Load spectrum compilation method for durability test of main vibration reduction and isolation device

Abstract

The invention relates to the field of helicopter main vibration reduction and isolation devices, in particular to a main vibration reduction and isolation device durability test load spectrum compilation method. The method comprises the steps that a high-low cycle durability load spectrum is compiled according to the axial load of a main reduction supporting rod borne by the rubber-corrugated pipe type hydraulic vibration isolator in the actual flight process;

Description

Technical Field

[0001] The present invention relates to the field of helicopter main reduction vibration isolation devices, and relates to a method for compiling a durability test load spectrum of a main reduction vibration isolation device. Background Art

[0002] The rubber-bellows type hydraulic shock isolator is composed of components such as an inner cylinder, an outer cylinder, a bellows, and an inertial mass. The shock isolator is filled with a fluid having a low density and a low viscosity, such as Figure 1a as shown. The inner cylinder and the outer cylinder are vulcanized into one body by rubber. The rubber not only plays a sealing role but also provides stiffness. When the inner cylinder reciprocates relative to the outer cylinder under the action of a harmonic base excitation, the fluid pressure in the sealed chamber changes accordingly, and then the inertial mass reciprocates. When the external excitation is at a certain specific frequency, the outer cylinder is in an equilibrium state under the action of the fluid pressure and the elastic force of the rubber, and at this time the outer cylinder does not move, that is, the base excitation of the inner cylinder is not transmitted to the outer cylinder, and this frequency is the anti-resonance frequency.

[0003] The rubber-bellows type hydraulic shock isolator is connected to the main reduction strut and together transmits the rotor load to the upper platform of the fuselage, and belongs to an important load-bearing component. According to the requirements, fatigue tests are carried out on the metal inner cylinder and the outer cylinder for verification, and durability tests are carried out on the elastomer for verification. In the past, the load spectrum for the durability test of the elastomer was mainly a high-cycle test load spectrum, and the low-cycle damage was ignored. Summary of the Invention

[0004] Object of the Invention: To provide a method for compiling a durability test load spectrum of a main reduction vibration isolation device, which can consider high and low cycle damages and compile low-cycle and high-cycle durability test load spectra.

[0005] Technical Solution:

[0006] Provided is a method for compiling a durability test load spectrum of a main reduction vibration isolation device, including:

[0007] Compiling a high and low cycle durability load spectrum according to the axial load of the main reduction strut borne by the rubber-bellows type hydraulic shock isolator during actual flight.

[0008] Further, compiling a high and low cycle durability load spectrum according to the axial load of the main reduction strut borne by the rubber-bellows type hydraulic shock isolator during actual flight, including:

[0009] Considering the damages caused by both the ground-air-ground cycle and the state change at the same time, sorting each state in reverse order according to the state loads in the flight load spectrum to construct a low-cycle load spectrum;

[0010] On the basis of the low-cycle load spectrum and the flight spectrum, using the method of damage equivalence to combine and simplify the high-cycle load spectrum.

[0011] Further, considering the damage caused by both the ground-air-ground cycle and the state change, sort each state in reverse order according to the state loads in the flight load spectrum to construct a low-cycle load spectrum, including:

[0012] Determine the typical mission profile of the helicopter according to the flight spectrum and the usage of the helicopter;

[0013] Obtain the number of occurrences N per hour of each flight spectrum state and the load F received by the main reduction vibration isolation device under the corresponding flight state;

[0014] Re-sort the flight spectrum states according to the load size in two ways:

[0015] Sort in descending order of load to obtain a large sequence;

[0016] Sort in ascending order of load to obtain a small sequence;

[0017] Re-construct the cycle pairs in the load spectrum according to the corresponding combination of the obtained large and small sequences;

[0018] Further simplify and merge the newly obtained load spectrum to obtain the final low-cycle load spectrum. The simplification and merging principle: Merge several states with the same or similar minimum load values. The merged number of occurrences is the sum of the numbers of occurrences of several states. The minimum load after merging is the minimum value among the minimum loads of several states, and the maximum load after merging is the maximum value among the maximum loads of several states.

