Blade vibration fatigue strength and three-dimensional fatigue crack propagation prediction method

Abstract

The invention discloses a blade vibration fatigue strength and three-dimensional fatigue crack propagation prediction method which comprises the following steps: carrying out uniaxial tensile test and fracture toughness measurement on a blade test piece material to obtain material mechanical parameters of the blade test piece material; performing a bending vibration fatigue test on the blade test piece to obtain the fatigue strength of the blade test piece; a three-dimensional fatigue fracture phase field model is constructed, and phase field simulation parameters are obtained through finite element calculation; based on material mechanical parameters and phase field simulation parameters, a blade three-dimensional simulation model is established by simulating a blade sample in a bending vibration fatigue test, a periodic pressure load is applied to a blade basin of the blade to simulate an aerodynamic load in the service process of the blade, the three-dimensional fatigue crack propagation behavior of the blade is calculated, and the vibration fatigue strength of the blade is predicted. According to the method, a three-dimensional fatigue fracture phase field model is established, numerical solution is performed by using a finite element method, the three-dimensional fatigue crack propagation behavior of the blade under the periodic vibration load can be effectively predicted, and the blade fatigue prediction accuracy is improved.

Description

Technical Field

[0001] The invention relates to blade fatigue behavior prediction, and in particular to a blade vibration fatigue strength and three-dimensional fatigue crack propagation prediction method. Background Art

[0002] The aerodynamic conditions inside aircraft engines are complex, and they are subjected to irregular dynamic loads during service, which can easily lead to structural deformation and vibration. Long-term vibration cycles can degrade the mechanical properties of materials and may cause structural fatigue failure. Compressor blades, as one of the main components of aircraft engines, are often damaged by vibrations because their function is to compress air for use in the combustion process. Cyclic dynamic loads lead to the initiation and propagation of fatigue cracks in compressor blades. The vibration characteristics and fatigue performance of blades directly affect the overall performance of the engine. In order to improve the durability and reliability of the engine, it is urgent to develop a method to predict the vibration fatigue strength and three-dimensional crack propagation behavior of compressor blades under vibration fatigue.

[0003] In the prior art, the study of vibration fatigue behavior of blades mainly includes vibration tests, theoretical modal analysis and numerical simulation. Vibration fatigue tests are costly, time-consuming and labor-intensive. It is also difficult to collect data from irregularly shaped blades. Therefore, theoretical models and numerical simulation methods are very important. Modal analysis and structural vibration frequency calculation mainly include methods such as discrete Fourier transform and autoregressive model. Frequency loss indicates blade failure. However, the shape and structure of real blades are complex, and modal analysis is difficult. In terms of numerical research, the deformation and movement of blades are usually analyzed using beam elements or plate elements. The distribution of stress and strain is calculated with the help of the finite element method (FEM), and then the fatigue life of the blade is predicted using empirical models. These empirical models include the Basquin equation, the Manson-Coffin model, the Cruse-Meyer model, the Ostergren model, etc. The prediction process is relatively complex, and the prediction accuracy depends on empirical parameters. The extended finite element method and the boundary element method are used to study blade fatigue failure, which can describe complex crack propagation forms and have relatively high prediction accuracy, but both methods require specific fracture criteria and need to re-divide the geometric shape according to the evolution of the crack.

[0004] Although scholars and engineers have conducted extensive research on the fatigue problem of compressor blades, the accuracy of predicting blade fatigue behavior under vibration loads remains an important issue. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a method for predicting blade vibration fatigue strength and three-dimensional fatigue crack propagation with improved prediction accuracy.

[0006] Technical solution: To solve the above problems, the present invention adopts a blade vibration fatigue strength and three-dimensional fatigue crack propagation prediction method, which includes the following steps:

[0007] Step 1: Perform a uniaxial tensile test on the blade specimen material and measure the fracture toughness of the material to obtain the stress-strain curve of the blade specimen material and obtain the mechanical parameters of the material by fitting; perform a bending vibration fatigue test on the blade specimen to obtain the fatigue strength of the blade specimen;

[0008] Step 2: Construct a three-dimensional fatigue fracture phase field model, and obtain phase field simulation parameters through finite element calculation based on the obtained material mechanical parameters and fatigue strength;

[0009] Step 3: Based on the material mechanical parameters of the blade specimen material obtained in step 1 and the phase field simulation parameters obtained in step 2, a three-dimensional simulation model of the blade is established in imitation of the blade specimen in the bending vibration fatigue test. A periodic pressure load is applied to the blade basin to simulate the aerodynamic load of the blade during service. The three-dimensional fatigue crack propagation behavior of the blade is calculated, and the vibration fatigue strength of the blade is predicted.

