Search Results (2,021)

Carbon fiber-reinforced polymer (CFRP) is favored as the primary material for thin-walled components in fields such as aerospace due to its excellent properties, including light weight, high specific strength, high specific stiffness, and ease of integrated manufacturing. These thin-walled parts require assembly and connection with other components using rivets or bolts, necessitating the drilling of a large number of holes in CFRP. However, owing to its macroscopic heterogeneity, anisotropy, and low interlaminar bonding strength, CFRP is prone to defects during drilling, such as delamination, burrs, tearing, fiber pull-out, and surface voids. These defects can significantly compromise the connection quality and fatigue life of the components and may even lead to part rejection. To avoid drilling defects and achieve high-quality machining of CFRP, it is essential to fundamentally understand the intrinsic relationship between its material characteristics, such as anisotropy and interlaminar properties, and machining-induced damage. This paper systematically reviews the primary defects in CFRP drilling and their formation mechanisms, identifying drilling forces, drilling heat, and tool wear as the core contributing factors. Based on this analysis, various process optimization methods from different perspectives are proposed to mitigate these drilling defects and improve surface quality, including the optimization of cutting parameters, tool improvement, enhancement of the drilling environment, optimization of drilling process strategies, and the application of advanced drilling technologies. Finally, the paper summarizes the research on CFRP drilling and provides an outlook on future developments. Full article

This study systematically investigates the influence of short carbon-fiber (SCF) content on the mechanical, thermal, and tribological properties of self-lubricating polyphenylene sulfide (PPS) composites filled with PTFE and MoS₂, addressing the critical need for high-wear resistance in Carbon-Fiber-Reinforced Thermoplastic (CFRTP) structural applications. The results identified 10 wt% SCF as the optimal content that achieved the best balance between load-bearing capacity and friction performance. The coefficient of friction μ and wear amount were reduced by 29.28% and 29.29%, respectively, compared to the PPS/PTFE/MoS₂ composite material without SCF, and by 14.67% and 20.75%, respectively, compared to the material with excessive SCF filling (20 wt%). Finite-Element Analysis-Representative Volume Element (FEA-RVE) reveals the mechanism by which excessive content of SCF at the microscopic level leads to a slight decrease in mechanical properties. Critically, the tribological performance exhibited a discrepancy with bulk mechanical properties: above 15 wt% SCF, the wear rate worsened despite high mechanical strength, revealing that increased fiber agglomeration and micro-abrasion effects were the primary causes of performance deterioration. Further in-depth XPS analysis revealed a synergistic lubrication mechanism: In the optimal sample, an ultra-dense PTFE transfer film was formed to mask the underlying MoS₂. This masking, coupled with the high surface activity of MoO₃ particles leads to stronger physicochemical interactions with the polymer matrix, ensures the exceptional durability and stability of the tribo-film. This research establishes a complete structure–performance relationship by integrating mechanical, thermal, and tribo–chemical mechanisms, offering critical theoretical guidance for the design of next-generation high-performance self-lubricating CFRTPs. Full article

One of the key challenges in using CFRP (Carbon Fiber Reinforced Polymer) structures is their susceptibility to low-energy impact damage, often indicated as barely visible impact damage (BVID). Such defects are difficult to detect and can compromise structural integrity. This study investigates the use of immobilized non-Newtonian fluids (NNF) as protective layers for CFRP composites subjected to low-energy impacts. Experimental tests were carried out with an Instron 9440 drop-weight impact tower (impact energy range 5–40 J) and high-speed imaging, comparing NNF coatings with rubber-based, caoutchouc-based, and spray-based protective layers. Non-destructive evaluation using computed tomography confirmed that NNF coatings dissipate impact energy through shear-thickening behavior, reducing delamination while preserving clear visual indicators of the impact site. Furthermore, the study assessed post-impact fatigue bending performance, revealing that the inclusion of NNF—either as an outer layer or as part of a sandwich structure—significantly enhanced the residual fatigue strength of the composites. Moreover, NNFs inherently preserve visible traces of penetration, thereby improving the detectability of impact locations through both unaided visual inspection and advanced imaging modalities such as computed tomography. In addition to external coatings, NNF was applied as a core in sandwich structures, demonstrating improved impact resistance compared to monolithic CFRP laminates and conventional CFRP–foam sandwiches. The protective performance was found to depend on fluid thickness and threshold shear rates required for viscosity transition, indicating that thicker layers do not always provide superior protection. Full article

