Search Results (322)

This study investigates the mechanical, morphological, and wear properties of SiO₂-filled tri-axial warp-knitted (TWK) glass fiber-reinforced vinyl ester matrix composites, with a focus on void fraction, tensile, flexural, hardness, and wear behavior. Adding SiO₂ fillers reduced void fractions, enhancing composite strength, with values ranging from 1.63% to 5.31%. Tensile tests revealed that composites with 5 wt% SiO₂ (GV1) exhibited superior tensile strength, Young’s modulus, and elongation due to enhanced fiber–matrix interaction. Conversely, composites with 10 wt% SiO₂ (GV2) showed decreased tensile performance, indicating increased brittleness. Flexural tests demonstrated that GV1 outperformed GV2, showcasing higher flexural strength, elastic modulus, and deflection, reflecting improved load-bearing capacity at optimal filler content. Shore D hardness tests confirmed that GV1 had the highest hardness among the specimens. SEM analysis revealed wear behavior under various loads and sliding distances. GV1 exhibited minimal wear loss at lower loads and distances, while higher loads caused significant matrix detachment and fiber damage. These findings highlight the importance of optimizing SiO₂ filler content to enhance epoxy composites’ mechanical and tribological performance. Full article

This study is among the first to characterize the tensile response of composites with quadriaxial glass fiber fabrics designed for marine structural applications. Four composite configurations were fabricated at laboratory scale, combining two matrix types (unsaturated polyester resin and epoxy resin) and the presence or absence of a Coremat Xi3 middle layer. Tensile tests were conducted at four test rates (10 mm/min, 200 mm/min, 500 mm/min, and 1000 mm/min), ranging from quasi-static to moderately dynamic conditions. Tests were conducted using the Instron 5982 universal testing machine (from Laboratory for Advanced Materials and Tribology, INCAS Bucharest, Romania). The specimens have a rectangular cross section, in agreement with SR EN ISO 527-4:2023. For strain measurements, an Instron advanced video extensometer (AVE) was used. Key mechanical parameters, such as maximum force, tensile strength, Young’s modulus, strain at break, and energy absorption, were extracted and analyzed. Results show that the polyester-based composite without a mat interlayer displayed the best overall performance, with the highest ultimate strength (~280 MPa), significant energy absorption (~106 J), and a consistent increase in ductility with increasing test rate. In contrast, the epoxy composite with Coremat Xi3 exhibited lower stiffness and strength, but higher strain and energy absorption at higher test rates, indicating a progressive failure behavior. These findings enhance the understanding of the tensile response of composites made of quadriaxial glass fiber fabric and provide valuable design data for structural components in marine environments, where both strength and energy absorption are essential. These insights support producers and end-users of non-crimp fabrics in making experimentally based selections of a composite, technological strategies, and design optimization. Full article

Fiber-reinforced composite materials exhibit orthotropic behavior, characterized by complex orthotropic engineering constants such as Young’s modulus, Poisson’s ratio, and shear modulus. It is widely recognized that basalt fibers possess superior resistance to elevated temperatures compared to glass fibers. However, the behavior of these fibers within composites at typical operational temperatures for automotive and consumer goods applications has not been thoroughly investigated. A novel measurement setup based on the non-destructive impulse excitation method has been developed for the automated identification of complex orthotropic engineering constants as a function of temperature. This study provides a comparative analysis of the identified engineering constants of bidirectionally fabric-reinforced glass and basalt composites with an epoxy matrix, across a temperature range from −20 °C to 60 °C. The results reveal only minimal differences in stiffness and damping behavior between the examined glass and basalt samples. Full article

This study explores the development and optimization of TiO₂-based photoactive coatings enhanced with silver (Ag)—to boost photocatalytic performance—for application on glass-fiber-reinforced polyester (GFRP) and epoxy (GFRE) composites. The influence of Ag content on the structural, physicochemical, and functional properties of the coatings was evaluated. The TiO₂-Ag coating showed the best performance and was tested under UV-A irradiation and visible light (Vis), with high efficiency in VOC degradation, self-cleaning, and microbial activity. The tests were repeated in multiple runs, showing high reproducibility in the results obtained. In GFRP, pollutant and microorganism removal ratios of more than 90% were observed. In contrast, GFRE showed a lower adhesion and stability of the coating. This result is attributed to incompatibility problems with the epoxy matrix, which significantly limited its functional performance. The results highlight the feasibility of using the TiO₂-Ag coating on GFRP substrates, even under visible light. Under real-world conditions for 351 days, the coating on GFRP maintained its stability. This type of material has high potential for application in modular building systems using sandwich panels, as well as in facades and automotive components, where self-cleaning and contaminant-control properties are essential. Full article

