A method for determining the vibration fatigue strength of an aeroengine blade

Abstract

The present invention relates to a method for determining the vibration fatigue strength of an aero-engine blade. By applying different stress levels with a gradually increasing fixed step size to the maximum stress point of the target blade, the stress level immediately preceding the stress level corresponding to the fracture of the target blade is determined as the vibration fatigue strength of the target blade. When applying different stress levels each time, the vibration stresses at the maximum stress point in the chord direction and the height direction of the blade are obtained through finite element vibration simulation. Then, based on the vibration stresses in each direction, combined with the initial residual stress and surface roughness of the maximum stress point, the actual working stresses in each direction are calculated. Next, the actual working stresses are equivalently synthesized into a uniaxial stress. Finally, the fatigue damage at the current stress level is determined using nCode software based on the synthesized uniaxial stress. The method of the present invention can calculate the vibration fatigue strength of the blade through computer-aided simulation, without the need to conduct fatigue performance measurement experiments, with low cost, and the entire process will not damage the blade.

Description

Technical Field

[0001] The present invention relates to the technical field of computer-aided machining of aero-engine blades, and particularly to a method for determining the vibration fatigue strength of aero-engine blades. Background Art

[0002] An aero-engine is a highly complex precision thermal machine and is the core component of an aircraft, providing the power required for the aircraft to fly. Blades are key components of an aero-engine and play a decisive role in the performance of the engine.

[0003] During the operation of an aero-engine, the blades are subjected to high-frequency vibration loads. When the vibration loads reach the fatigue limit, fatigue failure will occur, resulting in damage to the aero-engine and further affecting the reliability of the aircraft. Existing research shows that surface integrity parameters such as residual stress and surface roughness of the blades obtained by precision milling have a significant impact on the fatigue performance of the blades. Therefore, after the blades are prepared by milling, it is usually necessary to predict the vibration fatigue strength of the blades in order to reverse-optimize the milling parameters of the blades, and then obtain aero-engine blades that meet the reliability requirements of the aircraft.

[0004] During the vibration of the blades, the surface roughness does not change with time. However, the residual stress will decay with time, weakening the enhancing effect of the residual stress on the fatigue performance. Under the influence of the residual stress, both the mean stress and the stress amplitude of the blades are changing, making it difficult to directly predict the fatigue life.

[0005] In the prior art, among the methods for predicting the vibration fatigue strength of blades, the most widely used and relatively accurate method is to use the step vibration fatigue test method to determine the vibration fatigue strength of aero-engine blades. The step vibration fatigue test method is a vibration test that applies different true stress levels to the blades under actual conditions, and explores the final vibration fatigue strength by gradually increasing the stress level. The step vibration fatigue test method can not only provide detailed information about the vibration fatigue strength of the blades, but also simulate the stress state under actual working conditions by gradually increasing the stress level, so as to predict the reliability of the blades in actual use. However, the step vibration fatigue test method relies on multiple vibration fatigue tests on the blades, resulting in a high cost for the entire process of predicting the vibration fatigue strength of the blades, and the application of true stress during the vibration fatigue test process will damage the blades. Summary of the Invention

[0006] Based on this, in view of the above technical problems, it is necessary to provide a method for determining the vibration fatigue strength of aero-engine blades, which determines the vibration fatigue strength of the blades by means of computer-aided simulation, without the need to carry out fatigue performance measurement experiments, has a low cost, and does not damage the blades throughout the process.

[0007] The present invention provides a method for determining the vibration fatigue strength of an aeroengine blade, comprising the following steps:

[0008] Determine the position of the maximum stress point of the target blade;

[0009] Measure the initial residual stress and surface roughness of the maximum stress point;

[0010] Measure the S-N curve of the target blade material with a stress ratio of -1;

[0011] Take 1 / 4 to 1 / 3 of the ordinate value corresponding to the abscissa point 10 on the S-N curve as the stress level to be determined; 7

[0012] Use the stress level to be determined to perform finite element vibration simulation of the target blade to obtain the vibration stress of the maximum stress point in the chord direction and height direction of the blade. The chord direction and height direction are in the curved surface coordinate system;

[0013] Based on the initial residual stress and surface roughness of the maximum stress point and the vibration stress in the chord direction and height direction, calculate the actual working stress of the maximum stress point in the chord direction and height direction;

[0014] Synthesize the actual working stress of the maximum stress point in the chord direction and height direction into a uniaxial stress;

[0015] Calculate the fatigue damage of the target blade under the stress level to be determined according to the uniaxial stress;

[0016] Judge whether the sum of the fatigue damages of the target blade under all stress levels to be determined is greater than 1. If so, the current stress level is the final stress level, and subtract Δσ from the final stress level as the vibration fatigue strength of the target blade. Otherwise, increase the current stress level to be determined by Δσ as the new stress level to be determined, and then return to the step of using the stress level to be determined to perform finite element vibration simulation of the target blade to obtain the vibration stress of the maximum stress point in the chord direction and height direction of the blade, where Δσ represents the stress step.

