Search Results (263)

This study focuses on the influence of prolonged ultraviolet (UV) irradiation on the mechanical properties and surface microstructure of glass fiber-reinforced plastics (GFRPs) and basalt fiber-reinforced plastics (BFRPs), which are widely used in construction and transport infrastructure. The relevance of the research lies in the need to improve the reliability of composite materials under extended exposure to harsh climatic conditions. Experimental tests were conducted in a laboratory UV chamber over 2000 h, simulating accelerated weathering. Mechanical properties were evaluated using three-point bending, while surface conditions were assessed via profilometry and microscopy. It was shown that GFRPs exhibit a significant reduction in flexural strength—down to 59–64% of their original value—accompanied by increased surface roughness and microdefect depth. The degradation mechanism of GFRPs is attributed to the photochemical breakdown of the polymer matrix, involving free radical generation, bond scission, and oxidative processes. To verify these mechanisms, FTIR spectroscopy was employed, which enabled the identification of structural changes in the polymer phase and the detection of mass loss associated with matrix decomposition. In contrast, BFRP retained up to 95% of their initial strength, demonstrating high resistance to UV-induced aging. This is attributed to the shielding effect of basalt fibers and their ability to retain moisture in microcavities, which slows the progress of photo-destructive processes. Comparison with results from natural exposure tests under extreme climatic conditions (Yakutsk) confirmed the reliability of the accelerated aging model used in the laboratory. Full article

In this study, a new fibre combination for an interlayer hybrid fibre-reinforced polymer laminate was investigated to achieve pseudo-ductile behaviour in tensile tests. The chosen high-strain fibre for this purpose was S-Glass, and the low-strain fibre was flax. These materials were chosen because of their relatively low environmental impact compared to carbon/carbon and carbon/glass hybrids. An analytical model was used to find an ideal combination of the two materials. With that model, the expected stress–strain relation could also be predicted analytically. The modelling was based on preliminary tensile tests of the two basic components investigated in this research: unidirectional laminates reinforced with either flax fibres or S-Glass fibres. Hybrid specimens were then designed, produced in a heat-assisted pressing process, and subjected to tensile tests. The strain measurement was performed using distributed fibre optic sensing. Ultimately, it was possible to obtain repeatable pseudo-ductile stress–strain behaviour with the chosen hybrid when the specimens were subjected to quasi-static uniaxial tension in the direction of the fibres. The intended damage-mode, consisting of a controlled delamination at the flax-fibre/glass-fibre interface after the flax fibres failed, followed by a load transfer to the glass fibre layers, was successfully achieved. The pseudo-ductile strain averaged 0.52% with a standard deviation of 0.09%, and the average load reserve after delamination was 145.5 MPa with a standard deviation of 48.5 MPa. The integrated fibre optic sensors allowed us to monitor and verify the damage process with increasing strain and load. Finally, the analytical model was compared to the measurements and was partially modified by neglecting the Weibull strength distribution of the high-strain material. 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

In today’s aviation industry, research and studies are carried out to manufacture and design lightweight, high-performance materials. One of the materials developed in line with this goal is glass laminate aluminum-reinforced epoxy (GLARE), which consists of thin aluminum sheets and S2-glass/epoxy layers. Because of its high impact resistance and excellent fatigue and damage tolerance properties, GLARE is used in different aircraft parts, such as the wing, fuselage, empennage skins, and cargo floors. In this study, a survey was carried out and a low-velocity impact model for GLARE materials was developed using the ABAQUS (2014) version V6.14 software and compared with the results of low-velocity impact tests performed according to the American Society for Testing and Materials (ASTM) D7136 standard. This article introduces a novel integrated approach that combines detailed numerical modeling with experimental validation of GLARE 4A FMLs under low-velocity impact. Leveraging ABAQUS, a robust FEM featuring explicit analysis, cohesive resin interfaces, and custom VUMAT subroutines was developed to accurately simulate energy absorption, dent depth, and delamination. The precise model’s predictions align well with test results performed according to ASTM D7136 standards, exhibiting less than a 0.1% deviation in the displacement (dent depth)–time response, along with deviations of 4.3% in impact energy–time and 5.2% in velocity–time trends at 5.5 ms. Full article

This study proposes a bionic helical configuration design concept, focusing on glass-fiber-reinforced polymer matrix composites. Through a combination of experimental and numerical simulation methods, it systematically investigates the resistance to multiple impacts and damage tolerance. The research designs and fabricates two types of bionic laminates: a cross-helical and a symmetric-helical structures. By conducting repeated impact experiments at 5 J of energy for 1, 5, 10, and 15 impact times and employing advanced characterization techniques, such as ultrasonic C-scan and X-ray CT, the study reveals the mechanisms of interlaminar damage propagation and failure characteristics. Based on experimental findings, a finite element model encompassing the entire impact process and post-impact compression behavior is established. Utilizing this model, three optimized novel bionic configurations are further developed, providing new insights and theoretical support for the structural design of high-performance impact-resistant polymer matrix composites. Full article

