Method for measuring glue layer thickness and determining curing pressure in composite material glue joint repair
By using a three-layer sandwich prefabricated structure in composite material bonding repair, a pressure-thickness relationship model was measured and established, solving the problems of difficult measurement of adhesive layer thickness and inaccurate selection of curing pressure. This enabled direct measurement and scientific quantitative control of adhesive layer thickness, improving the stability of repair quality and simplifying the process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-21
- Publication Date
- 2026-05-15
AI Technical Summary
In the process of adhesive bonding repair of composite material patches, the thickness of the adhesive layer is difficult to measure directly and accurately, and there is a lack of simple and low-cost methods to establish a quantitative relationship between curing pressure and adhesive layer thickness, resulting in unstable repair quality.
A three-layer sandwich prefabricated structure of 'release membrane-adhesive-release membrane' was adopted. By preparing multiple adhesive layer test pieces under different curing pressures, the thickness was measured and a pressure-thickness relationship model was established to determine the optimal curing pressure.
It enables direct and accurate measurement and scientific quantitative control of adhesive layer thickness, improving the reliability and consistency of repair quality, simplifying the process, and reducing costs.
Smart Images
Figure CN122034384A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for determining the thickness of the adhesive layer and the curing pressure in composite material bonding repair, and belongs to the field of composite material bonding repair technology. Background Technology
[0002] In the adhesive bonding repair of composite material patches, adhesive layer thickness is one of the key factors affecting repair quality. An excessively thin adhesive layer can lead to insufficient bond strength, while an excessively thick layer can cause stress concentration and reduce the fatigue performance of the joint. Theoretically, there exists an optimal adhesive layer thickness range for different repaired structures, patch materials, and adhesive systems. However, in actual repair processes, the adhesive layer is encapsulated between the patch and the substrate, making it difficult to directly and non-destructively measure its true thickness after curing. Currently, indirect methods such as ultrasonic testing are commonly used for post-repair evaluation, but these methods are greatly affected by equipment precision, material acoustic properties, and structural geometry, resulting in uncertain measurement results and making them unsuitable for real-time optimization of process parameters. Furthermore, the final adhesive layer thickness is mainly determined by curing pressure, adhesive rheological properties, and interfacial gaps, but a simple and low-cost method to directly establish a quantitative relationship between "curing pressure and adhesive layer thickness" is currently lacking. This leads to process personnel relying heavily on experience to set pressures, resulting in a rudimentary control of adhesive layer thickness and difficulty in ensuring stable repair quality. Therefore, there is an urgent need to develop a method that can directly, accurately, and at low cost obtain the actual thickness of the cured adhesive layer and scientifically guide the selection of curing pressure. Summary of the Invention
[0003] To address the problems in the prior art, this invention provides a method for measuring the adhesive layer thickness and determining the curing pressure in composite material bonding repair.
[0004] The objective of this invention can be achieved through the following technical solutions: The method for measuring adhesive layer thickness and determining curing pressure in composite material bonding repair includes the following steps: Step 1: Identify the area to be repaired on the part to be repaired, and determine the optimal adhesive layer thickness based on the area to be repaired; Step 2: Cut two layers of release film, and evenly apply the uncured adhesive to the first layer of release film. The coated area is the patch bonding area. Then cover it with the second layer of release film to form a three-layer sandwich prefabricated body of "release film-adhesive-release film". Step 3: Place the sandwich preform on the adhesive interface of the area to be repaired, then place the composite material patch on the sandwich preform, cure according to the adhesive curing temperature and the set pressure, and take out the adhesive layer test piece between the two release films after curing. Step 4: Based on Step 2 and Step 3, multiple adhesive layer specimens of different thicknesses are prepared under different curing pressures. The thickness of multiple adhesive layer specimens is measured to obtain multiple sets of corresponding data on curing pressure and adhesive layer specimen thickness. Based on multiple sets of corresponding data, a pressure-thickness relationship model is established. Step 5: Obtain the optimal curing pressure based on the optimal adhesive layer thickness and pressure-thickness relationship model.
[0005] Optionally, the part to be repaired in step one can be a simulated test piece or an actual repair piece; depending on the characteristics of the structure to be repaired, if the original structural state cannot be restored, an actual repair piece is used, otherwise a simulated test piece is used.
[0006] Optionally, when using actual repair parts for simulated repair, the area to be repaired should be covered and protected to prevent the adhesive from flowing and contaminating the repair area during the adhesive curing process; When a simulated test piece is used for simulated repair and is not reused, there is no need to cover the area to be repaired. However, if the simulated test piece needs to be reused, then the area to be repaired must be covered.
