Search Results (352)

This study investigates the impact of partially replacing cement with fly ash (FA) on the mechanical performance of fiber-reinforced rubberized concrete (FRRC) incorporating waste tyre rubber and recycled macro-synthetic fibers (MSF). FRRC mixtures were prepared with varying fly ash replacement levels (0%, 25%, and 50%), rubber aggregate contents (0%, 10%, and 20% by volume of fine aggregate), and macro-synthetic fiber dosages (0% to 1% by total volume). The fresh properties were evaluated through slump tests, while hardened properties including compressive strength, splitting tensile strength, and flexural strength were systematically assessed. Results demonstrated that fly ash substitution up to 25% improved the interfacial bonding between rubber particles, fibers, and the cementitious matrix, leading to enhanced tensile and flexural performance without significantly compromising compressive strength. However, at 50% replacement, strength reductions were more pronounced due to slower pozzolanic reactions and reduced cement content. The inclusion of MSF effectively mitigated strength loss induced by rubber aggregates, improving post-cracking behavior and toughness. Overall, an optimal balance was achieved at 25% fly ash replacement combined with 10% rubber and 0.5% fiber content, producing a more sustainable composite with favorable mechanical properties while reducing carbon and ecological footprints. These findings highlight the potential of integrating industrial by-products and waste materials to develop eco-friendly, high-performance FRRC for structural applications, supporting circular economy principles and reducing the carbon footprint of concrete infrastructure. Full article

Due to its superior maneuverability and concealment, the micro flapping-wing aircraft has great application prospects in both military and civilian fields. However, the development and optimization of lightweight materials have always been the key factors limiting performance enhancement. This paper designs the flapping mechanism of a single-degree-of-freedom miniature flapping wing aircraft. In this study, T800 carbon fiber composite material was used as the frame material. Three typical wing membrane materials, namely polyethylene terephthalate (PET), polyimide (PI), and non-woven kite fabric, were selected for comparative analysis. Three flapping wing configurations with different stiffness were proposed. These wings adopted carbon fiber composite material frames. The wing membrane material is bonded to the frame through a coating. Inspired by bionics, a flapping wing that mimics the membrane vein structure of insect wings is designed. By changing the type of membrane material and the distribution of carbon fiber composite materials on the wing, the stiffness of the flapping wing can be controlled, thereby affecting the mechanical properties of the flapping wing aircraft. The modal analysis of the flapping-wing structure was conducted using the finite element analysis method, and the experimental prototype was fabricated by using 3D printing technology. To evaluate the influence of different wing membrane materials on lift performance, a high-precision force measurement experimental platform was built, systematic tests were carried out, and the lift characteristics under different flapping frequencies were analyzed. Through computational modeling and experiments, it has been proven that under the same flapping wing frequency, the T800 carbon fiber composite material frame can significantly improve the stiffness and durability of the flapping wing. In addition, the selection of wing membrane materials has a significant impact on lift performance. Among the test materials, the PET wing film demonstrated excellent stability and lift performance under high-frequency conditions. This research provides crucial experimental evidence for the optimal selection of wing membrane materials for micro flapping-wing aircraft, verifies the application potential of T800 carbon fiber composite materials in micro flapping-wing aircraft, and opens up new avenues for the application of advanced composite materials in high-performance micro flapping-wing aircraft. Full article

Carbon fiber-reinforced polymer (CFRP) laminates have been widely coated on aged and damaged structures for recovering or enhancing their structural performance. The health conditions of the coated composite structures have been given high attention, as they are critically important for assessing operational safety and residual service life. However, the current problem is the lack of an efficient, long-term, and stable monitoring technique to characterize the structural behavior of coated composite structures in the whole life cycle. For this reason, bare and packaged fiber Bragg grating (FBG) sensors have been specially developed and designed in sensing networks to monitor the structural performance of CFRP-coated composite beams under different loads. Some optical fibers have also been inserted in the CFRP laminates to configure the smart CFRP component. Detailed data interpretation has been conducted to declare the strengthening process and effect. Finite element simulation and simplified theoretical analysis have been conducted to validate the experimental testing results and the deformation profiles of steel beams before and after the CFRP coating has been carefully checked. Results indicate that the proposed FBG sensors and sensing layout can accurately reflect the structural performance of the composite beam structure, and the CFRP coating can share partial loads, which finally leads to the downward shift in the centroidal axis, with a value of about 10 mm. The externally bonded sensors generally show good stability and high sensitivity to the applied load and temperature-induced inner stress variation. The study provides a straightforward instruction for the establishment of a structural health monitoring system for CFRP-coated composite structures in the whole life cycle. Full article

