A method for reconstructing the tenon-and-mortise joint of a retired wind turbine blade root

Abstract

The application discloses a kind of outer embrace mortise joint reconstruction methods of decommissioned wind power blade root, belong to wind power equipment remanufacturing technical field.Decommissioned blade is cut and separated into blade main body with complete blade tip and blade root section retaining original connecting structure;End beam plate of main body is cut and shaped into a bowtie-shaped tenon, corresponding mortise is set on the back outer surface of the cut blade root plate, and the outer embrace type mortise nesting structure of beam plate sandwiching blade root plate is formed by using outside buckling mode, after resin bonding and curing, glass fiber hand lay-up reinforcement is implemented at three connecting nodes, and finally, the reconstruction is completed by using original embedded bolt sleeve connection custom flange plate.The application adopts back outer buckling type slotting assembly, and the quality of adhesive bonding is fully visible and controllable.The slotting processing has high standardization degree and low difficulty, the outer surface is smooth and uniform after forming, the original blade root structure strength is completely inherited, and the double connection of chemical bonding and mechanical locking is combined, so that the high-reliability, low-cost remanufacturing and degradation reuse of decommissioned blade can be realized.

Description

Technical Field

[0001] This invention belongs to the field of wind power equipment remanufacturing and retired wind turbine blade recycling technology. Specifically, it relates to a method for remanufacturing retired wind turbine blade roots by external tenon and mortise joint. Through the external tenon and mortise structure with grooves on the back of the blade root plate and fastening to the outside of the beam plate, a high-strength connection between the retired blade body and the original blade root is achieved. Finally, it is adapted to the target wind turbine hub to achieve downgraded reuse. This is a high-value utilization technology that meets the national standards for remanufacturing. Background Technology

[0002] Wind turbine blades are the core wind-catching components of wind turbine generators. They are mainly made of glass fiber reinforced epoxy resin composite materials through a vacuum infusion process. A typical structure includes a unidirectional fiber main beam, a biaxial fabric skin, a shear web, and a lightweight core. The main beam fibers are arranged axially and bear more than 80% of the bending load; the skin fibers are mostly in a ±45° direction to maintain the aerodynamic shape and bear in-plane loads; the web connects the upper and lower beams, bears shear loads, and maintains the cross-sectional shape.

[0003] With the development of my country's wind power industry, the megawatt-class units that were put into operation in the early stages have entered the retirement period. It is estimated that the amount of retired wind turbine blades in my country will reach about 11,400 tons around 2025. The disposal of retired blades has become a resource and environmental problem that the industry urgently needs to solve.

[0004] Existing technologies for the disposal of decommissioned blades are mainly divided into four categories, all of which have significant shortcomings: landfill and incineration cause serious pollution and complete waste of resources; mechanical crushing and recycling is a downgraded use that completely destroys aerodynamic and structural value; pyrolysis and chemical recycling are costly and cause fiber performance degradation, and have not yet been applied on a large scale; and the overall reuse of blades is limited by the mismatch of the blade root interface, resulting in extremely limited application scenarios.

[0005] To address the interface mismatch issue, an industry-standard remanufacturing solution has emerged that involves cutting the original blade root into plates and creating internal slots to nest the beams and plates. This solution improves material utilization compared to discarding the original blade root, but it still suffers from the following insurmountable technical drawbacks: Firstly, the bonding quality is not visible, and the process stability is poor. The inner groove is a closed working space, and the thickness of the adhesive layer, the fullness of the adhesive, and the bonding state of the interface cannot be directly observed after assembly. Defects such as insufficient adhesive, thin adhesive, and voids are difficult to detect and repair during construction. The bonding quality is highly dependent on the operator's experience, resulting in poor batch consistency and hidden quality risks.

[0006] Secondly, the grooving process is difficult and has a low tolerance for error. The inner grooving needs to follow the original shape of the blade and the natural slope and inclination of the main beam. The grooving angle, depth, and curvature must be precisely adapted to the beam shape, which requires extremely high measurement accuracy and processing control. The process is difficult, inefficient, and it is difficult to guarantee consistency in batch production.

[0007] Third, the irregular outer surface makes post-processing complex. After the inner groove design is formed, the outer surface of the blade root retains the original blade's slope, height difference, and irregular curved surface, resulting in poor appearance flatness. The subsequent reinforcement, glue repair, shaping, and leveling processes are cumbersome, increasing the time and cost of remanufacturing.

[0008] Therefore, the industry urgently needs a blade root remanufacturing technology that can overcome the above-mentioned defects. By improving the grooving and assembly methods, it can achieve visible and controllable bonding quality, standardized processing, and a smooth and uniform appearance. At the same time, it can retain the advantages of original blade root inheritance and reuse, and bow-tie double connection, thereby further improving the quality and efficiency of retired blade remanufacturing.

[0009] Furthermore, the remanufacturing of retired blades must comply with standards such as the "General Technical Requirements for Remanufacturing of Mechanical Products" (GB / T 28618-2012), ensuring that product performance is no less than that of new products, making full use of existing components, and that quality is controllable and traceable. Existing solutions still do not meet the ideal remanufacturing requirements in terms of process controllability and appearance quality. Summary of the Invention

[0010] To address the shortcomings of existing internal slotting and nesting methods, such as invisible bonding quality, high processing difficulty, and poor appearance flatness, this invention provides a method for remanufacturing retired wind turbine blade roots using external tenon and mortise joints. This method employs back-side external snap-fit ​​slotting and assembly to achieve full visibility of bonding quality, standardized processing, and a smooth appearance. At the same time, it fully inherits the structural strength of the original blade root and constructs a dual connection system of external tenon and mortise joints, improving the controllability, consistency, and economy of the remanufacturing process.

