The transition toward sustainable and low-carbon energy systems has become a global necessity due to the environmental and economic impacts of fossil fuel consumption. In this context, wind energy has emerged as one of the fastest-growing renewable energy technologies, with a continuously increasing contribution to global electricity production [1,2,3]. Historical developments have shown that material selection plays a critical role in wind turbine performance, as early metallic blade designs suffered from premature failures due to insufficient strength and fatigue resistance [2,3,4]. With the rapid growth of wind energy systems, turbine sizes have significantly increased, leading to more demanding structural requirements for turbine components, particularly blades. Wind turbine blades directly influence power generation efficiency, structural reliability, and overall system cost. Therefore, the use of fiber-reinforced polymer (FRP) composites has become standard due to their high specific strength, low density, and corrosion resistance [4,5,6].

Wind turbine blades operate under complex cyclic loading conditions caused by variable wind loads, gravitational forces, and rotational effects. During their service life, blades are expected to withstand approximately 10⁸ loading cycles, making fatigue behavior a critical design parameter [7,8,9,10,11,12,13,14]. Fatigue-related damage is commonly observed in critical regions such as blade roots and bonded joints, where stress concentrations are dominant [15,16,17].

Among composite materials, glass fiber-reinforced polymers (GFRP) are widely used due to their cost-effectiveness and acceptable mechanical performance [5,18,19,20,21,22]. However, carbon fiber-reinforced polymers (CFRP) have gained increasing attention in recent years because of their superior stiffness-to-weight and strength-to-weight ratios, enabling significant weight reduction and improved structural performance [4,23,24,25].

In addition to material selection, structural design approaches play a crucial role in improving blade performance. Techniques such as variable thickness distribution and optimized fiber orientations along the blade length have been shown to enhance strength, reduce weight, and increase energy efficiency [26,27,28]. Moreover, adhesive bonding methods are widely preferred in composite blade manufacturing due to their ability to provide uniform stress distribution and improved fatigue resistance compared to mechanical fastening methods [29,30,31,32,33,34,35,36]. However, adhesive joints are sensitive to peel stresses, which may lead to premature failure if not properly designed [35,36,37].

Recent studies have focused on improving composite performance through hybrid material systems, nano-reinforcements, and advanced manufacturing techniques. These approaches aim to enhance mechanical performance, delay damage initiation, and extend service life while maintaining economic feasibility [1,38,39,40,41]. In particular, the integration of CFRP into structurally critical regions such as spar caps has been shown to significantly improve aeroelastic stability, reduce blade weight, and enhance energy production efficiency [24,42,43].

In this context, the present study aims to evaluate the role of CFRP composites in wind turbine blade applications, focusing on their mechanical advantages, fatigue behavior, and contribution to structural optimization compared to conventional GFRP materials.

In this study, a comprehensive literature review was conducted to investigate the structural characteristics, material selection criteria, manufacturing processes, and design principles of composite materials used in wind turbine blades. The primary objective is to systematically compile existing knowledge and provide a reliable reference for researchers and engineers working in wind energy and composite materials. For this purpose, peer-reviewed journal articles, books, and technical reports were analyzed in detail, focusing on material requirements, composite classifications, blade structures, and production techniques [51,52,53,54,55,56,57,58].

Wind energy, as a highly variable and dynamic renewable energy source, generates complex aerodynamic, mechanical, and environmental loads on turbine blades. Variations in wind speed over time and across different geographical regions directly affect bending, torsional, and fatigue loads acting on the blades [51]. As demand for higher power capacity increases, turbine blade lengths have significantly increased, leading to higher structural loads. This trend has necessitated the use of lightweight materials with high strength and superior fatigue resistance, resulting in the replacement of conventional metallic materials with advanced composite materials [52].

Structurally, wind turbine blades are complex systems designed to ensure both aerodynamic efficiency and mechanical durability. A typical blade consists of an outer shell forming the aerodynamic surface, internal load-bearing structures such as spar caps, and shear webs that maintain structural integrity. These components collectively enable the blade to withstand varying wind loads while minimizing deformation, as illustrated in Figure 1 [53]. Among the various design considerations, fatigue behavior is particularly critical, as turbine blades are subjected to continuous cyclic loading throughout their service life [17].

