A method for predicting creep deformation of a turbine disk based on a coupled creep constitutive model

Abstract

The present invention discloses a method for predicting the creep deformation of a turbine disk based on a coupled creep constitutive model. Aiming at the creep deformation of the turbine disk under a complex multi-stress field, the relationship curve between creep strain and time at different stress levels is obtained by means of a uniaxial creep test of a standard test bar. According to the combined time-hardening creep constitutive model and the θ-parameter method creep constitutive model, the material creep characteristic parameters at different stress levels are obtained. In the CREEP user subroutine provided by the finite element software ABAQUS, the two constitutive models are coupled and calculated by applying environmental stress to each integration point. The creep strain and creep deformation of each integration point are calculated within each time increment step to predict the creep deformation of the turbine disk under different stresses. This method overcomes the problem of being unable to accurately predict the creep deformation behaviors of both the low-stress and high-stress parts in an aero-engine turbine disk simultaneously, and can predict the creep deformation under a complex stress field.

Description

Technical Field

[0001] The present invention relates to the technical field of turbine disk creep prediction, and particularly to a method for predicting the creep deformation of a turbine disk based on a coupled creep constitutive model. Background Art

[0002] Creep refers to the phenomenon that metals undergo slow plastic deformation under the action of a continuous stress at a certain temperature. The occurrence of the creep phenomenon is the result of the combined action of temperature, stress, and time. Its process mainly includes three stages: the first stage of decelerating creep, the second stage of constant-rate creep, and the third stage of accelerating creep. Its characteristic is that the relationship between deformation, stress, and external force no longer maintains a one-to-one correspondence, and this deformation still has an irreversible deformation property even when the stress is less than the yield limit.

[0003] The service environment of the turbine disk of an aeroengine is harsh. It is not only impacted by high-temperature and high-pressure gas, but also subjected to complex mechanical stress and thermal stress. Moreover, during the long-term service process, the creep property will not only cause excessive plastic deformation, resulting in wear and collision, affecting the normal operation and assembly of the aeroengine, but may even cause creep fracture, leading to catastrophic failure of the turbine disk and resulting in engine failure, with unthinkable consequences. Predicting the creep of the aeroengine turbine disk can provide effective support for the improvement of the turbine disk design scheme. An accurate and reliable creep constitutive model is the basis for predicting the creep deformation of the aeroengine turbine disk. In the relevant research on the creep deformation analysis of the turbine disk in the prior art, most of the research uses a single constitutive model for research and analysis, such as the Norton creep constitutive model, the combined time-hardening creep constitutive model, and the θ-parameter method creep constitutive model, which are widely used in engineering. However, the stress distribution span generated by the aeroengine turbine disk in the working environment is relatively large, which may cause different stages of creep to coexist in the component. Using a single creep constitutive model may not be able to accurately predict the creep deformation of different stages of the low-stress and high-stress parts of the aeroengine turbine disk simultaneously, resulting in distortion of the creep prediction results. Summary of the Invention

[0004] The object of the present invention is to provide a method for predicting the creep deformation of a turbine disk based on a coupled creep constitutive model. This method overcomes the problem of being unable to accurately predict the creep deformation behavior of the low-stress and high-stress parts of the aeroengine turbine disk simultaneously and can accurately predict the creep deformation under a complex stress field.

[0005] The object of the present invention is achieved by the following technical solutions:

[0006] A method for predicting the creep deformation of a turbine disk based on a coupled creep constitutive model, the method comprising:

[0007] Step 1. For the creep deformation of the turbine disk under complex multi-stress fields, use the uniaxial creep test of standard test bars to obtain the relationship curves between creep strain and time at different stress levels;

[0008] Step 2. According to the combined time-hardening creep constitutive model and the θ-parameter method creep constitutive model, fit and regress the test data at different stress levels to obtain the material creep characteristic parameters at different stress levels;

[0009] Step 3. In the CREEP user subroutine provided by the finite element software ABAQUS, couple and calculate the combined time-hardening creep constitutive model and the θ-parameter method creep constitutive model by applying environmental stresses to each integration point;

[0010] Step 4. Establish a three-dimensional finite element model of the turbine disk in ABAQUS, apply the working load and temperature field to the established model, and obtain the stress, strain, and temperature of each integration point of the three-dimensional finite element model of the turbine disk through numerical simulation;

[0011] Step 5. Use the CREEP user subroutine provided by the finite element software ABAQUS to calculate the creep strain, creep deformation, and relaxation stress of each integration point step by step within each time increment, and predict the creep deformation of the turbine disk under different stresses.

[0012] As can be seen from the technical solutions provided by the present invention above, the above method overcomes the problem of being unable to accurately predict the creep deformation behaviors of both low-stress and high-stress parts in an aeroengine turbine disk simultaneously, and can accurately predict the creep deformation under complex stress fields, which has important guiding significance for the study of the creep deformation behavior of an actual turbine disk in its working environment. Description of the Drawings

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0014] Figure 1 It is a schematic flow chart of the method for predicting the creep deformation of a turbine disk based on a coupled creep constitutive model provided by an embodiment of the present invention;

[0015] Figure 2 It is a schematic diagram of the change of creep strain with time of the GH4169 superalloy described in an embodiment of the present invention at stress levels from 300 MPa to 800 MPa;

[0016] Figure 3It is a diagram showing the fitting results of creep strain of the coupled creep constitutive model adopted in the embodiment of the present invention at stress levels from 300 MPa to 800 MPa;

[0017] Figure 4 It is a schematic diagram showing the simulation and fitting results of creep strain of a standard test bar simulated by the coupled creep constitutive model adopted in the embodiment of the present invention at a stress level of 500 MPa;

