Service life evaluation test system and method for bending fatigue of hydraulic conduit under composite working conditions

Abstract

The invention discloses a hydraulic conduit composite working condition bending fatigue life evaluation test system and method, and relates to the technical field of hydraulic conduit reliability test, and the system comprises a vibration test system, a conduit installation clamp, an oil pressure pump source, and a stress acquisition and monitoring system. The method comprises the following steps of: directly simulating a temperature, pressure and vibration coupling action environment of a hydraulic conduit in actual work to obtain a relational expression between a fatigue strength limit of a conduit test piece and temperature, pressure and vibration stress; and finally, the bending fatigue life of the aircraft hydraulic conduit can be evaluated by measuring the temperature, pressure and vibration stress environment of the aircraft hydraulic conduit in actual work in combination with a relational expression curve obtained by a test.

Description

Technical Field

[0001] The present invention relates to the technical field of hydraulic conduit reliability testing, and in particular to a life assessment testing system and method for hydraulic conduit composite working condition bending fatigue. Background Art

[0002] The piping system is a crucial component of aircraft engines. During actual operation, the piping is typically exposed to high temperatures and high pressures. Consequently, the piping system is subjected to a variety of thermodynamic and vibration environments during operation. As engine capabilities continue to improve, the requirements for the structural strength of the associated piping system are also increasing, necessitating ground testing to assess the reliability of the piping system. However, currently, most duct fatigue tests still consider only the vibration environment. This simplified test fails to account for the coupling effects of heat, high pressure, and vibration, resulting in insufficient assessment. Furthermore, research on fatigue testing and life assessment specifically designed for the temperature, pressure, and vibration environments experienced by ducts is virtually nonexistent.

[0003] The current aircraft duct bending fatigue test is under-assessed, resulting in ducts that have passed ground tests still having leakage and breakage problems on aircraft. Summary of the Invention

[0004] The present invention aims to provide a life assessment test system and method for the bending fatigue of hydraulic conduits under combined working conditions. The system directly simulates the temperature, pressure, and vibration coupling environment in which the hydraulic conduits are exposed during actual operation to obtain a relationship expression between the fatigue strength limit of the conduit test piece and the temperature, pressure, and vibration stress. Finally, by measuring the temperature, pressure, and vibration stress environment in which the hydraulic conduits are exposed during actual operation on an aircraft and combining the relationship expression curve obtained through the test, the bending fatigue life of the aircraft hydraulic conduits can be assessed.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is as follows:

[0006] A life evaluation test system for hydraulic conduit under composite working conditions bending fatigue, including a vibration test system, a conduit installation fixture, an oil pressure pump source and a stress acquisition and monitoring system.

[0007] The vibration test system includes a vibration table, a vibration controller and an acceleration sensor, wherein the acceleration sensor is arranged on the table of the vibration table; the vibration controller is connected to the vibration table signal;

[0008] The catheter installation fixture includes a mounting seat, the bottom of which is fixedly connected to the vibration table surface. The mounting seat is a hollow cylindrical structure that passes through from top to bottom. An annular cavity is provided inside the hollow cylinder.

[0009] The outer surface of the hollow cylindrical structure is provided with a plurality of mounting holes, and the mounting seat is connected to the hydraulic conduit test piece through the mounting holes. One end of the hydraulic conduit test piece is a fixed end, and the other end of the hydraulic conduit test piece is a free end. The fixed end of the hydraulic conduit test piece is connected to the mounting holes, and a plug is installed at the free end of the hydraulic conduit test piece.

[0010] The stress acquisition and monitoring system includes a strain gauge for acquiring stress data of the catheter test piece, the strain gauge being mounted on a fixed end of the catheter test piece;

[0011] The mounting seat is also provided with an oil filling port, through which the oil pressure pump source is connected to the annular cavity inside the mounting seat;

[0012] The vibration table top is also provided with a high and low temperature test box which completely covers the vibration table top, the catheter installation fixture and the hydraulic catheter test piece; the high and low temperature test box is provided with a heating device and a temperature sensor.

[0013] The bottom of the mounting seat is provided with a base for fixed connection with the vibration table. The base is a circular ring structure. The bottom surface of the circular ring structure is fixedly connected to the vibration table surface, and the top surface of the circular ring is integrally formed with the mounting seat.

[0014] The fixed end of the hydraulic conduit test piece is connected to the mounting hole via a straight-through adapter;

[0015] The inner end of the mounting hole is a 37° sealing cone surface; the end of the straight-through adapter mounting base connection end is a 37° sealing cone surface that closely matches the short sealing cone surface in the mounting hole.

[0016] The two ends of the straight-through adapter are respectively a mounting seat connection end and a conduit connection end, both of which are threaded, and the middle is a hexagonal bolt head for easy installation using a wrench; the straight-through adapter mounting seat is connected to the mounting seat through the end using threads.

[0017] The 37° sealing cone surface of the mounting hole and the straight-through adapter ensures excellent sealing performance at the connection interface even in high oil pressure and vibration environments. The straight-through adapter's catheter connection end can be designed with different sizes and structures to suit different test catheter specifications. When testing with catheters of different specifications, there is no need to replace the entire mounting fixture; simply replace the straight-through adapter to simultaneously test catheters of different specifications.

