Method for evaluating fatigue life of weld joint of hydrogen turbine air inlet shell of engine

Abstract

The invention discloses a method for evaluating fatigue life of a weld joint of a hydrogen turbine air inlet shell of an engine. The method comprises the following steps: firstly, constructing a finite element model of a turbine air inlet shell welding seam by acquiring three-dimensional characteristics of a welding seam area and combining material parameters; on the basis, a transfer function and a stress power spectral density function of the structure are calculated through modal response analysis and random vibration analysis, a random vibration fatigue life prediction model based on an equivalent SN curve criterion is obtained, and an S-N curve obtained through an experiment and containing average stress is equivalent to an S-N curve under zero average stress; the problem of interference of average stress on random vibration fatigue life analysis is solved, and the experiment cost and time are remarkably reduced. And in combination with a plurality of stress range probability empirical formulas, multi-dimensional accurate prediction of the fatigue life is realized.

Description

Technical Field

[0001] The present invention relates to the assessment of structural fatigue life, and particularly to a method for assessing the fatigue life of the weld of an engine hydrogen turbine intake housing. Background Art

[0002] With the development of aero-engine technology, turbine engines are increasingly widely used in the aviation field. Their working environment is extremely harsh, facing challenges such as high temperature, high pressure, and complex vibration loads. Especially in the weld area of the engine turbine intake housing, due to the long-term coupling effect of thermal stress and mechanical stress, it becomes one of the weak links of structural fatigue failure. Therefore, assessing the fatigue life of the weld area has important engineering significance.

[0003] Different from the steel or aluminum alloy used in traditional industrial welds, the weld area of aero-engines usually uses alloy materials with special properties. To meet the requirements of extreme working conditions, these materials exhibit unique mechanical and thermal properties. For example, materials such as nickel-based superalloys and titanium alloys are widely used in the engine weld area to ensure their strength and oxidation resistance in high-temperature environments. However, due to the non-linear behavior and complex fatigue properties of these materials, the traditional fatigue life assessment method based on the standard S-N curve cannot be directly applied. Summary of the Invention

[0004] Object of the Invention: Aiming at the above disadvantages, the present invention provides a method for assessing the fatigue life of the weld of an engine hydrogen turbine intake housing made of special materials.

[0005] Technical Solution: To solve the above problems, the present invention adopts a method for assessing the fatigue life of the weld of an engine hydrogen turbine intake housing, including the following steps: Step 1: Obtain the structural characteristics and material parameters of the weld area of the standard specimen of the engine hydrogen turbine intake housing weld. Based on the obtained structural characteristics and material parameters, establish a finite element model of the standard specimen of the engine hydrogen turbine intake housing weld, and conduct a fatigue test on the standard specimen of the engine hydrogen turbine intake housing weld to obtain the S-N curve; Step 2: Based on the finite element model, conduct a frequency response analysis on the engine hydrogen turbine intake housing structure to construct the transfer function of the engine hydrogen turbine intake housing structure; Step 3: Perform zero mean stress correction on the S-N curve obtained from the fatigue test; Step 4: Calculate the stress power spectral density of the engine hydrogen turbine intake housing structure through the transfer function, determine the vibration frequency range of random vibration, determine the empirical formula for stress range probability prediction according to the vibration frequency range, and then establish a random vibration fatigue life prediction model by combining the corrected S-N curve with the linear cumulative damage theory; Step 5: According to the random vibration fatigue life prediction model, predict the life of the weld of the engine hydrogen turbine intake housing.

[0006] Further, the specific steps for obtaining the structural characteristics and material parameters of the weld zone of the standard specimen of the engine hydrogen turbine intake housing weld are as follows: Grind and polish, slice and sample, CT scan and mechanical test the standard specimen of the engine hydrogen turbine intake housing weld to obtain the structural characteristics and material parameters of the weld, including three-dimensional dimensions, mechanical characteristics, etc., and establish a finite element model of the engine hydrogen turbine intake housing weld in finite element modeling software.

[0007] Further, perform a frequency response analysis on the structure of the engine hydrogen turbine intake housing, calculate the responses such as displacement, velocity, acceleration or stress of the structure under different frequency excitations, determine the natural modes and modal shapes of the structure, and obtain the transfer function of the structure, that is, the input-output relationship. The expression of the transfer function is usually as follows: ; Among them, is the transfer function, indicating the input and the output relationship. is the frequency domain representation of the input signal, such as the applied force, acceleration or displacement, is the frequency domain response of the output signal, such as the displacement, velocity or stress response of the structure, and f is the frequency. By comparing the input excitation signal and the corresponding response signal at different frequencies before and after the frequency response analysis, the transfer function can be constructed.

