Aircraft hydraulic conduit high-cycle fatigue performance test assembly and method

Abstract

The invention discloses an aircraft hydraulic conduit high cycle fatigue performance test assembly and method, and relates to the conduit fatigue performance test field, and the test assembly comprises a pipe arc fatigue sample and a clamping assembly; the pipe arc fatigue test sample belongs to one part of the aircraft hydraulic conduit; the pipe arc fatigue test sample is of a dumbbell-like pipe arc structure with a narrow middle part and two wide ends; the pipe arc fatigue test sample comprises a hole-free pipe arc fatigue test sample or a pipe arc fatigue test sample with an elliptical hole; an elliptical hole is formed in the middle of the pipe arc fatigue sample with the elliptical hole; the non-porous pipe arc fatigue test sample is used for a tension-tension fatigue test, and the elliptical hole pipe arc fatigue test sample is used for a tension-compression fatigue test; the clamping assembly comprises a clamping block, a positioning rod and a pin, the clamping block abuts against the pipe arc fatigue sample, and the positioning rod penetrates through the clamping block and is in clearance fit with the clamping block; a rectangular hole is formed in the positioning rod, and the pin penetrates through the rectangular hole of the positioning rod and is in clearance fit with the positioning rod; according to the invention, the fatigue characteristics of the aircraft hydraulic conduit can be directly reflected, the pipe arc fatigue test sample is not easy to break when being clamped, the axial torsion of the test sample is prevented, and data support is provided for the fatigue test and characterization mode of the aircraft hydraulic conduit.

Description

Technical Field

[0001] This invention relates to the field of duct fatigue performance testing, specifically to a component and method for testing the high-cycle fatigue performance of aircraft hydraulic ducts. Background Technology

[0002] In related technologies, piping components, acting as vital lifelines for media and energy transmission, are critical and fundamental components widely used in aircraft. Hydraulic conduits, in particular, operate at the highest pressures and have the most stringent reliability requirements within the entire piping system. During service, they are subjected to the combined loads of internal fluid pressure and high-frequency vibrations from the aircraft's structural framework, making them prone to fatigue failure that compromises structural integrity. This can lead to leaks and other problems in aircraft hydraulic lines, directly impacting overall aircraft performance and flight safety. Therefore, to improve the reliability of aircraft hydraulic lines, the fatigue characteristics of the conduits themselves must be fully considered.

[0003] In related technologies, the rotational bending fatigue test of aircraft hydraulic pipelines only tests the pipe connection components. Due to the coupling influence of multiple factors such as pipe joint structure and connection process, the test results cannot directly reflect the fatigue characteristics of the conduit itself. It only plays the role of component performance evaluation and reverse correction, and is difficult to help the forward design of hydraulic pipeline forming.

[0004] Therefore, there is an urgent need for methods to test the fatigue performance of aircraft hydraulic ducts. Summary of the Invention

[0005] In view of this, the present invention provides a high-cycle fatigue performance testing component and method for aircraft hydraulic conduits, in order to solve the technical problems in related technologies where it is impossible to directly test the fatigue characteristics of the aircraft hydraulic conduits themselves, and where the clamping section of the aircraft hydraulic conduits is prone to breakage.

[0006] In a first aspect, the present invention provides a high-cycle fatigue performance testing assembly for aircraft hydraulic conduits, comprising: a pipe arc fatigue specimen and a clamping assembly; the pipe arc fatigue specimen is part of the aircraft hydraulic conduit; the pipe arc fatigue specimen is a dumbbell-shaped pipe arc structure that is narrow in the middle and wide at both ends; the pipe arc fatigue specimen includes a non-porous pipe arc fatigue specimen or a pipe arc fatigue specimen with an elliptical hole; the pipe arc fatigue specimen with an elliptical hole has an elliptical hole in the middle; the non-porous pipe arc fatigue specimen is used for tensile fatigue testing, and the pipe arc fatigue specimen with an elliptical hole is used for tensile-compression fatigue testing; the clamping assembly includes a first clamping block, a second clamping block, a first positioning rod, a second positioning rod, a first pin, and a second pin, the first clamping block and the second clamping block both abut against the pipe arc fatigue specimen, the first positioning rod passes through the first clamping block and is clearance-fitted with the first clamping block, the second positioning rod passes through the second clamping block and is clearance-fitted with the second clamping block; both the first positioning rod and the second positioning rod have rectangular holes, the first pin passes through the rectangular hole of the first positioning rod and is clearance-fitted with the first positioning rod; the second pin passes through the rectangular hole of the second positioning rod and is clearance-fitted with the second positioning rod.