[0010] Furthermore, in step 1, a uniaxial tensile test is performed on the blade specimen material according to the ASTM E8 / E8M-13a metal material tensile test method, and the material mechanical parameters include Young's modulus, Poisson's ratio, ultimate strength, and fracture toughness.

[0011] Furthermore, in step 1, the method of performing a bending vibration fatigue test on the blade specimen includes a step-by-step loading method, a lifting method, and a grouping method. The test conditions of the bending vibration fatigue test are 3×10 7 Second cycle.

[0012] Furthermore, when the blade specimen is subjected to a bending vibration fatigue test with step-by-step loading, the fatigue strength of the blade specimen is:

[0013]

[0014] Among them, σ e is the fatigue strength of the blade specimen under a given number of cycles, N is the given number of fatigue cycles, σ p is the maximum stress level of the previous stress step, σ f is the maximum stress level of the last stress step, and n is the number of cycles to failure in the last stress step.

[0015] Furthermore, in step 2, the three-dimensional fatigue fracture phase field model includes:

[0016] Stress balance equation:

[0017]

[0018] in, is the gradient operator, σ is the stress tensor;

[0019] Fracture order parameter evolution equation:

[0020]

[0021] Among them, c is the fracture phase field order parameter, η is the dynamic coefficient, l is the interface width, G c is the critical fracture energy density, t is the time, is the fracture energy density decay function, is the historical variable driving crack growth.

[0022] Furthermore, the fracture energy density attenuation function for:

[0023]

[0024] in, is the accumulated tensile elastic strain energy during fatigue loading, α T is the energy threshold value, and κ is the exponential parameter. The phase field simulation parameters include interface width, energy threshold and exponential parameter.

[0025] Furthermore, in step 3, the stress ratio of the periodic pressure load applied to the blade basin is -1; the vibration fatigue behavior of the blade under different pressure loads is simulated, and for the 3×10 7 Under the cycle, the maximum value of the internal fracture order parameter of the blade reaches the critical value 1, which indicates that the stress at the dangerous point of the blade under this pressure load is the vibration fatigue strength of the blade.

[0026] The present invention also adopts a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the computer program.

[0027] The present invention also requires 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.

[0028] Beneficial effects: Compared with the prior art, the significant advantage of the present invention is that by establishing a three-dimensional fatigue fracture phase field model and using the finite element method for numerical solution, the three-dimensional fatigue crack growth behavior of the blade under periodic vibration load can be effectively predicted, the blade vibration fatigue crack growth law can be revealed, and the blade fatigue prediction accuracy can be improved. The present invention can also be used for the vibration fatigue strength and three-dimensional fatigue crack growth prediction of surface-strengthened blades. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic flow chart of the prediction method of the present invention;

[0030] Figure 2 It is a schematic diagram of the uniaxial tensile stress-strain curve of TC17 titanium alloy in the present invention;

[0031] Figure 3 It is a geometrical schematic diagram of the TC17 simulated blade in the present invention;

[0032] Figure 4 It is a schematic diagram of fracture order parameters for simulating the three-dimensional fatigue crack propagation process of a blade in the present invention;

[0033] Figure 5 It is a comparison chart of the vibration fatigue strength prediction value and the test value in the present invention. DETAILED DESCRIPTION

[0034] like Figure 1 As shown, a method for predicting blade vibration fatigue strength and three-dimensional fatigue crack growth in this embodiment is as follows:

[0035] Step 1: Perform a uniaxial tensile test on the compressor blade specimen material according to the ASTM E8 / E8M-13a metal material tensile test method, measure the material fracture toughness, obtain the material stress-strain curve, and fit the material mechanical parameters such as Young's modulus, Poisson's ratio, ultimate strength, and fracture toughness.

