A life prediction method for turbine blade trapezoidal wave thermomechanical fatigue test

Abstract

The purpose of the present invention is to provide a method for predicting the life of a turbine blade trapezoidal wave thermomechanical fatigue test. According to the damage mechanism of the material under thermomechanical load, the purely mechanical low-cycle fatigue damage and the persistent creep damage (including the loading stage, the load holding stage, and the unloading stage) are respectively calculated. The linear cumulative damage principle is used to calculate the thermomechanical fatigue damage of the low-cycle and creep interaction of a single cycle, and then the life of the turbine blade is predicted. The present invention is simple to calculate, uses the existing data in the material manual, and has a wide range of applications.

Description

Technical Field

[0001] The present invention relates to a gas turbine, in particular to a gas turbine blade. Background Art

[0002] A gas turbine is a rotating mechanical device that converts the thermal energy of high-temperature, high-pressure combustion gas into mechanical energy. The turbine rotor is an important component that converts the thermal energy of gas into kinetic energy and outputs power and torque. It works in a high-temperature, high-speed environment. The rotor speed is as high as 10,000 rpm, and the operating temperature of the high-pressure turbine blades is above 700°C. The working environment is very harsh. How to evaluate the life of turbine blades is particularly important. In order to accurately evaluate the life of turbine blades, thermal engine composite fatigue tests are generally carried out in component tests. Since thermal engine fatigue tests are complex, fatigue test cycles are long, and test costs are expensive, it is very meaningful to find a method to predict the test results.

[0003] The current thermomechanical fatigue tests on turbine blades generally adopt triangular wave or trapezoidal wave forms. Since most of them use induction heating, heating and cooling take time, and too fast will cause higher thermal stress. Therefore, the heating and cooling process accounts for most of the total test time, which has a great impact on the long-term life of materials working at high temperatures. Summary of the invention

[0004] The object of the present invention is to provide a life prediction method for a turbine blade trapezoidal wave thermomechanical fatigue test taking into account the interaction between creep rupture and low cycle.

[0005] The object of the present invention is achieved in that:

[0006] The present invention provides a turbine blade trapezoidal wave thermomechanical fatigue test life prediction method, which is characterized by:

[0007] A method for predicting the life of a turbine blade trapezoidal wave thermomechanical fatigue test, characterized by:

[0008] (1) Determine the material constants E and σ' f , b, ε' f , c, K', n', coefficients a0, a1, a2, a3 of the comprehensive curve equation of persistent heat intensity parameters;

[0009] (2) Thermomechanical fatigue damage D TMF Classification as low cycle fatigue damage D LCF , creep damage;

[0010] (3) Determine the nominal stress spectrum and peak nominal stress Valley nominal stress A is the area of ​​the test section;

[0011] (4) Determine the nominal strain spectrum and peak nominal strain Valley nominal strain

[0012] (5) Determine the nominal stress range Δσ N =σ N1 -σ N2 ;

[0013] (6) Determine the nominal strain range Δε N =ε N1 -ε N2 ;

[0014] (7) Determine the stress concentration factor. The ratio of the maximum stress of the test section to the average stress of the section is obtained by finite element calculation as an approximate value of the stress concentration factor;

[0015] (8) Determine the true peak stress σ based on the cyclic stress-strain curve of the material 1 、True peak strain ε1:

[0016]

[0017] (9) Determine the true stress range Δσ and true strain range Δε based on the hysteresis loop of the material:

[0018]

[0019] The valley true stress σ is obtained from the stress range and strain range formula 2 , valley true strain ε2;

[0020] σ2=σ1-Δσ

[0021] ε2=ε1-Δε

[0022] Determine the low cycle fatigue life N under constant amplitude loading * ;

[0023] (10) Determine the low cycle fatigue life N under constant amplitude loading * :

[0024] Select the modified Morrow mean stress equation Or the SWT parameter model Perform iterative calculations;

[0025] In the formula, the average stress

[0026] (11) Determine low-cycle fatigue damage under constant amplitude loading

[0027] (12) Obtaining the comprehensive curve equation of the lasting heat strength parameters from the material parameters

[0028] (13) Determine the stress levels in the loading and unloading stages as The temperature level is the high temperature holding temperature T1; the stress level in the high temperature holding stage is σ 1 , the temperature level is the high temperature holding temperature T1;

[0029] (14) Determine the blade permanent fracture time tr1, tr2, tr3 during the trapezoidal wave temperature loading, high temperature holding, and temperature unloading stages:

[0030]

[0031] Where P LM1 =T1(lgt r1 +c);

[0032]

[0033] Where P LM2 =T1(lgt r2 +c);

[0034]

[0035] Where P LM3 =T1(lgt r3 +c);

[0036] (15) Determine the creep damage of the blades in each stage of a single cycle of trapezoidal wave temperature loading, high temperature holding, and temperature unloading

[0037] (16) Determine the total damage D of a single cycle under trapezoidal wave loading TMF =D LCF +Dc1+Dc2+Dc3;

[0038] (17) Determine the life of blades under thermomechanical cyclic loading under trapezoidal wave loading

[0039] The present invention may also include:

[0040] 1. In step (13), the loading and unloading stress levels are taken as stress amplitudes, and the temperature is taken as the high temperature holding temperature.

