A method for determining the creep-fatigue test load of a turbine disk

Abstract

This invention discloses a method for determining the creep-fatigue test load of a turbine disk, belonging to the field of aero-engine technology. The method includes: performing transient stress and creep analysis on the turbine disk, calculating the fatigue damage component and creep damage component at each stage, and accumulating the total fatigue damage value and total creep damage value within a complete flight cycle; determining the flight state with the maximum total damage as the standard cycle; and using this standard cycle as the sole benchmark, collaboratively determining a complete set of test parameters: setting the maximum creep damage state temperature as the test temperature, determining the test speed from the maximum stress, calculating the number of test cycles from the stress, and calculating the peak load holding time from the stress. This invention achieves precise collaborative design of thermo-mechanical loads, ensuring a high degree of simulation of actual operating conditions in the test, and providing a scientific basis for engine life determination.

Description

Technical Field

[0001] This invention relates to the field of aero-engine technology, and in particular to a method for determining the creep-fatigue test load of a turbine disk. Background Technology

[0002] As a core hot-end component of aero-engines, the high-pressure turbine disk operates in an extremely harsh environment, enduring the coupled effects of high centrifugal loads from high-speed rotation, thermal loads from high-temperature exhaust gases, and cyclic loads from frequent start-stop cycles. Its primary failure mode is a composite damage type dominated by creep damage and low-cyclic fatigue damage. Creep damage originates from the continuous action of high temperature and high stress under extreme conditions such as cruise, leading to the accumulation of related plastic deformations in the material. Fatigue damage is mainly caused by cyclic plastic strain during transient processes such as takeoff, acceleration, and deceleration. The interaction between creep and fatigue damage significantly accelerates the initiation and propagation of turbine disk cracks, posing a severe challenge to the engine's service safety and lifespan reliability.

[0003] To efficiently and accurately assess the lifespan and reliability of turbine disks in the laboratory, it is necessary to transform the complex actual flight conditions of the engine into a test load spectrum that is executable in the laboratory and has damage equivalence. However, existing technologies have significant shortcomings in determining test parameters. Some methods only consider fatigue damage to determine the test load, completely ignoring the contribution of creep damage, resulting in test results that cannot truly reflect the combined damage mechanism in actual service. Chinese patent application CN119903670A discloses a method for compiling an accelerated mission test spectrum. Although this method considers both fatigue and creep damage, its core idea is to select the maximum fatigue damage point and the maximum creep damage point separately for different assessment points to independently calculate the number of cycles and the holding time. This method has two key drawbacks: First, it severs the interaction between creep and fatigue damage in the same dangerous location and under the same service conditions, lacking a unified benchmark that can represent the most dangerous damage state; second, the test parameters it determines, such as temperature, holding time, and number of cycles, are extracted from different assessment points and damage modes and simply combined. There is a lack of physical correlation and logical consistency between the parameters, making it impossible to accurately reproduce the actual damage state and damage evolution path of the component under the most dangerous working conditions.