[0007] In one optional embodiment, the tube arc fatigue specimen is a tube arc structure obtained by first cutting along a first plane of the aircraft hydraulic conduit and then cutting a transition arc along a second plane; the first plane is a plane parallel to the central axis of the aircraft hydraulic conduit and at a predetermined distance; the first plane and the second plane are perpendicular; the center of the transition arc is on the cross-section at 1 / 2 of the axial direction of the aircraft hydraulic conduit; the radius of the transition arc of the tube arc fatigue specimen with an elliptical hole is greater than the radius of the transition arc of the tube arc fatigue specimen without a hole; the center of the elliptical hole is located at the midpoint of the line connecting the centers of the two transition arcs, the minor axis of the elliptical hole is perpendicular to the central axis of the aircraft hydraulic conduit, and the major axis of the elliptical hole is parallel to the central axis of the aircraft hydraulic conduit.

[0008] In one optional embodiment, the tube arc fatigue specimen includes a clamping section, a transition section, and a test section; both the clamping section and the transition section are tube arcs with the same inner and outer radii as the aircraft hydraulic conduits; the arc length of the clamping section is greater than or equal to the arc length of the transition section; the arc length of the transition section decreases sequentially along the axial direction and then increases sequentially; the test section is the cross-section corresponding to the minimum arc length of the transition section; the arc length of the transition section of the tube arc fatigue specimen with elliptical holes is greater than the arc length of the transition section of the tube arc fatigue specimen without holes.

[0009] In one optional embodiment, the preset distance is 1 / 2 to 3 / 4 of the outer wall radius of the aircraft hydraulic conduit; the area of ​​the test section of the non-porous tube arc fatigue specimen and the tube arc fatigue specimen with elliptical hole is less than 1 / 3 and 1 / 2 of the cross-sectional area of ​​the clamping section, respectively.

[0010] In one alternative embodiment, the surface roughness of both the transition arc and the elliptical hole is less than Ra0.2.

[0011] In one optional embodiment, the first clamping block is a cylinder with a crescent-shaped cross-section; the second clamping block is a cylinder with a sycee-shaped cross-section; the cross-sections of the first clamping block, the second clamping block, and the clamping section together form a circular cross-section; both the first and second clamping blocks include a contact surface and a clamping surface; the contact surfaces of the first and second clamping blocks respectively contact the outer and inner walls of the clamping section of the tube arc fatigue specimen; the clamping surfaces of the first and second clamping blocks are adapted to cooperate with the fixtures of the fatigue performance testing device to fix the tube arc fatigue specimen on the fatigue performance testing device; both the first and second clamping blocks include circular positioning holes of the same size; the first positioning rod passes through the circular positioning hole of the first clamping block and is clearance-fitted with the first clamping block; the second positioning rod passes through the circular positioning hole of the second clamping block and is clearance-fitted with the second clamping block; the clamping surfaces of the first and second clamping blocks are provided with a groove in the middle, and the first and second clamping blocks together form an annular groove after being fitted together.

[0012] In one optional embodiment, the center of the circular cross-section is on the same axis as the center point of the test cross-section; the portions of the first clamping block and the second clamping block near the end of the test cross-section and in contact with the clamping section have rounded chamfered structures.

[0013] Secondly, the present invention also provides a method for testing the high-cycle fatigue performance of aircraft hydraulic conduits, applied to the high-cycle fatigue performance testing assembly for aircraft hydraulic conduits as described in any one of claims 1-7, comprising: The fatigue test of the tube arc fatigue specimen was carried out using a stress control method; the tube arc fatigue specimen included a non-porous tube arc fatigue specimen or a tube arc fatigue specimen with an elliptical hole. Based on the fatigue test results, calculate the average stress of the test section, and plot the first fitted SN curve based on the average stress of the test section; Construct a finite element model of a tube arc fatigue specimen under axial loading; Based on the finite element model of axial loading of tube arc fatigue specimen, the local maximum stress of the test section is obtained, and the second fitted SN curve is plotted based on the local maximum stress of the test section. Based on the first and second fitted SN curves, the fatigue life boundary of high failure risk points of pipes used in aircraft hydraulic pipelines is predicted.

[0014] In one optional embodiment, the formula for calculating the average stress of the test section of the non-porous tubular arc fatigue specimen is as follows: ; ; ; ; ; ; ; in, w The width of the test section of the tube arc fatigue specimen. d This refers to the inner diameter of the aircraft's hydraulic lines. D The outer diameter of the aircraft's hydraulic lines. S The area of ​​the test section, mean For average stress, L For load.

[0015] In one optional embodiment, the formula for calculating the average stress of the test section of the tube arc fatigue specimen with elliptical holes is obtained by reasoning and transformation based on the formula for calculating the average stress of the test section of the tube arc fatigue specimen without holes.

