Method for calculating creep damage equivalent stress of turbine blade

Abstract

The invention belongs to the technical field of aero-engines, and particularly relates to a method for calculating creep damage equivalent stress of a turbine blade, which comprises the following steps of: S1, selecting a state with the maximum damage from a plurality of working states of the turbine blade as an equivalent state under the condition of not considering creep stress relaxation; s2, enabling the damage of other working states to be equivalent to the equivalent state, and obtaining the total equivalent time t4 of the equivalent state; and S3, considering creep stress relaxation according to the equivalent state, calculating the life L4 based on the temperature T1 and the equivalent stress sigma 4, and obtaining accumulated damage D4. According to the method, hundreds of life analysis points can be simplified into an equivalent design state, the efficiency of the endurance life analysis process is improved, and the reliability of life design is ensured.

Description

Technical Field

[0001] This application belongs to the field of aero-engine technology, and specifically relates to a method for calculating the equivalent stress of creep damage in turbine blades. Background Technology

[0002] Aero-engines operate under complex conditions. Turbine blades are subjected to thermal, centrifugal, and aerodynamic loads in harsh environments, and their lifespan directly impacts the overall engine lifespan. Throughout the engine's lifespan, turbine blades operate under varying loads, wide speed ranges, and temperatures, undergoing numerous matching processes and operating conditions. Calculating each of these conditions individually would be extremely labor-intensive and unsustainable for engineering development. Therefore, research into simplified methods for calculating creep damage equivalent stress is urgently needed in the process of calculating engine lifespan, aiming to improve the efficiency of turbine blade lifespan calculations while ensuring computational reliability.

[0003] The existing design method mainly adopts the "Guideline for Strength Design Test of Aero-turbine Engines". This method is based on the principle of linear cumulative damage of materials under sustained static load conditions in several operating states and the assumption of using an equivalent strength reserve state. It allows the conversion of all states into one state to determine the equivalent sustained strength reserve and life reserve.

[0004] In the engineering design process, life design requirements involve many states. If creep and elastoplastic analysis are considered for each state in order to obtain the stress level at critical locations, the amount of calculation is huge and the work efficiency is low. Summary of the Invention

[0005] To address the aforementioned problems, this application provides a method for calculating the equivalent stress of creep damage in turbine blades, comprising the following steps:

[0006] Step S1: Without considering creep stress relaxation, select the state with the greatest damage from multiple operating states of the turbine blade as the equivalent state.

[0007] Step S2: Equip the damage of each other working state to the equivalent state to obtain the total equivalent time t4 of the equivalent state;

[0008] Step S3: Consider creep stress relaxation based on the equivalent state, calculate lifetime L4 based on temperature T1 and equivalent stress σ4, and obtain cumulative damage D4.

[0009] Preferably, the step of studying four equivalent solutions is included before step S1:

[0010] Option 1: Without considering creep stress relaxation, calculate lifetime L1 and damage D1 based on temperature T1 and initial stress σ1;

[0011] Option 2: Considering creep stress relaxation, determine the equivalent stress σ2 based on the working time, and calculate the life L2 and damage D2;

[0012] Option 3: Considering creep stress relaxation, determine the equivalent stress σ3 based on the failure time, and calculate the lifetime L3 and damage D3;

[0013] Option 4: Use the equivalent state method described in claim 1 to determine the equivalent stress σ4, and calculate the lifetime L4 and damage D4.

[0014] Preferably, the method for obtaining the equivalent stress in Scheme 3 includes:

[0015] Record the stress values ​​at each point according to the calculated time step;

[0016] Calculate the time and stress of the integral segment;

[0017] Based on integral stress and temperature, the corresponding lifetime is calculated using the stress-life curve or the combined thermal strength parameter curve.

[0018] Calculate the damage corresponding to the integral segment. When the total accumulated damage reaches 1, use the thermal strength parameter comprehensive curve parameters to obtain the equivalent stress.