The use of composite materials within extreme environments is an exciting frontier in which a wealth of cutting-edge developments have taken place recently. Although there is vast knowledge of composites’ behaviour in standard room temperature and humidity, there is a great need to understand their performance in ‘hot/wet’ conditions, as these are the conditions of their envisaged applications. One of the key failure mechanisms within composites is interlaminar fracture, commonly referred to as delamination. The environmental effects of moisture and elevated temperatures on interlaminar fracture toughness are therefore essential design considerations for laminated aerospace-grade composite materials. IM7/8552, a toughened epoxy/carbon fibre reinforced polymer, was experimentally characterised in both ‘Dry’ and ‘Wet’ conditions at 23 °C and 90 °C. A moisture uptake study was conducted during the ‘Wet’ conditioning of the material in a 70 °C/85% relative humidity environment. Dynamic mechanical thermal analysis was carried out to determine the effect of moisture on the glass transition temperature of the material. Mode I initiation and propagation fracture properties were determined using double cantilevered beam specimens and Mode II initiation fracture properties were deduced using end-notched flexure specimens. The effects of precracking and the methodology of high-temperature testing are discussed in this report. Mode I interlaminar fracture toughness, $G_{IC}$, was found to increase with elevated temperatures and moisture content, with $G_{IC}=0.205{\mathrm{kJ}/\mathrm{m}}^2$ in ‘Dry 23 °C’ conditions increasing by 26% to $G_{IC}=0.259{\mathrm{kJ}/\mathrm{m}}^2$ in ‘Wet 90 °C’ conditions, demonstrating that the material exhibited its toughest behaviour in ‘hot/wet’ conditions. Increased ductility due to matrix softening and fibre bridging caused by temperature and moisture were key contributors to the elevated $G_{IC}$ values. Mode II interlaminar fracture toughness, $G_{IIC}$, was observed to decrease most significantly when moisture or elevated temperature was applied individually, with the combination of ‘hot/wet’ conditions resulting in an 8% drop in $G_{IIC}$, with $G_{IIC}=0.586{\mathrm{kJ}/\mathrm{m}}^2$ in ‘Dry 23 °C’ conditions and $G_{IIC}=0.541{\mathrm{kJ}/\mathrm{m}}^2$ in ‘Wet 90 °C’ conditions. The coupled effect of fibre-matrix interface degradation and increased plasticity due to moisture resulted in a relatively small knockdown on $G_{IIC}$ compared to $G_{IC}$ in ‘hot/wet’ conditions. Fractographic studies of the tested specimens were conducted using scanning electron microscopy. Noteworthy surface topography features were observed on specimens of different fracture modes, moisture saturation levels, and test temperature conditions, including scarps, cusps, broken fibres and river markings. The qualitative features identified during microscopy are critically examined to extrapolate the differences in quantitative results in the various environmental conditions. Full article

Thermoplastic fiber metal laminates (FMLs) are hybrid material systems that consist of a thin aluminum alloy sheet bonded to plies of fiber-reinforced adhesive. They provide excellent properties like fatigue strength, damage-tolerant properties, and inherent resistance to corrosion. However, they are still challenging materials in terms of the metal–composite interface, which is the weakest link in this material system. In this paper, an experimental–numerical method for the determination of the fracture stress and energy for metal–composite interlayer is presented and verified. The proposed method utilizes four different experimental tests: DCB test (interface opening—mode I), ENF test (interface shearing—mode II), MMB test (mixed-mode I+II—opening with the shearing of the interface) and three-point bending test (3PB). For each test, digital twin in the form of a numerical model is prepared. The established numerical models for DCB and ENF allowed us to determine fracture stress and energy for mode I and mode II, respectively. On the basis of the numerical and experimental (from the MMB test) data, the B-K exponent is determined. Finally, the developed material model is verified in a three-point bending test, which results in mixed-mode conditions. The research is conducted on the thermoplastic FML made of aluminum alloy sheet and glass fiber reinforced polyamide 6. The research presented is complemented by fundamental mechanical tests, image processing and Scanning Electron Microscopy (SEM) analysis. As an effect, for the tested material, fracture parameters are determined using the described method. Full article