[0019] Further, for the i-th cycle pair, re-construct the cycle pairs in the load spectrum according to the corresponding combination of the two obtained sorts, including:

[0020] If the load with remaining cycle times in the (i - 1)-th cycle pair belongs to the large sequence, obtain the minimum load and the load with remaining cycle times in the unconstructed loads in the small sequence as the maximum load and the minimum load of the i-th cycle pair; Select the smaller cycle times from the cycle times of the minimum load in the unconstructed loads and the remaining cycle times as the cycle times of the i-th cycle pair;

[0021] If the load with remaining cycle times in the (i - 1)-th cycle pair belongs to the small sequence, obtain the maximum load and the load with remaining cycle times in the unconstructed loads in the large sequence as the maximum load and the minimum load of the i-th cycle pair; Select the smaller cycle times from the cycle times of the maximum load in the unconstructed loads and the remaining cycle times as the cycle times of the i-th cycle pair.

[0022] Further, on the basis of the low-cycle load spectrum and the flight spectrum, use the method of damage equivalence to combine and simplify the high-cycle load spectrum, including:

[0023] Take the state of the final low - cycle load spectrum as the state of the high - cycle load spectrum;

[0024] For each high - cycle load spectrum, the static load value of the state is taken as the maximum load value of the corresponding low - cycle load spectrum;

[0025] According to the static load values of each state of the high - cycle load spectrum, simplify and merge the original flight spectrum. The principle of simplification and merger is: if the static load value of the original flight spectrum state is lower than a preset threshold compared with the static load value of a certain state of the high - cycle load spectrum, then the sum of the cycle numbers of all states merged into the same high - cycle load spectrum in the original flight spectrum is used as the cycle number of the state of this high - cycle load spectrum;

[0026] According to the damage equivalence principle and the low - cycle load spectrum, calculate the dynamic load value corresponding to the high - cycle load spectrum.

[0027] Further, after compiling the high - and low - cycle durability load spectrum, the method further includes:

[0028] Take the rubber elastomer of the rubber - bellows type hydraulic vibration isolator as the test piece, and stick strain gauges at the middle part of the outer cylinder of the rubber - bellows type hydraulic vibration isolator to measure the axial force;

[0029] Install the rubber - bellows type hydraulic vibration isolator on the durability test bench of the main reduction vibration isolation device;

[0030] According to the high - and low - cycle durability load spectrum, apply the load and conduct the durability test.

[0031] Further, the load application method is:

[0032] The load is applied from 0 to the maximum load of the first low - cycle spectrum block, keep the load unchanged, and at the same time cycle the first high - cycle spectrum block. Then the load is reduced to the minimum load of the first low - cycle spectrum block, and repeat to complete the first low - cycle spectrum block, and so on for the subsequent spectrum blocks.

[0033] Further, the method further includes:

[0034] During the test process, conduct load or displacement monitoring to ensure that the test load application meets the requirements; every 5 hours of durability test assessment, the test piece should be subjected to an on - line static stiffness test and an appearance inspection of the test piece; during the normal - temperature test process, if cracks or obvious damages appear on the test piece, the test should be suspended, and then the test piece should be removed and parked for at least 24 hours before a comprehensive performance test;

[0035] When the on - line measurement of the test piece first shows that the static stiffness change exceeds 20%, then the test piece should be removed and parked for at least 24 hours before a comprehensive performance test. Subsequently, the proportional relationship can be obtained according to the change degree of the on - line measured stiffness and the change degree of the performance test stiffness. Refer to the change situation of the on - line stiffness measurement and the proportional situation of the performance test stiffness change to determine whether to remove the test piece for performance testing;

[0036] After the test, record the appearance inspection and performance data of the test piece at this time, and pay special attention to the initial signs of damage and the development trend of damage of the test piece.

[0037] Beneficial effects:

[0038] The present invention targets a rubber-bellows hydraulic vibration isolator structure and compiles a high- and low-cycle durability load spectrum based on the load characteristics of the rubber elastic body, thereby obtaining the mean time to failure (MTTF) of the rubber elastic body. Based on the characteristics of the high- and low-cycle durability load spectrum, the high- and low-cycle loads are fully combined during the test process, facilitating the application of the test load and shortening the test cycle.

[0039] Due to limited research on the durability of the elastomer structure of rubber-bellows hydraulic isolators for helicopters in China, and the lack of a high- and low-cycle test verification method that simultaneously considers damage, the safe use of rubber-bellows hydraulic isolators cannot be guaranteed. This paper provides a method for compiling a load spectrum for durability tests of a main vibration damper and isolation device. By optimizing the application of high- and low-cycle test load spectra, it can determine the mean time to failure and safety inspection interval for rubber-bellows hydraulic isolators, thereby ensuring the safe use of rubber-bellows hydraulic isolators for helicopters. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1a It is a structural diagram of a rubber-bellows type hydraulic vibration isolator.