In recent times, fiber reinforced polymer composite materials have become more popular due to their remarkable features such as high specific strength, high stiffness and durability. Particularly, Carbon Fiber Reinforced Polymer (CFRP) composites are one of the most prominent materials used in the field of transportation and building engineering, replacing conventional materials due to their attractive properties as mentioned. In this work, a CFRP laminate is fabricated with carbon fiber mats and epoxy by a hand layup technique. Alumina (Al₂O₃) micro particles are used as a filler material, mixed with epoxy at different weight fractions of 0% to 4% during the fabrication of CFRP laminates. The important objective of the study is to investigate the influence of alumina micro particles on the mechanical performance of the laminates through characterization for various physical and mechanical properties. It is revealed from the results of study that the mass density of the laminates steadily increased with the quantity of alumina micro particles added and subsequently, the porosity of the laminates is reduced significantly. The SEM micrograph confirmed the constituents of the laminate and uniform distribution of Al₂O₃ micro particles with no significant agglomeration. The hardness of the CFRP laminates increased significantly for about 60% with an increase in weight % of Al₂O₃ from 0% to 4%, whereas the water gain % gradually drops from 0 to 2%, after which a substantial rise is observed for 3 to 4%. The improved interlocking due to the addition of filler material reduced the voids in the interfaces and thereby resist the absorption of water and in turn reduced the plasticity of the resin too. Tensile, flexural and inter-laminar shear strengths of the CFRP laminate were improved appreciably with the addition of alumina particles through extended grain boundary and enhanced interfacial bonding between the fibers, epoxy and alumina particles, except at 1 and 3 wt.% of Al₂O₃, which may be due to the pooling of alumina particles within the matrix. Inclusion of hard alumina particles resulted in a significant drop in impact strength due to appreciable reduction in softness of the core region of the laminates. Full article

In carbon-fiber-reinforced composites, hydroxyl and carboxyl groups are formed on the carbon fiber surface as a result of the oxidation process applied to the fibers. These groups strengthen the interfacial bond between the fibers and the epoxy resin. In addition, the silanization process chemically bonds amino and glycidyl groups to the fiber surface, further improving adhesion and thus optimizing the performance of the joint. In light of this, the primary objective of the present study is to optimize the performance of adhesive joints by applying oxidation and silane modifications to the fibers added to the adhesive and the bonded metal materials. In this study, carbon fibers underwent oxidation treatment for 5, 10, and 20 min, followed by silanization with 3-aminopropyltriethoxysilane (APTES) and glycidoxypropyltrimethoxysilane (GPTMS) silane agents. Additionally, the surfaces of the bonded aluminum materials were subjected to a 10 min oxidation process, followed by silanization with APTES and GPTMS silane agents. The tensile test performance of single-lap joints, bonded using chemically surface-treated aluminum and composite adhesives containing 2 wt.% chemically treated carbon fibers, was experimentally investigated. According to the contact angle measurement results obtained in this study, aluminum materials subjected to oxidation treatment exhibited superhydrophilic behavior, whereas materials subjected to silanization displayed hydrophilic behavior. A similar trend was observed in the fibers. The performance of adhesive joints increased by approximately 14% when only the aluminum materials underwent oxidation treatment. Moreover, the addition of 2 wt.% carbon fibers to the adhesive enhanced the joint performance by approximately 31%. However, when oxidation treatments of varying durations were applied to both the aluminum materials and the fibers, the joint performance improved by approximately 35% to 40%. When silanization treatments were applied in addition to the oxidation treatments on aluminum and fiber surfaces, the joint performance increased by approximately 68% to 70%. These findings were corroborated through analyses performed using 3D profilometry and Scanning Electron Microscopy (SEM) imaging. Full article