[0011] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for reconstructing decommissioned wind turbine blade roots by external tenon and mortise joints, comprising the following steps: S1 Blade Cutting and Separation: Based on the installed parameters of the target wind turbine, determine the total length of the blade after modification, cut and separate the retired wind turbine blade along the cutting line to obtain the blade body with complete blade tip and aerodynamic shape, as well as the original blade root section with complete pre-embedded bolt sleeve connection structure.

[0012] The blade is divided into aerodynamic and connecting functional sections. The main body section retains the blade tip and airfoil, inheriting all aerodynamic value; the root section retains the pre-embedded bolt sleeves and composite material matrix, inheriting all connecting and load-bearing value, laying the foundation for subsequent separate processing and reassembly. The original blade root's laminated structure and bolt connection function are 100% reused, avoiding waste of high-value components; the blade's main aerodynamic parameters are fully preserved, ensuring the power generation performance after modification. This method is suitable for all decommissioned wind turbine blades with intact main structures, regardless of the original blade root interface form and size, and can be adapted to new hubs through cutting and remanufacturing.

[0013] The main body length of the blades retained after cutting is 6 to 15 meters, which corresponds to the commonly used blade length of 100kW to 1MW distributed wind turbines. This is the mainstream adaptation range for the downgrading and reuse of retired large-megawatt blades. The original airfoil curve, torsion angle distribution, and chord length distribution aerodynamic parameters of the blades are completely preserved, which is the core prerequisite for ensuring power generation efficiency.

[0014] S2 End Structure Pretreatment: The leading edge skin and trailing edge skin within a set length range are cut off along the axial direction towards the blade tip at the cut end of the blade body, exposing the upper beam plate and lower beam plate arranged opposite each other within this length range, as well as the web plate connecting the upper beam plate and lower beam plate, and the beam plate surface is polished and cleaned.

[0015] The skin mainly maintains the aerodynamic shape at the blade root connection section. After reconstruction, this area is covered by the connecting structure and its function can be replaced. Therefore, it is cut off to expose the main beam plate as the connecting substrate. Grinding and cleaning remove surface contaminants and aging layers to ensure the strength of the bonding interface.

[0016] The axial length of the skin removed is 300-800mm, which can be flexibly adjusted according to load requirements, taking into account both connection strength and structural weight; grinding and cleaning exposes a clean fiber-reinforced composite material surface to avoid interface contamination leading to bonding failure.

[0017] S3 Bowtie Tenon Processing: The exposed upper and lower beams are cut into bowtie-shaped symmetrical cross-sections that are wide at both ends and narrow in the middle, serving as tenons for external tenon-and-mortise joints.

[0018] The ends of the equal-width beams are machined into a bowtie shape. This serves several purposes: first, it creates a concave waist structure that, when snapped into a mortise, achieves mechanical interlocking, constructing a dual connection system of "chemical bonding and mechanical locking"; second, it maximizes the bonding perimeter and area within a limited axial length, enhancing the bonding load-bearing capacity; and third, the beveled transition ensures a smooth load transfer, avoiding stress concentration caused by abrupt changes in the cross-section. The bowtie-shaped cross-section increases the bonding area by 40%–60% compared to a uniform-width rectangle, significantly improving connection strength. The concave waist structure forms a natural mechanical barrier, maintaining the connection even if the adhesive layer fails partially, greatly increasing safety redundancy.

[0019] The minimum width of the bow-tie symmetrical cross-section structure is 50% to 70% of the original width of the beam and slab. This ratio takes into account both the mechanical locking effect and the strength of the beam and slab itself. If the width is too narrow, it will weaken the strength of the beam and slab. If the width is too small, the locking effect will be insufficient. The two ends of the wide part and the middle concave waist are connected by two beveled transition sections. After cutting, the edges of the bow-tie shape are rounded with a radius of 3 to 5 mm to remove sharp corners and burrs, eliminate stress concentration sources, and prevent edge cracking and delamination under load.

[0020] S4 Leaf root plate cutting and back mortise processing: The original leaf root section obtained from the cutting is cut along the axial direction into upper leaf root plate and lower leaf root plate. On the back outer surface of the upper leaf root plate and the lower leaf root plate, near the end of the blade body, through grooves that fit the shape of the bow tie tenon are processed to serve as mortises for the external tenon and mortise joint. The depth of the groove is consistent with the thickness of the beam plate, and the groove runs through the thickness direction of the leaf root plate.

[0021] The cylindrical original blade root is split into upper and lower plates, which are then connected to the upper and lower beam plates respectively. The core improvement lies in changing the slotting position from the inner side to the outer surface of the back. This is the key difference between this invention and existing inner-side slotting solutions: the back slotting working surface is open, not limited by the slope of the original blade shape, and can be uniformly processed horizontally and straight without the need for slope adjustment, significantly reducing processing difficulty, standardizing dimensions, and improving batch consistency; the slot depth is consistent with the thickness of the beam plate, forming a through slot, allowing the beam plate to be completely embedded in the slot to form a through nest, maximizing the bonding area and making load transfer more direct. The slotting processing efficiency is improved, the cost is reduced, and the dimensional consistency of batch products is significantly improved; the through nest maximizes the bonding area and strengthens the load-bearing capacity of the connection nodes.