In this study, to optimize the lightweight design of power battery cases for new energy vehicles and meet impact resistance requirements, the mechanical properties of honeycomb sandwich composites were experimentally investigated by varying carbon/glass fiber hybrid ratios. Carbon fiber and glass fiber hybrid laminates were used as the panel, and the aluminum honeycomb was used as the core layer to prepare sandwich composite materials through vacuum-assisted resin infusion (VARI). Then, the flexural and impact properties of honeycomb sandwich composites with different hybrid ratios were tested, respectively. The damage morphology and the damage mechanism of the hybrid composites were analyzed by 3D profile scanning. The results demonstrated that compared to glass fiber-reinforced panels, hybrid panels significantly enhanced the flexural load-bearing capacity of the sandwich composites, exhibiting maximum increases of 26.5% and 34.38% in the L direction and W direction, respectively. Carbon fiber effectively improved the impact resistance of specimens, with the maximum impact load increasing by 53.09% and energy absorption showing measurable enhancement, while glass fiber improves toughness and reduces the severity of damage. This study includes damage analysis and mechanical behavior change analysis of composite materials, which can provide a reference for the application of composite materials in the battery box shell. Full article

Polyester-glass laminates are widely used to reinforce underground steel fuel tanks due to their excellent corrosion resistance and mechanical performance. However, the management of these composites at the end of their service life poses significant challenges, particularly in terms of material recovery and environmental impact. This study investigates both the structural benefits and recyclability of polyester-glass laminates. Numerical simulations confirmed that reinforcing corroded steel tank shells with a 5 mm GFRP (Glass Fiber Reinforced Polymer) coating reduced the maximum equivalent stress by nearly 50%, significantly improving mechanical integrity. In parallel, thermogravimetric and microscopic analyses were conducted on waste GFRP samples subjected to pyrolysis, gasification, and combustion. Among the methods tested, pyrolysis proved to be the most favorable, allowing substantial organic degradation while preserving the structural integrity of the glass fiber fraction. However, microscopy revealed that the fibers were embedded in a dense char matrix, requiring additional separation processes. Although combustion leaves the fibers physically loose, pyrolysis is favored due to better preservation of fiber mechanical properties. Combustion resulted in loose and morphologically intact fibers but exposed them to high temperatures, which, according to the literature, may reduce their mechanical strength. Gasification showed intermediate performance in terms of energy recovery and fiber preservation. The findings suggest that pyrolysis offers the best trade-off between environmental performance and fiber recovery potential, provided that appropriate post-treatment is applied. This work supports the use of pyrolysis as a technically and environmentally viable strategy for recycling polyester-glass laminates and encourages further development of closed-loop composite waste management. Full article

This study investigates the mechanical performance of basalt fiber-reinforced polymer (BFRP) laminates as a suitable alternative to conventional glass fiber-reinforced composites for marine applications. The laminates were produced by varying the main process parameters: the fiber type was either glass or basalt; the resin material was either polyester or vinylester; the fiber orientation in selected layers was set to either 0°/90°, or to ±45° by rotating the woven fabrics during lay-up, and finally the manufacturing technique was either hand lay-up or vacuum infusion. Three-point flexural tests with different spans were conducted to evaluate the flexural behavior and fracture mechanisms. The best-performing configuration, based on glass fibers and vacuum infusion, achieved a maximum flexural strength of about 500 MPa, while basalt-based laminates reached values of up to 400 MPa. Basalt laminates exhibited the highest flexural modulus, with values exceeding 24 GPa. An increase in span length from 120 mm to 220 mm resulted in a reduction in flexural strength of approximately 6–18% depending on the laminate configuration, highlighting the influence of loading conditions on mechanical behavior. The effect of the manufacturing processes was also evaluated using an analysis of variance. This showed that fiber type, manufacturing method, and span significantly influenced the mechanical performance. Full article

Acid-etched zirconia has emerged as a high-strength alternative to traditional glass ceramics for laminate veneers in aesthetic dentistry. This randomized, double-blind controlled clinical trial aimed to evaluate the one-year clinical performance of zirconia veneers etched with a hydrofluoric-nitric acid mixture and bonded using a 10-methacryloyloxydecyl dihydrogen phosphate (MDP) containing polymeric adhesive system, compared to lithium disilicate veneers. Fifty-two patients were treated with either translucent zirconia or lithium disilicate veneers, and restorations were bonded using light-cured resin-based adhesives. Clinical parameters, including veneer survival, esthetics, marginal adaptation, postoperative sensitivity, and periodontal health, were assessed using modified United States Public Health Service (USPHS) criteria and periodontal indexes at 2 weeks, 6 months, and 12 months. Both materials showed high survival rates with no statistically significant differences in clinical outcomes. One zirconia veneer debonded early but was successfully rebonded without fracture, while one lithium disilicate veneer fractured upon debonding. The findings support the viability of acid-etched zirconia veneers bonded with polymer-based adhesives as a durable and esthetic restorative option. The study highlights the clinical relevance of polymeric bonding systems in enhancing zirconia veneer performance and reinforces their role in modern adhesive dentistry. Full article