Prefabricated unidirectional carbon fiber reinforced polymer (CFRP) composite strips are extensively used as a means of infrastructure rehabilitation through adhesive bonding to the external surface of structural concrete elements. Most data to date are from laboratory tests ranging from a few months to 1–2 years providing an insufficient dataset for prediction of long-term durability. This investigation focuses on the assessment of the response of three different prefabricated CFRP systems exposed to water, seawater, and alkaline solutions for 5 years of immersion in deionized water conducted at three temperatures of 23, 37.8 and 60 °C, all well below the glass transition temperature levels. Overall response is characterized through tensile and short beam shear (SBS) testing at periodic intervals. It is noted that while the three systems are similar, with the dominant mechanisms of deterioration being related to matrix plasticization followed by fiber–matrix debonding with levels of matrix and interface deterioration being accelerated at elevated temperatures, their baseline characteristics and distributions are different emphasizing the need for greater standardization. While tensile modulus does not degrade appreciably over the 5-year period of exposure with final levels of deterioration being between 7.3 and 11.9%, both tensile strength and SBS strength degrade substantially with increasing levels based on temperature and time of immersion. Levels of tensile strength retention can be as low as 61.8–66.6% when immersed in deionized water at 60 °C, those for SBS strength can be 38.4–48.7% at the same immersion condition for the three FRP systems. Differences due to solution type are wider in the short-term and start approaching asymptotic levels within FRP systems at longer periods of exposure. The very high levels of deterioration in SBS strength indicate the breakdown of the materials at the fiber–matrix bond and interfacial levels. It is shown that the level of deterioration exceeds that presumed through design thresholds set by specific codes/standards and that new safety factors are warranted in addition to expanding the set of characteristics studied to include SBS or similar interface-level tests. Alkali solutions are also shown to have the highest deteriorative effects with deionized water having the least. Simple equations are developed to enable extrapolation of test data to predict long term durability and to develop design thresholds based on expectations of service life with an environmental factor of between 0.56 and 0.69 for a 50-year expected service life. Full article

This research investigates a novel hybrid E-glass fiber coated with a thin amorphous carbon (coke) layer, referred to as GF@C, designed to enhance the affinity of fiber with a polymer matrix. Acrylonitrile butadiene styrene (ABS), an engineering thermoplastic, was selected as the matrix to form the composite. The carbon coating was produced by pyrolyzing a lubricant oil (Lo) layer applied to the glass fiber strands. To promote the formation of graphite crystallites during carbonization, a small amount (x wt.% of Lo) of coronene (Cor) was added to Lo as a dopant. The resulting doped fibers, denoted GF@C_Lo-Cor(x%), were embedded in ABS at 70 wt.%, leading to significant improvements in mechanical properties. At the optimal doping level (x = 5), the composite achieved a Young’s modulus of 1.02 GPa and a tensile strength of 6.96 MPa, substantially higher than the 0.4 GPa and 3.81 MPa observed for the composite with the pristine GF. This enhancement is attributed to a distribution of graphite crystallites and their graphitization extent in the carbon coating, which improves interfacial bonding and increases chain entanglement. Additionally, GF@C_Lo-Cor(x%)–ABS composites (x = 0 and 5) exhibit significantly higher dielectric constant–temperature profiles than GF–ABS, attributed to the formation of diverse chain adsorption states on the C-coating. Full article

This study presents the development of a manufacturing process for a double-serpentine (DS) exhaust nozzle for unmanned aerial vehicles (UAVs) based on carbon fiber-reinforced silicon carbide matrix composites (C/SiCs). The DS nozzle is designed to reduce infrared emissions from hot exhaust plumes, a critical factor in enhancing stealth performance during UAV operations. The proposed nozzle structure was fabricated using a multilayer configuration consisting of an inner C/SiC layer for thermal and oxidation resistance, a silica–phenolic insulation layer to suppress heat transfer, and an outer carbon fiber-reinforced polymer matrix composite (CFRPMC) for mechanical reinforcement. The C/SiC layer was produced by liquid silicon infiltration, preceded by pyrolysis and densification of a phenolic-based CFRPMC preform. The final nozzle was assembled through precision machining and bonding of segmented components, followed by lamination of the insulation and outer layers. Mechanical and thermal property tests confirmed the structural integrity and performance under high-temperature conditions. Additionally, oxidation and ablation tests demonstrated the excellent durability of the developed C/SiC. The results indicate that the developed process is suitable for producing large-scale, complex-shaped, high-temperature composite structures for stealth UAV applications. Full article

The design of automobile chassis structures is fundamentally linked to the optimization of mass and structural robustness. While conventional chassis structures predominantly utilize metals, achieving further mass reduction and enhanced rigidity necessitates the adoption of composite sandwich materials, typically comprising carbon fiber-reinforced polymer (C.F.R.P.) laminate skins bonded to an aluminum honeycomb core. This study focuses on presenting a framework methodology for minimizing the mass of a race car chassis by calculating an optimal baseline lamination sequence through the modification of the composite material parameters on either side of the aluminum core, using an optimization algorithm (O.A.), finite element (F.E.) analysis, composite mechanics theory, and failure criteria. Optimal solutions were derived by varying the laminae orientation and sequence parameters under two scenarios: unconstrained and constrained laminae angles. The optimization results indicate that the proposed lamination scheme reduces mass by 12.36 kg (41.66%) compared to the original lamination, with constraints imposed on laminae angles having no significant impact on the ultimate optimal outcome. Full article

