Advanced Carbon Fiber Reinforced Composite Materials

Composite booms for solar sails have been prototyped by using innovative smart materials. Shape memory polymer composites (SMPCs) have been manufactured by interposing SMP layers between carbon-fiber-reinforced (CFR) plies. A polyimide membrane has been embedded into the CFR-SMPC frame of the sail during lamination. The sail’s size has been limited to 250 × 250 mm² to allow its testing on Earth. The feasibility of large sail deployments has been shown by prototyping small CFR-SMPC elements to insert only in the folding zones. Numerical simulation by finite element modeling allowed for predicting the presence of wrinkles close to the frame’s vertexes in the cases of large sails under solar radiation pressures. Nevertheless, the frame’s configuration, with SMPC booms at all the edges of the sail membrane, seems to be suitable for drag sails instead of propulsion. On-Earth recovery tests have been performed on 180° folded sails by using flexible heaters. After an initial induction time, the maximum rate was reached with a following drop. In the case of two heaters per folding zone, the angular recovery rate reached the maximum value of about 30 deg/s at the power of 34 W, and full recovery was made in 20 s. Full article

The aim of this study was to characterise the microstructural organisation of staple carbon fibre-reinforced polymer composites and to investigate their mechanical properties. Conventionally, fibre-reinforced materials are manufactured using continuous fibres. However, discontinuous fibres are crucial for developing sustainable structural second-life applications. Specifically, aligning staple fibres into yarn or tape-like structures enables similar usage to continuous fibre-based products. Understanding the effects of fibre orientation, fibre length, and compaction on mechanical performance can facilitate the fibres’ use as standard engineering materials. This study employed methods ranging from microscale to macroscale, such as image analysis, X-ray computed tomography, and mechanical testing, to quantify the microstructural organisations resulting from different alignment processing methods. These results were compared with the results of mechanical tests to validate and comprehend the relationship between fibre alignment and strength. The results show a significant influence of alignment on fibre orientation distribution, fibre volume fraction, tortuosity, and mechanical properties. Furthermore, different characteristics of the staple fibre tapes were identified and attributed to kinematic effects during movement of the sliver alignment unit, resulting in varying tape thicknesses and fuzzy surfaces. Full article

The integration of mesoscale modeling and macroscale experimentation has emerged as a promising approach for understanding and predicting the mechanical behavior and fatigue performance of fiber-reinforced polymer composites. In this work, the mean field homogenization technique is implemented to predict the fatigue performance of the carbon-fiber-reinforced polymer composites under cyclic loading conditions. To predict the number of fatigue cycles, Modified Gerber criteria are used with the stress-based Tsai–Hill failure indicator. Fatigue strength factor (α) and creep rupture strength factor (β) are experimentally evaluated and further implemented in a computational approach to predict fatigue life cycles of the composite. The effect of composite constituents, stress ratio, and loading direction are investigated in detail against the fatigue performance of the composite. Fatigue cycles are predicted at individual matrix and fiber levels at various stress ratios of 0.2, 0.4, 0.6, and 0.8 at different loading inclinations. The experimental results are compared with the mesoscale S–N curves. Full article

This study improved homemade apparatus for characterizing the interfacial shear strength (IFSS) of carbon-fiber-reinforced polyphenylene sulfide (PPS/CF) composites. The upgraded generation II experimental device includes a newly developed experimental clamp for samples, as well as testing systems. Compared with the initial generation I apparatus and the commercial Toei instrument, the generation II device is easier and more efficient to operate. The average interfacial adhesion values obtained using these devices were consistently approximately 40 MPa, with relatively low data scatter, showing excellent repeatability and applicability during microbond tests. Notably, the generation II experimental device was equipped with an additional high-frequency data-capturing tool to identify the debonding peak force more precisely, which demonstrated a higher interfacial shear strength of 42.81 MPa during testing. Therefore, the new instrument was able to reflect the change in the interfacial stress state during the interface debonding process more accurately and reliably. Full article

Self-structural health monitoring (SHM) functionalities for fiber-reinforced polymer composites have become highly sought after to ensure the structural safety of newly advancing components in the automotive, civil, mechanical, and aerospace industries. This paper introduces a self-damage detection and memory (SDDM) hybrid composite material, where the structural carbon fiber tow is transformed into a piezoresistive sensor network, and the structural glass fiber operates as electrical insulation. In this study, SDDM specimens were fabricated, and tensile and impact tests were performed. The tensile tests of SDDM specimens find two distinct loading peaks: first where the carbon fiber fails, and second where the glass fiber fails. A linear correlation was observed between the carbon fiber resistance and composite strain up to a threshold, beyond which a sharp nonlinear increase in resistance occurred. The resistance then approached infinity, coinciding with the first loading peak and failure of the carbon fiber elements. This demonstrates the potential for a damage early warning threshold. Additionally, the effect of stitching the sensor tow in a zig-zag pattern over a large area was investigated using tailored fiber placement (TFP) of 1-loop, 3-loop, and 5-loop specimens. Tensile testing found that increasing the number of loops improved the sensor’s accuracy for strain sensing. Furthermore, impact tests were conducted, and as the impact energy progressively increased, the sensor resistance permanently increased. This illustrates a capability for self-memory of microdamage throughout the life cycle of the structure, potentially useful for predicting the remaining life of the composite. Full article