[0018] The oil pressure pump source is provided with a pressure gauge for real-time monitoring of the supply pressure;

[0019] The high and low temperature test chamber is provided with a through hole, and the oil filling pipe of the oil pressure pump source, the strain gauge measuring wire and the acceleration sensor measuring wire are connected to the installation fixture, the strain gauge and the acceleration sensor installed inside the high and low temperature test chamber through the through hole;

[0020] A life assessment test method for hydraulic conduit under combined working conditions bending fatigue, wherein the life assessment test system for hydraulic conduit under combined working conditions is used to perform a hydraulic conduit under combined working conditions bending fatigue life assessment test on a hydraulic conduit test piece, comprises the following steps:

[0021] S1. Evaluation test preparation: Assemble the life evaluation test system for hydraulic pipe composite working condition bending fatigue and prepare for the evaluation test, including:

[0022] Connect the fixed end of the hydraulic conduit test piece to the mounting table, install a plug on the free end of the hydraulic conduit test piece, and install a strain gauge on the fixed end of the hydraulic conduit test piece. Install the high and low temperature test chamber on the vibration table and completely cover the test conduit and fixture.

[0023] S2. Simulate test environment: adjust the temperature in the high and low temperature test chamber, adjust the supply pressure of the oil pressure pump source, and simulate the test environment of the hydraulic catheter test piece;

[0024] S3. Adjust the strain gauge reading: set the initial reading of the strain gauge under the simulated test environment to "0";

[0025] S4. Start the bending fatigue test: The vibration controller sets the vibration stress value, sends a sinusoidal fixed-frequency signal through the vibration controller, and adjusts the vibration amplitude through the vibration console to make the stress reach the predetermined level. Then, the bending fatigue test is performed, the stress at the root of the catheter is monitored, and the number of vibrations is recorded.

[0026] The step S4 further includes: performing fatigue tests multiple times on hydraulic conduit test pieces of the same specification by setting different vibration stress values ​​and simulating test environments;

[0027] S5. Bending fatigue test completed: The vibration number is set by the vibration controller, and the hydraulic conduit test piece leaking during vibration is disassembled until all hydraulic conduit test pieces leak or the hydraulic conduit test piece vibrates more than the measured number of times under the current stress without leakage, and the vibration bending fatigue test is completed;

[0028] The step S5 further includes: observing the pressure gauge on the oil pressure pump source during the bending fatigue test; when the pressure on the pressure gauge drops to 85% of the initial value, pausing the test to observe whether the hydraulic conduit test piece leaks; if the hydraulic conduit test piece leaks, removing the leaking hydraulic conduit test piece and plugging the leaking mounting hole with a plug; if the hydraulic conduit test piece does not leak, re-punching the hydraulic conduit test piece to ensure that the pressure inside the hydraulic conduit test piece is at the pressure under the simulated test environment, and continuing the bending fatigue test;

[0029] S6. Obtaining the (S, P, T)-N curve: After the bending fatigue test is completed, the number of cycles of the hydraulic conduit test piece is counted, and the stress-life curve of the hydraulic conduit test piece under the simulated test environment is obtained, and its expression is fitted;

[0030] In step S6, obtaining the stress-life curve specifically includes the following steps:

[0031] S61, statistically calculating the average vibration cycle number N of the hydraulic conduit test piece (3);

[0032] The average number of vibration cycles is calculated by the following formula:

[0033]

[0034] Where n is the number of test samples of the hydraulic conduit test piece, N i is the number of vibration cycles of the i-th hydraulic conduit test piece;

[0035] S62, fitting the stress-life curves of the hydraulic conduit test piece (3) under different simulated test environments by averaging the number of vibration cycles under different stress conditions under the same simulated test environment;

[0036] S63. The relationship between the bending fatigue life of the hydraulic conduit test piece (3) and temperature, pressure, and stress is fitted through stress-life curves under different simulated test environments. The expression is named (S, P, T)-N curve, which is expressed as:

[0037] N=f(S,P,T)

[0038] Where N is the average number of vibration cycles of the hydraulic conduit test piece, S is the vibration stress, P is the internal pressure of the conduit, and T is the ambient temperature of the conduit;

[0039] S7. Life Assessment: By measuring the temperature, pressure, and vibration stress values ​​of ducts of different specifications and installation positions on the aircraft under actual operating conditions, combined with the (S, P, T)-N curves obtained from the test, the bending fatigue life of hydraulic ducts of different specifications and installation positions on the aircraft can be assessed.

[0040] Beneficial effects of the present invention:

[0041] 1. The life assessment test system for the composite working condition bending fatigue of the hydraulic conduit of the present invention has a simple structure and can be directly modified from an existing vibration table, which is low-cost; the conduit installation fixture of the present invention is universal and can be installed for conduits of different specifications, and only the straight-through adapter needs to be replaced, and it has good sealing performance; the conduit installation fixture can install multiple hydraulic conduit test pieces at the same time, and has the function of supplying oil pressure to multiple hydraulic conduit test pieces at the same time and fixing multiple hydraulic conduit test pieces to the vibration table at the same time; using this fixture can improve test efficiency.