[0004] Therefore, there is an urgent need for a method for determining test parameters of high-pressure turbine disks based on physical mechanisms and capable of synergistically considering creep-fatigue interaction effects. This method needs to establish a quantitative mapping relationship from "actual flight profile" to "bench test spectrum" based on the principle of damage equivalence, so as to scientifically and accurately determine a complete set of directly executable test parameters. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for determining the load in turbine disk creep-fatigue testing. This method precisely locates the "standard cycle" that causes the maximum total damage and, based on the damage structure and stress characteristics of this cycle, establishes a quantitative damage equivalence relationship between actual flight conditions and laboratory test parameters. This results in a set of scientific, self-consistent load spectrum parameters that can be directly used for bench testing, ensuring that the test truly reflects the damage state of the component under the most dangerous conditions and significantly improving the accuracy and reliability of life assessment.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for determining the creep-fatigue test load of a high-pressure turbine disk includes the following steps: S1. Based on the engine flight profile, perform transient thermo-mechanical coupled stress analysis on the turbine disk, identify all stress cycles in key areas, and calculate the fatigue damage component of each stress cycle and the total fatigue damage value within a complete flight cycle. At the same time, determine the stress cycle with the greatest fatigue damage; S2. Perform creep analysis on key components of the turbine disk, calculate the creep damage components at each stress holding stage, and the total creep damage value accumulated over a complete flight cycle. And determine the flight state with the largest creep damage value and its corresponding temperature; S3. Based on the analysis results of steps S1 and S2, calculate the total damage to key components under each flight condition. ,in and the total damage The maximum flight condition is defined as a standard cycle, and the maximum stress value corresponding to the standard cycle is determined. And the stress cycle form is 0→ →0; S4. Based on the aforementioned standard cycle, determine a complete set of test parameters, specifically including: Determine the test temperature The temperature corresponding to the maximum creep damage state identified in step S2 is determined as the test temperature. ; Determine the peak rotational speed of the test At the test temperature The following measures are taken to ensure that the stress in the critical parts of the turbine disk reaches the maximum stress value. To achieve this, the peak rotational speed was obtained through finite element analysis. ; Determine the number of test cycles : Through the turbine disk material at the test temperature The lifespan model under the given conditions was used to calculate the lifespan at the peak rotational speed of the test. The number of cycles within the test stress range determined by the test valley rotation speed. Then, based on the total fatigue damage value of the standard cycle... Through formula The number of experimental cycles was calculated. ; Determine peak load duration At the test temperature and the maximum stress value Below, using a creep damage model, the total creep damage generated during all peak load holding stages in the experiment is made equal to the creep damage value of the standard cycle. This allows us to calculate the total hold-up time, which is then combined with the number of test cycles. Determine the peak hold-up time for each cycle. .

[0008] Furthermore, step S1 involves calculating the fatigue damage component for each stress cycle and the total fatigue damage value within a complete flight cycle. Specifically, this includes: using the rainflow counting method to identify all stress cycles in critical areas, totaling n cycles, and calculating the fatigue damage component for each cycle. ,in The design requirement for the number of cycles is the i-th stress cycle. The fatigue life under this stress cycle is calculated using a material life model; then, the total fatigue damage within a complete flight cycle is calculated by summing. .

[0009] Furthermore, step S2 involves calculating the creep damage components at each stress holding stage and the total creep damage value accumulated over a complete flight cycle. Specifically, this includes: when the temperature of the critical component meets the conditions for creep to occur, using a creep constitutive model to calculate the creep strain increment at each stress holding stage. The total number of stress retention stages is m; combined with the material's creep fracture ductility Calculate the creep damage component at each stage. Then, the total creep damage accumulated over a complete flight cycle is calculated by summation. The creep constitutive model is the Norton creep model, and the condition for creep to occur is the temperature of the critical components. ,in is the melting point temperature of the turbine disk material.

[0010] Furthermore, the test valley speed mentioned in step S4 is the test peak speed. 5%, at which point the corresponding test stress range is 0.9975. The number of cycles The turbine disk material at the test temperature Below, the test stress range is 0.9975. Calculated.

[0011] Furthermore, the determination of peak load time in step S4 Specifically, it includes: First, through the formula Calculate total holding time ,in For turbine disk material under stress and temperature The creep rupture time under these conditions; Then, through the formula Determine the peak hold-up time for each test cycle. .

[0012] Furthermore, the key components mentioned in steps S1 and S2 include at least one of the following: the mortise and tenon of the turbine disk, the center hole, and the hub transition area.

[0013] Furthermore, in step S1, the transient thermo-mechanical coupling stress analysis is performed using the finite element method, taking into account the changes in turbine disk material properties with temperature.

[0014] Furthermore, in step S4, a complete set of test load spectrum parameters is finally determined and output, including at least the test temperature. The peak rotational speed of the test The test valley speed, the number of test cycles and the peak load duration .

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. Clear physical mechanism and accurate damage equivalence: This invention uses damage rather than load as the equivalent core, quantifies creep and fatigue damage through numerical simulation, and defines the "standard cycle" working condition with the greatest total damage. All test parameters are determined with the goal of reproducing this most dangerous damage state, ensuring that the test conditions originate from the physical essence and the results are true and reliable.

[0016] 2. Coordinated design of test parameters with strong systematicity: This invention links test temperature with the maximum creep damage state, peak rotational speed with the maximum mechanical stress, cycle number with fatigue damage, and holding time with creep damage and the linkage between temperature and stress. The entire set of parameters is designed in a coordinated and quantitative manner around the unified benchmark of "standard cycle," achieving a scientific, decoupled, and correlated relationship between thermal load and mechanical load, with logical self-consistency.