Automated fiber placement (AFP) is a method to manufacture complex composite parts in an automatable and scalable process. Thermoplastic in situ AFP has received more attention in recent years for its use in high-performance, aerospace applications that use low-melting polyaryletherketone (LM-PAEK) composites. Although in situ AFP is a promising technology for the automated and economical manufacturing of composites, the production of a mold is still a considerable expense. Using large-scale additive manufacturing, molds can be manufactured in a short time frame for a fraction of the cost of traditional molds. By using polyamide 6 (PA6), a polymer incompatible with LM-PAEK, a bond can be created, which holds a laminate in the desired form during production and allows for demolding. Due to the thermoplastic nature of PA6, a mold can be manufactured using large-scale, extrusion-based additive manufacturing. This study investigates the suitability of 3D-printed molds composed of PA6 for the AFP of CF/LM-PAEK laminates. To this end, peel tests and shear tests were conducted to investigate the influence of the process temperature, the area of heating and the consolidation pressure on the bond of these incompatible polymers. A shear strength of up to 2.83 MPa and a peel strength of up to 0.173 N·mm⁻¹ were achievable. The principal suitability of PA6 as a mold material for the AFP of CF/LM-PAEK was demonstrated. Full article

The present work aims at studying the effect of the reinforcing fabric areal weight on the mechanical properties of composite laminates in carbon-fiber-reinforced polymers. Three different pre-impregnated 2 × 2 twill weaves, characterized by the different areal weight values of 380, 630, and 800 g/m² were used to produce laminates. These areal weights were selected to represent typical values used in structural application. A hand lay-up technique followed by an autoclave cycle curing was employed to produce the laminates. The desired final thickness of the laminates was obtained by laying-up a different ply number, as a function of the areal weight and thickness of each fabric. Uniaxial tensile and in-plane shear response tests were performed on samples obtained from laminates after curing. Furthermore, the presence of voids in composite materials were detected by performing resin digestion tests. Finally, light optical microscopy and stereomicroscopy analyses allowed observing the different arrangement of the plies in the cross-sections of laminates after curing and evaluating the degree of compaction as a function of the reinforcing fabric used. It was demonstrated that the fabric areal weight significantly affects the mechanical performances of the composite laminates; specifically, the decrease in the areal weight of the twill weave leads to an increase in tensile strength, elastic modulus, and in-plane shear stress, i.e., of about 56.9%, 26.6%, and 55.4%, respectively, if 380 g/m² and 800 g/m² fabrics are compared. These results are crucial for an optimal material selection during the design process for industrial applications and help to better understand composite material behavior. Full article

In the current study, the interlaminar fracture toughness behavior of high-performance carbon fiber-reinforced plastics (CFRPs) modified with Bis-maleimide (BMI) resin was investigated under Mode II quasi-static and fatigue remote loading conditions. Specifically, CFRPs were locally integrated with BMI resin, either nano-modified with graphene nano-platelets (GNPs) or unmodified, using the melt electro-writing process (MEP) technique. Following the modification, two types of CFRPs were manufactured: (a) CFRPs with pure BMI resin and (b) CFRPs with GNP-modified resin. Quasi-static tests demonstrated that the interlaminar fracture toughness properties of both modified CFRPs were significantly improved compared to the unmodified/reference CFRPs. Conversely, fatigue tests were conducted under displacement control, with crack length measurement performed using a traveling microscope. Delamination length and load quantities were measured at specific cycle intervals. The results indicated that both modified CFRPs exhibited enhanced resistance to delamination under Mode II fatigue loading, with earlier crack arrest, compared against the reference CFRPs. Additionally, the CFRPs displayed low healing efficiency (H.E.) after the healing cycle was activated. Overall, this approach shows promise in improving the delamination resistance of CFRPs under Mode II. Full article