[0041] Figure 1b This is a schematic diagram of load application for a rubber-bellows type hydraulic vibration isolator.

[0042] Figure 2 This is a schematic diagram of the low-frequency load spectrum compilation method.

[0043] Figure 3 This is a schematic diagram of the high-frequency load spectrum compilation method.

[0044] Figure 4 It is a schematic diagram of the load spectrum of the durability test of the main vibration reduction and isolation device. DETAILED DESCRIPTION

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

[0046] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "center", "axial direction", "vertical", "upper", "lower", "upper end", "bottom end", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings, and are 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 thus should not be construed as a limitation on the protection scope of the present invention.

[0047] The objective of the present invention is to provide a method for compiling a durability test load spectrum for a main reduction vibration isolation device, including aspects such as test platform construction, test load determination, optimization of test load spectrum loading, and test control technology.

[0048] The specific steps include:

[0049] Step 1: Prepare test pieces and supporting parts, and install patches.

[0050] Step 2: Design fixtures and simulate the boundaries of the test pieces.

[0051] Step 3: Apply characteristic loads.

[0052] Step 4: Conduct pre-test inspections.

[0053] Step 5: Conduct a durability test and ensure periodic inspections during the test.

[0054] Step 6: Conduct inspections after the test is terminated to determine the average failure time of the structural elastomer.

[0055] The following takes the durability test method for the elastomer of a rubber-bellows type hydraulic vibration isolator as an example to further explain the present invention in detail in conjunction with the drawings and appendices:

[0056] Step 1: The rubber-bellows type hydraulic vibration isolator consists of components such as an inner cylinder, an outer cylinder, a bellows, and a rubber elastomer. The structural schematic diagram is as Figure 1aAs shown. The rubber elastomer is the test piece, and the other components are the supporting parts. During the test, if any of the other components are damaged except for the inner cylinder, outer cylinder, and rubber elastomer, replace the spare parts or dummy parts and continue the test. During the test, strain gauges are attached to the middle part of the metal outer cylinder to measure the axial force.

[0057] Step 2: Install the test piece of the rubber-bellows type hydraulic shock absorber on the durability test bench of the main reduction shock absorber. Use dummy lugs at both ends to simulate the actual structure for connection. The test fixture should ensure the coaxiality of the test fixture, the test piece, and the loading direction to avoid generating additional loads. The test fixture should fully consider the material strength and ensure easy loading and unloading with a large strength margin. During the test, an air-cooling device is required to ensure the ambient temperature of the test piece. The axial load is applied through the actuator as Figure 1b shown.

[0058] Step 3: Compile a high-low cycle durability load spectrum according to the axial load of the main reduction strut borne by the rubber-bellows type hydraulic shock absorber during actual flight.

[0059] When compiling the low-cycle load spectrum, consider the damage caused by both the ground-air-ground cycle and the change of state. To ensure flight safety, a relatively conservative method is adopted to sort each state according to the maximum and minimum loads respectively to construct the low-cycle load spectrum, as Figure 2 shown. The specific method is as follows:

[0060] 1. Determine the typical mission profile of the helicopter according to the flight spectrum and the usage of the helicopter.

[0061] 2. Obtain the number of occurrences N per hour of each flight spectrum state and the load F borne by the main reduction shock absorber in the corresponding flight state.

[0062] 3. Re-sort the flight spectrum states in two ways according to the load magnitude:

[0063] a. Sort in descending order of load;

[0064] b. Sort in ascending order of load.

[0065] 4. Re-construct the load spectrum according to the two obtained sorts for corresponding combination. Take the smaller value for the number of occurrences, and use the remaining number of occurrences for the next state, and so on.

[0066] 5. Further simplify and merge the newly obtained load spectrum to obtain the final low-cycle load spectrum. The simplification and merging principle: Merge several states with the same or similar minimum load values. The number of occurrences after merging is the sum of the numbers of occurrences of several states. The minimum load after merging takes the minimum value among the minimum loads of several states, and the maximum load after merging takes the maximum value among the maximum loads of several states.