[0017] 3. Comprehensive and executable test parameters: The final output includes a complete set of specific parameters such as test temperature, peak speed, valley speed, peak load holding time, and number of test cycles, providing clear, closed-loop, and operable input instructions for bench testing, avoiding the arbitrariness of human experience.

[0018] 4. High engineering practical value: The method of this invention has clear steps and rigorous logic, and is easy to promote and apply in engineering practice. It can provide a powerful technical tool for the design finalization, safety assessment and life extension evaluation of high-pressure turbine disks, and has significant engineering and economic value. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the method for determining the creep-fatigue test load of a turbine disk according to an embodiment of the present invention. Detailed Implementation

[0021] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0022] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] This invention provides a method for determining the creep-fatigue test load of a turbine disk, using a high-pressure turbine disk of an aero-engine as the implementation object, the material of which is powder metallurgy FGH96 high-temperature alloy. Figure 1 As shown, the method described in this embodiment of the invention includes the following steps: S1: Transient thermo-mechanical coupling analysis and fatigue total damage calculation First, based on a typical flight mission profile including engine start-up, maximum climb, and high-speed cruise phases, a high-precision three-dimensional finite element model of the high-pressure turbine disk was established. Time-varying speed and temperature boundary conditions were applied, and transient thermo-mechanical coupled stress analysis was performed using the finite element method. The changes in material properties such as the elastic modulus and thermal expansion coefficient of the FGH96 alloy with temperature were considered throughout the process. The stress-strain field evolution of several key weak points, including the tenon groove, center hole, and hub transition area, was analyzed and obtained.

[0024] For the aforementioned critical components, the rainflow counting method was used to count and extract stress-time histories, identifying all stress cycles at these critical locations. Through comprehensive comparison, the stress amplitude at the root of the tenon groove in the high-pressure turbine disk was found to be the highest, indicating the most severe stress concentration; therefore, it was determined to be the most dangerous critical component. Subsequent analysis focused on this tenon groove, which has a total of n stress cycles. Using the material life model (such as strain-life curves) of FGH96 alloy at the corresponding temperature, the fatigue life of each stress cycle was calculated. The design requirement for the number of stress cycles is given for each stress cycle according to the design task requirements. The fatigue damage component for each cycle is calculated using the following formula:

[0025] in, The design requirement for the number of cycles is the i-th stress cycle. This represents the fatigue life under this stress cycle, calculated using a material life model.

[0026] By summing the damage components from all n cycles, the total fatigue damage value within a complete flight cycle can be calculated. According to calculations in this embodiment of the invention, the high-pressure turbine disk tenon groove is the location with the greatest fatigue damage, and the total fatigue damage is... =6.67×10 -5 Meanwhile, analysis determined that the stress cycle from start-up to the stable phase of maximum takeoff is the stress cycle that causes the greatest fatigue damage.

[0027] S2: Creep Analysis and Identification of Maximum Creep Damage State From the finite element analysis results, the stress time histories of key parts of the turbine disk (especially the root of the tenon groove) were extracted for each stress retention stage in the flight profile. and temperature time history Through comparison, during the "maximum takeoff" and subsequent "high-temperature cruise" phases, the root of the tenon groove, simultaneously subjected to extremely high centrifugal stress and high-temperature combustion gas erosion, is the area with the highest risk of creep damage, with a total of m stress retention stages. The melting point temperature of FGH96 alloy... ( The melting point of the turbine disk material is approximately 1260℃, and the temperature at the root of the tenon groove is... Reaching the stage of 650℃ (approximately 923K) satisfies This criterion for the occurrence of creep. When temperature... At this time, there is no creep damage, and the creep damage is 0.

[0028] The transient creep rate at each stress-holding stage was calculated using the Norton creep constitutive model:

[0029] in, Let be the creep constant of the material. The creep stress index is... The apparent activation energy of creep. This is the universal gas constant.

[0030] Integrating the creep rate over time yields the creep strain increment for each stress holding stage. The calculation formula is as follows:

[0031] in, This marks the beginning of the stress retention phase. This marks the end of the flight phase.

