Fatigue limit prediction method for coating treatment blade of aero-engine

Abstract

The invention discloses a fatigue limit prediction method for an aero-engine coating treatment blade, and belongs to the technical field of aero-engines, and the method comprises the steps: obtaining a stress-strain curve of a stainless steel blade matrix through a uniaxial tensile test, and determining a constitutive model of a coating through a nanoindentation inversion analysis method; carrying out a coating blade fatigue test on a vibration table; establishing a finite element model of the coated blade in Abaqus; simulating a fatigue test of the coated blade on a vibration table by using a finite element method; establishing a blade fatigue limit prediction model considering coating treatment; extracting circumferential effective stress parameters of the dangerous point position of the coated blade; substituting the effective stress parameters into the established prediction model to obtain a fatigue limit prediction result, and mutually verifying the prediction result and a test result; according to the method for predicting the fatigue limit of the coating-treated blade of the aero-engine, the influence of coating treatment on the fatigue performance of the blade is considered, the fatigue limit of the coating-treated blade can be predicted, and the precision of a prediction result is high.

Description

Technical Field

[0001] The invention relates to the technical field of aeroengines, and in particular to a method for predicting fatigue limits of coating-treated blades of an aeroengine. Background Art

[0002] Aircraft engine blades are one of the most numerous and harshest working environment components in aircraft engines. During service, aircraft engine blades are subjected to vibration stresses induced by various aerodynamic and mechanical reasons. Since aircraft engine blades work in complex environments such as high temperature, humidity and alternating stress for a long time, anti-corrosion coating treatment of engine blades can effectively protect the blades and prevent them from being eroded by corrosive media. However, coating treatment may affect the surface state of stainless steel blades and their high-cycle fatigue performance. Therefore, factors such as coating and blade configuration must be considered when constructing a fatigue limit prediction model suitable for aircraft engine blades. A fatigue limit prediction model for stainless steel simulated blades considering the coating-substrate stress gradient effect was established, and the error of the model was verified by conducting simulated blade vibration fatigue tests. The fatigue limit prediction model for stainless steel blades with coating treatment for aircraft engines established can provide theoretical support and guidance standards for setting safe working loads for engine blades, which has positive significance for ensuring the safe operation of aircraft engines. Summary of the invention

[0003] The purpose of the present invention is to provide a method for predicting the fatigue limit of a coating-treated blade of an aero-engine, taking into account the influence of coating treatment on the fatigue performance of the blade, and predicting the fatigue limit of the coating-treated blade.

[0004] To achieve the above object, the present invention provides a method for predicting the fatigue limit of a coating-treated blade of an aero-engine, comprising the following steps:

[0005] S1. The stress-strain curve of the stainless steel blade substrate is obtained by uniaxial tensile test, and the constitutive model of the coating is determined by nanoindentation inversion analysis;

[0006] S2. Carry out fatigue test on the coated blade on a vibration table, and determine the fatigue limit of the coated blade by finding the frequency and using the step-by-step load loading method;

[0007] S3. Establish a finite element model of the coated blade in Abaqus;

[0008] S4. Use finite element method to simulate the fatigue test of coated blades on a vibration table;

[0009] S5. Establish a blade fatigue limit prediction model considering coating treatment;

[0010] S6, extracting the circumferential effective stress parameters at the dangerous point of the coated blade and importing them into the prediction model to calculate the fatigue limit;

[0011] S7. Substitute the effective stress parameters into the established prediction model to obtain fatigue limit prediction results, and verify the prediction results with the test results.

[0012] Preferably, the specific steps of S1 are as follows:

[0013] S11. The stress-strain curve of the stainless steel blade substrate is obtained by uniaxial tensile test, and the JC constitutive model of formula (1) is obtained by fitting;

[0014] σ=1296+1716ε 0.765 (1)

[0015] Among them, σ is stress and ε is strain;

[0016] S12. Since the coating is relatively thin, the constitutive model of the coating is determined by the nanoindentation inversion analysis method. The hardness and elastic modulus of the coating are determined by the nanoindentation test. The characteristic stress σ is calculated by formula (2) and formula (3): r and characteristic strain ε r ;

[0017]

[0018]

[0019] Among them, E r is the composite elastic modulus, H is the coating hardness;

[0020] S13. Determine the hardening index n and yield strength σ by formula (4) and formula (5) r ;

[0021]

[0022]

[0023] Among them, h r is the residual depth after unloading, h m is the maximum penetration depth, σ y is the yield stress;

[0024] S14, finally determine the constitutive model of the coating as formula (6);

[0025] σ=936.99(1+73.97ε) 0.681 (6).