To further enrich the side-filling structure system of goaf-retaining roadways and explore the compression reaction mechanism of the composite in the support environment of underground mine roadways, this paper introduces a double-wall hollow composite pier structure (FPRSC structure) that is composed of the fiber-reinforced polymer (FRP) composite and polyvinyl chloride plastic (PVC) as restraint materials and the infill material featured with a high water-to-powder ratio. A total of 16 circular specimens with a diameter and height of 100 mm were tested to explore the axial performance of the combined support structure. The main control variables in the present research included the water-to-cement ratio of the high-water material (e.g., 2:1, 3:1, and 4:1), the thickness of the FRP pipe (i.e., 6 mm and 3 mm), the inner diameter of the PVC pipe (i.e., 29 mm and 22 mm), as well as the thickness of the PVC pipe (1.5 mm and 5 mm). Test results showed that the high-water material was under triaxial stress due to the double-wall tube binding, and the bearing capacity of the composite was higher than that of the single material. Meanwhile, the FPRSC structure exhibited obvious strain-hardening characteristics when the infill material is under the combined constraints of double-wall hollow tubes. Moreover, the ratio of PVC-c, FRP-A, and high-water material with a water–cement ratio of 3:1 shows the best axial mechanical properties. The new composite pier structure with high toughness and strength has wide application prospects in the field of goaf retention in deep underground mines. Full article

Carbon-fiber-reinforced polymer (CFRP) composites are widely used in industries such as aerospace due to their lightweight nature and high strength. However, weak interfacial bonding strength is one of the main problems of resin-based composites. In this study, a prepreg was prepared by melt mixing. By dispersing nanoreinforcement particles in the resin, the interlaminar shear strength of the CFRP was increased by approximately 23.6%. When only 0.5 wt% multiwalled carbon nanotube (MWCNT) was used for reinforcement, scanning electron microscopy (SEM) micrographs showed that cracks were hindered by the MWCNTs during propagation, causing crack deflection. At the same time, the mechanism of MWCNTs pulling out increased the energy required for crack propagation. When only 0.5 wt% graphene oxide (GO) was added, the reinforcement effect was inferior to that of using the same amount of MWCNTs. The laminar structure formed by GO and the resin matrix adhered to the carbon fiber surface, reducing the degree of destruction of the resin matrix, but its hindering effect on crack propagation was weak. When 0.5 wt% of MWCNT and GO mixture was added, the interlayer shear strength increased from 55.6 MPa in the blank group to 68.7 MPa. The laminar structure of GO provided a platform for the MWCNTs to form a mesh structure inside its matrix. At the same time, the tubular structure of the MWCNTs inhibited the stacking of GO, providing better dispersion and forming a synergistic enhancement effect. Full article

In this study, carbon nanotubes (CNTs) are functionalized through diazonium salt reaction to introduce polar groups onto their surfaces. These functionalized CNTs (FCNTs) are added into PPO solutions at different loadings (0 wt%, 0.5 wt%, 1 wt%, 1.5 wt%) and used for electrospinning. The results show that the addition of FCNTs facilitate the production of PPO veils having small fiber diameters. The veils are used as interleaves in CF/EP composite laminates. The Mode I and Mode II interlaminar fracture toughness tests reveal that PPO veils containing 0.5 wt% FCNTs exhibit the optimal toughening. G_ICⁱⁿⁱ and G_IIC have an improvement of approximately 120% and 180% over the untoughened samples, respectively, which is 15% and 26% higher than that of PPO veils containing no CNTs, respectively. The toughening mechanism is also analyzed using scanning electron microscopy (SEM). Full article

Carbon fiber-reinforced plastic (CFRP) has been widely investigated as a reinforcement material to address the corrosion and durability issues of reinforced concrete (RC). To improve the strain of FRP grids, we investigated the effect of single-fiber types, hybrid ratios, and stacking patterns on the strain of the composite materials. Blended fabrics in which different fibers are woven were used to further improve the strain of carbon fibers (CFs). In the blended fabrics, CFs with high tensile strength were mixed with high-strain glass fibers (GFs) or aramid fibers (AFs). Fibers with different mechanical properties were mixed to improve the strain without reducing the tensile strength of the composite materials. The fiber arrangement direction was controlled by CF/GF blended fabric. CFs are arranged in the direction parallel to the tensile load direction with no strength degradation, and GFs are arranged in the direction perpendicular to the increase in strain. Compared to the mechanical properties of the single CF composites, the fabrics obtained via an FRP mixing method proposed in this study showed an increase in the tensile strength by 7% from 568.17 to 608.34 MPa with no strength degradation and an increase in strain by 34% from 0.97% to 1.30%. Full article