[0022] The width of a single leaf root plate is 3 to 4 times the original width of the beam plate, ensuring sufficient load-bearing area and edge allowance; the axial length is 1.5 times the length of the exposed beam plate, providing sufficient overlap and bonding length; the outer contour of the machined groove is 1.5 to 2.5 mm larger on one side than the outer contour of the bow tie tenon, forming a uniform bonding gap with a total thickness of 3 to 5 mm, providing filling space for the resin adhesive and ensuring uniform adhesive layer thickness; a gap consistent with the bonding gap is left between the bottom of the groove and the bottom of the tenon for filling with resin adhesive, so that the entire nesting interface is covered by the adhesive layer, with no hard contact, ensuring uniform load transfer.

[0023] When cutting the original blade root section, the pre-embedded bolt sleeve structure inside the blade root is preserved without damage. After cutting, the upper blade root plate, lower blade root plate and the support structure all have complete original pre-embedded bolt sleeves, inheriting the bolt connection function of the original blade root, providing a mature and reliable connection foundation for subsequent flange installation.

[0024] S5 External Tenon-and-Mortar Nesting Bonding and Curing: Wind power-specific structural resin adhesive is evenly applied to the inner surface of the bow-tie tenon and the inner wall of the back mortise. The upper blade root plate is placed inside the upper beam plate, and the lower blade root plate is placed inside the lower beam plate. The upper beam plate is snapped into the back mortise of the upper blade root plate from the outside, and the lower beam plate is snapped into the back mortise of the lower blade root plate from the outside, forming an external nesting structure in which the beam plate covers the end of the blade root plate. After pressure fixing, curing is carried out, and the beam plate and the corresponding blade root plate are bonded together through the resin adhesive layer.

[0025] Unlike internal embedding methods, this assembly method employs an external snap-fit ​​mechanism. During assembly, the adhesive surface, adhesive layer thickness, adhesive fullness, and bonding gaps are fully visible, allowing for immediate detection of defects such as insufficient adhesive or gaps. Inspection is intuitive, and rework is convenient, completely eliminating the quality risks associated with internal grooving. During pressurization, the beam and plate can undergo slight deformation adjustments, automatically adapting to the bonding angle and creating a self-locking pre-tightening effect that tightens with each snap, replacing the forced, hard-on bonding method. The bonding quality is controllable throughout the process, significantly reducing the rate of hidden defects and greatly improving process stability. The self-locking pre-tightening formed after pressing results in a tighter interface and stronger structural stability. The external nesting structure allows the beam and plate to clamp the leaf root plate from the outside, resulting in a more rational force transmission path and superior anti-peeling performance.

[0026] The structural resin adhesive is a special epoxy structural adhesive for wind turbine blades. After curing, the tensile shear strength is not less than 25MPa. It has good compatibility with the blade matrix material and is resistant to aging and fatigue. The curing conditions are 72 hours at room temperature or 6 hours at 60℃, which matches the industry's common curing process. During the pressure fixing process, the beam plate deforms moderately to adapt to the fitting angle, forming a self-locking pre-tightening effect, which improves the interface fit and the overall structure.

[0027] S6 Support Structure Filling and Installation: The support structure is prepared using the remaining material after the original leaf root section is cut. The support structure is then filled and bonded to all the gaps between the upper leaf root plate and the lower leaf root plate.

[0028] The cavity between the upper and lower blade root plates can be transformed into an approximately solid cross-section by filling it with a full-length support structure. This significantly improves the cross-sectional stiffness, torsional stiffness, and compressive stability, preventing cross-sectional distortion and instability. Simultaneously, the remaining material from the original blade root is utilized, enabling in-situ reuse of waste materials and further enhancing material utilization. The stiffness and stability of the blade root section are significantly improved, eliminating the risk of cross-sectional deformation under complex loads. All original blade root materials are fully utilized, with no excess waste, achieving a material utilization rate exceeding 90%.

[0029] The support structure is a plate-like component resembling a web plate, made from the remaining material of the original leaf roots. The axial length of the support structure is consistent with the length of the upper and lower leaf root plates, and the width matches the spacing between the upper and lower leaf root plates, completely filling the gap between them and ensuring support throughout the entire length. The support structure is bonded and fixed to the upper and lower leaf root plates with resin adhesive, and a glass fiber hand-laid reinforcement layer is set at the junction to ensure a firm connection and coordinated load-bearing.

[0030] S7 Multi-node Manual Layup Reinforcement: After the bonding and curing are completed, multiple layers of glass fiber cloth are manually laid across the surface of three connection nodes and resin adhesive is applied. After curing, a glass fiber manual layup reinforcement layer is formed. The three nodes are the junction of the beam plate and the blade root plate, the junction of the blade root plate and the exposed composite material of the blade body, and the junction of the blade root plate and the supporting structure. Before manual layup, all openings of the pre-embedded bolt sleeves are sealed with removable protective plugs, which are removed after the layup has cured.

[0031] Reinforcement was implemented at three key weak points: the junction between the beam / slab and the blade root plate was reinforced to ensure the integrity of the tie joint; a smooth transition of cross-sectional stiffness was achieved at the junction between the blade root plate and the main structure to eliminate stress concentration; and the connection strength of the internal supports was enhanced at the junction between the blade root plate and the supporting structure. This comprehensive reinforcement at all three points integrates all independent components into a unified composite structure through chemical cross-linking, resulting in overall performance far superior to single-node reinforcement. The addition of a protective plug step effectively prevents the applied resin from flowing into the internal threads of the embedded bolt sleeves, avoiding problems such as bolt assembly failure or reduced preload due to thread blockage. All weak connection areas were effectively reinforced, significantly improving the overall structural integrity and fatigue performance, and effectively inhibiting crack initiation and propagation.