[0008] Further, perform zero mean stress correction on the S-N curve obtained from the fatigue test, and equivalent the S-N curve of the fatigue test with non-zero mean stress to the S-N curve of zero mean stress. The zero mean stress correction methods include the Goodman method and the Soderberg method, as follows: ; ; Among them, represents the equivalent zero mean stress; represents the stress amplitude at the i-th point of the S-N curve of the fatigue test; is the stress mean value at the i-th point of the S-N curve of the fatigue test, represents the yield strength, represents the tensile strength.

[0009] The Goodman method shows a linear relationship on the stress-strain diagram, where the ultimate strength and fatigue limit are two extreme points on the coordinate axes. As the mean stress increases, the amplitude of the alternating stress that the material can withstand gradually decreases until the material yields or fails. On the stress-strain diagram, the Soderberg criterion appears as a straight line, but its endpoint is at the yield strength rather than the ultimate strength.

[0010] Furthermore, by solving the resulting stress power spectral density, the input of random vibration is usually expressed as the acceleration power spectral density. , which defines the energy distribution of the excitation acceleration in the frequency domain, where f is the frequency. represents the power of the excitation acceleration at a certain frequency. Then, from the transfer function , the power spectral density of the stress at frequency f can be solved. ; ; This formula indicates that the power spectral density of the stress is proportional to the square of the acceleration power spectral density and the transfer function. At each frequency point, the transfer function converts the input energy of the acceleration excitation into the output energy of the stress response.

[0011] Furthermore, the Dirlik method, Steinberg method, and Bendat method are used to predict the probability of the stress range.

[0012] For the Dirlik stress range probability formula, it is a formula used to estimate the fatigue damage caused by random vibration from the stress power spectral density (PSD). This formula is based on the power spectral density data and calculates the probability distribution of the stress range through a frequency domain method. The specific formula is as follows: ; where the probability density function represents the probability that the stress range S appears in a certain range. The parameters M, Z, Q, R, D1, D2, and D3 are coefficients related to the power spectral characteristics and can be calculated from the stress power spectral density. Specifically as follows: ; ; ; ; ; .

[0013] Calculate the stress power spectral moment: , then: ; .

[0014] For the Steinberg method, it is generally assumed that the peak distribution of stress follows a normal distribution model. Therefore, this method directly gives the distribution probability of the stress range. Specifically as follows: The probability of stress occurring at the 1σ level is 68.3%, the probability of stress occurring at the 2σ level is 27.1%, and the probability of stress occurring at the 3σ level is 4.43%. Among them, σ is the root mean square stress, which can be combined with the stress power spectral density function Solve: ; The Bendat method assumes that the stress range S follows a Rayleigh distribution, and its probability density function is: ; Among them, σ is the root mean square stress, and the solution method is the same as above. All three of these methods are applicable to the prediction of stress range under random vibration environments, especially applicable to situations with complex random loads in engineering, such as aerospace devices, mechanical equipment, etc.

[0015] Furthermore, it is assumed that the damage to the fatigue life by each load cycle is linearly cumulative. When the cumulative damage reaches 1, the structure undergoes fatigue failure. Its expression is: ; Among them, is the cumulative damage, is the number of cycles at a certain stress level, is the maximum number of cycles obtained from the S-N curve at this stress level. When the structure reaches its fatigue life and fails.

[0016] The S-N curve can usually be described by the following power relationship: ; Among them, S is the stress amplitude, that is, the stress range, N is the number of cycles, m is the slope of the S-N curve of the material, and C is the fatigue strength coefficient. The S-N curve (stress-life curve) is a basic characterization of the fatigue performance of materials, which describes the number of fatigue cycles N that materials can withstand under different stress amplitudes S.