[0036] In this embodiment, TC17 titanium alloy is selected as the compressor blade specimen material. A uniaxial tensile test is performed on the TC17 titanium alloy. The stress-strain curve is shown in FIG. Figure 2 , determine the material mechanical parameters as shown in Table 1.

[0037] Table 1: Mechanical properties of TC17 titanium alloy

[0038] Parameter name Parameter Value Young's modulus 112GPa Poisson's ratio 0.301 Fracture toughness <![CDATA[9.3×10 4 N / m]]> Strength limit 1106.4MPa Yield Strength 954.3MPa

[0039] Step 2: According to HB5277-84 "Vibration fatigue test method for engine blades and materials" and GB / T24176-2009 "Statistical plan and analysis method for fatigue test data of metal materials", use the vibration fatigue test system to perform bending vibration fatigue test on the blade to obtain the vibration fatigue strength of the specimen.

[0040] According to the leading edge simulation blade design method, the geometric dimensions and stress distribution characteristics of the leading edge of the real blade are taken into account. The leading edge simulation blade is designed based on the geometric dimensions and stress distribution of the maximum stress position of the leading edge of a certain type of engine fan blade under the first-order vibration mode. The simulated blade geometry is shown in the figure below. Figure 3 The electronically controlled vibration system was used, the stress ratio was set to -1, and the step method was used to perform high-cycle vibration fatigue tests. 7The cycle is infinite life. The high cycle fatigue strength test value of TC17 simulated blade is obtained according to the critical distance method, see Table 2.

[0041] Table 2: TC17 simulated blade high cycle vibration fatigue test results

[0042] Sample No. Fatigue strength(MPa) 1 549.68 2 558.54 3 563.50

[0043] Step 3: Construct a three-dimensional fatigue fracture phase field model and complete program development and finite element implementation.

[0044] The phase field fatigue fracture model mainly includes:

[0045] Stress balance equation:

[0046]

[0047] in, is the gradient operator and σ is the stress tensor.

[0048] Fracture order parameter evolution equation:

[0049]

[0050] Among them, c(x,y,z) is the fracture phase field order parameter, η is the dynamic coefficient, l is the interface width, G c is the critical fracture energy density, t is the time, is the fracture energy density decay function, As the historical variable driving crack extension, the maximum elastic energy experienced at the time step is taken, that is,

[0051]

[0052] The fracture energy decay function is in the form of:

[0053]

[0054] in, is the accumulated tensile elastic strain energy during fatigue loading, α T is the energy threshold value, and κ is the exponential parameter. According to the one-dimensional uniaxial tensile fracture simulation calculation of TC17 titanium alloy, the interface width is determined by combining the uniaxial tensile test and the fracture toughness test, and the energy threshold and exponential parameter are calibrated based on the vibration fatigue strength test value. The calibrated TC17 model parameters are shown in Table 3.

[0055] Table 3: Phase field model parameters of TC17 titanium alloy

[0056] Parameter name Parameter Value Interface width 1.0mm Fatigue threshold <![CDATA[1.1625×10 7 J / m 3 ]]> Fatigue Index 0.13

[0057] Step 4: Establish a three-dimensional simulation model of the blade based on the blade specimen in the vibration fatigue test, apply a periodic pressure load at the blade basin to simulate the aerodynamic load during the compressor service process, calculate the three-dimensional fatigue crack propagation behavior of the blade, and predict the vibration fatigue strength of the blade.

[0058] A simulation model of the blade was established in Abaqus and the mesh was divided. The mechanical parameters of the TC17 titanium alloy such as Young's modulus, Poisson's ratio, strength limit, critical fracture toughness, etc. measured in step 1, and the phase field simulation parameters such as interface width, energy threshold and index parameter determined by fitting in step 3 were input into the three-dimensional fatigue fracture phase field calculation model. The stress ratio of the periodic pressure load applied to the blade basin is -1 to ensure that the blade load is consistent with the vibration caused by the aerodynamic load. The vibration fatigue behavior of the blade under different pressure loads was simulated. If the pressure is 3×10 7 Under the cycle, the maximum value of the internal fracture order parameter of the blade reaches the critical value 1, which indicates that the stress at the dangerous point of the blade under this pressure load is the vibration fatigue strength of the blade. The vibration fatigue strength and three-dimensional fatigue crack growth behavior of the blade are obtained through batch calculation of the finite element program. When the peak value of the pressure load is 1.5MPa, the three-dimensional fatigue crack growth process of the blade is as follows Figure 4 The comparison between the predicted value of vibration fatigue strength of the blade simulated by TC17 and the test value of vibration fatigue strength obtained in step 2 is shown in the figure below: Figure 5 , where the red solid dot abscissa represents the test value of vibration fatigue strength, the ordinate represents the predicted value, the two dotted lines represent the ±5% error band, and the solid dot falls between the two dotted lines, indicating that the error between the predicted value and the test value does not exceed 5%.

