Dynamic repairing method for deformation hole of composite material

Abstract

The invention discloses a dynamic repair method for a deformation hole of a composite material, which adopts an electromagnetic pull gun pull-in operation, effectively prevents impact damage on the surface of the composite material, avoids reverse rod clamping, and is simple and convenient to operate and convenient to disassemble a test piece. The core rod is designed to be of a multi-section structure, the repairing precision and quality are ensured, the positioning device is composed of a baffle, a slotted gasket and a guide shaft, and accurate positioning is ensured. According to the method, a control system of process parameters is perfected, the influence of the installation rate is fully considered, the minimum installation voltage is determined by calculating the installation resistance, then the appropriate voltage is selected accordingly, meanwhile, the average installation rate of the core rod is calculated according to the installation voltage, and the electromagnetic pull gun is set according to the related process parameters to complete repairing. The method is suitable for repairing the composite material deformation holes of various sizes, and it is ensured that the fatigue performance of the repaired connecting piece reaches the standard.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aircraft maintenance, in particular to a dynamic repair method for a composite material deformed hole. BACKGROUND

[0002] During the overhaul of the aircraft reaching the service life, problems such as hole deformation, hole eccentricity, hole edge crack, etc. may be encountered, and such potential problems also have a greater impact on the load capacity and fatigue life of the connecting structure. Therefore, how to avoid product scrapping or realize connection repair in production and overhaul to ensure high-quality connection of composite material structures is one of the key technical problems for promoting the application amount and level of new aircraft composite material structures in China.

[0003] To deal with the problems such as hole deformation in maintenance, generally, one level of fastener is increased and special parts are made for repair. These methods need to re-customize fasteners, the process flow is complex, and the hole diameter increase will reduce the load capacity of the connecting piece, which is not suitable for hole repair in main load-bearing parts, and has great limitations.

[0004] In the cold extrusion strengthening process of the metal plate bushing, the current strengthening method is still in the quasi-static loading method. However, the quasi-static loading method is prone to problems such as rod jamming and rod breaking due to the large extrusion resistance. However, the literature "The Effect of Mandrel Speed upon the Residual Stress Distribution around Cold Expanded Hole" confirms through finite element simulation that different mandrel speeds have different strengthening effects on the test piece.

[0005] Patent No. 202310958660.X discloses a composite material structure bushing strengthening method based on electromagnetic loading. This method uses electromagnetic loading technology to complete the bushing strengthening of the composite material structure, and determines the discharge voltage through the dynamic extrusion friction total resistance. However, the pressing-in method used in this method is prone to impact damage to the surface of the composite material. In addition, the electromagnetic generator will rebound together with the mandrel after hitting the test piece, which is prone to the problem of reverse rod jamming. After the strengthening is completed, the mandrel must be removed from the electromagnetic generator before the composite material structure part can be removed, and the operation process is complicated, which makes it difficult to apply in practice. At the same time, this method does not fully consider the influence of the installation speed, and cannot directly determine the average installation speed through the installation voltage, resulting in imperfect process parameter control. SUMMARY

[0006] In view of the technical problems in the above background art, the present application provides a dynamic repair method for a composite material deformed hole, which solves the problem of composite material assembly hole in aircraft maintenance.

[0007] The application is implemented by adopting the following technical solutions: The working device of the dynamic repairing method is an electromagnetic puller. When the voltage of the capacitor C in the driving circuit reaches the set value, the thyristor SCR is turned on. Subsequently, the capacitor C releases a pulse strong current to the main coil, a magnetic field is formed around the main coil, and an eddy current is induced in the secondary coil to generate a new magnetic field. The two magnetic fields interact to generate a high-amplitude and low-pulse-width Lorentz force, so that the electromagnetic puller pulls the mandrel out of the bushing, and the dynamic repairing process of the composite hole is completed.

[0008] The mandrel is composed of a guide section, a transition section, a working section, a rear cone section and a threaded connection section. The diameter of the working section is determined by the extrusion amount required by the installation of the bushing. The guide section plays a guiding role in the initial stage of the movement of the mandrel, ensures the movement of the mandrel along the symmetry axis of the bushing in the subsequent process, and ensures the quality of the extruded part. The rear cone section plays a stabilizing and buffering role in the rebound of the bushing extruded by the working section.

