Carbon Fiber Reinforced Plastic Composites Research Articles

Experimental investigation on the effect of dry and multi-jet cryogenic cooling on the machinability and hole accuracy of CFRP composites

In this work, the drilling performance of carbon fibre reinforced plastic (CFRP) composites is analysed in terms of thrust force (Fn), torque (Mz), specific cutting energy (SCE), delamination factor (Fd), and hole quality under dry and cryogenic cooling conditions. An in-house developed multi-jet liquid nitrogen (LN2) delivery setup is used for experimental trials. This LN2 delivery system is retrofitted to an existing machine tool to enable the movement of jets along the axis of the spindle for better reachability of LN2 to the cutting zone during the drilling operation. Experiments are conducted using the full factorial technique considering four levels of spindle rotational speed (N), four levels of feed rate (fr), and two cutting conditions i.e., dry and cryogenic cooling. Results show increased Fn up to 35% and decreased Mz up to 24.46% using cryogenic drilling as compared to dry drilling. Moreover, SCE is reduced up to 35% using cryogenic drilling than in dry drilling. Entry Fd is decreased up to 21.55% under cryogenic drilling as compared to dry drilling. At higher N input and lower fr, the exit Fd can be reduced by up to 9% using cryogenic drilling as compared with dry drilling. In terms of hole quality, cylindricity (CYL) decreased by up to 42.69%, lower deviation in average hole size, and decreased average surface roughness (Ra) up to 20% when using cryogenic drilling. The results show that using the multi-jet cryogenic cooling system provides enhanced composite machinability and sustainability for industrial use.

Environmental affected mechanical performance of additively manufactured carbon fiber–reinforced plastic composites

Due to their attractive strength-to-weight ratios, stiffness-to-weight ratios, thermal expansion, corrosion resistance, and vibration resistance properties, carbon fiber reinforced plastic (CFRP) composites have been widely used in applications ranging from aerospace to sporting goods. Considering some of the advantages of additive manufacturing (AM) over traditional subtractive methods, AM is being used to fabricate CFRP composites. For the fabrication method, several investigations have been conducted on materials and processing effects on the mechanical performance of the composites. However, no studies have investigated the effects of environmental conditions on mechanical performance. This study reports the environmental (temperature and relative humidity) affected mechanical performance of AM fabricated CFRP composites exposed to three different environmental conditions: warm–wet, warm–dry, and cold–dry, compared to samples tested immediately after fabrication under normal ambient conditions. The result was that the warm temperatures have insignificant effects on the mechanical performance of the composites, while near-zero degree cold temperatures have significant effects after the 96 h and 250 h short-term exposure periods. The result also showed the temperature to have more significant effects on mechanical properties than relative humidity. Under the warm conditions, the dry humidity resulted in a slight increase in material mechanical properties over the nominal ambient condition, while the wet humidity showed an insignificant reduction in material mechanical properties.

Significantly improving mechanical properties of epoxy resin-based carbon fiber-reinforced plastic composites via introducing oxazolidinone segments

Herein, the oxazolidinone (OX) segments have been successfully introduced into carbon fiber-reinforced plastic (CFRP) composites via the bulk polymerization of the isocyanate and epoxy (EP) groups to significantly promote the mechanical properties. Through the bulk polymerization, the OX segments in epoxy resin (OX epoxy resin) have been formed, verified via the Fourier transform infrared (FT-IR) spectroscopy. Afterward, in order to obtain the cured OX epoxies, the as-prepared OX epoxy resin has been mixed with the pure EP resin for further curing. Thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA) have shown that the cured OX epoxies have exhibited improved thermal resistance and higher Tg than the cured neat epoxies. After introducing OX segments, the flexural strength, flexural modulus, and impact strength of the cured OX epoxies have been promoted by 30.1%, 12.1%, and 82.9%, respectively. Moreover, the mechanical properties of CFRP composites, fabricated from OX epoxy resin and T1100 carbon fibers, have been improved as well and in particular, the flexural strength, flexural modulus, impact strength, interlaminar shear strength, and compressive strength after the impact of the composites have been improved by 25.9%, 8.4%, 23.6%, 35.5%, and 23.8%, respectively. Furthermore, the impact damage of the composite laminates has been analyzed via Ultrasonic C-scan.