[0026] Preferably, in step S2, the stress ratio of the coated blade fatigue test is R=-1.

[0027] Preferably, in step S3, the size ratio of the coated blade finite element model to the test piece is 1:1.

[0028] Preferably, the specific steps of S4 are as follows:

[0029] S41, fix the petiole in all directions;

[0030] S42, through harmonic response analysis, it is found that the first-order natural frequency of the blade is around 1053Hz;

[0031] S43. In the simulation experiment, an exciting force in the vertical direction is applied to simulate the loading conditions in the actual test.

[0032] Preferably, the specific steps of S5 are as follows:

[0033] S51. Combining the Basquin and Walker models, we get formula (7). Taking the logarithm of both ends of formula (7), we get the fatigue limit prediction model, which is formula (8);

[0034]

[0035]

[0036] Where a is the material parameter, N f is fatigue life, σ max is the fatigue limit, y is the average stress influencing parameter, and R is the stress ratio;

[0037] S52, calculating the omnidirectional gradient stress influence factor ΔT;

[0038] S53. Calculate stress concentration influence factor K s ;

[0039] S54, introduce the omnidirectional gradient stress influence factor ΔT and stress concentration influence factor K s , establish a fatigue limit prediction model for simulating the omnidirectional gradient stress field of the blade, and calculate the fatigue limit σ of the simulated blade max ;

[0040] S55. Bring each parameter into the fatigue limit prediction model of the omnidirectional gradient stress field of the coating-substrate multilayer structure to obtain the fatigue limit of the coated stainless steel blade.

[0041] Preferably, the specific steps of S52 are as follows:

[0042] S521. Taking the fatigue damage danger point as the base point, take a series of equidistant points in the tip direction, symmetry axis direction, petiole direction and thickness direction of the blade, and record the corresponding stress values;

[0043] S522, respectively normalizing the distance values ​​and stress values ​​affected by the four groups of gradient stress fields, and drawing distance-stress normalization curves;

[0044] S523, the omnidirectional gradient stress influence factor ΔT is calculated based on the stress gradient value and the gradient stress field influence distance value obtained by simulation, and the formula is as follows:

[0045] ΔT=(b1·S1)+(b2·S2)+(b3·S3)+(b4·S4) (9)

[0046] Among them, S1, S2, S3, S4 are the areas enclosed by the distance-stress normalized curves in the four directions of the leaf tip, symmetry axis, petiole and thickness, respectively; b1, b2, b3, b4 are weighting coefficients, b1+b2+b3+b4=1;

[0047] The calculation formulas for s1, s2, and S3 are as follows:

[0048]

[0049] The calculation formula of S4 is as follows:

[0050]

[0051] The calculation formula of χ(r) is as follows:

[0052]

[0053] Among them, L is the influence distance of the gradient stress field of the blade stress peak point in this direction, σ(r) is the stress field, r is the field diameter, χ(r) is the stress gradient, t is the coating thickness, and T is the blade thickness.

[0054] Preferably, the specific steps of S53 are as follows:

[0055] S531. In order to study and analyze the actual influence of stress concentration effect on fatigue damage danger points, under the same loading conditions, actual simulated blade aerodynamic uniform load loading finite element simulation experiment and no-draft simulated blade aerodynamic uniform load loading finite element simulation experiment were carried out to study the stress concentration effect caused by the draft angle;

[0056] S532, get stress concentration influence factor K s The formula is as follows:

[0057]

[0058] Among them, σ1 is the maximum stress value of the fatigue failure point of the actual simulated blade, and σ2 is the stress value of the corresponding point of the simulated blade without draft.

[0059] Preferably, the specific steps of S54 are as follows:

[0060] S541, introduce the omnidirectional gradient stress influence factor ΔT and stress concentration influence factor K s We get formula (14);

[0061]

[0062] S542. Taking the logarithm of both sides of formula (14), the fatigue limit prediction model for simulating the omnidirectional gradient stress field of the blade is obtained as formula (15);

[0063]

[0064] S543, material parameter a, stress gradient influence factor ΔT, stress concentration influence factor K s Bring it into the fatigue limit prediction model, and the fatigue life N f The fatigue limit σ is calculated max , when N f =10 7 When the simulated blade fatigue limit σ is obtained max .

