Carbon Fiber Reinforced Polymer Composites Research Articles

Enhanced mechanical performance and damping behavior of CFRP composites through exfoliated MWCNT functionalization

In evaluating high-performance multiwall carbon nanotube (MWCNT) based carbon fiber composites, effective chemical functionalization of fillers for sufficient exfoliation and precise interface interactions with resin matrix are challenging to attain due to significant interlayer cohesive energy and inactive surfaces of composites. Herein, we demonstrate an effective way to produce carbon fiber-reinforced polymer (CFRP) composite with amended interfacial characteristics via incorporation of MWCNT through oxidation followed by silane functionalization with their exfoliation levels (0/48/60/72 h). The surface functional elements, morphological changes, elemental groups, quantitative information, and thermal degradation of silane functionalized MWCNTs were characterized by FESEM/HR-TEM, XRD, UV, and TG-DTA analysis, respectively. The influence of silane functionalized MWCNT reinforcement on CFRP's mechanical properties were examined using tensile, flexural, ILSS, and damping behavior was analyzed through impulse excitation technique (IET). The resulting silane-modified MWCNTs with 60 h oxidation (OAC-60) infused CFRP demonstrated significant enhancement in flexural strength (73.8%), tensile strength (58.2%), interlaminar shear strength (28.5%) compared to pure-CFRP.

An interlaminar fatigue damage model based on property degradation of carbon fiber-reinforced polymer composites

Interface delamination is a significant damage mechanism in fiber-reinforced polymer (FRP) laminated composites caused by interlaminar normal and shear stresses. This is due to the low interlaminar properties including interface stiffness and strength that continuously degrade to cause fatigue crack nucleation and growth. In this respect, an interlaminar fatigue damage model is proposed to accurately address the reliability aspect of the FRP composite materials and structures. The model considers a damage process that consists of two stages: (1) fatigue damage evolution due to interlaminar properties degradation to the onset of crack nucleation. A cyclic cohesive zone model with a bilinear softening behavior is introduced along with the fatigue life model to capture the mean stress effect of the interface. This is followed by (2) the crack nucleation process leading to the physical separation/debonding of the interface material point, as governed by the cycle-dependent fracture energy dissipation. The mechanical prediction of the interlaminar fatigue damage process is illustrated through finite element simulation of a mixed-mode flexural test of a carbon fiber-reinforced polymer (CFRP) composite beam subjected to fatigue loading. The results indicate that the interlaminar normal and shear crack opening displacement increases exponentially with the larger number of load cycles. In addition, the high-stress gradient is limited to the interface crack front zone with the normal and shear stress peaks at 69.2 and 16.5 % of the respective interlaminar strength. Moreover, controlled interlaminar crack growth is initially foreseen at 7.0 × 10-6 mm/cycle, followed by an abrupt crack “jump” at 287,000 load cycles.

Upcycling of Carbon Fiber/Thermoset Composites into High‐Performance Elastomers and Repurposed Carbon Fibers

AbstractRecycling of carbon fiber‐reinforced polymer composites (CFRCs) based on thermosetting plastics is difficult. In the present study, high‐performance CFRCs are fabricated through complexation of aromatic pinacol‐cross‐linked polyurethane (PU−AP) thermosets with carbon fiber (CF) cloths. PU−AP thermosets exhibit a breaking strength of 95.5 MPa and toughness of 473.6 MJ m−3 and contain abundant hydrogen‐bonding groups, which can have strong adhesion with CFs. Because of the high interfacial adhesion between CF cloths and PU−AP thermosets and high toughness of PU−AP thermosets, CF/PU−AP composites possess a high tensile strength of >870 MPa. Upon heating in N,N‐dimethylacetamide (DMAc) at 100 °C, the aromatic pinacols in the CF/PU−AP composites can be cleaved, generating non‐destructive CF cloths and linear polymers that can be converted to high‐performance elastomers. The elastomers are mechanically robust, healable, reprocessable, and damage‐resistant with an extremely high tensile strength of 74.2 MPa and fracture energy of 149.6 kJ m−2. As a result, dissociation of CF/PU−AP composites enables the recovery of reusable CF cloths and high‐performance elastomers, thus realizing the upcycling of CF/PU−AP composites.