[0007] Optionally, the optimal adhesive layer thickness is obtained by finite element simulation analysis or theoretical analysis based on the structural form of the area to be repaired, service load conditions, and material system, and on parameters such as the shear / peel strength, durability, and process feasibility of the adhesive repair joint.
[0008] Optionally, in step two, the release liner is a polytetrafluoroethylene film, a polyimide film, or other film that does not adhere to the adhesive, and the cut release liner is larger than the size of the area to be repaired.
[0009] Optionally, after the second layer of the isolation film is applied in step two, large air bubbles inside need to be initially removed by gentle squeezing or rolling.
[0010] Optionally, in step four, the thickness of the adhesive layer test piece is measured at multiple points, and the arithmetic mean or weighted average of the thickness data measured at multiple points is calculated to obtain the thickness value of the adhesive layer test piece.
[0011] Optionally, the pressure-thickness relationship model is established by performing linear regression, polynomial fitting, or exponential fitting on multiple sets of corresponding data.
[0012] The beneficial effects of this invention are: 1. Direct and accurate measurement: The three-layer sandwich prefabricated body of "separator-adhesive-separator" can obtain cured adhesive layer samples consistent with the actual working conditions without damage, realizing direct and accurate measurement of thickness, avoiding the indirectness, complexity and error of non-destructive testing.
[0013] 2. Simple method and low cost: No expensive and complicated online monitoring or special non-destructive testing equipment is required. It can be implemented using only conventional curing tools, ordinary isolation membranes and measuring instruments.
[0014] 3. Strong process guidance and scientific quantification: It can systematically and quickly establish a quantitative relationship model of "curing pressure-adhesive layer thickness" under specific material and process systems. Based on this model, the optimal process parameters for achieving the target adhesive layer thickness can be accurately deduced, upgrading adhesive layer thickness control from "empirical judgment" to "scientific quantification", significantly improving the reliability and consistency of repair quality. Attached Figure Description
[0015] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.
[0016] Figure 1 This is a schematic diagram of the simulated curing process of the present invention.
[0017] Figure 2 This is a schematic diagram illustrating the isolation treatment of the area to be repaired according to the present invention.
[0018] Figure 3 This is a schematic diagram of the three-layer sandwich preform of "isolation membrane-adhesive-isolation membrane" prepared according to the present invention.
[0019] Figure 4 This is a schematic diagram of the composite material patch of the present invention placed on top of a three-layer sandwich preform.
[0020] Figure 5 This is a schematic diagram of the adhesive layer specimen structure of the present invention.
[0021] In the diagram: 1. Composite material patch, 2. Release membrane, 3. Adhesive, 4. Protective isolation zone, 5. Part to be repaired. Detailed Implementation
[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0023] Please see Figure 1-5 As shown, the method for measuring adhesive layer thickness and determining curing pressure in composite material bonding repair is as follows: Step 1: Identify the part to be repaired (5). Based on the structural characteristics, determine whether to perform simulated curing on the actual part or to prepare a simulated test piece that can restore the original structural state for simulated curing. If the original structural state cannot be restored well, simulated repair must be performed on the actual part. In this case, protective tape or other special materials should be used to isolate the repair area (i.e., the area to be repaired) to prevent the adhesive liquid from flowing and contaminating the area to be repaired during the curing process of the adhesive (3). The protective isolation area (4) should be slightly larger than the area to be repaired. If a simulated test piece is used for simulated repair and is not reused, no protective treatment is required, and multiple sets of pressure tests can be carried out simultaneously using multiple simulated test pieces.
[0024] Step 2: Determine the optimal adhesive layer thickness. Considering the structural form, service load conditions, and material system of the area to be repaired, use finite element simulation analysis or theoretical calculations to comprehensively consider factors such as shear / peel strength, durability, and process feasibility of the adhesive repair, and determine the optimal theoretical value or range D for the adhesive layer thickness. min and D max .
[0025] Step 3: Cut the release film 2. Cut two layers of release film 2 (such as polytetrafluoroethylene film, polyimide film or other film that does not adhere to adhesive 3). The size of release film 2 should be slightly larger than the size of the area to be repaired to facilitate peeling later.
[0026] Step 4: Prepare the adhesive preform. Apply uncured adhesive 3 evenly to the first release film, covering the patch bonding area. Then cover it with the second release film, and gently press or roll to initially remove large air bubbles, forming a stable three-layer sandwich preform of "release film 2 - adhesive 3 - release film 2".