The epoxy-bonded joint between carbon-fiber-reinforced bismaleimide (CF-BMI) and quartz-fiber-reinforced bismaleimide (QF-BMI) composites can meet the structure–function integration requirements of next-generation aviation equipment, and the structural design of their bonding zones directly affects their service performance. Hence, in this study, the carbon-fiber-reinforced bismaleimide composite ZT7H/5429, the woven quartz-fiber-reinforced bismaleimide composite QW280/5429, and epoxy adhesive film J-116 were used as research materials to investigate the influence of the bonding area size on the mechanical properties, and this study proposes a novel design methodology combining radial basis function (RBF) neuron machine learning with the NSGA-II algorithm to enhance the mechanical properties of the bonded components. First, a finite element simulation model considering 3D hashin criteria and cohesion was established, and its accuracy was verified with experiments. Second, the RBF neuron model was trained using the finite element tensile strength and shear strength data from various adhesive layer parameter combinations. Then, the multi-objective parameter optimization of the surrogate model was accomplished through the NSGA-II algorithm. The research results demonstrate a high consistency between the finite element simulation results and experimental outcomes for the epoxy-bonded CF/QF-BMI composite joint. The stress distribution of the adhesive layers is similar under the different structural parameters of adhesive films, though the varying structural dimensions of the adhesive layers lead to distinct failure modes. The trained RBF neuron model controls the prediction error within 2.21%, accurately reflecting the service performance under various adhesive layer parameters. The optimized epoxy-bonded CF/QF-BMI composite joint exhibits 16.1% and 11.2% increases in the tensile strength and shear strength, respectively. Full article

Recycled wood fiber (RWF) obtained through the multi-stage processing of waste wood serves as an eco-friendly green construction material, exhibiting lightweight, porous, and high toughness characteristics that demonstrate significant potential as a cementitious reinforcement, offering strategic advantages for environmental protection and resource recycling. In this study, high-performance sulfoaluminate cement (SAC)-RWF composites prepared by modifying RWFs with nano-silica (NS) and a silane coupling agent (KH560) were developed and their effects on mechanical properties, shrinkage behavior, hydration characteristics, and microstructure of SAC-RWF composites were systematically investigated. Optimal performance was achieved at water–cement ratio of 0.5 with 20% RWF content, where the KH560-modified samples showed superior improvement, with 8.5% and 14.3% increases in 28 d flexural and compressive strength, respectively, compared to the control groups, outperforming the NS-modified samples (3.6% and 8.6% enhancements). Both modifiers improved durability, reducing water absorption by 6.72% (NS) and 7.1% (KH560) while decreasing drying shrinkage by 4.3% and 27.2%, respectively. The modified SAC composites maintained favorable thermal properties, with NS reducing thermal conductivity by 6.8% through density optimization, whereas the KH560-treated specimens retained low conductivity despite slight density increases. Micro-structural tests revealed accelerated hydration without new hydration product formation, with both modifiers enhancing cementitious matrix hydration product generation by distinct mechanisms—with NS acting through physical pore-filling, while KH560 established Si-O-C chemical bonds at paste interfaces. Although both modifications improved mechanical properties and durability, the KH560-modified SAC composite group demonstrated superior overall performance than the NS-modified group, providing a technical pathway for developing sustainable, high-performance recycled wood fiber cement-based materials with balanced functional properties for low-carbon construction applications. Full article

Polyaryletherketone (PAEK) polymers inherently exhibit low surface activity, leading to poor adhesive bonding performance when using epoxy-based adhesives. In this study, low-temperature plasma surface modification was conducted on carbon fiber-reinforced polyetherketone ketone (CF/PEKK) composites to investigate the influence of plasma treatment parameters on their lap shear strength. Surface characterization was systematically performed using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle analysis to evaluate morphological, chemical, and wettability changes induced via plasma treatment. The results demonstrated a significant enhancement in lap shear strength after plasma treatment. Optimal bonding performance was achieved at a treatment speed of 10 mm/s and a nozzle-to-substrate distance of 5 mm, yielding a maximum shear strength of 28.28 MPa, a 238% improvement compared to the untreated control. Notably, the failure mode transitioned from interfacial fracture in the untreated sample to a mixed-mode failure dominated by cohesive failure of the adhesive and substrate. Plasma treatment substantially reduced the contact angle of CF/PEKK, indicating improved surface wettability. SEM micrographs revealed an increased micro-porous texture on the treated surface, which enhanced mechanical interlocking between the composite and adhesive. XPS analysis confirmed compositional alterations, specifically elevated oxygen-containing functional groups on the plasma-treated surface. These modifications facilitated stronger chemical bonding between CF/PEKK and the epoxy resin, thereby validating the efficacy of plasma treatment in optimizing surface chemical activity and adhesion performance. Full article

