Search Results (817)

The transient heat-transfer behavior of hybrid natural-fiber-reinforced epoxy composites containing 0–5 wt% conch shell filler and 20–35 wt% combined banana–bagasse fiber reinforcement was evaluated using active infrared thermography. A standardized protocol comprising 30 s of convective heating with 100 °C hot air followed by 60 s of natural cooling was applied to seven composite configurations tested in triplicate. The transient response was analyzed in three phases: active heating (0–30 s), thermal lag (30–57 s), and natural cooling (57–90 s). Maximum temperature ($T_{max}$), heating rate ($R_h$), cooling rate ($R_c$), and a thermal retention ratio ($TR$) were extracted and statistically validated by one-way ANOVA with Bonferroni correction. For specimens exhibiting zero within-group variance at the camera display resolution, significance was confirmed using exact permutation tests. Filler incorporation (3–5 wt%) was the dominant factor governing peak-temperature reduction; F5B15S10 (5 wt% filler, 25 wt% total fiber) achieved the lowest $T_{max}$ (33.80 °C, 4.57 °C below neat epoxy). Cooling efficiency was primarily governed by fiber content; F3B15S20 (3 wt% filler, 35 wt% total fiber) demonstrated the most efficient heat dissipation ($TR=0.721$). These findings demonstrate that heating resistance and cooling efficiency are governed by partially independent mechanisms, enabling tailored material design. This study indicates that the proposed transient thermographic protocol provides a valuable reference to thermal management design of hybrid biocomposites in automotive interior and building envelope applications. Full article

Lightweight polymer composites with effective electromagnetic interference (EMI) shielding are of increasing interest for advanced electronic and aerospace applications; however, conventional glass fiber-reinforced polymers (GFRPs) exhibit inherently low electrical conductivity, limiting their shielding performance. In this study, a hierarchical hybrid conductive architecture was developed by integrating graphene-coated multiaxial glass fiber fabrics with carbon black (CB)-reinforced epoxy matrices to enhance EMI shielding behavior in the X-band (8–12 GHz). Graphene coatings were deposited onto glass fibers via a surfactant-assisted ultrasonic dispersion method, while carbon black (0–1 wt.%) was incorporated into the epoxy matrix using ultrasonication-assisted mixing. Multilayer composites were fabricated using a vacuum bagging process. X-ray diffraction analysis revealed that the composites retained a predominantly amorphous epoxy/glass fiber matrix while exhibiting broad carbon-related diffraction features associated with disordered graphitic domains. Electrical conductivity measurements indicated that all composites remained in the insulating regime (~10⁻⁹ S/m), suggesting that a fully interconnected conductive network was not established within the investigated filler range. Despite the absence of a continuous conductive network, measurable EMI shielding performance was achieved. The composite containing 0.25 wt.% CB exhibited the highest shielding effectiveness, reaching approximately 12 dB at ~11.2 GHz. Analysis of the shielding contributions showed that absorption contributions (SEA) were consistently higher than reflection contributions (SER) across the studied frequency range. Morphological observations revealed that well-dispersed CB at low loading facilitated the formation of localized conductive domains that may contribute to tunneling-assisted polarization and interfacial charge accumulation. At higher CB contents, particle agglomeration reduced dispersion quality and limited effective pathway formation, while dynamic mechanical analysis indicated enhanced stiffness at low CB loading. FTIR results confirmed the absence of new chemical bonding, indicating that CB acts as a physically dispersed conductive filler. Overall, the results show that effective EMI shielding can be achieved in electrically insulating composites through the combined effect of hierarchical structural design and localized conductive features. This approach provides a practical pathway for developing lightweight EMI shielding materials with controlled filler loading and preserved structural integrity for aerospace and electronic applications. Full article