Upcycling of Carbon Fiber/Thermoset Composites into High-Performance Elastomers and Repurposed Carbon Fibers.

Recycling of carbon fiber-reinforced polymer composites (CFRCs) based on thermosetting plastics is difficult. In the present study, high-performance CFRCs are fabricated through complexation of aromatic pinacol-cross-linked polyurethane (PU-AP) thermosets with carbon fiber (CF) cloths. PU-AP thermosets exhibit a breaking strength of 95.5 MPa and toughness of 473.6 MJ m-3 and contain abundant hydrogen-bonding groups, which can have strong adhesion with CFs. Because of the high interfacial adhesion between CF cloths and PU-AP thermosets and high toughness of PU-AP thermosets, CF/PU-AP composites possess a high tensile strength of >870 MPa. Upon heating in N,N-dimethylacetamide (DMAc) at 100 °C, the aromatic pinacols in the CF/PU-AP composites can be cleaved, generating non-destructive CF cloths and linear polymers that can be converted to high-performance elastomers. The elastomers are mechanically robust, healable, reprocessable, and damage-resistant with an extremely high tensile strength of 74.2 MPa and fracture energy of 149.6 kJ m-2. As a result, dissociation of CF/PU-AP composites enables the recovery of reusable CF cloths and high-performance elastomers, thus realizing the upcycling of CF/PU-AP composites.

Structural performance of RC beams strengthened with hybrid bonded CFRP

Debonding at the interface between externally-bonded (EB) carbon fiber-reinforced polymer (CFRP) composites and the concrete limits the performance of CFRP-strengthened reinforced concrete (RC) beams. To mitigate the interface debonding and improve the material utilizing efficiency of CFRP, a hybrid-bonding (HB) technique was developed. HB CFRP system combines the adhesive bonding and mechanical fastening (i.e., anchoring the CFRP plate through bolted cover steel plate bonded on the surface of the CFRP plate). When interfacial debonding occurs, the friction between the steel cover plate and the CFRP plate and the reacted normal stress at the interface enhanced d the concrete aggregates interlocking and the bond strength of CFRP-to-concrete interface. Additionally, the normal stresses can be also activated through pre-tightening the anchors. Five HB CFRP-strengthened RC beams, two conventional EB CFRP-strengthened RC beams, and two un-strengthened RC beams were tested. Two different steel cover plates lengths and three different pre-tightening torques were adopted. The test results demonstrated that the HB technique improved the local bond behavior in the anchored regions, resulting in higher strength utilization efficiency of CFRP and increased load-carrying capacity of the strengthened beams. Such improvement was more significant when longer steel cover plates and higher pre-tightening torques were deployed.

Cryogenic thermal conductivity of carbon fiber reinforced polymer composite laminates

Carbon fiber reinforced polymer (CFRP) composites with excellent mechanical properties and low thermal conductivity are promising materials for cryogenic facility support structures. However, the temperature dependence and stacking sequence dependence of the laminates’ thermal conductivities challenge their thermo-mechanical design. Previous work dealing with the cryogenic thermal conductivity of laminates was relatively inadequate, and the effect of stacking sequence has not been sufficiently clarified. Herein, the cryogenic thermal conductivity of CFRP composite was investigated, and a theoretical model for the out-of-plane thermal conductivity of laminate was developed. To this end, the thermal conductivities of epoxy resin and laminates were measured at temperatures from 20 K to 293 K. The cryogenic thermal conductivity of carbon fiber was then extrapolated. Subsequently, a theoretical model was developed based on the thermal-electrical analogy method to evaluate the effect of stacking sequence. The obtained model was then validated by numerical analysis and experimental work. Lastly, the effects of lay-up angles and component properties on out-of-plane conductivity were examined. The test results suggested longitudinal thermal conductivity of composites exhibiting significant temperature dependence, with a decreasing trend recorded from 6.317 Wm−1K−1 to 0.355 Wm−1K−1 and transverse thermal conductivity decline from 0.626 Wm−1K−1 to 0.156 Wm−1K−1. The theoretical analysis indicated that the stacking sequence could reduce the out-of-face thermal conductivity by up to approximately 6.5 %, while the lay-up angle did not show any influence. In sum, novel insights into the cryogenic thermal conductivity of CFRP composites were provided, with guidance for the design and analysis of CFRP composites in cryogenic applications.