[0019] Preferably, the following agreement should be made before performing the calculation:

[0020] Stress convention: Calculated based on equivalent stress;

[0021] Model convention: Calculation results are obtained using 2D models, supplemented by 3D model calculation results;

[0022] For handling over-temperature points: remove state points with a lifespan reserve of less than 1, and select the location with the second greatest damage for analysis.

[0023] Preferably, the method is applicable to critical assessment points of aero-engine turbine blades, and improves the efficiency of long-term life analysis by simplifying multi-condition calculations into single-condition calculations.

[0024] A turbine blade life assessment system includes:

[0025] The data acquisition module is used to acquire time, temperature, and stress parameters of the turbine blades under multiple operating conditions;

[0026] An equivalent processing module is used to implement the method for calculating the equivalent stress of creep damage of turbine blades as described in any one of claims 1-5, and to determine the equivalent state and equivalent stress.

[0027] The life calculation module calculates the turbine blade's life reserve Kt and cumulative damage based on the equivalent processing results.

[0028] Preferably, the result comparison module is used to compare the calculation results of four equivalent schemes, and it is recommended to use scheme four for long-term lifetime assessment.

[0029] The visualization module is used to display the creep curves and life assessment results at the assessment locations.

[0030] The technical problem to be solved by this invention is to calculate the life of turbine blades under various working conditions in accordance with the requirements of turbine blade life design, and obtain the stress level at key locations. In order to reduce the workload and improve work efficiency, from the perspective of engineering practice, a simplified method for creep damage equivalent stress is developed to replace multiple working conditions with one working condition. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the creep curve at the assessment location.

[0032] Figure 2 This is a diagram showing the assessment location. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are only some embodiments of this application, not all embodiments. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings. Design Scheme Description

[0034] Four equivalent schemes were studied for creep damage equivalent stress:

[0035] Method 1: Without considering creep stress relaxation (temperature T1, initial stress σ1), calculate the lifetime L1 and obtain the damage D1;

[0036] Method 2: Considering creep stress relaxation, the equivalent stress is equivalent to the working time in this state (temperature T1, equivalent stress σ2), the life L2 is calculated, and the damage D2 is obtained;

[0037] Method 3: Considering creep stress relaxation, the equivalent stress is equivalent to the failure time (fracture time) (temperature T1, equivalent stress σ3), the lifetime L3 is calculated, and the damage D3 is obtained;

[0038] Method 4: Without considering creep stress relaxation, select the state with the greatest damage as the equivalent state, and equate the damage of other states to this state to obtain the total equivalent time t4 of the equivalent state. Then, based on the equivalent state, consider creep stress relaxation (temperature T1, equivalent stress σ4) to calculate the lifetime L4, and obtain the cumulative damage D4.

[0039] Some conventions in design

[0040] During the design process, some agreements need to be made:

[0041] Stress convention: Calculated based on equivalent stress;

[0042] Model convention: All results are calculated using 2D models. If 3D model results are available, please also include them.

[0043] For handling over-temperature points, the assessment location can be removed (it is recommended to remove several state points with a lifespan reserve of less than 1) and the location with the second greatest damage can be selected for analysis.

[0044] Method 3: A method for obtaining equivalent stress

[0045] For Method 3, which requires calculating the stress at sustained fracture (damage equals 1), the method is shown in Table 1, and opinions are provided. Figure 1 .

[0046] Table 1. Equivalent stress obtained

[0047]

[0048] Note: * indicates that the lifetime (h) corresponding to the stress and temperature in the integral segment is obtained by using the parameters of the stress-life curve or the thermal strength parameter composite curve (the parameters are modified according to different materials).

[0049] Analysis of the results of the example

[0050] For a certain type of engine, key locations such as Figure 2 The comparison results of the calculations using the four methods for assessment point 1 are shown in Table 2.

