A method for improving the fit of a composite bonded repair metal structure

Abstract

The present application relates to the technical field of aircraft body structure repair, in particular to a method for improving the adhesion of composite material bonding repair metal structure, comprising the following steps: determining the damage range by visual inspection and non-destructive testing method; then using artificial polishing method to pretreat the surface of the damaged part; preparing composite patch material, adhesive and related auxiliary materials; laying the patch according to the design requirements; packaging the vacuum bag, installing the heating unit and curing; post-processing the patch; checking the composite patch; according to the gap size and area size of different regions, cutting the appropriate size of glass fiber fabric; marking the installation position of the patch by using the red pencil line method; mixing the glue; cutting a layer of glass cloth, the size of which is larger than the total size of the required filling size, and the glass cloth is treated by dipping in glue. The present application can effectively control the thickness of the glue layer, increase the controllability of the repair process, improve the tensile shear strength after bonding, effectively improve the actual repair effect, and meet the actual use requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aircraft body structure repair, in particular to a method for improving the adhesion of composite material bonding repair metal structure. BACKGROUND

[0002] Composite material pre-cured patches are often used to strengthen damaged metal structures, and the connection methods mainly include mechanical connection, bonding connection and hybrid connection. Bonding connection is a connection method that has high efficiency and can uniformly transfer stress, making the reinforcing fibers play their maximum performance, and its application is increasingly widespread. Carbon fiber composite materials are often the first choice for composite material patches due to their light weight and high strength. However, due to the potential difference between carbon fiber and metal materials, improper handling can introduce electrochemical corrosion problems. Traditional composite material bonding repair metal structure patches are usually pre-formed according to the shape of the damaged structure model, using carbon fiber pre-impregnated material plus one layer of glass fiber pre-impregnated material, as shown in Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 However, due to differences between the actual structure and the model during the manufacturing process, the bonding interface thickness is uneven, as shown in Figure 5 、 Figure 6 Even when the gap is large, traditional methods use chopped fiber mixed glue to fill, but the glue layer has poor load transmission capacity. The above problems all lead to unreliable bonding repair quality. At the same time, due to the existence of gaps, the bonded structure has weak repair areas, which can accelerate the failure of the patch during structure use, posing a challenge to the long-term safety of the aircraft in service.

[0003] For example: "Chinese patent CN202010732218.1 A wet bonding repair method for solving the crack of complex metal surface structure of an aircraft (publication date 20201201)" discloses a method for repairing complex surface metal structure crack damage using composite fabric impregnated with structural glue. The advantages of this method are that it is suitable for special material systems and complex structure forms, and traditional mechanical connection cannot meet the normal pin requirements, making it difficult to restore the strength of the metal structure. The use of composite material wet bonding repair can well fit the structure shape and make up for the defect of insufficient repair strength. The disadvantage of this method is that the patch strength performance is poorer than that of the pre-cured patch, and defects such as pores are easy to occur during the repair process, making it difficult to guarantee the repair reliability. SUMMARY

[0004] In the traditional process of bonding repair of metal with composite material, glass fiber and carbon fiber are integrally preformed, and then bonded to the repair area by structural adhesive. The integrally formed patch is formed according to the numerical model of the structure theory. Due to the difference between the actual damaged structure and the numerical model caused by machining, the fit of the actual structure and the patch is difficult to guarantee. According to the requirements of bonding repair, the thickness of the adhesive layer needs to be controlled at 0.1-0.2mm and other technical problems. The present application provides a method for improving the fit of the bonding repair of metal structure with composite material. By preforming the carbon fiber composite patch, the actual repair area structure characteristics are checked and installed, the gap size at different regions is determined by means of a plug gauge and other tools, the required number of glass fiber layers is calculated, and the glass fiber is impregnated with structural adhesive to differentially fill and attach at different parts of the repair area. This method can fill and attach the gap in different regions, solve the problem of incompatibility between the numerical model and the actual manufactured patch, and add continuous fiber structure to the glass fiber cloth to compensate for the discontinuity of the short-cut fiber and the poor load transfer ability when filling, significantly improve the bonding strength, and easily control the thickness of the adhesive layer.