Additive Manufacturing of Carbon Fiber Reinforced Plastic Composites: The Effect of Fiber Content on Compressive Properties

The additive manufacturing (AM) of carbon fiber reinforced plastic (CFRP) composites continue to grow due to the attractive strength-to-weight and modulus-to-weight ratios afforded by the composites combined with the ease of processibility achievable through the AM technique. Short fiber design factors such as fiber content effects have been shown to play determinant roles in the mechanical performance of AM fabricated CFRP composites. However, this has only been investigated for tensile and flexural properties, with no investigations to date on compressive properties effects of fiber content. This study examined the axial and transverse compressive properties of AM fabricated CFRP composites by testing CF-ABS with fiber contents from 0%, 10%, 20%, and 30% for samples printed in the axial and transverse build orientations, and for axial tensile in comparison to the axial compression properties. The results were that increasing carbon fiber content for the short-fiber thermoplastic CFRP composites slightly reduced compressive strength and modulus. However, it increased ductility and toughness. The 20% carbon fiber content provided the overall content with the most decent compressive properties for the 0–30% content studied. The AM fabricated composite demonstrates a generally higher compressive property than tensile property because of the higher plastic deformation ability which characterizes compression loaded parts, which were observed from the different failure modes.

An Application of The PROMETHEE Method To Select The Best Response for Carbon Fibre Reinforced Plastic Drilling in Machining Operations

The manufacture of carbon fibre reinforced plastic (CFRP) composites from carbon fibres fused with epoxy matrix, deploying the hand layup method has raised considerable attention. Within this research domain, drilling with various tools such as coated and uncoated drills is of great significance. Unfortunately, the use of intuition and experience to select the best parameter in the drilling operation has been known to be less efficient, causing the inadequate distribution of drilling resources to actualize the effectiveness of drilling parameters. Energy wastages are also associated with the present practice of intuition in drilling process. In this study, a novel approach of PROMETHEE I and II are presented to avoid ineffectiveness in drilling resource distribution and select the best drilling operations parameters. The proposed method utilizes experimental data from the literature to verify the method's performance. This study helps in reducing waste due to the inadequate distribution of drilling operations sources. PROMETHEE analyses the drilling parameters of the CFRP composites using preference functions that map the differences among alternatives during machining judgments. Out of the six responses examined, the best response is exit delamination with a weight of 0.059, surface roughness with a weight of 0.031emerged as the second position, torque weighing 0.003 took the 3rd position while the last position is entry delamination, weighing -0.102.

Recyclable separation and recovery of carbon fibers from CFRP composites: Optimization and mechanism

• Carbon fibers are recovered from CFRP via chemical swelling and electrochemical oxidation. • Solvent DMSO is recyclable in this separation and recovery method. • Recovered carbon fibers exhibit good surface morphology and mechanical properties. Chemical swelling and electrochemical oxidation are combined to realize the separation and recovery of carbon fibers from carbon fiber-reinforced plastic (CFRP) in dimethyl sulfoxide (DMSO) at normal temperature and pressure. The results showed that the depolymerization rate of epoxy resin in CFRP increased with increasing ammonium acetate concentration and current density, and the influence of the current density was more significant than that of the concentration. Microscopic analysis showed that the recycled carbon fibers had few residual resin on their surfaces and mild electrochemical oxidation etching, and recycled carbon fiber monofilament achieved a tensile strength and an interfacial shear strength that were 93.55% and 118.76% those of the original fibers.