[0065] Preferably, the fatigue limit prediction model of the omnidirectional gradient stress field of the coating-substrate multilayer structure in S55 is as follows:

[0066]

[0067] Among them, N f is fatigue life, σ max is the fatigue limit, a is the material parameter, y is, R is, K s is the stress concentration influencing factor, and ΔT is the omnidirectional gradient stress influencing factor.

[0068] Therefore, the present invention adopts the above-mentioned method for predicting fatigue limit of blades treated with coating of an aero-engine, which has the following beneficial effects:

[0069] (1) Considering the thin and brittle characteristics of the coating, the constitutive parameters of the coating were effectively obtained by using the nanoindentation inversion analysis method;

[0070] (2) The influence of coating on the fatigue limit of blades is considered from the perspective of stress field, and a fatigue limit prediction model for blades coated with omnidirectional gradient stress field is proposed. This model improves the calculation efficiency while ensuring the calculation accuracy.

[0071] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1This is a flow chart of a method for predicting fatigue limit of a blade treated with coating of an aero-engine according to the present invention;

[0073] Figure 2 The fatigue limit prediction method of the coating-treated blade of an aero-engine is obtained by simulating 15 materials with different elastic moduli (50-150 GPa) and characteristic stresses (0.5-2 GPa). with lnε r Distribution diagram of ;

[0074] Figure 3 is the hardening index n of the fatigue limit prediction method of the coating-treated blade of an aero-engine according to the present invention, Three-dimensional surface graph composed of three parameters;

[0075] Figure 4 A top view of a finite element model of a method for predicting fatigue limit of a blade treated with a coating of an aero-engine according to the present invention;

[0076] Figure 5 A front view of a finite element model of a method for predicting fatigue limit of a blade treated with a coating of an aero-engine according to the present invention;

[0077] Figure 6 A side view of a finite element model of a method for predicting fatigue limit of a blade treated with a coating of an aero-engine according to the present invention;

[0078] Figure 7 Four groups of normalized curves of gradient stress field affecting distance value and stress value of a method for predicting fatigue limit of an aero-engine coating treated blade according to the present invention are shown, wherein (a) is a distance-stress normalized curve in the tip direction, (b) is a distance-stress normalized curve in the petiole direction, (c) is a distance-stress normalized curve in the blade surface direction, and (d) is a distance-stress normalized curve in the thickness direction.

[0079] Figure 8 This is a diagram showing the result of a finite element simulation experiment of a method for predicting the fatigue limit of an aero-engine coating-treated blade according to the present invention, which actually simulates the aerodynamic uniformly distributed load on the blade;

[0080] Fig. 9 This is a diagram showing the results of a finite element simulation experiment of a method for predicting the fatigue limit of an aero-engine coating-treated blade without a draft simulation blade and aerodynamic uniform load loading. DETAILED DESCRIPTION

[0081] The following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0082] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0083] Example

[0084] like Figure 1 As shown, the present invention provides a method for predicting fatigue limit of a coating-treated blade of an aero-engine, comprising the following steps:

[0085] S1. The stress-strain curve of the stainless steel blade substrate was obtained through uniaxial tensile test, and the constitutive model of the coating was determined by nanoindentation inversion analysis.

[0086] S11. The stress-strain curve of the stainless steel blade substrate is obtained by uniaxial tensile test, and the JC constitutive model of formula (1) is obtained by fitting;

[0087] σ=1296+1716ε 0.765 (1)

[0088] Among them, σ is stress and ε is strain.

[0089] S12. Since the coating is relatively thin, the constitutive model of the coating is determined by the nanoindentation inversion analysis method. The hardness and elastic modulus of the coating are determined by the nanoindentation test. The characteristic stress σ is calculated by formula (2) and formula (3): r and characteristic strain ε r .

[0090]

[0091] Among them, E r is the composite elastic modulus, and H is the hardness of the coating.