Composite materials with carbon and glass fibers in an epoxy matrix are widely used systems due to their excellent mechanical parameters, and machining is a standard finishing operation in their manufacture. Previous studies focused exclusively on the characteristics of the fibers released into the air. This work aimed to analyze the nature of the material waste that remains on the work surface after machining. The dust on the work surface is made up of fibers and a polymer matrix, and due to its dimensions and chemical stability, it is a potentially dangerous inhalable material currently treated as regular waste. The smallest sizes of destroyed carbon fibers were generated during drilling and grinding (0.1 μm), and the smallest glass fiber particles were generated during milling (0.05 μm). Due to their nature, carbon fibers break by a tough fracture, and glass fibers by a brittle fracture. In both cases, the rupture of the fibers was perpendicular to or at an angle to the longitudinal axis of the fibers. The average lengths of destroyed carbon fibers from the tested processes ranged from 15 to 20 µm and 30 to 60 µm for glass fibers. Full article

Recent reports of the release of large numbers of respirable and critically long fiber-shaped fragments from mesophase pitch-based carbon fiber polymer composites during machining and tensile testing have raised inhalation toxicological concerns. As carbon fibers and their fragments are to be considered as inherently biodurable, the fiber pathogenicity paradigm motivated the development of a laboratory test method to assess the propensity of different types of carbon fibers to form such fragments. It uses spallation testing of carbon fibers by impact grinding in an oscillating ball mill. The resulting fragments were dispersed on track-etched membrane filters and morphologically analyzed by scanning electron microscopy. The method was applied to nine different carbon fiber types synthesized from polyacrylonitrile, mesophase or isotropic pitch, covering a broad range of material properties. Significant differences in the morphology of formed fragments were observed between the materials studied. These were statistically analyzed to relate disintegration characteristics to material properties and to rank the carbon fiber types according to their propensity to form respirable fiber fragments. This tendency was found to be lower for polyacrylonitrile-based and isotropic pitch-based carbon fibers than for mesophase pitch-based carbon fibers, but still significant. Although there are currently only few reports in the literature of increased respirable fiber dust concentrations during the machining of polyacrylonitrile-based carbon fiber composites, we conclude that such materials have the potential to form critical fiber morphologies of WHO dimensions. For safe-and-sustainable carbon fiber-reinforced composites, a better understanding of the material properties that control the carbon fiber fragmentation is imperative. Full article

Carbon fiber reinforced polymers (CFRPs) are increasingly used in the aerospace industry because of their robust mechanical properties and strength to weight ratio. A significant drawback of CFRPs is their resistance to formability when drawing continuous CFRPs into complex shapes as it tends to bridge, resulting in various defects in the final product. However, CFRP made from Stretch Broken Carbon Fiber (SBCF) aims to solve this issue by demonstrating superior formability compared to conventional continuous CFRPs. To study and validate the performance of SBCF, a statistical design of the experiment was conducted using three different types of CFRPs in tow/tape form. Hexcel (Stamford, CT, USA) IM7-G continuous carbon fiber impregnated with Huntsman (The Woodlands, TX, USA) RDM 2019-053 resin system, Hexcel SBCF impregnated with RDM2019-053 resin, and Montana State University manufactured SBCF impregnated with Huntsman RDM 2019-053 resin were tested in a multitude of forming trials and the data were analyzed using a statistical model to evaluate the forming behavior of each fiber type. The results show that for continuous fiber CFRP tows forming, Fmax and Δmax do not show statistical significance based on temperature fluctuations; however, in SBCF CFRP tows forming, Fmax and Δmax is dominated by the temperature and geometry has a low statistical influence on the Fmax. The lower dependence on tool geometry at higher temperatures indicates possibly superior formability of MSU SBCF. Overall findings from this research help define practical testing methods to compare different CFRPs and provide a repeatable approach to creating a statistical model for measuring results from the formability trials. Full article

Among the various welding techniques used to bond thermoplastic composites, induction welding stands out as a fast, clean, and contact-free process that shortens the welding time and prevents the weight increase of mechanical fastening, such as rivets and bolts. In this study, we manufactured polyetheretherketone (PEEK)-resin-based thermoplastic carbon fiber (CF) composite materials at different automated fiber placement laser powers (3569, 4576, and 5034 W) and investigated their bonding and mechanical characteristics after induction welding. The quality of the composite was evaluating using various techniques, including optical microscopy, C-scanning, and mechanical strength measurements, and a thermal imaging camera was used to monitor the surface temperature of the specimen during its processing. The results revealed that the preparation conditions of the polymer/carbon fiber composites, such as the laser power and surface temperature, significantly affect the quality and performance of the induction-welding-bonded composites. A lower laser power during preparation resulted in weaker bonding between components of the composite and yielded samples with a lower shear stress. Full article