Advanced non-destructive evaluation of impact damage growth in carbon-fiber-reinforced plastic by electromechanical analysis and machine learning clustering

In this study, advanced structural health monitoring was conducted on carbon-fiber-reinforced plastic (CFRP) through a non-destructive self-sensing method wherein impact damage growth was tested using the electromechanical properties of the material. The electrical resistance in CFRP composite structures was measured in real time during impact testing. The health state of the structures was monitored in real time during impact energy absorption. Based on the electromechanical data of the CFRP composite structures, k-means clustering and principal component analysis were used to identify the damage types in these structures. Previous self-sensing methods are limited to identifying different damage types, such as delamination, matrix cracking, and fiber breakage. However, the proposed advanced method can identify different damage types in composite structures using only electromechanical behavior. The applicability of the method was verified by using it to assess the impact damage on a three-dimensional wind turbine blade. Thus, this study successfully designed a condition-based monitoring method for analyzing the damage type of CFRP composites and monitoring their current health state, and demonstrated an industry application of the proposed method.

A Comparative Study on the Electrical and Piezoresistive Sensing Characteristics of GFRP and CFRP Composites with Hybridized Incorporation of Carbon Nanotubes, Graphenes, Carbon Nanofibers, and Graphite Nanoplatelets.

In this study, hybridized carbon nanomaterials (CNMs), such as carbon nanotubes (CNTs)–graphene, CNT–carbon nanofibers (CNFs), or CNT–graphite nanoplatelet (GNP) materials were embedded in glass-fiber-reinforced plastic (GFRP) or carbon-fiber-reinforced plastic (CFRP) composites to obtain electrical/piezoresistive sensing characteristics that surpass those of composites with only one type of CNM. In addition, to quantitatively assess their sensing characteristics, the materials were evaluated in terms of gauge factor, peak shift, and R-squared values. The electrical property results showed that the GFRP samples containing only CNTs or both CNTs and graphene exhibited higher electrical conductivity values than those of other composite samples. By evaluating piezoresistive sensing characteristics, the CNT–CNF GFRP composites showed the highest gauge factor values, followed by the CNT–graphene GFRP and CNT-only GFRP composites. These results are explained by the excluded volume theory. The peak shift and R-squared value results signified that the CNT–graphene GFRP composites exhibited the best sensing characteristics. Thus, the CNT–graphene GFRP composites would be the most feasible for use as FRP composite sensors.

Thermal barrier coating for carbon fiber-reinforced composite materials

Carbon fiber-reinforced plastic (CFRP) composites are widely employed in lightweight and high performance applications including supercars, aero-vehicles, and space components. However, although carbon fibers are thermally stable, the low thermal endurance of the matrix materials remains a critical problem in terms of the performance of the material. In this study, we proposed a new, Al 2 O 3 -based thermal barrier coating (TBC) for the CFRP composites. The TBC comprised α-phase Al 2 O 3 particles with a mean diameter of 9.27 μm. The strong adhesion between the TBC and the CFRP substrate was evaluated using a three-point bending test. When the CFRP substrate was subjected to a 500–700 °C flame, the 1.45-mm thick TBC protected the CFRP substrate remarkably by reducing the surface temperature to 188–228 °C. The thermo-mechanical responses of this TBC/CFRP composite were analyzed after thermal shock tests. Surprisingly, 50% of the pristine flexural strength of the TBC/CFRP composite was preserved, whereas that of neat CFRP was reduced significantly by 95%.

Micromechanical Modeling of Unidirectional CFRP Composites with Proportional Stressing

In this paper, we present a computational micromechanical analysis of unidirectional (UD) carbon fiber-reinforced plastics (CFRPs) using representative volume elements (RVEs). The RVEs consist of randomly distributed fibers, matrix, and interfaces between the fibers and matrix. Periodic boundary conditions (PBCs) and proportional stressing are implemented to facilitate micromechanical analysis of the composites under controlled stress states. In particular, the failure mechanisms of the RVEs under combined transverse and in-plane shear stressing are investigated. The ratio of in-plane shear stress over transverse stress is kept constant during each simulation. By varying this ratio, the mechanical responses of composites under different stress states are systematically studied and the failure envelopes for different fiber volume fractions are extracted. We find the failure envelope converges as the fiber volume fraction increases. The framework developed in this study can be extended to different stress states allowing us to conveniently examine the failure criteria for UD CFRP composites comprehensively.