[0005] The technical problems to be solved by the present application are solved by the following technical solutions:

[0006] A method for improving the fit of the bonding repair of metal structure with composite material, comprising the following steps:

[0007] Step (1) determine the damage range by visual inspection and non-destructive testing method, and mark the repair area with a marker pen;

[0008] Step (2) then use manual polishing method to pretreat the surface of the damaged part;

[0009] Step (3) prepare composite patch materials, adhesives and related auxiliary materials;

[0010] Step (4) lay the patch according to the design requirements, and compact it layer by layer. Every 2-3 layers of prepreg patch are laid and pressed, and the temperature is controlled at not higher than 60 DEG C by using an electric iron to extrude the layer or a vacuum extraction method to remove the bubbles between the layers;

[0011] Step (5) package the vacuum bag, install the heating unit and cure;

[0012] Step (6) patch post-processing: remove the edge forming burrs of the patch;

[0013] Step (7) check and install the composite patch: fit the composite patch with the repaired area, and judge the gap size and area size of different regions of the fitting surface by using a plug gauge and lime powder;

[0014] Step (8) according to the size of the gap between different regions and the area of the region, cut the appropriate size of the glass fiber fabric, while preparing a small amount of chopped fiber for filling the gap, repeat step (7) until the fit;

[0015] Step (9) mark the installation position of the patch with red lines;

[0016] Step (10) glue preparation: according to the adhesive selected in step (3), weigh the corresponding components and mix them thoroughly;

[0017] Step (11) cut a layer of glass cloth, which should be larger than the total size of the required filling, and then immerse the glass cloth in glue;

[0018] Step (12) cut the glass fiber cloth after immersion into the required shape for filling;

[0019] Step (13) structural bonding: first, evenly apply the prepared glue to the metal area to be repaired, then separately paste the glass fiber prepreg, and finally cover the composite repair patch, while scraping off the excess glue around the edges;

[0020] Step (14) pre-fixing: due to the flowability of the glue during the repair process, the repaired part needs to be pre-fixed using the experimental clamping device;

[0021] Step (15) heating and curing: according to the adhesive selected in step (3), determine the curing temperature and time, and use the heat repair instrument to control the temperature and use the electric heating blanket for auxiliary heating;

[0022] Step (16) remove the heating system and use ultrasonic A-scan to detect the quality of the bonded repair to ensure that there are no gaps, delamination, and internal defects.

[0023] Preferably, the patch material in step (3) is CCF300 / QY8911 prepreg material.

[0024] Preferably, the adhesive in step (3) is J-352 structural adhesive.

[0025] Preferably, the heating unit in step (5) is a heat press tank, and the maximum curing temperature is 220°C.

[0026] Preferably, the glass fiber fabric in step (8) is CF3031 carbon fiber woven fabric.

[0027] Preferably, the adhesive in step (10) is mixed in a ratio of 10:3 according to the two components.

[0028] Preferably, if multiple layers of glass fiber cloth are needed to be bonded in step (12), the subsequent added glass fiber cloth should be as consistent as possible with the direction of the previously laid fiber.

[0029] Preferably, the curing temperature of the adhesive in step (15) is 60°C and the heat preservation time is 3h.

[0030] The beneficial effects of this invention are:

[0031] Compared with traditional repair methods, it has the following advantages: First, the addition of an extra layer of structural adhesive to impregnate the fiberglass fabric can effectively control the thickness of the adhesive layer and increase the controllability of the repair process; Second, by filling the gaps at the bonding interface through differential filling of the fiberglass fabric with structural adhesive, the patch can fit better with the machine body structure, improve the tensile and shear strength after bonding, effectively improve the actual repair effect, and meet the actual use requirements. Attached Figure Description

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0033] Figure 1 Schematic diagram of bonding of prefabricated integral composite fiberglass parts;

[0034] Figure 2 A schematic diagram showing the independent addition of fiberglass bonding;

[0035] Figure 3 This is a schematic diagram of an ideal adhesive bonding state;

[0036] Figure 4 for Figure 3 Enlarged diagram of point a in the diagram;

[0037] Figure 5 This is a schematic diagram of an actual adhesive bonding defect;

[0038] Figure 6 for Figure 5 Enlarged diagram of point b in the diagram;

[0039] Figure 7 This is a schematic diagram of the improved adhesive bonding state;

[0040] Figure 8 for Figure 7 Enlarged diagram of point c in the diagram;

[0041] Figure 9 This is a load-displacement curve;

[0042] Figure 10 The maximum load curve of the sample;

[0043] Figure 11 The graph shows the maximum tensile shear strength of the sample. Detailed Implementation

[0044] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0045] As Figure 1 shown,

[0046] A method for improving the adhesion of composite material bonding repair metal structure, comprising the following steps:

[0047] Step (1) Determine the damage range by visual inspection and non-destructive testing methods, and mark the repair area with a marker pen.