Microencapsulated phase change materials (MCPCM) as a green energy storage material not only prevent leakage of phase change materials but also increase the heat transfer area of phase change materials. Extensive previous work has shown that the performance of MCPCM depends on the shell material and MCPCM with polymers, as the shell material suffers from low mechanical strength and low thermal conductivity. In this study, a novel MCPCM with hybrid shells of melamine-urea-formaldehyde (MUF) and sulfonated graphene (SG) was prepared by in situ polymerization using SG-stabilized Pickering emulsion as a template. The effects of SG content and core/shell ratio on the morphology, thermal properties, leak-proof properties, and mechanical strength of the MCPCM were investigated. The results showed that the incorporation of SG into the shell of MUF effectively improved the contact angles, leak-proof performance, and mechanical strength of the MCPCM. Specifically, the contact angles of MCPCM-3SG were reduced by 26°, the leakage rate was reduced by 80.7%, and the breakage rate after high-speed centrifugation was reduced by 63.6% compared to MCPCM without SG. These findings suggest that the MCPCM with MUF/SG hybrid shells prepared in this study has great potential for application in thermal energy storage and management systems. Full article

The objective of this study is to prepare CNT/AlSi10Mg composites using mechanical ball milling combined with SPS. The study investigates the influence of ball-milling time and CNT content on the mechanical and corrosion resistance of the composite. This is performed to address the challenge of CNTs dispersion and to understand how CNTs impact the mechanical and corrosion resistance of the composites. The morphology of the composites was characterized using scanning electron microscopy (SEM) transmission electron microscopy (TEM) and Raman spectroscopy, and the mechanics and corrosion resistance of the composite materials were tested. The results demonstrate that the uniform dispersion of CNTs can significantly enhance both the mechanical properties and corrosion resistance of the material. Specifically, when the ball-milling time was 8 h, CNTs were uniformly dispersed in the Al matrix. The CNT/AlSi10Mg composite shows the best interfacial bonding when the mass fraction of CNTs is 0.8 wt.%, with a tensile strength of −256 MPa. This is 69% higher than the original matrix material without the addition of CNTs. Moreover, the composite exhibited the best corrosion resistance. Full article

Self-healing panels were prepared using vinyl ester (VE) and vascular abaca fibers (unidirectional) through the hand lay-up process. Initially, two sets of abaca fibers (AF) were prepared by filling the healing resin VE and hardener and stacking both core-filled unidirectional fibers in a 90° direction to obtain sufficient healing. The experimental results demonstrated that the healing efficiency increased by approximately 3%. SEM-EDX analysis further confirmed the healing process by exhibiting spill-out resin and the respective fibers’ major chemical elements at the damaged site after self-healing. The tensile, flexural, and Izod impact strengths of self-healing panels indicated improved strengths of 7.85%, 49.43%, and 53.84%, respectively, compared with fibers with empty lumen-reinforced VE panels due to the presence of a core and interfacial bonding between the reinforcement and matrix. Overall, the study proved that abaca lumens could effectively serve as healing carriers for thermoset resin panels. Full article

In recent years, numerous studies have explored the benefits of utilizing prestressed carbon fiber-reinforced polymer (CFRP) for strengthening concrete structures. However, research on the reinforcement of prestressed CFRP on full-scale hollow RC box girders, particularly damaged bridges, remains limited. In this study, both experiments and finite element analysis (FEA) were performed to investigate the flexural behavior of full-scale hollow RC box girders with varying degrees of damage, which were strengthened using CFRP with different levels of prestress. The adhesive behavior of the CFRP–concrete interface was considered in the FEA. Numerical simulations were conducted to assess the flexural behaviors of the girders, including failure modes, yield and ultimate loads, and deflections. The results revealed that the application of prestressed CFRP efficiently increased the yield and ultimate loads of the box girders. Specifically, when the degree of damage of the hollow box girder was less than 23%, the flexural bearing capacity of the repaired girder could be recovered after being strengthened with two prestressed CFRP strips measuring 50 mm in width and 3 mm in thickness. However, the risk of premature debonding at the CFRP–concrete interface increased when the prestressing level of CFRP and degree of damage of hollow RC box girders exceeded 35% and 40%, respectively. These findings suggest that the use of prestressed CFRP may be a promising method for repairing damaged hollow RC box girders, but careful consideration of the degree of damage and prestressing level would be necessary to ensure the effectiveness and safety of the repair. Full article

