Search Results (365)

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

Fibre-reinforced polymer composites incorporating synthetic reinforcements such as glass and carbon fibres are widely used due to their superior mechanical performance. However, their energy-intensive production and end-of-life disposal contribute to an increased carbon footprint and significant environmental burden. Natural fibre-reinforced composites have emerged as promising low impact alternatives, but variability in their mechanical performance and the lack of controlled comparative studies limit their structural application. This study presents a controlled experimental comparison of alkaline-treated unidirectional flax/epoxy and hemp/epoxy composites fabricated using the vacuum-assisted resin infusion moulding (VARIM) process. Alkali treatment was employed to enhance the fibre–matrix interfacial bonding. Mechanical characterization was conducted through tensile, flexural, impact, interlaminar shear strength (ILSS), and Vickers microhardness testing in accordance with relevant ASTM and ISO standards. The flax/epoxy composites exhibited superior in-plane mechanical performance including, 9.1% higher tensile modulus, 13.8% higher flexural strength and 20.5% higher flexural modulus compared to hemp/epoxy composites. A significant improvement was observed in impact performance, with hemp composites showing 87.4% higher impact strength, indicating enhanced resistance to dynamic loading. Conversely, hemp/epoxy composites demonstrated a 10.6% higher ILSS, suggesting improved interfacial shear resistance and fibre interlocking. These findings confirm that the fibre type significantly influences composite performance, with flax fibres providing superior stiffness and strength, while hemp fibres offer better interlaminar shear behaviour and impact strength. Scanning Electron Microscopy (SEM) fractographic analysis was additionally conducted on fracture surfaces to characterize failure mechanisms and fibre–matrix interfacial morphology. The present study provides a reliable comparative framework for material selection and demonstrates the potential of flax- and hemp-based composites as sustainable alternatives for lightweight structural applications. This study supports the development of sustainable composite materials and contributes to the United Nations Sustainable Development Goals (SDGs), particularly SDG 12 (Responsible Consumption and Production), SDG 13 (Climate Action), and SDG 11 (Sustainable Cities and Communities). Full article

The growing diffusion of dealcoholized wines calls for a deeper understanding of how information and sensory evaluation jointly shape consumer acceptance, particularly in traditional wine markets. This study investigates the effects of different combinations of information and tasting on sensory evaluation and willingness-to-pay for a partially dealcoholized red wine. A between-subjects experiment was conducted during a scientific festival in Apulia (Italy), where participants were assigned to three conditions (INFO-SENS, SENS, INFO) and evaluated a non-commercialized Apulian Primitivo (1.5% ABV), produced through low-temperature vacuum evaporation and not pasteurized. Sensory attributes (visual, olfactory, gustatory, overall) were rated on 9-point hedonic scales, and WTP for a 125 mL glass was elicited using a payment card. The results show that the information-only group (INFO) reported the highest WTP, compared to the tasting-only group (SENS). Information exposure increased visual and olfactory evaluations, but not gustatory ratings. Prior knowledge of NoLo wines was associated with negative expectations, though this effect was attenuated by information. Overall, within this experimental setting, information emerged as a key driver of perceived value outweighing sensory liking, although the two remained positively correlated. These findings highlight the importance of transparent communication in fostering acceptance and repositioning dealcoholized wine as a credible category within traditional markets. Full article

We present a vacuum-assisted Polymethyl methacrylate (PMMA) impregnation process for cotton textiles, coupled with a physics-aware bidirectional artificial neural network (ANN) framework, to both predict and tune the natural fiber composite response from a compliant and flexible to a stiff and strong behavior. Cotton fabric samples were impregnated with acetone-borne PMMA baths, ranging from 0 to 5 wt.% polymer concentration. After drying, the PMMA formed conformal fiber coatings and inter-fiber bridges, with optimal load transfer observed at approximately 0.5–1.0 wt.%. Mechanical properties, including the elastic modulus, tensile strength, ductility, and toughness, were measured alongside Differential Scanning Calorimetry (DSC), Glass Transition Temperature (T_g), Change in heat capacity at constant pressure (ΔCp), gravimetry, and morphology tests. Rule-of-mixtures, porosity, and thermal constraints were embedded as regularization within the ANN loss functions to improve the physical consistency of the training. The forward and inverse models achieved sub-percent prediction errors with narrow bootstrap confidence intervals. It was found that removing physics regularization notably increases forward model error (by fivefold), as well as the inverse model error by one order of magnitude. Full article