The mechanical properties and real-time damage evolution of sustainable concrete (SC) containing 100% recycled concrete aggregate (RCA) under the combined action of hybrid steel and polyolefin fibers were studied. Inspired by solving the massive effects on the environment from construction waste, as well as to improve the lower mechanical performance of lower-grade RCA, the effect of combining high-stiffness hooked-end steel fibers and flexible macro-polyolefin fibers within RCA was investigated. Six different mix designs were considered: plain, single-fiber (100% steel and 100% polyolefin) and three hybrid composites with varying fractions of the steel/polyolefin fibers (25/75, 50/50, and 75/25). Compressive, tensile and flexural strengths were determined by mechanical testing. During compressive testing, the damage evolution was monitored using low-cost acoustic emission (AE) as a non-destructive technique. Cumulative hits analysis, amplitude distributions, and the statistical b-value parameter were used for damage characterization. The results show that steel fiber significantly increased compressive strength (an increase of up to 13.8%), and the 50/50 hybrid mix showed a high synergistic effect, yielding the highest tensile (4.86 MPa) and flexural (25.54 MPa) strengths. AE analysis identified different damage fingerprints: Based on amplitude analysis, steel-fiber composites exhibited high-amplitude events (which may be attributable to fiber pull-out); polyolefin-fiber composites generated medium-amplitude events (may have resulted from distributed microcracking); and hybrid mixes displayed a mixed amplitude distribution. The b-value analysis provided insight into progressive damage and revealed that the hybrid fibers induce stable, diffuse damage that prevents the brittle failure of plain recycled aggregate concrete (RAC). The results show that hybrid fiber reinforcement can be a reliable approach to enhance the mechanical performance and crack resistance of RAC. Furthermore, low-cost acoustic emission (AE) serves as an effective non-destructive method for monitoring damage progression within the material. Full article

The rapid emergence of antimicrobial resistance has intensified the need for advanced therapeutic platforms capable of improving the efficacy, stability, and targeted delivery of antimicrobial agents. Electrospun nanofibers have emerged as highly promising materials for biomedical applications due to their large surface area, high porosity, tunable morphology, and ability to incorporate a broad range of bioactive compounds. This review provides a comprehensive overview of the design, fabrication, and biomedical applications of electrospun bioactive nanofibers functionalized with antimicrobial drugs. It presents the main nanofiber fabrication techniques, with particular emphasis on electrospinning and the influence of solution, process, and environmental parameters on fiber morphology and drug-loading efficiency. Natural, synthetic, and hybrid polymer systems commonly employed in electrospun antimicrobial nanofibers are analyzed in relation to their physicochemical properties, biocompatibility, and therapeutic performance. In addition, the review highlights different drug incorporation strategies, including encapsulation, immobilization, and surface coating, as well as the mechanisms of action of antimicrobial agents. Recent advances in nanotechnology-based antimicrobial systems and their role in overcoming analytical, biopharmaceutical, and drug-delivery limitations are also examined. Furthermore, the review addresses current challenges related to scalability, reproducibility, stability, and clinical translation of electrospun nanofibers. Finally, future perspectives focusing on multifunctional, stimuli-responsive, and personalized antimicrobial nanofiber systems are discussed as promising directions for combating bacterial infections and reducing the global burden of antimicrobial resistance. Full article

