Fatigue verification method for guide cylinder of automatic inclinator

Abstract

The invention belongs to the field of fatigue verification, and relates to a fatigue verification method for an automatic inclinator guide cylinder. The method comprises the steps that the fatigue strength of the guide cylinder is designed according to the service life requirement; after the guide cylinder is subjected to engineering trial-manufacturing, a strain gauge is pasted on a guide cylinder trial-manufactured piece, and two load measurement channels which are perpendicular to each other are obtained; carrying out load calibration on the guide cylinder according to measurement results of the two load measurement channels, and determining a load calibration coefficient; and completing the fatigue verification of the guide cylinder according to the guide cylinder fatigue test and the acquisition and spectrum compiling of the test flight load.

Description

Technical Field

[0001] The present invention belongs to the field of fatigue verification and relates to a fatigue verification method for an actuator cylinder. Background Art

[0002] As Figure 1 shown, the actuator is a key part of the helicopter or autogyro control system. The actuator slides up and down along the internal cylinder structure to achieve collective pitch control, and tilts around the large spherical hinge structure inside it to achieve cyclic pitch control. The combination of the two can achieve collective pitch and cyclic pitch control simultaneously. The helicopter or autogyro realizes flight control through the collective pitch, cyclic pitch of the actuator or a combination of both. Therefore, the actuator is a key component of the helicopter or autogyro.

[0003] The large spherical hinge in the actuator is installed on the cylinder. The large spherical hinge can slide up and down on the cylinder, but the lateral displacement of the large spherical hinge on the cylinder is restricted. Therefore, the large spherical hinge transmits a lateral concentrated force to the cylinder. This concentrated force is in the xy plane in the figure and is generally named the cylinder load. The outer surface of the large spherical hinge is a sphere. The acting point of the cylinder load passes through the center of the sphere of the large spherical hinge, but moves up and down with the position of the large spherical hinge on the cylinder. Since the large spherical hinge has a certain working stroke when moving on the cylinder, the acting point of the cylinder load is also within the range of the working stroke. The cylinder is fixed to the helicopter reducer or the airframe structure by a circle of bolts. Therefore, the cylinder load is also transmitted to the reducer or the airframe structure through the connection structure. The cylinder load transmitted by the large spherical hinge is a complex high-cycle fatigue load. Once fatigue failure occurs in the cylinder and its connection under the fatigue load, it will lead to helicopter control failure and even aircraft crash. Therefore, during the engineering design stage of the helicopter or autogyro, the actuator cylinder needs to undergo strict fatigue verification.

[0004] In the prior art, there is a lack of a complete fatigue verification method for the actuator cylinder. Summary of the Invention

[0005] Object of the Invention: The present invention provides a complete fatigue verification method for the actuator cylinder, covering fatigue strength design, strain gage pasting, load calibration, fatigue test, load measurement and life assessment of the cylinder.

[0006] Technical Solution:

[0007] Provide a fatigue verification method for an actuator cylinder, including:

[0008] Design the fatigue strength of the cylinder according to the life requirement;

[0009] After the engineering trial production of the cylinder, paste strain gages on the cylinder trial production part to obtain two mutually perpendicular load measurement channels;

[0010] Calibrate the load of the guide tube according to the measurement results of two load measurement channels to determine the load calibration coefficient;

[0011] Complete the fatigue verification of the guide tube based on the fatigue test of the guide tube, the acquisition and spectrum compilation of flight test loads.

[0012] Furthermore, design the fatigue strength of the guide tube according to the life requirements, including:

[0013] Under the condition that the load application position is at the upper limit of the large ball joint stroke, use engineering calculation methods or finite element methods to obtain the stresses of the guide tube and its connecting bolts under different load conditions, that is, the first relationship between load and stress;

[0014] According to the first relationship and the calculated load spectrum of the guide tube, analyze and obtain the stress spectrum of the guide tube and its connecting bolts, and calculate the fatigue strength of the guide tube in combination with the safety S-N curve and working time ratio of the materials of the guide tube and its connecting bolts;

[0015] Improve and iteratively update the structure of the guide tube based on the analysis results until the life requirements are met.

