A method for repairing core layer damage in composite sandwich structures

Abstract

This invention belongs to the field of composite sandwich structure repair technology, and discloses a method for repairing core layer damage in composite sandwich structures. By removing the core layer through opening and then filling with sealant, the damage to the skin is minimized, preserving the original structure to the greatest extent. This solves the technical problems of significant strength reduction and susceptibility to secondary damage after debonding repair of composite sandwich structures in existing technologies. Furthermore, compared to mechanical connection repair after debonding, the strength performance of the repaired area is superior to that of the original core layer, with less impact on aircraft aerodynamic performance and a longer service life. In addition, this method has low repair costs and good economic efficiency.

Description

Technical Field

[0001] This invention relates to the field of composite sandwich structure repair technology, and in particular to a method for repairing core layer damage in composite sandwich structures. Background Technology

[0002] Composite sandwich structures are typically composed of an upper skin, a core layer, and a lower skin. The core layer can be made of lightweight materials such as honeycomb core or foam core. These structures are commonly used in aircraft horizontal and vertical stabilizers and landing gear doors due to their advantages of being lightweight, high-strength, corrosion-resistant, and having good fatigue resistance.

[0003] During manufacturing and service, composite sandwich structures inevitably suffer from impact, compression, and fatigue loads, leading to damage such as core layer collapse, tearing, and debonding. This, in turn, degrades the structural mechanical properties, reducing the safety and reliability of the structure during service. Currently, the commonly used method for core layer damage repair is the patch repair method, which requires extensive removal of the skin above the damaged area to expose the damaged core layer. This method is destructive, causing irreversible structural damage to the skin and significantly expanding the scope of structural damage. It disrupts the original force transmission path of the sandwich structure, reducing the overall strength and stability of the component. Furthermore, the repaired sandwich structure exhibits poor dimensional accuracy and structural consistency, with significant residual stress concentration, making it prone to secondary damage. Summary of the Invention

[0004] The purpose of this invention is to provide a method for repairing core layer damage in composite sandwich structures, in order to solve the technical problems in the prior art where damage repair causes significant damage to the skin, the strength of the composite sandwich structure decreases drastically after repair, and it is prone to secondary damage.

[0005] To achieve this objective, the present invention adopts the following technical solution: A method for repairing core layer damage in a composite sandwich structure is provided, comprising the following steps: S1: Drill a central hole and multiple vent holes on the skin of the composite sandwich structure. The central hole is located in the area to be repaired, and the multiple vent holes are arranged circumferentially at intervals on the outer periphery of the central hole, and are all located on the outer periphery of the area to be repaired. S2: Place the protective plate on the upper surface of the composite material sandwich structure. The protective plate has a first hole and a plurality of second holes. The first hole is coaxially arranged with the central hole, and the plurality of second holes correspond one-to-one with the plurality of exhaust holes. S3: The reamer passes through the central hole and, driven by the drive mechanism, can remove the internal core layer of the area to be repaired, forming a cavity to be repaired; S4: Remove the core layer debris from the cavity to be repaired; S5: Remove the protective plate, fill the cavity to be repaired with sealant, and cure the sealant; S6: A layer of prepreg is laid on the skin of the composite sandwich structure, the prepreg covering the central hole and the plurality of vent holes.

[0006] As an alternative method for repairing core layer damage in composite sandwich structures, step S0 is included before step S1: drying the area to be repaired.

[0007] As an alternative method for repairing core layer damage in composite sandwich structures, a protective layer is provided in the non-repair area of ​​the composite sandwich structure.

[0008] As an alternative method for repairing core layer damage in composite sandwich structures, the reamer includes a connected vertical rod and a horizontal rod. The vertical rod extends in a vertical direction and is located at the output end of the drive mechanism. The horizontal rod extends in a horizontal direction, and a cutting portion is provided at the end of the horizontal rod away from the vertical rod.

[0009] As an alternative method for repairing core layer damage in composite sandwich structures, the crossbar has a polygonal cross-section.