[0092] Fifteen materials with different elastic modulus (50-150 GPa) and characteristic stress (0.5-2 GPa) were designed for simulation. with lnε r The distribution relationship diagram of Figure 2 As shown, the distribution relationship between the two is fitted to obtain the functional relationship of formula (3);

[0093]

[0094] S13. Determine the hardening index n and yield strength σ by formula (4) and formula (5)r ; Figure 3 is the hardening index n, The three-dimensional surface graph composed of the three parameters, the coating hardening index model is determined by formula (4);

[0095]

[0096]

[0097] Among them, h r is the residual depth after unloading, h m is the maximum indentation depth, σ y is the yield stress.

[0098] S14. The constitutive model of the coating is finally determined as formula (6).

[0099] σ=936.99(1+73.97ε) 0.681 (6)

[0100] S2. Carry out fatigue test of coated blades on a vibration table, determine the fatigue limit of coated blades by finding frequency and adopting step-by-step load loading method, and the stress ratio of coated blade fatigue test is R=-1.

[0101] S3, such as Figure 4-Figure 6 As shown, a finite element model of the coated blade is established in Abaqus, and the size ratio of the coated blade finite element model to the test piece is 1:1.

[0102] S4. Use the finite element method to simulate the fatigue test of the coated blade on the vibration table.

[0103] S41, fix the petiole in all directions;

[0104] S42. The first-order natural frequency of the blade is determined to be 1053 Hz through harmonic response analysis;

[0105] S43. In the simulation experiment, an exciting force in the vertical direction is applied to simulate the loading conditions in the actual test.

[0106] S5. Establish a blade fatigue limit prediction model taking coating treatment into account.

[0107] S51. Combining the Basquin and Walker models, we get formula (7). Taking the logarithm of both ends of formula (7), we get the fatigue limit prediction model, which is formula (8);

[0108]

[0109]

[0110] Where a is the material parameter, Nf is fatigue life, σ max is the fatigue limit, y is the average stress influence parameter, and R is the stress ratio;

[0111] S52. Calculate the omnidirectional gradient stress influence factor ΔT.

[0112] S521. Taking the fatigue damage danger point as the base point, select a series of equidistant points in the four directions of the blade tip, symmetry axis, petiole and thickness, and record the corresponding stress values.

[0113] S522, respectively normalize the distance values ​​and stress values ​​of the four groups of gradient stress fields, and draw distance-stress normalization curves, such as Figure 7 As shown, the horizontal axis is the normalized value of distance, and the vertical axis is the normalized value of stress.

[0114] S523, calculating and calculating the formula of the omnidirectional gradient stress influence factor ΔT based on the stress gradient value and the gradient stress field influence distance value obtained by simulation;

[0115] ΔT=(b1·S1)+(b2·S2)+(b3·S3)+(b4·S4)=(0.2×(0.2×0.297416)+0.422886)+(0.2×0.419779)+(0.4×0.764789)≈0.5339318 (9)

[0117] Among them, S1, S2, S3, S4 are the areas enclosed by the distance-stress normalized curves in the four directions of the leaf tip, symmetry axis, petiole and thickness, respectively; b1, b2, b3, b4 are weighting coefficients, b1+b2+b3+b4=1;

[0118] The calculation formulas for S1, S2, and S3 are as follows:

[0119]

[0120] The calculation formula of S4 is as follows:

[0121]

[0122] The calculation formula of χ(r) is as follows:

[0123]

[0124] Among them, L is the influence distance of the gradient stress field of the blade stress peak point in this direction, σ(r) is the stress field, r is the field diameter, χ(r) is the stress gradient, t is the coating thickness, and T is the blade thickness.

[0125] S53. Calculate stress concentration influence factor K s .

[0126] S531. In order to study and analyze the actual influence of stress concentration effect on fatigue damage danger point, under the same loading conditions, actual simulation blade aerodynamic uniform load loading finite element simulation experiment and no draft simulation blade aerodynamic uniform load loading finite element simulation experiment were carried out to study the stress concentration effect caused by the draft angle. The experimental results are as follows: Figure 8 and Fig. 9 As shown;

[0127] S532, get stress concentration influence factor K s Formula and calculation;

[0128]

[0129] Among them, σ1 is the maximum stress value of the fatigue failure point of the actual simulated blade, and σ2 is the stress value of the corresponding point of the simulated blade without draft.

[0130] S54, introduce the omnidirectional gradient stress influence factor ΔT and stress concentration influence factor K s , establish a fatigue limit prediction model for simulating the omnidirectional gradient stress field of the blade, and calculate the fatigue limit σ of the simulated blade max .