[0016] Furthermore, the o point of the guide tube coordinate system is the center point of the upper end face of the guide tube, the xy plane is the installation plane of the guide tube; the z axis is perpendicular to the installation plane and upward; the guide tube installation surface is the plane where the guide tube installation connecting bolts are located;

[0017] Paste strain gauges on the prototype of the guide tube to obtain two mutually perpendicular load measurement channels, including:

[0018] Stick two groups of strain gauges between the lower limit of the large ball joint stroke and the guide tube installation surface, ensure that the guide tube strain gauge section where the two groups of strain gauges are located is parallel to the guide tube installation surface, one group of strain gauges is symmetric about the y axis and installed on the x axis, and the other group of strain gauges is symmetric about the x axis and installed on the y axis;

[0019] Form two load measurement channels by forming a full bridge for the two groups of strain gauges.

[0020] Furthermore, calibrate the load of the guide tube according to the measurement results of two load measurement channels to determine the load calibration coefficient, including:

[0021] Fix the guide tube on the tooling fixture through the installation bolts according to the installation requirements, and use the load application device to apply the load to the large ball joint, so as to transfer it to the guide tube; at this time, the large ball joint can be at any position within the large ball joint stroke range; the direction of the applied load is applied along the x direction or the y direction;

[0022] Measure the distance from the center of the large ball joint to the plane where the strain gauges are located as the force arm;

[0023] The voltage output values in the x and y directions are obtained through two load measurement channels;

[0024] The actual bending moment is calculated based on the loads applied in the x and y directions and the moment arms;

[0025] Determine the bending moment-voltage relationship between the actual bending moment and the voltage output values in the x and y directions, and use the coefficients of the bending moment-voltage relationship as the load calibration coefficients of the guide cylinder.

[0026] Furthermore, based on the fatigue test of the guide cylinder, the acquisition and spectrum compilation of the flight test loads, the fatigue verification of the guide cylinder is completed, including:

[0027] Step 1: When the load is applied at the lower limit position of the large ball joint, the stresses of the guide cylinder and its connecting bolts under different load conditions are obtained according to the engineering calculation method or the finite element method, that is, the second relationship between the load and the stress;

[0028] Step 2: Calculate the fatigue test load F of the guide cylinder according to the calculated load spectrum of the guide cylinder and the average S-N curve of the materials of the guide cylinder and its connecting bolts, F = F S ±F d where F S is the static load of the fatigue test of the guide cylinder, covering at least 90% of the static loads in the calculated load spectrum of the guide cylinder, and F d is the dynamic load of the fatigue test of the guide cylinder, and its variation law is in the form of a sine or cosine curve;

[0029] Step 3: Calculate the stresses corresponding to the static and dynamic loads of the fatigue test through the second relationship;

[0030] Step 4: After the static stress correction of the static and dynamic stresses of the fatigue test, the equivalent dynamic stress of the fatigue test is obtained. If the number of cycles corresponding to the equivalent dynamic stress in the average S-N curve is much greater than m times the target number, the dynamic load of the fatigue test is increased according to the fatigue strength. If the number of cycles corresponding to the equivalent dynamic stress in the average S-N curve is less than n times the target number, the dynamic load of the fatigue test is decreased according to the fatigue strength until the number of cycles corresponding to the adjusted equivalent dynamic stress in the average S-N curve approaches the target number;

[0031] Step 5: Fix the guide cylinder on the tooling fixture through the installation bolts according to the installation requirements, use the load application device to apply the load to the large ball joint. At this time, the large ball joint is at the lower limit position of the large ball joint stroke. Only fatigue tests need to be carried out on the guide cylinder in one direction of x or y. Adjust the load frequency of the dynamic load of the guide cylinder fatigue test. When each load cycle reaches the preset number of times, upgrade the dynamic load of the guide cylinder fatigue test and continue the test until the guide cylinder structure fails;

[0032] Step 6: Use 1 to 6 identical guide tubes to conduct the fatigue test in Step 5. Finally, obtain the safe fatigue limit of the bending moment of the strain gauge profile of the guide tube by integrating all the fatigue test data of the guide tubes, the shape of the average S-N curve, and the reduction coefficient.