[0016] In one optional embodiment, the stress ratio of the stress control method for the non-porous tube arc fatigue specimen and the tube arc fatigue specimen with elliptical holes is greater than or equal to 0.1 and -1, respectively, the cyclic loading frequency is 10~25Hz, and the number of repeated experiments for each stress point is at least 1.

[0017] Based on the fact that test results in related technologies cannot directly reflect the fatigue characteristics of aircraft hydraulic conduits and that the conduit clamping ends are prone to breakage, this invention proposes a high-cycle fatigue performance testing method for aircraft hydraulic conduits. By specially treating the size and shape of the pipe arc fatigue specimen and the clamping assembly, and combining theoretical calculations and numerical simulations of finite element models, fatigue data support is provided for the life assessment of aircraft hydraulic pipelines. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a three-dimensional structural view of a high-cycle fatigue performance testing assembly for aircraft hydraulic conduits according to an embodiment of the present invention. Figure 2 This is a front view of a non-porous tubular arc fatigue specimen according to an embodiment of the present invention; Figure 3This is a three-dimensional structural view of a non-porous tubular arc fatigue specimen according to an embodiment of the present invention; Figure 4 This is a top view of the first clamping block and the second clamping block according to an embodiment of the present invention; Figure 5 This is a perspective view of the structure after the first clamping block and the second clamping block are separated according to an embodiment of the present invention; Figure 6 This is a perspective view of the structure after the first clamping block and the second clamping block are combined according to an embodiment of the present invention. Figure 7 This is a three-dimensional view of the arc fatigue specimen with an elliptical hole according to an embodiment of the present invention; Figure 8 This is a schematic flowchart of a high-cycle fatigue performance testing method for aircraft hydraulic conduits according to an embodiment of the present invention. Figure 9 This is a stress distribution diagram of a test section of a tube arc fatigue specimen under axial loading according to an embodiment of the present invention; Figure 10 It is a graph showing the variation of the average stress and local maximum stress of the test section with load according to an embodiment of the present invention; Figure 11 This is a fitted SN curve diagram of the average stress and local maximum stress of the test section according to an embodiment of the present invention; Figure label: 1. Fatigue specimen of tube without pores; 11. Transition arc; 12. Clamping section; 13. Transition section; 14. Test section; 2. Clamping assembly; 21. First clamping block; 22. Second clamping block; 23. First positioning bar; 24. Second positioning bar; 25. First pin; 26. Second pin; 27. Rectangular hole; 28. Fitting surface; 29. ​​Clamping surface; 291. Groove; 30. Circular positioning hole; 31. Rounded chamfer structure; 4. Fatigue specimen of tube with elliptical hole; 41. Elliptical hole. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions for tensile-tensile fatigue testing of non-porous tubular arc fatigue specimens in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. For tensile-tensile and tensile-compression fatigue testing of tubular arc fatigue specimens with elliptical holes, only the stress ratio setting needs to be changed; the remaining procedures can be performed with reference to the above technical solutions. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the purpose of simplifying the description of this invention and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0024] Figure 1 This invention illustrates a high-cycle fatigue performance testing assembly for aircraft hydraulic piping, comprising: a pipe arc fatigue specimen and a clamping assembly 2; the pipe arc fatigue specimen is part of the aircraft hydraulic conduit; the pipe arc fatigue specimen has a dumbbell-shaped pipe arc structure that is narrow in the middle and wide at both ends, and includes a non-porous pipe arc fatigue specimen 1 or a pipe arc fatigue specimen 4 with elliptical holes, respectively as shown in the figure. Figure 2 and Figure 7 As shown; wherein, the tube arc fatigue specimen with elliptical hole has an elliptical hole 41 in the middle; the tube arc fatigue specimen 1 without hole is used for tensile fatigue testing, and the tube arc fatigue specimen 4 with elliptical hole is used for tensile-compression fatigue testing; the clamping assembly 2 includes a first clamping block 21, a second clamping block 22, a first positioning rod 23, a second positioning rod 24, a first pin 25, and a second pin 26; the first clamping block 21 and the second clamping block 22 both abut against the tube arc fatigue specimen 1, the first positioning rod 23 passes through the first clamping block 21 and is clearance-fitted with the first clamping block 21, and the second positioning rod 24 passes through the second clamping block 22 and is clearance-fitted with the second clamping block 22; both the first positioning rod 23 and the second positioning rod 24 are provided with rectangular holes 27, the first pin 25 passes through the rectangular hole 27 of the first positioning rod 23 and is clearance-fitted with the first positioning rod 23; the second pin 26 passes through the rectangular hole 27 of the second positioning rod and is clearance-fitted with the second positioning rod 24.

[0025] It should be noted that the clearance fit distance needs to be small enough.