Carbon nanotube (CNT)-reinforced composites are promising advanced materials due to their exceptional mechanical properties. This paper presents a comprehensive investigation of the mechanical behavior of CNT/epoxy composites through theoretical modeling and experimental validation. An equivalent cylindrical fiber model was developed to transform CNTs into effective reinforcement phases, enabling the application of classical composite mechanics. Three reinforcement configurations were analyzed: two unidirectional short fiber models (aligned and staggered) and a three-dimensional four-directional braided long-fiber model. The effects of geometric parameters, including the diameter-to-thickness ratio (D/t) and fiber aspect ratio, on the effective elastic moduli were systematically evaluated. Static and dynamic compression experiments were conducted using an MTS 810 testing system and a Split Hopkinson Pressure Bar (SHPB) to examine the influence of loading rate, vacuum treatment, and reinforcement type (CNT, SiC, and hybrid SiC/CNT) on composite strength. The results indicated that 3 wt% CNT reinforcement increases the Young’s modulus by 30% under static loading and enhanced the dynamic compressive strength under impact loading. The vacuum degassing process significantly affected composite quality, with insufficient vacuum leading to strength degradation due to void formation. Theoretical predictions using Mori–Tanaka and dilute methods showed good agreement with experimental results at low reinforcement volume fractions. Scanning electron microscopy revealed uniform CNT dispersion and provided insights into failure mechanisms, including CNT pull-out and breakage. This work contributes to the understanding of structure–property relationships in CNT-reinforced polymer composites and provides guidelines for achieving their optimal design. Full article

Future lunar missions, like the International Lunar Research Station (ILRS), demand single-launch multi-point operations, urgently requiring reusable energy-absorbing structures. Integrating shape memory alloy (SMA) into honeycombs offers a promising solution; however, deformation exceeding the SMA’s recoverable limit induces structural residual deformation, altering the configuration and degrading subsequent energy absorption. To address this, we propose a semi-analytical, data-calibrated hybrid model predicting SMA honeycomb residual deformation. A four-stage linear constitutive model is established capturing superelasticity and martensitic yielding. Cell walls are idealized as equivalent beams. Using layered fiber integration and numerical interpolation, a nonlinear moment–curvature relationship is constructed, enabling rapid structural residual deflection evaluation from material residual strains. Finite element results confirm that initial residual deformation stabilizes the honeycomb into a reusable configuration, governing subsequent plateau stresses. Calibrated by uniaxial test data, the proposed model accurately predicts residual deformation ratios and reusable plateau stresses with errors within 8%. By bridging material-level strain with structural-level deformation, this approach circumvents computationally expensive full-scale simulations and costly experimental trials, providing a highly efficient tool for designing reusable SMA absorbers. Full article

Hybrid conductive materials have attracted increasing attention due to their combined electrical conductivity, mechanical flexibility, and sustainability. In this work, new hybrid materials based on polyaniline (PANI)-wrapped multi-walled carbon nanotubes (MWCNTs) and microfibrous cellulosic substrates were developed and assessed for photocatalytic degradation of a model dye pollutant. First, in situ oxidative polymerization of aniline in formic acid (FA) was conducted in the presence of MWCNTs to afford stable dispersions of carboxylated polyaniline-wrapped carbon nanotubes (c-PANI/MWCNTs). Next, the dispersions were used for affordable impregnation of microfibrous cellulosic filter paper. The influence of the initiator type—potassium peroxodisulfate (KPS) and hydrogen peroxide—on polymer–nanotube interactions, stabilization and surface deposition was emphasized. The structural, surface, morphological and thermal properties of the obtained dispersions and cellulose nanocomposites were systematically investigated using Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and thermal gravimetric analysis. The results revealed strong interfacial interactions between c-PANI and the pristine MWCNTs, resulting in improved dispersion stability and effective and even surface deposition of the conductive c-PANI/MWCNT hybrids into the cellulose fiber mesh. The photocatalytic degradation of 5 ppm methylene blue (MB) dye in the presence of the developed nanocomposite materials under UV-A illumination was studied. The results showed that the c-PANI@MWCNT-impregnated cellulose substrates exhibited enhanced photocatalytic ability (up to 83% degree of degradation of MB dye) in comparison with the pure c-PANI. Full article