[0010] As an optional method for repairing core layer damage in composite sandwich structures, step S3 includes: S31: Using a first reamer with a first radial dimension, drill a first cylindrical cavity at the core layer of the area to be repaired; S32: Using a second reamer with a second radial dimension, expand the hole in the first cylindrical cavity to form a second cylindrical cavity, wherein the second radial dimension is larger than the first radial dimension; Repeat step S32, using reamers with progressively larger radial dimensions to enlarge the hole based on the cylindrical cavity formed by the previous reamer, until a cavity with the target aperture is obtained.

[0011] As an alternative method for repairing core layer damage in composite sandwich structures, in step S4, a clamping tool is first used to clamp the core layer fragments in the cavity to be repaired, and then a vacuum adsorption tool is used to adsorb the debris in the cavity to be repaired.

[0012] As an alternative method for repairing damage to the core layer of a composite sandwich structure, the curing temperature of the sealant is lower than the curing temperature of the composite sandwich structure.

[0013] As an alternative method for repairing core layer damage in composite sandwich structures, before injecting sealant into the cavity to be repaired, an endoscope is passed through the central hole to observe the removal of the core layer in the cavity to be repaired.

[0014] As an optional method for repairing damage to the core layer of a composite sandwich structure, in step S5, sandpaper is used to polish the cured sealant.

[0015] The beneficial effects of this invention are: This invention provides a method for repairing core layer damage in composite sandwich structures. By removing the core layer through opening and then filling with sealant, the damage to the skin is minimized, preserving the original structure to the greatest extent possible. This solves the technical problems of significant strength reduction and susceptibility to secondary damage after debonding repair of composite sandwich structures in existing technologies. Furthermore, compared to mechanical reconnection repair after debonding, the strength performance of the repaired area is superior to that of the original core layer, with minimal impact on aircraft aerodynamic performance and a longer service life. In addition, this method has low repair costs and good economic efficiency. Attached Figure Description

[0016] Figure 1 This is a flowchart of a method for repairing core layer damage in composite sandwich structures provided in a specific embodiment of the present invention; Figure 2 This is a schematic diagram of the first process in the repair process of the composite material sandwich structure provided in the specific embodiments of the present invention; Figure 3 This is a schematic diagram of the second process in the repair process of composite material sandwich structure provided in the specific embodiments of the present invention; Figure 4 This is a schematic diagram of the third process in the repair process of composite material sandwich structure provided in the specific embodiments of the present invention; Figure 5 This is a schematic diagram of the fourth process in the repair process of composite material sandwich structure provided in the specific embodiments of the present invention; Figure 6 This is a schematic diagram of the fifth process in the repair process of composite material sandwich structure provided in the specific embodiments of the present invention; Figure 7 This is a schematic diagram of the sixth process in the repair process of composite material sandwich structure provided in the specific embodiments of the present invention; Figure 8 This is a schematic diagram of the seventh process in the repair process of composite material sandwich structure provided in the specific embodiments of the present invention; Figure 9 This is a schematic diagram of the eighth process in the repair process of composite material sandwich structure provided in the specific embodiments of the present invention; Figure 10 This is a schematic diagram of the ninth process in the repair process of composite material sandwich structures provided in the specific embodiments of the present invention.

[0017] In the picture: 100. Composite material sandwich structure; 101. Area to be repaired; 102. Unrepaired area; 200. Chamber to be repaired; 1. Center hole; 2. Vent hole; 3. Protective plate; 4. Reamer; 41. Vertical rod; 42. Horizontal rod; 421. Cutting part; 5. Drive mechanism; 6. Prepreg; 7. Endoscope; 8. Potting gun. Detailed Implementation