[0131] S541, introduce the omnidirectional gradient stress influence factor ΔT and stress concentration influence factor K s We get formula (11);

[0132]

[0133] S542. Taking the logarithm of both sides of formula (11), the fatigue limit prediction model for simulating the omnidirectional gradient stress field of the blade is obtained as formula (12);

[0134]

[0135] S543, material parameter a, stress gradient influence factor ΔT, stress concentration influence factor K s Bring it into the fatigue limit prediction model, and the fatigue life N f The fatigue limit σ is calculated max , when N f =10 7 When the simulated blade fatigue limit σ is obtained max .

[0136] S55. Bring each parameter into the fatigue limit prediction model of the omnidirectional gradient stress field of the coating-substrate multilayer structure to obtain the fatigue limit of the coated stainless steel blade.

[0137] The fatigue limit prediction model of the omnidirectional gradient stress field of the coating-substrate multilayer structure is as follows:

[0138]

[0139] Among them, N f is fatigue life, σ max is the fatigue limit, a is the material parameter, y is, R is, K s is the stress concentration influencing factor, and ΔT is the omnidirectional gradient stress influencing factor.

[0140] Known N f =10 7 , a=0.0000468041, y=0.61627907, R=-1, K=1.314172, ΔT=0.5339318, the fatigue limit prediction model of the coating-substrate multilayer structure omnidirectional gradient stress field calculates that the fatigue limit of the coated stainless steel blade is 667.03MPa.

[0141] S6. Extract the circumferential effective stress parameters at the dangerous point of the coated blade and import them into the prediction model to calculate the fatigue limit.

[0142] S7. Substitute the effective stress parameters into the established prediction model to obtain fatigue limit prediction results, and verify the prediction results predicted by the fatigue prediction model with the test results.

[0143] Therefore, the present invention adopts the above-mentioned method for predicting the fatigue limit of an aircraft engine coating-treated blade, takes into account the influence of coating treatment on the fatigue performance of the blade, and can predict the fatigue limit of the coating-treated blade with high prediction accuracy.

[0144] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for predicting fatigue limit of coated blades of an aero-engine, characterized in that: The following steps are involved: S1. The stress-strain curve of the stainless steel blade substrate is obtained by uniaxial tensile test, and the constitutive model of the coating is determined by nanoindentation inversion analysis; S2. Carry out fatigue test on the coated blade on a vibration table, and determine the fatigue limit of the coated blade by finding the frequency and using the step-by-step load loading method; S3. Establish a finite element model of the coated blade in Abaqus; S4. Use finite element method to simulate the fatigue test of coated blades on a vibration table; S5. Establish a blade fatigue limit prediction model considering coating treatment; S6, extracting the circumferential effective stress parameters at the dangerous point of the coated blade and importing them into the prediction model to calculate the fatigue limit; S7. Substitute the effective stress parameters into the established prediction model to obtain fatigue limit prediction results, and verify the prediction results with the test results.

2. The fatigue limit prediction method for aero-engine coating treated blade according to claim 1, characterized in that: The specific steps of S1 are as follows: S11. The stress-strain curve of the stainless steel blade substrate is obtained by uniaxial tensile test, and the JC constitutive model of formula (1) is obtained by fitting; σ=1296+1716ε 0.765 (1) Where σ is stress and ε is strain; S12. Determine the constitutive model of the coating by nanoindentation inversion analysis, determine the hardness and elastic modulus of the coating by nanoindentation test, and calculate the characteristic stress σ by formula (2) and formula (3): r and characteristic strain ε r ; Among them, E r is the composite elastic modulus, H is the coating hardness; S13. Determine the hardening index n and yield strength σ by formula (4) and formula (5) r ; Among them, h r is the residual depth after unloading, h m is the maximum indentation depth, σ y is the yield stress; S14, finally determine the constitutive model of the coating as formula (6); σ=936.99(1+73.97ε) 0.681 (6)。 3. The method for predicting fatigue limit of a coating-treated blade of an aero-engine according to claim 1, characterized in that: In step S2, the stress ratio of the coated blade fatigue test is R=-1.

4. The method for predicting fatigue limit of a coating-treated blade of an aero-engine according to claim 1, characterized in that: In step S3, the size ratio of the coated blade finite element model to the test piece is 1:

1.