The selection of materials for wind turbine blades is governed by several key requirements, including low density, high specific strength and stiffness, excellent fatigue resistance, and environmental durability. In addition, manufacturability and cost-effectiveness play significant roles in the design process. Parameters such as specific strength and specific rigidity are decisive factors in material selection, making fiber-reinforced polymer composites the most suitable materials for these applications [54].

Composite materials, particularly glass fiber-reinforced polymers (GFRP) and carbon fiber reinforced polymers (CFRP), have become the dominant materials in modern wind turbine blades due to their high strength-to-weight ratio, fatigue resistance, and design flexibility [2]. These materials significantly reduce blade weight, thereby decreasing structural loads and improving overall energy efficiency. Furthermore, their manufacturability into complex geometries enables the development of large-scale, high-performance turbine designs. The evolution of wind turbine technology and associated material developments is summarized in Table 1 [55,56,57,58].

Wind turbines can be classified based on several criteria, including axis orientation, number of blades, operating speed, power capacity, gearbox configuration, and installation location. These classifications directly influence aerodynamic performance, structural design, and application areas. The general classification of energy systems and the schematic representation of wind energy conversion are shown in Figure 2 and Figure 3, respectively [60].

In terms of axis orientation, wind turbines are mainly categorized as horizontal-axis, vertical-axis, and inclined-axis turbines. Among these, horizontal-axis wind turbines are the most widely used due to their high aerodynamic efficiency, typically reaching 45-50%, as illustrated in Figure 4 [51,63,64,65,66].

Vertical axis wind turbines, on the other hand, offer advantages such as independence from wind direction and ease of maintenance. However, they suffer from lower efficiency and limited self-starting capability (Figure 5) [63,64,65,66,68,69].

Inclined-axis turbines are relatively uncommon and are primarily investigated experimentally (Figure 6) [63,64,65,66,68,69,70].

Another important classification is based on the number of blades. Wind turbines may have single, double, triple, or multiple blades; however, three-bladed configurations are the most widely used due to their balanced aerodynamic performance and structural stability. These configurations are illustrated in Figure 7 [63,64,65,66,68,69,70,71].

The main components of a wind turbine, including rotor blades, gearbox, generator, tower, and control systems, are shown in Figure 8 and Figure 9 [72].

Composite materials used in wind turbine blades are defined as engineered materials formed by combining two or more constituents with distinct physical or chemical properties to achieve superior performance characteristics [74,75]. Typically, these materials consist of a matrix phase and a reinforcement phase, as shown in Figure 10 [76].

Composite materials are generally classified based on reinforcement type (fiber, particle, or flake) and matrix type (polymer, metal, ceramic, or carbon-carbon), as illustrated in Figure 11 [77,78,79,80,81,82,83].

Among these, polymer matrix composites (PMCs) are the most widely used in wind turbine blades due to their low density, high strength, corrosion resistance, and ease of manufacturing. Polymer matrices are further divided into thermoplastic and thermoset materials. Thermoplastics offer advantages such as recyclability and high production rates, whereas thermosets provide superior thermal stability and mechanical performance due to their cross-linked molecular structure [84,85,86,87]. The mechanical performance of composite materials is largely determined by the type of reinforcement used. Glass fibers are the most commonly used reinforcement due to their low cost and good mechanical properties. In contrast, carbon fibers are preferred in regions requiring higher stiffness and fatigue resistance. Aramid fibers offer high impact resistance and low density, whereas ceramic fibers are mainly used in high-temperature applications due to their cost and specialized properties [88,89,90].

In addition to fiber-reinforced structures, sandwich composite structures are widely used in wind turbine blades to achieve high stiffness with minimal weight. These structures consist of face sheets and lightweight core materials such as PVC, PET foams, or balsa wood, which enhance bending stiffness and structural efficiency. A schematic representation of sandwich structures is provided in Figure 12 [90].