[0026] In one optional embodiment, the pipe arc fatigue specimen is a pipe arc structure obtained by first cutting along the first plane of the aircraft hydraulic conduit and then cutting a transition arc 11 along the second plane; the first plane is a plane parallel to the central axis of the aircraft hydraulic conduit and at a predetermined distance; the first plane and the second plane are perpendicular; the center of the transition arc 11 is on the cross section at 1 / 2 of the axial direction of the aircraft hydraulic conduit; the radius of the transition arc 11 of the pipe arc fatigue specimen 4 with elliptical hole is larger than the radius of the transition arc 11 of the pipe arc fatigue specimen 1 without hole; the center of the elliptical hole 41 is located at the middle position of the line connecting the centers of the two transition arcs 11, the minor axis of the elliptical hole 41 is perpendicular to the central axis of the aircraft hydraulic conduit, and the major axis of the elliptical hole 41 is parallel to the central axis of the aircraft hydraulic conduit.

[0027] Specifically, the pipe fatigue test specimen is a dumbbell-shaped pipe arc structure. First, the entire aircraft hydraulic conduit is cut into a pipe arc along the first plane along the axial direction. Then, transition arcs are machined on both sides of the pipe arc. The second plane (i.e., the sectional plane) of the transition arcs on both sides is symmetrical along the central axis of the original aircraft hydraulic conduit and is perpendicular to the first plane (i.e., the axial sectional plane).

[0028] Among them, such as Figure 2 As shown, the black dot represents the center of the transition arc 11, which is located on the cross-section at 1 / 2 of the axial direction of the aircraft hydraulic line.

[0029] In one optional embodiment, the pipe arc fatigue specimen includes a clamping section 12, a transition section 13, and a test section 14; both the clamping section 12 and the transition section 13 are pipe arcs with the same inner and outer radii as the aircraft hydraulic conduits; the arc length of the clamping section 12 is greater than or equal to the arc length of the transition section 13; the arc length of the transition section 13 decreases sequentially along the axial direction and then increases sequentially; the test section 14 is the cross-section corresponding to the minimum arc length of the transition section.

[0030] Among them, such as Figure 2 and Figure 3 As shown, taking the non-porous tubular arc fatigue specimen 1 as an example, there are two clamping sections 12, which are respectively connected to the two ends of the transition arc 11; the transition section 13 is the part corresponding to the aforementioned cutting of the transition arc 11, located in the middle of the two clamping sections 12. Figure 2 The section between the two dotted lines is the transition section 13, while the test section 14 is the cross section corresponding to the narrowest part of the transition section 13. That is, the test section 14 is the cross section corresponding to the minimum arc length of the pipe arc in the transition section.

[0031] In one optional embodiment, the preset distance is 1 / 2 to 3 / 4 of the outer wall radius of the aircraft hydraulic conduit; the area of ​​the test section 14 of the non-porous tube arc fatigue specimen 1 and the tube arc fatigue specimen 4 with elliptical holes is less than 1 / 3 and 1 / 2 of the cross-sectional area of ​​the clamping section 12, respectively.

[0032] It should be noted that the entire tube arc fatigue specimen has no parallel section. The test position is the shortest distance between the transition arcs 11 on both sides, and the corresponding cross section is the test section 14. The two ends of the specimen are the clamping sections 12. By adjusting the shortest distance between the transition arcs 11 on both sides, the area of ​​the test section 14 of the tube arc fatigue specimen 1 without holes and the tube arc fatigue specimen 4 with elliptical holes is less than 1 / 3 and 1 / 2 of the cross-sectional area of ​​the clamping section 12, respectively.

[0033] In one alternative embodiment, the surface roughness of both the transition arc 11 and the elliptical hole 41 is less than Ra0.2.

[0034] When cutting the arc fatigue specimen from the aircraft hydraulic conduit, the original inner and outer surfaces of the aircraft hydraulic conduit are preserved, and only the surface of the transition arc is polished. The polishing direction is parallel to the loading direction, and its surface roughness is within Ra0.2.

[0035] In one optional embodiment, the first clamping block 21 is a cylinder with a crescent-shaped cross-section; the second clamping block 22 is a cylinder with a gold ingot-shaped cross-section, such as... Figure 4 and Figure 5 As shown. The cross-sections of the first clamping block 21, the second clamping block 22, and the clamping section 12 together form a circular cross-section, as shown. Figure 6 As shown; the first clamping block 21 and the second clamping block 22 each include a contact surface 28 and a clamping surface 29; the contact surface 28 of the first clamping block 21 and the second clamping block 22 respectively contact the inner wall and the outer wall of the clamping section 12 of the tube arc fatigue specimen; the clamping surface 29 of the first clamping block 21 and the second clamping block 22 is adapted to cooperate with the fixture of the fatigue performance testing device to fix the tube arc fatigue specimen on the fatigue performance testing device; the first clamping block 21 and the second clamping block 22 each include a circular positioning hole 30 of the same size; the first positioning rod 23 passes through the circular positioning hole 30 of the first clamping block 21 and is clearance-fitted with the first clamping block 21; the second positioning rod 24 passes through the circular positioning hole 30 of the second clamping block 22 and is clearance-fitted with the second clamping block 22; the clamping surface 29 of the first clamping block 21 and the second clamping block 22 are provided with a groove 291 in the middle, and the first clamping block and the second clamping block together form an annular groove after they are attached.

