Search Results (650)

The glass fiber-reinforced polymer (GFRP) materials of wind turbine blades can be recovered and recycled by crushing, thereby solving one of the most perplexing problems facing the wind energy sector. This process yields selectively crushed wind turbine blade (SCWTB), a novel waste that is almost exclusively composed of GFRP composite fibers that can be revalued in terms of their use as a raw material in concrete production. In this research, the fresh and mechanical performance of concrete made with 1.5%, 3.0%, 4.5%, and 6.0% SCWTB is studied. Once incorporated into concrete mixes, SCWTB waste slightly reduced slumps due to the large specific surface area of the fibers, and the stitching effect of the fibers on mechanical behavior was generally adequate, as scanning electron microscopy demonstrated good fiber adhesion within the cementitious matrix. Thus, despite the increase in the content of water and plasticizers when adding this waste to preserve workability, the compressive strength only decreased in the long term with the addition of 6.0% SCWTB, a value of 45 MPa always being reached at 28 days; Poisson’s coefficient remained constant from 3.0% SCWTB; splitting tensile strength was maintained at around 4.7 MPa up to additions of 3.0% SCWTB; and the flexural strength of mixes containing 6.0% and 1.5% SCWTB was statistically equal, with a value near 6.1 MPa. Furthermore, all mechanical properties of the concrete except for flexural strength were improved with additions of SCWTB compared to raw crushed wind turbine blade, which apart from GFRP composite fibers contains approximately spherical polymer and balsa wood particles. Flexural strength was conditioned by the proportion of fibers, their dimensions, and their strength, which were almost identical for both waste types. SCWTB would be preferable for applications in which compression stresses predominate. Full article

In recent years, the construction industry has faced challenges related to rising material costs, labor shortages and environmental sustainability, resulting in an increased interest in modular construction cores composed of recycled materials, such as XPS, PUR, PLW and GFRP, from waste from the truck body industry. Two resins, PUR and polyester, were used to bond these recycled composites. Physical, chemical and mechanical analyses showed that the panels formed with PUR resin had superior workability due to the higher open time of the resin, 11.3% better thermal conductivity than the commercial PLW panel (SP-PLW) and reduced porosity compared to those using polyester resin. The mechanical performance of the panels improved with higher structural reinforcement content (PLW and GFRP). Compared to a commercial panel (SP-PLW), the SP-RCM1 recycled panel showed 4% higher performance, demonstrating its potential for sustainable building applications. Thermal and microscopic characterizations showed good adhesion of the materials in the best performing formulations related to higher thermal stability. Therefore, this research aims to demonstrate the feasibility of using waste from the car industry in the manufacture of sandwich panels for modular construction to address these issues. Full article

This study investigates the mechanical properties of Glass Fiber-Reinforced Plastic (GFRP) pipes in the circumferential direction using the split-disk method, with a focus on understanding the influence of aggressive environmental conditions. The split-disk method was used to determine the key mechanical properties, including the hoop tensile strength and modulus, and also the Poisson’s ratio, which are critical for the performance of GFRP pipes under internal pressure. The experiment was conducted under controlled laboratory conditions, and the results were analyzed to assess the effects of exposure to aggressive environments (saltwater and alkaline solutions at 20 °C and 50 °C). The correlations between the UTS, elastic modulus, and Poisson’s ratio highlight how GFRP pipes degrade under environmental exposure. As the UTS decreases, so do the stiffness and lateral deformability, with the most significant reductions occurring in chemically aggressive environments at high temperatures. Exposure to an alkaline solution weakens the GFRP pipes, with the strength dropping more sharply at higher temperatures, with the UTS decreasing by 21%. Saltwater exposure reduces the elastic modulus, especially at higher temperatures, with a 14% decrease, accelerating material degradation and reducing deformation resistance. An alkaline solution further lowers the modulus, with a 21% decrease at 50 °C, showing the lowest stiffness. Air exposure, in contrast, has a less severe effect, with the pipes retaining much of their mechanical integrity. These findings collectively suggest that environmental degradation affects the overall mechanical behavior of GFRP pipes, providing valuable insights for the design and maintenance of GFRP piping systems, particularly in industries where exposure to aggressive environments is common. This study underscores the importance of considering environmental factors in the material selection and design processes to ensure the long-term reliability of GRP pipes. Full article