[0009] The positioning device is composed of a baffle, a slotted washer and a guide shaft. The baffle is provided with a threaded hole and a large hole with a size tolerance of +0.02mm, and the coaxiality of the two is 0.02mm. The slotted washer is used for limiting the bushing, and the size tolerance of the inner diameter is +0.01mm, which ensures that the inner diameter edge is located at the middle position of the bushing, and can effectively limit the bushing. The guide shaft is used for positioning the test piece and is composed of four sections. The diameters of the first two sections are the same as the inner diameter of the slotted washer and the bushing respectively, and the size tolerances are both-0.01mm. The coaxiality requirement is 0.02mm, which ensures the positioning accuracy.

[0010] Specifically, the process of the dynamic repairing method of the deformed composite hole is as follows: Step 1, drill the deformed composite hole to ensure that the hole is circular and the hole wall quality is qualified; Step 2, reaming the composite laminate to make it reach the specified size; Step 3, place the bushing into the hole of the composite laminate; Step 4, fix the composite laminate with the bushing on the positioning device. Specifically, first place the slotted washer in the baffle, then rotate the guide shaft into the threaded hole of the baffle, then cooperate the test piece with the guide shaft, and finally fix the test piece, then rotate the guide shaft out of the baffle, and complete the precise positioning of the test piece and the slotted washer.

[0011] Step 5, pass the threaded section of the mandrel through the bushing, and then rotate it into the adapter of the electromagnetic puller; Step 6, calculate the minimum installation voltage of the dynamic repairing of the composite hole according to the installation resistance, and then determine the appropriate installation voltage combined with the actual situation.

[0012] Step 7, calculate the average installation rate of the mandrel according to the installation voltage.

[0013] Step 8, according to the process parameters calculated in step 6 and step 7, set the installation voltage of the electromagnetic puller and charge, after charging, press the discharge switch, complete the dynamic repair of the composite deformation hole, and record the average installation rate.

[0014] As a further illustration of the present application, the installation resistance is specifically as follows:

[0015] Friction force Related to the thickness of the CFRP laminate And the mandrel speed :

[0016] In the formula, The inner diameter of the bushing, The friction factor between the contact surface of the bushing and the mandrel, The radial stress on the bushing. Constant , , And The values of the material properties and load size.

[0017] Shear resistance Also related to the thickness of the CFRP laminate :

[0018] In the formula, The diameter of the position where the bushing shears, The shear stress on the shear surface.

[0019] According to the above formula, the installation resistance is calculated as:

[0020] As a further illustration of the present application, when the electromagnetic force generated by the electromagnetic loading device is equal to the installation resistance considering energy dissipation, the minimum installation voltage can be calculated by combining the electromagnetic force formula and the installation resistance formula:

[0021] Among them, K RLC is the system constant of the oscillation circuit, which can be fitted by multiple electromagnetic loading tests; The energy conversion rate.

[0022] As a further illustration of the present application, according to the propagation of stress waves in solids, the maximum equivalent installation rate Is expressed as:

[0023] wherein, is the propagation speed of stress wave in the mandrel, is the density of the mandrel material, S is the cross-sectional area of the mandrel. The mandrel speed after installation is:

[0024] wherein, m is the mass of the mandrel. The installation time t can be expressed as:

[0025] The average installation speed v is calculated as:

[0026] The present application has the following advantages compared with the prior art: the present application uses an electromagnetic pull gun to perform a dynamic repair process for a composite material deformation hole, compared with a press-in type bushing reinforcement method, can effectively prevent the surface of the composite material from being damaged by impact, and avoid the problem of reverse rod clamping caused by mandrel rebound. The operation process of the present method is simple and has good practical applicability. In addition, by fully considering the influence of the installation speed, the number of tests required to determine the process parameters is reduced, the average installation speed can be directly determined according to the installation voltage, and the control system of the process parameters is improved. The present method is suitable for repairing composite material deformation holes of various sizes, and ensures that the fatigue performance of the repaired connecting piece meets the standard.

[0027] The present application will be described in detail below in combination with the drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a dynamic repair method working device and driving circuit for a composite material deformation hole provided by the present application; Figure 2 is a mandrel structure design drawing provided by the present application; Figure 3 is a positioning device structure design drawing provided by the present application; Figure 4 is a size drawing of the baffle provided by the present application; Figure 5 is a size drawing of the slotted washer provided by the present application; Figure 6 is a size drawing of the guide shaft provided by the present application; Figure 7 is a flowchart for implementing a dynamic repair method for a composite material deformation hole provided by the present application; Figure 8 is a comparison chart of the minimum installation voltage calculated by the present application and the value obtained by experiment; Figure 9 is a comparison chart of the average installation rate obtained by the present application at different installation voltages and the value obtained by experiment.