Claims

1. A method for predicting blade vibration fatigue strength and three-dimensional fatigue crack growth, characterized in that: The following steps are involved: Step 1: Perform a uniaxial tensile test on the blade specimen material and measure the fracture toughness of the material to obtain the stress-strain curve of the blade specimen material and obtain the mechanical parameters of the material by fitting; perform a bending vibration fatigue test on the blade specimen to obtain the fatigue strength of the blade specimen; Step 2: Construct a three-dimensional fatigue fracture phase field model, and obtain phase field simulation parameters through finite element calculation based on the obtained material mechanical parameters and fatigue strength; Step 3: Based on the material mechanical parameters of the blade specimen material obtained in step 1 and the phase field simulation parameters obtained in step 2, a three-dimensional simulation model of the blade is established in imitation of the blade specimen in the bending vibration fatigue test. A periodic pressure load is applied to the blade basin to simulate the aerodynamic load of the blade during service. The three-dimensional fatigue crack propagation behavior of the blade is calculated, and the vibration fatigue strength of the blade is predicted.

2. The blade vibration fatigue strength and three-dimensional fatigue crack growth prediction method according to claim 1, characterized in that: In step 1, a uniaxial tensile test is performed on the blade specimen material according to the ASTM E8 / E8M-13a metal material tensile test method, and the material mechanical parameters include Young's modulus, Poisson's ratio, ultimate strength, and fracture toughness.

3. The blade vibration fatigue strength and three-dimensional fatigue crack growth prediction method according to claim 1, characterized in that: In step 1, the method of performing bending vibration fatigue test on the blade specimen includes step-by-step loading method, lifting method, and grouping method. The test conditions of the bending vibration fatigue test are 3×10 7 Second cycle.

4. The blade vibration fatigue strength and three-dimensional fatigue crack growth prediction method according to claim 3 is characterized in that: When the blade specimen is subjected to a bending vibration fatigue test with step-by-step loading, the fatigue strength of the blade specimen is: Among them, σ e is the fatigue strength of the blade specimen under a given number of cycles, N is the given number of fatigue cycles, σ p is the maximum stress level of the previous stress step, σ f is the maximum stress level of the last stress step, and n is the number of cycles to failure in the last stress step.

5. The blade vibration fatigue strength and three-dimensional fatigue crack growth prediction method according to claim 1, characterized in that: In step 2, the three-dimensional fatigue fracture phase field model includes: Stress balance equation: in, is the gradient operator, σ is the stress tensor; Fracture order parameter evolution equation: Among them, c is the fracture phase field order parameter, η is the dynamic coefficient, l is the interface width, G c is the critical fracture energy density, t is the time, is the fracture energy density decay function, is the historical variable driving crack growth.

6. The blade vibration fatigue strength and three-dimensional fatigue crack growth prediction method according to claim 5, characterized in that: The fracture energy density decay function for: in, is the accumulated tensile elastic strain energy during fatigue loading, α T is the energy threshold, and κ is the exponential parameter.

7. The blade vibration fatigue strength and three-dimensional fatigue crack growth prediction method according to claim 6, characterized in that: The phase field simulation parameters include interface width, energy threshold and index parameter.

8. The blade vibration fatigue strength and three-dimensional fatigue crack growth prediction method according to claim 7, characterized in that: In step 3, the stress ratio of the periodic pressure load applied to the blade basin is -1; the vibration fatigue behavior of the blade under different pressure loads is simulated. 7 Under the cycle, the maximum value of the internal fracture order parameter of the blade reaches the critical value 1, which indicates that the stress at the dangerous point of the blade under this pressure load is the vibration fatigue strength of the blade.

9. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to claim 1 to claim 8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to claim 1 to claim 8 are implemented.

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