Polymer matrix composites (PMCs) have become the dominant material class in wind turbine blade applications due to their superior specific strength, excellent fatigue resistance, and high corrosion durability under harsh environmental conditions. The relatively low density of polymer matrices, combined with their ease of processing, enables efficient manufacturing of large-scale and geometrically complex blade structures. In particular, thermoset matrices provide high-dimensional stability and long-term environmental resistance, which are critical for achieving the 20-30 years service life expected of modern wind turbines. Compared to metal and ceramic matrix composites, PMCs offer a more favorable balance between structural performance, manufacturability, and cost, making them the most suitable choice for wind energy applications.

Composite materials can be broadly classified by reinforcement type, which directly influences their mechanical behavior and structural performance under complex loading conditions. As illustrated in Figure 13 and Figure 14, composites may consist of continuous, discontinuous, or particulate reinforcements. Among these, continuous fiber-reinforced composites are predominantly used in wind turbine blades due to their superior load-carrying capacity and fatigue resistance under cyclic aerodynamic loading conditions [91,92].

The mechanical performance of fiber-reinforced composites is also strongly affected by the weave pattern of the reinforcement. In plain weave (plain knit) fabrics, fibers alternately pass over and under each other, resulting in a balanced and symmetric structure. However, the inherent fiber crimp in this configuration reduces effective load transfer efficiency, resulting in lower mechanical properties. For this reason, plain weave structures are generally limited to low-stress regions in wind turbine blades (Figure 15) [81].

In contrast, twill weave fabrics exhibit reduced fiber crimp due to their staggered over-under pattern, which improves surface smoothness and mechanical performance. Twill and multi-axial fiber architectures are therefore preferred in high-load regions of wind turbine blades, where enhanced fatigue resistance and strength are required (Figure 16) [81].

Composite materials provide several critical advantages in wind turbine blade design. Their high specific strength enables lightweight structures, reducing centrifugal and gravitational loads while improving aerodynamic efficiency. Additionally, their directional strength allows fiber orientations to be tailored according to load paths, particularly in flapwise and edgewise loading directions. Composites also exhibit excellent corrosion resistance, ensuring durability under environmental exposure such as UV radiation, moisture, and temperature fluctuations. Furthermore, their high impact resistance and design flexibility allow the production of complex aerodynamic geometries while reducing assembly requirements and maintenance needs [81]. Despite these advantages, composite materials also present certain limitations. These include relatively high material and manufacturing costs, limited high-volume production capabilities, and the need for specialized design and fabrication expertise. Moreover, their thermal resistance is dependent on matrix properties, and environmental factors such as humidity and temperature variations may influence long-term mechanical behavior [81].

Laminate design is another critical factor determining the structural performance of composite materials. Laminates are formed by stacking multiple layers with different fiber orientations, and their configuration significantly affects bending stiffness, torsional rigidity, and fatigue life. A unidirectional laminate, in which all fibers are aligned in the same direction, provides maximum strength along the loading axis and is typically used in regions subjected to uniaxial stress (Figure 17) [81,94].

Angle-ply laminates consist of layers oriented at angles other than 0° and 90°, allowing improved resistance to multi-directional loads (Figure 18) [94].

Cross-ply laminates, formed by alternating 0° and 90° fiber orientations, provide balanced in-plane stiffness and are widely used in structural applications (Figure 19) [94].

More advanced laminate configurations include symmetric, antisymmetric, asymmetric, and quasi-isotropic (semi-isotropic) stacking sequences. Symmetric laminates ensure balanced bending behavior, while antisymmetric configurations improve torsional stiffness. Quasi-isotropic laminates, such as [0/±45/90]s, provide nearly uniform in-plane properties and are commonly used in complex loading environments. A schematic representation and deformation diagram of fiber-reinforced composites are shown in (Figure 20) [81].

Fiber orientation is one of the most influential parameters affecting composite mechanical behavior. Fibers aligned parallel to the applied load (0° orientation) exhibit maximum tensile strength, whereas perpendicular orientations (90°) provide minimal load-carrying capacity. Multi-directional laminates enable more uniform load distribution but may reduce peak strength compared to unidirectional configurations. Therefore, optimizing fiber orientation is essential for achieving both high strength and balanced structural performance. Fabric-laminated composites and layer orientation examples are shown in Figure 21 [75,76,78].

