A method for repairing composite material structures using an I-shaped patch design

Abstract

A method for repairing composite material structures using an I-shaped patch design includes the following steps: Step 1: After determining the number of layers to be removed from the damaged area, the damaged area is processed into an "I-shaped" structure; Step 2: Based on the patch repair layer with the smallest diameter or area, the lower patch with a larger diameter or area is cut into N (N≥2) parts according to the process separation surface; Step 3: Under pre-compaction temperature, the splicing area between the parts of the cut patch in Step 2 is pressed under high pressure to complete the overall splicing process of the patch; Step 4: After sequentially stacking the upper patches, the structure is sealed and cured to complete the repair process. This method can improve the mechanical properties of the composite material structure after damage repair and is applicable to the repair process of laminated structures such as composite skins and sandwich composite panels.

Description

Technical Field

[0001] This invention relates to the field of composite material repair technology, and in particular to a method for repairing composite material structures using an I-shaped patch design. Background Technology

[0002] Composite materials, with their superior lightweight advantages, are widely used in various structural components across aerospace, rail transportation, weaponry, and many other fields. As their applications expand and usage increases, the resulting repair market is also enormous. For composite material panels in laminated or sandwich structures such as skins, wall panels, and shells, after structural damage, a common approach is to remove the damaged area, process it into a stepped or inverted pyramid shape, and then repair it using the same material system. This restores the structural integrity while imparting certain mechanical properties to the damaged structure.

[0003] However, with traditional stepped or inverted pyramid repair solutions, the mechanical properties of composite material structures can only recover to about 55% of the original structure. Both strength and stiffness are significantly reduced compared to the original structure. Although this meets the delivery and application requirements, the decline in mechanical properties makes the damaged area prone to secondary damage during subsequent service, posing a potential risk to the service safety of the structure or equipment.

[0004] To address the aforementioned problems, this invention provides a novel repair method applicable to the repair process of composite laminate structures or sandwich composite panels, which can effectively improve the mechanical properties of the composite structure after damage repair. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for repairing composite material structures using a quasi-I-shaped patch design. By cutting specific patches, the accessibility of the entire patch stacking process is ensured, which can improve the mechanical properties of the composite material structure after damage repair. This method is applicable to the repair process of laminated structures such as composite skin and sandwich composite material panels.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for repairing composite material structures using an I-beam patch design includes the following steps:

[0008] Step 1: After determining the number of damage removal layers, process the damaged area into an "I-shaped" structure;

[0009] Step 2: Based on the repair layer with the smallest diameter or area, cut the lower patch with a larger diameter or area into N (N≥2) parts according to the process separation surface;

[0010] Step 3: Press the splicing area between the parts of the patch that have been cut in Step 2 under high pressure at the pre-compaction temperature, and complete the overall splicing process of the patch.

[0011] Step 4: After layering the upper patches, seal and cure them to complete the repair process.

[0012] Furthermore, in step 1, if the number of damage removal layers is 2, in the order from the surface to the inside, if the surface layer (1) is the layer with the smallest damage removal diameter or area, then the size or area of ​​the inner layer layer (2) is greater than the size and area of ​​the layer (1), that is, it is necessary to satisfy that at least one patch size or area of ​​the inner layer is greater than at least one patch size or area on its upper side.

[0013] Furthermore, in step 1, when the number of damage removal layers is 3, if the middle layer ply (2) is the layer with the smallest damage removal diameter or area, then the size or area of ​​the inner layer ply (3) must be larger than the size and area of ​​ply (2). There is no restriction relationship between the size and area of ​​ply (3) and the surface ply (1), that is, it is necessary to satisfy that at least one patch size or area of ​​the inner layer is larger than at least one patch size or area on its upper side.

[0014] Furthermore, in step 1, when the number of damage removal layers is n (n>3) in the order from the outside to the inside, it is also necessary to ensure that at least one patch size or area in the inner layer is smaller than at least one patch size or area on its upper side. For example, if the damage removal layer ply (n-1) is the layer with the smallest damage removal diameter or area, then the size or area of ​​the damage removal layer ply (n) must be larger than the size or area of ​​the damage removal layer ply (n-1) to form an "I-shaped" patch layout.

[0015] Furthermore, in step 2, the patch is defined from the inside out as repair layer (1), repair layer (2), ..., repair layer (n), which respectively repair the damage removal layer ply (n), damage removal layer ply (n-1), ..., damage removal layer ply (1), where (n>3).

[0016] Furthermore, in step 2, the process separation surface is used to guide the patch cutting method, which facilitates the subsequent patch repair and stacking process. The cutting method is designed based on the simulation results and is designed for the load mode, and must meet the requirements of load or bearing capacity.