[0017] Furthermore, combining the Miner linear cumulative damage criterion with the S-N curve of equivalent zero mean stress, the fatigue life of the weld is solved respectively under the three prediction stress range probability methods of Dirlik, Steinberg, and Bendat For the Dirlik method, the number of cycles n(S) of a certain stress range S passing through per unit time is: ; Among them, p(S) is the Dirlik stress range probability density, and E(peak) is the peak factor, and its magnitude can be calculated by the following formula: ; Combining the Miner linear cumulative damage criterion with the S-N curve can solve the fatigue damage D per unit time Dirlik : ; Let D Dirlik = 1 to obtain the fatigue life T Dirlik as follows: ; For the Steinberg method, the distribution probability of the stress range is directly given, and the number of cycles per unit time is: ; ; ; where v0 is the zero crossing rate, and its expression is as follows: ; Combining the Miner linear cumulative damage criterion with the S-N curve, the fatigue damage D per unit time Steinberg is: ; Let D Steinberg = 1 to obtain the fatigue life T Steinberg as follows: ; For the Bendat method, both it and the Dirlik method give the probability density of the stress range. However, due to the different analysis frequency bands, replacing the number of final peaks E(peak) with the zero crossing rate v0, the frequency life expression is the same as that of T Dirlik and is: ; The present invention also employs a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the steps of the above method are implemented.

[0018] The present invention also employs a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the above method are implemented.

[0019] Beneficial effects: Compared with the prior art, the present invention has significant advantages. Especially for the weld materials in special fatigue tests, by obtaining the structural characteristics, the accurate assessment of the weld fatigue life under random vibration conditions is achieved. This model fully considers the influence of factors such as weld size, morphology, and position on the random vibration fatigue behavior. Based on the three-dimensional finite element model of the weld of the engine hydrogen turbine intake shell, the frequency domain response characteristics of the structure under random vibration are calculated. At the same time, the present invention uses various methods to perform zero mean stress equivalent treatment on the S-N curve. In fatigue analysis, by converting the actual working conditions (including alternating stress and mean stress) into equivalent fully alternating stress conditions, the life prediction process under complex loads is simplified, the experimental cost is reduced, and a conservative life assessment is provided for engineering design. The present invention also combines various stress range probability distribution prediction methods, making the fatigue life prediction more accurate and comprehensive. This method is highly innovative and has good robustness, especially suitable for the fatigue life assessment of special weld materials such as aero engines, and has broad prospects for popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic flow chart of the evaluation method of the present invention.

[0021] Figure 2 It is a schematic diagram of the finite element model of the weld area of the engine hydrogen turbine intake shell in the present invention.

[0022] Figure 3 It is a schematic diagram of the S-N experimental curve of the weld specimen of the engine hydrogen turbine intake shell made of GH4169 nickel-based superalloy material in the present invention.

[0023] Figure 4 It is a schematic diagram of the S-N equivalent zero mean stress curve of the weld specimen of the engine hydrogen turbine intake shell made of GH4169 nickel-based superalloy material in the present invention.

[0024] Figure 5 It is a schematic diagram of the predicted random vibration weld fatigue life situation in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] As Figure 1 shown, in this embodiment, a method for evaluating the fatigue life of the weld of the engine hydrogen turbine intake shell includes the following steps: Step 1: Grind, polish, slice, sample, perform CT scanning and mechanical tests on the standard specimen of the weld of the engine hydrogen turbine intake shell to obtain the structural characteristics and material parameters of the weld, including three-dimensional dimensions, mechanical characteristics, etc., and establish a finite element model of the weld of the engine hydrogen turbine intake shell in the finite element modeling software as Figure 2As shown. Fatigue tests were carried out on the weld test pieces obtained by slicing and sampling, and their S-N curves were obtained as shown in Table 1. Since the stress ratio of the weld test pieces is 0.1 and the mean stress is not zero, the S-N curve correction method with equivalent zero mean stress will be used subsequently to eliminate the influence of the mean stress on the fatigue behavior of the structure.

[0026] Table 1 S-N curve data of the weld of the engine hydrogen turbine inlet housing made of GH4169 nickel-based superalloy

[0027] Step 2: Conduct a frequency response analysis on the engine hydrogen turbine inlet housing structure, and calculate the transfer function of the overall structure according to the input excitation and output response.

[0028] Step 3: Use two equivalent zero mean stress methods, namely the Goodman method and the Soderberg method, to correct the test S-N curve respectively. The corrected data are shown in Table 2.

[0029] Table 2 S-N curve data with equivalent zero mean stress

[0030] Step 4: Calculate the stress power spectral density of the structure through the transfer function, determine the vibration frequency range of random vibration, determine the empirical formula for stress range probability prediction according to the vibration frequency range, and establish a random vibration fatigue life prediction model according to the determined empirical formula and the corrected S-N curve parameters combined with the linear cumulative damage theory.