Thermoplastic fiber metal laminates (TFMLs) are lightweight hybrid materials combining metallic layers with fiber-reinforced thermoplastic composites, offering a high strength-to-weight ratio. Existing studies indicate a limited range of polymer matrices used in such structures, most commonly polyamide 6 (PA6). In this work, polybutylene terephthalate (PBT) was selected as a potential alternative matrix because literature data indicate its lower moisture absorption and good dimensional stability compared with PA6. A comparative analysis of TFMLs based on aluminum and carbon fabric-reinforced composites with PA6 and PBT matrices was conducted. Static tensile tests were performed on base materials, composites, and laminates, supported by analytical modeling using the superposition method and fractographic analysis. The results showed that fiber orientation and polymer content significantly affect stiffness, strength, and damage evolution. Fiber orientation remains the governing factor, controlling load transfer and damage initiation. Laminates with 0/90° fibers exhibited the highest strength, while ±45° configurations showed reduced performance due to shear-dominated deformation. The polymer primarily acts as a matrix, ensuring structural integrity, with comparable mechanical properties for both systems. Delamination at the metal–composite interface was identified as the dominant failure mechanism. Full article

Engineered cementitious composite (ECC) is a high-performance strain-hardening material widely used in durable infrastructure, yet its complex multi-parameter interactions make accurate mixture design and performance prediction challenging. This study aims to establish an EDFrame, which is an integrated prediction framework for engineered cementitious composite (ECC). First, two original datasets of ECC’s tensile stress and strain are collected from the comprehensive and authoritative literature, comprising 18 features and 10 categories of single or hybrid fibers. Data augmentation is then performed using a constraints-modified Conditional Tabular Generative Adversarial Network (Tuned-CTGAN), with two traditional methods for comparison. A One-Dimensional Convolutional Neural Network with a residual module (1D-Residual CNN) is developed to predict tensile stress and strain, and its performance was compared against five popular machine learning models. The interpretability of the proposed model has been achieved through Partial Dependence Plot (PDP) and Kernel SHAP analyses. The results demonstrate that Tuned-CTGAN effectively generates reliable synthetic data, significantly improving the R² of 1D-Residual CNN from 0.8658 to 0.9128 for tensile stress and from 0.8433 to 0.9378 for tensile strain, outperforming all compared models. PDP analysis identifies optimal fiber content (1.5–2%) and fiber length (12–20 mm) ranges for enhanced tensile performance, while SHAP analysis reveals fiber length and diameter as the most critical features influencing tensile stress and strain, respectively. The proposed EDFrame provides a robust and interpretable solution for ECC performance prediction, supporting efficient and accurate mixture design in engineering practice. Full article

Hybrid organic–inorganic composites based on biopolymers and nanoclays are attracting increasing interest for the development of functional materials in biomedical and agricultural applications. In this work, elongated alginate/halloysite nanotube (Alg/HNT) composite filaments were fabricated through a wet-spinning process assisted by syringe-based extrusion. Alg/HNT dispersions with different inorganic/organic ratios were first screened in terms of colloidal stability and injectability in order to identify suitable formulations for extrusion. The influence of key processing parameters, including the extrusion flow rate and calcium chloride concentration in the coagulation bath, was then systematically investigated to elucidate their effect on filament morphology and structure. Optical and scanning electron microscopy revealed that filament diameter can be tuned by varying the CaCl₂ concentration, while partial alignment of alginate chains along the extrusion direction was observed. Halloysite nanotubes were homogeneously distributed within the polymer matrix, mainly as micro-sized aggregates. Finally, the nanotubes were chemically functionalized with caffeine, as a model molecule, and incorporated into the alginate filaments, demonstrating the feasibility of introducing specific functionalities into wet-spun Alg/HNT composite fibers. These results establish a reproducible strategy for the fabrication of alginate/HNT filaments with tunable morphology and functionalizable nanotube interfaces, providing a versatile platform for the development of sustainable hybrid biopolymer materials. Full article