[0032] The fiberglass cloth is made of ±45° biaxial cloth or plain weave cloth, which is good at bearing shear and peel loads. A total of 4 to 8 layers are laid at each node, and the size of each layer of fiberglass cloth increases by 20 to 30 mm, forming a stepped overlap structure to achieve a gradual transition in stiffness and avoid new stress concentration. After each layer is laid, an epoxy resin is applied and compacted to remove air. The total thickness after curing is 2 to 4 mm, ensuring that the fibers are fully impregnated and there are no defects such as air bubbles or missing glue.

[0033] S8 Flange Assembly Connection: Prepare a flange plate that is compatible with the target wind turbine hub interface. Utilize the original pre-embedded bolt sleeves and matching bolts retained in the upper blade root plate, support structure, and lower blade root plate to synchronously fix and connect the flange plate to the end faces of the three components, thus completing the remanufacturing of the blade root of the retired blade.

[0034] The flange plate features a standardized interface adapted to the target hub, completely resolving the mismatch issue of the original blade root interface. Utilizing existing pre-embedded bolts eliminates the need for drilling new holes in the composite material, avoiding defects such as delamination and stress concentration caused by drilling. Furthermore, the original bolt structure has been designed and verified, ensuring sufficient connection strength and reliability. The interface offers flexible adaptation, covering target wind turbines of different power ratings. The bolt connection reuses the original mature structure, ensuring reliable quality and convenient assembly, thus fully inheriting the original blade root connection function.

[0035] The flange plate is a circular steel structure made of Q355 or higher strength grade structural steel, which meets the strength and fatigue requirements of wind power. The bolt holes on the flange plate correspond one-to-one with the pre-embedded bolt sleeves. The upper blade root plate, support structure and lower blade root plate are clamped together along the axis by bolts to form an integral force system, so that the three-layer structure can work together to bear the load and the load can be evenly distributed to avoid overload of a single layer.

[0036] The beneficial effects of this invention compared to the prior art are: 1. This invention features a back-mounted external snap-fit ​​grooved assembly, where the beam and plate snap together from the outside, creating a completely open assembly interface. The internal groove is a closed space, obscuring the adhesive layer and concealing defects. The external snap-fit ​​assembly exposes the entire process of adhesive application, bonding, and pressing to the visible range, allowing for immediate detection and correction of issues such as insufficient adhesive, air bubbles, and poor bonding. This significantly reduces the adhesive defect rate, eliminates reliance on operator experience for process quality, significantly improves batch consistency, and ensures greater connection reliability.

[0037] 2. This invention features a groove on the outer surface of the blade root plate's back side, allowing for uniform horizontal and straight machining without needing to adapt to the blade's slope. In contrast, the inner groove requires conforming to the main beam's curved surface, demanding extremely high measurement and machining accuracy. The back groove is a planar machining process, ensuring a unified benchmark and simplified technology, enabling standardized mass production. This significantly reduces machining difficulty and cost, improves processing efficiency, and results in better product dimensional consistency, making it more suitable for large-scale remanufacturing applications.

[0038] 3. In this invention, the groove depth is consistent with the beam / slab thickness, and the beam / slab is completely embedded in the groove to form a through-type nesting. The entire interface, including the bottom of the groove, is covered by the adhesive layer. In contrast, the inner groove is typically a semi-deep groove with a limited bonding area; the through-type nesting allows the entire thickness of the beam / slab to participate in bonding, maximizing the theoretical bonding area, and the complete adhesive coverage ensures more uniform load transfer. This significantly improves the static load-bearing capacity of the connection joint, resulting in a more uniform stress distribution, no localized stress concentration, and superior fatigue performance.

[0039] 4. This invention uses external clamping and pressure, with the beam and plate automatically adapting to the fitting angle through moderate deformation, forming a self-locking pre-tightening. Internal embedding involves a hard-on-hard forced fit, where the interface fit is greatly affected by processing precision. External clamping utilizes the moderate deformation of the beam and plate for adaptive alignment, creating a self-locking effect that tightens with pressure, resulting in a more compact interface fit. Higher interface fit, more uniform adhesive layer thickness, stronger structural integrity and stability, and less tendency to loosen during long-term operation.

[0040] 5. After the back groove is formed, the outer surface of the blade root is a complete flat surface without slopes or irregular curved surfaces. The inner groove design retains the irregular curvature of the original blade's outer surface, requiring extensive shaping and leveling later; the outer wrapping design has a flat outer surface, requiring only simple reinforcement and sealing. The subsequent finishing process is greatly simplified, reducing labor time and costs, and the finished product has a neat and uniform appearance, meeting the appearance quality requirements of remanufactured products.

[0041] 6. In this invention, both the cutting and grooving avoid the pre-embedded bolt sleeves, utilizing the existing bolts to connect the flange without requiring new holes. Drilling composite materials on-site easily leads to hidden defects such as delamination and splitting, resulting in significant variations in connection strength. The original pre-embedded bolt sleeves are integrally molded during manufacturing and have been verified through whole-machine testing, demonstrating reliability far exceeding that of on-site processing. This avoids structural damage to the composite material caused by secondary drilling, ensures flange connection strength based on the original design, and provides convenient assembly and stable quality.

[0042] 7. This invention features a high degree of freedom in the externally mounted beams on both sides, allowing for flexible filling of the central support structure. In contrast, the internally embedded assembly space is closed, making alignment and adjustment difficult; the externally mounted assembly offers ample operating space, making alignment, opening, and fitting more convenient, and the support structure can be fully or partially filled as needed. This reduces construction difficulty, increases the tolerance for errors, enhances process flexibility, and can adapt to reinforcement requirements of different load levels.