Ultrasonic welding (UW) is a well-established technique for joining thermoplastic composites and has recently been utilized in the aerospace and automotive industries. In the case of thermoset composites (TSCs), a polymer-based material placed at the welding interface called an energy director (ED) is required. The choice of the coupling layer material is linked to several requirements, such as processing temperature, high adhesion to the thermoset composites (TSCs) adherend and mechanical strength of the resulting welded joints. In this work, the authors investigated the possibility of using Poly-vinyl-butyral (PVB) reinforced with graphite nanoplatelets (GNPs) as a coupling layer in the UW of TSC adherents. The effect of GNPs aspect ratio and content on the weldability of carbon fiber-reinforced plastics (CFRP) has been investigated. PVB/GNPs nanocomposites with different filler contents (from 0.5 wt% to 2 wt%) and different aspect ratios (100 and 2100) have been fabricated. The influence of the viscoelastic properties of the flat EDs on weldability has been assessed. Finally, an improvement of lap shear strength (LSS) of 80% was found for nanocomposites with 0.5 wt% of high-aspect-ratio GNPs with respect to neat PVB. The use of high damping nanocomposites as coupling materials for TSCs paves the way for a new generation of EDs in UW. Full article

Carbon-fiber-reinforced epoxy-matrix composite (CFRP) laminates with thin plies have strong damage-resistance properties compared with standard prepregs. The static and fatigue tensile fracture behavior of cross-ply CFRP laminates with thin plies should be further studied to establish the applicability of thin-ply prepregs for industrial structures. In this study, the static and fatigue tensile properties of cross-ply, high-strength polyacrylonitrile (PAN)-based carbon-fiber (T800SC)-reinforced epoxy-matrix composites with thin plies were investigated. The fiber orientations of the CFRP specimens were set to cross-ply with [0/90]_10S (subscript S means symmetry), [(0)₅/(90)₅]_2S, and [(0)₁₀/(90)₁₀]_S. The static and fatigue tensile characteristics of the cross-ply CFRPs with thick plies with [0/90]_2S and [(0)₂/(90)₂]_S were also investigated for comparison. Under static loading, the tensile strength and failure strain of the thinnest 90°-ply-CFRP specimens were more than 5% higher than those of the other 90°-ply-thickness specimens. However, the tensile moduli and Poisson’s ratios were comparable between the cross-ply CFRPs with thin and thick plies. Under fatigue loading, the fatigue responses of the thinnest 90°-ply-CFRP specimens were 3% higher than those of the other 90°-ply-thickness specimens during lower-fatigue-cycle testing (<10⁵ cycles). However, during higher-fatigue-cycle testing (>10⁵ cycles), the fatigue responses decreased, with a decrease in the 90°-ply thickness, and the fatigue characteristics of the thinnest 90°-ply-CFRP specimen were 7% lower than those of the other cross-ply thin- and thick-ply-CFRP specimens. Full article

In this study, the chemical state change of recycled carbon fiber (rCF) surfaces and the mechanism of the oxygen functional groups according to nitric acid treatment at various times and temperatures were investigated to upcycle the carbon fiber recovered from used carbon composite. When treated with nitric acid at 25 °C, the carbon fiber surface demonstrated the same tensile properties as untreated carbon fiber (CF) for up to 5 h, and the oxygen functional group and polar surface energy of C–O (hydroxyl group) and C=O (carbonyl group) increased slightly compared to the untreated CF up to 5 h. On the other hand, at 100 °C, the tensile properties slightly decreased compared to untreated CF up to 5 h, and the amount of C–O and C=O decreased and the amount of O=C–O (lactone group) started to increase until 1 h. After 1 h, the amount of C-O and C=O decreased significantly, and the amount of O=C–O increased rapidly. At 5 h, the amount of oxygen functional groups increased by 92%, and the polar surface energy increased by 200% compared to desized CF. It was determined that the interfacial bonding force increased the most because the oxygen functional group, O=C–O, increased greatly at 100 °C and 5 h. Full article

In the present study, how side-feeding of NiCF during twin-screw extrusion processing influences the fiber aspect ratio and thermal, mechanical, electrical, and electromagnetic properties of nickel-coated carbon fiber (NiCF)-reinforced polyamide 6 (PA6) composites was explored. For this, the fiber length distribution, thermal stability, heat deflection temperature, dynamic mechanical property, tensile, flexural, electrical resistivity, and electromagnetic interference shielding effectiveness (EMI SE) properties of NiCF/PA6 composites were extensively investigated. Chopped NiCF was regularly fed via either a main feeder or a side feeder and NiCF/PA6 pellets with different fiber-feeding pathways were prepared. The side-feeding effect of NiCF on the fiber length distribution and the composite properties was studied. The thermal stability, heat deflection temperature, storage modulus, tensile, flexural, and surface resistivity, and EMI SE properties of the NiCF/PA6 composites strongly depended not only on the NiCF content but also on the feeding method (main-feeding or side-feeding) upon extrusion processing, indicating that the fiber length distribution relevant to the fiber aspect ratio was critically important to enhance the composites’ properties. As a result, the NiCF/PA6 composites produced via side-feeding of NiCF exhibited an NiCF distribution longer than that produced via main-feeding, leading to enhancement of the thermal stability, heat deflection temperature, storage modulus, tensile, flexural, and EMI SE properties, strongly depending on the NiCF content. Full article

