Turbine disc alloy fatigue life prediction method considering residual stress relaxation evolution

Abstract

The invention discloses a turbine disc alloy fatigue life prediction method considering residual stress relaxation evolution, which comprises the following steps: determining the size of a notch-containing simulation part of a turbine disc, and carrying out size optimization based on a dangerous point and a stress gradient; establishing a three-point bending finite element model, simulating a residual stress field and a work hardening field introduced by laser shock peening (LSP), and obtaining stress-strain states after a first period and a stable period through cyclic loading; compared with the prior art, the fatigue life prediction method has the advantages that by introducing the stress-strain state after the residual stress field is stabilized and combining a Walker index correction model, the problem of prediction deviation caused by neglecting subsequent relaxation in a traditional method is solved, the fatigue life margin is accurately evaluated, and the fatigue life prediction accuracy is improved. And an optimization basis is provided for the design of the turbine disc, so that the service cycle is prolonged within a safety threshold.

Description

Technical Field

[0001] The present invention relates to the technical field of material fatigue prediction, specifically a fatigue life prediction method for turbine disk alloys considering the relaxation evolution of residual stress. Background Art

[0002] Laser Shock Peening (LSP) technology is closely related to the demands of high-end manufacturing fields such as aerospace, nuclear power, and ocean engineering. LSP forms a deep compressive residual stress field and gradient nanostructure on the material surface through laser-induced shock waves, significantly improving the corrosion resistance and fatigue performance of materials. It has become one of the key technologies in aero-engine manufacturing. It is very important to incorporate the improvement of fatigue life margin brought by LSP into the turbine disk life design consideration.

[0003] A large number of studies on the residual stress relaxation of LSP components are based on the assumption that the residual stress relaxes significantly in the early stage and then stabilizes, ignoring the influence of subsequent cyclic loads on residual stress relaxation. The research on residual stress relaxation under cyclic loads is relatively limited, especially the lack of scientific understanding of residual stress relaxation and evolution under high-temperature and high-stress conditions. For example, a fatigue life prediction method considering the residual stress relaxation effect applied by Nanjing University of Aeronautics and Astronautics with the application number CN202210103839.2, and a fatigue life prediction method applied by Ocean University of China with the application number 20241049909.5

[0004] Currently, there is no accurate fatigue life prediction method for turbine disk simulation parts considering the relaxation evolution of residual stress in China. Aiming at the above defects, the present invention proposes a prediction method considering the continuous relaxation evolution of residual stress under cyclic loads, which significantly improves the prediction accuracy by establishing a dynamic stress-strain model and modifying the life equation. Summary of the Invention

[0005] (I) Technical Problem

[0006] The present invention provides a fatigue life prediction method for turbine disk alloys considering the relaxation evolution of residual stress, aiming to solve the technical problems mentioned in the background art.

[0007] (II) Technical Content

[0008] To solve the above technical problems, the technical solution of the present invention is: a fatigue life prediction method for turbine disk alloys considering the relaxation evolution of residual stress, including the following steps:

[0009] S1. Determine the size of the turbine disk notched simulation part, and optimize the size based on the critical point and stress gradient;

[0010] S2. Establish a three-point bending finite element model to simulate the residual stress field and work-hardening field introduced by laser shock peening (LSP), and obtain the stress-strain state after the first cycle and the stable cycle through cyclic loading;

[0011] S3. Perform fatigue life prediction based on the modified Manson-Coffin equation and the SWT method, where the Walker exponent is introduced to characterize the sensitivity of the material to the mean stress, and the Walker exponent is calculated by the following formula:

[0012]

[0013] In the formula, σ 0.2 is the yield strength, and σ b is the tensile strength;

[0014] S4. Combine the stress-strain state after the stabilization of the residual stress field and use the modified SWT model to predict the fatigue life. The SWT model is:

[0015]

[0016] Among them, σ max is the maximum stress, ε a is the total strain amplitude, σ′ f and ε′ f are the fatigue strength coefficient and fatigue ductility coefficient respectively, b and c are fatigue index parameters, and E is the elastic modulus;

[0017] S5. Substitute the damage parameter SWT based on the critical plane method into the SWT model to obtain the modified SWT model:

[0018]

[0019]

[0020] Furthermore, in step S2, the inverse eigenstrain method is used to establish the residual stress field, combined with the mesh division of the quarter model and the cyclic loading boundary conditions.

[0021] Furthermore, the Walker exponent is determined through uniaxial tensile test data and is correlated with the stress ratio to improve the prediction accuracy under asymmetric cyclic loading.

[0022] Furthermore, the fatigue strength coefficient σ′ f and the fatigue ductility coefficient ε′ f are calculated based on the uniaxial tensile test data of the material by the improved slope method. The formula is as follows:

[0023]

[0024] Where, σ b is the tensile strength, and ψ is the reduction of area.

[0025] (3) Technical effects

[0026] The advantages of the present invention compared with the prior art are as follows: By introducing the stress-strain state after the stabilization of the residual stress field and combining with the Walker index correction model, the prediction deviation caused by ignoring the subsequent relaxation in the traditional method is solved. The fatigue life margin is accurately evaluated, providing an optimization basis for the design of turbine disks, and extending the service life within the safety threshold. By combining finite element simulation with a parametric model, the dependence on a large number of physical tests is reduced, and the R & D efficiency is improved. Description of the drawings

[0027] Figure 1 is a schematic diagram of the notched specimen of the present invention.