[0017] In one embodiment, determining the position of the maximum stress point of the target blade is based on the ANSYS software and comprises the following steps:

[0018] Import the three-dimensional model of the target blade into the static analysis module for preprocessing;

[0019] Apply a sinusoidal fluctuating acceleration load with an arbitrary period to the three-dimensional model of the target blade after preprocessing using at least 8 load steps, calculate and select to output the equivalent stress nephogram of the target blade;

[0020] Determine the position of the maximum stress point of the target blade according to the equivalent stress nephogram. ​

[0021] In one embodiment, the finite element vibration simulation of the target blade is carried out using the to-be-determined stress level, and the vibration stresses of the maximum stress point in the chord direction and the height direction of the blade are obtained based on the ANSYS software, including the following steps:

[0022] Import the three-dimensional model of the target blade into the static analysis module for preprocessing;

[0023] Calculate the sinusoidal fluctuation acceleration load of the finite element vibration simulation of the target blade according to the to-be-determined stress level;

[0024] Apply the sinusoidal fluctuation acceleration load of the finite element vibration simulation of the target blade to the three-dimensional model of the preprocessed target blade using at least 8 load steps, calculate and select to output the directional stress nephogram of the target blade in the chord direction and the height direction;

[0025] Determine the vibration stresses of the maximum stress point in the chord direction and the height direction of the blade respectively according to the directional stress nephograms in the chord direction and the height direction.

[0026] In one embodiment, importing the three-dimensional model of the target blade into the static analysis module for preprocessing includes the following steps:

[0027] Set the blade root of the three-dimensional model of the target blade as a fixed constraint;

[0028] Conduct a mesh independence analysis on the three-dimensional model of the target blade.

[0029] In one embodiment, the surface roughness of the maximum stress point includes the arithmetic mean height of the profile, the maximum peak-to-valley depth, the ten-point height of the micro-irregularities, and the equivalent valley curvature radius of the profile in the chord direction and the height direction of the maximum stress point.

[0030] In one embodiment, calculating the actual working stresses of the maximum stress point in the chord direction and the height direction of the blade based on the initial residual stress and surface roughness of the maximum stress point and the vibration stresses in the chord direction and the height direction includes the following steps:

[0031] Calculate the residual stresses in the stable attenuation stage of the maximum stress point in the chord direction and the height direction according to the initial residual stresses of the maximum stress point in the chord direction and the height direction. The calculation formula is:

[0032] ,

[0033] In the formula, is the initial residual stress of the maximum stress point in the chord direction, is the residual stress of the maximum stress point in the stable attenuation stage in the chord direction, is the initial residual stress of the maximum stress point in the height direction, is the residual stress at the stable attenuation stage of the maximum stress point in the blade height direction;

[0034] Calculate the stress concentration factors of the maximum stress point in the chord direction and the blade height direction according to the surface roughness of the maximum stress point. The calculation formula is:

[0035] ,

[0036] In the formula, K st-x represents the stress concentration factor of the maximum stress point in the chord direction, K st-y represents the stress concentration factor of the maximum stress point in the blade height direction, R a-x represents the arithmetic mean of the profile in the chord direction, R y-x represents the maximum peak-to-valley depth in the chord direction, R z-x represents the ten-point height of the micro-irregularity in the chord direction, ρ x represents the equivalent valley curvature radius of the profile in the chord direction, R a-y represents the arithmetic mean of the profile in the blade height direction, R y-y represents the maximum peak-to-valley depth in the blade height direction, R z-y represents the ten-point height of the micro-irregularity in the blade height direction, ρ y represents the equivalent valley curvature radius of the profile in the blade height direction, n represents the characterization coefficient of different stress states;

[0037] Calculate the actual working stresses of the maximum stress point in the chord direction and the blade height direction respectively based on the residual stress, stress concentration factor and vibration stress at the stable attenuation stage of the maximum stress point in the chord direction and the blade height direction. The calculation formula is:

[0038] ,

[0039] In the formula, represents the actual working stress of the maximum stress point in the chord direction, represents the vibration stress of the maximum stress point in the chord direction, represents the actual working stress of the maximum stress point in the blade height direction, represents the vibration stress of the maximum stress point in the blade height direction, t represents time.