[0031] Step 5: According to the random vibration fatigue life prediction model, achieve a high-precision evaluation of the random vibration fatigue life of the weld of the engine hydrogen turbine inlet housing.

[0032] The specific implementation steps are as follows. First, obtain the geometric structure characteristics of the weld area of the engine hydrogen turbine inlet housing, including information such as the size, morphology, and position of the weld. These structural characteristics directly determine the stress distribution and fatigue life of the weld under fatigue loads. In addition, material parameters (such as elastic modulus, Poisson's ratio, yield strength, etc.) are crucial for the fatigue performance of the weld. Based on these structural and material parameters, establish a three-dimensional finite element model of the turbine inlet housing weld to simulate its mechanical response behavior under actual working conditions. Figure 2 The finite element mesh model at the weld of the engine hydrogen turbine inlet housing is shown. Among them, hexahedron refined meshes are used at the weld, and tetrahedron meshes are used for the rest. This finite element model can not only accurately reflect the local stress concentration in the weld area but also provide data such as stress and strain for subsequent analysis.

[0033] Next, perform a frequency response analysis on the constructed three-dimensional global finite element model. The purpose of the frequency response analysis is to obtain the dynamic characteristics of the weld structure under random vibration environment, especially the transfer function of the overall structure. The transfer function describes the relationship between the input excitation (such as random vibration load) and the output response (such as stress or displacement) of the system, and is one of the key steps in random vibration fatigue analysis. Through this step, the vibration response amplitude of the weld at different frequencies can be determined, providing a necessary basis for the subsequent calculation of stress power spectral density.

[0034] Subsequently, due to the particularity of the weld material, the standard S-N curve generally cannot be directly applied. The S-N curve of the weld material needs to be obtained through fatigue tests. As Figure 3 shown, if the stress ratio of the experimental conditions is not -1, the equivalent zero mean stress method needs to be used to correct the experimental S-N curve. Through methods such as the Goodman method or the Soderberg method, the fatigue data containing the mean stress is equivalent to the data under zero mean stress. As Figure 4 shown are the S-N curves corrected by the Goodman method and the Soderberg method. This step not only considers the stress changes of the weld under complex load conditions but also takes into account the fatigue characteristics of the actual material, ensuring the accuracy of the fatigue life prediction model.

[0035] Then, use the transfer function to calculate the stress power spectral density (PSD) of the weld structure. The stress power spectral density describes the stress energy distribution of the structure in different frequency ranges under random vibration excitation. Combining prediction formulas for various stress range probability distributions (such as the Dirlik method, the Steinberg method, and the Bendat method), the fatigue damage of the weld can be further evaluated. These methods are each applicable to different vibration frequency bandwidth situations. The Dirlik method is suitable for describing broadband random vibration processes, while the Steinberg method and the Bendat method can effectively describe the stress range distribution of the weld under narrowband random vibration. Considering these three methods simultaneously can provide a more comprehensive assessment of the fatigue life. By combining these stress probability distribution formulas with the corrected S-N curve and the Miner linear cumulative damage theory, a random vibration fatigue life prediction model for the weld is established. This model can accurately estimate the cumulative fatigue damage of the weld at different load frequencies and stress amplitudes.

[0036] Finally, based on the established fatigue life prediction model, predict the fatigue life of the weld of the engine hydrogen turbine intake housing. As Figure 5The predicted weld fatigue life is shown as follows. In this process, the model comprehensively considers the complexity of random vibration, the structural characteristics and material properties of the weld, as well as various fatigue damage accumulation mechanisms. Through this process, the fatigue life estimation of the weld under the random vibration environment can be obtained, providing a reliable basis for the design, maintenance, and life assessment of the key parts of the engine. This model is not only applicable to the current fatigue life assessment of the weld of the hydrogen turbine intake housing, but also can be extended to the fatigue life analysis of other similar structures and special weld materials.