[0043] 8. The bowtie-shaped tenon and the back mortise of this invention are nested together and bonded with resin adhesive. This triple load-bearing mechanism of chemical bonding, mechanical locking, and external clamping ensures that failure of any one mechanism will not lead to overall failure. The connection strength and reliability are far superior to single-bonded structures, possessing fail-safe characteristics. Stepped ply reinforcement is applied at all three joints, eliminating all weak points with abrupt stiffness changes, achieving a smooth transition across the entire cross-section, significantly improving the overall structural integrity, extending fatigue life, and eliminating any obvious weak points.

[0044] 9. In this invention, the original blade root is completely transformed into a blade root plate and support structure, while the main body of the blade retains its complete aerodynamic shape. This maximizes the reuse of existing high-value components and avoids waste and damage from secondary processing. The material utilization rate exceeds 92%, and the power generation efficiency can reach more than 95% of that of a new blade of the same specification, resulting in economic benefits far exceeding those of material-level recycling.

[0045] 10. This invention reuses existing components throughout the entire process, resulting in an environmentally friendly and pollution-free process with product performance meeting standards. It complies with all remanufacturing requirements in GB / T 28618-2012 and is a typical remanufacturing technology. Compared to manufacturing new blades, it saves over 80% of materials and energy, making it environmentally friendly. Attached Figure Description

[0046] The present invention will now be further described with reference to the accompanying drawings.

[0047] Figure 1 A schematic diagram of the overall cutting and separation of retired blades.

[0048] Figure 2 This is a three-dimensional structural diagram of the present invention.

[0049] Figure 3 This is a schematic diagram of the main structure of the present invention.

[0050] Figure 4 for Figure 3 A sectional view of section AA in the middle.

[0051] Figure 5 for Figure 3 A sectional view of section BB in the middle.

[0052] Figure 6 This is a schematic diagram of the leaf root plate in this invention.

[0053] In the diagram: 1 is the blade body, 2 is the original blade root, 3 is the blade tip, 7 is the upper beam plate, 8 is the lower beam plate, 9 is the upper blade root plate, 10 is the lower blade root plate, 11 is the upper blade root plate groove, 12 is the lower blade root plate groove, 15 is the support structure, 16 is the flange plate, and 17 is the pre-embedded bolt sleeve / bolt hole. Detailed Implementation

[0054] The following is in conjunction with the appendix Figure 1 To be continued Figure 6 The present invention will be further described in detail with reference to specific embodiments.

[0055] This embodiment takes the remanufacturing of a 1.5MW decommissioned wind turbine blade into a blade adapted for a 200kW distributed wind turbine as an example, and elaborates on the process, connection principle and technical effect in detail. All process parameters and structural features correspond to the claims.

[0056] The original decommissioned blade was 38m long, with a main beam made of unidirectional glass fiber reinforced epoxy resin. The original blade root diameter was 1.8m, and it was connected using pre-embedded bolt sleeves (36 M36 bolts, pitch circle diameter 1600mm). Non-destructive testing showed that the blade body had no cracks, delamination, or other structural damage, meeting the remanufacturing requirements. The target wind turbine hub interface uses 12 M20 bolts, with a pitch circle diameter of 680mm, and the redesigned total length is 12m.

[0057] Step 1: Cutting and separating the blades Based on the target wind turbine power, hub interface, and installation space, the total length of the modified blade was determined to be 12m. A 12m measurement was taken from the original blade root end to the blade tip in three directions, and a circular cutting line was marked. A diamond wire saw was used to water-cool the blade along the cutting line to prevent resin degradation and fiber delamination caused by high-temperature cutting, ensuring the material properties at the cut were intact.

[0058] After cutting, the blade is divided into two parts: a blade body 1 with a length of 12m, which has a complete blade tip 3, and all aerodynamic parameters such as the original airfoil curve, twist angle distribution, and chord length distribution are completely preserved; and the original blade root 2 section with a length of about 26m, which has a complete pre-embedded bolt sleeve 17 connection structure inside.

[0059] This step separates the aerodynamic functional section from the connecting functional section, both of which retain their core value, laying the foundation for subsequent external remanufacturing. All original blade roots are retained without any waste.

[0060] Step 2: End structure pretreatment Measure 500mm from the cut end face of the blade body 1 along the axial direction towards the blade tip 3 and mark the pre-treatment area. Use an angle grinder with a diamond cutting disc to remove the leading and trailing edge skin of this area in layers, controlling the thickness of each layer to be 2-3mm to avoid excessive cutting force in a single operation that could damage the main beam.

[0061] After the skin is removed, the upper beam plate 7 and the lower beam plate 8, which are arranged opposite each other, are exposed. Then, the exposed web plate connecting the upper beam plate 7 and the lower beam plate 8 is removed.

[0062] Subsequently, the surfaces of the upper beam plate 7 and the lower beam plate 8 were sanded with 80-grit sandpaper to remove residual resin, contaminants and surface aging layers, exposing a clean fiber-reinforced composite material surface. This ensures the interfacial bonding strength for subsequent bonding and avoids bonding failure due to interfacial contamination.

[0063] This step precisely separates load-bearing and non-load-bearing components, preserving the core shear and torsion-resistant structure, and providing a clean and reliable adhesive substrate for subsequent external connections.