[0040] In one embodiment, the actual working stresses of the maximum stress point in the chord direction and the blade height direction are synthesized into a uniaxial stress based on the signed Von-Mises formula, and the synthesis calculation formula is:

[0041] ,

[0042] In the formula, represents the uniaxial stress, represents the determination factor of the stress state, .

[0043] In one embodiment, the fatigue damage of the target blade at a to-be-determined stress level is calculated according to the uniaxial stress, including the following steps:

[0044] Calculate the minimum cross-sectional area of the uniaxial tension-compression fatigue standard specimen model;

[0045] Calculate the product of the minimum cross-sectional area and the uniaxial stress as the uniaxial tension-compression load;

[0046] Input the uniaxial tension-compression fatigue standard specimen model and the uniaxial tension-compression load into the ANSYS transient dynamics analysis module, and calculate to obtain the load spectrum of the uniaxial tension-compression fatigue standard specimen model;

[0047] Input the uniaxial tension-compression fatigue standard specimen model and the load spectrum of the uniaxial tension-compression fatigue standard specimen model into the nCode software to obtain the life contour map of the uniaxial tension-compression fatigue standard specimen model;

[0048] Take the minimum life value in the life contour map of the uniaxial tension-compression fatigue standard specimen model as the life of the target blade at the to-be-determined stress level;

[0049] Calculate the fatigue damage of the target blade at the to-be-determined stress level according to the life of the target blade at the to-be-determined stress level, and the calculation formula is:

[0050] ,

[0051] In the formula, D represents the fatigue damage of the target blade at the to-be-determined stress level, N represents the life of the target blade at the to-be-determined stress level.

[0052] In one embodiment, Δσ is 10 MPa, 50 MPa or 100 MPa.

[0053] The beneficial effects of the present invention are as follows: By simulating and applying different stress levels with a gradually increasing fixed stress step Δσ to the maximum stress point of the target blade, when the sum of fatigue damages under all stress levels is greater than 1, the target blade fractures, and the stress level immediately preceding the stress level at which the target blade fractures is taken as the vibration fatigue strength of the target blade. When applying different stress levels each time, the vibration stresses at the maximum stress point in the chord direction and the height direction of the blade are obtained through finite element vibration simulation. Then, based on the vibration stresses in each direction, combined with the initial residual stress and surface roughness of the maximum stress point, the actual working stresses in each direction are calculated. Next, the actual working stresses are equivalently synthesized into a uniaxial stress, and finally, the fatigue damage under the current stress level is determined based on the synthesized uniaxial stress. The method of the present invention determines the vibration fatigue strength of the blade through computer-aided simulation, without the need to conduct fatigue performance measurement experiments, with low cost and without damaging the blade throughout the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 FIG. is a schematic diagram of the stress composition at the maximum stress point of the blade provided in an embodiment of the present invention in a non-vibrating state;

[0055] Figure 2 FIG. is an equivalent stress contour map provided in an embodiment of the present invention;

[0056] Figure 3 FIG. is a life contour map of a uniaxial tension-compression fatigue standard specimen model provided in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0057] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0058] When using the step-by-step vibration fatigue test method to determine the vibration fatigue strength of the blade, multiple vibration fatigue tests are often required. The cost of a single vibration fatigue test is several thousand or even tens of thousands, making the entire step-by-step vibration fatigue test method have a relatively high cost. In addition, the actual real stress is applied to the blade during the vibration fatigue test, and this process will damage the blade, and may ultimately lead to the blade being unusable. The method of the present invention can determine the vibration fatigue strength of the blade through computer-aided simulation, without the need to conduct fatigue performance measurement experiments, with low cost and without damaging the blade throughout the process.

[0059] In one embodiment, the method for determining the vibration fatigue strength of the aero-engine blade in this embodiment includes the following steps:

[0060] S101. Determine the position of the maximum stress point of the target blade.

[0061] The crack source of fatigue failure of the blade under vibration conditions occurs at the maximum stress point on the surface of the blade. Therefore, in this embodiment, the vibration fatigue strength of the blade is calculated based on the maximum stress point.

[0062] S102. Measure the initial residual stress and surface roughness of the maximum stress point.