[0048] Step (2) Then use manual polishing method to pretreat the surface of the damaged part to enhance the bonding strength.

[0049] Step (3) Prepare composite patch material, adhesive and related auxiliary materials. In this embodiment, the patch material is selected as CCF300 / QY8911 prepreg material; the adhesive is selected as J-352 structural adhesive.

[0050] Step (4) Lay the patch according to the design requirements, and compact it layer by layer. Every 2-3 layers of prepreg patch are laid and pressed, and the temperature is controlled not to exceed 60℃ by using electric iron to squeeze the layer or vacuum method to remove the bubbles between the layers.

[0051] Step (5) Package the vacuum bag, install the heating unit and cure. In this embodiment, the heating unit is a hot press tank, and the maximum curing temperature is 220℃.

[0052] Step (6) Patch post-processing: remove the edge forming burrs of the patch.

[0053] Step (7) Check the composite patch: fit the composite patch with the repaired area, and judge the gap size and area size of different areas of the fitting surface by using plug gauges and lime powder.

[0054] Step (8) According to the gap size and area size of different areas, cut the appropriate size of glass fiber fabric, and prepare a small amount of chopped fiber for filling the gap. Repeat step (7) until the fitting is completed.

[0055] Step (9) Mark the installation position of the patch with red lines;

[0056] Step (10) Glue preparation: according to the adhesive selected in step (3), weigh the corresponding components and mix them evenly and thoroughly. In this embodiment, the J-352 structural adhesive is mixed according to the ratio of 10:3 of the two components.

[0057] Step (11) Cut a layer of glass cloth, which requires the size to be larger than the total size of the required filling size, and perform glass cloth impregnation treatment.

[0058] Step (12) cut the impregnated glass fiber cloth into the shape required for filling, noting that if a region requires patching with multiple layers of glass fiber cloth, the subsequently added glass fiber cloth should be as consistent as possible with the direction of the previously laid fiber.

[0059] Step (13) structural gluing: evenly apply the prepared glue to the metal region to be repaired, then separately paste the glass fiber prepreg, and finally cover the composite repair patch, while scraping off the excess glue around the periphery.

[0060] Step (14) pre-fixing: due to the flowability of the glue during the repair process, the repair part needs to be pre-fixed using the experimental clamping device.

[0061] Step (15) heating and curing: according to the selected adhesive in step (3), determine the curing temperature and time, and use the heat repair instrument to control the temperature and the electric heating blanket to assist in heating. In this embodiment, the curing temperature of J-352 structural adhesive is 60℃, and the holding time is 3h.

[0062] The success of the composite patch repair process for metal structural parts depends on the medium adhesive, which plays a crucial role. In order to obtain good gluing effect, a structural adhesive with high shear strength and peel strength, corrosion resistance, aging resistance and impact resistance should be selected, and the adhesive should generally match the curing temperature of the composite patch.

[0063] Step (16) remove the heating system, and use ultrasonic A-scan to detect the gluing repair quality to ensure that there are no gaps, delamination and internal defects.

[0064] The repaired gluing state is shown in Figure 7 、 Figure 8 .

[0065] In order to verify the gluing performance of the repaired part after the process in the present application, the following tests are performed.

[0066] The width size (25mm±0.25mm) of the test piece is measured using a vernier caliper, and each piece is measured three times to obtain the average value, with the unit being mm. The specific values are shown in Tables 1 and 2.

[0067] Table 1 Metal piece size

[0068]

[0069] Table 2 Composite piece size

[0070]

[0071]

[0072] The bonding length size (12.5 mm ± 0.25 mm) of the test piece was measured using a vernier caliper, three times for each piece, and the average value was taken, in mm, as shown in Table 3 below.

[0073] Table 3 Bonding length size

[0074]

[0075] The load-displacement curves of different samples were fitted into a graph, as shown in Figure 9 , in which #1-#9 (red curve) represents the relationship between displacement and load of the sample after bonding, which is manually added with glass fiber alone; #10-#18 (black curve) represents the relationship between displacement and load of the sample after bonding, which is integrally formed with glass fiber and carbon fiber.

[0076] Analysis of test results

[0077] The original experimental data were processed to sort out the maximum tensile shear load of different samples, as shown in Table 4 below and Figure 10 .

[0078] Table 4 Maximum tensile shear load of different samples

[0079]

[0080] The original experimental data were processed to sort out the maximum tensile shear strength of different samples, as shown in Table 5 below and Figure 11 .