The application of composite materials in the wind energy industry has significantly evolved with advances in materials science and manufacturing technologies. Glass fiber-reinforced polymers (GFRP) remain the most widely used materials due to their cost-effectiveness and adequate mechanical performance, while carbon fiber-reinforced polymers (CFRP) are increasingly utilized in load-critical regions to enhance stiffness and reduce structural weight. These materials are typically combined with thermoset matrices such as epoxy, which provide high mechanical performance and processing advantages [2,96,97].

Manufacturing processes such as hand lay-up and vacuum infusion play a crucial role in determining the quality of composite structures. Among these, vacuum infusion has become the preferred technique for large-scale wind turbine blades, as it ensures uniform resin distribution, reduces void content, and enhances structural integrity. In these processes, dry fiber reinforcements and core materials, such as PVC foam or balsa wood, are placed in a mold, and resin is introduced under vacuum pressure to create a dense and durable composite structure.

Sandwich composite structures are widely used in wind turbine blades to achieve high stiffness-to-weight ratios. These structures consist of lightweight core materials bonded between stiff composite face sheets, significantly improving bending performance without increasing weight. Foam cores and balsa wood are commonly used due to their excellent mechanical properties and low density. Despite the significant advancements in composite materials, ongoing research focuses on improving recyclability, sustainability, and long-term durability. The increasing demand for larger wind turbines with capacities exceeding 8-10 MW continues to drive innovation in hybrid composite systems, advanced manufacturing techniques, and environmentally sustainable materials. Rotor blades in modern wind turbine systems consist primarily of two main structural components, namely the external shell and the internal load-carrying spar system. The shell defines the aerodynamic profile of the blade and is composed of suction and pressure-side surfaces, while the spar system provides structural rigidity by transferring aerodynamic, gravitational, and inertial loads toward the blade root. Within the spar structure, vertical elements are generally referred to as shear webs, whereas horizontal elements are known as spar caps. These components extend along the blade span from the root region toward the tip and are designed to resist bending and torsional loads under operational conditions. Rectangular and I-beam type configurations are commonly employed in practical applications, as they provide efficient load distribution and high structural stiffness (Figure 22) [8,98].

Wind turbine blades convert the kinetic energy of the wind into mechanical energy through rotational motion. Structurally, the blade is divided into three main regions: root, mid-span, and tip. The root region, located near the rotor hub connection, is typically subjected to the highest stress levels and initially exhibits a circular cross-section to improve structural strength. The mid-span region plays a dominant role in energy capture and aerodynamic efficiency, whereas the tip region requires precise geometric optimization due to its sensitivity to flow variations and structural flexibility. In modern designs, the blade geometry gradually transitions from structurally dominant root sections to aerodynamically optimized tip sections, ensuring an optimal balance between strength and efficiency (Figure 23 and Figure 24) [8,99,100].

Although the external shape defines aerodynamic performance, the internal structural integrity of the blade is ensured by shear webs and spar caps. These components function as internal beam-like structures that carry most of the mechanical loads generated during operation (Figure 25) [2].

The blade is typically manufactured by bonding the two shell halves with structural adhesives, thereby forming a closed aerodynamic profile (Figure 26).

Under aerodynamic loading, compressive stresses occur on the suction side while tensile stresses develop on the pressure side. These loads are transferred through the shell to the spar caps, which act as primary load-carrying elements. At the same time, shear webs prevent relative displacement between the upper and lower shell surfaces, maintaining structural integrity (Figure 27) [78].

Aerodynamic performance is governed by airfoil geometry, which is designed to maximize lift generation while minimizing drag. Airfoils such as NACA profiles are widely used in wind turbine applications due to their well-documented aerodynamic characteristics (Figure 28) [102].

The lift force is generated due to pressure differences between the suction and pressure sides of the airfoil, in accordance with Bernoulli’s principle, where increased flow velocity leads to reduced static pressure [80,81]. The aerodynamic force system acting on the airfoil consists of lift and drag components, which act perpendicular and parallel to the incoming flow direction, respectively (Figure 29) [103].