[0029] In the figure, 1 is a composite laminate, 2 is a mandrel, 3 is a bushing, 4 is an electromagnetic puller, 5 is a slotted washer, 6 is a first baffle, and 7 is a guide shaft. DETAILED DESCRIPTION

[0030] The specific embodiments of the present application are described in detail below, but it should be understood that the scope of protection of the present application is not limited by the specific embodiments. Based on the examples in the present application, all other examples obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0031] The following examples refer to Figures 1-9 .

[0032] The reinforcement method provided in the present embodiment uses T700 carbon fiber, the layering sequence is [45 / 0 / -45 / 90 / 45 / 0 / -45 / 90 / -45 / 0] s , the single-layer thickness is 0.13 mm, the total thickness of the composite laminate is 2.6 mm, and the bushing is made of 321 stainless steel (0Cr18Ni10Ti); the composite hole is 6.02 mm, the inner diameter of the bushing is 4.82 mm, and the outer diameter is 6.02 mm. The bushing is a one-time seamless metal bushing, and the machining precision of the outer diameter and the inner diameter of the bushing is relatively high, the size tolerance is ±0.005 mm, and the surface roughness Ra of the inner wall and the outer wall is less than 0.8.

[0033] As shown in Figure 1 , during the dynamic installation of the bushing, 380V alternating current is converted into direct current by a rectifier bridge to charge the capacitor C. When the voltage of the capacitor C reaches the set value, the silicon controlled rectifier SCR is turned on. Subsequently, the capacitor C releases a pulse strong current to the main coil, which forms a magnetic field around the main coil and induces eddy current in the secondary coil, thereby generating a new magnetic field around the coil. The magnetic fields around the secondary coil and the main coil interact to generate a high-amplitude, low-pulse-width Lorentz force. Finally, the core rod with a diameter greater than the inner diameter of the bushing is driven through the bushing by the adapter of the electromagnetic puller, and the dynamic repair of the composite hole is completed.

[0034] The mandrel is composed of a guide section, a transition section, a working section, a rear cone section, and a threaded connection section. Among them, the diameter of the working section is The extrusion amount of the interference bushing is determined. The diameter of the guide section is 0.2 mm smaller than the inner diameter of the bushing, and the guide section plays a guiding role in the initial stage of the movement of the mandrel, ensures the movement of the mandrel along the symmetry axis of the bushing in the subsequent process, and ensures the quality of the extruded part. The rear cone section plays a stabilizing and buffering role in the springback of the bushing extruded through the working section. In order to ensure the accuracy of the extrusion amount, the size tolerance of the diameter of the working section is set to ±0.005 mm, and the surface roughness Ra of the transition section, the working section and the rear cone section of the mandrel needs to be controlled within the range of less than 0.8.

[0035] The positioning device is composed of a baffle, a slotted washer and a guide shaft, and the cooperation relationship is shown in Figure 3 The center of the baffle is provided with an M10 threaded hole with a length of 8 mm and a Φ28 large hole with a length of 7 mm and a size tolerance of +0.02 mm, and the coaxiality of the two is 0.02 mm. The slotted washer is used for limiting the position of the bushing, and the size tolerance of the inner diameter is +0.01 mm, which ensures that the inner diameter edge is located at the middle position of the bushing and can effectively limit the position of the bushing. In this embodiment, the inner diameter D2 of the slotted washer is 5.4 mm. The guide shaft is the key to positioning the test piece, which is composed of four sections. The diameters of the first two sections are the same as the inner diameter of the slotted washer and the bushing, and the size tolerances are both-0.01 mm. The lengths of the first two sections are 7 mm and 4 mm respectively, the threaded section is an M10 external thread with a length of 8 mm, and the coaxiality of the three sections is 0.02 mm, which ensures the positioning accuracy.

[0036] The complete process of the dynamic repair method of the composite material deformed hole provided by the present application is as follows: Step 1, drill the deformed composite material hole 1, and ensure that the drilled composite material hole is circular and the hole wall quality is qualified.

[0037] Step 2, reaming the composite material laminate 1 to the specified size.