[0036] It should be noted that the contact surfaces 28 of the first clamping block 21 and the second clamping block 22 can respectively contact the inner and outer walls of the clamping section 12 through surface-to-surface contact. Preferably, the inner diameters of the first clamping block 21 and the second clamping block 22 are equal to the nominal outer and inner diameters of the aircraft hydraulic conduit. During machining, the outer diameters of the first clamping block 21 and the second clamping block 22 are equal and within the allowable range of the clamp jaws. Preferably, the clamp is a hydraulic clamp V-type clamp.

[0037] Preferably, both the first clamping block 21 and the second clamping block 22 are processed by wire cutting. The mating surface 28 that mates with the clamping section 12 of the tube arc fatigue specimen 1 does not need to be polished, and its rough surface is retained to enhance the clamping effect.

[0038] Preferably, to ensure the fit between the first clamping block 21 and the second clamping block 22 and the tube arc fatigue specimen 1, the upper deviation of the first clamping block 21 and the lower deviation of the inner diameter of the second clamping block 22 are both set to 0mm during processing.

[0039] In one optional embodiment, the center of the circular cross-section is on the same horizontal line as the center point of the test cross-section 14; the portions of the first clamping block 21 and the second clamping block 22 near one end of the test cross-section 14 and fitting the clamping section 12 have a rounded chamfered structure 31, such as... Figure 1 and Figure 5 As shown.

[0040] When the clamping surfaces of the first clamping block 21 and the second clamping block 22 are adapted to cooperate with the fixture of the fatigue performance testing device, the radii of the outer cylindrical surfaces (i.e., clamping surfaces 29) of the two clamping blocks are equal and concentric when the fixture is clamping, and the center of the test section 14 of the tube arc fatigue specimen is located at the center of the circle to ensure the centering of the load.

[0041] Specifically, by matching the inner and outer diameter dimensions of the tube arc fatigue specimen, the distance between the inner and outer centers of the first clamping block 21 and the second clamping block 22 is controlled so that the center of the tube arc fatigue specimen is located at the outer center of the first clamping block 21 and the second clamping block 22, so as to ensure that the geometric center of the test section 14 coincides with the central axis of the fatigue performance testing device.

[0042] Preferably, the edges of the first clamping block 21 and the second clamping block 22, which are close to the test section 14 of the clamping section 12 of the tube arc fatigue specimen, are stress concentration points. In order to prevent the sharp edges of the clamping blocks from wearing down the tube arc during cyclic loading and causing the clamping end to break, the edges of the clamping blocks close to the test section 14 are chamfered with a chamfer radius of 2 mm and polished with a roughness controlled within Ra0.8.

[0043] In addition, such as Figure 8 As shown, this embodiment of the invention also provides a method for testing the high-cycle fatigue performance of aircraft hydraulic conduits, applied to a high-cycle fatigue performance testing component for aircraft hydraulic conduits, specifically including: S1. Fatigue tests were conducted on the tube arc fatigue specimens using a stress control method. The tube arc fatigue specimens included either a non-porous tube arc fatigue specimen 1 or a tube arc fatigue specimen 4 with an elliptical hole.

[0044] In one optional embodiment, the stress ratio of the stress control method for the non-porous tube arc fatigue specimen 1 and the tube arc fatigue specimen 4 with elliptical holes is greater than or equal to 0.1 and -1, respectively, the cyclic loading frequency is 10~25Hz, and the number of repeated experiments for each stress point is at least 1.

[0045] S2. Based on the fatigue test results, calculate the average stress of the test section and plot the first fitted SN curve based on the average stress of the test section.

[0046] It should be noted that, unlike the circular cross-section of traditional fatigue specimens, the stress distribution within the test section of the tubular arc fatigue specimen is uneven. Therefore, it is necessary to plot the SN curve based on the experimental data to characterize the fatigue performance of the aircraft hydraulic duct.

[0047] Preferably, a logarithmic function is used to plot the first fitted SN curve. Because stress concentration exists at the test section, using the average stress to fit the SN curve would underestimate the fatigue performance of the pipe. Therefore, this curve is used to characterize the lower limit of the fatigue performance of aircraft hydraulic conduits.

[0048] S3. Construct a finite element model of the tube arc fatigue specimen under axial loading.