[0042] 2. The life assessment method for bending fatigue of hydraulic conduits of the present invention takes into account the coupling effects of temperature, pressure and vibration of hydraulic conduits in actual operation. It can directly perform vibration bending fatigue tests on the temperature and pressure environment in which the conduit is actually located. The test results are more reference-oriented and can provide an important basis for formulating the fatigue allowable limit of hydraulic conduits. It has important engineering practical value.

[0043] 3. This invention takes into account the coupling effects of temperature, pressure, and vibration in the actual operation of hydraulic conduits. The life assessment expression (S, P, T)-N curve is more reliable than the traditional stress-life curve. By measuring the actual temperature, pressure, and vibration stress of the aircraft hydraulic conduits and combining it with the life assessment expression (S, P, T)-N curve, fatigue life assessment can be performed on all conduits of different locations and specifications on the aircraft, and the estimated hydraulic conduit life is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a structural schematic diagram of a life evaluation test system for hydraulic conduit composite working condition bending fatigue according to the present invention.

[0045] Figure 2 This is a structural diagram of a catheter installation fixture of a life evaluation test system for a hydraulic catheter under composite working condition bending fatigue according to the present invention.

[0046] Figure 3 This is a structural diagram of a mounting base of a life evaluation test system for a hydraulic conduit under composite working conditions bending fatigue according to the present invention.

[0047] Figure 4 It is a top view of a mounting base of a life evaluation test system for a hydraulic conduit under composite working conditions bending fatigue according to the present invention.

[0048] Figure 5 This is a cross-sectional view of a mounting seat in a conduit mounting fixture used in a life evaluation test system for a hydraulic conduit under composite working condition bending fatigue according to the present invention.

[0049] Figure 6 This is a structural diagram of a straight-through adapter of a life evaluation test system for a hydraulic conduit under composite working conditions bending fatigue according to the present invention.

[0050] Figure 7 This is an installation effect diagram of a catheter installation fixture and a hydraulic catheter test piece of a life evaluation test system for a hydraulic catheter under composite working conditions bending fatigue of the present invention.

[0051] Figure 8 This is a structural diagram of a hydraulic conduit test piece in a life evaluation test system for a hydraulic conduit under composite working conditions bending fatigue according to the present invention.

[0052] Figure 9 It is a schematic diagram of the oil filling path during the test of a life assessment test system and method for hydraulic conduit composite working condition bending fatigue of the present invention.

[0053] Figure 10 It is a flow chart of a life evaluation test method for a hydraulic conduit under composite working conditions bending fatigue according to the present invention.

[0054] Figure 11 This is an example diagram of the SN curve fitted by combining bending fatigue test data of a certain material conduit under a specific temperature and pressure environment in an application example of the present invention.

[0055] Figure 12 The SN curve of a certain material catheter test piece in an application example of the present invention is obtained under an environment of a temperature of 85° C. and an internal pressure of 28 MPa.

[0056] Figure 13 This is the SN curve obtained for a certain material catheter test piece in an application example of the present invention at a temperature of 135° C. and a catheter internal pressure of 28 MPa.

[0057] Figure 14 This is the SN curve obtained for a catheter test piece made of a certain material in an application example of the present invention at a temperature of 25° C. and an internal pressure of 35 MPa.

[0058] Figure 15 This is the SN curve obtained for a certain material catheter test piece in an application example of the present invention at a temperature of 85°C and an internal pressure of 35 MPa.

[0059] Figure 16 This is the SN curve obtained for a certain material catheter test piece in an application example of the present invention at a temperature of 135° C. and an internal pressure of 35 MPa.

[0060] Among them, 1. Vibration test system; 11. Vibration table; 12. Vibration controller; 13. Acceleration sensor; 2. Catheter mounting fixture; 21. Mounting seat; 22. Annular cavity; 23. Mounting hole; 24. Oil filling port; 25. Base; 26. Straight-through adapter; 3. Hydraulic catheter test piece; 31. Fixed end; 32. Free end; 33. Plug; 4. Strain gauge; 5. Oil pressure pump source; 6. High and low temperature test chamber. DETAILED DESCRIPTION

[0061] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0062] Example 1

[0063] This embodiment provides Figure 1-9 The life evaluation test system for hydraulic conduit composite working condition bending fatigue shown in the figure includes a vibration test system 1, a conduit installation fixture 2, an oil pressure pump source 5 and a stress acquisition and monitoring system.

[0064] The vibration test system 1 includes a vibration table 11, a vibration controller 12 and an acceleration sensor 13. The acceleration sensor 13 is arranged on the table of the vibration table 11; the vibration controller 12 is connected to the vibration table 11 by signal;

[0065] like Figure 2-5 As shown, the catheter mounting fixture 2 includes a mounting seat 21, the bottom of which is fixedly connected to the surface of the vibration table 11. The mounting seat 21 is a hollow cylindrical structure that passes through from top to bottom. An annular cavity 22 is provided inside the hollow cylinder, and a plurality of mounting holes 23 are provided on the outer circumference of the hollow cylindrical structure. The mounting seat 21 is connected to the hydraulic catheter test piece 3 through the mounting holes 23. One end of the hydraulic catheter test piece 3 is a fixed end 31, and the other end of the hydraulic catheter test piece 3 is a free end 32. The fixed end 31 of the hydraulic catheter test piece 3 is connected to the mounting hole 23, and the free end 32 of the hydraulic catheter test piece 3 is installed with a plug 33.