[0041] 2. The loading waveform of the thermomechanical fatigue test is a trapezoidal waveform, and the load is tensile controlled.

[0042] 3. Thermomechanical fatigue test is constant amplitude cyclic loading.

[0043] The advantages of the present invention are: the present invention calculates low cycle fatigue damage and creep damage (loading stage, load holding stage, unloading stage) respectively according to the material properties, and uses the linear cumulative damage principle to superimpose the damage of each part to obtain single cycle damage, and then predicts the life. The present invention is simple to calculate, uses the existing data in the material manual, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a flow chart of the present invention;

[0045] Figure 2 Schematic diagram of the load spectrum of the trapezoidal wave thermomechanical fatigue test on turbine blades. DETAILED DESCRIPTION

[0046] The present invention is described in more detail below with reference to the accompanying drawings:

[0047] Combination Figure 1-2 The solution adopted by the present invention is to provide a method for predicting the life of a turbine blade trapezoidal wave thermomechanical fatigue test. The implementation steps of the method are as follows:

[0048] Step 1: Determine material parameters based on the trapezoidal wave peak and valley temperature;

[0049] Step 2: Determine the nominal stress spectrum based on the peak tensile force and the test cross-sectional area;

[0050] Step 3: Determine the nominal strain spectrum according to the formula;

[0051] Step 4: Determine the nominal stress range;

[0052] Step 5: Determine the nominal strain range;

[0053] Step 6: Obtain an approximate value of the stress concentration factor through finite element calculation based on the key areas of concern;

[0054] Step 7: Determine the peak true stress and peak true strain according to the material cyclic stress-strain curve and Neuber formula cyclic iteration;

[0055] Step 8: Determine the true stress range and true strain range based on the material hysteresis loop and Neuber formula iteration;

[0056] Step 9: Obtain the valley true stress and valley true strain according to the stress range and strain range calculation formula;

[0057] Step 10: Select the strain-life equation to obtain the single-cycle low-cycle fatigue life;

[0058] Step 11: According to the linear cumulative damage principle, obtain the single-cycle low-cycle fatigue damage;

[0059] Step 12: Obtain the comprehensive equation of the lasting heat strength parameters according to the material parameters;

[0060] Step 13: Obtain the stress and temperature levels at each stage of heating, high temperature holding, and cooling according to the test conditions;

[0061] Step 14: Calculate the creep rupture time in the heating, high temperature holding and cooling stages through cyclic iterations;

[0062] Step 15: According to the linear cumulative damage principle, the creep damage in the heating, high temperature holding and cooling stages under a single cycle is calculated respectively;

[0063] Step 16: Calculate the low cycle fatigue and creep fatigue composite cumulative damage of a single cycle;

[0064] Step 17: Calculate the thermomechanical fatigue life of turbine blades based on the linear cumulative damage principle;

[0065] The loading waveform of the test is a trapezoidal waveform, a tensile control test, and the test loading diagram for specific conditions is shown in Figure 2 .

[0066] The present invention provides a method for predicting the life of a turbine blade trapezoidal wave thermomechanical fatigue test, and the specific implementation method is as follows:

[0067] Determine the material constants E and σ' f , b, ε' f , c, K', n', coefficients a0, a1, a2, a3 of the comprehensive curve equation of lasting heat intensity parameters.

[0068] Thermomechanical fatigue damage D TMF Classification as low cycle fatigue damage D LCF , creep damage (loading stage D C1 , Load holding phase D C2 Uninstallation phase D C3 ).

[0069] Determine the nominal stress spectrum, peak nominal stress Valley nominal stress A is the area of ​​the test section.

[0070] Determine the nominal strain spectrum, peak nominal strain Valley nominal strain

[0071] Determine the nominal stress range Δσ N =σ N1 -σ N2 .

[0072] Determine the nominal strain range Δε N =ε N1-ε N2 .

[0073] Determine the stress concentration factor Kt, and use finite element software to calculate the ratio of the maximum stress of the test section to the average stress of the section as an approximate value of the stress concentration factor.

[0074] Determine the true peak stress σ from the cyclic stress-strain curve of the material 1 , true peak strain ε1.

[0075]

[0076] The true stress range Δσ and true strain range Δε are determined based on the hysteresis loop of the material.

[0077]

[0078] The valley true stress σ is obtained from the stress range and strain range formula 2 , valley true strain ε2.