To address the challenges of limited samples, class imbalance, and real-time requirements in surface defect detection for solar vacuum glass collector tubes, this study proposes an improved lightweight RT-DETR-based method. Specifically, DICM is introduced into the backbone to improve multi-directional and multi-scale feature extraction, HAFB is embedded in the neck to enhance the fusion of local details and global semantics, and transfer learning is adopted to alleviate data scarcity under small-sample conditions. Experiments on a self-built defect dataset of solar vacuum glass collector tubes show that the proposed method outperforms the original RT-DETR and several mainstream detectors in terms of Precision, Recall, mAP@0.5, and F1-score while maintaining favorable inference speed and model compactness. Under the same hardware conditions, the proposed model achieves an mAP@0.5 of 0.95, an inference speed of 83.21 FPS, and a model size of 82.36 MB. These results demonstrate the feasibility of the proposed method for real-time online defect detection in industrial scenarios. Full article

The aim of the study was to investigate the effect of enriching carrot slices by NFC (not from concentrate) juices from chokeberry (CH), sea buckthorn (SB), cherry (CHE) and carrot (CA) before microwave-vacuum (MVD) and freeze-drying (FD) carrot on the physicochemical and thermal properties. While water activity (AW) was not dependent on enrichment treatment but only on drying method, NFC juices significantly enriched carrot slices with biocomponents. Freeze-dried samples, as a reference, had significantly lower AW than those dried by the MVD method. Both FD and MVD-dried samples had comparable polyphenol content and DPPH antioxidant activity (AA), but the MVD-dried samples exhibited higher ABTS antioxidant activity. Carrot enrichment in chokeberry and cherry juices resulted in up to six and 10 times higher TPC than in the raw material. In addition, samples enriched in these juices and dried with FD proved to be the most stable in terms of water state and glass transition temperature (61.4 and 69.6 °C) and water activity (approx. 0.10). In FTIR analysis, all samples exhibited similar spectral shapes, indicating similar chemical composition and functional group composition. Only in the spectral region below 900 cm⁻¹ were unique molecular vibrations induced by various organic compounds present. Enriching carrot in juices and MVD can lead to increased hardness (Fmax and breaking work), although this is associated with increased crispness, resulting from the microstructure with a large number of small pores, especially in MVD samples enriched with cherry, chokeberry, and carrot juices, with scores of 8.0–8.4 In this respect, the average crispness rating of the MVD samples (7.2) exceeded that of the FD samples (6.8). If there is a requirement for crunchiness in the future production of dried vegetables as snacks, changes in hardness should be prioritized, along with color and biocomponent content. Full article

In this work, Ce-doped ZnO thin films at various contents of cerium were deposited on glass substrates by thermal vacuum evaporation to study the influence of Ce concentration on their optical, structural, morphological, and photocatalytic behavior. Pure ZnO and Ce-doped ZnO films doped with 2% and 5% Ce were characterized by SEM, XRD, AFM, UV–VIS spectroscopy, and ellipsometry. The XRD analysis confirmed that all the films retained the hexagonal wurtzite structure, while Ce incorporation induced lattice strain and reduced crystallite size, particularly at higher doping levels. SEM and AFM studies showed that films with 2% Ce exhibited smaller grain size and lower roughness, whereas 5% Ce-doped films showed grain growth and increased roughness. Pure ZnO films displayed high transparency (>90%), whereas Ce incorporation caused a red shift in the absorption edge and narrowing of the optical band gap due to defect-related states and lattice distortion. Photocatalytic experiments revealed that Ce doping improved charge carrier separation and increased the number of oxygen vacancies. Among all samples, the 2% Ce-doped ZnO film demonstrated the highest photocatalytic efficiency. These findings highlight the importance of controlled Ce doping in tuning the microstructure, optical properties, and photocatalytic performance of ZnO thin films, making them suitable for environmental remediation and optoelectronic applications. Full article

The crystal structure regulation of Ti₃O₅ by Al₂O₃ doping and its effect on the optical properties of TiO₂ films prepared by electron beam evaporation were systematically studied. Ti₃O₅ coating materials with different Al₂O₃ doping contents (0–50 at%) were prepared by vacuum melting, and the corresponding TiO₂ films were deposited on K9 glass substrates via electron beam vacuum evaporation. The phase structure, phase transition temperature, chemical composition and optical properties of the materials and films were characterized by XRD, DSC, EDS, XPS, UV-Vis and AFM. Results show that Al₂O₃ doping induces the phase transition of Ti₃O₅ from a room-temperature stable β-phase to a high-temperature stable λ-phase, with complete transition at 5 at% doping. Al³⁺ with a smaller ionic radius causes lattice contraction and local distortion of Ti₃O₅, enabling stabilization at room temperature of the λ-phase. For TiO₂ films, 12.5 at% doping is the optimal state with the stable composition transfer under this condition. With the increase in Al₂O₃ doping content, the refractive index and extinction coefficient of TiO₂ films decrease continuously, while the optical band gap and surface roughness show an increasing trend. The changes in optical properties are mainly ascribed to the low refractive index of Al₂O₃, lattice compressive strain effect and oxygen vacancy passivation induced by Al³⁺. This study clarifies the regulation effect of Al₂O₃ doping on Ti₃O₅ phase transition and TiO₂ film optical properties, and provides theoretical basis and experimental reference for the doping modification of TiO₂ films and their practical applications in consumer electronics and optical filter devices. Full article