A typical airfoil geometry is defined by parameters such as chord length, camber, thickness distribution, and angle of attack. The leading edge is the point where airflow first interacts with the airfoil, while the trailing edge is the flow exit region. The chord line is defined as the straight line connecting these two points, and the angle of attack is the angle between the chord line and the incoming flow direction. Aerodynamic forces are generally assumed to act at the quarter-chord point (c/4), where lift, drag, and pitching moment are analyzed for performance evaluation (Figure 30 and Figure 31) [104,105,106].

From a materials perspective, wind turbine blade design is strongly influenced by requirements such as high strength-to-weight ratio, fatigue resistance, and environmental durability. Composite materials, particularly glass fiber-reinforced polymers (GFRP) and carbon fiber-reinforced polymers (CFRP), are widely used due to their superior mechanical performance and low density characteristics (Table 2) [83].

In large-scale turbines, hybrid composite systems are commonly employed to optimize cost and structural efficiency (Figure 32).

Modern blade structures frequently incorporate sandwich composite configurations consisting of lightweight core materials such as balsa wood or polymer foams, bonded between stiff composite face sheets. This configuration significantly improves bending stiffness while minimizing weight (Figure 33, Figure 34, and Figure 35) [107,108].

Manufacturing processes such as hand lay-up, vacuum bagging, and vacuum infusion are widely used in composite blade production. Among these, vacuum infusion is preferred for large-scale applications due to its ability to reduce void content and improve laminate quality (Figure 36, Figure 37, and Figure 38) [16,51,52].

During operation, wind turbine blades are subjected to complex loading conditions including aerodynamic forces, gravitational effects, and centrifugal loads. These loads induce internal stresses and strains, which may lead to failure mechanisms such as delamination, fiber breakage, adhesive debonding, and surface cracking (Figure 39) [114,115,116,117,118]. The primary structural resistance against these loads is provided by spar caps, while shear webs distribute shear stresses and maintain geometric stability of the blade cross-section [16,51].

In terms of structural behavior, rotor blades operate as cantilever beams, in which flapwise and edgewise bending loads represent the dominant stress modes. Flapwise bending is primarily resisted by spar caps, whereas edgewise bending is largely carried by the outer shell structure [17]. Load transfer between blade components is achieved through different joining techniques, including mechanical fastening, adhesive bonding, and hybrid systems. Adhesive bonding plays a critical role in composite blade structures, providing uniform stress distribution and eliminating stress concentrations associated with mechanical fasteners (Figure 40) [119].

However, mechanical fastening methods such as bolts and rivets introduce localized stress concentrations and may reduce composite continuity due to drilling-induced fiber damage (Figure 41) [120,121,122].

Adhesive joints exhibit high resistance to shear and tensile loads but are more sensitive to peel stresses. Failure typically occurs either at the adhesive–substrate interface or within the adhesive layer itself. To overcome limitations of individual joining methods, hybrid connections that combine mechanical fasteners and adhesives are increasingly used in wind turbine blade structures to enhance load-carrying capacity and structural reliability [35,36,120].

This study presents a comprehensive evaluation of composite materials used in wind turbine blades, with particular emphasis on material selection, manufacturing techniques, joining methods, and structural performance. The findings clearly indicate that the transition from conventional metallic materials to fiber-reinforced polymer (FRP) composites has been a key factor in enabling the development of modern, large-scale wind turbine blades.

The results demonstrate that glass fiber-reinforced polymers (GFRP) remain the most widely used materials due to their cost-effectiveness and adequate mechanical performance, while carbon fiber-reinforced polymers (CFRP) are increasingly utilized in critical load-bearing regions that require higher stiffness and fatigue resistance. The high strength-to-weight and stiffness-to-weight ratios of these materials significantly reduce structural loads while supporting longer blade spans, thereby directly improving energy capture efficiency.

In manufacturing processes, advanced composite fabrication techniques such as vacuum infusion and vacuum bagging have shown superior performance compared to conventional hand lay-up methods. These processes minimize defects such as void formation, fiber misalignment, and delamination, resulting in improved laminate quality and enhanced mechanical reliability. Among these, vacuum infusion has emerged as the most effective method for large-scale blade production due to its ability to ensure uniform resin distribution and consistent structural integrity.