[0028] Figure 2 is a schematic diagram of the comparison result of the life prediction under all load conditions of the present invention.

[0029] Figure 3 is a schematic diagram of the mesh division and loading method of the quarter model of the present invention. Detailed implementation manners

[0030] The following further describes the present invention in detail with reference to the drawings. Taking the notched simulation part of FGH4098 alloy after laser shock peening as an example in this embodiment, the fatigue life prediction is carried out, and the specimen size and loading method are as Figure 1 shown.

[0031] Combined with Fig. Figure 1 to Fig. Figure 3 , the fatigue life prediction method of the turbine disk alloy considering the residual stress relaxation evolution includes the following steps:

[0032] S1. Determine the size of the notched simulation part of the turbine disk, and optimize the size based on the critical point and stress gradient;

[0033] S2. Establish a three-point bending finite element model to simulate the residual stress field and work hardening field introduced by laser shock peening (LSP), and obtain the stress-strain state after the first cycle and the stable cycle through cyclic loading;

[0034] S3. Conduct fatigue life prediction based on the modified Manson-Coffin equation and the SWT method, where the Walker index is introduced to characterize the sensitivity of the material to the mean stress, and the Walker index is calculated by the following formula:

[0035]

[0036] Where, σ 0.2is the yield strength, σ b is the tensile strength;

[0037] S4. Combine the stress-strain state after the residual stress field stabilizes, and use the modified SWT model to predict the fatigue life. The SWT model is:

[0038]

[0039] where, σ max is the maximum stress, ε a is the total strain amplitude, σ′ f and ε′ f are the fatigue strength coefficient and fatigue ductility coefficient respectively, b and c are fatigue index parameters, and E is the elastic modulus; for the fatigue behavior of FGH4098 alloy at 650 °C, the parameters of this equation are shown in the following table:

[0040]

[0041] S5. Substitute the damage parameter SWT based on the critical plane method into the SWT model to obtain the modified SWT model:

[0042]

[0043] In step S2, the inverse eigenstrain method is used to establish the residual stress field, combined with the mesh division of the quarter model and the cyclic loading boundary conditions.

[0044] The Walker exponent is determined from the uniaxial tensile test data and is related to the stress ratio to improve the prediction accuracy under asymmetric cyclic loading.

[0045] The fatigue strength coefficient σ′ f and the fatigue ductility coefficient ε′ f are calculated based on the uniaxial tensile test data of the material by the improved slope method. The formula is as follows:

[0046]

[0047] In the formula, σ b is the tensile strength, and ψ is the reduction of area.

[0048] The test results of this example under various load conditions at 650 °C are compared with the two simulation results as follows:

[0049]

[0050] The above describes the present invention and its implementation manners. Such description is not restrictive. What is shown in the drawings is only one of the implementation manners of the present invention, and the actual structure is not limited thereto. In general, if those of ordinary skill in the art are inspired by it and, without departing from the gist of the present invention, design similar structural manners and embodiments to this technical solution without creative efforts, they shall fall within the protection scope of the present invention.

Claims

1. A method for predicting fatigue life of turbine disk alloys considering residual stress relaxation evolution, characterized in that: The following steps are involved: S1. Determine the size of the turbine disk notched simulation part and optimize the size based on the dangerous point and stress gradient; S2. Establish a three-point bending finite element model to simulate the residual stress field and work hardening field introduced by laser shock strengthening (LSP), and obtain the stress-strain state after the first cycle and the stable cycle through cyclic loading; S3. Fatigue life prediction is performed based on the modified Manson-Coffin equation and the SWT method, in which the Walker index is introduced to characterize the sensitivity of the material to the average stress, and the Walker index is calculated by the following formula: In the formula, σ 0.2 is the yield strength, σ b is the tensile strength; S4. Combining the stress-strain state after the residual stress field is stabilized, the fatigue life is predicted using the modified SWT model, where the SWT model is: Among them, σ max is the maximum stress, ε a is the total strain amplitude, σ′ f and ε′ f are fatigue strength coefficient and fatigue ductility coefficient respectively, b and c are fatigue index parameters, and E is elastic modulus; S5. Substitute the damage parameter SWT based on the critical surface method into the SWT model to obtain the modified SWT model:

2. The method for predicting fatigue life of turbine disk alloy considering residual stress relaxation evolution according to claim 1, characterized in that: The residual stress field in step S2 is established by using the inverse eigenstrain method in combination with the meshing of the quarter model and the cyclic loading boundary conditions.

3. The method for predicting fatigue life of turbine disk alloy considering residual stress relaxation evolution according to claim 1, characterized in that: The Walker index is determined from uniaxial tensile test data and correlated to stress ratios to improve prediction accuracy under asymmetric cyclic loading.

4. The method for predicting fatigue life of turbine disk alloy considering residual stress relaxation evolution according to claim 1, characterized in that: The fatigue strength coefficient σ′ f and fatigue ductility coefficient ε′ f Based on the uniaxial tensile test data of the material, it is calculated by the improved slope method, and the formula is as follows: In the formula, σ b is the tensile strength and ψ is the area reduction rate.

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