[0018] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar components or components having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0019] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; a mechanical connection or an electrical connection; a direct connection or an indirect connection through an intermediate medium; or the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0020] In the description of this invention, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0022] like Figures 1 to 10 As shown, the present invention provides a method for repairing core layer damage in a composite sandwich structure, comprising the following steps: S1: Drill a central hole 1 and multiple vent holes 2 on the skin of the composite sandwich structure 100. The central hole 1 is located in the area to be repaired 101, and the multiple vent holes 2 are arranged circumferentially on the outer periphery of the central hole 1, and are all located on the outer periphery of the area to be repaired 101. Specifically, in this embodiment, the above steps involve using a drilling tool to drill a central hole 1 and multiple vent holes 2 on the skin of the composite material sandwich structure 100. The central hole 1 is located in the area to be repaired 101. The multiple vent holes 2 are spaced circumferentially on the outer periphery of the central hole 1, and are all located on the outer periphery of the area to be repaired 101.

[0023] Reference Figure 2 and Figure 3 As shown, in this embodiment, the central hole 1 is approximately located at the geometric center of the area to be repaired 101. Three vent holes 2 are provided, spaced circumferentially around the outer periphery of the central hole 1, and all are located in the non-repair area 101. The included angle α between any two adjacent vent holes 2 is 120°. The centers of the three vent holes 2 lie on the circumference of the enclosing circle. Figure 2 The circle shown by the dashed line is the envelope circle, which is concentric with the central hole 1. The radial dimension of the envelope circle is slightly larger than the radial dimension of the area to be repaired 101, meaning that the area of ​​the envelope circle can completely cover the area of ​​the area to be repaired 101.

[0024] In other embodiments, four, five, or even more vent holes 2 may be provided. Preferably, there are 3 to 6 vent holes 2. If the number of vent holes 2 is too small, the internal and external air pressure balance of the composite material sandwich structure 100 cannot be ensured. If the number of vent holes 2 is too large, it will increase the drilling process during the repair process and reduce the repair efficiency.

[0025] Optionally, before step S1, step S0 is included: drying the area 101 to be repaired to remove moisture from the pores and cavities of the core layer. The core layer after drying is harder, which not only makes it less prone to collapse and chipping during drilling, but also makes the hole walls more regular. It can also prevent moisture from the skin surface from penetrating into the core layer during drilling, thus preventing further expansion of the debonding area.

[0026] Considering that drilling may damage the non-repair area 102, a protective layer is provided on the surface of the non-repair area 102 of the composite material sandwich structure 100. The protective layer is adhered to the upper surface of the skin of the non-repair area 102. It should be noted that after the repair work is completed, the protective layer needs to be removed from the surface of the non-repair area 102. The removal of the protective layer will not damage the skin of the non-repair area 102. Therefore, the tape used to apply the protective layer is preferably a low-tack pressure-sensitive adhesive, a peelable pressure-sensitive adhesive, or a UV peelable adhesive.

[0027] Specifically, the protective layer can be a rigid plate material such as a metal plate or a plastic plate, or a flexible material such as a rubber pad, silicone pad, or cloth. Its main function is to cover the non-repair area 102 and prevent accidental damage to the skin of the non-repair area 102 during the operation. As long as it can achieve the above-mentioned protective function, the material is not specifically limited here.

[0028] S2: Place the protective plate 3 on the upper end face of the composite material sandwich structure 100. The protective plate 3 has a first hole and a number of second holes. The first hole is coaxially arranged with the central hole 1, and the number of second holes corresponds one-to-one with the number of exhaust holes 2. In this specific embodiment, the above steps involve placing the protective plate 3 on the upper surface of the composite material sandwich structure 100. The protective plate 3 has a first hole and multiple second holes. The first hole is coaxially arranged with the central hole 1, and the multiple second holes correspond one-to-one with multiple exhaust holes 2.

[0029] Specifically, the protective plate 3 is preferably a metal plate. Metal plates have extremely high impact resistance, which can effectively resist external impacts and accidental bumps. They are also structurally stable, not easily deformed, have a long service life, and low maintenance costs.

[0030] For example, in this embodiment, the protective plate 3 has three second holes, and the three second holes correspond one-to-one with the three exhaust holes 2.

[0031] Understandably, the area of ​​the protective plate 3 must at least cover the central hole 1 and the three exhaust holes 2.