[0081] Table 4 Maximum tensile shear strength of different samples

[0082]

[0083] According to the strength calculation formula in GB / T 7124-2008 Adhesive Tensile Shear Strength Test Standard:

[0084] t = P / (B x L)

[0085] In the formula: t - adhesive tensile shear strength, MPa;

[0086] P - maximum load of sample shear failure, N;

[0087] B - sample lap width, mm;

[0088] L - sample lap length, mm.

[0089] From the experimental data, the average tensile shear load of the test piece bonded by manually adding glass fiber cloth (#1-9) during repair is 8.58 kN, and the tensile shear strength is 26.83 MPa; the average tensile shear load of the sample bonded after the glass fiber and carbon fiber are integrally formed (#10-18) is 6.79 kN, and the tensile shear strength is 20.24 MPa. In comparison, the load bearing capacity of the way of adding glass fiber alone is increased by 26.36%, and the tensile shear strength is increased by 32.56%.

[0090] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above-mentioned embodiments, and the above-mentioned embodiments and descriptions in the specification are only the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for improving the bonding adhesion of composite materials in adhesive repair of metal structures, characterized in that: Includes the following steps: Step (1) Determine the extent of damage through visual inspection and non-destructive testing methods, and mark the repair area with a marker pen; Step (2) Next, the damaged area is pre-treated by manual polishing; Step (3) Prepare composite patch materials, adhesives and related auxiliary materials; Step (4) Lay out the patch according to the design requirements and compact it layer by layer. For every 2 to 3 layers of prepreg patch, use an electric iron to press the layers at a temperature not exceeding 60°C or vacuum the air to remove air bubbles between the layers. Step (5) Seal the vacuum bag, install the heating unit and cure; Step (6) Post-processing of the patch: Remove the burrs from the edges of the patch; Step (7) Inspection and installation of composite material patch: Fit the composite material patch to the area to be repaired, and use a plug gauge and lime powder to determine the gap size and area of ​​different areas of the mating surface; Step (8) Cut appropriate size glass fiber fabric according to the gap size and area of ​​different areas, and prepare a small amount of short fiber to fill the gap. Repeat step (7) until they are bonded. Step (9) Mark the installation position of the patch with a red pen; Step (10) Adhesive preparation: Weigh the corresponding components according to the adhesive selected in step (3) and mix them evenly and thoroughly; Step (11) Cut a layer of glass cloth, requiring the size to be larger than the total required filling size, and impregnate the glass cloth with resin; Step (12) Cut the impregnated fiberglass cloth into the required filling shape; Step (13) Structural bonding: First, apply the prepared adhesive evenly to the metal area to be repaired, then attach the glass fiber prepreg separately, and finally cover it with the composite material repair patch, while scraping off the excess adhesive around the perimeter. Step (14) Pre-fixation: Because the adhesive is fluid during the repair process, the repaired parts need to be pre-fixed using an experimental clamping device; Step (15) Heating and curing: Based on the adhesive selected in step (3), determine the curing temperature and time, and use a heat repair instrument to control the temperature and an electric heating blanket to assist in heating; Step (16) The heating system is removed, and ultrasonic A-scan is used to inspect the quality of the adhesive repair to ensure that there are no gaps or internal defects of delamination.

2. The method for improving the bonding adhesion of composite material adhesive repair of metal structures according to claim 1, characterized in that: In step (3), the patch material is CCF300 / QY8911 prepreg material.

3. The method for improving the bonding adhesion of composite material adhesive repair of metal structures according to claim 1, characterized in that: In step (3), the adhesive is J-352 structural adhesive.

4. The method for improving the bonding adhesion of composite material adhesive repair of metal structures according to claim 1, characterized in that: In step (5), the heating unit is an autoclave with a maximum curing temperature of 220°C.

5. The method for improving the bonding adhesion of composite material adhesive repair of metal structures according to claim 1, characterized in that: In step (8), the glass fiber fabric is CF3031 carbon fiber woven fabric.

6. The method for improving the bonding performance of composite material adhesive repair of metal structures according to claim 1, characterized in that: In step (12), if an area needs to be patched with multiple layers of fiberglass cloth, the fiberglass cloth added later should be kept in the same direction as the previously laid fiber.

7. The method for improving the bonding adhesion of composite material adhesive repair of metal structures according to claim 1, characterized in that: In step (15), the curing temperature of the adhesive is 60℃ and the heat preservation time is 3h.

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