[0032] strain increment Creep fracture ductility of the material (FGH96 alloy) in the corresponding state Combined, the creep damage components at each stage are calculated using the following formulas. :

[0033] By summing the damage components from all m stress-holding stages, the total creep damage value accumulated over a complete flight cycle is calculated. Total creep damage value in this embodiment =0.02. Analysis determined that the "maximum takeoff stage" was the state that produced the maximum creep damage, and the highest working temperature at the bottom of the tenon groove under this state was recorded as 650℃.

[0034] S3: Determine the "Standard Cycle" Based on the analysis results of steps S1 and S2, the entire flight profile is traversed through all states, and the total damage of the critical parts (which are the most dangerous parts at this time, i.e., the previously determined tenon root) is calculated in each flight state. Comparative analysis revealed that, within the flight state range of "stable condition from start-up to maximum takeoff," the total damage... The maximum value is reached. Therefore, this flight state is defined as the "standard cycle," which represents the most severe and dangerous operating condition for turbine disk damage in actual service.

[0035] The maximum stress of the turbine disk during the entire flight cycle was obtained based on transient thermo-mechanical coupled finite element analysis, corresponding to the maximum stress value of the standard cycle. The stress at the root of the tenon of the turbine disk under maximum takeoff conditions is simplified to 0→ →0 pulsating cycle. This standard cycle is the sole baseline for all experimental parameters in subsequent co-designs.

[0036] S4: Determination of test load parameters This step aims to translate the damage parameters of the "standard cycle" into specific, actionable test parameters, determining a complete set of test parameters based on the standard cycle, specifically including: Determine the test temperature The temperature corresponding to the maximum creep damage state identified in step S2 is directly set as the constant test temperature for the entire bench test. The test temperature was set at 650°C, the highest working temperature at the bottom of the tenon under standard cyclic conditions. This is to ensure that the test is conducted in the most creep-destructive thermal environment.

[0037] Determine the peak rotational speed of the test Valley speed: At a predetermined test temperature of 650℃, to ensure that the stress in the critical parts of the turbine disk (tenon root) precisely reaches the maximum stress of the "standard cycle". To achieve the target rotational speed, the corresponding rotational speed was calculated iteratively using a finite element model to obtain the experimental peak rotational speed. The speed is 12500 rpm. Based on the standard capability of the rotary disc tester, the valley speed is set as the peak speed. 5%, or 625 rpm. The corresponding valley stress at this point is calculated to be 0.0025. The test stress range is 0.9975. The stress range of this test is 0.9975. From the peak speed of the test The value was determined jointly with the experimental valley rotation speed, which is 0.9975. = -0.0025 .

[0038] Determine the number of test cycles Based on the material life model of FGH96 alloy at a test temperature of 650℃, the calculation was performed at a test stress range of 0.9975. Loop number under pulsating loop loading The number of test cycles is calculated using the following formula. :

[0039] Total damage at the turbine disk tenon location =6.67×10 -5 Substituting into the formula, the total number of experimental cycles is calculated. It is 15,000 times.

[0040] Determine peak load duration At the determined test temperature and maximum stress value Below, using a creep damage model, the total creep damage generated during all peak load holding stages in the experiment is made equal to the creep damage value of the standard cycle. This allows us to calculate the total hold-up time, which is then combined with the number of test cycles. Determine the peak hold-up time for each cycle. Specifically: First, calculate the total load-bearing requirements. Consult the FGH96 alloy at 650℃ and stress... Creep fracture time characteristics under certain conditions Using formulas Substitute =0.02, the total holding time required to achieve equivalent creep damage is calculated. It takes 375 hours.

[0041] Then, calculate the peak hold-up time for each cycle. This is obtained using the following formula:

[0042] Will =375 hours and the result of the previous calculation Substituting the value of 15000 into the formula, the final calculation yields the holding time required for each test cycle at the peak speed (12500 rpm). It lasts for 90 seconds.