First study of quantitative relationship between electric polarization and electromagnetic interference (EMI) shielding effectiveness of CFRP

This study investigates the electric polarization, including direct current (DC) and alternating current (AC), and electromagnetic interference (EMI) shielding capabilities within the microwave range (2.5–3.9 GHz) of cross-ply continuous carbon fiber-reinforced polymer (CFRP) composites, constructed by stacking prepreg composites. The DC conductivity of CFRP was evaluated using a multimeter, while the AC relative permittivity was measured with electronic test equipment (LCR meter). To describe the relationship between shielding effectiveness and polarization behavior, the EMI shielding of CFRP was assessed using the waveguide method, presenting a quantitative description of this relationship for the first time. Results indicate a decrease in DC conductivity with increasing specimen thickness due to increasing defects. Conversely, AC permittivity increases with specimen thickness, attributed to a rise in charged carriers and associated carrier-atom interactions. Skin depth δ, at a given thickness, follows a trend of initial decrease and subsequent increase with rising frequency; at a given frequency, it increases with decreasing specimen thickness. The interaction between CFRP and radiation is primarily reflective, with the reflection coefficient being much higher than the absorption coefficient across the frequency range, escalating with specimen thickness. Shielding effectiveness (SET) and absorption loss (SEA) display an initial increase followed by a decrease with rising frequency, whereas reflection loss (SER) sees a slight increase. For the smallest thickness, SEA per unit thickness exceeds 3120 dB/m and 7960 dB/m using specimen and carbon thickness, respectively. The absorption loss predominantly arises from the interaction of the electric field with electric dipoles formed by carrier-atom interaction at defects.

Analyzing the Tensile Strength of Carbon Fiber-Reinforced Epoxy Composites Using LabVIEW Virtual Instrument

Carbon fiber-reinforced polymer composites are widely used materials in the aircraft industry, automotive sector, marine applications, civil engineering, and daily consumer goods, due to their superior mechanical properties at a relatively low density compared to metallic materials. The studied composites are composed of an epoxy resin matrix in which three layers of carbon fiber fabric are embedded, oriented at 0 and 90 degrees. Carbon fiber-reinforced polymer composites were manufactured using the Vacuum Assisted Resin Transfer Molding technique. The tensile failure mechanism in carbon fiber-reinforced polymer composites is an extremely complex phenomenon influenced by numerous factors. This study aims to evaluate the mechanical behavior of carbon fiber-reinforced composites through tensile testing and to compare experimentally obtained results with those calculated using the mixture rule. Additionally, the behavior of the materials under tensile stress was analyzed using the digital image correlation method. Estimating mechanical properties based on the mixture rule is a common practice in the design phase of polymer composites. This study s novelty and originality lie in its anticipation of the tensile strength and modulus of elasticity of the studied composites. This anticipation was achieved using a virtual instrument developed in the LabVIEW graphical programming environment. The experimentally obtained results for the tensile characteristics of the studied materials are suitable for this type of composite. These results were compared with estimates derived from the mixture rule, and the absolute error was determined.

Variable orientation in material extrusion of short carbon fiber reinforced polymer composites with high thermal conductivity

Controllable orientation architecture possesses tunable thermal behavior for effective heat dissipation in unidirectional product fields, meanwhile without interference with adjacent components. Herein, we proposed a variable orientation strategy in material extrusion of short carbon fiber (SCF) reinforced polymer composites framework with spatially tunable thermal properties. It was achieved due to the following reasons: (Ⅰ) Inherent shear flow in the nozzle; (Ⅱ) Increasing tensile flow by changing the ratio between the printing speed of monofilament and the feeding speed of filament (Vp/f); (Ⅲ) Further surface tension due to thinning monofilament by varying Vp/f. The SCF with different orientations and content reinforced polyether-ether-ketone (PEEK) composites were successfully fabricated. The microcosmic orientation of SCF could be programmed from a three-layer hierarchical framework to a single-layer oriented framework at different Vp/f. Benefit from variable orientation, the through-plane thermal conductivity of SCF/PEEK composites achieved a thermal conductivity enhancement of 173.9 %. In addition, the simulated application of SCF/PEEK composites in the CPU of the computer showed excellent heat transfer during heating. Further, the thermal conductivity mechanism of the synergistic influence between Vp/f and SCF content was analyzed by cross-sectional microstructure. The proposed strategy in this work for fabricating variable orientation of SCF reinforced polymer composites showcases great application prospects in electronic devices and unidirectional product fields.