[0032] S3: The reamer 4 passes through the central hole 1. Under the drive of the drive mechanism 5, the reamer 4 can remove the internal core layer of the area to be repaired 101 to form the cavity to be repaired 200. In this specific embodiment, the above steps involve passing the reamer 4 through the central hole 1. Under the drive of the drive mechanism 5, the reamer 4 can remove the internal core layer of the area to be repaired 101, forming the cavity to be repaired 200.

[0033] Specifically, such as Figures 3 to 5 As shown, the reamer 4 includes a connected vertical rod 41 and a horizontal rod 42. The vertical rod 41 extends vertically and is located at the output end of the drive mechanism 5. The horizontal rod 42 extends horizontally, and a cutting portion 421 is provided at the end of the horizontal rod 42 away from the vertical rod 41. The cutting portion 421 is used to cut the inner core layer of the area to be repaired 101. That is, the reamer 4 is L-shaped, which facilitates the reamer 4 to pass smoothly through the central hole 1 and extend into the interior of the area to be repaired 101, thereby ensuring smooth cutting of the core layer. Under the drive of the drive mechanism 5, the reamer 4 can rotate around the axis of the vertical rod 41, so that the cutting portion 421 at the end of the horizontal rod 42 performs circumferential cutting on the core layer. Preferably, the vertical rod 41 and the horizontal rod 42 are integrally formed to improve the overall strength of the reamer 4.

[0034] For example, the drive mechanism 5 is a motor commonly used in the art.

[0035] To facilitate operation, a mounting shell is provided on the outer side of the drive mechanism 5, and a grip is provided on the outer peripheral wall of the mounting shell. In actual operation, the operator can hold the drive mechanism 5 by hand, making operation relatively comfortable. In addition, the mounting shell also provides a certain degree of protection for the drive mechanism 5.

[0036] Furthermore, such as Figure 5 As shown, the cross-section of the crossbar 42 is polygonal. The polygonal cross-section can significantly improve the overall rigidity and vibration resistance of the auger 4, and can also evenly transmit the cutting torque to multiple sides, effectively avoiding stress concentration and improving cutting efficiency.

[0037] In this specific embodiment, the cross section of the crossbar 42 is a regular hexagon, and the cutting portion 421 consists of three chamfers located at the end of the crossbar 42. In other embodiments, the cross section of the crossbar 42 may also be a quadrilateral, a pentagon, etc., and the specific shape and size of the cutting portion 421 may be set as needed, without any specific limitation here.

[0038] It should be noted that the edge of the end of the crossbar 42 away from the vertical bar 41 is preferably ground at a certain angle to form a sharper edge, thereby improving the cutting efficiency of the core layer.

[0039] Specifically, step S3 includes: S31: Using a first reamer 4 with a first radial dimension, drill a first cylindrical cavity in the core layer of the area to be repaired 101; S32: Using a second reamer 4 with a second radial dimension, the hole is enlarged based on the first cylindrical cavity to form a second cylindrical cavity, wherein the second radial dimension is larger than the first radial dimension; Repeat step S32, using reamers 4 with progressively larger radial dimensions to enlarge the hole based on the cylindrical cavity formed by the previous reamer 4, until a cavity 200 to be repaired with the target aperture is obtained.

[0040] In other words, such as Figure 6 As shown, firstly, a small radial cutter 4 is used to cut part of the core layer of the area to be repaired 101, and then... Figure 7 As shown, using a reamer 4 with a slightly larger radial dimension, continue cutting. Then, use reamers 4 with gradually increasing radial dimensions in sequence to continue radial cutting on the basis of the cylindrical cavity formed by the previous reamer 4 until the core layer in the area to be repaired 101 is completely cut off.

[0041] Since the vent hole 2 is located in the non-repair area 102, when the core layer inside the vent hole 2 is completely cut off, it indicates that the internal core layer of the area to be repaired 101 has been cut off.