[0027] Step 5: Simulate the curing process. Place the aforementioned sandwich prefabricated body on the adhesive interface of the area to be repaired, then place the composite material patch 1 on the sandwich prefabricated body. Curing is then performed according to the curing temperature of adhesive 3 and the set pressure. Depending on the actual pressure conditions of the repair area, pressure can be applied using vacuum bags, presses, airbags, magnets, or clamps. A repair diagram is shown below. Figure 1 As shown.
[0028] Step 6: Remove the adhesive layer. After curing, due to the presence of the release liner 2, the cured adhesive layer will not adhere to the composite material patch 1 and the part to be repaired 5. The core preform at the bonding interface can be directly removed, and the two release liners 2 can be peeled off to obtain a fully cured independent adhesive layer test piece.
[0029] Step 7: Thickness measurement point planning. On the removed adhesive layer test piece, plan multiple representative thickness measurement points (such as center point, four corner points, crack corresponding points, etc.) to ensure that the measurement results can reflect the uniformity of the thickness.
[0030] Step 8: Thickness measurement. Use measuring tools (such as vernier calipers, micrometers, spiral micrometers or laser thickness gauges) to accurately measure the thickness at each planned point on the adhesive layer test piece and record the thickness value d-{ij} at each point (i represents the i-th pressure test group, and j represents the j-th measurement point).
[0031] Step 9: Data calculation. Take the arithmetic mean of the thickness values of the measurement points of the same adhesive layer test piece, or calculate the weighted average based on the thickness distribution, as the representative adhesive layer thickness Di of this group of tests under pressure Pi.
[0032] Step 10: Establish a pressure-thickness relationship model. Change the curing pressure value (e.g., set it to P1, P2, P3, ..., Pn), repeat steps 3-8, and conduct n independent experiments to obtain a set of corresponding data pairs (P1, D1), (P2, D2), ..., (Pn, Dn). Using these data points, establish a quantitative relationship curve or empirical formula F between curing pressure p and adhesive layer thickness D through mathematical methods (linear regression, polynomial fitting, or exponential fitting, etc.): D = f(P).
[0033] Step 11: Determine the optimal curing pressure. Substitute the target value of the optimal adhesive layer thickness d-optimal (or the median value within the range) determined in Step 2 into the relational model F established in Step 10. Calculate the theoretical optimal curing pressure P-optimal required to achieve d-optimal. Considering process fluctuations, P-optimal can be used as a central value to determine a reasonable curing pressure control window [P-optimal-ΔP, P-optimal+ΔP], which can be used to guide actual adhesive bonding repairs. ΔP represents the fluctuation range of the curing pressure.
[0034] Step 12: Perform the actual adhesive bonding repair work according to the curing pressure determined in Step 11.
[0035] This method uses a "separation membrane sandwiched with adhesive" structure to simulate the real adhesive interface and then cures it, thereby enabling the non-destructive acquisition of complete adhesive layer test pieces.
[0036] Through simulation experiments, the thickness of the adhesive layer under different pressures was obtained. By data fitting, the system established a relationship between "curing pressure and adhesive layer thickness". This relationship was then used to deduce the optimal process pressure, enabling proactive and precise control of the adhesive layer thickness.
[0037] The invention will be further illustrated below using the example of repairing cracks in aluminum alloys with composite material bonding.
[0038] A fatigue crack with a length of 10 mm has developed in a certain structure. Five simulated test specimens capable of restoring the original structural state are prepared. Composite material patches and DP490 adhesive are used to bond and repair the simulated test specimens. The patch dimensions are 80×60×4 mm (length×width×thickness). Five sets of pressure tests are planned to determine the optimal curing pressure.
[0039] By establishing a finite element model and considering the crack damage and load-bearing characteristics at the location, the optimal thickness of the adhesive layer was determined to be 0.2 mm.
[0040] 3. Use protective tape to isolate the area to be repaired, such as... Figure 2 As shown.
[0041] 4. Cut 10 pieces of release film, each measuring 100×80mm, and divide them into 5 groups of 2 pieces each. Figure 3 As shown.
[0042] 5. Apply DP490 evenly to the first layer of the release liner, with the coating size being the patch size, i.e., 60×80mm. Then cover it with the second layer of the release liner, and use roller pressing to initially remove large air bubbles, preparing 5 three-layer sandwich prefabricated bodies of "release liner-adhesive-release liner". The prepared sandwich prefabricated bodies are as follows. Figure 4 As shown.
[0043] 6. Place the fabricated sandwich prefabricated body on the surface of the aluminum alloy area to be repaired, and then place the pre-cured composite material patch on the sandwich prefabricated body. Apply pressure using a pre-set special fixture at pressures of 0.03 MPa, 0.04 MPa, 0.05 MPa, 0.06 MPa, and 0.07 MPa. Place the repair structure in an oven for curing at 80℃ for 30 minutes.