[0033] Further, the method further includes:

[0034] Install the guide tubes with completed strain gauges and calibration on the helicopter or autogyro for implementing the load measurement work;

[0035] During the flight test, collect the time-domain loads of the two load channels of the guide tube within a certain period of time under various weights, centers of gravity, altitudes, and flight states according to the requirements of the measured load measurement.

[0036] Prepare the measured load spectra of the two load measurement channels through load classification and rainflow counting, and draw the life curves of the two load measurement channels. The abscissa of the life curve is the life, and the ordinate is the safe fatigue limit.

[0037] Further, the method further includes:

[0038] Compare the measured load spectra of the two load measurement channels of the guide tube, select the more severe measured load spectrum, and combine it with the safe fatigue limit obtained from the guide tube fatigue test; Substitute it into the life curve corresponding to the more severe measured load spectrum for life assessment.

[0039] Further, the method further includes:

[0040] Combine the life curves of the two load measurement channels. For a series of life points in the two life curves, find the corresponding two safe fatigue limits respectively. After squaring the two safe fatigue limits and then taking the square root to calculate a new fatigue limit, use this series of life points and the new fatigue limit to draw a new life curve, and use the safe fatigue limit obtained from the guide tube fatigue test for life assessment.

[0041] Beneficial effects:

[0042] This application can make the fatigue verification work of the guide tube more comprehensive. By implementing different operations at different positions of the large ball joint, the situation of insufficient fatigue verification of the guide tube is avoided. Description of the Drawings

[0043] Figure 1 It is a schematic structural diagram of the swashplate.

[0044] Figure 2 It is a guide tube fatigue verification diagram of the swashplate. Detailed Implementation Modes

[0045] To make the objectives, technical solutions, and advantages of the present application more clear, the following will describe in more detail the technical solutions in the embodiments of the present application in conjunction with the accompanying drawings in the embodiments of the present application. In the drawings, the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The described embodiments are part of the embodiments of the present application, rather than all of the embodiments. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present application, and should not be construed as a limitation to the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application. The following will explain in detail the embodiments of the present application in conjunction with the accompanying drawings.

[0046] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "center", "axial direction", "vertical", "upper", "lower", "upper end", "bottom end", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the protection scope of the present invention.

[0047] The steps for fatigue verification of the guide cylinder include:

[0048] 1. Fatigue strength design of the guide cylinder: Use engineering calculation methods or finite element methods to obtain the stresses of the guide cylinder and its connecting bolts under the guide cylinder load. During the strength design process, the position where the guide cylinder load is applied is at the upper limit of the large spherical hinge stroke. At this time, the stresses of the guide cylinder and its connecting bolts are the most severe. According to the relationship between the load and stress and the guide cylinder calculation load spectrum provided by the load department, analyze to obtain the stress spectrum of the guide cylinder and its connecting bolts. Combine the safety S-N curve of the materials of the guide cylinder and its connecting bolts and the working time ratio to calculate the fatigue strength of the guide cylinder. Improve and iterate the guide cylinder based on the analysis results, and the iteration goal is to meet the final life requirements;

[0049] 2. Strain gage pasting on the guide cylinder: After the engineering trial production of the guide cylinder, paste strain gages on the guide cylinder trial production parts. The pasting position is between the lower limit of the large spherical hinge stroke and the guide cylinder installation surface as Figure 2 shown. The strain gage channels include two groups of strain gages, and the two groups of strain gages are arranged at a 90° angle. After the strain gages are pasted on the guide cylinder, form two load measurement channels by forming a full bridge for the two groups of strain gages;