5. The method for predicting fatigue limit of a coating-treated blade of an aero-engine according to claim 1, characterized in that: The specific steps of S4 are as follows: S41, fix the petiole in all directions; S42. The first-order natural frequency of the blade is determined to be 1053 Hz through harmonic response analysis; S43. In the simulation experiment, an exciting force in the vertical direction is applied to simulate the loading conditions in the actual test.

6. The method for predicting fatigue limit of a coating-treated blade of an aero-engine according to claim 1, characterized in that: The specific steps of S5 are as follows: S51. Combining the Basquin and Walker models, we get formula (7). Taking the logarithm of both ends of formula (7), we get the fatigue limit prediction model, which is formula (8); Among them, a is the material parameter, N f is fatigue life, σ max is the fatigue limit, y is the average stress influence parameter, and R is the stress ratio; S52, calculating the omnidirectional gradient stress influence factor ΔT; S53. Calculate stress concentration influence factor K s ; S54, Introducing ΔT and K s , establish a fatigue limit prediction model for simulating the omnidirectional gradient stress field of the blade, and calculate the fatigue limit σ of the simulated blade max ; S55. Bring each parameter into the fatigue limit prediction model of the omnidirectional gradient stress field of the coating-substrate multilayer structure to obtain the fatigue limit of the coated stainless steel blade.

7. The method for predicting fatigue limit of a coating-treated blade of an aero-engine according to claim 6, characterized in that: The specific steps of S52 are as follows: S521. Taking the fatigue damage danger point as the base point, take a series of equidistant points in the tip direction, symmetry axis direction, petiole direction and thickness direction of the blade, and record the corresponding stress values; S522, respectively normalizing the distance values ​​and stress values ​​affected by the four groups of gradient stress fields, and drawing distance-stress normalization curves; S523, the omnidirectional gradient stress influence factor ΔT is calculated based on the stress gradient value and the gradient stress field influence distance value obtained by simulation, and the formula is as follows: ΔT=(b1·S1)+(b2·S2)+(b3·S3)+(b4·S4) (9) Among them, S1, S2, S3, S4 are the areas enclosed by the distance-stress normalized curves in the four directions of the leaf tip, symmetry axis, petiole and thickness, respectively; b1, b2, b3, b4 are weighting coefficients, b1+b2+b3+b4=1; The calculation formulas for S1, S2, and S3 are as follows: The calculation formula of S4 is as follows: The calculation formula of χ(r) is as follows: Among them, L is the influence distance of the gradient stress field of the blade stress peak point in this direction, σ(r) is the stress field, r is the field diameter, χ(r) is the stress gradient, t is the coating thickness, and T is the blade thickness.

8. The method for predicting fatigue limit of a coating-treated blade of an aero-engine according to claim 6, characterized in that: The specific steps of S53 are as follows: S531. Under the same loading conditions, the actual simulated blade aerodynamic uniform load loading finite element simulation experiment and the undrafted simulated blade aerodynamic uniform load loading finite element simulation experiment were carried out to study the stress concentration effect caused by the draft angle; S532, get stress concentration influence factor K s The formula is as follows: Among them, σ1 is the maximum stress value of the fatigue failure point of the actual simulated blade, and σ2 is the stress value of the corresponding point of the simulated blade without draft.

9. The method for predicting fatigue limit of a coating-treated blade of an aero-engine according to claim 8, characterized in that: The specific steps of S54 are as follows: S541, introduce the omnidirectional gradient stress influence factor ΔT and stress concentration influence factor K s We get formula (14); S542. Taking the logarithm of both sides of formula (14), the fatigue limit prediction model for simulating the omnidirectional gradient stress field of the blade is obtained as formula (15); S543, material parameter a, stress gradient influence factor ΔT, stress concentration influence factor K s Bring it into the fatigue limit prediction model, and the fatigue life N f The fatigue limit σ is calculated max , when N f =10 7 When the simulated blade fatigue limit σ is obtained max .

10. The method for predicting fatigue limit of a coating-treated blade of an aero-engine according to claim 9, characterized in that: The fatigue limit prediction model of the omnidirectional gradient stress field of the coating-substrate multilayer structure in S55 is as follows: Among them, N f is fatigue life, σ max is the fatigue limit, a is the material parameter, y is, R is, K s is the stress concentration influencing factor, and ΔT is the omnidirectional gradient stress influencing factor.

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