[0049] S4. Based on the finite element model of the tube arc fatigue specimen under axial loading, obtain the local maximum stress of the test section, and plot the second fitted SN curve based on the local maximum stress of the test section.

[0050] Specifically, an axially loaded finite element model of the tube arc fatigue specimen was constructed to simulate and calculate the local maximum stress level of the test section under different average stresses. Simultaneously, a second fitted SN curve was plotted using a logarithmic function. Since a stress gradient exists at the stress concentration point, and the surrounding stress gradually decreases, using the local maximum stress to fit the SN curve would overestimate the fatigue performance of the tube. Therefore, this curve is used to characterize the upper limit of the fatigue performance of tubes used in aircraft hydraulic lines.

[0051] S5. Based on the first and second fitted SN curves, the fatigue life boundary of high failure risk points of the pipes used in aircraft hydraulic pipelines is estimated.

[0052] Specifically, based on the lower and upper limits of the fatigue performance of aircraft hydraulic conduits, the fatigue life boundary of high-failure-risk points in aircraft hydraulic pipelines can be predicted. The smaller the difference between the local maximum stress and the average stress in the test section of the pipe arc fatigue specimen, the closer the upper and lower limits of the SN curve are, and the more accurate the fatigue life assessment of the component. Therefore, the width of the test section and the radius of the transition arc of the pipe arc fatigue specimen can be optimized through finite element simulation to reduce the stress concentration in the test section.

[0053] In one optional embodiment, the formula for calculating the average stress of the test section of the non-porous tube arc fatigue specimen 1 is as follows: ; ; ; ; ; ; ; in, w The width of the test section of the tube arc fatigue specimen. d This refers to the inner diameter of the aircraft's hydraulic lines. D The outer diameter of the aircraft's hydraulic lines. S The area of ​​the test section, mean For average stress, L For load.

[0054] In one optional embodiment, the formula for calculating the average stress of the test section of the tube arc fatigue specimen 4 with elliptical holes is obtained by a simple inference transformation based on the formula for calculating the average stress of the test section of the tube arc fatigue specimen without holes.

[0055] Based on the fact that test results in related technologies cannot directly reflect the fatigue characteristics of aircraft hydraulic conduits and that the conduit clamping ends are prone to breakage, this invention proposes a high-cycle fatigue performance testing method for aircraft hydraulic conduits. By specially treating the size and shape of the pipe arc fatigue specimen and the clamping assembly, and combining theoretical calculations and numerical simulations of finite element models, fatigue data support is provided for the life assessment of aircraft hydraulic pipelines.

[0056] To verify the technical effect of the present invention, high-strength TA18 pipes used in aircraft hydraulic systems were selected for high-cycle fatigue performance testing: The nominal composition of the high-strength TA18 tubing used in aircraft hydraulic lines is Ti-3Al-2.5V. The selected specifications are an outer diameter of 18 mm and a wall thickness of 1.5 mm. Its basic mechanical properties are as follows:

[0057] The tube arc fatigue specimen is a dumbbell-shaped tube arc structure, wider at both ends and narrower in the middle. The axial cut surface of the tube arc fatigue specimen is parallel to the central axis of the entire tube, at a distance of 5.2 mm. The two sides have symmetrically distributed transition arcs with a radius of 30 mm, and the cut surfaces of the arcs are perpendicular to the axial cut surface. The cross-sectional width at the center of the transition arc is 2 mm, which has the minimum cross-sectional area and is the test section of the specimen.

[0058] After the tube arc fatigue specimen is cut, the original inner and outer surfaces of the tube are retained, and only the transition arc section is polished. The polishing direction is parallel to the loading direction, and the surface roughness is controlled within Ra0.2.

[0059] The first and second clamping blocks are machined from No. 45 mold steel. They are large and small clamping blocks, one in the shape of a crescent moon and the other in the shape of a gold ingot. The clamping surface (i.e., the outer cylindrical surface) of both the first and second clamping blocks has a radius of 10mm, and the nominal radii of the contact surfaces are 9mm and 7.5mm, respectively, which are equal to the radii of the outer and inner cylindrical surfaces of the aircraft hydraulic lines.

[0060] To ensure proper contact between the clamping blocks and the cylindrical surface of the tubular arc fatigue specimen, specific machining tolerances are specified for the clamping components: the upper tolerance for the clamping surface radius of the first clamping block is 0 mm, and the lower tolerance is -0.02 mm; the lower tolerance for the clamping surface radius of the second clamping block is 0 mm, and the upper tolerance is 0.02 mm. Furthermore, the contact surfaces of the first and second clamping blocks near the test section must be chamfered and polished with a chamfer radius of 1 mm and a surface roughness within Ra0.8.