This article presents, in detail, design considerations for a thin-walled glass fiber reinforced plastic (GFRP) liner on a fluid-cooled stator lamination of an electric motor. In addition to structural requirements due to the cooling fluid pressure, the GFRP liner needs to guarantee impermeability. Analytical considerations deriving from different coefficients of thermal expansion (CTEs) determine the two-layered laminate design. Empirical investigations show two innovative, simple, and, therefore, efficient test setups for the leakage of liquid media through a GFRP liner. The weeping investigations employ two different GFRP systems with four different configurations of interfiber failure (IFF) and, therefore, crack densities. The weeping investigations show that at least one ply in the laminate needs to be flawless regarding IFF cracks in order to guarantee the sealing function. Alternatively, a third sealing layer can be used. Full article

The push for sustainability in all facets of manufacturing has led to an increased interest in biomass as an alternative to non-renewable materials. Hemp bast fiber mats were produced from a bacterial retting process, named BFM, as the fiber reinforcement. The objective of this study was to evaluate the feasibility of laminating BFM with polylactic acid (PLA) for a composite panel product. Since both BFM and PLA are biodegradable, the resulting BFM-PLA composites will be 100% biodegradable. PLA pallets were processed into thin polymer sheets which served as the matrix. The BFM and PLA plates were laminated in five layers and compression-molded into composite panels. Experiments were conducted on the three BFM-to-PLA ratios (35/65, 45/55, and 50/50). Mechanical properties (tensile and bending properties) and physical properties (thickness swell and water absorption) were tested and compared to the currently commercial sheet molding compound (SMC) from fiber glass. The thermal behavior of the BFM/PLA composites was characterized using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The developed BFM/PLA composite product is a sustainable alternative to existing synthetical fiber-reinforced polymer (FRP) that is biodegradable in landfill at the end of life. Full article

Due to the anisotropic structure and mechanical properties of composite laminates, internal damage cracks can easily occur. In this study, orthotropic anisotropic glass-fiber-reinforced polymer composites were used as the repair object. Firstly, the anisotropic material was analyzed using the finite element method, the self-healing structural compliance, water head loss, and volume percentage of the microvascular network were taken as the objective functions, and the topology optimization of the microvascular network structure was carried out using non-dominated soring genetic algorithm II. Secondly, the self-healing material with a wall-less microvascular network was prepared via the vacuum-assisted resin transfer molding process and the embedded wire removal method. Finally, the light repair performance was tested using the three-point bending test. The results show that in the case of no intervention for light repair, the average maximum failure load of the self-healing structure after embedding the microvascular network can reach 94.06% of that before embedding; with the introduction of real-time light repair, the average maximum failure load of the self-healing structure with light repair was increased by 4.1% compared with the self-healing structure without light repair. Meanwhile, the second peak load of the light-repaired structure can reach 51.36% of the average maximum failure load, which is 28.56% higher than that of the non-light-repaired structure. Full article

A study of cryogenic drilling in sandwich composites was carried out. The materials used were carbon-fiber-reinforced polymer sandwich sheets with an inner foamed polyvinyl chloride core, composites with applications including protection structures of polar engineering equipment. The purpose of this study was to determine the feasibility of drilling at low temperatures using this composite by analyzing the thrust forces and the inlet and outlet diameters of the hole due to their influence on hole quality and their importance in a preassembly operation. Experimental tests were performed in laminates with thicknesses of 12 mm and 6 mm, drilling with liquid nitrogen (LN₂) as a refrigerant to reach temperatures below −120 °C under cutting conditions of 2000–6000 rpm for drill bit rotation speeds and 200–600 mm/min for feed rates. Variables such as thrust forces and circularity error were measured, and a design of experiments, analysis of variance, and regression models allowed us to identify the influence of cutting conditions and foam thickness. Optimal cutting conditions were identified and contrasted: 2100–3100 rpm for drill bit rotation speeds and 200–320 mm/min for feed rates. The diameters achieved low deviations, H7 and H8 tolerances for inlet and outlet diameters, respectively, which allows for avoiding additional preassembly operations, which can be important during plate assembly using LN₂ and in maintenance operations. Although good results have been obtained with other materials such as glass-fiber- and carbon-fiber-reinforced polymers, this sandwich material is lighter. Full article