[0050] 3. Load calibration of the guide tube: Fix the guide tube on the tooling fixture through the guide tube mounting bolts according to the installation requirements. The load application device applies the load on the guide tube through the large spherical hinge. At this time, the large spherical hinge can be at any position within the stroke range of the large spherical hinge. Measure the distance between the center of the large spherical hinge and the patch section to calculate the actual bending moment of the patch section under the calibration load. The concentrated force load directions along the X and Y directions are respectively used to calibrate the load measurement channels in the X and Y directions. The number of unidirectional loading levels (including the zero-load level) for the calibration load is 5 - 6 levels. The calibration process needs to be carried out in both positive and negative directions, and the number of calibration repetitions is not less than 3 times. The calibration error should not be greater than 3%. Finally, obtain the relationship between the actual bending moment of the patch section and the voltage output value of the load measurement channel, and obtain the load calibration coefficient of the guide tube through fitting;

[0051] 4. Fatigue test of the guide tube: Obtain the relationship between the guide tube load and the stress of the guide tube and its connecting bolts according to the engineering calculation method or the finite element method. At this time, the guide tube load is at the lower limit position of the large spherical hinge. Calculate the fatigue test load F = F S ±F d according to the calculated load spectrum of the guide tube and the average S - N curve of the material of the guide tube and its connecting bolts, where F s is the static load of the guide tube fatigue test, generally covering 90% of the static loads in the calculated load spectrum of the guide tube, and F d is the dynamic load of the guide tube fatigue test. The change law of the dynamic load in the fatigue test is generally in the form of a sine or cosine curve. Through the relationship between the load and the stress, the stresses corresponding to the static and dynamic loads in the fatigue test can be obtained. The equivalent dynamic stress in the fatigue test is obtained after correcting the static and dynamic stresses in the fatigue test by the static stress. The number of cycles corresponding to the equivalent dynamic stress in the average S - N curve should be approximately around 1 million times. If the number of cycles is much greater than 1 million times, then appropriately increase the dynamic load in the fatigue test. If the number of cycles is much less than 1 million times, then appropriately reduce the dynamic load in the fatigue test. Finally, make the number of cycles approximately reach 1 million times. Fix the guide tube on the tooling fixture through the guide tube mounting bolts according to the installation requirements. The load application device applies the fatigue test load on the guide tube through the large spherical hinge. At this time, the large spherical hinge is at the lower limit position of the large spherical hinge stroke. The cross-section of the guide tube is generally circular. Therefore, only fatigue tests need to be carried out on the guide tube in one direction. This load direction should be in the XY plane, and there should be a calibrated load measurement channel in this direction. Adjust the load frequency to ensure that the change law of the test dynamic load is basically in the form of a sine or cosine curve. When the load cycle reaches 500,000 - 1 million times, upgrade the dynamic load in the fatigue test of the guide tube. The upgrade ratio is generally 10% - 30% until the structure fails. The number of fatigue tests of the guide tube is 1 - 6 pieces. Finally, comprehensively obtain the fatigue limit of the bending moment of the patch section of the guide tube based on all the fatigue test data of the guide tube, the shape of the average S - N curve, and the reduction coefficient;

[0052] 5. Acquisition and Spectral Compilation of Helicopter Flight-Test Loads: Install the strain gage that has been pasted and calibrated on the helicopter or autogyro for load measurement work. During the flight test, collect the time-domain loads of the two load channels of the strain gage within a certain period under various weights, centers of gravity, altitudes, and flight states according to the requirements of actual load measurement. Compile the measured load spectra of the two load measurement channels through load classification and rainflow counting, and plot the life curves of the two load measurement channels. The abscissa of the life curve is the life, and the ordinate is the safety fatigue limit of the bending moment of the strain gage paste section;