[0038] Step 3, place the bushing 2 into the hole of the composite material laminate. The height of the bushing h is consistent with the thickness of the composite material laminate used.

[0039] Step 4, fix the composite material laminate with the bushing on the positioning device. The specific operation is as follows: first, place the slotted washer in the baffle, then rotate the guide shaft into the threaded hole of the baffle. Then, cooperate the test piece with the guide shaft to ensure the stability of the test piece. After fixing the test piece, rotate the guide shaft out of the baffle to complete the precise positioning of the test piece and the slotted washer.

[0040] Step 5, pass the threaded section of the mandrel through the bushing, and then rotate the threaded section into the adapter of the electromagnetic pull gun.

[0041] ​Step 6, calculate the minimum installation voltage required for the dynamic repair of the composite hole. On this basis, combined with the actual situation, determine the appropriate installation voltage to ensure the smooth progress of the installation process and reduce the cost of trial and error.

[0042] In the embodiment, the installation resistance is composed of two parts: one part is the friction force between the mandrel and the bushing , and the other part is the shear resistance caused by the extrusion amount for overcoming the elastic-plastic deformation of the bushing and the CFRP hole wall , which is opposite to the direction of the mandrel movement, as shown in Figure 3 . The calculation formula of the installation resistance is:

[0043] The friction force is related to the thickness of the CFRP laminate :

[0044] wherein, is the inner diameter of the bushing, is the friction factor between the contact surface of the bushing and the mandrel, and is the radial stress received by the bushing. According to the principle of tribology, sliding speed will cause surface layer heating, deformation and chemical changes, etc., thereby significantly affecting the friction coefficient. The size of is related to the speed of the mandrel:

[0045] wherein, the values of the constants , , and are determined by the material properties and the load size.

[0046] Therefore, the friction force is specifically:

[0047] During the installation of the bushing, the bushing material first undergoes elastic deformation under the action of shear force, and at this time the deformation is small. As the mandrel continues to move, the shear force gradually increases, and the material enters the plastic deformation stage, and the molecular chain begins to slip, resulting in permanent deformation. In this process, local areas of the metal will undergo plastic flow, and at this time the shear resistance can be represented as:

[0048] wherein, is the diameter of the position of the bushing where shear deformation occurs, Shear stress on the shear plane.

[0049] Therefore, the shear resistance Specifically,

[0050] According to the above formula, the installation resistance is calculated as:

[0051] The electromagnetic driving device in the embodiment generally controls the size of the electromagnetic force by adjusting the discharge voltage, and the calculation formula of the electromagnetic force is:

[0052] In the formula, is a function of time; K is a system constant of the RLC oscillation circuit, which can be fitted by multiple electromagnetic loading tests; ω is the angular frequency of the discharge current; is time When the electromagnetic force generated by the electromagnetic loading device is equal to the installation resistance, the installation voltage at this time can be calculated by combining the electromagnetic force formula and the installation resistance formula:

[0053] Since the electromagnetic energy is mainly converted into mechanical energy of the driving head and the mandrel and friction heat energy generated by overcoming resistance, the calculation formula of the equivalent discharge energy generated by a single time in the electromagnetic loading process is:

[0054] In the formula, is the energy conversion rate.

[0055] Therefore, the estimated value of the minimum installation voltage required by the dynamic hole repair method can be estimated as is:

[0056] Step 7, calculate the average installation rate of the mandrel according to the installation voltage.

[0057] When the average installation rate of the mandrel needs to be controlled according to the voltage in the embodiment, the following calculation needs to be performed.

[0058] According to the propagation of stress waves in solids, the maximum equivalent installation rate is expressed as:

[0059] In the formula, is the propagation speed of the stress wave in the mandrel, the density of the mandrel material, S the cross-sectional area of the mandrel. During the installation process, the speed of the mandrel will gradually decrease, and the energy dissipated in this process is mainly used to overcome the installation resistance, so the mandrel speed after the installation is completed is:

[0060] wherein, m the mass of the mandrel. Using the kinematic formula, the installation time t can be expressed as:

[0061] The average installation speed v is:

[0062] Step 8, according to the process parameters calculated in steps 6 and 7, set the installation voltage to charge the electromagnetic pull gun, press the discharge switch after the charging is completed, complete the dynamic repair process of the composite material deformation hole, and record the average installation speed.

