finished dimensions owing to the significant tool wear caused by the carbon fiber. To turn CFRP and maintain high dimensional accuracy, the authors proposed a novel combination of conventional turning and electrical discharge-assisted turning (EDAT). In this study, the capability to control the machinability of EDAT under low-voltage conditions was experimentally investigated. The relationship between the discharge voltage, frequency, and depth of discharge influence of the carbon fibers was clarified.

Feasibility Study of Single-Point Incremental Forming for Discontinuous-Fiber CFRP Using Oil-Bath Heating

Although, three-dimensional printing has several advantages, however there are currently many limitations. In particular, printed products using composite materials such as fiber-reinforced plastic have yet to achieve the same mechanical properties as those obtained from conventional manufacturing methods. In addition, fabricating thin plates or thin shell shapes with sufficient strength is challenging. Incremental forming enables high-mix, low-volume production of thin sheets. This method applies incremental deformation to thin sheets, the desired shape is obtained by accumulating the deformation, and no dies are required. Carbon-fiber-reinforced plastic (CFRP) materials have high specific strength. Discontinuous-fiber CFRP is capable of large plastic deformation under appropriate conditions due to the discontinuity of the reinforcement, and its mechanical properties are nearly isotropic due to the random fiber arrangement. The authors focused on this property and studied the application of single-point incremental forming to discontinuous carbon-fiber-reinforced polyamides. In this study, the workpiece was formed by heating it locally to a deformable temperature by the frictional heat between the rotating tool and the workpiece. The forming experiment was also conducted in an oil bath to keep the entire material at a suitable forming temperature. The results showed that the spindle speed affected forming results even in an oil bath and that heating using an oil bath suppressed deviations from the sine law for thickness and wall angle due to elastic deformation.

Feasibility study of an integrated pre‐curing and forming process for 6061 Al alloy and carbon fiber hybrid composites

AbstractThis article proposes a 6061‐T6 Al alloy and carbon fiber hybrid composite material pre‐curing and forming integrated new process, which can significantly reduce the hybrid composite material processing time, improve the production efficiency, and provide the possibility of hybrid composite materials in automotive parts applications. The process started by placing hand‐stacked carbon fiber reinforced plastic (CFRP) composites on the surface of 6061 Al alloy sheets, followed by bonding and pre‐curing of the CFRP to the Al alloy sheets through two different sets of dies in a hydraulic press, and ultimately full curing in an aging furnace. Mechanical properties of the CFRP/Al hybrid composite material were measured by flexural tests. The results show that the flexural strength of CFRP/Al hybrid composites with different layups ([90]12, [0/45/90/−45]3, and [0]12) was increased by 159%, 93.4%, and 67.9%, respectively, compared with the single 6061 Al alloy. According to the macro‐morphological observation, [90]12 lay‐up parts have the least thinning. According to the microstructure observation, no obvious cracks or voids were found in the [90]12 lay‐up parts. Elongated cracks and void defects could be found in the [0]12 lay‐up parts. For the [0/45/90/−45]3 lay‐up parts, voids are mainly exist in ±45°layups. The results of the spring‐back analysis show that the standard deviation of the formed parts obtained from the three lay‐up methods is within 1 mm, indicating that the forming effect is good.Highlights New process improves productivity and reduces production costs The flexural strength of CFRP/Al hybrid parts is greatly improved [90]°12 lay‐up parts have the least thinning and no cracks were found The forming precision of the three lay‐up parts is good

Effect of nano-silica modified resin on the interface strength and toughness of Al/CFRP hybrid laminates

In order to improve the interfacial strength and toughness of aluminum alloys and CFRP (carbon fiber reinforced plastics) hybrid laminates, modified resin with lower porosity was prepared by adding nano silica treated with silane coupling agent into epoxy resin. Al/CFRP hybrid laminates with modified resin were prepared by physical liquid deposition method and hot-press process. The strength and toughness of Al/CFRP hybrid laminates with modified resin were evaluated by tensile shear test and end notch fracture (ENF) test. The experimental results showed that the interfacial shear strength of Al/CFRP hybrid modified resin laminates is 18.8 ± 0.8 MPa and the fracture energy is 1546.33 ± 10.26 J /m2, which is 28.76 % and 15.38 % higher than that of Al/CFRP hybrid laminates with raw resin, respectively. The well-dispersed silicon nanoparticles effectively mitigate internal stress during the cross-linking process of the modified resin, thereby diminishing the dimensions of microcracks within the modified resin. The transition layer of the modified resin interface formed a cooperative and smooth structure. This structure can ensure that the transition of elements in the interface layer is smooth, and it is not easy to cause stress concentration. The formation of new bonds (C-Si bonds) at the interface of the modified resin indicates an enhancement of bonding strength at the interface, superimposing upon van der Waals forces, thereby enhancing the adhesive strength of the modified resin interface.