New partially bio-based, waste-derived composites are manufactured from date palm surface fibers (DPSF), waste coffee filters (CFP), and disposable medical isolation gowns (MIG). These three disposable raw materials fill landfills and create an environmental problem. Therefore, the objective of this current study is to use such materials in creating promised thermal insulation and sound absorption boards. Six hybrid composites with different compositions were made using Polyvinyl acetate (PVA) wood adhesive as a binder. Three of them were made of DPSF and MIG, and the other three were composed of DPSF and the CFP. Different tests were performed on the developed composites, such as thermal conductivity measurements, sound absorption and noise reduction determination, surface morphology image analysis, thermogravimetric analysis, and three-point bending tests. The results showed that the thermal conductivity coefficients for the hybrids DPSF + MIG and DPSF + CFP are in the ranges 0.0493–0.0613 W/(m·K) and 0.052–0.065 W/(m·K), respectively, over the temperature range 24–82 °C. The sound absorption coefficient (SAC) is greater than 0.4 for all composites at frequency bands greater than 500 Hz. The noise reduction coefficient (NRC) is ≥0.45 for all composites. Surface morphology images of the composites were also reported. The results also show that the composites are thermally stable at temperatures up to 258.3 °C. The flexural modulus ranges between 5.0 and 8.46 MPa for the medical isolation gown composites and 2.49 and 5.57 MPa for the coffee filter paper composites. The hybrid composites have a lower moisture content of 0.51% to 2.5%. These promising results support the use of these composites for thermal insulation and sound absorption in building construction as alternatives to conventional thermal insulations derived from crude fuels. Full article

Agricultural waste materials can serve as functional constituents in cement-based composites through three pathways: (i) organic bio-aggregates that lower density and alter thermal behavior, (ii) lignocellulosic fibers that control cracking and improve post-cracking resistance, and (iii) agro-ash supplementary cementitious materials (SCMs) that densify pore structure and reduce permeability when ash quality and curing are controlled. This review draws on 98 papers, with coconut shell aggregate and coir/coconut fibers as the core focus; agro-ash SCMs (notably palm oil fuel ash, POFA, and rice husk ash, RHA) enter where they clarify mechanisms or inform hybrid design. Rather than cataloging compressive-strength data, the synthesis is organized around controllable process inputs (feedstock conditioning, mix design, curing) and the interface-governed mechanisms that determine performance: interfacial transition zone (ITZ) character and pore connectivity. In coconut shell systems, density reductions come at a cost: elastic modulus drops and moisture sensitivity rises unless shell conditioning, particle packing, and matrix refinement are managed. In fiber systems, gains in toughness and residual capacity are bounded by mixing workability and by the long-term stability of the fiber–matrix bond under alkaline and wet–dry exposure. A mix must first meet strength, serviceability, and transport requirements before its embodied impact is compared with conventional alternatives. The contribution is to reframe these systems around controllable processing and interface mechanisms instead of tabulated strength values; preparation, treatment, and characterization data are consolidated into bounded design windows, an explicit core versus supporting evidence convention is applied, and sustainability is judged under functional equivalency rather than per-volume carbon. Full article

High-strength, high-modulus polyimide (PI) fibers are a type of high-performance organic fiber known for their exceptional high-temperature resistance. When blended with carbon fibers to prepare hybrid composite materials, they have the potential to strike a balance between rigidity and toughness, thereby offering a composite structure with high modulus, strength and high toughness. In this study, a series of hybrid fiber-reinforced composites were fabricated using high-strength, high-modulus PI fibers together with carbon fibers as reinforcements and a PI resin matrix. The effects of the hybrid ratio on the tensile, compressive and flexural properties, as well as the failure modes, were systematically investigated. Experimental results showed that, compared to pure PI fiber composites, the hybrid fiber composites exhibited significant improvements in the compressive and flexural properties, in accordance with the hybrid law. Specifically, the hybrid composites demonstrated a negative hybrid effect in terms of tensile properties, whereas they exhibited a positive hybrid effect in terms of compressive and flexural properties. In high-temperature flexural tests, the addition of carbon fibers significantly enhanced the retention of the properties at 300 °C and 370 °C; for instance, the incorporation of carbon fibers at a volume fraction of 24% enhanced the flexural strength retention rate of the composite laminate at 300 °C from 37% to 66%, and remarkably increased the modulus retention rate from 50% to 94%, showing great advantages of the hybrid composite in a load-bearing structure at elevated temperatures. Full article

