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

Abstract

The application discloses a turbine disc alloy fatigue life prediction method considering residual stress relaxation evolution, and comprises the following steps: determining the size of a notched simulation piece of a turbine disc, and performing size optimization based on a dangerous point and a stress gradient; establishing a three-point bending finite element model to simulate a residual stress field and a work hardening field introduced by laser shock peening (LSP), and acquiring stress and strain states after the first cycle and after a stable cycle through cyclic loading; and performing fatigue life prediction based on a modified Manson-Coffin equation and a SWT method. Compared with the prior art, the method has the advantages that by introducing the stress and strain states after the residual stress field is stabilized, and combining a Walker index correction model, the prediction deviation caused by the traditional method in neglecting subsequent relaxation is solved, the fatigue life margin is accurately evaluated, an optimization basis is provided for turbine disc design, and the service cycle of the turbine disc is prolonged within a safety threshold.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material fatigue prediction, in particular to a turbine disc alloy fatigue life prediction method considering residual stress relaxation evolution. BACKGROUND

[0002] Laser shock peening (LSP) technology is closely related to the needs of high-end manufacturing fields such as aerospace, nuclear power, and marine 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 and fatigue performance of the material. It has become one of the key technologies in the manufacture of aero-engines. It is very important to include the fatigue life margin improvement brought by LSP into the turbine disc life design consideration.

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

[0004] At present, there is no turbine disc simulation fatigue life prediction method that accurately considers the evolution of residual stress relaxation. The present application proposes a prediction method that considers the continuous relaxation evolution of residual stress under cyclic loading by establishing a dynamic stress-strain model and modifying the life equation, which significantly improves the prediction accuracy. SUMMARY

[0005] (I) Technical problem

[0006] The present application provides a turbine disc alloy fatigue life prediction method considering residual stress relaxation evolution, 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 application is as follows: a turbine disc alloy fatigue life prediction method considering residual stress relaxation evolution, comprising the following steps:

[0009] S1, determine the size of the turbine disc notched simulation piece, and optimize the size based on the dangerous 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 after the stable cycle through cyclic loading.

[0011] S3. Fatigue life prediction is performed based on the modified Manson-Coffin equation and the SWT method, where the Walker index is introduced to characterize the material's sensitivity to mean stress, and the Walker index is calculated using the following formula:

[0012]

[0013] In the formula, σ 0.2 For yield strength, σ b Tensile strength;

[0014] S4. Based on the stress-strain state after the residual stress field has stabilized, the fatigue life is predicted using the modified SWT model, which is:

[0015]

[0016] Where, σ max For the maximum stress, ε a For the total strain amplitude, σ′ f and ε′ f These 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 surface method into the SWT model to obtain the modified SWT model:

[0018]

[0019]

[0020] Furthermore, the residual stress field described in step S2 is established using the inverse eigenstrain method, combined with the meshing of the quarter-model and cyclic loading boundary conditions.

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

[0022] Furthermore, the fatigue strength coefficient σ′ f and fatigue ductility coefficient ε′ f Based on uniaxial tensile test data of the material, the result was calculated using a modified slope method, as shown in the following formula:

[0023]

[0024] In the formula, σ b ψ represents tensile strength, and ψ represents the reduction of area.

[0025] (III) Technical Effects

[0026] The advantages of this invention compared to existing technologies are as follows: By introducing the stress-strain state after the residual stress field has stabilized, and combining it with the Walker exponent correction model, the prediction bias caused by neglecting subsequent relaxation in traditional methods is resolved. It accurately assesses fatigue life margins, providing an optimization basis for turbine disk design and extending its service life within safe thresholds. Furthermore, by combining finite element simulation with parametric models, it reduces reliance on extensive physical testing, improving R&D efficiency. Attached Figure Description

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

[0028] Figure 2 This is a schematic diagram showing the comparison results of lifetime prediction under all load conditions in this invention.