The increasing demand for sustainable materials has intensified the interest in natural fiber-reinforced composites (NFRCs) as environmentally friendly alternatives to synthetic composites. However, NFRCs often face limitations in thermal stability, restricting their use in high-temperature environments. To address this, the present study explores the hybridization of cellulosic flax fibers with protein-based wool fibers to improve thermal stability without compromising mechanical integrity. Wool–flax hybrid composites were fabricated using a bio-based epoxy resin through a resin infusion technique with different fiber proportions. The flexural properties of these composites were evaluated under varying temperature conditions to assess the influence of fiber composition and thermal conditions. This study specifically examined the impact of wool fiber content on the flexural performance of the composites under thermal conditions, including behavior near and above the matrix’s glass transition temperature. The results showed that the flexural properties of the hybrid biocomposites were significantly affected by temperature. Compared with specimens tested at room temperature, the flexural modulus of all variants decreased by 85–94%, while the flexural strength declined by 79–85% at 120 °C, depending on the variant. The composite variant with a higher wool content (variant 3W) exhibited enhanced flexural performance, demonstrating an average of 15% greater flexural strength than other variants at 60 °C and 5% higher at 120 °C. These findings suggest that incorporating wool fibers into flax-based composites can effectively improve thermal stability while maintaining flexural properties, supporting the development of sustainable biocomposites for structural applications. Full article

Natural composites find application in various fields because of their low specific weight and low investment cost. But due to their inherent nature, natural composites have lower strength and tend to absorb moisture, which makes them weak. In this work, woven glass, mono-bi-filament polypropylene, and polyester fibers in an epoxy matrix were developed with four and five different stacking layers of texture utilizing the hand-layup procedure. However, understanding the directional dependence of material properties is necessary for the application of these new materials. Three distinctive plates were fabricated for the purpose of the investigation. The laminated plates were tested on a universal testing machine (UTM) and a flexible test setup to examine the mechanical properties of the polymer fiber. By adding short fibers such as polypropylene, polyester fibers in a random manner improved the mechanical strength of the polymer composite compared to the other fiber types such as woven glass fiber sheets and woven polypropylene sheets placed in the middle of the composite. This is because short polymer fibers bond well with epoxy resin and have very good bonding strength. Full article

Hybrid fiber-reinforced polymer-laminated composites are often used under icy conditions (such as for reinforcing parts in aircraft frames and bridge beams), where there is an urgent demand for deicing. In this paper, besides the different mechanical properties of laminates along the longitudinal carbon fiber (CF) and glass fiber (GF) directions, the anisotropic electrothermal behavior of a hybrid glass/carbon fiber-reinforced epoxy (GCF/EP) is also investigated, as well as its deicing performance and self-repairing capability. The surface equilibrium temperature of GCF/EP composites can conveniently be adjusted by tuning the current magnitude and its flow direction. Compared to the longitudinal CF direction of the GCF/EP, where 0.3 A was loaded to achieve a surface equilibrium temperature of 122.8 °C, a much weaker current (0.03 A) was needed to load along the longitudinal GF direction to reach almost the same temperature. However, besides the higher flexural strength and fast temperature response, along the longitudinal CF direction, the GCF/EP exhibited excellent deicing performance, including a shorter time and larger energy efficiency. Furthermore, the self-repairing ability of the GCF/EP and its effect on the deicing performance of the composite were characterized. Studying the Joule heating effect of GCF/EP composite laminates and their corresponding deicing performance lays the foundation for their design and practical application in icy environments. Full article

The effect of the interaction between silica (nS) and hydroxyapatite (nHap) nanomaterials on the characteristics of unidirectional glass-fiber-reinforced epoxy (GF/Ep) composite systems is investigated in this work. The goal of the study is to use these nanofillers to improve the microstructure and mechanical characteristics. Pultrusion was used to produce hybrid nanocomposites while keeping the GF loading at a consistent 75% by weight. The hybrid nanocomposites were made with a total filler loading of 6 wt.%, including nHap, and a nS loading ranging from 2 to 4 wt.%. The mechanical performance of the composite was greatly improved by the use of these nanofillers. Compared to neat GF/Ep, hybrid nanocomposites with 6 wt.% combined fillers exhibited increased hardness (14%), tensile strength (25%), interlaminar shear strength (21.3%), and flexural strength (33%). These improvements are attributed to efficient filler dispersion, enhanced fiber-matrix adhesion, and crack propagation resistance. Incorporating 4 wt.% nS alone improved hardness (6%), tensile strength (9%), tensile modulus (21%), interlaminar shear strength (11.4%), flexural strength (12%), and flexural modulus (14%). FTIR analysis indicated Si-O-Si network formation and increased hydrogen bonding, supporting enhanced interfacial interactions. Ultraviolet reflectance measurements showed increased UV reflectivity with nS, especially in hybrid systems, due to synergistic effects. Impact strength also improved, with a notable 11.6% increase observed in the hybrid nanocomposite. Scanning and transmission electron microscopy confirmed that the nanofillers act as secondary reinforcements within the matrix. These hybrid nanocomposites present a promising material choice for various industries, including marine structural applications and automotive components. Full article