[0051] Table 2 Comparison of Calculation Results of Four Methods for a Certain Type of Engine

[0052]

[0053] Analysis of the calculation results leads to the following conclusions: Among the four methods, Method 1 does not consider the effect of stress relaxation after creep, and the calculated results are too conservative, making it essentially unusable; Method 3 considers the equivalent stress up to fracture, requiring calculations to reach a damage level of 1, and the calculated results are too optimistic, so it is not recommended; Method 2 involves a large workload due to multiple states, and is therefore not adopted. Method 4 is recommended for assessing tack life.

[0054] The creep damage equivalent stress calculation method developed in this invention can simplify hundreds of life analysis points into one equivalent design state, improving the efficiency of the long-term life analysis process and ensuring the reliability of life design.

[0055] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for calculating the equivalent stress of creep damage in turbine blades, characterized in that, Includes the following steps: Step S1: Without considering creep stress relaxation, select the state with the greatest damage from multiple operating states of the turbine blade as the equivalent state. Step S2: Equip the damage of each other working state to the equivalent state to obtain the total equivalent time t4 of the equivalent state; Step S3: Consider creep stress relaxation based on the equivalent state, calculate lifetime L4 based on temperature T1 and equivalent stress σ4, and obtain cumulative damage D4.

2. The method for calculating equivalent stress due to creep damage in turbine blades as described in claim 1, characterized in that, Prior to step S1, there is also a step of studying four equivalent schemes: Option 1: Without considering creep stress relaxation, calculate lifetime L1 and damage D1 based on temperature T1 and initial stress σ1; Option 2: Considering creep stress relaxation, determine the equivalent stress σ2 based on the working time, and calculate the life L2 and damage D2; Option 3: Considering creep stress relaxation, determine the equivalent stress σ3 based on the failure time, and calculate the lifetime L3 and damage D3; Option 4: Use the equivalent state method described in claim 1 to determine the equivalent stress σ4, and calculate the lifetime L4 and damage D4.

3. The method for calculating equivalent stress due to creep damage in turbine blades as described in claim 1, characterized in that, The method for obtaining the equivalent stress in Scheme 3 includes: Record the stress values ​​at each point according to the calculated time step; Calculate the time and stress of the integral segment; Based on integral stress and temperature, the corresponding lifetime is calculated using the stress-life curve or the combined thermal strength parameter curve. Calculate the damage corresponding to the integral segment. When the total accumulated damage reaches 1, use the thermal strength parameter comprehensive curve parameters to obtain the equivalent stress.

4. The method for calculating equivalent stress due to creep damage in turbine blades as described in claim 1, characterized in that, The following agreements need to be made before performing the calculations: Stress convention: Calculated based on equivalent stress; Model convention: Calculation results are obtained using 2D models, supplemented by 3D model calculation results; For handling over-temperature points: remove state points with a lifespan reserve of less than 1, and select the location with the second greatest damage for analysis.

5. The method for calculating equivalent stress due to creep damage in turbine blades according to claim 1, characterized in that, The method is applicable to key assessment points of aero-engine turbine blades, and improves the efficiency of long-term life analysis by simplifying multi-condition calculations into single-condition calculations.

6. A turbine blade life assessment system, characterized in that, include: The data acquisition module is used to acquire time, temperature, and stress parameters of the turbine blades under multiple operating conditions; An equivalent processing module is used to implement the method for calculating the equivalent stress of creep damage of turbine blades as described in any one of claims 1-5, and to determine the equivalent state and equivalent stress. The life calculation module calculates the turbine blade's life reserve Kt and cumulative damage based on the equivalent processing results.

7. The turbine blade life assessment system according to claim 6, characterized in that, The system further includes, characterized in that, The results comparison module is used to compare the calculation results of four equivalent schemes. Scheme four is recommended for long-term lifetime assessment. The visualization module is used to display the creep curves and life assessment results at the assessment locations.

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