[0067] The high-frequency load spectrum is simplified by using the damage equivalence method. The principle of simplification is to make the load value as equivalent as possible to the load value of the corresponding low-frequency state. The damage equivalence principle is to equate the corresponding loads in different states into an equivalent load. The damage caused by this equivalent load is equal to the damage caused by the loads before the equivalence. For example, Figure 3 The specific method is as follows:

[0068] 1. Determine the high-cycle load spectrum state based on the number of low-cycle load spectrum states.

[0069] 2. The static load value of each high-cycle load spectrum is the corresponding maximum load value of the low-cycle load spectrum.

[0070] 3. According to the state static load value of the high-cycle load spectrum, the original flight spectrum is simplified and merged. The principle of simplification and merging is: the state static load value of the original flight spectrum is similar to and slightly lower than the state static load value of the high-cycle load spectrum. The sum of the number of cycles of all states in the original flight spectrum merged into the same high-cycle load spectrum is taken as the state cycle number of the high-cycle load spectrum.

[0071] 4. According to the damage equivalence principle, the dynamic load value corresponding to the high-cycle load spectrum is calculated.

[0072] According to the above method, the high and low cycle load spectrum of the durability test of the rubber-bellows hydraulic vibration isolator can be obtained as shown in Table 1. At the same time, in order to facilitate the test loading and test load adjustment, the Figure 4 The specific loading method is: the load is loaded from 0 to the maximum load of the first low-frequency spectrum block, and the load is kept unchanged. At the same time, the first high-frequency spectrum block is cycled, and then the load is reduced to the minimum load of the first low-frequency spectrum block. The first low-frequency spectrum block is completed back and forth, and the subsequent spectrum blocks are analogous.

[0073] Step 4: From the receipt of the test piece to the installation of the test piece, as well as the entire durability test process, the elastic part of the rubber-bellows type hydraulic vibration isolator must be corroded by the organic solution. Before the test begins, the damper needs to be preheated by applying a load displacement of 1mm±2mm for 5 minutes, and a static stiffness test is performed as the initial static stiffness;

[0074] Step 5: During the test, load or displacement monitoring shall be carried out to ensure that the test load is applied as required. After every 5 hours of durability test assessment, the test piece shall be subjected to an online static stiffness test and the appearance of the test piece shall be inspected. During the normal temperature test, if cracks or obvious damages occur to the test piece, the test shall be suspended, and the test piece shall be removed and parked for at least 24 hours before a comprehensive performance test is carried out. When the static stiffness change of the test piece measured online exceeds 20% for the first time, the test piece shall be removed and parked for at least 24 hours before a comprehensive performance test is carried out; subsequently, the proportional relationship can be obtained based on the degree of change in the measured online stiffness and the degree of change in the stiffness during the performance test, and whether to remove the test piece for performance test shall be determined by referring to the change in the measured online stiffness and the proportional change in the stiffness during the performance test. After the test is completed, record the appearance inspection situation and performance data of the test piece at this time, and special attention shall be paid to the initial damage signs and the development trend of the damage of the test piece.

[0075] Step 6: Visually inspect and tap the test piece after the test is completed and record the results.

[0076] Those skilled in the art will readily conceive of other embodiments of the present disclosure after considering the specification and practicing the disclosure 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 illustrative, and the true scope and spirit of the present disclosure are pointed out by the following claims.

[0077] 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 method for compiling a durability test load spectrum of a main reduction vibration isolation device, characterized in that, Including: Prepare a high-low cycle durability load spectrum according to the axial load of the main reduction strut borne by the rubber-bellows type hydraulic vibration isolator during actual flight.

2. The method according to claim 1, wherein Prepare a high-low cycle durability load spectrum according to the axial load of the main reduction strut borne by the rubber-bellows type hydraulic vibration isolator during actual flight, including: Considering the damage caused by both the ground-air-ground cycle and the state change, sort each state in ascending and descending order according to the state load in the flight load spectrum to construct a low cycle load spectrum; Based on the low cycle load spectrum and the flight spectrum, simplify the high cycle load spectrum by combining spectra using the damage equivalence method.