[0063] Specifically, the surface roughness of the maximum stress point includes the arithmetic mean deviation of the profile, the maximum peak-to-valley depth, the ten-point height of micro-irregularities, and the equivalent valley curvature radius of the profile in the chord direction and span direction of the blade.

[0064] S103. Measure the S-N curve of the target blade material with a stress ratio of -1.

[0065] S104. Take 1 / 4 to 1 / 3 of the ordinate value corresponding to the abscissa point 10 7 as the stress level to be determined.

[0066] It should be noted that in the field of fatigue mechanics, 10 7 is used as the demarcation point between finite cycles and infinite cycles. Therefore, in this embodiment, the abscissa point is selected as 10 7 . Selecting 1 / 4 to 1 / 3 of the ordinate value as the initial stress level to be determined can reduce the number of iterations of the method in this embodiment and reduce the computational amount.

[0067] S105. Use the stress level to be determined to perform finite element vibration simulation of the target blade to obtain the vibration stress of the maximum stress point in the chord direction and span direction. The chord direction and span direction are in the curved surface coordinate system.

[0068] It should be noted that the vibration stress of the maximum stress point in the curved surface coordinate system includes the stress in the chord direction, the span direction, and the direction perpendicular to the plane where the chord direction and span direction are located. However, since the stress value in the perpendicular plane is very small, the stress in the perpendicular plane is ignored in this embodiment.

[0069] S106. Calculate the actual working stress of the maximum stress point in the chord direction and span direction based on the initial residual stress, surface roughness, and vibration stress in the chord direction and span direction of the maximum stress point.

[0070] As Figure 1 shown, when the blade is in the non-vibration state, the actual stress received by the maximum stress point is composed of the stress concentration effect caused by the initial residual stress and surface roughness. Since the blade will be affected by vibration stress in the vibration state, the final actual working stress of the blade is composed of the initial residual stress, the vibration stress caused by blade vibration, and the stress concentration effect caused by surface roughness.

[0071] S107. Synthesize the actual working stresses of the maximum stress point in the chord direction and the span direction of the blade into a uniaxial stress.

[0072] S108. Calculate the fatigue damage of the target blade at the to-be-determined stress level according to the uniaxial stress.

[0073] Specifically, in this embodiment, the nCode software is used to calculate the fatigue damage of the target blade at the to-be-determined stress level. Since the nCode software cannot calculate the fatigue damage of the maximum stress point, the fatigue damage simulation of uniaxial tension and compression is adopted in this embodiment to equivalently replace the calculation of the fatigue damage of the maximum stress point.

[0074] S109. Judge whether the sum of the fatigue damages of the target blade at all to-be-determined stress levels is greater than 1. If so, the current stress level is the final stress level, and subtract Δσ from the final stress level to obtain the vibration fatigue strength of the target blade. Otherwise, increase the current to-be-determined stress level by Δσ as the new to-be-determined stress level, and then return to the step of obtaining the vibration stresses of the maximum stress point in the chord direction and the span direction of the target blade by using the finite element vibration simulation of the target blade with the to-be-determined stress level.

[0075] Specifically, Δσ represents the stress step, that is, the fixed stress difference between two adjacent stress levels. Δσ is 10 MPa, 50 MPa or 100 MPa, preferably 50 MPa. When the sum of the fatigue damages at all to-be-determined stress levels is greater than 1, the target blade breaks at the maximum stress point. At this time, subtract Δσ from the to-be-determined stress level that causes the target blade to break at the maximum stress point to obtain the vibration fatigue strength of the target blade.

[0076] Adopting the method for determining the vibration fatigue strength of the aero-engine blade in this embodiment, except that the initial residual stress and surface roughness of the maximum stress point and the S-N curve with a stress ratio of -1 of the target blade material need to be measured experimentally, the remaining steps are all carried out by finite element simulation calculation in the computer, without the need to carry out fatigue performance measurement experiments, with low cost and the whole process will not damage the blade.

[0077] In one of the embodiments, determining the position of the maximum stress point of the target blade is based on the ANSYS software, including the following steps:

[0078] S201. Import the three-dimensional model of the target blade into the static analysis module for preprocessing.

[0079] Specifically, importing the three-dimensional model of the target blade into the static analysis module for preprocessing includes the following steps:

[0080] S2011. Set the blade root of the three-dimensional model of the target blade as a fixed constraint.

[0081] S2012. Perform a mesh independence analysis on the 3D model of the target blade. In this embodiment, the maximum mesh size obtained from the mesh independence analysis is set to 0.4 mm.