[0042] In addition, when the core layer is initially cut, the drive mechanism 5 can be operated at a higher speed to achieve rapid cutting. When the core layer in the area to be repaired 101 is almost completely cut off, the speed of the drive mechanism 5 is reduced to prevent the reamer 4 from causing large-area damage to the core layer in the non-repair area 102.

[0043] S4: Remove core debris from the chamber 200 to be repaired; Specifically, in this embodiment, the above steps involve removing core layer fragments from the chamber 200 to be repaired. Specifically, a clamping tool is first used to grasp the core layer fragments within the chamber to be repaired, removing any fragments that can be grasped. Then, a vacuum suction tool is used to remove debris from the chamber 200 to be repaired, ensuring that the chamber 200 is clean and free of residual fragments.

[0044] For example, in this embodiment, the clamping tool is a tweezer commonly used in the art. The tweezer passes through the central hole 1 to remove larger pieces of debris. The vacuum suction tool is a negative pressure suction nozzle commonly used in the art. The suction end of the negative pressure suction nozzle passes through the central hole 1, and under the action of vacuum suction force, all the debris in the chamber 200 to be repaired is sucked out.

[0045] S5: Remove the protective plate 3, fill the cavity 200 to be repaired with sealant, and cure the sealant; In this specific embodiment, the above steps involve removing the protective plate 3, injecting sealant into the chamber 200 to be repaired until it is full, and then curing the sealant.

[0046] like Figure 8 As shown, to ensure that there are no residual core layer fragments or debris in the chamber 200 to be repaired, before injecting the sealant, the endoscope 7 is passed through the central hole 1 and extended into the chamber 200 to be repaired to carefully observe its internal condition.

[0047] Specifically, refer to Figure 9 Use a potting gun 8 to inject sealant into the cavity 200 to be repaired through the central hole 1. The sealant is a commonly used substance in this field. Operators can flexibly choose the specific type of sealant according to actual needs, which will not be elaborated on here.

[0048] When sealant overflows from the upper surface of the composite sandwich structure 100 at the vent 2, it indicates that the cavity 200 to be repaired has been filled with sealant, and the injection of sealant can be stopped.

[0049] The sealant is then cured using a thermosetting apparatus to transform it from a liquid to a solid state. The curing temperature of the sealant is lower than that of the composite sandwich structure 100 to avoid thermal damage to the composite sandwich structure 100 during the curing process, thus protecting the bonding strength of the non-repair area 102.

[0050] It is understandable that the potting glue gun 8, endoscope 7 and thermosetting apparatus mentioned above are all existing mature equipment. Their specific structures and working principles refer to existing technologies, and will not be elaborated on here.

[0051] S6: A layer of prepreg 6 is laid on the skin of the composite sandwich structure 100, the prepreg 6 covering the central hole 1 and multiple vent holes 2.

[0052] The above steps, specifically in this embodiment, refer to... Figure 10 A layer of prepreg 6 is laid on the skin of the composite sandwich structure 100. The prepreg 6 covers the central hole 1 and multiple vent holes 2, sealing the central hole 1 and multiple vent holes 2 while providing reinforcement and enhancing the stability of the composite sandwich structure 100. Resin film is preferably used for bonding the prepreg 6, as it is convenient and quick to use and has excellent adhesive properties, ensuring a firm bond to the prepreg 6.

[0053] Because the sealant injection was stopped only after sealant overflowed from vent hole 2, vent hole 2 was already filled with sealant, and some sealant had even overflowed onto the outside of the skin. After curing, the upper surface of the skin may have uneven solid sealant. To ensure the flatness of the prepreg 6, the cured sealant was first sanded with sandpaper to remove excess solid sealant, so that the upper surface of the skin in the area to be repaired 101 was flat.

[0054] For example, in this embodiment, alumina sandpaper is used for polishing. Alumina sandpaper has excellent durability and a long service life, typically 1.5 to 2 times that of silicon carbide sandpaper. Furthermore, the rounded shape of alumina particles provides excellent surface finish.