This study investigates the influence of hybrid additives and cutting parameters on the surface roughness (R_a) of drilled Glass Fiber Reinforced Polymer (GFRP) composites. Nine composite panels were fabricated with varying concentrations of wax (0%, 1%, 2%) and graphene (0%, 0.25%, 2%). Drilling experiments were conducted on a CNC milling machine using a range of cutting velocities (50–200 m/min) and feeds (0.02–0.08 mm/rev), and the resulting surface roughness was measured using a profilometer. The results demonstrate that cutting velocity is the most dominant parameter, contributing to 69% of the variability in surface roughness, followed by feed (16%). The incorporation of additives, specifically 1 wt% wax and 0.25 wt% graphene, produced a synergistic effect, yielding the lowest average surface roughness (≈2.9 µm) and the most stable machining process. Higher cutting velocities increased roughness due to thermal effects, while increasing feeds improved surface finish by reducing frictional heating. The findings indicate that an optimal combination of moderate additive concentrations and controlled machining parameters can significantly enhance the surface integrity and process repeatability in the drilling of GFRP composites. Full article

Polymer-based composites have emerged as viable alternatives to metals for applications requiring reduced weight, corrosion resistance, and cost-effectiveness; however, their relatively low mechanical strength remains a significant limitation. This study evaluates the flexural performance of unsaturated polyester composites reinforced with coconut shell charcoal (CC) powder at filler contents of 0%, 10%, 20%, and 30% by weight, in accordance with ASTM D790. The incorporation of 20 wt% CC yielded the highest flexural strength of 132.43 MPa, representing a 153% improvement compared to pure polyester (52.10 MPa). Flexural modulus also increased substantially at this composition, indicating enhanced stiffness resulting from improved interfacial bonding and efficient stress transfer. In contrast, increasing the filler content beyond 20 wt% resulted in a reduction of up to 32% in strength, attributed to particle agglomeration and void formation. Overall, the results identify 20 wt% CC as the optimal reinforcement level, significantly improving energy absorption and bending resistance, thereby positioning this composite as a promising candidate for lightweight structural applications. Full article

Out-of-autoclave (OoA) processing has emerged as a promising route for manufacturing high-performance polymer composites while reducing energy consumption and production complexity. The authors investigate the effect of curing temperature on the thermo-mechanical performances of carbon fiber-reinforced composites produced via resin infusion. Five laminates composed of six carbon fiber plies were arranged in a [90/0/45/−45/0/90] lay-up and infused with an epoxy resin cured at 25, 40, 50, 60, and 70 °C. The influence of the processed temperatures of the mechanical properties was evaluated through tensile and three-point bending tests, whereas thermal performance was analyzed using Heat Deflection Temperature (HDT) measurements and differential scanning calorimetry (DSC). The results demonstrate an improvement in stiffness, strength, and HDT with increasing the curing temperature, with the 40–50 °C range yielding the most balanced enhancement in mechanical and thermal responses. DSC analyses confirm that higher curing temperatures promote a more complete crosslinking reaction, consistent with the improved laminate performance. Overall, the findings highlight the critical role of controlled thermal curing in optimizing OoA polymer composite systems and support their suitability for energy-efficient applications. Full article