[0063] Referring to Figure 8 , the minimum installation voltage calculated by the method provided in the embodiment is in good agreement with the test value, proving the accuracy of the calculation method.

[0064] Referring to Figure 9 , the average installation speed under different voltages calculated by the method provided in the embodiment is in good agreement with the test value, proving the accuracy of the calculation method.

[0065] Although embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for dynamic repair of deformable holes in composite materials, characterized in that, The method includes: Step 1: Drill holes in the deformed composite material to ensure that the hole circumference is circular and the hole wall quality is up to standard. Step 2: Ream the composite laminate to achieve the specified dimensions; Step 3: Place the bushing into the hole in the composite laminate; Step 4: Fix the composite laminate with bushings onto the positioning device; Step 5: Pass the threaded section of the mandrel through the bushing and then screw it into the adapter of the electromagnetic pull gun. Step 6: Calculate the minimum installation voltage for dynamic repair of composite material holes based on the installation resistance, and then determine the appropriate installation voltage based on the actual situation. Step 7: Calculate the average installation rate of the mandrel based on the installation voltage; Step 8: Based on the process parameters calculated in Steps 6 and 7, set the installation voltage of the electromagnetic gun and charge it. After charging is completed, press the discharge switch to complete the dynamic repair of the deformed holes in the composite material and record the average installation rate.

2. The method for dynamic repair of deformable holes in composite materials according to claim 1, characterized in that, The positioning device consists of a baffle, a slotted washer, and a guide shaft. The baffle has a threaded hole at its center and a large hole with a dimensional tolerance of +0.02mm, and the coaxiality of the two is 0.02mm. The slotted washer is used to limit the bushing, and its inner diameter has a dimensional tolerance of +0.01mm, ensuring that the edge of the inner diameter is located in the middle of the bushing, effectively limiting the bushing. The guide shaft is used to position the specimen and consists of four sections. The diameters of the first two sections are the same as the inner diameters of the slotted washer and the bushing, respectively, and the dimensional tolerances are both -0.01mm, with a coaxiality requirement of 0.02mm.

3. The method for dynamic repair of deformable holes in composite materials according to claim 2, characterized in that, Step 4 is as follows: First, place the slotted washer inside the baffle, then screw the guide shaft into the threaded hole of the baffle, then mate the specimen with the guide shaft, and finally fix the specimen and screw the guide shaft out of the baffle to complete the precise positioning of the specimen and the slotted washer.

4. The method for dynamic repair of deformable holes in composite materials according to claim 1, characterized in that, The mandrel consists of a guide section, a transition section, a working section, a rear conical section, and a threaded connection section. The diameter of the working section is determined by the amount of extrusion required for the installation of the bushing. The guide section plays a guiding role in the initial stage of the mandrel's movement, while the rear conical section plays a stabilizing and buffering role against the rebound of the bushing after being extruded by the working section.

5. The method for dynamic repair of deformable holes in composite materials according to claim 1, characterized in that, The method for calculating installation resistance is as follows: friction With CFRP laminate thickness and mandrel speed related: In the formula, The inner diameter of the bushing. It is the coefficient of friction between the contact surfaces of the bushing and the mandrel. The radial stress on the bushing is a constant. , , and The value is determined by the material properties and the magnitude of the load. Shear resistance Similarly, the thickness of the CFRP laminate is the same. related: In the formula, The diameter is the location where the bushing undergoes shear deformation. The shear stress on the shear plane; Based on the above formula, the installation resistance is calculated as follows: 。 6. The method for dynamic repair of deformable holes in composite materials according to claim 5, characterized in that, The minimum installation voltage is: in, K The system constant of the RLC oscillating circuit can be obtained by fitting through multiple electromagnetic loading tests; This refers to the energy conversion rate.

7. The method for dynamic repair of deformable holes in composite materials according to claim 6, characterized in that, The average installation rate of the mandrel is calculated based on the installation voltage, specifically as follows: Maximum equivalent installation rate Represented as: In the formula, The propagation speed of the stress wave in the mandrel. The density of the mandrel material, S For the cross-sectional area; Mandrel speed after installation for: In the formula, m For the mandrel mass, using kinematic formulas, the installation time... t Represented as: Calculated average installation rate v for: 。 8. A dynamic repair system for deformable holes in composite materials, characterized in that, The system is used to perform the repair method as described in any one of claims 1-7.

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