[0082] S202. Apply a sinusoidal fluctuating acceleration load for an arbitrary period to the 3D model of the preprocessed target blade using at least 8 load steps, and calculate and select to output the equivalent stress nephogram of the target blade.

[0083] Exemplarily, the finally output equivalent stress nephogram is as Figure 2 shown, and the output equivalent stress nephogram can directly show the position of the maximum stress point P max , P max which is generally located at the transition fillet of the back surface of the blade. Figure 2 The maximum stress point in

[0084] S203. Determine the position of the maximum stress point of the target blade according to the equivalent stress nephogram.

[0085] In one embodiment, the vibration stress of the maximum stress point in the chord direction and the height direction of the target blade is obtained by performing a finite element vibration simulation of the target blade using a pending stress level, based on the ANSYS software, including the following steps:

[0086] S301. Import the 3D model of the target blade into the static analysis module for preprocessing.

[0087] S302. Calculate the sinusoidal fluctuating acceleration load for the finite element vibration simulation of the target blade according to the pending stress level.

[0088] S303. Apply the sinusoidal fluctuating acceleration load for the finite element vibration simulation of the target blade to the 3D model of the preprocessed target blade using at least 8 load steps, and calculate and select to output the directional stress nephogram of the target blade in the chord direction and the height direction.

[0089] Since the deformation and stress of the material satisfy a linear relationship, therefore, under the same load type and boundary conditions, the stress field of the blade is equal to the actual one. So in this embodiment, during the finite element simulation of the blade, an equivalent acceleration load is applied, that is, the sinusoidal fluctuating acceleration load for the finite element vibration simulation of the target blade, so as to obtain the actual equivalent stress field of the blade to obtain the directional stress nephogram in the chord direction and the height direction. Among them, the calculation formula for the equivalent sinusoidal fluctuating acceleration load for the finite element vibration simulation of the target blade is

[0090] ,

[0091] where, is the equivalent sinusoidal fluctuating acceleration load, is the current stress level. Specifically, without considering surface roughness and surface residual stress and only considering mechanical vibration, the value of the stress level is equal to the stress at the maximum stress point y in the direction caused by mechanical vibration.

[0092] S304. Determine the vibration stresses of the maximum stress point in the chord direction and the span direction of the target blade according to the directional stress nephograms in the chord direction and the span direction respectively.

[0093] Specifically, the vibration stresses and stress magnitudes in each direction are shown in the directional stress nephograms in the chord direction and the span direction.

[0094] In the method of this embodiment, the vibration stresses of the maximum stress point of the target blade in the chord direction and the span direction in the curved surface coordinate system are determined through finite element analysis and calculation by ANSYS software.

[0095] In one embodiment, based on the initial residual stress, surface roughness of the maximum stress point, and the vibration stresses in the chord direction and the span direction, calculate the actual working stresses of the maximum stress point in the chord direction and the span direction, including the following steps:

[0096] S401. Calculate the residual stresses of the maximum stress point in the stable decay stage in the chord direction and the span direction according to the initial residual stresses of the maximum stress point in the chord direction and the span direction. The calculation formula is:

[0097] ,

[0098] In the formula, is the initial residual stress of the maximum stress point in the chord direction, is the residual stress of the maximum stress point in the stable decay stage in the chord direction, is the initial residual stress of the maximum stress point in the span direction, is the residual stress of the maximum stress point in the stable decay stage in the span direction.

[0099] Under the vibration condition of the blade, the residual stress decays with time. After experiencing rapid decay in the early stage, the decay rate of the residual stress decreases and enters the stable decay stage. Therefore, in this embodiment, the residual stress in the stable decay stage is used to calculate the actual working stress.

[0100] S402. Calculate the stress concentration coefficients of the maximum stress point in the chord direction and the span direction according to the surface roughness of the maximum stress point. The calculation formula is:

[0101] ,

[0102] In the formula,K st-x Indicates the stress concentration coefficient of the maximum stress point in the chord direction of the blade. K st-y Indicates the stress concentration coefficient of the maximum stress point in the height direction of the blade. R a-x Indicates the arithmetic mean of the profile in the chord direction of the blade. R y-x Indicates the maximum peak-to-valley depth in the chord direction of the blade. R z-x Indicates the ten-point height of the micro-irregularity in the chord direction of the blade. ρ x Indicates the equivalent valley curvature radius of the profile in the chord direction of the blade. R a-y Indicates the arithmetic mean of the profile in the height direction of the blade. R y-y Indicates the maximum peak-to-valley depth in the height direction of the blade. R z-y Indicates the ten-point height of the micro-irregularity in the height direction of the blade. ρ y Indicates the equivalent valley curvature radius of the profile in the height direction of the blade. n Indicates the characterization coefficient of different stress states. K st Indicates the stress concentration coefficient.