High-strength carbon fiber-reinforced polyether-ether-ketone composites with longer fiber retention length manufactured via screw extrusion-based 3D printing

The mechanical properties of 3D-printed carbon fiber-reinforced polymer composites play a pivotal role in engineering applications. However, the preparation of high-performance composites through material extrusion remains a great challenge. In this study, four fiber-reinforced polyether-ether-ketone (CF/PEEK) composites with varying fiber lengths were manufactured by a homemade screw extrusion 3D printer and evaluated for their application potential. A systematic exploration was conducted on the influence of fiber length and annealing on the mechanical performance of samples. The results demonstrated that increasing fiber length and annealing enhanced the tensile and flexural strengths of components while diminishing impact strength and ductility. With an average fiber retention length of 209 μm, the annealed parts displayed exceptional tensile and flexural strengths of 169.8 MPa and 223.3 MPa, respectively, marking a 143% and 88% improvement over unannealed pure PEEK. Longer fiber retention length, higher crystallinity, and fewer internal flaws contribute to the improved mechanical performance of the samples. This study provides a broader scope for the preparation and application of 3D-printed high-performance composites.

Enhancing the Longitudinal Compressive Strength of Freeform 3D-Printed Continuous Carbon Fiber-Reinforced Polymer Composite Laminate Using Magnetic Compaction Force and Nanofiber Z-Threads.

Low fiber-direction compressive strength is a well-recognized weakness of carbon fiber-reinforced polymer (CFRP) composites. When a CFRP is produced using 3D printing, the compressive strength is further degraded. To solve this issue, in this paper, a novel magnetic compaction force-assisted additive manufacturing (MCFA-AM) method is used to print CFRP laminates reinforced with carbon nanofiber (CNF) z-threads (i.e., ZT-CFRP). MCFA-AM utilizes a magnetic force to simultaneously levitate, deposit, and compact fast-curing CFRP prepregs in free space and quickly solidifies the CFRP laminate part without any mold nor supporting substrate plate; it effectively reduces the voids. The longitudinal compressive test was performed on five different sample types. ZT-CFRP/MCFA-AM samples were printed under two different magnetic compaction rolling pressures, i.e., 0.5 bar and 0.78 bar. Compared with the longitudinal compressive strength of a typical CFRP manufactured by the traditional out-of-autoclave-vacuum-bag-only (OOA-VBO) molding process at the steady-state pressure of 0.82 bar, the ZT-CFRP/MCFA-AM samples showed either comparable results (by -1.00% difference) or enhanced results (+7.42% improvement) by using 0.5 bar or 0.78 bar magnetic rolling pressures, respectively.

Laser Three-Dimensional incremental Multi-Routine interval scanning for quantitative removal of CFRP: Defect Analysis, ablation mechanism and strategy optimization

Deliberating on the necessity for precise removal of impaired sectors within the realm of aerospace industry's composite material rehabilitation, a novel method is proposed using a nanosecond laser to achieve quantitative removal of carbon fiber reinforced polymers (CFRP) via the three-dimensional incremental multi-routine interval scanning (3D-IMRIS). This study for the first time establishes a finite element simulation of multi-routine laser machining CFRP considering anisotropy, which aims at combining experiments and numerical simulation to analyze the ablation mechanism of CFRP in different modes, and optimize the removal strategy. The results reveal that the processing defects mainly consist of fiber expansion and thermal damage. This expansion can be attributed to the reconfiguration of carbon atoms in the fibers exhibiting a low level of graphitization, induced by transient heating and high-temperature gradients caused by laser interaction. In addition, the primary removal mechanisms for CFRP composites are photothermal ablation and thermo-mechanical peeling effect. The 3D-IMRIS mode effectively addresses the challenge of heat accumulation during laser processing by redirecting it towards heat utilization, resulting in a remarkable 94.2% reduction in the overall back Heat-Affected Zone (HAZ). Furthermore, the optimized scanning strategy increased material removal efficiency by 308.7% during 32 repeated scans, while the micro surface defects are also less.