[0053] 6. Life Assessment of the Strain Gage: The first method is to compare the measured load spectra of the two load measurement channels of the strain gage, select the more severe one of the measured load spectra, and combine it with the safety fatigue limit of the bending moment of the paste section obtained from the fatigue test of the strain gage / to conduct life assessment. The second method is to combine the life curves of the two load measurement channels. For a series of life points in the two life curves, find the corresponding two safety fatigue limits respectively. After squaring and then taking the square root of the sum of the squares of the two safety fatigue limits, calculate the new fatigue limit. Use this series of life points and the new fatigue limit to plot a new life curve, and conduct comprehensive life assessment using the safety fatigue limit of the bending moment of the paste section obtained from the fatigue test of the strain gage.

[0054] Those skilled in the art will readily conceive of other embodiments of the present disclosure after considering the specification and the practice disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include known common knowledge or conventional technical means in the technical field not disclosed in the present disclosure. The specification and examples are only regarded as exemplary, and the true scope and spirit of the present disclosure are pointed out by the following claims.

[0055] It should be understood that the present disclosure is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present disclosure is only limited by the appended claims.

Claims

1. A fatigue verification method for an actuator guide tube, characterized in that, Including: Design the fatigue strength of the guide cylinder according to the life requirements; After the engineering trial production of the guide cylinder, paste strain gauges on the trial production parts of the guide cylinder to obtain two mutually perpendicular load measurement channels; Calibrate the load of the guide cylinder according to the measurement results of the two load measurement channels to determine the load calibration coefficient; Complete the fatigue verification of the guide cylinder according to the fatigue test of the guide cylinder, the acquisition and compilation of the flight test load; 2. The method according to claim 1, characterized in that, Design the fatigue strength of the guide cylinder according to the life requirements, including: Under the condition that the load application position is at the upper limit of the large ball joint stroke, use the engineering calculation method or the finite element method to obtain the stresses of the guide cylinder and its connecting bolts under different load application conditions, that is, the first relationship between the load and the stress; According to the first relationship and the guide cylinder calculated load spectrum, analyze and obtain the stress spectrum of the guide cylinder and its connecting bolts, and calculate the fatigue strength of the guide cylinder in combination with the safety S-N curve and the working time ratio of the materials of the guide cylinder and its connecting bolts; Improve and iterate the structure of the guide cylinder according to the analysis results until the life requirements are met; 3. The method according to claim 2, wherein The o point of the guide cylinder coordinate system is the center point of the upper end face of the guide cylinder, the xy plane is the guide cylinder installation plane; the z axis is perpendicular to the installation plane and upward; the guide cylinder installation surface is the plane where the guide cylinder installation connecting bolts are located; Paste strain gauges on the trial production parts of the guide cylinder to obtain two mutually perpendicular load measurement channels, including: Stick two groups of strain gauges between the lower limit of the large ball joint stroke and the guide cylinder installation surface, ensure that the guide cylinder strain gauge section where the two groups of strain gauges are located is parallel to the guide cylinder installation surface, one group of strain gauges is symmetric about the y axis and installed on the x axis, and the other group of strain gauges is symmetric about the x axis and installed on the y axis; Form two full-bridge groups of the two groups of strain gauges to form two load measurement channels; 4. The method according to claim 3, wherein Calibrate the load of the guide cylinder according to the measurement results of the two load measurement channels to determine the load calibration coefficient, including: Fix the guide cylinder on the fixture through the installation bolts according to the installation requirements, and use the load application device to apply the load to the large ball joint, so as to transfer it to the guide cylinder; at this time, the large ball joint can be at any position within the large ball joint stroke range; the direction of the load application force is applied along the x direction or the y direction; Measure the distance from the center of the large ball joint to the plane where the strain