Macroscopic structures consisting of two or more materials are called composites. The decreasing reserves of the world’s oil reserve and the environmental pollution of existing energy and production resources made the use of recycling methods inevitable. There are mechanical, thermal, and chemical recycling methods for the recycling of thermosets among composite materials. The recycling of thermoset composite materials economically saves resources and energy in the production of reinforcement and matrix materials. Due to the superior properties such as hardness, strength, lightness, corrosion resistance, design width, and the flexibility of epoxy/vinylester/polyester fibre formation composite materials combined with thermoset resin at the macro level, environmentally friendly sustainable development is happening with the increasing use of composite materials in many fields such as the maritime sector, space technology, wind energy, the manufacturing of medical devices, robot technology, the chemical industry, electrical electronic technology, the construction and building sector, the automotive sector, the defence industry, the aviation sector, the food and agriculture sector, and sports equipment manufacturing. Bonded joint studies in composite materials have generally been investigated at the level of a single composite material and single joint. The uncertainty of the long-term effects of different composite materials and environmental factors in single-lap bonded joints is an important obstacle in applications. The aim of this study is to investigate the effects of single-lap bonded GFRP (glass fibre-reinforced polymer) and CFRP (carbon fibre-reinforced polymer) specimens on the material at the end of seawater exposure. In this study, 0/90 orientation twill weave seven-ply GFRP and eight-ply CFRP composite materials were used in dry conditions (without seawater soaking) and the hand lay-up method. Seawater was taken from the Aegean Sea, İzmir province (Selçuk/Pamucak), in September at 23.5 °C. This seawater was kept in different containers in seawater for 1 month (30 days), 2 months (60 days), and 3 months (90 days) separately for GFRP and CFRP composite samples. They were cut according to ASTM D5868-01 for single-lap joint connections. Moisture retention percentages and axial impact tests were performed. Three-point bending tests were then performed according to ASTM D790. Damage to the material was examined with a ZEISS GEMINESEM 560 scanning electron microscope (SEM). The SEM was used to observe the interface properties and microstructure of the fracture surfaces of the composite samples by scanning images with a focused electron beam. Damage analysis imaging was performed on CFRP and GFRP specimens after sputtering with a gold compound. Moisture retention rates (%), axial impact tests, and three-point bending test specimens were kept in seawater with a seawater salinity of 3.3–3.7% and a seawater temperature of 23.5 °C for 1, 2, and 3 months. Moisture retention rates (%) are 0.66%, 3.43%, and 4.16% for GFRP single-lap bonded joints in a dry environment and joints kept for 1, 2, and 3 months, respectively. In CFRP single-lap bonded joints, it is 0.57%, 0.86%, and 0.87%, respectively. As a result of axial impact tests, under a 30 J impact energy level, the fracture toughness of GFRP single-lap bonded joints kept in a dry environment and seawater for 1, 2, and 3 months are 4.6%, 9.1%, 14.7%, and 11.23%, respectively. At the 30 J impact energy level, the fracture toughness values of CFRP single-lap bonded joints in a dry environment and in seawater for 1, 2, and 3 months were 4.2%, 5.3%, 6.4%, and 6.1%, respectively. As a result of three-point bending tests, GFRP single-lap joints showed a 5.94%, 8.90%, and 12.98% decrease in Young’s modulus compared to dry joints kept in seawater for 1, 2, and 3 months, respectively. CFRP single-lap joints showed that Young’s modulus decreased by 1.28%, 3.39%, and 3.74% compared to dry joints kept in seawater for 1, 2, and 3 months, respectively. Comparing the GFRP and CFRP specimens formed by a single-lap bonded connection, the moisture retention percentages of GFRP specimens and the amount of energy absorbed in axial impact tests increased with the soaking time in seawater, while Young’s modulus was less in three-point bending tests, indicating that CFRP specimens have better mechanical properties. Full article