Curing processes for carbon-fiber-reinforced polymer composites via microwave heating are promising alternatives to conventional thermal curing because this technology results in nonhomogeneous temperature distributions, which hinder its further development in industries. This paper proposes a novel method for improving heating homogeneities by employing three-dimensional motion with respect to the prepreg laminate used in the microwave field by using a recently developed microwave system. The maximum temperature deviation on the surface of the laminate can be controlled within 8.7 °C during the entire curing process, and it produces an average heating rate of 1.42 °C/min. The FT−IR analyses indicate that microwave heating would slightly influence hydroxyl and methylene contents in the cured laminate. The DMA measurements demonstrate that the glass transition temperatures can be improved by applying proper microwave-curing processes. Optical microscopy and mechanical tests reveal that curing the prepreg laminate by using a multistep curing process that initially cures the laminate at the resin’s lowest viscosity for 10 min followed by curing the laminate at a high temperature for a short period of time would be favorable for yielding a sample with low void contents and the desired mechanical properties. All these analyses are supposed to prove the feasibility of controlling the temperature difference during microwave-curing processes within a reasonable range and provide a cured laminate with improved properties compared with conventional thermally cured products. Full article

Hybrids of fluorinated graphite/MoS₂ (FGr@MoS₂) were prepared via a hydrothermal method and used as lubricating additives to take full advantage of the synergy between FGr and MoS₂ in carbon-fiber-reinforced polymer (CFRP). The results show a 21.6% reduction in the friction coefficient compared to the neat sample when the CFRP was filled with 1.2 wt.% FGr@MoS₂ hybrids. The addition of 1.5 wt.% FGr@MoS₂ resulted in a 60.9% reduction in the wear rate compared to neat CFRP. For the 1.2 wt.% FGr@MoS₂-reinforced CFRP, the friction coefficient maintained a relatively steady value of approximately 0.46 at various temperatures, indicating frictional stability. However, the wear rate increased by 13.95% at 60 °C compared to that at room temperature. The interfacial bonding force between the FGr@MoS₂ hybrid and the matrix, as well as the adhesive force with the surface of the counterpart ball, is improved, caused by the heterostructure of FGr@MoS₂, resulting in enhanced mechanical properties and formation efficiency as well as the transfer film on the surface of the counterpart ball. The results suggest that an FGr@MoS₂ micro-nano structure is a promising additive to be applied in polymer tribology. Full article

In this study, the characteristics of a composite material composed of polypropylene (PP) and ultrahigh molecular weight polyethylene (UHMWPE) are investigated. The elastic properties of the PP/UHMWPE composite material composed of short UHMWPE fibers with a low aspect ratio and long UHMWPE fibers with a high aspect ratio are compared and analyzed. In addition, the elastic properties of the PP/UHMWPE composite materials are calculated via finite element analysis and the Halpin–Tsai model by changing the volume fraction of the UHMWPE fibers. The results show that when UHMWPE fibers with a low aspect ratio and volume fraction are used, the results of the modulus of elasticity based on the finite element analysis are consistent with those obtained using the Halpin–Tsai model, although the fiber volume fraction of the UHMWPE fibers increases. Meanwhile, the deviation between the results yielded by both methods increases with the aspect ratio of the fiber. In terms of the shear modulus, the Halpin–Tsai model shows a linear trend. The results from the finite element analysis differ significantly from those of the Halpin–Tsai model owing to the random orientation of the UHMWPE fibers inside the fiber. Using a contour graph constructed based on the finite element analysis results, the aspect ratio and volume fraction of the UHMWPE fibers can be inversely calculated based on the elastic properties when synthesizing a PP/UHMWPE fiber composite. In future studies, the interfacial bonding properties of UHMWPE fibers and PP should be compared and analyzed experimentally. Full article

At present, most carbon fibres are used as reinforcement for polymers. Fabrication technologies for carbon-fibre-reinforced polymers (CFRPs) are now reaching a mature state that effectively replaces metals in various technical fields, including aerospace, sporting equipment, civil engineering, etc. However, there are many structures in which metal alloys cannot be replaced with CFRPs because of, firstly, the limited temperatures that plastics can survive, and secondly, the relatively low fracture toughness of CFRPs. This has led researchers to develop carbon-fibre/metal-matrix composites (CFMMCs), considering aluminium, titanium, and nickel alloys as potential matrix materials. The present paper presents a review of the corresponding results, focusing on those obtained in the current century. Full article