This study investigates the fracture toughness of adhesive joints between carbon fiber-reinforced polymer composites (CFRP) and boron-alloyed high-strength steel under Mode I and II loading, based on linear elastic fracture mechanics (LEFM). Two adhesive types were examined: the excess resin from the prepreg composite, forming a thin layer, and a toughened structural epoxy (Sika Power-533), designed for the automotive industry, forming a thick layer. Modified double cantilever beam (DCB) and end-notched flexure (ENF) specimens were used for testing. The results show that using Sika Power-533 increases the critical energy release rate by up to 30 times compared to the prepreg resin, highlighting the impact of adhesive layer thickness. Joints with the thick Sika adhesive performed similarly regardless of whether uncoated or Al–Si-coated steel was used, indicating the composite/Sika interface as the failure point. In contrast, the thin resin adhesive layer exhibited poor bonding with uncoated steel, which detached during sample preparation. This suggests that, for thin layers, the resin/steel interface is the weakest link. These findings underline the importance of adhesive selection and layer thickness for optimizing joint performance in composite–metal hybrid structures. Full article

Composite materials have the advantages of high strength and low weight, and are therefore used in many areas. However, in humid and marine environments, mechanical properties may deteriorate due to moisture diffusion, especially in glass fiber reinforced polymers (GFRP) and carbon fiber reinforced polymers (CFRP). This study investigated the damage formation and changes in mechanical properties of single-layer adhesive-bonded GFRP and CFRP connections under the effect of sea water. In the experiment, 0/90 orientation, twill-woven GFRP (7 ply) and CFRP (8 ply) plates were produced as prepreg using the hand lay-up method in accordance with ASTM D5868-01 standard. CNC Router was used to cut 36 samples were cut from the plates produced for the experiments. The samples were kept in sea water taken from the Aegean Sea, at 3.3–3.7% salinity and 23.5 °C temperature, for 1, 2, 3, 6, and 15 months. Moisture absorption was monitored by periodic weighings; then, the connections were subjected to three-point bending tests according to the ASTM D790 standard. The damages were analyzed microscopically with SEM (ZEISS GEMINI SEM 560). As a result of 15 months of seawater storage, moisture absorption reached 4.83% in GFRP and 0.96% in CFRP. According to the three-point bending tests, the Young modulus of GFRP connections decreased by 25.23% compared to dry samples; this decrease was 11.13% in CFRP. Moisture diffusion and retention behavior were analyzed according to Fick’s laws, and the moisture transfer mechanism of single-lap adhesively bonded composites under the effect of seawater was evaluated. Full article

The modified asphalt with high softening point was prepared by air oxidation polymerization with coal liquefied asphalt as raw material. The quality control model regarding the coking value and softening point of the product were established based on the DFSS (Design for Six Sigma) and RSM (response surface method). By means of elemental analysis, infrared, XPS, XRD, nuclear magnetic, MALDI-TOF and other characterization methods, the composition and structure characteristics of the modified asphalt were analyzed. Using the target product as raw material, general base asphalt carbon fiber was prepared by spinning, pre-oxidation and carbonization. The results show that the fitting effect of the quality control model about the coking value and softening point of the product is good, and the operating window range of the polymerization process parameters corresponding to the preparation of target product is wide. It can be found that the oxidation time and oxidation temperature has the most significant effect on the coking value and softening point of products, respectively, and all of them show a positive correlation. The dealkylation reaction and oxidative crosslinking reaction were carried out at the same time, and the bridging products of methylene bridging products, ether–oxygen bonds, carbonyl bonds, anhydride bonds and other oxygen-containing groups were generated. The properties of carbon fiber prepared with the target product are better: the tensile strength is 775 MPa, the elastic modulus is 68.6 GPa and the elongation at break is 1.13%. Full article