[0066] like Figure 8 As shown, the stress acquisition and monitoring system includes a strain gauge 4 for acquiring stress data of the catheter test piece, and the strain gauge 4 is installed at the fixed end 31 of the catheter test piece;

[0067] The mounting seat 21 is also provided with an oil filling port 24, and the oil pressure pump source 5 is connected to the annular cavity 22 inside the mounting seat 21 through the oil filling port 24;

[0068] The vibration table 11 is also provided with a high and low temperature test box 6 that completely covers the vibration table 11, the catheter installation fixture 2 and the hydraulic catheter test piece 3; the high and low temperature test box 6 is provided with a heating device and a temperature sensor.

[0069] like Figure 9 As shown, in this embodiment, the vibration test system 1 is used to provide a vibration environment of sinusoidal excitation. The vibration is transmitted to the mounting table through the vibration table 11 and finally acts on the hydraulic conduit test piece 3. The vibration controller 12 sends a sinusoidal vibration signal to control the vibration table 11 to generate sinusoidal excitation. The vibration table 11 is equipped with an acceleration sensor 13 to measure the actual vibration acceleration value and feed the vibration acceleration value back to the vibration control controller through the vibration controller 12. The vibration control controller adjusts the output control voltage according to the fed-back measured vibration acceleration value so that the measured vibration acceleration value is consistent with the preset value, thereby completing the vibration closed-loop control.

[0070] The mounting seat 21 is a hollow cylindrical structure that passes through from top to bottom. An annular cavity 22 is provided inside the hollow cylinder, and the annular cavity 22 allows oil to flow inside. The outer circular surface of the hollow cylinder is provided with an outwardly extending oil filling port 24, which is communicated with the annular cavity 22. At the same time, the oil filling port 24 can be connected to the oil pressure pump source 5; the outer wall of the annular boss of the mounting seat 21 has 12 internally threaded mounting holes 23 in a uniform circumferential array, and the mounting holes 23 are communicated with the annular cavity 22.

[0071] The hydraulic conduit test piece 3 is installed on the vibration table 11 through the conduit mounting fixture 2; one end of the hydraulic conduit test piece 3 is a conduit fixed end 31, and the other end is a conduit free end 32, and the conduit free end 32 is installed with a plug 33; the conduit fixed end 31 is connected to the mounting hole 23 through the outer sleeve nut, thereby connecting the hydraulic conduit test piece 3 to the vibration table 11.

[0072] The strain gauge 4 is installed on the fixed end 31 of the catheter test piece, about 5 mm away from the root of the fixed end 31;

[0073] The oil pressure pump source 5 is used to generate an oil pressure environment. During the test, oil is filled into the hydraulic catheter test piece 3 through the catheter mounting fixture 2, and the oil pressure inside the catheter test piece is kept at the working pressure state to be measured. During the test, the oil flows through the oil filling port 24 on the mounting seat 21 through the inner cavity of the mounting seat 21 and the hydraulic catheter test piece 3, reaches the interior of the hydraulic catheter test piece 3, fills all the hydraulic catheter test pieces 3, and forms oil pressure.

[0074] The high and low temperature test box 6 is used to generate a temperature environment. The high and low temperature test box 6 is installed on the vibration table 11 and completely covers the catheter test piece and the catheter installation fixture 2, so that the temperature environment of the catheter test piece during the test is consistent with that during actual operation.

[0075] Example 2

[0076] The difference between this embodiment and embodiment 1 is that, in this embodiment, Figure 2-5As shown, a base 25 for fixedly connecting to the vibration table 11 is provided at the bottom of the mounting seat 21. The base 25 is a circular ring structure. The bottom surface of the circular ring structure is fixedly connected to the table surface of the vibration table 11, and the top surface of the circular ring is integrally formed with the mounting seat 21. The rest of the structure is the same as that of Example 1.

[0077] In this embodiment, the mounting seat 21 and the base 25 are jointly an annular structure formed by rotating an inverted "T"-shaped cross-section, which is composed of an annular base 25 and an annular boss; the annular base 25 of the mounting seat 21 is designed with two circles of through holes in a circumferential array, which are the vibration table 11 connection mounting holes 23, and the mounting seat 21 and the vibration table 11 are connected by bolts through the vibration table 11 connection mounting holes 23. The vibration table 11 connection mounting holes 23 are distributed on the inner and outer sides of the mounting seat 21, which can make the fixture have good stability in a vibration environment.

[0078] Example 3

[0079] The difference between this embodiment and embodiment 1 is that, in this embodiment, Figure 6-8 As shown, the fixed end 31 of the hydraulic conduit test piece 3 is connected to the mounting hole 23 via a straight-through adapter 26;

[0080] The inner end of the mounting hole 23 is a 37° sealing cone surface; the end of the straight-through adapter 26 mounting seat 21 connecting end is a 37 sealing cone surface that closely matches the short sealing cone surface in the mounting hole 23.

[0081] The straight-through adapter 26 has two ends, one for connecting to the mounting base 21 and the other for connecting to the conduit, both of which are threaded. A hexagonal bolt head is located in the middle for easy installation with a wrench. The through end of the straight-through adapter 26 is threadedly connected to the mounting base 21. The remaining structure is the same as in Example 1.