Acoustic emission waveforms for damage monitoring in composite materials: Shifting in spectral density, entropy and wavelet packet transform

Signal-based acoustic emission data are analysed in this research work for identifying the damage modes in carbon fibre–reinforced plastic (CFRP) composites. The research work is divided into three parts: analysis of the shifting in the spectral density of acoustic waveforms, use of waveform entropy for selecting the best wavelet and implementation of wavelet packet transform (WPT) for identifying the damage process. The first two methodologies introduced in this research work are novel. Shifting in the spectral density is introduced in analogous to ‘flicker noise’ which is popular in the field of waveform processing. The entropy-based wavelet selection is refined by using quadratic Renyi’s entropy and comparing the spectral energy of the dominating frequency band of the acoustic waveforms. Based on the method, ‘dmey’ wavelet is selected for analysing the waveforms using WPT. The slope values of the shifting in spectral density coincide with the results obtained from WPT in characterising the damage modes. The methodologies introduced in this research work are promising. They serve the purpose of identifying the damage process effectively in the CFRP composites.

Lamb wave-based damage detection of composite structures using deep convolutional neural network and continuous wavelet transform

Carbon fiber reinforced plastics composites have been widely used in aerospace, automotive and other fields for its superior performance. To avoid possible risks, Lamb waves-based structural heath monitoring techniques have been applied to detect the internal damage of these composites. However, due to their intrinsic high degree of anisotropy which makes the failure mode complicated under fatigue loads, an accurate and timely method for damage detection of these composites is still challenging to realize. This paper proposes a novel method for detecting the internal delamination of the carbon fiber reinforced plastics by combining deep convolutional neural network and continuous wavelet transform. This data-driven method can effectively leverage the large amount of data without relying on complex feature extraction. After converting the time series signal into a two-dimensional time–frequency image by the continuous wavelet transform technique, the convolutional neural network model is applied to classify the images. Based on the prediction results of different paths by the model, a damage localization method is also proposed for ply delamination. An experimental study is implemented to verify the effectiveness of this method. The result shows this method is a useful technique for precise diagnosis and positioning of delamination damage in the composite structures.

Impact damage localization and mode identification of CFRPs panels using an electric resistance change method

Electric resistance change method (ERCM) has shown potential as a good candidate for performing in-situ damage sensing in carbon fiber reinforced plastic composites (CFRPs), however, studies that investigated the impact damage localization and mode identification of CFRPs were limited. This paper investigates a novel ERCM technique for damage localization and mode identification in CFRPs under normal impact load with energies of 50 and 80 J. The impact damage characteristics of the CFRPs were firstly analyzed, and the corresponding electrical resistance was measured. A damage localization algorithm was designed according to the resistance characteristics obtained by the theoretical calculation and simulation. A relationship between CFRPs thickness and the electrical resistance was built, and damage modes were analyzed with assistance of computed tomography observations. Results show that the electric resistance changes between electrode networks could be used to help imaging the damage positions with a very high accuracy (6% error). The linear relationship between the electrical resistance, incident energy, and the panel thickness could be adopted to predict the damage modes in CFRPs after impact.

Analysis and prediction of interlayer stress and strain of composites such as CFRP irradiated by laser

In order to further reveal the interaction mechanism between laser and composites such as carbon fiber reinforced plastics (CFRP), this paper proposed, constructed, and verified a finite element method (FEM) for accurately analyze and predict the interlayer thermal stress and strain of CFRP through numerical simulation. Firstly, the FEM was constructed based on the theoretical analysis of the temperature, stress-strain distribution in CFRP composites irradiated by laser, which is consistent with the experimental conditions. Then, the accuracy of FEM was verified through experiments. Finally, the verified FEM was successfully extended to a more general and complex situation. This method can not only highly restore the arbitrary CFRP interlayer and directional stress in complex conditions such as different laying modes, different material ratios, and different fixed constraints, but also predict the strain trend of materials. Simultaneously, it can also make an accurate quantitative analysis of the thickness-stress distribution at any point in it. All these are difficult to achieve by current methods, so the proposal of this method can effectively fill up the gap in the current research on this issue, and will undoubtedly have significant reference value and universal guiding significance for future research.