Zero group velocity feature in CFRP-Nomex honeycomb structure and its use for debonding detection

Carbon fiber reinforced plastic (CFRP) − Nomex adhesive honeycomb structures are widely used in aerospace due to their excellent properties. However, debonding defects pose a significant challenge to structural safety due to their hidden nature and high risk. In this work, to address the debonding detection in the CFRP-Nomex honeycomb structure, a method based on the zero group velocity (ZGV) feature is proposed. By calculating the dispersion curve of the structure, it is found that there is the ZGV on the S1 branch. Further analysis revealed that this ZGV feature is generated by the repulsion between the S2 and S1 branches. The simulation and experimental analysis of the acoustic propagation characteristics in the honeycomb structure confirmed the presence of the ZGV feature with its energy localized near the exciting point. When debonding defects occur in the honeycomb structure, this feature disappears. Therefore, the ZGV feature can be used for the debonding detection of CFRP-Nomex honeycomb structures. Compared with ultrasonic C-scan, the results demonstrate that the proposed method can accurately detect and locate debonding defects with a diameter of 20 mm. Due to its simplicity, the method does not require sophisticated equipment or complex signal processing procedures, making it suitable for in-service inspection.

Barely visible impact damage detection in CFRP composite using vibrothermography with narrowband sweep excitation

The extensive use of carbon fiber-reinforced plastic (CFRP) composite materials in various industries has posed new challenges for conducting effective structural health monitoring and nondestructive evaluation techniques. Based on local defect resonance (LDR), the vibrothermography with narrowband sweep excitation is proposed to detect BVIDs in the CFRP composite. The response spectrum of displacement at the impact crater was collected by a laser Doppler vibrometer, which was used to determine the frequency range of narrowband sweep excitation. The frequency range was further validated by the analysis of local defect resonance for thermal responses, and the sweep duration was also optimized. Subsequently, the proposed vibrothermography was employed to detect BVIDs with varying severity. The impact damage could be efficiently activated and a significant temperature rise was generated in the defective areas, which enhances the temperature contrast of the thermal images and facilitates the quantification of defects.

Fatigue properties and damage evolution of CFRP/Al bolted joint under high load level using micro-CT technology

Although bolted jointsbetween aluminum alloy (Al) and carbon fiber reinforced plastic (CFRP) are often used in engineering, the specific cause of fatigue failure in these joints is still not understood. The tension–tension fatigue experiments were performed on CFRP/AL bolted single lap joints (SLJs) at high load levels in this investigation. Two stacking sequences ([±45]12 and [0/90, ±45]3s), were developed together with multiple load levels LR ranging from 0.75 to 0.96. Micro X-ray computed tomography (µCT) was used for non-destructive testing, three-dimensional (3D) models were reconstructed, and pores were measured and assessed to further explore the fatigue failure mechanism of CFRP. The results showed that although CFRP failed at greater load levels, Al failures occurred at lower load levels. At a ratio of 0.923 to 0.95, a competitive failure was also observed. The results of CT analysis showed that holes appeared to start and grow significantly in the ± 45 layer. Pores will enlarge and agglomerate when the load level and number of cycles increase. This research investigated how CT technology can be used in CFRP fatigue experiments.

Multi-objective optimization of variable-stiffness composite for CFRP-winding buckle arrestor by using NSGA-Ⅲ

This study introduces a multi-objective optimization method utilizing the NSGA-III algorithm to tailor the fiber shape of variable-stiffness CFRP (Carbon Fiber Reinforced Plastics) shell structures. Combined with offshore oil and gas engineering, this method is employed to perform fiber shape optimization design for CFRP-winding buckle arrestors. Based on cubic polynomial path functions' contour lines, curved fibers are represented and fitted using the Curvature Minimum Bi-Arc (CMBiArc) interpolation NURBS curve method. Employing the NSGA-III algorithm, the fiber shapes of a CFRP laminate are optimized under manufacturing constraints, targeting mean compliance, fundamental frequency, and fiber curvature. With the study of numerical modeling, buckling crossover mode and arresting efficiency, multi-objective optimization is carried out for fiber shape of CFRP-winding buckle arrestors designed for subsea pipelines. With the goal of maximizing arresting efficiency, structural fundamental frequency, and minimizing fiber curvature, the method yields an enhanced CFRP-winding arrestor design, which demonstrates a high practicability through a layered design approach. By parametric study of optimization result and comparison with slip-on arrestor, the feasibility of the optimization method and the practical value of the novel improved arrestor are substantiated.