[0082] In this embodiment, the 37° sealing cone surface of the mounting hole 23 and the straight-through adapter 26 can ensure good sealing performance of the connection interface under high oil pressure and vibration environments; the catheter connection end of the straight-through adapter 26 can be designed with different sizes and structures according to different test catheter specifications; when using catheters of different specifications to conduct tests, there is no need to replace the entire mounting fixture; only the straight-through adapter 26 needs to be replaced to enable simultaneous testing of catheters of different specifications.

[0083] The conduit connection end of the straight-through adapter 26 can be designed with different sizes and structures to accommodate different test conduit specifications. When testing with conduits of varying specifications, the entire mounting fixture need not be replaced; simply replacing the straight-through adapter 26 allows for simultaneous testing of conduits of varying specifications. The conduit mounting fixture 2 in this embodiment can simultaneously mount twelve hydraulic conduit test pieces 3, supplying hydraulic pressure to each of the twelve test pieces and securing them to the vibration table 11.

[0084] Example 4

[0085] Compared with Example 1, the present embodiment differs in that, in the present embodiment, a pressure gauge for real-time monitoring of the supply pressure is provided on the oil pressure pump source 5; a through hole is provided on the high and low temperature test box 6, and the oil filling pipe of the oil pressure pump source 5, the measuring wire of the strain gauge 4 and the measuring wire of the acceleration sensor 13 are connected to the mounting fixture, the strain gauge 4 and the acceleration sensor 13 installed inside the high and low temperature test box 6 through the through hole; the remaining structure is the same as that of Example 1.

[0086] In this embodiment, a pressure gauge for real-time monitoring of the supply pressure is provided on the oil pressure pump source 5. The pressure gauge is used to monitor in real time whether the supply pressure of the oil pressure pump source 5 is reduced. When the supply pressure of the oil pressure pump source 5 is significantly reduced, it can be indicated that the hydraulic catheter test piece 3 has leaked during the bending fatigue test.

[0087] By providing a through hole on the high and low temperature test box 6, it is convenient to assemble the life evaluation test system of the hydraulic conduit composite working condition bending fatigue and prepare for the evaluation test.

[0088] Example 5

[0089] This embodiment provides Figure 9 A hydraulic conduit composite working condition bending fatigue life assessment test method is shown, wherein the hydraulic conduit composite working condition bending fatigue life assessment test system is used to perform a hydraulic conduit composite working condition bending fatigue life assessment test on a hydraulic conduit test piece 3, including the following steps:

[0090] S1. Evaluation test preparation: Assemble the life evaluation test system for hydraulic pipe composite working condition bending fatigue and prepare for the evaluation test, including:

[0091] Connect the fixed end 31 of the hydraulic conduit test piece 3 to the mounting table, install a plug 33 on the free end 32 of the hydraulic conduit test piece 3, and install a strain gauge 4 on the fixed end 31 of the hydraulic conduit test piece 3. Install the high and low temperature test chamber 6 on the vibration table 11, and completely cover the test conduit and the fixture.

[0092] S2. Simulating the test environment: adjusting the temperature in the high and low temperature test chamber 6 and the supply pressure of the oil pressure pump source 5 to simulate the test environment of the hydraulic catheter test piece 3;

[0093] S3. Adjust the reading of strain gauge 4: set the initial reading of strain gauge 4 under the simulated test environment to "0";

[0094] S4. Start the bending fatigue test: The vibration controller 12 sends a sinusoidal fixed-frequency signal according to the vibration stress value set by the vibration controller 12, and adjusts the vibration amplitude through the vibration console so that the stress reaches a predetermined level. The bending fatigue test is performed, the stress at the root of the catheter is monitored, and the number of vibrations is recorded;

[0095] The step S4 further includes: performing fatigue tests multiple times on the hydraulic conduit test piece 3 of the same specification by setting different vibration stress values ​​and simulating test environments;

[0096] S5. Bending fatigue test completed: The vibration controller sets the number of vibrations, and the hydraulic conduit test piece 3 that leaks during vibration is disassembled until all hydraulic conduit test pieces 3 leak or the hydraulic conduit test piece 3 vibrates for more than the measured number of vibrations under the current stress without leaking, and the vibration bending fatigue test is completed.

[0097] The step S5 further includes: observing the pressure gauge on the oil pressure pump source 5 during the bending fatigue test; when the pressure on the pressure gauge drops to 85% of the initial value, pausing the test to observe whether the hydraulic conduit test piece 3 leaks; if the hydraulic conduit test piece 3 leaks, removing the leaking hydraulic conduit test piece 3 and plugging the leaking mounting hole 23 with a plug 33; if the hydraulic conduit test piece 3 does not leak, re-punching the hydraulic conduit test piece 3 to ensure that the pressure inside the hydraulic conduit test piece is at the pressure under the simulated test environment, and continuing the bending fatigue test;

[0098] S6. Obtaining the (S, P, T)-N curve: After all bending fatigue tests are completed, the number of cycles of the hydraulic conduit test piece 3 is counted, and the stress-life curve of the hydraulic conduit test piece 3 under the simulated test environment is obtained, and its expression is fitted;

[0099] In step S6, obtaining the stress-life curve specifically includes the following steps:

[0100] S61, statistically calculating the average vibration cycle number N of the hydraulic conduit test piece (3);

[0101] The average number of vibration cycles is calculated by the following formula:

[0102]

[0103] Where n is the number of test samples of the hydraulic conduit test piece, N i is the number of vibration cycles of the i-th hydraulic conduit test piece;

[0104] S62, fitting the stress-life curves of the hydraulic conduit test piece (3) under different simulated test environments by averaging the number of vibration cycles under different stress conditions under the same simulated test environment;

[0105] S63. The relationship between the bending fatigue life of the hydraulic conduit test piece (3) and temperature, pressure, and stress is fitted through stress-life curves under different simulated test environments. The expression is named (S, P, T)-N curve, which is expressed as:

[0106] N=f(S,P,T)

[0107] Where N is the average number of vibration cycles of the hydraulic conduit test piece, S is the vibration stress, P is the internal pressure of the conduit, and T is the ambient temperature of the conduit;

[0108] S7. Life Assessment: By measuring the temperature, pressure, and vibration stress values ​​of ducts of different specifications and installation positions on the aircraft under actual operating conditions, combined with the (S, P, T)-N curves obtained from the test, the bending fatigue life of hydraulic ducts of different specifications and installation positions on the aircraft can be assessed.

[0109] Application Examples

[0110] This application example conducts a hydraulic conduit composite bending fatigue life assessment test on a conduit made of a certain material under a specific temperature and pressure environment. The hydraulic conduit composite bending fatigue life assessment test method includes the following steps:

[0111] S1. Preparation for the evaluation test: Connect the fixed end 31 of the hydraulic conduit test piece 3 to the mounting table, install the plug 33 on the free end 32 of the hydraulic conduit test piece 3, and install the strain gauge 4 on the hydraulic conduit test piece 3 approximately 5 mm from the base of the fixed end 31. Install the high and low temperature test chamber 6 on the vibration table 11, and completely cover the test conduit and fixture.

[0112] S2. Simulating the test environment: adjusting the temperature in the high and low temperature test chamber 6 and the supply pressure of the oil pressure pump source 5 to simulate the test environment of the hydraulic catheter test piece 3;

[0113] S3. Adjust the reading of strain gauge 4: set the initial reading of strain gauge 4 under the simulated test environment to "0";

[0114] S4. Start the bending fatigue test: The vibration controller 12 sends a sinusoidal fixed-frequency signal according to the vibration stress value set by the vibration controller 12, and adjusts the vibration amplitude through the vibration console so that the stress reaches a predetermined level. The bending fatigue test is performed, the stress at the root of the catheter is monitored, and the number of vibrations is recorded;

[0115] The step S4 further includes: performing fatigue tests multiple times on the hydraulic conduit test piece 3 of the same specification by setting different vibration stress values ​​and simulating test environments;

[0116] S5. Bending fatigue test completed: The vibration controller sets the number of vibrations, and the hydraulic conduit test piece 3 that leaks during vibration is disassembled until all hydraulic conduit test pieces 3 leak or the hydraulic conduit test piece 3 vibrates for more than the measured number of vibrations under the current stress without leaking, and the vibration bending fatigue test is completed.

[0117] The step S5 further includes: observing the pressure gauge on the oil pressure pump source 5 during the bending fatigue test; when the pressure on the pressure gauge drops to 85% of the initial value, pausing the test to observe whether the hydraulic conduit test piece 3 leaks; if the hydraulic conduit test piece 3 leaks, removing the leaking hydraulic conduit test piece 3 and plugging the leaking mounting hole 23 with a plug 33; if the hydraulic conduit test piece 3 does not leak, re-punching the hydraulic conduit test piece 3 to ensure that the pressure inside the hydraulic conduit test piece is at the pressure under the simulated test environment, and continuing the bending fatigue test;

[0118] S6. Obtaining the (S, P, T)-N curve: After all bending fatigue tests are completed, the number of cycles of the hydraulic conduit test piece 3 is counted, and the stress-life curve of the hydraulic conduit test piece 3 under the simulated test environment is obtained, and its expression is fitted;

[0119] In step S6, obtaining the stress-life curve specifically includes the following steps:

[0120] S61. Statistically calculate the average number of vibration cycles N of the hydraulic conduit test piece;

[0121] The average number of vibration cycles is calculated by the following formula:

[0122]

[0123] Where n is the number of test samples of the hydraulic conduit test piece, N i is the number of vibration cycles of the i-th hydraulic conduit test piece;

[0124] S62. fitting the stress-life curves of the hydraulic conduit test piece under different simulated test environments by averaging the number of vibration cycles under different stress conditions under the same simulated test environment;

[0125] S63. The relationship between the bending fatigue life of the hydraulic conduit test piece and temperature, pressure, and stress is fitted by the stress-life curves under different simulated test environments. This expression is named the (S, P, T)-N curve, which is expressed as:

[0126] N=f(S,P,T)

[0127] Where N is the average number of vibration cycles of the hydraulic conduit test piece, S is the vibration stress, P is the internal pressure of the conduit, and T is the ambient temperature of the conduit;

[0128] In this application example, to estimate and evaluate fatigue strength or fatigue life, a relationship needs to be established that relates life to external load. The curve that reflects the relationship between external load S and specimen life N is called a stress-life curve, also known as a SN curve or Wöhler curve.