[0061] The fatigue performance testing device used in this embodiment of the invention employs a lower clamp for fixation and an upper clamp for actuation. Before the fatigue performance testing device clamps the tube arc fatigue specimen, the surface of the first clamping block is in contact with the outer surface of the clamping section of the tube arc fatigue specimen, and the surface of the second clamping block is in contact with the inner surface of the clamping section of the tube arc fatigue specimen. Then, a suitably sized elastic rubber ring is placed in the annular groove to constrain the first and second clamping blocks; preferably, the elastic rubber has a size of 6 mm. Finally, the first and second positioning rods are inserted from top to bottom into the circular positioning holes of the first and second clamping blocks, respectively, and then the first and second pins are inserted into the rectangular holes of the first and second clamping blocks, respectively. The two pins and the two circular positioning holes are fitted with a 0.05 mm clearance to prevent the specimen from twisting during clamping. After the tube arc fatigue specimen is combined with the clamping assembly, a hydraulic clamp with V-jaws is used to clamp the clamping surface of the clamping assembly, and the specimen is clamped on the Instron 8801 fatigue testing machine at a clamping pressure of 800 psi. Then, pull up the first and second pins to separate the first and second positioning bars from the first and second clamping blocks at one end of the tube arc fatigue specimen.

[0062] It should be noted that the upper clamp of the fatigue performance testing device must allow space for the first and second positioning bars to move upwards. The surfaces of both the first and second positioning bars must be polished to Ra1.6. If the first and second positioning bars are stuck in the circular positioning holes and cannot slide after the clamp is engaged, it indicates that the upper and lower clamping blocks have undergone axial torsion during the clamping process, and the clamp must be loosened and re-clamped.

[0063] After the specimen was clamped, fatigue testing was conducted at room temperature using stress control with a stress ratio of 0.1, a sinusoidal loading waveform, and a loading frequency of 20 Hz. Each stress level was tested once repeatedly. The test was stopped when the specimen fractured or reached 10... 7 The experiment terminates after a certain number of cycles.

[0064] Because the test cross-section of the tube arc fatigue specimen is not regular, refer to Figure 9 A significant stress gradient exists at the interface, with the location marked 131 on the cross-section indicating the point of maximum local stress. Fitting the SN curve based on the average stress underestimates the pipe's fatigue performance, while fitting the SN curve based on the local maximum stress overestimates it. Therefore, these two values ​​are used as the lower and upper limits of the pipe's fatigue performance, respectively, with the actual fatigue performance of the pipe falling between them.

[0065] The local maximum stress at the test section was obtained through numerical simulation, such as... Figure 10 As shown, the local maximum stress is roughly linearly related to the axial load, and the slope of the curve changes only slightly.

[0066] The upper and lower limits of the fitted SN curve were plotted using a logarithmic function, and the results are as follows: Figure 11 As shown.

[0067] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. An aircraft hydraulic conduit high cycle fatigue performance test assembly, characterized by, The utility model relates to a pipe arc fatigue test sample and clamping assembly, the pipe arc fatigue test sample belongs to a part of aircraft hydraulic pipeline, the pipe arc fatigue test sample is the pipe arc structure of two ends wide middle narrow dumbbell shape, the pipe arc fatigue test sample includes the pipe arc fatigue test sample of no hole or the pipe arc fatigue test sample of elliptic hole, the pipe arc fatigue test sample of elliptic hole is equipped with elliptic hole in the middle, the pipe arc fatigue test sample of no hole is used for tension-tension fatigue test, the pipe arc fatigue test sample of elliptic hole is used for tension-compression fatigue test, the clamping assembly includes first clamping block, second clamping block, first locating rod, second locating rod, first pin and second pin, first clamping block and second clamping block all abut with the pipe arc fatigue test sample, first locating rod is equipped with first clamping block and is gap cooperation with first clamping block, second locating rod is equipped with second clamping block and is gap cooperation with second clamping block, first locating rod and second locating rod all are equipped with rectangular hole, first pin is equipped with the rectangular hole of first locating rod and is gap cooperation with first locating rod, second pin is equipped with the rectangular hole of second locating rod and is gap cooperation with second locating rod. The pipe arc fatigue test sample is obtained by cutting a transition arc along a second plane after cutting along a first plane of the aircraft hydraulic pipeline, the first plane is parallel to the center axis of the aircraft hydraulic pipeline and has a predetermined distance, the first plane and the second plane are perpendicular, the center of the transition arc is on the cross section at 1 / 2 of the aircraft hydraulic pipeline in the axial direction, the radius of the transition arc of the pipe arc fatigue test sample with the elliptic hole is greater than that of the pipe arc fatigue test sample without the hole, the center of the elliptic hole is located at the middle position of the line connecting the centers of the two transition arcs, the short axis of the elliptic hole is perpendicular to the center axis of the aircraft hydraulic pipeline, and the long axis of the elliptic hole is parallel to the center axis of the aircraft hydraulic pipeline. The pipe arc fatigue test sample includes a clamping section, a transition section, and a test section, the clamping section and the transition section are pipe arcs with the same inner and outer radii as the aircraft hydraulic pipeline, the arc length of the clamping section is greater than or equal to the arc length of the transition section, the arc lengths of the transition section decrease and then increase in sequence along the axial direction, the test section is the cross section corresponding to the minimum arc length of the transition section, and the arc length of the transition section of the pipe arc fatigue test sample with the elliptic hole is greater than that of the pipe arc fatigue test sample without the hole.