A Comprehensive Study on the Optimization of Drilling Performance in Hybrid Nano-Composites and Neat CFRP Composites Using Statistical and Machine Learning Approaches

Carbon fiber-reinforced polymer (CFRP) composites have gradually replaced metals due to their exceptional strength-to-weight ratio compared to metallic materials. However, the drilling process often reveals various defects, such as surface roughness, influenced by different drilling parameters. This study explores the drilling quality of uni-directional CFRP composites, as well as hybrid Al2O3 alumina and hybrid SiC silicon carbide nano-composites, through experimental exploration using step, core, and twist drills. Response surface methodology (RSM) and statistical tools, including main effect plots, ANOVA, contour plots, and optimization techniques, were used to analyze the surface roughness of the hole. Optimization plots were drawn for optimal conditions, suggesting a spindle speed of 1500 rpm, feed of 0.01 mm/rev, and a 4 mm drill diameter for achieving minimum surface roughness. Furthermore, two machine learning models, artificial neural network (ANN) and random forest (RF), were used for predictive analysis. The findings revealed the robust predictive capabilities of both models, with RF demonstrating superior performance over ANN and RSM. Through visual comparisons and error analyses, more insights were gained into model accuracy and potential avenues for improvement.

Surface Quality Related to Face Milling Parameters in 3D Printed Carbon Fiber-Reinforced PETG

Three-dimensional printing technology holds significant potential for enhancing the flexibility and cost-efficiency of producing carbon fiber-reinforced polymer composites (CFRPs). However, it faces limitations such as challenges in achieving high surface qualityand precise dimensional accuracy and managing the distinctive anisotropic mechanical properties that it demonstrates. This study aims to explore the machinability of 3D printed PETG infused with 20% short carbon fiber and to assess the resulting surface roughness and burr formation. Employing a Design of Experiments (DoE) approach, three factors were considered: rotational speed, feed rate, and depth of cut. These factors were tested at varying levels—rotational speeds of 3000, 5500, and 8000 rpm; feed rates of 400, 600, and 800 mm/min; and depth of cut values of 0.2, 0.4, 0.6, and 0.8 mm. The evaluation of machinability relied on two key response parameters: surface roughness (Sa) determined from the milled surface and burr height measured on both sides using a roughness meter. The findings revealed a significant influence of milling parameters on both roughness and burr formation. However, the ideal conditions for minimizing roughness and reducing burr formation did not align. Furthermore, a comparative analysis was conducted between these results and the machinability of PETG under similar conditions.

Mitigating Crack Propagation in Hybrid Composites: An Experimental and Computational Study

The exceptional properties of carbon nanotubes (CNTs) make them ideal nanofillers for various composite materials. In carbon fiber-reinforced polymer (CFRP) composites. CNTs can be grown on the carbon fiber surface to act as a third interface between the fiber and the matrix. However, it was established that the uncontrolled random growth of CNTs could exacerbate delamination in composite structures. Thick nanofiller films could hinder the epoxy from seeping into the carbon fiber, resulting in insufficient interlaminar strength. Hence, the density and distribution of nanofillers play a crucial role in determining the hybrid composite fracture mechanisms. In this investigation, CNTs were grown using the low-temperature technique into specific patterns over carbon fibers to discern their derived composites’ fracture properties. The composite fracture energy release was probed using a double cantilever beam (DCB) test setup and digital image correlation (DIC) to monitor interlaminar crack propagation. A standard finite element simulation model based on the cohesive zone method (CZM) was also utilized to delineate fracture behaviors of the various composite configurations. Results conclude that a coarser pattern of CNT growth enhances resistance to crack propagation, thus improving the interlaminar fracture toughness of a composite structure.

Fatigue behavior of symmetric and asymmetric carbon and basalt fiber-reinforced polymer composites in transverse loading

Fatigue behavior of symmetric and asymmetric carbon and basalt fiber-reinforced polymer composites in transverse loading

Semantic segmentation of progressive micro-cracking in polymer composites using Attention U-Net architecture

The present study delivers a methodology for investigating the gradual damage development in a carbon fibre-reinforced cross-ply polymer composite during a sequence of thermo-mechanical loadings with the help of X-ray computed tomography. The procedure allows an in-depth analysis of the occurrence and nature of the multiple cracks that form within layers oriented perpendicular, or transverse, to the loading direction. This is achieved by using Attention U-Net architecture for semantic segmentation of the transverse cracks. The model shows promising results, through an ability to identify all the transverse cracks and reflect the damage progression. The described method provides a robust routine for analysing challenging polymer composite tomographic datasets.