[0017] Furthermore, in step 3, the pre-compaction temperature is determined by the viscosity-temperature curve of the patch resin matrix. A pressure of not less than 2 MPa is applied to the splicing area between the cut patch parts to ensure that the patch splicing area reaches the theoretical minimum single-layer curing thickness, thereby reducing the impact of the splicing process between the cut patch parts on the surface accuracy of the composite material parts after damage repair.

[0018] Furthermore, in step 3, the width of the splicing area is ≤1mm, and the outline of the patch is consistent with the outline of the corresponding damage removal layer.

[0019] The beneficial effects of this invention are:

[0020] This invention proposes a method for repairing composite material structures using an I-shaped patch layout design. Based on the mortise and tenon joint design concept in Chinese culture, it provides a stronger mechanical interlocking effect between the patch and the structural body. Furthermore, by performing specific patch cutting processes, the accessibility of the entire patch stacking process is ensured. This method can improve the mechanical properties of composite material structures after damage repair and is applicable to the repair process of laminated structures such as composite skins and sandwich composite panels.

[0021] I. Compared with traditional repair methods, this invention can improve the mechanical properties of the structure after damage repair;

[0022] Second, when the interior of a laminated plate structure is damaged, this invention can reduce the area to be removed and weaken the impact of the removal on the main structure compared to traditional repair methods.

[0023] Third, when the surface of a laminate structure is damaged, the improved mechanical properties of this invention can avoid the need for traditional reinforcement layers, minimizing the structural weight increase and impact on the structural profile after repairing the damaged parts.

[0024] Fourth, when the composite material panel of the sandwich structure is damaged, under the condition of the same damage removal area, the present invention can increase the bonding area between the patch and the core material and improve the peeling performance of the sandwich structure after damage repair.

[0025] Fifth, this invention can reduce material costs by replacing patch materials while maintaining the same mechanical property recovery rate, thus having an advantage in cost control. Attached Figure Description

[0026] Figure 1 This invention provides a top view and a corresponding side view of the damage removal contour of a composite material structure similar to an I-shaped patch, taking a 3-layer structure as an example, as provided by the present invention.

[0027] Figure 2 This invention provides a top view and a corresponding side view of the damage removal contour of a composite material structure similar to an I-shaped patch, taking a 3-layer structure as an example, as provided by the present invention.

[0028] Figure 3 The top view and corresponding side view are the outline of the patch repair layer (1) provided by the present invention after splicing the three parts.

[0029] The reference numerals in the accompanying drawings include:

[0030] 1-Carbon fiber fabric composite laminate structure; 2-Damage removal layer layup (1); 3-Damage removal layer layup (2); 4-Damage removal layer layup (3); 5-Patch repair layer (1); 6-Patch repair layer (2); 7-Patch repair layer (3); 8-Damage removal layer layup (3) 0° centerline; 9-Cutting line; 10-Patch repair layer (1) splicing area of ​​each cut part. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0032] like Figures 1 to 3 As shown, a method for repairing a composite material structure using an I-beam-like patch design includes the following steps:

[0033] Step 1: The damaged area of ​​the carbon fiber fabric composite laminate structure 1 is 58mm × 86mm. The number of layers to be removed is determined to be 3. The damaged area is then processed into an I-shaped structure as shown in the side view. Figure 1 As shown, the shape of the damage removal layer (2) 3 is a circle with a diameter of 100 mm, and the shapes of the damage removal layer (1) 2 and the damage removal layer (3) 4 are circles with a diameter of 126 mm; in this embodiment, the carbon fiber fabric composite laminate is selected as SYT45 / 3180, and the curing temperature is 180℃.

[0034] Step 2: The patch materials are labeled from the inside out as patch repair layer (1) 5, patch repair layer (2) 6, and patch repair layer (3) 7, respectively. Patch repair layer (2) 6 has the same outline as the damage removal layer layup (2) 3, and patch repair layer (3) 7 has the same outline as the damage removal layer layup (1) 2. Figure 2 As shown. The patch used in the damage removal layer layup (3) 4 is cut into 3 parts. The center line 8 of the damage removal layer layup (3) is offset 15mm upwards and downwards to the two sides to form the cutting line 9. The part after splicing the 3 parts of the cut patch is the patch repair layer (1). The splicing area 10 of each cut part of the patch repair layer (1) is as shown. Figure 3 As shown; in this embodiment, the patch material is selected as SYT45 / DS1209.5, the curing temperature is 150℃, and the cutting method is determined by analyzing the stress mode under bending or tensile loads during the service of the structure using ABAQUS to meet the load-bearing requirements.

[0035] Step 3: At a pre-compaction temperature of 85-90℃, apply a pressure of 2MPa to the splicing area of ​​each cut part of the patch repair layer (1) 5. The overlap width of the splicing area is 0.5mm. After the pressure is applied, suck out the excess adhesive generated during the pre-compaction process of each cut part of the patch repair layer (1) 5 to ensure that the thickness of each cut part of the patch repair layer (1) 5 reaches 0.188mm±0.01mm, thereby completing the overall splicing of the patch repair layer (1) 5.