The ultra-precision machining of micro-optics from low glass transition temperature (T_g) hydrophobic polymers is frequently compromised by thermal instability and kinematic constraints imposed by on-axis turning. To address these challenges, this study presents a novel clamping–cooling system engineered for the off-axis diamond turning of low-T_g polymers. The design integrates vacuum clamping for workpiece stabilization with an embedded microchannel network for efficient thermal management. Strategic material selection effectively balances thermal insulation with mechanical stability. Performance evaluations demonstrated robust thermal regulation: lens blank surface temperatures stabilized at 6 °C during stationary testing, and the system was able to drop below 0 °C under maximum cooling targets. This strict thermal control enabled achieving nanometer surface roughness. Ultimately, this modular system facilitates the scalable, simultaneous production of high-quality, polishing-free intraocular lenses (IOLs), advancing manufacturing capabilities for complex precision optics. Full article

A sandwich structure consists of a light core and two thin laminates bonded on both sides of the core. Sandwich structures have applications in structural constructions such as wind turbine blades and marine boats. These structures may experience low-velocity impacts from maintenance operations or during service conditions; thus, it is important to study these low-velocity impacts. In the current study, a sandwich structure was fabricated from PVC foam core and unidirectional glass fibres using the vacuum resin infusion method. The PVC foam core used was of 10–20 mm thickness while the face sheet had two different thicknesses. The panel was tested for impact strength using drop weight equipment at impact energies at three energy levels. The results were reported for damage area, force–time, force–displacement and energy–time curves. Full article

External leakage from valve stem packings is a critical safety and reliability issue in high-pressure hydrogen systems. This work aims to quantify how packing geometry and polymer selection influence stem sealing in a PN650 needle valve (316L body and stem). Two geometries were compared: a conical V-ring (chevron style) stack and a flat three-disc stack. Two polymer material sets were assessed: Vespel^® polyimide (SP-1/SP-21) and a glass-filled PTFE sealing element combined with a virgin PEEK back-up ring. Four assemblies (one per geometry/material combination) were first screened by hydrostatic pressure hold testing up to 1500 bar and by helium mass spectrometer leak measurements under vacuum. All assemblies sustained the hydrostatic overpressure hold with negligible decay. Vacuum helium screening produced leak rates between 3.7 × 10⁻¹⁰ and 9.5 × 10⁻¹⁰ mbar·l·s⁻¹, with the conical V-ring geometry consistently outperforming the disc stack. A more demanding helium test at 700 bar with external vacuum yielded leak rates of 3.6–3.7 × 10⁻⁸ mbar·l·s⁻¹, for conical assemblies. Based on the screening results and practical industrial considerations, the PTFE/PEEK conical configuration was selected for endurance testing and completed 2500 open/close cycles in 650 bar hydrogen without gland readjustment. Post-cycling checks confirmed continued tightness, including a qualitative helium pressure hold result near 700 bar and 0 bubbles in 10 min in the seat tightness test. Microscopy/EDX revealed limited wear with minor metallic transfer. The proposed multi-stage workflow provides a pragmatic route for the early qualification of stem packings for high-pressure hydrogen valves. Full article

This study investigates the degradation mechanisms of glass-fibre- and carbon-fibre-reinforced polymer (GFRP and CFRP, respectively) composites fabricated either with epoxy, vinyl-ester, or bio-epoxy resins under a hygrothermal environment. Composite laminates were manufactured using the vacuum-assisted resin infusion technique and exposed to high moisture and elevated in-service temperatures of 23 °C (room temperature), 40 °C and 60 °C for up to 125 days. Changes in the physical, microstructural, chemical and mechanical properties were then assessed. CFRP and GFRP composites showed distinct differences in their hygrothermal ageing depending on the resin system used in the manufacturing. CFRP composites consistently demonstrated higher stability than GFRP composites. Epoxy resin exhibited high resistance to water absorption and hydrolysis under hygrothermal exposure. After 125 days at 60 °C, glass/epoxy (GE) and carbon/epoxy (CE) composites retained 79.0% and 72.1% of their tensile strength and 46.9% and 72.6% of their interlaminar shear strength (ILSS), respectively. Vinyl-ester composites showed high mechanical retention, with glass/vinyl-ester (GV) and carbon/vinyl-ester (CV) retaining 70.8% and 83.1% of tensile strength and 67.5% and 80.3% of ILSS, respectively. Despite this mechanical stability, evidence of hydrolysis indicated ongoing chemical degradation of the vinyl-ester resin under prolonged hygrothermal exposure. In contrast, bio-epoxy composites exhibited relatively low overall durability. Glass/bio-epoxy (GB) retained 126.5% tensile strength and 68.8% ILSS, whereas carbon/bio-epoxy retained 61.0% tensile strength and 44.3% ILSS after 125 days at 60 °C. Overall, fibre and resin types were found to have a significant effect on the hygrothermal ageing of polymer composites. Full article