Currently, the main drivers for the production of phosphate glass fiber-reinforced composites are the growing demand for lightweight materials, reduced energy consumption, improved durability, and minimized environmental impact. This study aims to develop thermoset-based composites using chopped and continuous phosphate glass fibers (PGFs) combined with polyester and epoxy matrices, processed via contact molding. Physical, mechanical, thermal, and morphological characterizations were conducted. The addition of PGFs led to a steady increase in density and fiber volume fraction. For polyester composites with short PGFs, density rose from 1.60 g/cm³ (0 wt%) to 1.77 g/cm³ (22.8 wt%), with a corresponding volume fraction increase from 0% to 14.4%. Similarly, epoxy composites showed density values from 1.70 g/cm³ to 1.87 g/cm³ and volume fractions up to 15.2%. Thermogravimetric analysis (TGA) showed that as the fiber content increased, the thermal degradation of the resin was delayed, as evidenced by a rise in onset degradation temperature and greater residual mass—indicating improved thermal stability of the composites. Tensile strength increased from 20.8 MPa to 71.3 MPa (polyester) and from 26.8 MPa to 75.9 MPa (epoxy) with chopped fibers, reaching 145.7 MPa and 187.9 MPa, respectively, with continuous fibers. Flexural strength reached 167.9 MPa (polyester) and 218.0 MPa (epoxy) in continuous-fiber configurations. Young’s modulus values closely matched Hirsch model predictions. These findings confirm the potential of PGF-reinforced thermoset composites for high-performance and sustainable material applications. Full article

The growing demand for sustainable materials has driven interest in natural fiber-reinforced composites as eco-friendly alternatives to synthetic materials. This research investigates the fabrication and mechanical performance of hemp and sisal fiber-reinforced composites, with a focus on improving fiber–matrix bonding through alkali and fungal treatments. Experimental results show that fungal treatment significantly improves tensile and flexural strength, while hardness slightly decreases. Water absorption tests revealed moderate reductions in hydrophilicity compared to untreated samples, although absolute water uptake remains higher than conventional glass/epoxy composites. Microscopy analysis further confirmed enhanced fiber adhesion and structural integrity in treated specimens. These findings suggest that hybrid composites reinforced with hemp and sisal, particularly with fungal treatment, hold promise for low-to-medium load sustainable applications in the automotive interiors, packaging, and construction industries, where moderate mechanical performance and partial biodegradability are acceptable. This research contributes to the advancement of bio-based composite materials while acknowledging current limitations in long-term durability and complete biodegradability. Full article

The effects of benzoyl peroxide (BPO) and dimethylaniline (DMA) composition on the induction time and the tensile strength of thermoplastic acrylic (PMMA) resins have been investigated in this study. Eighteen resin formulations were prepared with different BPO/DMA ratios (2.0–9.5) and DMA contents (0.28–0.65 mol%), and it was observed that tensile strengths reached up to 66 MPa, and induction times (ITs) ranged from 100 to 207 min. Higher BPO/DMA ratios improved tensile strength but shortened IT, while greater DMA content accelerated curing. Polynomial regression models were successfully established, i.e., a third-order equation for the strength and a second-order equation for the IT, based on the BPO/DMA ratio and DMA content to identify the optimal formulation to balance the strength and the IT time. Two selected formulations, P-4-0.5 and P-3-0.3, were applied in vacuum-assisted resin infusion of glass fiber composites. The best-performing unidirectional (UD) laminate achieved a tensile strength of 1244 MPa. As regards ±45° biaxial (BX45) laminates, they exhibited a tensile strength of 124 MPa and a failure strain of 9.02%, which, while lower than that of epoxy, indicates competitive performance. These results demonstrate that the resin was well infused, resulting in 64% higher fiber volume fraction than typical infused glass/epoxy composites, and compositionally optimized PMMA resins can deliver epoxy-comparable strength and enhance damage tolerance in structural composite applications. Full article