Sandwich structures fabricated from an aluminium skinned foam enclosed within a carbon fibre reinforced composite structure have the potential application for high-performance on- and off-road automotive vehicles. The deformations and failure of these types of structures are presented, and results indicate that the application of aluminium face sheets with aluminium foam (AF) aids to prevent the delamination of the outer layers of carbon fibre reinforced polymers (CFRP). The load carrying capacity has been increased by utilising a manufacturing method to maintain the adhesion between the core and the skins until the failure stage is reached. The core shear and de-bonded issue associated with this type of sandwich structure can be addressed by this manufacture method. The peak average flexure load capacity of an aluminium foam sandwich structure (AFSS) with a completely wrapped around CFRP skin was 2800 N with a mass of 191 g. This compares favourably with previously used AFSS without the skins, which had a peak average load of 600 N and a mass of 125 g. An initial finite element model for comparison purposes has been developed to represent the structure’s behaviour and predict the associated failure loads. It is proposed that CFRP wrapped around AFSS enhances the structural performance without significant weight gain. Full article

In this study, a dynamic constitutive model for woven-carbon-fiber-reinforced plastics (CFRP) is formulated by combining dynamic tensile test data and fitting curves and incorporating variation rules established for the modulus of elasticity, strength, and fracture strain with respect to the strain rate. The dynamic constitutive model is then implemented with finite element software. The accuracy and applicability of the dynamic constitutive model are evaluated by comparing the numerically predicted load–displacement curves and strain distributions with the test data. The stress distribution, failure factor, modulus, and strength of the material under dynamic tension are also explored. The results show that the response simulated with the dynamic constitutive model is in good agreement with the experimental results. The strain is uniformly distributed during the elastic phase compared with the DIC strain field. Subsequently, it becomes nonuniform when stress exceeds 600 MPa. Then, the brittle fracture occurs. With the increase in the strain rate, the input modulus decreased, and the tensile strength increased. When the displacement was 0.13 mm, the simulation model was damaged at a low strain rate, and the stress value was 837.8 MPa. When it reached the high strain rate of 800 s⁻¹, no failure occurred, and the maximum stress value was 432.5 MPa. For the same specimen, the strain rate was the smallest on both clamped ends, and the modulus and strength were large at the ends and small in the middle. The fitting curve derived from the test data was completely input into the dynamic constitutive model to better capture the dynamic change in the material properties. Full article

Considerable uncertainties in the mechanical properties of composites not only prevent them from having efficient applications but also threaten the safety and reliability of structures. In order to determine the uncertainty in the elastic properties of unidirectional CFRP composites, this paper develops a probabilistic analysis method based on a micromechanics theoretical model and the Monte Carlo simulation. Firstly, four commonly used theoretical models are investigated by calculating the deterministic elastic parameters of three unidirectional CFRP composites, which are compared with experimental outcomes. According to error analyses, the bridging model is the most brilliant one, with errors lower than 6%, which suggests that it can be used in probabilistic analyses. Furthermore, constituent parameters are regarded as normally distributed random variables, and the Monte Carlo simulation was used to obtain samplings based on the statistics of constituent parameters. The predicted probabilistic elastic parameters of the T800/X850 composite coincide with those from experiments, which verified the effectiveness of the developed probabilistic analysis method. According to the probabilistic analysis results, the statistics of the elastic parameters, the correlations between the elastic parameters, and their sensitivity to the constituent’s properties are determined. The moduli E₁₁, E₂₂, and G₁₂ of the T800/X850 composite follow the lognormal distribution, namely, ln(E₁₁)~N[5.15, 0.028²], ln(E₂₂)~N[2.15, 0.024²], and ln(G₁₂)~N[1.48, 0.038²], whereas its Poisson’s ratio, v₁₂, obeys the normal distribution, namely, v₁₂~N(0.33, 0.012²). Additionally, the correlation coefficients between v₁₂ and E₁₁/E₂₂/G₁₂ are small and thus can be ignored, whereas the correlation coefficients between any two of E₁₁, E₂₂, and G₁₂ are larger than 0.5 and should be considered in the reliability analyses of composite structures. The developed probabilistic analysis method based on the bridging model and the Monte Carlo simulation is fast and reliable and can be used to efficiently evaluate the probabilistic properties of the elastic parameters of any unidirectional composite in the reliability design of structures in engineering practice. Full article