Claims

1. A method for evaluating the fatigue life of the weld of an engine hydrogen turbine intake housing, characterized in that, It includes the following steps: Step 1: Obtain the structural characteristics and material parameters of the weld zone of the weld standard specimen of the engine hydrogen turbine intake housing. Based on the obtained structural characteristics and material parameters, establish a finite element model of the weld standard specimen of the engine hydrogen turbine intake housing, and conduct a fatigue test on the weld standard specimen of the engine hydrogen turbine intake housing to obtain the S-N curve; Step 2: Based on the finite element model, conduct a frequency response analysis on the structure of the engine hydrogen turbine intake housing to construct the transfer function of the structure of the engine hydrogen turbine intake housing; Step 3: Conduct zero mean stress correction on the S-N curve obtained from the fatigue test; Step 4: Calculate the stress power spectral density of the structure of the engine hydrogen turbine intake housing through the transfer function, determine the vibration frequency range of random vibration, determine the empirical formula for stress range probability prediction according to the vibration frequency range, and then establish a random vibration fatigue life prediction model by combining the corrected S-N curve with the linear cumulative damage theory; Step 5: According to the random vibration fatigue life prediction model, conduct life prediction on the weld of the engine hydrogen turbine intake housing.

2. The evaluation method for the weld fatigue life of the engine hydrogen turbine intake housing according to claim 1, wherein The specific steps for obtaining the structural characteristics and material parameters of the weld zone of the weld standard specimen of the engine hydrogen turbine intake housing are: grinding and polishing, slicing and sampling, CT scanning and mechanical testing on the weld standard specimen of the engine hydrogen turbine intake housing. The structural characteristics and material parameters include three-dimensional dimensions and mechanical characteristics.

3. The evaluation method for the weld fatigue life of the engine hydrogen turbine intake housing according to claim 1, characterized in that, The frequency response analysis includes calculating the displacement response, velocity response, acceleration response or stress response of the structure of the engine hydrogen turbine intake housing under different frequency excitations, and obtaining the transfer function of the structure of the engine hydrogen turbine intake housing by comparing the input excitation signal and the corresponding response signal at different frequencies before and after the frequency response analysis.

4. The evaluation method for the weld fatigue life of the engine hydrogen turbine intake housing according to claim 1, characterized in that, For the zero mean stress correction of the S-N curve obtained from the fatigue test, the S-N curve with non-zero mean stress is equivalent to the S-N curve with zero mean stress. The methods for zero mean stress correction include the Goodman method and the Soderberg method; The expression of the Goodman method is: ； The expression of the Soderberg method is: ； Among them, represents the equivalent zero mean stress; represents the stress amplitude of the i-th point on the S-N curve; represents the mean stress of the i-th point on the S-N curve, represents the yield strength, represents the tensile strength.

5. The method for evaluating the weld fatigue life of the engine hydrogen turbine intake housing according to claim 4, characterized in that, In Step 4, the calculation of the stress power spectral density of the structure of the engine hydrogen turbine intake housing through the transfer function is specifically: calculating the stress power spectral density function of the structure of the engine hydrogen turbine intake housing through the transfer function of the structure of the engine hydrogen turbine intake housing under different frequency excitations and the random vibration acceleration power spectral density excitation. The stress power spectral density function G(f) at frequency f is: ； where, H(f) represents the transfer function at frequency f, and g(f) represents the random vibration acceleration power spectral density.

6. The evaluation method for the weld fatigue life of the engine hydrogen turbine intake housing according to claim 5, characterized in that The empirical formulas for stress range probability prediction include the empirical formula of the Dirlik method, the empirical formula of the Steinberg method and the empirical formula of the Bendat method; The empirical formula of the Dirlik method is: ； Among them, represents the probability of the stress range S occurring. M, Z, Q, R, D1, D2, and D3 represent coefficients related to the power spectrum characteristics and are obtained by calculating the stress power spectral density; In the Steinberg method, the peak distribution of stress follows a normal distribution model. The empirical formula of the Steinberg method is as follows: the probability of stress occurring at the 1σ level is 68.3%, the probability of stress occurring at the 2σ level is 27.1%, and the probability of stress occurring at the 3σ level is 4.43%. Among them, σ is the root mean square stress, and the expression is: ； The empirical formula of the Bendat method is: ； Among them, the stress range S follows a Rayleigh distribution.

7. The evaluation method for the weld fatigue life of the engine hydrogen turbine intake housing according to claim 6, characterized in that, The expression of the linear cumulative damage theory is: ； where D represents the cumulative damage, represents the number of cycles at a stress level, represents the maximum number of cycles obtained from the S-N curve at a stress level.

8. The evaluation method for the weld fatigue life of the engine hydrogen turbine intake housing according to claim 7, characterized in that, The S-N curve expression is: ； Among them, S represents the stress range, N represents the number of cycles, m represents the slope of the S-N curve of the material, and C represents the fatigue strength coefficient.

9. A computer device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method described in any one of claims 1 to 8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the method described in any one of claims 1 to 8.

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