TiO₂ films with a thickness of 20 nm were obtained by anodizing a titanium film with an aluminum sublayer on a glass substrate. The I–V characteristics were studied in a temperature range of 100–300 K. Three linear sections can be distinguished on the I–V curves in logarithmic coordinates with a bias voltage of up to 2.5 V. The first section is an ohmic section with a bias voltage sweep from 0 V. The second section is associated with the space-charge-limited currents. The third section is characterized by the flow of Poole–Frenkel currents. In the third section, the slope of the approximating line is greater than in the second one due to the flow of higher currents. This is explained by the transition of electrons from donor centers to trap levels, which leads to a decrease in the number of free traps available for capturing electrons injected from the contacts into the conduction band. The obtained values of the Fermi energy of 0.032 and 0.028 eV for temperatures from 100 to 300 K, respectively, indicate that the electron traps in the forbidden zone of TiO₂ are shallow. The value of the donor level energy E = 0.082 eV is close to the values of the activation energy of thermal conductivity. This indicates the formation of donor centers in anodic TiO₂ by the mechanism of donor vacancies. In anodic TiO₂ films, the concentration of electron traps is 10¹⁵ cm⁻³, which is approximately three orders of magnitude less than their concentration in anodic TiO₂ films obtained by vacuum deposition. Full article

Industrial conveyor systems commonly use steel flight bars, which can account for nearly 50% of the total system mass and significantly affect energy consumption. This study investigates epoxy matrix composites reinforced with glass, carbon, and Kevlar fibers as lightweight alternatives to steel flight bars. A multiscale analytical approach combining micromechanics, Classical Laminate Theory (CLT), and ply-level failure criteria is applied to evaluate the structural response under an industrial bending moment of 342.02 N·m. Tensile tests on vacuum-infused woven glass/epoxy laminates are used to validate micromechanical assumptions and calibrate elastic properties. Ply-wise analysis shows that carbon/epoxy laminates exhibit the lowest longitudinal stresses (≈43 MPa), followed by Kevlar/epoxy (≈53 MPa) and glass/epoxy (≈95 MPa), all well below their respective strength limits. Replacing steel flight bars (4.64 t) with composite alternatives reduces the moving mass to 0.68–0.82 t, corresponding to an 82–85% reduction. This mass reduction significantly lowers the required mechanical power, resulting in an estimated annual energy saving of R$ 8812.80 under continuous operation. Overall, the results demonstrate that polymer-matrix composite flight bars are structurally safe and energetically advantageous, with carbon/epoxy providing the highest mechanical efficiency. Full article

This work presents a study on the evaluation of the erosive wear behavior of laminated composites, manufactured using the vacuum-assisted resin infusion (VARI) method with a glass fiber-reinforced epoxy matrix modified with SiO₂ nanoparticles (0.0, 1.5, and 3.0 wt.%). Results indicate that nanoparticle concentration and dispersion state critically influence the mechanical and tribological performance. The composite FG-1.5-SiO₂ with 1.5 wt.% SiO₂ exhibited optimal nanoparticle distribution, as confirmed by FTIR, GIXRD, and SEM analyses, with the lowest surface roughness (Ra = 0.215 μm), highest hardness (35.58 HV), and highest elastic modulus (19.66 GPa). These enhancements contributed to a 38% improvement in erosion rate compared to the unmodified laminated composite, with the lowest total mass loss (0.0261 mg) and erosion rate (2.3360 × 10⁻⁵ mg/g). Profilometry and SEM results revealed shallower wear depths and reduced matrix removal, indicating stronger fiber–matrix interface integrity. In contrast, the 3.0 wt.% SiO₂ composite (FG-3-SiO₂) suffered from nanoparticle agglomeration, which increased surface roughness, diminished mechanical properties, and reduced erosion resistance to levels comparable to the unreinforced material. The results indicate that homogeneous dispersion at an optimal concentration (1.5 wt.%) is crucial for improving erosion resistance, while agglomeration at higher concentrations negates the potential benefits of nanoparticle incorporation. These findings highlight the need to optimize nanoparticle dispersion for the development of fiberglass/epoxy composites with greater durability and erosion resistance in demanding applications. Full article