gauges are located as the lever arm; Obtain the voltage output values in the x and y directions through the two load measurement channels; Calculate the actual bending moment according to the load applied in the x and y directions and the lever arm; Determine the bending moment-voltage relationship between the actual bending moment and the voltage output values in the x and y directions, and use the coefficient of the bending moment-voltage relationship as the load calibration coefficient of the guide cylinder; 5. The method according to claim 4, characterized in that Complete the fatigue verification of the guide cylinder according to the fatigue test of the guide cylinder, the acquisition and compilation of the flight test load, including: Step 1: When the load is applied to the lower limit position of the large ball joint, obtain the stresses of the guide cylinder and its connecting bolts under different load application conditions according to the engineering calculation method or the finite element method, that is, the second relationship between the load and the stress; Step 2: Calculate the fatigue test load F = F of the guide cylinder according to the load spectrum calculated based on the guide cylinder and the average S-N curve of the guide cylinder and its connecting bolts S ±F d , where F S is the static load of the guide cylinder fatigue test, covering at least 90% of the static load in the load spectrum calculated for the guide cylinder, and F d is the dynamic load of the guide cylinder fatigue test, and its variation law is in the form of a sine or cosine curve; Step 3: Calculate the stresses corresponding to the static and dynamic loads of the fatigue test through the second relationship; Step 4: Obtain the equivalent dynamic stress of the fatigue test by correcting the static and dynamic stresses of the fatigue test with the static stress. If the number of cycles corresponding to the equivalent dynamic stress in the mean S-N curve is much greater than m times the target number of cycles, increase the dynamic load of the fatigue test according to the fatigue strength. If the number of cycles corresponding to the equivalent dynamic stress in the mean S-N curve is less than n times the target number of cycles, decrease the dynamic load of the fatigue test according to the fatigue strength until the number of cycles corresponding to the adjusted equivalent dynamic stress in the mean S-N curve approaches the target number of cycles; Step 5: Fix the guide cylinder on the tooling fixture through the mounting bolts according to the installation requirements. Apply the load to the large ball joint using the load application device. At this time, the large ball joint is at the lower limit position of the large ball joint stroke. Only conduct the fatigue test on the guide cylinder in one direction of x or y. Adjust the load frequency of the dynamic load of the guide cylinder fatigue test. When each load cycle reaches the preset number of times, upgrade the dynamic load of the guide cylinder fatigue test and continue the test until the guide cylinder structure fails; Step 6: Conduct the fatigue test in Step 5 using 1 to 6 identical guide cylinders. Finally, obtain the safety fatigue limit of the bending moment of the strain gauge section of the guide cylinder by integrating all the fatigue test data of the guide cylinder, the shape of the mean S-N curve, and the reduction coefficient.

6. The method according to claim 5, wherein The method further includes: Install the guide cylinder with the strain gauges and calibration completed on the helicopter or rotorcraft for load measurement; During the flight test, collect the time-domain loads of the two load channels of the guide cylinder within a certain period of time under various weights, centers of gravity, altitudes, and flight states according to the actual load measurement requirements; Compile the measured load spectra of the two load measurement channels through load classification and rainflow counting, and plot the life curves of the two load measurement channels. The abscissa of the life curve is the life, and the ordinate is the safety fatigue limit.

7. The method according to claim 6, wherein The method further includes: Compare the measured load spectra of the two load measurement channels of the guide cylinder, select the more severe measured load spectrum, and combine it with the safety fatigue limit obtained from the fatigue test of the guide cylinder / Substitute it into the life curve corresponding to the more severe measured load spectrum for life assessment.

8. The method according to claim 6, wherein The method further includes: Combine the life curves of the two load measurement channels. For a series of life points in the two life curves, find the corresponding two safety fatigue limits respectively. Calculate the new fatigue limit by taking the square root of the sum of the squares of the two safety fatigue limits. Use this series of life points and the new fatigue limit to plot a new life curve, and conduct life assessment using the safety fatigue limit obtained from the guide cylinder fatigue test.

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