In this study, polyethylene terephthalate (PET) was substituted for 10%, 20%, and 30% of the sand volume in concrete. Compressive, splitting tensile, and flexural strength tests were applied to the concrete samples and stress–strain graphs were obtained. It was observed that PET substitution caused a decrease in the mechanical properties of the concrete. For this reason, the concrete with the best PET substitution rate (10%) was reinforced by wrapping it with carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP), and the same experiments were repeated. It was observed that a 10% PET substitution reduced the strength of the reference concrete by about 6%. However, wrapping the PET-substituted concrete with CFRP and GFRP increased the strength by about 1.9 and 1.5 times, respectively, surpassing that of the reference sample. In addition, this study provides a comprehensive database by bringing together experimental data from studies in which PET was used as a substitute by volume or weight instead of fine aggregate in concrete. The models proposed in this study, along with previous models, were tested for applicability. Similarly, the model suggestions in the literature for fiber-reinforced polymer (FRP)-confined concrete were tested with the experimental data in this study, and their suitability for PET-substituted concrete was discussed. Full article

Pultruded glass fiber-reinforced polymer (GFRP) materials are increasingly recognized in civil engineering for their exceptional properties, including a high strength-to-weight ratio, corrosion resistance, and ease of fabrication, making them ideal for composite structural applications. The use of concrete infill enhances the structural integrity of thin-walled GFRP sections and compensates for the low elastic modulus of hollow profiles. Despite the widespread adoption of concrete-filled pultruded GFRP tubes in composite beams, critical gaps remain in understanding their flexural behavior and failure mechanisms, particularly concerning design optimization and manufacturing strategies to mitigate failure modes. This paper provides a comprehensive review of experimental and numerical studies that investigate the impact of key parameters, such as concrete infill types, reinforcement strategies, bonding levels, and GFRP tube geometries, on the flexural performance and failure behavior of concrete-filled pultruded GFRP tubular members in composite beam applications. The analysis includes full-scale GFRP beam studies, offering a thorough comparison of documented flexural responses, failure modes, and structural performance outcomes. The findings are synthesized to highlight current trends, identify research gaps, and propose strategies to advance the understanding and application of these composite systems. The paper concludes with actionable recommendations for future research, emphasizing the development of innovative material combinations, optimization of structural designs, and refinement of numerical modeling techniques. Full article

This study analyzes the impact mechanical response of sandwich structures with foam and wood cores through experimental and numerical methods. The aim is to determine whether a sustainable core material, such as cork wood, can serve as a reliable alternative to the commonly used Polystyrene (PS) foam core in sandwich structures. Impact experiments were conducted at varying energy levels using an INSTRON CEAST 9350 drop tower, demonstrating the superiority of sandwich structures compared to single-material alternatives. Numerical models were developed in ABAQUS, where glass fiber reinforced polymer (GFRP) composite panels were represented using solid element C3D8R and the 3D Hashin failure criteria, which were incorporated via the user subroutine VUMAT. The results indicate that the contact force of the sandwich structure with a wood core surpassed that of the foam core counterpart. In both sandwich structures, damage initially occurred at the impact point on the surface, leading to plastic deformation and damage within the core, while the composite panel on the rear surface ultimately failed. These findings provide valuable insights for designers, enabling parametric studies to select appropriate core materials that enhance the impact resistance of sandwich structures. Full article

Carbon–glass hybrid fiber-reinforced epoxy polymer (C-GFRP) winding pipes integrated with the advantages of light weight, high strength, corrosion resistance, and cost-effectiveness offer immense potential to mitigate corrosion issues in oil, gas, and water transportation pipelines. In this study, C-GFRP winding pipes underwent accelerated aging tests through immersion in distilled water at temperatures of 25 °C, 40 °C, and 60 °C for 146 days. Water absorption tests were conducted to investigate the water absorption behavior of only CFRP- or GFRP-side absorbed water. Bending tests were performed to assess the evolution of the pipes’ flexural properties in two directions (GFRP or CFRP in tension). The results showed that the single-sided water absorption behavior adhered to the two-stage diffusion model. The diffusion coefficient, activation energy, and 146-day water absorption were all higher for the CFRP-side absorbed water compared to the GFRP-side absorbed water. The flexural strength and modulus of C-GFRP pipes were influenced by post-curing and resin hydrolysis/debonding. Initially, the flexural strength of CFRP in tension was higher than that of CFRP in tension. After 146 days of aging, the flexural strength of CFRP in tension was lower than that of CFRP in tension. Utilizing Arrhenius theory, the long-term lives were predicted for the flexural strength at temperatures of 5.4 °C, 12.8 °C, and 17.8 °C. The predicted lives of GFRP in tension were higher than those of CFRP in tension. Full article