Factor Selection in Drilling Unidirectional Carbon Fiber Reinforced Plastic Composite Plates with The HSS Drill Bit Using Analytic Hierarchy Process

The present state of competition within the plastic composite industry calls for efficiency to be competitive. However, in the drilling of carbon-fiber-reinforced plastic (CFRP) composites, the process engineer still lacks knowledge of the priority of parameters as parameters are chosen at random, and resources are deployed without justification on their importance and strength. Consequently, production crises and productivity losses persist. In this article, the analytic hierarchy process (AHP) method is deployed to evaluate the weights of criteria in a CFRP composite drilling operation. The establishment of the decision, alternatives, and criteria is accomplished, and pairwise comparisons are conducted to allow the computation of the importance weight of each criterion. The weight is then established. The proposed approach was illustrated with experimental data from the literature with a plastic drilling case. Six criteria were chosen as crucial in determining the drilling parameters of CFRP composites. The results reveal the following: thrust force (0.413), torque (0.253), eccentricity (0.151), surface roughness (0.115), delamination at entry (0.037) and delamination at exit (0.030). In a validation exercise to ascertain the consistency of the analysis, a consistent analysis was obtained. The novelty of the article is using the AHP approach on the drilling of CFRP composites. Practically, these results impact operator training, indicating that attention should be focused on thrust force control. The industrial applications of CFRP composites include the basic structures of automobiles, ships, and airplanes.

High-frequency vibration effects on the hole integrity in rotary ultrasonic drilling of carbon fiber-reinforced plastic composites

This investigation represented a fundamental research on the potential effects of the high-frequency vibration on the hole integrity involved in rotary ultrasonic drilling (RUD) of carbon fiber-reinforced plastic (CFRP) composites. It was found the increased thickness of the CFRP plate shrunk the flowing velocity of the coolant, which brought about the residual chippings gradually accumulated at the radial clearance between the tool and the material. Furthermore, the chipping accumulation at the clearance seriously increased the friction effects and the resultant thermal load, thus leading to the chipping adhesions on the tool surface and machined cylinder jamming at the central hole of the tool. The mutual constrain between two vertical bundles brought the delamination around the holes generated in conventional drilling (CD) process to a termination at the bundle interface. The ultrasonic superimposition reduced the thrust force of the diamond tool which provided inadequate energy for the delaminated fibers reaching the bundle interface. Moreover, hole position on the two-dimensional orthogonal fabrics significantly influenced the propagation of the delaminated fibers, which weakened the effects of the drilling parameters on the delamination dimensions. Additionally, superimposing an ultrasonic vibration prolonged the abrasive trajectories and increased their overlapping probability, and the induced smoothing effects resulted in the obvious reduction of the surface roughness. The tensile stress exerted on the margin of the machined surface was responsible for the initiation of the CD delamination. After the delaminated fibers reached the bundle interface, the further extrusion of tool brought about the margin suffered from the shear stress, thus leading to the collapse of the machined cylinder. Considering the thrust force of the diamond tool and the undrilled thickness of the machined surface, the critical conditions of the delamination initiation were developed, which revealing that the decreasing of the thrust force caused the reduction of the critical undrilled thickness.