[0079] σ2=σ1-Δσ

[0080] ε2=ε1-Δε

[0081] Determine the low cycle fatigue life N under constant amplitude loading * .

[0082] Select the modified Morrow mean stress equation Or the SWT parameter model Perform iterative calculations.

[0083] In the formula, the average stress

[0084] Determination of cumulative damage in a single cycle of low-cycle fatigue under constant amplitude loading

[0085] Obtaining the comprehensive curve equation of the lasting heat strength parameters from the material parameters

[0086] Determine the stress level in the loading and unloading stages as The temperature level is the high temperature holding temperature T1; the stress level in the high temperature holding stage is σ 1 , the temperature level is the high temperature holding temperature T1.

[0087] Determine the blade permanent fracture times tr1, tr2, and tr3 during the trapezoidal wave temperature loading, high temperature holding, and temperature unloading stages.

[0088]

[0089] Where P LM1 =T1(lgtr1 +c), T1 is related to the formula used to fit the comprehensive curve of persistent heat intensity parameters.

[0090]

[0091] Where P LM2 =T1(lgt r2 +c), T1 is related to the formula used to fit the comprehensive curve of persistent heat intensity parameters.

[0092]

[0093] Where P LM3 =T1(lgt r3 +c), T1 is related to the formula used to fit the comprehensive curve of persistent heat intensity parameters.

[0094] Determine the creep damage of the blades caused by each stage in a single cycle of trapezoidal wave temperature loading, high temperature holding, and temperature unloading

[0095] Determine the total damage D of a single cycle under trapezoidal wave loading TMF =D LCF +Dc1+Dc2+Dc3.

[0096] Determining the life of blades under thermomechanical cyclic loading under trapezoidal wave loading

Claims

1. A method for predicting the life of a turbine blade trapezoidal wave thermomechanical fatigue test, characterized by: (1) Determine the material constants E and σ' f , b, ε' f , c, K', n', coefficients a0, a1, a2, a3 of the comprehensive curve equation of persistent heat intensity parameters; (2) Thermomechanical fatigue damage D TMF Classification as low cycle fatigue damage D LCF , creep damage; (3) Determine the nominal stress spectrum and peak nominal stress Valley nominal stress A is the area of ​​the test section; (4) Determine the nominal strain spectrum and peak nominal strain Valley nominal strain (5) Determine the nominal stress range Δσ N =σ N1 -σ N2 ; (6) Determine the nominal strain range Δε N =ε N1 -ε N2 ; (7) Determine the stress concentration factor. The ratio of the maximum stress of the test section to the average stress of the section is obtained by finite element calculation as an approximate value of the stress concentration factor; (8) Determine the true peak stress σ1 and true peak strain ε1 according to the cyclic stress-strain curve of the material: (9) Determine the true stress range Δσ and true strain range Δε based on the hysteresis loop of the material: The valley true stress σ2 and valley true strain ε2 are obtained from the stress range and strain range formulas; σ2=σ1-Δσ ε2=ε1-Δε Determine the low cycle fatigue life N under constant amplitude loading * ; (10) Determine the constant amplitude loading low cycle fatigue life N * : Select the modified Morrow mean stress equation Or the SWT parameter model Perform iterative calculations; In the formula, the average stress (11) Determine low-cycle fatigue damage under constant amplitude loading (12) Obtaining the comprehensive curve equation of the lasting heat strength parameters from the material parameters (13) Determine the stress levels in the loading and unloading stages as The temperature level is the high temperature holding temperature T1; the stress level in the high temperature holding stage is σ1, and the temperature level is the high temperature holding temperature T1; (14) Determine the blade permanent fracture time tr1, tr2, tr3 during the trapezoidal wave temperature loading, high temperature holding, and temperature unloading stages: Where P LM1 =T1(lgt r1 +c); Where P LM2 =T1(lgt r2 +c); Where P LM3 =T1(lgt r3 +c); (15) Determine the creep damage of the blades in each stage of a single cycle of trapezoidal wave temperature loading, high temperature holding, and temperature unloading (16) Determine the total damage D of a single cycle under trapezoidal wave loading TMF =D LCF +Dc1+Dc2+Dc3; (17) Determine the life of blades under thermomechanical cyclic loading under trapezoidal wave loading 2. A turbine blade trapezoidal wave thermomechanical fatigue test life prediction method according to claim 1, characterized in that: In step (13), the loading and unloading stress levels are taken as stress amplitudes, and the temperature is taken as the high temperature holding temperature.

3. The method for predicting the life of a turbine blade trapezoidal wave thermomechanical fatigue test according to claim 1, characterized in that: The loading waveform of the thermomechanical fatigue test is a trapezoidal waveform, and the load is controlled by tension.

4. The method for predicting the life of a turbine blade trapezoidal wave thermomechanical fatigue test according to claim 1, characterized in that: Thermomechanical fatigue tests were performed under constant amplitude cyclic loading.

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