Geopolymer gel concrete (GPC) is a kind of environmentally friendly concrete, which has become a potential alternative material to replace ordinary concrete. Traditional mix design of GPC is carried out under experimental conditions, which is time-consuming and labor-intensive. Geopolymer concrete (GPC) is intended for use in hydraulic structures, which are often exposed to water environments. Water flow exerts significant abrasion and erosion on these structures. If the abrasion resistance (AR) of the material is poor, the service life and service quality of hydraulic structures will be substantially reduced under the action of water flow. Therefore, AR is a key performance indicator for GPC in hydraulic engineering applications. This abrasion resistance can be enhanced by using fibers (for example, steel fibers, polyvinyl alcohol (PVA) fibers, and basalt fibers) and nanomaterials. Furthermore, there is a complex nonlinear relationship between the proportions of fibers and nanoparticles added and the properties of GPC. In this study, the circular ring test method and the underwater steel ball test method were conducted to investigate the AR of nano-SiO₂ (NS) and hybrid fiber (NHF) reinforced geopolymer gel concrete (NHF-GPC). A backpropagation (BP) neural network (BPNN) model optimized by the Grey Wolf Optimizer (GWO) (GWO-BPNN) is established to predict the abrasion resistance strength (ARS) and the abrasion rate of NHF-GPC based on the circular ring test method. In addition, the ARS, abrasion rate, and average abrasion depth (AAD) based on the underwater steel ball test method were also predicted. The results indicate that the GWO-BPNN model demonstrates superior performance over the standard BPNN, exhibiting higher prediction accuracy, better fitting performance, and faster convergence speed. Specifically, for the circular ring test method abrasion rate prediction, GWO-BPNN reduced the root mean square error (RMSE) by 30.3% and lowered the mean absolute percentage error (MAPE) to 8.4%. The GWO-BPNN model established in this study can provide efficient and reliable theoretical support for the optimization of the NHF-GPC mix design. Full article

Glass fiber–reinforced polymer (GFRP) reinforcement provides an effective alternative to conventional steel in concrete structures due to its corrosion resistance. Nevertheless, the lower elastic modulus of GFRP necessitates careful consideration of serviceability behavior in GFRP-reinforced concrete members. This study presents a numerical sectional analysis model for predicting the flexural response and ultimate capacity of hybrid reinforced concrete beams incorporating embedded GFRP profiles in combination with either mild steel or GFRP reinforcement bars under monotonic static loading. The proposed model employs realistic nonlinear stress–strain relationships for concrete and steel, together with secant moduli of elasticity evaluated at different loading stages. Particular emphasis is placed on detailed stress distribution in flexural sections, including the contribution of tension stiffening in the post-cracking regime. The formulation integrates nonlinear constitutive material behavior with theoretical sectional equilibrium to evaluate the effective flexural secant stiffness. For practical serviceability assessment and to reduce dependence on complex analytical procedures, strain vectors and stiffness matrix components are derived using elasticity coefficients that reflect modulus degradation obtained from numerical analysis. The accuracy of the model is verified through comparison with experimental results, including ultimate flexural capacity and moment–deflection responses. Many crucial parameters were studied, such as the longitudinal reinforcement ratio, type of reinforcement, concrete compressive strength, position of the I-GFRP profile, and rotation of the I-GFRP profile. The results of this study demonstrated that both the longitudinal reinforcement ratio and the rotation of the I-GFRP profile have a significant influence on the ultimate load capacity and deflection behavior. The close agreement between numerical predictions and experimental observations demonstrates the reliability and applicability of the proposed model for structural engineering analysis and design. Full article