The pursuit of alternatives to nonrenewable materials has stimulated the development of sustainable materials with improved performance, particularly polymer composites reinforced with plant-based fibers. In this study, eucalyptus fibers were thermally treated and evaluated as eco-friendly reinforcements for polyester composites, aiming to enhance their physical and mechanical properties. The fibers were subjected to heat treatments between 140 and 230 °C in a Macro-ATG oven, followed by analyses of anatomical characteristics and chemical composition. Composites containing 25% fiber reinforcement were produced using an orthophthalic unsaturated polyester matrix catalyzed with methyl ethyl ketone peroxide, with untreated fibers used as references. Thermal treatment induced significant modifications in fiber morphology and composition, including increases in cell wall fraction at 170 and 200 °C and higher cellulose contents at 140 and 170 °C. Mechanical performance was assessed through tensile, flexural (modulus of rupture—MOR), modulus of elasticity (E_B), and impact tests. Composites reinforced with heat-treated fibers exhibited lower apparent density and, notably, those treated at 230 °C showed markedly reduced water absorption and enhanced tensile strength compared with the control. Overall, treatment at 230 °C proved most effective, highlighting the potential of thermally modified eucalyptus fibers as viable reinforcements for high-performance, bio-based polymer composites. Full article

One of the most critical damage modes affecting the structural performance of traditional composite materials, and therefore their durability, is the occurrence of interlaminar cracks (delamination), which are prone to grow under different loading conditions. In this study, the feasibility of repairing carbon fiber reinforced polymer (CFRP) laminates using structural adhesives was experimentally investigated by evaluating the Mode I interlaminar fracture toughness. Two unidirectional AS4 CFRP systems were analyzed, manufactured with epoxy 8552 and epoxy 3501-6 matrix resins. Mode I delamination behavior was characterized using Double Cantilever Beam (DCB) specimens. Three commercial structural adhesives were used in the repair process: two epoxy-based systems, (Loctite^® EA 9460™, manufactured by Henkel adhesives (Düsseldorf, Germany), and Araldite^® 2015 manufactured by Huntsman Advanced Materials (The Woodlands, TX, USA) and one low-odor acrylic adhesive, 3M Scotch-Weld^® DP8810NS manufactured by 3M Company (St. Paul, MN, USA). Adhesive joints were applied to previously fractured specimens, and the results were compared with those obtained from baseline composite specimens. The results indicate that repaired joints based on the 8552 matrix exhibited higher strain energy release rate (G_Ic) values, approaching those of the original material. The 3501-6 system showed increased fiber bridging, contributing to higher apparent fracture toughness. Among the adhesives evaluated, the acrylic-based adhesive provided the highest delamination resistance for both composite systems. Full article

This paper reviews the current state of research on the seismic behavior of precast segmental bridge piers, systematically elucidating their performance under different connection configurations in the context of accelerated bridge construction and resilience demands. Additionally, it compiles commonly used research methodologies and strategies for enhancing seismic performance. The evidence indicates that emulative precast segmental piers can closely match monolithic cast-in-place structures, with reported peak lateral strengths typically within about 10% and comparable yield and peak displacements, whereas non-emulative systems generally provide superior self-centering with smaller residual displacements. Experimental studies, theoretical analyses, and numerical simulations have all proven effective in characterizing the mechanical behavior of these piers; each approach has distinct advantages, and a synergistic integration of methods is recommended for comprehensive evaluation. Measurable improvements in seismic performance have been reported through hybrid connection systems, innovative detailing, supplementary energy-dissipating devices, and the use of high-performance materials such as ultra-high-performance concrete (UHPC), engineered cementitious composites (ECC), fiber-reinforced polymers (FRP), and shape memory alloys (SMA); for example, representative tests reported about a 30% increase in energy dissipation at drift ratios exceeding 3%, and SMA-based reinforcement has been reported to reduce residual drift by roughly 67% relative to steel reinforcement. Finally, future research directions are proposed to support the wider adoption of precast bridge piers in high-seismicity regions, including addressing challenges related to performance degradation under multi-hazard coupling conditions, insufficient design criteria for connections, and the need for rapid post-earthquake repair and resilience. Full article