Development of Unidirectional CFRP Reinforced Aluminum Bumper Reinforcement

<div class="section abstract"><div class="htmlview paragraph">Since bumper reinforcements are positioned at front/rear ends of vehicles, weight reduction of the bumper reinforcements enhances vehicle dynamic performance by reducing a yaw moment of inertia. CFRP (Carbon Fiber Reinforced Plastic) composites are attractive lightweight materials due to their excellent specific strength and rigidity. However, because of their relatively high cost, applications of CFRP materials to vehicle structural parts are limited. In this study we have developed a lightweight, structural part, which consists of a thin-walled Al (Aluminum) bumper reinforcement with a UD (Unidirectional)-CFRP sheet. The intention is to prevent an increased part cost by reducing the amount of Al and by minimizing the amount of CFRP. Compared to Al, UD-CFRP sheets have even higher tensile strength and modulus. When vehicles crash, bumper reinforcements may be subjected to bending force. If a UD-CFRP sheet is adhered on the tensile side of an Al bumper reinforcement, not only Al thickness on the tensile side, but also thickness on the compression side can be reduced due to movement of the bending neutral axis. In this design with a multi-material structure, bending strength of the developed part can’t be predicted by a full plastic moment which could normally be used to predict metal parts’ bending strength under large deformation. We employed a novel cross-section design method which can be used to predict bending strength of CFRP reinforced metal structures under large deformation. To validate the calculation method, three-point bending tests on the parts were carried out. Experimental data of bending strength were in the range of predicted bounds. Also, in order to launch the developed part, robustness of part’s performance was evaluated. Finally, the part was adapted to the rear bumper reinforcement of LEXUS RC-F. The part weight is 11 % lighter compared to the conventional, all-Al, bumper reinforcement.</div></div>

A micromechanical model of carbon fiber-reinforced plastic and steel hybrid laminate composites

The fracture strain of carbon fiber-reinforced plastics (CFRPs) within CFRP/steel hybrid laminate composites is reportedly higher than that of CFRPs due to transverse compressive stress induced by the steel lamina. A micromechanical model was developed to explain this phenomenon and also to predict the mechanical behavior of CFRP/steel hybrid laminate composites. First, the shear lag theory was extended to calculate stress distributions on fibers and matrix material in a CFRP under multiaxial stress condition, considering three deformation states of matrix (elastic and plastic deformation and fracture) and the transverse compressive stress. Then, the deformation behavior of CFRP was predicted using average stress in the ineffective region and the Weibull distribution of carbon fibers. Finally, the mechanical properties of CFRP/steel hybrid laminate composites were predicted by considering the thermal residual stress generated during the manufacturing process. The micromechanical model revealed that increased transverse compressive stress decreases the ineffective lengths of partially broken fibers in the CFRP and results in increased fracture strain of the CFRP, demonstrating the validity of the current micromechanical model.

Experimental and numerical studies of the open-hole compressive strength of thin-ply CFRP laminates

Thin prepregs with thickness of less than 0.06 mm support flexible lamination design because it is possible to apply various stacking sequences. The objective of this study is to elucidate the effects of the layer thickness and stacking sequence on the open-hole compressive (OHC) strength for thin-ply carbon fiber reinforced plastic composite (CFRP) laminates. Details of layer thickness and stacking sequence effects on the OHC strength for the thin-ply CFRP laminates were evaluated experimentally. Furthermore, finite element analyses incorporating Hashin’s 2-D failure criteria and a cohesive zone model were conducted to evaluate the damage progression behavior. Results demonstrated that the numerical model was useful for predicting the OHC strength of thin-ply CFRP laminates with various stacking sequences.

Ultrasonic machining of carbon fiber–reinforced plastic composites: a review

Carbon fiber–reinforced plastic (CFRP) composites are extensively being applied in manufacturing sectors because of their extraordinary characteristics. However, CFRP composites often require some extra machining processes to improve the dimensional accuracy and component integrity of CFRP composites in manufacturing industries. The ultrasonic machining (USM) process progressively has been examined due to its greater ability in machining difficult to cut, brittle, and hard materials such as CFRP composites and due to its relatively low machining cost. Furthermore, USM shows to be a promising process with better surface quality, lower cutting force, less or no fiber fracture, laminate delamination, and lower tool wear rate. Recently, USM has been extensively investigated by many researchers for the machining of CFRP composites. This paper explores the literature and presents a comprehensive review of the advances in USM of CFRP composites by classifying the studies reported in two perspectives. First, the review summarizes most of the reported studies starting from 2011 to 2020 based on the applied USM process, equipment/system/platform used to carry out experiments, considered process parameters and output variables, and challenges investigated or gap filled. Then, the reported studies are summarized considering the type of USM process variant, CFRP composite, adopted process parameters on machining characteristics, and their respective results and conclusions. The aim is to present the current research status in USM of CFRP composites and thus provide guidance and foundation for future research.