[0043] Finally, this embodiment of the invention establishes the creep-fatigue test load spectrum parameters for the turbine disk co-design and outputs a complete set of parameters, including: test temperature 650℃, peak test speed 12500 rpm, valley test speed 625 rpm, peak load holding time 90 seconds, and total test cycles 15000. Based on this complete set of parameters, bench test spectra can be directly compiled for evaluation.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations of the embodiments of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of determining a creep-fatigue test load for a turbine disk, the method comprising: determining a creep-fatigue test load for a turbine disk, the method characterized by, Includes the following steps: S1, based on the engine flight profile, performing transient thermal-mechanical coupled stress analysis on the turbine disk, identifying all stress cycles of the key parts, and calculating the fatigue damage component of each stress cycle and the total fatigue damage value within a complete flight cycle At the same time, the stress cycle with the maximum fatigue damage is determined S2, creep analysis is performed on the key parts of the turbine disk, and the creep damage components in each stress maintaining stage and the total creep damage value accumulated in a complete flight cycle are calculated and the flight state with the maximum creep damage value and its corresponding temperature are determined. S3. Based on the analysis results of steps S1 and S2, calculate the total damage to key components under each flight condition. ,in and the total damage The maximum flight condition is defined as a standard cycle, and the maximum stress value corresponding to the standard cycle is determined. And the stress cycle form is 0→ →0; S4. Based on the aforementioned standard cycle, determine a complete set of test parameters, specifically including: Determine the test temperature The temperature corresponding to the maximum creep damage state identified in step S2 is determined as the test temperature. ; Determine the peak rotational speed of the test At the test temperature The following measures are taken to ensure that the stress in the critical parts of the turbine disk reaches the maximum stress value. To achieve this, the peak rotational speed was obtained through finite element analysis. ; Determine the number of test cycles : Through the turbine disk material at the test temperature The lifespan model under the given conditions was used to calculate the lifespan at the peak rotational speed of the test. The number of cycles within the test stress range determined by the test valley rotation speed. Then, based on the total fatigue damage value of the standard cycle... Through formula The number of test cycles was calculated. ; Determine peak load duration At the test temperature and the maximum stress value Below, using a creep damage model, the total creep damage generated during all peak load holding stages in the experiment is made equal to the creep damage value of the standard cycle. This allows us to calculate the total hold-up time, which is then combined with the number of test cycles. Determine the peak hold-up time for each cycle. .

2. The method according to claim 1, characterized in that, Step S1 involves calculating the fatigue damage component for each stress cycle and the total fatigue damage value over a complete flight cycle. Specifically, this includes: using the rainflow counting method to identify all stress cycles in critical areas, totaling n cycles, and calculating the fatigue damage component for each cycle. ,in The design requirement for the number of cycles is the i-th stress cycle. The fatigue life under this stress cycle is calculated using a material life model; then, the total fatigue damage within a complete flight cycle is calculated by summing. .

3. The method according to claim 1, characterized in that, Step S2 involves calculating the creep damage components during each stress retention stage and the total creep damage value accumulated over a complete flight cycle. Specifically, this includes: when the temperature of the critical component meets the conditions for creep to occur, using a creep constitutive model to calculate the creep strain increment at each stress holding stage. The total number of stress retention stages is m; combined with the material's creep fracture ductility Calculate the creep damage component at each stage. Then, the total creep damage accumulated over a complete flight cycle is calculated by summation. .

4. The method according to claim 3, characterized in that, The creep constitutive model is the Norton creep model, and the condition for creep to occur is the temperature of the critical components. ,in This is the melting point temperature of the turbine disk material.

5. The method according to claim 1, characterized in that, The test valley speed mentioned in step S4 is the test peak speed. 5%, at which point the corresponding test stress range is 0.9975. .

6. The method according to claim 5, characterized in that, The number of cycles The turbine disk material at the test temperature Below, the test stress range is 0.9975. Calculated.

7. The method according to claim 1, characterized in that, Determining the peak load time in step S4 Specifically, it includes: First, through the formula Calculate total holding time ,in For turbine disk material under stress and temperature The creep rupture time under these conditions; Then, through the formula Determine the peak hold-up time for each test cycle. .

8. The method according to claim 1, characterized in that, The key components mentioned in steps S1 and S2 include at least one of the following: the mortise and tenon of the turbine disk, the center hole, and the hub transition area.

9. The method according to claim 1, characterized in that, In step S1, the transient thermo-mechanical coupled stress analysis is performed using the finite element method, taking into account the changes in turbine disk material properties with temperature.

10. The method according to claim 1, characterized in that, In step S4, a complete set of test load spectrum parameters is finally determined and output, including at least the test temperature. The peak rotational speed of the test The test valley speed, the number of test cycles and the peak load duration .

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