[0103] Specifically, under the vibration condition of the blade, the blade mainly bears tensile stress, so n = 2.

[0104] S403. Calculate the actual working stress of the maximum stress point in the chord direction and height direction of the blade respectively based on the residual stress, stress concentration coefficient and vibration stress in the stable attenuation stage of the maximum stress point in the chord direction and height direction of the blade. The calculation formula is:

[0105] ,

[0106] In the formula, Indicates the actual working stress of the maximum stress point in the chord direction of the blade. Indicates the vibration stress of the maximum stress point in the chord direction of the blade. Indicates the actual working stress of the maximum stress point in the height direction of the blade. Indicates the vibration stress of the maximum stress point in the height direction of the blade. t Indicates time. The stress level refers to the load. In this embodiment, the stress level changes during vibration, and different times correspond to different stress levels.

[0107] In one embodiment, the actual working stresses of the maximum stress point in the chord direction and the blade height direction are synthesized into a uniaxial stress based on the signed Von-Mises formula, and the synthesis calculation formula is:

[0108] ,

[0109] In the formula, represents the uniaxial stress, represents the judgment factor of the stress state, . The Von-Mises formula is the von Mises formula, which is a formula for stress equivalence.

[0110] In one embodiment, the fatigue damage of the target blade at the undetermined stress level is calculated according to the uniaxial stress, including the following steps:

[0111] S501. Calculate the minimum cross-sectional area of the uniaxial tensile-compressive fatigue standard specimen model;

[0112] The equivalent substitution needs to meet the requirements that no geometric structure influence is introduced after substitution, the stress state is exactly the same, and the load spectrum is exactly the same. Therefore, in this embodiment, the uniaxial tensile-compressive fatigue standard specimen model is used to simulate and eliminate the influence of the geometric structure. The diameter of the middle section of the uniaxial tensile-compressive fatigue standard specimen is 5 mm, and the fillets on both sides are 50 mm. When calculating the fatigue damage in the nCode software, the surface state of the uniaxial tensile-compressive fatigue standard specimen is set to be absolutely smooth.

[0113] S502. Calculate the product of the minimum cross-sectional area and the uniaxial stress as the uniaxial tensile-compressive load. In the uniaxial tensile-compressive simulation, the stress at the middle section of the standard specimen model needs to be consistent with the synthesized uniaxial stress. Therefore, the calculation formula of the uniaxial tensile-compressive load is .

[0114] S503. Input the uniaxial tensile-compressive fatigue standard specimen model and the uniaxial tensile-compressive load into the ANSYS transient dynamics analysis module, and calculate to obtain the load spectrum of the uniaxial tensile-compressive fatigue standard specimen model.

[0115] In order to ensure that the load spectra are the same before and after equivalence, transient dynamics simulation is used to provide the load spectrum for the nCode software. In the ANSYS transient dynamics analysis module, first, a fixed constraint is applied to the bottom of the uniaxial tensile-compressive fatigue standard specimen, and a frictionless constraint is applied to both sides of the cylindrical part. The purpose is to prevent the uniaxial tensile-compressive fatigue standard specimen from buckling during compression, resulting in non-convergence of the finite element calculation. The mesh is set as a hexahedral structured mesh, and the mesh is refined at the middle position of the test bar. The ANSYS transient dynamics analysis module calculates and outputs the load spectrum of the uniaxial tensile-compressive fatigue standard specimen model.

[0116] S504. Input the uniaxial tension-compression fatigue standard specimen model and its load spectrum into the nCode software to obtain the life contour map of the uniaxial tension-compression fatigue standard specimen model.

[0117] S505. Take the minimum life value in the life contour map of the uniaxial tension-compression fatigue standard specimen model as the life of the target blade under the to-be-determined stress level.

[0118] Exemplarily, as Figure 3 shown, Figure 3 the minimum life value in the shown life contour map is 3.108E5 cycle times, which is the life of the target blade under the to-be-determined stress level.

[0119] S506. Calculate the fatigue damage of the target blade under the to-be-determined stress level according to the life of the target blade under the to-be-determined stress level. The calculation formula is:

[0120] ,

[0121] In the formula, D represents the fatigue damage of the target blade under the to-be-determined stress level, N represents the life of the target blade under the to-be-determined stress level.