This article presents the application of infrared thermography as a nondestructive testing method (NDT) for detecting osmotic damage in glass-fiber-reinforced polymer (GFRP) and glass-reinforced polymer (GRP) boat hull structures. The aim of the conducted experiments is to explore the possibilities of applying active infrared thermography to real structures and to establish a procedure capable of filtering out anomalies caused by various thermal influences, such as thermal reflections from surrounding objects, geometry effects, and heat flow variations on the observed object. The methods used for post-processing IR signals include lock-in thermography (LT), pulse thermography (PT), pulse phase thermography (PPT), and gradient pulse phase thermography (GT). The practical application and advantages and disadvantages of infrared thermography in identifying osmotic damage in GFRP and GRP boat hulls will be illustrated through three case studies. Each case study is based on specific conditions and characteristics of different types of osmotic damage, enabling a thorough analysis of the effectiveness of the method in detecting and assessing the severity of the damage. The post-processed thermal images enable a clearer distinction between damaged and undamaged zones, improving the robustness of detection under realistic field conditions. Full article

The increasing complexity and production volume of glass-fiber-reinforced polymers (GFRP) present significant recycling challenges. This paper explores a potential use for mechanically recycled GFRP by blending it with high-density polyethylene (HDPE). This composite could be applied in products such as terrace boards, pipes, or fence posts, or as a substitute filler for wood flour and chalk. Recycled GFRP from post-consumer bus bumpers were ground and then combined with recycled HDPE in a twin-screw extruder at concentrations of 10, 20, 30, and 40 wt%. The study examined the mechanical and structural properties of the resulting composites, including the effects of aging and re-extrusion. The modulus of elasticity increased from 0.878 GPa for pure rHDPE to 1.806 GPa for composites with 40 wt% recycled GFRP, while the tensile strength ranged from 36.5 MPa to 28.7 MPa. Additionally, the porosity increased linearly from 2.65% to 7.44% for composites with 10 wt% and 40 wt% recycled GFRP, respectively. Aging and re-extrusion improved the mechanical properties, with the tensile strength of the 40 wt% GFRP composite reaching 34.1 MPa, attributed to a reduction in porosity by nearly half, reaching 3.43%. Full article

In this study, the short-beam shear strength (SBSS) retention of two types of glass fiber-reinforced polymer (GFRP) bars—sand-coated (SG) and ribbed (RG)—was subjected to alkaline, acidic, and water conditions for up to 12 months under both high-temperature and ambient laboratory conditions. Comparative assessments were also performed on older-generation sand-coated (SG-O) and ribbed (RG-O1 and RG-O2) GFRP bars exposed to identical conditions. The results demonstrate that the new-generation GFRP bars, SG and RG, exhibited significantly better durability in harsh environments and exhibited SBSS retentions varying from 61 to 100% in SG and 90–98% in RG under the harshest conditions compared to 56–69% in SG-O, 71–80% in RG-O1, and 74–88% in RG-O2. Additionally, predictive models using both artificial neural networks (ANNs) and linear regression were developed to estimate the strength retention. The ANN model, with an R² of 0.95, outperformed the linear regression model (R² = 0.76), highlighting its greater accuracy and suitability for predicting the SBSS of GFRP bars. Full article

Glass Fiber-Reinforced Composite (GFRP) has found widespread use in engineering structures due to its lightweight construction, high strength, and design flexibility. However, pure GFRP beams exhibit weaknesses in terms of stiffness, stability, and local compressive strength, which compromise their bending properties. In addressing these limitations, this study introduces innovative square GFRP beams infused with gypsum-based composites (GBIGCs). Comprehensive experiments and theoretical analyses have been conducted to explore their manufacturing process and bending characteristics. Initially, four types of GBIGC—namely, hollow GFRP beams, pure gypsum, steel-reinforced gypsum, and fiber-mixed gypsum-infused beams—were designed and fabricated for comparative analysis. Material tests were conducted to assess the coagulation characteristics of gypsum and its mechanical performance influenced by polyvinyl acetate fibers (PVAs). Subsequently, eight GFRP square beams (length: 1.5 m, section size: 150 mm × 150 mm) infused with different gypsum-based composites underwent four-point bending tests to determine their ultimate bending capacity and deflection patterns. The findings revealed that a 0.12% dosage of protein retarder effectively extends the coagulation time of gypsum, making it suitable for specimen preparation, with initial and final setting times of 113 min and 135 min, respectively. The ultimate bending load of PVA-mixed gypsum-infused GFRP beams is 203.84% higher than that of hollow beams, followed by pure gypsum and steel-reinforced gypsum, with increased values of 136.97% and 186.91%, respectively. The ultimate load values from the theoretical and experimental results showed good agreement, with an error within 7.68%. These three types of GBIGCs with significantly enhanced flexural performance can be filled with different materials to meet specific load-bearing requirements for various scenarios. Their improved flexural strength and lightweight characteristics make GBIGCs well suited for applications such as repairing roof beams, light prefabricated frames, coastal and offshore buildings. Full article