Stress and energy release rate analysis of cross-ply carbon fiber-reinforced plastic laminate with transverse cracks subjected to ultrasonic vibration using a variational approach

Application of carbon fiber reinforced plastics (CFRP) to structures that are subjected to increasingly high numbers of cyclic loads is expected to expand, so evaluation of fatigue properties up to the very-high cycle regime is essential to prove their long-term reliability. Conventional fatigue testing is not practical for such conditions owing to the excessive time required; ultrasonic fatigue testing, which can be performed at a frequency of 20 kHz, is an effective alternative. Stress distribution in ultrasonic fatigue testing differs from that in conventional fatigue testing because the specimen is resonated. The stress distribution of cross-ply laminates with transverse cracks subjected to resonance was calculated using a variational approach. The energy release rate was calculated based on the results of a previous study on transverse crack initiation. The results of the stress analysis are in good agreement with those of finite-element analysis. Quantitative evaluation of transverse crack initiation was also conducted.

Evaluation of matrix crack growth in interlaminar toughened quasi-isotropic carbon-fiber reinforced plastic laminates up to the very-high cycle regime by ultrasonic fatigue testing

It is time-consuming to conduct conventional hydraulic fatigue testing up to the very-high cycle fatigue (VHCF, N (number of cycles) ≥ 108) regime. Ultrasonic fatigue testing has been proposed as an accelerated alternative method. In this study, ultrasonic fatigue testing was conducted on interlaminar toughened quasi-isotropic carbon-fiber reinforced plastic (CFRP) laminates to evaluate the characteristics and mechanism of fatigue up to the VHCF regime. Hydraulic fatigue tests were conducted at the same stress ratio as a comparison. The resulting S–N diagrams showed a lower fatigue strength and different fatigue mechanisms for specimens subjected to ultrasonic fatigue tests compared with those subjected to hydraulic fatigue tests. The observed growth of the matrix crack density in each laminate layer was used to perform a shear-lag analysis to calculate the energy release rate considering off-axis matrix cracks. The results suggested different damage growth behaviors for specimens subjected to ultrasonic and conventional fatigue tests.

Investigation on grinding temperature characteristics of CF/PEEK and material removal mechanism under temperature treatments

Carbon fiber reinforced thermoplastic (CFRTP) composites grinding temperatures could even exceed the glass transition temperature (Tg) of the material due to heat accumulation, combined with the unknown material removal mechanism, resulting in machining defects. To investigate the grinding temperature distribution and maximum temperatures of carbon fiber-reinforced poly-ether-ether-ketone (CF/PEEK) composites, as a typical kind of CFRTP, an analytical temperature model considering the anisotropy was proposed based on the moving heat source theory, verified by the experimental results measured by the infrared camera. Further, the material removal mechanism under temperature treatments (below and above Tg) was also studied. In high temperatures (above Tg), there were many defects on surfaces after grinding, including resin smearing, severe deflection, fiber distortion, and grinding wheel clogging. Therefore, to reduce the grinding temperature below Tg, the vortex tube cooling-assisted grinding method was proposed in the research. The proposed method could reduce the grinding temperature in the grinding area, suppress resin smearing, improve the surface quality, enhance the elastic modulus and nano-hardness of the workpiece, and reduce the clogging of grinding wheels. This study provided a better understanding of the CF/PEEK grinding temperature characteristics and suggested a method to improve the grinding quality.

Tensile strength prediction of unidirectional polyacrylonitrile (PAN)-based carbon fiber reinforced plastic composites considering stress distribution around fiber break points

Recent advancements in enhancing the mechanical characteristics of carbon fibers open up new application possibilities for carbon fibre-reinforced plastic (CFRP) composites. Particularly in unidirectional CFRPs, which form the basal structure of CFRP laminates, developing a micromechanics model capable of predicting the tensile strength of unidirectional CFRPs based on carbon fiber mechanical characteristics is a current aspiration. This study conducted a stress distribution analysis around the fiber fracture point to predict the tensile strengths of unidirectional CFRPs prepared with five types of polyacrylonitrile (PAN)-based carbon fibers, each with unique mechanical characteristics. Numerical simulation results obtained using a unidirectional CFRP model that considered the stress concentration, fiber axial stress, and bimodal Weibull distribution were reasonably consistent with the experimental results for the tensile strengths of unidirectional CFRP composites, regardless of the differences in the mechanical characteristics of the fiber. Our findings can provide guidance for designing further enhanced high-performance CFRP materials.