This study investigates ultrasonic wave propagation in carbon fiber reinforced polymer (CFRP) composites containing foreign object debris (FOD) by introducing a novel method to characterize the depth and size of FOD, from a single captured waveform generated by an out-of-focus spherically focused transducer. Current methods of inspection utilize a raster approach to both detect and quantify FOD, which is limited to identifying FOD smaller than 4 mm. The method introduced in the present paper allows for a single point scan to detect and quantify FOD, as small as 0.5 mm, with the highest error in the depth estimation being less than 8%. This paper presents experimental testing to inform a finite element analysis of a full waveform simulation of an immersion tank inspection environment and compares waveforms between testing and simulation. A transient pressure acoustic model is developed in the COMSOL Multiphysics environment to simulate wave propagations. Simulation results provide waveform reflection and transmission at material interfaces, which will occur when there is an acoustic mismatch between materials. The transmitted ultrasonic wave is partially reflected toward the transducer upon encountering material interfaces between the water, CFRP laminate, and the FOD. Simulation results show that the acoustic profile and pressure of the reflected wave captured by the transducer allows an accurate identification of FOD depth and size within the composite structure, suggesting an alternative method of inspection to quantify FOD characteristics faster than through conventional approaches. Results show an increase in captured signal pressure of over 125% between the 0.5 mm FOD and the 1 mm FOD located on the mid-plane of the laminate, and 500% between the same 0.5 mm FOD and 1 mm FOD placed near the front wall. These results suggest the potential sensitivity limits for physical component. This work demonstrates that small FOD, which are often difficult to resolve and quantify under conventional raster-based inspection, can be reliably identified by intentionally positioning the specimen within the defocused region of a spherically focused transducer. Results are presented to correlate the reflected acoustic pressure amplitude to defect depth, transducer–specimen distance, and FOD size, providing an approach to quantitatively discriminate small defects that would otherwise produce ambiguous signals. Full article

The durability of the carbon fiber-reinforced polymer (CFRP)–concrete interface is a critical indicator for assessing the service life of composite structures in cold regions. This study systematically investigates the normal bond behavior under coupled deicing salt and freeze–thaw cycles through single-sided salt-frost tests on 126 specimens. The influence of surface roughness, number of freeze–thaw cycles, concrete strength grade, and CFRP material type was systematically evaluated. The results demonstrate that bond behavior is positively correlated with surface roughness, with the f₂ interface exhibiting optimal performance and increasing the ultimate capacity by up to 76.61% compared to the smooth interface. CFRP cloth showed superior bond retention compared to CFRP plates, which experienced a bond strength loss rate up to 26.90% higher than cloth specimens after six cycles. A critical performance threshold was identified between six and eight cycles, where the failure mode transitioned from cohesive adhesive failure to brittle interfacial debonding. Concrete matrix strength had a negligible effect compared to the dominant environmental damage. A two-parameter prediction model based on cycle count and roughness was established with high accuracy. SEM analysis confirmed that epoxy resin cracking, fiber–matrix debonding, and microcrack propagation in the concrete surface layer were the fundamental causes of macroscopic mechanical degradation. These findings provide a theoretical foundation for optimizing interface treatment and predicting the structural integrity of CFRP-strengthened systems in salt-frost regions. Full article

The M21 epoxy matrix is a toughened material designed to enhance the fracture resistance of carbon fiber-reinforced polymers (CFRPs). This study presents an experimental characterization of the shear and interlaminar properties required for validating computational damage models of hybrid laminated composite panels manufactured with the M21 material system. In-plane shear behavior was evaluated using ±45 (PM45) tests, while interlaminar fracture properties were characterized through double cantilever beam (DCB) and end-notched flexure (ENF) tests. The results demonstrate that hybrid laminates exhibit high interfacial fracture toughness, with notably increased resistance observed in woven–woven and unidirectional–woven interface pairs. Parametric studies identified cohesive strength and fracture energy as the dominant parameters governing delamination behavior in numerical simulations. Corresponding values were extracted for each interface type, enabling accurate representation of damage initiation and propagation in finite element models. To the authors’ knowledge, this work provides the first experimental dataset for the listed M21-based hybrid unidirectional–woven and woven–woven interfaces, establishing a benchmark for future modeling and simulation of toughened composite structures. Full article