[0064] Step 3: Processing the bowtie-shaped tenon The exposed ends of the upper beam plate 7 and lower beam plate 8 are machined according to the design dimensions. Precision milling is performed using a five-axis CNC milling machine, with the machining path along the axial direction of the main beam fibers to avoid transversely cutting the main load-bearing fibers. After milling, the machined surface is finely sanded with fine sandpaper to remove micro-cracks. A bow-tie symmetrical cross-section structure is machined: the end closest to the cut end retains its original width of 300mm, narrows to a minimum width of 180mm (60% of the original width) after moving 200mm inward along the axial direction, and then extends outward by 200mm to a width of 220mm. The final cut length is 500mm, forming a bow-tie shape that is wide at both ends and concave in the middle, serving as the tenon for the external tenon and mortise. The bevel angle of the narrowed section is approximately 16°, and the bevel angle of the extended section is approximately 5.7°, with a smooth transition through the bevel angles.

[0065] After processing, all edges of the bowtie shape are rounded with a radius of 4mm to remove burrs and sharp corners, eliminate stress concentration sources, and prevent edge cracking and delamination under load.

[0066] The processed bowtie tenon combines the advantages of mechanical locking and a large bonding area, providing a structural foundation for subsequent external high-strength connections.

[0067] Step 4: Leaf root plate splitting and back mortise processing Two sections of the original leaf root, which were cut and retained, were symmetrically cut along the axial direction into two pieces, resulting in the upper leaf root plate 9 and the lower leaf root plate 10. Each leaf root plate is 900mm wide, three times the original width of the beam; its axial length is 750mm, 1.5 times the length of the exposed beam. Care was taken during the cutting process to avoid the internal embedded bolt sleeves 17, ensuring the structural integrity was not damaged.

[0068] Core process: Back grooving. On the outer back surface of the upper blade root plate 9 (the side away from the web), near the blade body, a groove 11 is machined using CNC milling; a corresponding groove 12 is machined on the lower blade root plate 10. The groove outline perfectly matches the bowtie tenon shape, and the overall single-sided dimension of the groove is 2mm larger than the tenon, forming a uniform bonding gap with a total thickness of 4mm; the groove depth is consistent with the beam plate thickness, meaning the groove extends through the blade root plate thickness direction. A 2mm gap, the same as the bonding gap, is left at the bottom of the groove. After assembly, this gap is also filled with resin adhesive to ensure that the entire tenon-mortise interface is covered by the adhesive layer, with no hard contact.

[0069] After grooving, the inner wall of the groove is sanded and cleaned to remove dust and oil, ensuring the quality of the bonding interface. The remaining leaf root material is cut off and stored for later use in constructing the support structure.

[0070] Because the groove is cut on the outer surface of the back, the working surface is completely open, and a uniform flat reference can be used for processing. There is no need to adjust the slope according to the inner slope of the blade, which greatly reduces the processing difficulty, improves the dimensional accuracy and consistency, and significantly improves the processing efficiency.

[0071] This step transforms the cylindrical original leaf root into a plate-shaped component with a back mortise, while fully inheriting the pre-embedded bolt connection function of the original leaf root, providing a standardized connection base for external tenon and mortise assembly.

[0072] Step 5: External tenon and mortise nesting bonding and curing Epoxy structural adhesive specifically designed for wind power is selected, prepared according to the specified weight ratio, and degassed after thorough mixing. The resin adhesive is then evenly applied to the inner surface of the bow-knot tenons of the upper beam plate 7 and the lower beam plate 8, as well as the inner walls of the upper leaf root plate groove 11 and the lower leaf root plate groove 12.

[0073] Place the upper leaf root plate 9 inside the upper beam plate 7 and the lower leaf root plate 10 inside the lower beam plate 8. After aligning the positions, fasten the beam plates from the outside to the inside, so that the bow tie tenon is embedded into the back groove, forming an outer nesting structure of "beam plate clamping leaf root plate".

[0074] During the fastening process, the adhesive surface, adhesive layer thickness, adhesive fullness, and bonding gap are all visible. The adhesive filling status can be observed at any time, and insufficient adhesive or air bubbles can be added and adjusted immediately, completely eliminating the hidden danger of the inner groove not being visible.

[0075] A specialized jack is used to apply uniform radial pressure, causing excess adhesive to be squeezed out evenly from the gaps, ensuring a uniform adhesive layer thickness without air bubbles or missing adhesive, thus improving bonding quality. During the pressing process, the beam and plate can undergo moderate elastic deformation, automatically fine-tuning the fitting angle to achieve an optimal fit with the curved surface of the groove, resulting in a self-locking pre-tightening effect that tightens as it is pressed together.

[0076] With the fixture in place, the resin is cured at room temperature for 72 hours to fully cure and form a resin adhesive layer. The tensile shear strength of the cured adhesive layer is ≥28MPa, meeting the design requirements.

[0077] After curing, the bowtie tenon and the back mortise form a strong chemical bond through the resin adhesive layer; at the same time, the concave waist structure forms a mechanical interlock. When the node is subjected to axial tensile force, the concave waist side wings and the groove wall form a mechanical barrier, distributing a large portion of the load; the external clamping structure allows the beam plate to tightly hug the leaf root plate from the outside, resulting in superior anti-peeling performance. Ultimately, a triple load-bearing system of "chemical bonding, mechanical interlocking, and external clamping" is formed, with connection reliability far exceeding that of ordinary inner lap joints.

[0078] Step 6: Installation of supporting structure Using the remaining blade root material from step 4, a plate-shaped support structure 15, mimicking the shape of a web, is cut and processed. The axial length of the support structure 15 is 750mm, consistent with the lengths of the upper blade root plate 9 and the lower blade root plate 10; its width perfectly matches the spacing between the upper and lower blade root plates, filling all the gaps between them after installation. The support structure 15 also retains the original blade root's pre-embedded bolt sleeve 17 structure.