The evaluation of joining methods highlights that adhesive bonding is the most effective technique for composite blade structures, primarily because it provides uniform stress distribution and superior fatigue resistance. However, its performance is highly dependent on proper surface preparation and curing conditions. Mechanical fastening, while advantageous for assembly and maintenance, introduces stress concentrations and potential structural weaknesses due to fiber discontinuities. Hybrid joining methods, which combine adhesive bonding with mechanical fastening, offer a balanced solution by improving joint strength, reducing stress concentrations, and enhancing overall structural reliability.

Furthermore, the results emphasize that damage mechanisms such as delamination, fiber breakage, adhesive debonding, and matrix cracking are critical factors affecting blade performance and service life. These damage modes are strongly influenced by local stress concentrations and cyclic loading conditions. Therefore, accurate prediction of stress distribution and careful design of load paths are essential to prevent premature failure.

Overall, the findings confirm that integrating advanced composite materials, optimized manufacturing techniques, and efficient joining methods enables the production of lightweight, high-performance, and durable wind turbine blades. This integration plays a crucial role in increasing turbine efficiency, extending service life, and reducing maintenance and operational costs. Additionally, ongoing developments in material technology and structural design are expected to further enhance blade performance and support the continued growth of wind energy systems.

The literature reviewed in this study clearly demonstrates that the advancement of wind turbine blade technology is strongly dependent on developments in composite materials, manufacturing processes, and structural design optimization. The transition from conventional metallic materials to fiber-reinforced polymer (FRP) composites has enabled the production of lighter, longer, and more aerodynamically efficient rotor blades, which are essential for modern large-scale wind energy systems. From a material perspective, glass fiber-reinforced polymers (GFRP) remain the most commonly used materials in wind turbine blade manufacturing due to their cost-effectiveness and acceptable mechanical properties. However, carbon fiber-reinforced polymers (CFRP) provide significantly higher stiffness-to-weight and strength-to-weight ratios, making them particularly suitable for structurally critical regions such as spar caps. Literature findings indicate that the selective use of CFRP in these regions can reduce blade weight by approximately 20–30%, which leads to reduced gravitational loading, improved aeroelastic stability, and enhanced energy conversion efficiency. Manufacturing techniques directly influence the structural integrity and fatigue performance of composite blades. Advanced processes such as vacuum infusion and vacuum bagging significantly improve laminate quality by reducing void content, enhancing fiber wet-out, and ensuring uniform resin distribution. Compared to traditional hand lay-up methods, these techniques provide superior mechanical consistency and are therefore preferred in large-scale wind turbine blade production. Joining techniques are another critical factor affecting blade performance. Adhesive bonding is widely adopted due to its ability to distribute stresses uniformly across bonded surfaces and eliminate stress concentrations associated with mechanical fasteners. However, its performance is highly dependent on proper surface preparation, curing conditions, and environmental resistance. Mechanical fastening methods, while advantageous for assembly and maintenance, introduce discontinuities in the fiber structure and localized stress concentrations that may weaken composite performance. Hybrid joining systems, combining adhesive bonding with mechanical fastening, offer an improved balance between strength, reliability, and damage tolerance. The literature also identifies several critical damage mechanisms in wind turbine blades, including delamination, fiber breakage, matrix cracking, and adhesive debonding. These failures are primarily driven by cyclic loading, aerodynamic forces, and local stress concentrations, particularly in high-risk regions such as blade roots and spar-shear web interfaces. Accurate prediction of these stress distributions and optimization of fiber orientation are therefore essential to ensure long-term structural reliability and prevent premature failure. From a structural standpoint, the use of fiber-reinforced composites enables tailoring of mechanical properties to load paths, a key advantage in wind turbine blade design. Spar caps act as the main load-bearing elements resisting flapwise bending, while shear webs transfer shear loads between blade surfaces. The outer shell maintains aerodynamic shape and contributes to load distribution, whereas adhesive joints ensure structural continuity between components.

Overall, this study confirms that the integration of advanced composite materials, optimized manufacturing techniques, and efficient joining methods is essential for achieving high-performance wind turbine blades. These developments significantly enhance energy efficiency, reduce operational and maintenance costs, and extend service life. Future research is expected to focus on hybrid material systems, smart composites, automated manufacturing technologies, and sustainable recycling methods, thereby further improving the performance and environmental sustainability of wind energy systems.