[0036] Step 4: After layering the patch repair layer (2)6 and the patch repair layer (3)7 in sequence, seal and cure to complete the repair process.

[0037] The manufacturing process of the comparison part, that is, the preparation process of composite material repair specimens with traditional stepped patch design:

[0038] Step 1: A comparative test was conducted using a damaged area of ​​the same size, 58mm × 86mm. The damaged area of ​​the composite laminate structure was processed into a stepped shape in the side view, i.e., from the surface to the inside. The damage removal layers of the specimens in the comparative test were circular with diameters of 152mm, 126mm and 100mm for specimen lay-up (1), specimen lay-up (2) and specimen lay-up (3), respectively. In this embodiment, the composite laminate was also selected as SYT45 / 3180, with a curing temperature of 180℃.

[0039] Step 2: Using the same patch material, the patch repair layer (1), patch repair layer (2) and patch repair layer (3) of the sample are laid on the sample layup (3), sample layup (2) and sample layup (1) respectively from the inside to the outside, and then sealed and cured to complete the repair process; In this embodiment, the patch material is SYT45 / DS1209.5 and the curing temperature is 150℃.

[0040] Comparing the mechanical properties of the specimens, the maximum static load in the bending test of the structure after repair using the traditional stepped patch design was 306.8 N, while the maximum static load in the bending test of the structure after repair using the I-shaped patch design was 382.2 N, representing a performance improvement of 24.6%.

[0041] Comparing the damage removal areas between samples, the damage removal area of ​​the traditional stepped patch design is 8843.34 mm. 3 The damage removal area using the I-shaped patch design is 7538.32 mm. 3 The rate of reduction in the impact of damage removal on the main structure was 14.8%.

Claims

1. A method of repairing a composite structure employing a design of a hat- shaped patch, characterized in that, It comprises the following steps: Step 1: After determining the number of damage removal layers, the damage area is processed into a "I-shaped" structure; According to the order from the surface to the inside, when the number of damage removal layers is n and n>3, the size or area of at least one patch in the inner layer is also required to be larger than that of at least one patch in the upper layer, such as the n-1 damage removal layer is the layer with the smallest damage removal diameter or area, then the size or area of the n damage removal layer is required to be larger than that of the n-1 damage removal layer to form a "I-shaped" patch layout; Step 2: Based on the smallest patch repair layer with the smallest diameter or area, the patches with a larger diameter or area than the smallest patch repair layer are cut into N parts according to the process separation surface, and N≥2; Step 3: The splicing area between the cut patches in step 2 is pressed at a pre-compaction temperature, and the overall splicing process of the patches is completed; Step 4: After sequentially stacking the upper patches, encapsulating and curing, the repair process is completed.

2. The method of claim 1, wherein the repair patch is designed in a shape of a I-beam. In step 1, according to the order from the surface to the inside, when the number of damage removal layers is 2, such as the surface layer is the layer with the smallest damage removal diameter or area, then the size or area of the inner layer is larger than that of the surface layer, that is, at least one patch in the inner layer is required to be larger than at least one patch in the upper layer.

3. The method of claim 1, wherein the composite structure repair using the I-beam like patch design is characterized by, In step 1, according to the order from the surface to the inside, when the number of damage removal layers is 3, such as the middle layer is the layer with the smallest damage removal diameter or area, then the size or area of the inner layer is larger than that of the middle layer, and the size and area between the inner layer and the surface layer have no restricted relationship, that is, at least one patch in the inner layer is required to be larger than at least one patch in the upper layer.

4. The method of claim 1, wherein the composite structure repair using the I-beam like patch design is characterized by, In step 2, the patches are set from the inside to the surface as the 1st repair layer, the 2nd repair layer,..., and the nth repair layer, which respectively repair the corresponding n damage removal layer, n-1 damage removal layer,..., and 1 damage removal layer, where n>3.

5. The method of claim 1, wherein the composite structure repair using a quasi-I- beam patch design is characterized by, In step 2, the process separation surface is used to guide the patch cutting method, which is convenient for subsequent patch repair stacking process. The cutting method is designed based on the simulation results according to the load mode, which needs to meet the premise of load or bearing.

6. The method of claim 1, wherein the composite structure repair using a quasi-I- beam patch design is characterized by, In step 3, the pre-compaction temperature is determined by the viscosity-temperature curve of the patch resin matrix. A pressure not less than 2MPa is applied to the splicing area between the cut patches to ensure that the splicing area of the patch reaches the minimum value of the theoretical single-layer curing thickness, and to reduce the influence of the splicing process between the cut patches on the precision of the composite part surface after damage repair.

7. The method of claim 1, wherein the composite structure repair using a quasi-I- beam patch design is characterized by, In step 3, the width of the splicing area is ≤1mm, and the contour of the patch is consistent with the contour of the corresponding damage removal layer.

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