[0044] 7. After curing, remove the adhesive layer and peel off the two release films 2 to obtain a fully cured, independent adhesive layer test piece. The adhesive layer test piece is shown below. Figure 5 As shown.
[0045] 8. Take the four corners and the middle point of the adhesive layer in the bonding area of the patch as measurement points, and use vernier calipers to measure and record the adhesive layer test piece.
[0046] 9. Calculate the average thickness of each adhesive layer test piece. The results of the 5 sets of tests are summarized in Table 1.
[0047] Table 1 Thickness of adhesive layer test pieces 10. By fitting the data in Table 1, the empirical formula for the relationship between the adhesive layer thickness D and the curing pressure is obtained as follows: , where A and K are constants related to adhesive 3. For the adhesive in this embodiment, A is 0.6175 and K is 23.6817.
[0048] 11. By fitting the function, the optimal curing pressure P required for a 0.2mm thick adhesive layer was determined to be 0.0476MPa. Considering process application and control, the final curing pressure was set to 0.045MPa.
[0049] 12. Perform adhesive bonding repairs on the actual structure according to the determined curing pressure.
[0050] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.
Claims
1. A method for measuring adhesive layer thickness and determining curing pressure in composite material bonding repair, characterized in that, Includes the following steps: Step 1: Identify the area to be repaired on the part to be repaired, and determine the optimal adhesive layer thickness based on the area to be repaired; Step 2: Cut two layers of release film, evenly apply the uncured adhesive to the first layer of release film, the area to be pasted is the patch area, and then cover it with the second layer of release film to form a three-layer sandwich prefabricated body of "release film-adhesive-release film"; Step 3: Place the sandwich preform on the adhesive interface of the area to be repaired, then place the composite material patch on the sandwich preform, cure according to the adhesive curing temperature and the set pressure, and take out the adhesive layer test piece between the two release films after curing. Step 4: Based on Step 2 and Step 3, multiple adhesive layer specimens of different thicknesses are prepared under different curing pressures. The thickness of multiple adhesive layer specimens is measured to obtain multiple sets of corresponding data on curing pressure and adhesive layer specimen thickness. Based on multiple sets of corresponding data, a pressure-thickness relationship model is established. Step 5: Obtain the optimal curing pressure based on the optimal adhesive layer thickness and pressure-thickness relationship model.
2. The method for measuring adhesive layer thickness and determining curing pressure in composite material bonding repair according to claim 1, characterized in that, The part to be repaired in step one can be a simulated test piece or an actual repair piece; depending on the characteristics of the structure to be repaired, if the original structural state cannot be restored, an actual repair piece is used, otherwise a simulated test piece is used.
3. The method for measuring adhesive layer thickness and determining curing pressure in composite material bonding repair according to claim 2, characterized in that, When using actual repair parts for simulated repair, the area to be repaired must be covered and protected to prevent the adhesive from flowing and contaminating the repair area during the curing process. When a simulated test piece is used for simulated repair and is not reused, there is no need to cover the area to be repaired. However, if the simulated test piece needs to be reused, then the area to be repaired must be covered.
4. The method for measuring adhesive layer thickness and determining curing pressure in composite material bonding repair according to claim 3, characterized in that, The optimal adhesive layer thickness is obtained through finite element simulation analysis or theoretical calculation based on the structural form of the area to be repaired, service load conditions, and material system, taking into account parameters such as adhesive repair shear / peel strength, durability, and process feasibility.
5. The method for measuring adhesive layer thickness and determining curing pressure in composite material bonding repair according to claim 1, characterized in that, In step two, the separator is a polytetrafluoroethylene film or a polyimide film, and the cut size of the separator is larger than the size of the area to be repaired.
6. The method for measuring adhesive layer thickness and determining curing pressure in composite material bonding repair according to claim 5, characterized in that, After the second layer of the isolation film is applied in step two, the internal air bubbles need to be removed by squeezing or rolling.
7. The method for measuring adhesive layer thickness and determining curing pressure in composite material bonding repair according to claim 1, characterized in that, In step four, the thickness of the adhesive layer test piece is measured at multiple points, and the arithmetic mean or weighted average of the thickness data measured at multiple points is calculated to obtain the thickness value of the adhesive layer test piece.
8. The method for measuring adhesive layer thickness and determining curing pressure in composite material bonding repair according to claim 1, characterized in that, The pressure-thickness relationship model is established by performing linear regression, polynomial fitting, or exponential fitting on multiple sets of corresponding data.