This study investigates the degradation mechanisms of fiber-reinforced polymer (FRP) matrices in composite insulators under partial discharge (PD) conditions. The degradation products may further cause deterioration of the electrical and chemical resistance (ECR) glass fibers. Using pyrolysis–gas chromatography-mass spectrometry (PY-GC-MS) and high-performance liquid chromatography–tandem mass spectrometry (HPLC-MS-MS), the thermal degradation gas and liquid products of the degraded FRP matrix were analyzed, revealing the presence of organic acids. These acids form when the epoxy resin’s cross-linked bonds break at high temperatures, generating anhydrides that hydrolyze into carboxylic acids in the presence of moisture. The hydrolyzation process is accelerated by hydroxyl radicals produced during PD. The resulting carboxylic acids deteriorate the glass fibers within the FRP matrix by degrading surface coupling agents and reacting with the alkali metal–silica network, leading to the substitution and precipitation of metal ions. Organic acids, particularly carboxylic acids, were found to have a more severe deteriorating effect on glass fibers compared to inorganic acids, with high temperatures exacerbating this process. These findings provide critical insights into the deterioration mechanisms of FRP under operational conditions, offering valuable guidance for optimizing manufacturing processes and enhancing the longevity of composite insulators. Full article

This study presents a new approach to chemical processing using pyridine-based solvolysis to produce high-quality glass fiber from epoxy composites. Pyridine was chosen due to its solubility parameter, which precisely matches the parameters calculated for the epoxy matrix segment. Experiments with exposure in a pyridine medium demonstrated effective swelling and the potential for destruction. The solvolysis experiments were conducted in a round-bottomed flask with a reflux condenser and stirrer, under ambient conditions (20 °C) until the boiling point was reached (115.2 °C). Additionally, data from experimental studies conducted at subcritical temperatures before reaching 280 °C are presented. The dependences of changes in the mass of composites on time and temperature during the solvolysis process were determined. The tensile strength of the recovered fibers was examined, and thermogravimetric analysis was used to determine their properties. Fiberglass recovered at the boiling point is characterized by 91% tensile strength and 20% residual degradation products on the surface. The residual strength of fiberglass-reinforced plastic (FGRP) is 70.3%. The use of subcritical pyridine helps improve the quality of plastic products made from recycled fibers. This process retains 93% of the residual tensile strength for fibers that have been processed at 250 °C for two hours. Recycled fibers also contain 2.82% organic components on their surfaces. Using this material results in an increase in flexural strength of FGRP by 16.1%, compared to the reference samples. Full article

Composite materials have been extensively utilized in unmanned aerial vehicles (UAVs) and other aerospace applications due to their unique advantages, while laser countermeasures have emerged as a critical approach in anti-UAV warfare. Different laser modes produce significantly different effects. In this study, we have mainly considered the ablation and damage characteristics of composite materials affected by continuous wave (CW) and pulsed laser (PL) modes. Through comparative analysis of damage morphologies and elemental variations, the damage characteristics and mechanisms of composite materials have been studied, and thermodynamic models have been established. The results demonstrate that the damage produced using the CW mode is primarily thermal ablation, induced through power intensification, whereas the PL mode predominantly causes thermal stress fractures via energy concentration. This investigation provides fundamental references for optimizing laser-based counter-UAV systems. Full article

Polyphenylene sulfide (PPS) is becoming increasingly valuable in the electrical, electronic, and automotive industries. In particular, PPS composites reinforced with glass fiber (GF) have better dimensional stability and mechanical properties than conventional PPS materials and can be used in applications like electric vehicle capacitor housing. In the electric vehicle industry, the epoxy-molding process is essential for manufacturing capacitor housings, where the bonding strength between the PPS/GF composites and epoxy significantly affects the durability of the product. However, the inert surface characteristics of polymers like PPS limit their interaction with epoxy, decreasing the bonding strength. This study was aimed at enhancing the bonding strength between PPS/GF composites and epoxy by modifying the PPS surface using atmospheric-pressure plasma treatment. The surface modification resulted in increased surface roughness and the introduction of polar functional groups, which improved both mechanical interlocking and chemical affinity to the epoxy. Surface changes were analyzed using atomic force microscopy and scanning electron microscopy, and chemical characterization was conducted using X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. Surface energy was determined via contact angle measurements, and bonding strength was evaluated through single-lap shear tests. The results showed a 55% increase in surface energy and a 24.8% improvement in bonding strength due to the surface modification. Full article