[0122] For the method for determining the vibration fatigue strength of an aero-engine blade of the present invention, the calculation of the blade vibration fatigue strength is simplified to the calculation of the vibration fatigue strength at the maximum stress point. Based on the set stress levels, the finite element method is used to calculate the vibration stress, and the actual predicted stress of each direction component at the maximum stress point is calculated in combination with the surface roughness and the surface initial residual stress. Then, the actual predicted stresses of each direction component are equivalently synthesized into a uniaxial stress, and the nCode software is used to determine the fatigue damage brought by the synthesized uniaxial stress to the maximum stress point, that is, the fatigue damage brought to the blade is determined. During the calculation process, the stress levels are gradually increased to determine the fatigue damage to the blade, and a judgment condition is set. When the sum of the fatigue damages of all stress levels is greater than 1, at this time, the maximum stress point fractures, that is, it can be considered that the target blade fractures. Then, it is considered that the stress level applied last time is the vibration fatigue strength of the target blade. This method is mainly based on the finite element method for simulation, and there is no need to carry out fatigue performance measurement experiments, with low cost and no damage to the blade integrity.

[0123] The above embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it cannot be understood as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A method for determining the vibration fatigue strength of an aeroengine blade, characterized in that: The following steps are involved: Determine the location of the maximum stress point of the target blade; measuring the initial residual stress and the surface roughness at the maximum stress point; Measure the SN curve of the target blade material with a stress cycle ratio of -1; Take the horizontal coordinate point 10 on the SN curve 7 The corresponding 1 / 4~1 / 3 of the ordinate value is taken as the undetermined stress level; Using the undetermined stress level to perform finite element vibration simulation of the target blade to obtain the vibration stress of the maximum stress point in the blade chord direction and the blade height direction, wherein the blade chord direction and the blade height direction are in a curved surface coordinate system; Calculating the actual working stress of the maximum stress point in the chord direction and the blade height direction based on the initial residual stress and surface roughness of the maximum stress point and the vibration stress in the chord direction and the blade height direction; The actual working stress of the maximum stress point in the blade chord direction and the blade height direction is synthesized into a uniaxial stress; Calculating fatigue damage of a target blade at the to-be-determined stress level according to the uniaxial stress; Determine whether the sum of fatigue damage of the target blade under all pending stress levels is greater than 1. If so, the current stress level is the final stress level, and the final stress level is subtracted by Δσ as the vibration fatigue strength of the target blade. Otherwise, the current pending stress level is increased by Δσ as the new pending stress level, and then returns to the step of using the pending stress level to perform finite element vibration simulation of the target blade to obtain the vibration stress of the maximum stress point in the blade chord direction and the blade height direction, wherein Δσ represents the stress step.

2. The method for determining the vibration fatigue strength of an aircraft engine blade according to claim 1, characterized in that: The determination of the position of the maximum stress point of the target blade is performed based on ANSYS software, and includes the following steps: Import the three-dimensional model of the target blade into the static analysis module for preprocessing; Using at least 8 load steps to load a sinusoidal fluctuation acceleration load of any period on the preprocessed three-dimensional model of the target blade, calculate and select the output equivalent stress cloud diagram of the target blade; The position of the maximum stress point of the target blade is determined according to the equivalent stress cloud diagram.

3. The method for determining the vibration fatigue strength of an aircraft engine blade according to claim 1, characterized in that: The method of using the undetermined stress level to perform finite element vibration simulation of the target blade to obtain the vibration stress of the maximum stress point in the blade chord direction and the blade height direction is based on ANSYS software and includes the following steps: Import the three-dimensional model of the target blade into the static analysis module for preprocessing; Calculate the sinusoidal fluctuation acceleration load of the target blade finite element vibration simulation according to the undetermined stress level; Using at least 8 load steps to load the preprocessed three-dimensional model of the target blade with the sinusoidal fluctuation acceleration load of the finite element vibration simulation of the target blade, calculate and select the output directional stress cloud map of the target blade in the blade chord direction and the blade height direction; The vibration stress of the maximum stress point in the blade chord direction and the blade height direction is determined respectively according to the directional stress cloud diagram in the blade chord direction and the blade height direction.

4. The method for determining the vibration fatigue strength of an aircraft engine blade according to claim 2 or 3, characterized in that: The method of importing the three-dimensional model of the target blade into the statics analysis module for preprocessing includes the following steps: Setting a blade root of the three-dimensional model of the target blade as a fixed constraint; A grid-independent analysis is performed on the three-dimensional model of the target blade.