[0079] Resin adhesive is applied to the upper and lower surfaces of the support structure 15, which is then inserted into the cavity between the upper and lower blade root plates. The position is adjusted so that its end face is flush with the end face of the blade root plate. After the bonding and curing, glass fiber is manually laid up to reinforce the junction of the support structure 15 and the upper and lower blade root plates, forming a glass fiber manual layup reinforcement layer to ensure a firm connection.

[0080] The full-length filled support structure 15 transforms the original hollow cross section into an approximately solid cross section, which greatly improves the bending, torsional stiffness and compressive stability of the blade root section and can effectively prevent cross section distortion and instability; at the same time, it achieves 100% utilization of the original blade root material, with no excess waste generated, and further improves the material utilization rate.

[0081] Step 7: Multi-node manual lay-up reinforcement After the adhesive has cured, all openings of the pre-embedded bolt sleeves 17 are sealed one by one with removable rubber protective plugs. Then, the three key connection nodes are reinforced by manual surface lay-up: The first point: the junction of the upper beam slab 7 and the upper leaf root slab 9, and the junction of the lower beam slab 8 and the lower leaf root slab 10, where the beam slab and leaf root slab are laid across each other to reinforce the integrity of the knotted nested nodes.

[0082] The second point: at the junction of the upper leaf root plate 9, the lower leaf root plate 10 and the exposed composite material of the blade body 1, the leaf root plate and the blade body are bridged to achieve a smooth transition of cross-sectional stiffness and eliminate stress concentration caused by abrupt changes in cross-section.

[0083] The third point: at the junction of the subsequent support structure and the upper and lower leaf root plates, the support structure and leaf root plate layers are bridged to enhance the connection strength of the internal support.

[0084] Six layers of ±45° biaxial fiberglass cloth were laid in each area, with each layer increasing in coverage by 25mm to create a stepped overlap structure. Each layer was coated with epoxy resin and compacted with a scraper and roller to remove air and ensure full fiber impregnation. After all layers were laid, they were cured at room temperature for 72 hours to form a hand-laid fiberglass reinforcement layer with a total thickness of approximately 3mm after curing. After curing, the protective plugs were removed, revealing clean bolt holes. The surface was then sanded and finished to remove any burrs or sharp edges.

[0085] Three full reinforcements ensure a smooth transition in all areas of abrupt stiffness change, effectively reducing stress concentration and inhibiting crack initiation and propagation; the reinforcing layer forms a chemical cross-link with the composite matrix on both sides, integrating all components into an integrated composite structure, significantly improving overall performance.

[0086] Step 8: Flange assembly and connection Flange plate 16 is manufactured according to the target wind turbine hub parameters. It is made of Q355B structural steel, with an outer diameter of 800mm and a thickness of 25mm. Twelve φ22mm bolt holes are made on flange plate 16 at the positions corresponding to the pre-embedded bolt sleeves 17, with a pitch circle diameter of 680mm, which perfectly matches the target hub interface.

[0087] The flange plate 16 is attached to the end face of the upper leaf root plate 9, the support structure 15, and the lower leaf root plate 10. After adjusting the coaxiality, the original matching bolts are inserted and tightened symmetrically according to the specified torque. The three-layer structure is clamped and fixed axially by the pre-embedded bolt sleeve 17 to form an integral force-bearing system.

[0088] The flange plate 16 integrates the upper blade root plate 9, the support structure 15, and the lower blade root plate 10 into a single unit through clamping action. During blade operation, the load is transferred from the beam plate to the blade root plate through the external tenon and mortise joint, and then evenly to the flange plate 16 through the three-layer structure, finally reaching the hub. The load distribution is uniform, with no local overload. Because the original pre-embedded bolt sleeve 17 is used for connection, no new holes need to be drilled, avoiding damage to the composite material during drilling. The connection strength and reliability are guaranteed by the original design.

[0089] Through the above steps, the remanufacturing of the external tenon-and-mortise blade root of the retired blade is completed. The finished product, after testing, showed that the static strength of the connection nodes met 1.5 times the design load requirement, and after 3000 hours of continuous operation, there was no loosening or cracking. The measured power generation efficiency reached 96% of that of a new blade of the same specification, the material utilization rate exceeded 92%, and the modification cost was only 18% of that of a new blade of the same specification. The controllability of the bonding quality, processing efficiency, and appearance flatness were significantly better than the internal grooving scheme, and all indicators met expectations and complied with remanufacturing standards.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Anyone skilled in the art can implement the present invention smoothly according to the above description. However, any modifications or alterations made by those skilled in the art without departing from the scope of the present invention's technical solution to the disclosed technical content to create equivalent embodiments are still within the protection scope of the present invention's technical solution.