Low-frequency vibration assisted self-pierce riveting (LV-SPR) of carbon fiber reinforced composite and aluminum alloy

Self-pierce riveting (SPR) has been widely applied to join carbon fiber-reinforced polymer (CFRP) composites and high-strength metallic plates in the automotive and aerospace fields. However, the CFRP is often damaged by rivet piercing owing to its brittleness as well as the relatively small interlocking that forms between the rivet leg and high-strength plate owing to the hard deformation characteristics. Therefore, in this study, a novel low-frequency vibration-assisted self-pierce riveting (LV-SPR) technology is proposed, which utilizes the vibration effect in softening the metal and reducing interfacial friction at room temperature. In riveting experiments involving CFRP and 5052 aluminum alloy utilizing 37Cr4 semi-hollow rivets, LV-SPR exhibited a significant reduction of 68.2% in the riveting force compared to the traditional SPR process. The decreased riveting pressure in LV-SPR effectively mitigated the CFRP damage by 36.2%, which was caused by a reduction in the interfacial friction force between the rivet and CFRP laminate. Moreover, owing to the improved deformation capacity of the rivet and alloy plate by the vibration softening effect, the lateral expansion of the rivet leg in the aluminum alloy was enlarged by 36.4% compared to that using the traditional self-piercing riveting (T-SPR) process. Microscopic characterization revealed that vibrations notably promoted grain refinement and enlarged the subgrain structures of the rivets and alloy plates. Finally, by superposing oscillations, the shear strength of the connection joint increased by 13.5% compared to the T-SPR joint. The proposed LV-SPR was validated as an effective technique to increase the connection strength of high-performance plates, which can efficiently improve the structural safety and promote the widespread application of CFRP/alloys in automobiles and aircrafts.

Mechanical recycling of carbon fibre reinforced polymers. Part 1: influence of cutting speed on recycled particles and composites properties

ABSTRACT Scientific advances and technological requirements to develop carbon fibre-reinforced polymers (CFRP) with excellent strength-to-weight ratios led to the high consumption of CFRP composites. The mechanical recycling of CFRP is a simpler, more economical, and environmentally responsible solution for effectively recovering this structural material that contains epoxy resin and carbon fibre. CFRP laminates were placed on a Computer Numerical Control (CNC) and milling cutting at 1100, 1800, and 2500 rpm. The recovered CFRP particles were mixed with acrylonitrile butadiene styrene (ABS) using the melt intercalation approach. Recovered CFRP particles increased the molecular mobility and reduced the thermal stability of ABS. The main differences between the ABS and the composites were a more pronounced necking region in the ABS than in the composites and a notable reduction in strain. The strain of the ABS was 27.58%, while in the composites, it was 4.29, 4.02, and 3.51%, depending on the cutting speed. Thus, ductility decreased up to 87% in the composites. This work’s successful CFRP mechanical recycling method provides epoxy powder, individual carbon fibres, and CFRP particles, opening a research field of great economic and environmental relevance in developing new materials.

Influence of fibre steering on the bearing performance of bolted joints in 3D printed pseudo-woven CFRP composites

Aiming to improve the bearing performance of bolted joints in carbon fibre reinforced polymer (CFRP) composites, this study investigates the impact of steered fibre paths around the hole edge within pseudo-woven (interlaced) composites that are manufactured by 3D printing. The influence of fibre steering on the crack initiation and propagation was examined through double-lap bearing tests performed on four distinct cases. Parallel to the comprehensive experimental study, digital image correlation (DIC) and X-ray computed microtomography (micro-CT) scans were performed to aid in understanding and identifying the various damage mechanisms in each specimen type. Results revealed that different patterns provided varying bearing abilities, with an employed pattern improving the initial bearing strength, initial fracture energy and ultimate fracture energy of the 3D printed pseudo-woven composite by 23.5%, 363.7% and 29.6%, respectively. Consequently, fibre steering in composites is found to be a promising method to tailor the bearing behaviour of bolted joints as required.