To promote the application of molybdenum tailings as the fine aggregate in concrete in construction engineering and verify the feasibility of fiber-reinforced polymer (FRP) material for strengthening molybdenum tailings concrete columns, this study takes a short circular molybdenum tailings concrete column reinforced by glass FRP (GFRP) as the research object. The influences of the molybdenum tailings content (0%, 25%, 50%, 75%, and 100%), the concrete grade (C30, C40, and C50), and the layer number (0, 1, and 2) of the GFRP sheet on the axial compressive capacity of the molybdenum tailings concrete column are investigated. The experimental phenomena and failure modes of the unreinforced and GFRP-reinforced columns are analyzed. The axial compressive strengths of the unreinforced and GFRP-reinforced columns are then compared. The load–strain curve and load–displacement curve of typical molybdenum tailings concrete columns are presented. Subsequently, six classical strength models for FRP-reinforced concrete are used to calculate the axial compressive strength of the confined specimens. The results show that the best classical model has a predictive accuracy with an absolute relative deviation (ARD) of 8.5%. To provide a better prediction of the compressive strength of the GFRP-reinforced molybdenum tailings concrete column, the best classical model is further improved, and the ARD of the modified model is only 5.87%. Full article

Milling parts made from glass fiber-reinforced polymer (GFRP) composite materials are recommended to achieve the geometric shapes and dimensional tolerances required for large parts manufactured using the spray lay-up technique. The quality of the surfaces machined by milling is significantly influenced by the temperature generated in the cutting zone. This study aims to develop an Artificial Neural Network (ANN) model to predict the temperature generated when milling GFRP. The ANN model for temperature prediction was created using a virtual instrument developed in the graphical programming language LabVIEW. Predicting temperature is crucial because excessive heat during milling can lead to several issues, such as tool wear and thermal degradation in the polymer matrix. The temperature in the tool–workpiece contact surface during the milling process was measured using a thermography technique with a ThermaCAM SC 640 camera (provided by FLIR Systems AB, Danderyd, Sweden), and the data were analyzed using the ThermaCAM Researcher Professional 2.8 SR-2 software. Experimental research shows that the cutting speed has a much more significant effect on the temperature in the cutting zone compared to axial depth of cut and feed speed. The maximum temperature of 85.19 °C was measured in the tool–workpiece contact zone during machining at a cutting speed of 75.39 m/min, a feed rate of 250 mm/min, and an axial depth of cut of 12 mm. This temperature rise occurred due to the larger contact area and heightened friction resulting from the abrasive characteristics of the reinforcement material. Full article

This paper aimed to understand the AE signal characteristics and damage mechanism of wind turbine blade main spar materials with different defects during the damage evolution process. According to the typical delamination and wrinkle defects in wind turbine blades, the GFRP composite with defects is artificially prefabricated. Through acoustic emission experiments, the mechanical properties and acoustic emission characteristic trends of wind turbine blade main spar composites with different defects under tensile loading conditions were analyzed, and the damage evolution mechanism of different defects was explained according to the microscopic results. The results show that the existence of artificial defects will not only affect the mechanical properties of composite materials but also affect the damage evolution process of the materials. The size and location of delamination defects and the different aspect ratio of the wrinkle defects have a certain influence on the damage mechanism of the material. K-means cluster analysis of AE parameters identified the damage models of GFRP composites. The types of damage modes of delamination defects and wrinkle defects are the same, and the range of characteristic frequency is roughly the same. This study has important reference significance for structural damage monitoring and damage evolution research of wind turbine blade composites. Full article