Fiber-reinforced polymer composites (FRPCs) are increasingly used in construction due to their high performance and low environmental footprint. However, their widespread adoption has raised concerns over end-of-life management, particularly under European regulations mandating high recycling rates for construction and demolition waste (CDW). This study evaluates different systems for the chemical recycling of FRPCs through microwave (MW)-assisted solvolysis using green solvents, including deep eutectic solvents (DESs) and biobased acetic acid. The process targets thermoset resin depolymerization while preserving fiber integrity, operating at reduced temperatures (≤230 °C) and lower energy demand than conventional techniques, such as pyrolysis. A systematic experimental design was applied to CDW-derived polyester composites and extended to industrial epoxy and vinyl ester composites. Among the tested solvents, glacial acetic acid + ZnCl₂ (5 wt.%), achieved the highest degradation efficiency, exceeding 94% in small-scale trials and maintaining over 78% upon upscaling. Recovered fibers showed moderate property retention, with tensile strength and elongation losses of ~30% and ~45% for infusion-based epoxy composites, while those from pultrusion-based epoxy composites exhibited 16–19% and retained similar properties to the virgin material, respectively. The method facilitates fiber recovery with limited degradation and aligns with circular economy principles through solvent reuse and minimizing environmental impact. Full article

Unlike typical fiber-reinforced polymers, aerospace composites consist of 90% carbon and 10% glass fabrics impregnated with thermosetting resin. Due to the strong bonding between fibers and the thermoset nature of the matrix, recycling these materials is particularly challenging. This study evaluates mechanical recycling of aircraft composite waste via industrial grinding and chemical recycling through a solvolysis process. Recovered fibrous fractions were integrated into an epoxy matrix at 50 wt% loading using hot-pressing and into polyamide 12 at 15 wt% via a twin-screw extrusion process. The mechanical results showed that chemically recycled fibers in epoxy reached a flexural modulus of 9.9 GPa and strength of 112 MPa, significantly outperforming mechanically recycled fillers (6.1 GPa and 98.0 MPa) compared to virgin carbon fibers (11.3 GPa and 132 MPa). In PA12, the addition of chemically recycled fibers yielded a 2.14 GPa modulus and a 67.7 MPa strength. Furthermore, life cycle assessment confirmed that both recycling routes drastically reduce global warming potential and aquatic ecotoxicity compared to landfilling. These findings indicate that while mechanical recycling is simpler, chemical solvolysis provides a superior pathway for the high-value circular reuse of complex aerospace waste in new thermoplastic and thermoset applications. Full article

This paper presents the design, manufacturing, instrumentation and validation by tests (ground and icing wind tunnel) of a full-scale Hybrid Laminar Flow Control (HLFC) leading-edge demonstrator based on Airbus A330 outer wing plan-form. The Ground-Based Demonstrator (GBD) was developed to reproduce a full-scale, realistic wing section integrating into the leading-edge three key systems: micro-perforated skin for the hybrid laminar flow control suction system (HLFC), the hot-air Wing Ice Protection System (WIPS) and a folding “bull nose” Krueger high-lift device. The demonstrator combines a superplastic-formed and diffusion-bonded (SPF/DB) perforated titanium skin mounted on aluminum ribs jointed with a carbon-fiber-reinforced polymer (CFRP) wing box. Titanium internal ducts were designed to ensure uniform hot-air distribution and structural compatibility with composite components. Manufacturing employed advanced aeronautical processes and precision assembly under INCAS coordination. Ground tests were performed using a dedicated hot-air and vacuum rig delivering up to 200 °C and 1.6 bar, thermocouples and pressure sensors. The results confirmed uniform heating (±2 °C deviation) and stable operation of the WIPS without structural distortion. Relevant tests were performed in the CIRA Icing Wind Tunnel facility, verifying the anti-ice protection system and Krueger device. The successful design, fabrication, testing and validation of this multifunctional leading edge—featuring integrated HLFC, WIPS and Krueger systems—demonstrates the readiness of the concept for subsequent aerodynamic testing. Full article