3. The method according to claim 2, characterized in that, Considering the damage caused by both the ground-air-ground cycle and the state change, sort each state in ascending and descending order according to the state load in the flight load spectrum to construct a low cycle load spectrum, including: Determine the typical mission profile of the helicopter according to the flight spectrum and the usage of the helicopter; Obtain the number of occurrences N per hour of each flight spectrum state and the load F borne by the main reduction vibration isolation device in the corresponding flight state; Re-sort the flight spectrum states according to the load magnitude in two ways: Sort in descending order of load to obtain a large sequence; Sort in ascending order of load to obtain a small sequence; Re-construct the cycle pairs in the load spectrum according to the corresponding combination of the obtained large and small sequences; Further simplify and combine the newly obtained load spectrum to obtain the final low cycle load spectrum. The simplification and combination principle: Combine several states with the same or similar minimum load values. The combined number of occurrences is the sum of the numbers of occurrences of several states. The minimum load after combination is the minimum value among the minimum loads of several states, and the maximum load after combination is the maximum value among the maximum loads of several states.

4. The method according to claim 3, characterized in that For the i-th cycle pair, re-construct the cycle pairs in the load spectrum according to the corresponding combination of the two obtained sorts, including: If the load with remaining cycle times in the (i - 1)-th cycle pair belongs to the large sequence, obtain the minimum load and the load with remaining cycle times in the small sequence that have not participated in the construction of the load as the maximum load and the minimum load of the i-th cycle pair; Select the smaller cycle times from the cycle times of the minimum load that has not participated in the construction of the load and the remaining cycle times as the cycle times of the i-th cycle pair; If the load with remaining cycle times in the (i - 1)-th cycle pair belongs to the small sequence, obtain the maximum load and the load with remaining cycle times in the large sequence that have not participated in the construction of the load as the maximum load and the minimum load of the i-th cycle pair; Select the smaller cycle times from the cycle times of the maximum load that has not participated in the construction of the load and the remaining cycle times as the cycle times of the i-th cycle pair.

5. The method according to claim 3, wherein Based on the low cycle load spectrum and the flight spectrum, simplify the high cycle load spectrum by combining spectra using the damage equivalence method, including: Take the states of the final low cycle load spectrum as the states of the high cycle load spectrum; The static load value of each state of the high cycle load spectrum takes the maximum load value of the corresponding state of the low cycle load spectrum; According to the static load values of each state of the high-cycle load spectrum, the original flight spectrum is simplified and merged. The principle of simplification and merging is as follows: if the static load value of the original flight spectrum state is lower than the static load value of a certain state of the high-cycle load spectrum by a preset threshold, then the sum of the cycle numbers of all states in the original flight spectrum merged into the same high-cycle load spectrum is used as the state cycle number of the high-cycle load spectrum; According to the damage equivalence principle and the low-cycle load spectrum, the dynamic load value corresponding to the high-cycle load spectrum is calculated.

6. The method according to claim 5, wherein After compiling the high and low cycle durability load spectra, the method further includes: The rubber elastic body of the rubber-bellows hydraulic vibration isolator is used as a test piece, and a strain gauge is attached to the middle part of the outer cylinder of the rubber-bellows hydraulic vibration isolator to measure the axial force; Install the rubber-bellows type hydraulic vibration isolator on the durability test bench of the main vibration reduction and isolation device; According to the high and low cycle durability load spectrum, load is applied and durability test is carried out.

7. The method according to claim 6, wherein The load loading method is: The load is loaded from 0 to the maximum load of the first low-frequency spectrum block, and the load is kept unchanged. At the same time, the first high-frequency spectrum block is cycled, and then the load is reduced to the minimum load of the first low-frequency spectrum block. The first low-frequency spectrum block is completed back and forth, and the subsequent spectrum blocks are analogous.

8. The method according to claim 7, wherein The method further comprises: During the test, load or displacement monitoring is performed to ensure that the test load meets the requirements. After every 5 hours of durability test, the test piece should undergo an online static stiffness test and an appearance inspection. During the normal temperature test, if the test piece shows cracks or obvious damage, the test should be suspended, and the test piece should be removed and left for at least 24 hours before a comprehensive performance test. When the static stiffness of the test piece changes by more than 20% for the first time during online measurement, the test piece should be removed and left for at least 24 hours before a comprehensive performance test. Subsequently, a proportional relationship can be derived based on the degree of stiffness change in online measurement and the degree of stiffness change in performance test. The decision on whether to remove the test piece for performance test can be made based on the change in online stiffness measurement and the proportional relationship between the stiffness change in performance test. After the test, record the appearance inspection and performance data of the test piece at this time, and pay special attention to the initial signs of damage and the development trend of damage of the test piece.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, the method according to any one of claims 1 to 8 is implemented.

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