Claims

1. A method for reconstructing decommissioned wind turbine blades using external tenon-and-mortise joints at the blade root, characterized in that... Includes the following steps: S1. Blade cutting and separation; The total length of the blades after modification is determined based on the installed parameters of the target wind turbine. The decommissioned wind turbine blades are cut and separated along the cutting line to obtain the blade body with complete blade tip and aerodynamic shape, as well as the original blade root section with complete pre-embedded bolt sleeve connection structure. S2. End structure pretreatment; Cut the leading edge skin and trailing edge skin within a set length range along the axial direction towards the blade tip at the cut end of the blade body, exposing the upper beam plate and lower beam plate arranged opposite each other within this length range, and cut off the web plate connecting the exposed upper beam plate and lower beam plate, and grind and clean the surface of the beam plate. S3. Tenon machining; The exposed upper and lower beams are cut into symmetrical cross-sections that are wide at both ends and narrow in the middle, which will serve as tenons for external tenon-and-mortise joints. S4. Leaf root plate cutting and back mortise processing; The original leaf root segment obtained by cutting is axially split into upper leaf root plate and lower leaf root plate. On the back outer surface of the upper leaf root plate and the lower leaf root plate, near the end of the blade body, through grooves that fit the shape of the tenon are respectively processed to serve as mortises for external tenon and mortise joints. The depth of the groove is consistent with the thickness of the beam plate, and the groove runs through the thickness direction of the leaf root plate. S5. Installation of supporting structure filling; A support structure was prepared using the remaining material after the original leaf root segment was cut. The support structure was then filled and bonded to all the gaps between the upper and lower leaf root plates. S6, Multi-node manual layup reinforcement; After the bonding and curing are completed, multiple layers of fiberglass cloth are manually laid across the surface of the three connection nodes and resin adhesive is applied. After curing, a fiberglass manual lay-up reinforcement layer is formed. The three nodes are the junction of the beam plate and the blade root plate, the junction of the blade root plate and the exposed composite material of the blade body, and the junction of the blade root plate and the supporting structure. Before manual lay-up, all openings of the pre-embedded bolt sleeves are sealed with removable protective plugs, which are removed after the lay-up has cured. S7. Flange assembly connection; A flange plate adapted to the hub interface of the target wind turbine is prepared. The flange plate and the end faces of the three components are synchronously fixed and connected by the original pre-embedded bolt sleeves and matching bolts retained in the upper blade root plate, support structure and lower blade root plate, thus completing the remanufacturing of the blade root of the retired blade.

2. The method for reconstructing decommissioned wind turbine blade roots using mortise and tenon joints according to claim 1, characterized in that, In step S3, the minimum width of the symmetrical cross-section structure is 50% to 70% of the original width of the beam and slab. The two wide ends and the middle concave waist are connected by two beveled transition sections. After cutting, the edges are rounded with a radius of 3 to 5 mm.

3. The method for reconstructing decommissioned wind turbine blade roots using mortise and tenon joints according to claim 1, characterized in that, In step S4, the width of a single leaf root plate is 3 to 4 times the original width of the beam plate, and the axial length is 1.5 times the length of the exposed beam plate; the outer contour of the processed groove is 1.5 to 2.5 mm larger on one side than the outer contour of the tenon, forming a uniform bonding gap with a total thickness of 3 to 5 mm; a gap consistent with the bonding gap is left between the bottom of the groove and the bottom of the tenon.

4. The method for reconstructing decommissioned wind turbine blade roots using mortise and tenon joints according to claim 1, characterized in that, In step S5, the structural resin adhesive is a special epoxy structural adhesive for wind turbine blades, with a tensile shear strength of not less than 25 MPa after curing; the curing conditions are 72 hours at room temperature or 6 hours at 60°C; during the pressure fixing process, the beam plate deforms moderately to adapt to the fitting angle, forming a self-locking pre-tightening effect.

5. The method for reconstructing decommissioned wind turbine blade roots using mortise and tenon joints according to claim 1, characterized in that, In step S6, the fiberglass cloth is selected as ±45° biaxial cloth or plain weave cloth, and 4 to 8 layers are laid at each node. The size of each layer of fiberglass cloth increases by 20 to 30 mm, forming a stepped overlapping structure. After each layer is laid, an epoxy resin adhesive is applied and compacted to remove air. The total thickness after curing is 2 to 4 mm.

6. The method for reconstructing decommissioned wind turbine blade roots using mortise and tenon joints according to claim 1, characterized in that, In step S7, the support structure is a web-like plate made from the remaining material of the original leaf root; the axial length of the support structure is consistent with the length of the upper and lower leaf root plates, and the width matches the spacing between the upper and lower leaf root plates, completely filling the gap between them; the support structure is bonded and fixed to the upper and lower leaf root plates with resin glue, and a glass fiber hand-laid reinforcement layer is set at the junction.

7. The method for reconstructing decommissioned wind turbine blade roots using mortise and tenon joints according to claim 1, characterized in that, In step S8, the flange plate is a circular steel structure made of structural steel with a strength grade of Q355 or higher; the bolt holes on the flange plate correspond one-to-one with the pre-embedded bolt sleeves, and the upper leaf root plate, the support structure, and the lower leaf root plate are clamped together axially to form an integral force-bearing system by bolts.

8. The method for reconstructing decommissioned wind turbine blade roots using external tenon-and-mortise joints according to claim 1, characterized in that, In step S2, the axial length of the skin removed is 300-800 mm; grinding and cleaning remove residual resin and contaminants from the beam surface to expose a clean fiber-reinforced composite material surface.

9. The method for reconstructing decommissioned wind turbine blade roots using mortise and tenon joints according to claim 1, characterized in that, In step S1, the length of the main body of the blade after cutting is 6 to 15 m, and the original airfoil curve, twist angle distribution, chord length distribution and other aerodynamic parameters of the blade are completely preserved.

10. The method for reconstructing decommissioned wind turbine blade roots using mortise and tenon joints according to claim 1, characterized in that, In step S4, when cutting the original blade root section, the pre-embedded bolt sleeve structure inside the blade root is preserved undamaged. After cutting, the upper blade root plate, lower blade root plate and the support structure all have complete original pre-embedded bolt sleeves inside.

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