[0029] Figure 3 This is a schematic diagram of the mesh generation and loading method of the quarter model of this invention. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings. This embodiment uses a laser-shock-strengthened FGH4098 alloy notched simulated part as an example to predict fatigue life. The sample size and loading method are as follows: Figure 1 As shown.

[0031] Combined with appendix Figure 1 To be continued Figure 3 A method for predicting the fatigue life of turbine disk alloys considering the evolution of residual stress relaxation includes the following steps:

[0032] S1. Determine the dimensions of the turbine disk with notches, and optimize the dimensions based on the critical points and stress gradients;

[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 after the stable cycle through cyclic loading.

[0034] S3. Fatigue life prediction is performed based on the modified Manson-Coffin equation and the SWT method, where the Walker index is introduced to characterize the material's sensitivity to mean stress, and the Walker index is calculated using the following formula:

[0035]

[0036] In the formula, σ 0.2For yield strength, σ b Tensile strength;

[0037] S4. Based on the stress-strain state after the residual stress field has stabilized, the fatigue life is predicted using the modified SWT model, which is:

[0038]

[0039] Where, σ max For the maximum stress, ε a For the total strain amplitude, σ′ f and ε′ f Here, denoted by , we have 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℃, the parameters of this equation are shown in the table below:

[0040]

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

[0042]

[0043] The residual stress field established in step S2 is constructed using the inverse eigenstrain method, combined with the mesh generation of the quarter-model and cyclic loading boundary conditions.

[0044] The Walker index is determined using uniaxial tensile test data and correlated with stress ratios to improve prediction accuracy under asymmetric cyclic loading.

[0045] The fatigue strength coefficient σ′ f and fatigue ductility coefficient ε′ f Based on uniaxial tensile test data of the material, the result was calculated using a modified slope method, as shown in the following formula:

[0046]

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

[0048] The results of the test under multiple load conditions at 650℃ in this embodiment are compared with the results of the two simulations as follows:

[0049]

[0050] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for predicting the fatigue life of a turbine disk alloy considering the evolution of residual stress relaxation, characterized in that, The method comprises the following steps: S1, determining the size of the notched turbine disk simulation piece, and optimizing the size based on the dangerous point and stress gradient; S2, establishing a three-point bending finite element model to simulate the residual stress field and work hardening field introduced by laser shock peening (LSP), and obtaining the stress and strain state after the first cycle and the stable cycle through cyclic loading; S3, predicting the fatigue life based on the modified Manson-Coffin equation and the SWT method, wherein the Walker index is introduced to represent the sensitivity of the material to the average stress, and the Walker index is calculated by the following formula: where σ 0.2 is the yield strength, σ b is the tensile strength; S4, combining the stress and strain state after the residual stress field is stable, and using the modified SWT model to predict the fatigue life, wherein the SWT model is: 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 the fatigue exponent parameters, and E is the elastic modulus; S5, substituting the damage parameter SWT based on the critical plane method into the SWT model to obtain the modified SWT model:

2. The method of predicting the fatigue life of a turbine disk alloy considering the evolution of residual stress relaxation according to claim 1, characterized in that, In step S2, the residual stress field is established by using the inverse eigenstrain method, and the grid division of the quarter model and the cyclic loading boundary condition are combined.

3. The method of predicting the fatigue life of a turbine disk alloy considering the evolution of residual stress relaxation according to claim 1, characterized in that, The Walker index is determined by uniaxial tensile test data, and is associated with the stress ratio to improve the prediction accuracy under asymmetric cyclic loading.

4. The method of predicting the fatigue life of a turbine disk alloy considering the evolution of residual stress relaxation of claim 1, wherein, the fatigue strength coefficient σ' f and the fatigue ductility coefficient ε' f Based on the uniaxial tensile test data of the material, it is obtained by improved slope method, and the formula is as follows: In the formula, σ b is the tensile strength and ψ is the reduction of area.

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