[0129] Figure 11 In this application example, a certain material catheter test piece is placed at a temperature of 20°C and an internal pressure of 28 MPa. By fitting the catheter bending fatigue test data, the SN curve under a specific temperature and pressure environment can be obtained. Figure 11 As shown in Figure 2, when the stress level of the conduit is above 600 MPa, the fatigue life of the specimen increases slowly as the stress level decreases. For example, when the vibration stress level of the conduit is 700 MPa, its vibration cycle fatigue life is 10 5 When the vibration stress level of the conduit is 650 MPa, its vibration cycle fatigue life is 3×10 5 When the stress level is lower than 600MPa, the fatigue life of the specimen increases sharply as the stress decreases. When the vibration stress level of the conduit is less than or equal to 480MPa, the fatigue life of the specimen increases sharply as the stress decreases. 7 After the vibration cycle, the catheter test piece still did not leak. At this specific temperature and pressure, the stress limit value of the catheter without leakage is 480 MPa.

[0130] Figure 12 This is the SN curve of a certain material catheter test piece in this application example, obtained at a temperature of 85°C and an internal pressure of 28 MPa.

[0131] Figure 13 This is the SN curve of a certain material catheter test piece in this application example, obtained at a temperature of 135°C and an internal pressure of 28 MPa.

[0132] Figure 14 This is the SN curve of a certain material catheter test piece in this application example, obtained at a temperature of 25°C and an internal pressure of 35 MPa.

[0133] Figure 15 This is the SN curve of a certain material catheter test piece in this application example obtained at a temperature of 85°C and an internal pressure of 35 MPa.

[0134] Figure 16 This is the SN curve of a certain material catheter test piece in this application example obtained at a temperature of 135°C and an internal pressure of 35 MPa.

[0135] The (S, P, T)-N curve can be obtained by repeating the catheter bending fatigue test under different temperature and pressure environments and fitting the SN curve under different temperature and pressure environments.

[0136] S7. Life evaluation: The bending fatigue life of the catheter test piece made of a certain material in this application example can be evaluated using the (S, P, T)-N curve obtained in step S6.

[0137] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. A life assessment test system for hydraulic pipe composite working condition bending fatigue, characterized by: It includes a vibration test system (1), a catheter installation fixture (2), an oil pressure pump source (5) and a stress acquisition and monitoring system. The vibration test system (1) comprises a vibration table (11), a vibration controller (12) and an acceleration sensor (13), wherein the acceleration sensor (13) is arranged on the table surface of the vibration table (11); the vibration controller (12) is connected to the vibration table (11) via signals; The catheter mounting fixture (2) includes a mounting seat (21), the bottom of the mounting seat (21) is fixedly connected to the table top of the vibration table (11), the mounting seat (21) is a hollow cylindrical structure that passes through from top to bottom, and an annular cavity (22) is provided inside the hollow cylinder. The outer surface of the hollow cylindrical structure is provided with a plurality of mounting holes (23); the mounting seat (21) is connected to the hydraulic conduit test piece (3) through the mounting holes (23); one end of the hydraulic conduit test piece (3) is a fixed end (31); the other end of the hydraulic conduit test piece (3) is a free end (32); the fixed end (31) of the hydraulic conduit test piece (3) is connected to the mounting holes (23); and a plug (33) is installed at the free end (32) of the hydraulic conduit test piece (3); The stress acquisition and monitoring system comprises a strain gauge (4) for acquiring stress data of the catheter test piece, wherein the strain gauge (4) is mounted on a fixed end (31) of the catheter test piece; The mounting seat (21) is also provided with an oil filling port (24), and the oil pressure pump source (5) is connected to the annular cavity (22) inside the mounting seat (21) through the oil filling port (24); The vibration table (11) is also provided with a high and low temperature test box (6) that completely covers the vibration table (11), the catheter installation fixture (2) and the hydraulic catheter test piece (3); a heating device is provided in the high and low temperature test box (6).

2. The hydraulic pipe composite working condition bending fatigue life assessment test system according to claim 1 is characterized by: The bottom of the mounting seat (21) is provided with a base (25) for fixed connection with the vibration table (11); the base (25) is a circular ring structure; the bottom surface of the circular ring structure is fixedly connected to the table surface of the vibration table (11); the top surface of the circular ring is integrally formed with the mounting seat (21).

3. The hydraulic pipe composite working condition bending fatigue life assessment test system according to claim 1 is characterized by: The fixed end (31) of the hydraulic conduit test piece (3) is connected to the mounting hole (23) via a straight-through adapter (26).

4. The hydraulic pipe composite working condition bending fatigue life assessment test system according to claim 3 is characterized by: The inner end of the mounting hole (23) is a 37° sealing cone surface; the end of the connecting end of the straight-through adapter (26) mounting seat (21) is a 37° sealing cone surface that closely matches the short sealing cone surface in the mounting hole (23).

5. The hydraulic pipe composite working condition bending fatigue life assessment test system according to claim 3 is characterized by: The two ends of the straight-through adapter (26) are respectively the mounting seat (21) connection end and the conduit connection end and both are provided with threads, and the middle is a hexagonal bolt head; the straight-through adapter (26) mounting seat (21) is connected to the mounting seat (21) through the end using threads.