Bayesian data-driven framework for structural health monitoring of composite structures under limited experimental data

Ultrasonic-guided waves can be used to monitor the health of thin-walled structures. However, the run of experimental damage tests on materials like carbon fiber-reinforced plastics can be impractical and costly. Instead, numerical models can be used to create hybrid datasets to train machine learning algorithms, integrating data from numerical and experimental tests. This paper presents a Bayesian-driven framework to compensate for limited experimental data regarding Lamb wave propagation in composite plates. Using Bayesian inference, the framework updates a numerical finite element model, considering observed uncertainties by sampling posterior probability density functions for input parameters using Markov–Chain Monte Carlo simulations with the Metropolis-Hastings algorithm. A neural network surrogate model speeds-up these simulations, leading to a model that replicates the uncertain experimental setup. This model then generates data to augment true experimental data. Finally, a one-dimensional convolutional neural network is trained on a three different datasets to analyze Lamb wave signals and assess damage. Comparing training strategies shows the hybrid dataset augmented by samples generated by the updated FE model gives the most accurate damage size predictions.

Design of rose thorn biomimetic micro-protrusion for metals and CFRTP easily disassembled joining

This study focuses on the joining techniques for metals and carbon fiber reinforced thermoplastic (CFRTP) to address the pursuit of lightweight vehicles and high recycling efficiency. The innovative concept of ‘easy-disassembly joining’ is introduced for the first time, aiming for robust joint strength and efficient disassembly/recycling of end-of-life vehicles. Inspired by rose thorn morphology and natural performances, bionic micro-protrusions are explored as intermediate structures to facilitate the easy disassembly joining between metals and CFRTP. The primary focus of the study revolves around the design strategy of micro-protrusions inspired by rose thorns. The objective is to identify the most effective micro-protrusion shapes by understanding the interplay of its geometrical parameters, including base shape, apex position, profile curvature, and stress distribution under diverse loads. Utilizing static stress numerical simulations, the study conclusively identifies an elliptical base shape with the apex positioned slightly above the right edge of the structure. The outer profile adopts a circular arc, and the inner profile follows a conical curve. This configuration effectively mitigates stress concentration at the bottom, which interfaces with the metal substrate and the smaller areas around the apex. This research introduces an innovative concept for metal-CFRTP joining and applies bionic principles in engineering solutions. By promoting lightweight and sustainable structures through enhanced disassembly efficiency, it contributes to groundbreaking advancements in the field.

Uncut fiber analysis using fiber deflection and cutting forces in carbon fiber-reinforced plastics during rotation of the cutting tool

Cutting, milling, and drilling during the manufacture of carbon fiber-reinforced plastics (CFRPs) is an active field of research. It is challenging to analyze cutting characteristics during cutting tool rotation because the chip thickness, fiber cutting angle, and specific cutting force change. Here, we used a mechanical model to study the cutting forces and fiber deflections that develop as the cutting tool rotates during CFRP milling. The fiber and matrix were modeled as a beam, and the cutting force and fiber deflection were analyzed according to the fiber cutting angle. We explored how uncut fiber status and surface roughness were affected. If the fiber deflection caused by transverse cutting forces was not eliminated before the cutting tool rotation angle attained 180°, some fibers were not cut. Serious defects developed when uncut fibers were not generated at certain fiber orientation angles.

A Comparative Study of Micromechanical Analysis Models for Determining the Effective Properties of Out-of-Autoclave Carbon Fiber-Epoxy Composites.

This study aims to critically assess different micromechanical analysis models applied to carbon-fiber-reinforced plastic (CFRP) composites, employing micromechanics-based homogenization to accurately predict their effective properties. The paper begins with the simplest Voigt and Reuss models and progresses to more sophisticated micromechanics-based models, including the Mori-Tanaka and Method of Cells (MOC) models. It provides a critical review of the areas in which these micromechanics-based models are effective and analyses of their limitations. The numerical analysis results were confirmed through finite element simulations of the periodic representative volume element (RVE). Furthermore, the effective properties predicted by these micromechanics-based models were validated via experiments conducted on IM7/5320-1 composite material with a fiber volume fraction of 0.62.