5. The method for determining the vibration fatigue strength of an aircraft engine blade according to claim 4, characterized in that: The surface roughness of the maximum stress point includes the arithmetic mean value of the profile of the maximum stress point in the blade chord direction and the blade height direction, the maximum peak-to-valley depth, the ten-point height of the microscopic roughness, and the equivalent valley bottom curvature radius of the profile.

6. The method for determining the vibration fatigue strength of an aircraft engine blade according to claim 5, characterized in that: The method of calculating the actual working stress of the maximum stress point in the chord direction and the blade height direction based on the initial residual stress and the surface roughness of the maximum stress point and the vibration stress in the chord direction and the blade height direction comprises the following steps: The residual stress of the maximum stress point in the chord direction and the blade height direction in the stable attenuation stage is calculated according to the initial residual stress of the maximum stress point in the chord direction and the blade height direction. The calculation formula is: ， In the formula, is the initial residual stress at the maximum stress point in the chord direction, is the residual stress at the stable decay stage of the maximum stress point in the chord direction, is the initial residual stress at the maximum stress point in the blade height direction, is the residual stress at the stable decay stage of the maximum stress point in the blade height direction; The stress concentration factor of the maximum stress point in the blade chord direction and the blade height direction is calculated according to the surface roughness of the maximum stress point, and the calculation formula is: ， In the formula, K st-x It represents the stress concentration factor of the maximum stress point in the chord direction. K st-y It represents the stress concentration factor of the maximum stress point in the blade height direction, R a-x represents the arithmetic mean of the blade chord profile, R y-x Indicates the maximum peak-to-valley depth in the blade chord direction, R z-x Indicates the ten-point height of the microscopic unevenness in the blade chord direction, ρ x represents the equivalent valley curvature radius of the blade chord direction profile, R a-y represents the arithmetic mean of the leaf height profile, R y-y Indicates the maximum peak-to-valley depth in the leaf height direction, R z-y Indicates the ten-point height of the microscopic unevenness in the leaf height direction, ρ y represents the equivalent valley curvature radius of the leaf height profile, n Characterization coefficients representing different stress states; The actual working stress of the maximum stress point in the chord direction and the blade height direction is calculated based on the residual stress, stress concentration factor and vibration stress in the stable attenuation stage of the maximum stress point in the chord direction and the blade height direction, respectively. The calculation formula is: ， In the formula, Indicates the actual working stress at the maximum stress point in the blade chord direction, represents the vibration stress at the maximum stress point in the blade chord direction, Indicates the actual working stress at the maximum stress point in the blade height direction, represents the vibration stress at the maximum stress point in the blade height direction, t Indicates time.

7. The method for determining the vibration fatigue strength of an aircraft engine blade according to claim 6, characterized in that: Based on the signed Von-Mises formula, the actual working stress of the maximum stress point in the blade chord direction and the blade height direction is synthesized into a uniaxial stress, and the synthetic calculation formula is: ， In the formula, represents the uniaxial stress, The determining factor of the stress state, .

8. The method for determining the vibration fatigue strength of an aircraft engine blade according to claim 7, characterized in that: The step of calculating fatigue damage of a target blade at the to-be-determined stress level according to the uniaxial stress comprises the following steps: Calculate the minimum cross-sectional area of ​​the uniaxial tension-compression fatigue standard specimen model; Calculating the product of the minimum cross-sectional area and the uniaxial stress as the uniaxial tensile and compressive load; The uniaxial tension-compression fatigue standard specimen model and the uniaxial tension-compression load are input into the ANSYS transient dynamics analysis module to calculate the load spectrum of the uniaxial tension-compression fatigue standard specimen model; Input the uniaxial tension-compression fatigue standard specimen model and the load spectrum of the uniaxial tension-compression fatigue standard specimen model into nCode software to obtain the life cloud diagram of the uniaxial tension-compression fatigue standard specimen model; The minimum life value in the life cloud diagram of the uniaxial tension-compression fatigue standard specimen model is used as the life of the target blade under the undetermined stress level; The fatigue damage of the target blade under the undetermined stress level is calculated according to the life of the target blade under the undetermined stress level, and the calculation formula is: ， In the formula, D represents the fatigue damage of the target blade under the undetermined stress level, N Represents the life of the target blade under the undetermined stress level.

9. The method for determining the vibration fatigue strength of an aircraft engine blade according to claim 1, characterized in that: Δσ is 10 MPa, 50 MPa or 100 MPa.

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