2. The high-cycle fatigue performance test assembly of claim 1, wherein, The predetermined distance is 1 / 2 to 3 / 4 of the outer wall radius of the aircraft hydraulic pipeline, and the areas of the test sections of the pipe arc fatigue test samples without the hole and with the elliptic hole are less than 1 / 3 and 1 / 2 of the cross-sectional area of the clamping section, respectively.

3. The high-cycle fatigue performance test assembly of claim 2, wherein, The surface roughness of the transition arc and the elliptic hole is less than Ra0.

2.

4. The high-cycle fatigue performance test assembly of claim 3, wherein, ​ 5. The high-cycle fatigue performance test assembly of claim 2, wherein, ​ 6. The high-cycle fatigue performance test assembly of claim 3, wherein, The first clamp block is a column with a cross section in the shape of a moon, and the second clamp block is a column with a cross section in the shape of a ingot; the cross sections of the first clamp block, the second clamp block and the clamping section jointly form a circular cross section; the first clamp block and the second clamp block each include a fitting surface and a clamping surface; the fitting surfaces of the first clamp block and the second clamp block respectively fit with the outer wall and the inner wall of the clamping section of the pipe-arc fatigue test sample, and the clamping surfaces of the first clamp block and the second clamp block are adapted to cooperate with the clamp of the fatigue performance testing device to fix the pipe-arc fatigue test sample on the fatigue performance testing device; the first clamp block and the second clamp block each include a circular positioning hole with the same size, the first positioning rod is arranged in the circular positioning hole of the first clamp block and cooperates with the first clamp block in a gap, and the second positioning rod is arranged in the circular positioning hole of the second clamp block and cooperates with the second clamp block in a gap; the clamping surfaces of the first clamp block and the second clamp block are provided with grooves in the middle, and the first clamp block and the second clamp block jointly form an annular groove after being fitted.

7. The high-cycle fatigue performance test assembly of claim 6, wherein, The center of the circular cross section and the center point of the test section are on the same axis; the portions of the first clamp block and the second clamp block close to the test section and fitting the clamping section are smooth chamfer structures.

8. A method for testing high-cycle fatigue performance of an aircraft hydraulic conduit, applied to the assembly for testing high-cycle fatigue performance of an aircraft hydraulic conduit according to any one of claims 1 to 7, characterized in that, The method comprises the following steps: The fatigue test is performed on the pipe-arc fatigue test sample by using a stress control method; The pipe-arc fatigue test sample includes a non-hole pipe-arc fatigue test sample or an elliptical hole pipe-arc fatigue test sample; According to the fatigue test result, the average stress of the test section is calculated, and a first fitting S-N curve is drawn according to the average stress of the test section; An axial loading finite element model of the pipe-arc fatigue test sample is constructed; Based on the axial loading finite element model of the pipe-arc fatigue test sample, the local maximum stress of the test section is obtained, and a second fitting S-N curve is drawn according to the local maximum stress of the test section; According to the first fitting S-N curve and the second fitting S-N curve, the high failure risk point fatigue life boundary of the pipe material for the aircraft hydraulic pipeline is estimated.

9. The method of claim 8, wherein, The average stress calculation formula of the test section of the non-hole pipe-arc fatigue test sample is: ； ； ； ； ； ； ； wherein, w is the width of the test section of the tube arc fatigue specimen, d is the inner diameter of the aircraft hydraulic line, D is the outer diameter of the aircraft hydraulic line, S is the area of the test section, mean is the average stress, L is the load.

10. The method of claim 9, wherein, The average stress calculation formula of the test section of the elliptical hole pipe-arc fatigue test sample is obtained by reasoning and transforming the average stress calculation formula of the test section of the non-hole pipe-arc fatigue test sample.

11. The method of claim 10, wherein, The stress ratios of the stress control methods of the non-hole pipe-arc fatigue test sample and the elliptical hole pipe-arc fatigue test sample are greater than or equal to 0.1 and -1 respectively, the cycle loading frequency is 10-25 Hz, and the number of repeated experiments at each stress point is at least 1.

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