6. The hydraulic pipe composite working condition bending fatigue life assessment test system according to claim 1 is characterized by: The oil pressure pump source (5) is provided with a pressure gauge for real-time monitoring of the supply pressure.

7. The hydraulic conduit composite working condition bending fatigue life assessment test system according to claim 1 is characterized by: The high and low temperature test box (6) is provided with a through hole, and the oil filling pipe of the oil pressure pump source (5), the strain gauge (4) measuring wire and the acceleration sensor (13) measuring wire are connected to the installation fixture, the strain gauge (4) and the acceleration sensor (13) inside the high and low temperature test box (6) through the through hole.

8. A life assessment test method for hydraulic conduit under combined working conditions bending fatigue, characterized by: A hydraulic conduit composite working condition bending fatigue life assessment test system according to any one of claims 1 to 7 is used to perform a hydraulic conduit composite working condition bending fatigue life assessment test on a hydraulic conduit test piece (3), comprising the following steps: S1. Preparation for evaluation test: Assemble the life evaluation test system for hydraulic pipe composite working condition bending fatigue and prepare for evaluation test. S2. Simulating the test environment: adjusting the temperature in the high and low temperature test chamber (6), adjusting the supply pressure of the oil pressure pump source (5), and simulating the test environment of the hydraulic conduit test piece (3); S3. Adjust the reading of the strain gauge (4): set the initial reading of the strain gauge (4) under the simulated test environment to "0"; S4, starting the bending fatigue test: by setting the vibration stress value through the vibration controller (12), the vibration controller (12) sends a sinusoidal fixed-frequency signal, and the vibration amplitude is adjusted by the vibration control console so that the stress reaches a predetermined level, and the bending fatigue test is performed, the stress at the root of the catheter is monitored, and the number of vibrations is recorded; S5. Completion of the bending fatigue test: the vibration number is set by the vibration controller, and the hydraulic conduit test piece (3) leaking during the vibration is disassembled until all the hydraulic conduit test pieces (3) leak or the hydraulic conduit test piece (3) vibrates more than the measured number of times under the current stress without leakage, and the vibration bending fatigue test is completed; S6. Obtaining the (S, P, T)-N curve: After the bending fatigue test is completed, the number of cycles of the hydraulic conduit test piece (3) is counted, and the stress-life curve of the hydraulic conduit test piece (3) under the simulated test environment is obtained, and its expression is fitted; S7. Life Assessment: By measuring the temperature, pressure, and vibration stress values ​​of ducts of different specifications and installation positions on the aircraft under actual operating conditions, combined with the (S, P, T)-N curves obtained from the test, the bending fatigue life of hydraulic ducts of different specifications and installation positions on the aircraft can be assessed.

9. The life evaluation test method for hydraulic pipe composite working condition bending fatigue according to claim 8, characterized in that: In step S1, the evaluation test preparation specifically includes: connecting the fixed end (31) of the hydraulic conduit test piece (3) to the mounting table, installing a plug (33) on the free end (32) of the hydraulic conduit test piece (3), installing a strain gauge (4) on the fixed end (31) of the hydraulic conduit test piece (3), installing a high and low temperature test chamber (6) on the vibration table (11), and completely covering the test conduit and the fixture.

10. The life evaluation test method for hydraulic pipe composite working condition bending fatigue according to claim 8, characterized in that: The step S4 also includes: setting different vibration stress values ​​and simulating test environments for the hydraulic conduit test pieces (3) of the same specifications to perform fatigue tests multiple times.

11. The life evaluation test method for hydraulic pipe composite working condition bending fatigue according to claim 8, characterized in that: The step S5 further includes: observing the pressure gauge on the oil pressure pump source (5) during the bending fatigue test; when the pressure on the pressure gauge drops to 85% of the initial value, pausing the test to observe whether the hydraulic conduit test piece (3) leaks; if the hydraulic conduit test piece (3) leaks, removing the leaking hydraulic conduit test piece (3), plugging the leaking mounting hole (23) with a plug (33); if the hydraulic conduit test piece (3) does not leak, re-punching the hydraulic conduit test piece (3) to make the pressure inside the hydraulic conduit test piece equal to the pressure under the simulated test environment, and continuing the bending fatigue test.

12. The life evaluation test method for hydraulic pipe composite working condition bending fatigue according to claim 8, characterized in that: In step S6, obtaining the stress-life curve specifically includes the following steps: S61. Statistically calculate the average number of vibration cycles N of the hydraulic conduit test piece; The average number of vibration cycles is calculated by the following formula: Where n is the number of test samples of the hydraulic conduit test piece, N i is the number of vibration cycles of the i-th hydraulic conduit test piece; S62. fitting the stress-life curves of the hydraulic conduit test piece under different simulated test environments by averaging the number of vibration cycles under different stress conditions under the same simulated test environment; S63. The relationship between the bending fatigue life of the hydraulic conduit test piece and temperature, pressure, and stress is fitted by the stress-life curves under different simulated test environments. This expression is named the (S, P, T)-N curve, which is expressed as: N=f(S,P,T) Where N is the average number of vibration cycles of the hydraulic conduit test piece, S is the vibration stress, P is the internal pressure of the conduit, and T is the ambient temperature of the conduit.

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