[0055] This method involves removing the core layer through opening and then filling with sealant, resulting in minimal damage to the skin and preserving the original structure to the greatest extent possible. It solves the technical problem in existing technologies where the strength of composite sandwich structures significantly decreases after 100% debonding repair, and secondary damage is common. Furthermore, compared to mechanical reconnection repair after debonding, the repaired area exhibits superior strength compared to the original core layer, with minimal impact on aircraft aerodynamics and a longer service life. In addition, this method has lower repair costs and is economically viable.

[0056] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for repairing core layer damage in a composite sandwich structure, characterized in that, Includes the following steps: S1: Drill a central hole (1) and multiple vent holes (2) on the skin of the composite sandwich structure (100). The central hole (1) is located in the area to be repaired (101). The multiple vent holes (2) are arranged circumferentially on the outer periphery of the central hole (1) and are all located on the outer periphery of the area to be repaired (101). S2: Place the protective plate (3) on the upper surface of the composite material sandwich structure (100). The protective plate (3) has a first hole and a plurality of second holes. The first hole is coaxially arranged with the central hole (1), and the plurality of second holes correspond one-to-one with the plurality of exhaust holes (2). S3: The reamer (4) passes through the central hole (1), and under the drive of the drive mechanism (5), the reamer (4) can remove the inner core layer of the area to be repaired (101) to form the cavity to be repaired (200). S4: Remove the core layer debris from the chamber (200) to be repaired; S5: Remove the protective plate (3), fill the cavity to be repaired (200) with sealant, and cure the sealant; S6: A layer of prepreg (6) is laid on the skin of the composite sandwich structure (100), the prepreg (6) being able to cover the central hole (1) and the plurality of vent holes (2).

2. The method for repairing core layer damage in a composite sandwich structure according to claim 1, characterized in that, Before step S1, step S0 is also included: drying the area (101) to be repaired.

3. The method for repairing core layer damage in a composite sandwich structure according to claim 1, characterized in that, The non-repair area (102) of the composite sandwich structure (101) is provided with a protective layer.

4. The method for repairing core layer damage in a composite sandwich structure according to claim 1, characterized in that, The reamer (4) includes a vertical rod (41) and a horizontal rod (42) connected together. The vertical rod (41) extends in the vertical direction and is located at the output end of the drive mechanism (5). The horizontal rod (42) extends in the horizontal direction, and a cutting part (421) is provided at the end of the horizontal rod (42) away from the vertical rod (41).

5. The method for repairing core layer damage in a composite sandwich structure according to claim 4, characterized in that, The cross section of the crossbar (42) is polygonal.

6. The method for repairing core layer damage in a composite sandwich structure according to claim 1, characterized in that, Step S3 includes: S31: Using a first reamer with a first radial dimension, drill a first cylindrical cavity at the core layer of the area to be repaired (101); S32: Using a second reamer with a second radial dimension, expand the hole in the first cylindrical cavity to form a second cylindrical cavity, wherein the second radial dimension is larger than the first radial dimension; Repeat step S32, using reamers with progressively larger radial dimensions to enlarge the hole based on the cylindrical cavity formed by the previous reamer, until a cavity (200) with the target aperture is obtained.

7. The method for repairing core layer damage in a composite sandwich structure according to claim 1, characterized in that, In step S4, a clamping tool is first used to clamp the core layer fragments in the chamber to be repaired (200), and then a vacuum adsorption tool is used to adsorb the debris in the chamber to be repaired (200).

8. The method for repairing core layer damage in a composite sandwich structure according to claim 1, characterized in that, The curing temperature of the sealant is lower than that of the composite sandwich structure (100).

9. The method for repairing core layer damage in a composite sandwich structure according to claim 1, characterized in that, Before injecting sealant into the cavity to be repaired (200), the endoscope (7) is passed through the central hole (1) to observe the removal of the core layer in the cavity to be repaired (200).

10. The method for repairing core layer damage in a composite sandwich structure according to claim 1, characterized in that, In step S5, sandpaper is used to polish the cured sealant.

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