[0018] Figure 5 It is a schematic diagram showing the simulation and fitting results of creep strain of a standard test bar simulated by the coupled creep constitutive model adopted in the embodiment of the present invention at a stress level of 700 MPa. Detailed implementation manners

[0019] Next, in combination with the accompanying drawings in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments, which do not constitute a limitation to the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0020] As Figure 1 shown is a schematic flow chart of a method for predicting creep deformation of a turbine disk based on a coupled creep constitutive model provided by an embodiment of the present invention. The method includes:

[0021] Step 1: For the creep deformation under the complex multi-stress field of the turbine disk, use the uniaxial creep test of a standard test bar to obtain the relationship curve between creep strain and time at different stress levels;

[0022] In this step, for the creep deformation under the complex multi-stress field of the turbine disk, a tensile test of a uniaxial creep test bar made of GH4169 superalloy with the same material as the turbine disk is carried out to obtain the relationship curve between creep strain and time of this material at a working temperature of 650 °C, a service duration of 1600 h, and a working load within the stress range of 300 MPa to 800 MPa. As Figure 2 shown is a schematic diagram of the change of creep strain with time of the GH4169 superalloy at stress levels from 300 MPa to 800 MPa described in the embodiment of the present invention;

[0023] Among them, the stress range in the uniaxial creep test bar tensile test should cover the maximum stress to the minimum stress of the turbine disk.

[0024] Step 2: According to the combined time-hardening creep constitutive model and the θ-parameter method creep constitutive model, perform fitting regression on the test data at different stress levels to obtain the material creep characteristic parameters at different stress levels;

[0025] In this step, the relationship curves of creep strain and time under different stress levels are analyzed. At low stress levels, the proportion of the first and second stages of creep in the service life of the turbine disk is the largest. As the stress increases, the occurrence time of the third stage of creep gradually advances. The large creep deformation in the third stage will put the component in a dangerous state or even cause fracture.

[0026] In the turbine disk, due to its working load, the range of its working stress span is relatively large, resulting in the possible coexistence of different creep stages in the turbine disk. In order to ensure that the creep constitutive model accurately describes the steady-state creep behavior of the first and second stages of creep and predicts the occurrence time of the third stage, the relationship curves of creep strain and time under different stresses are respectively used to fit and regress the material characteristic parameters by using the θ-parameter method creep constitutive model for the third stage of creep. The fitting formula of the θ-parameter method creep constitutive model is shown in the following formulas (1) and (2):

[0027]

[0028] lgθ i =a i +b i T+c i σ+d i Tσ(2)

[0029] The combined time-hardening creep constitutive model for the first and second stages of creep is used to fit and regress the material characteristic parameters. The fitting formula of the combined time-hardening creep constitutive model is shown in the following formula (3):

[0030]

[0031] In formula (1), θ 1 、θ 2 、θ 3 、θ 4 are influence coefficients, obtained from formula (2); a i 、b i 、c i 、d i are the creep characteristic parameters of the material in the θ-parameter method creep constitutive model, i = 1, 2, 3, 4; ε cr is the creep strain; t is the time; T is the temperature; σ is the stress, with the unit of MPa; e is the natural constant; as Figure 3 shown is the creep strain fitting result diagram of the embodiment of the present invention using the coupled creep constitutive model under the stress level from 300 MPa to 800 MPa;

[0032] In formula (3), C 1 、C 2 、C 3 、C 4 、C5 , C 6 , C 7 is the creep characteristic parameter of the material in the combined time-hardening creep constitutive model.

[0033] Step 3: In the CREEP user subroutine provided by the finite element software ABAQUS, couple the combined time-hardening creep constitutive model and the θ-parameter method creep constitutive model through the form of applying environmental stress to each integration point for calculation;

[0034] In this step, write a CREEP user subroutine through the finite element software ABAQUS. In the written CREEP user subroutine, according to the ABAQUS external interface regulations, three variable return values of the combined time-hardening creep constitutive model and the θ-parameter method creep constitutive model need to be defined respectively according to the explicit and implicit integration methods, which are:

[0035] The explicit creep integration return value, that is, the creep strain increment DECRA(1); the implicit creep integration return value, that is, the derivative of the creep strain increment with respect to the creep strain DECRA(2); the derivative of the creep strain increment with respect to the equivalent stress DECRA(5);

[0036] The corresponding formulas for the three variable return values deduced according to the combined time-hardening creep constitutive model are as follows:

[0037]

[0038]

[0039]

[0040] The corresponding formulas for the three variable return values deduced according to the θ-parameter method creep constitutive model are as follows:

[0041]

[0042]

[0043]

[0044] In the CREEP user subroutine, couple the two constitutive models by applying environmental stress to each integration point and defining the variable return values DECRA(1), DECRA(2), and DECRA(5) for calculation;

[0045] For example, in the CREEP user subroutine, the environmental stress is judged for each integration point. If the current integration point is between 300 MPa and 550 MPa, the combined time hardening creep constitutive model is used for iterative calculation and the variable return values DECRA(1), DECRA(2), and DECRA(5) are defined; if the current integration point is between 550 MPa and 800 MPa, the θ-parameter method creep constitutive model is used for iterative calculation and the variable return values DECRA(1), DECRA(2), and DECRA(5) are defined.

[0046] In ABAQUS, a finite element model of a standard test bar is established, and the CREEP user subroutine is verified by uniaxial creep simulation under the same boundary conditions as the uniaxial creep test of the standard test bar.

[0047] For example, in ABAQUS, a finite element model of a standard test bar is established. The form of fixing one end and applying different tensile forces at the other end is used to simulate the creep deformation of GH4169 superalloy under different stresses. The CREEP user subroutine is called to perform uniaxial creep simulation calculations on the finite element model of the standard test bar, and the simulation accuracy of creep strain under 500 MPa and 700 MPa stresses is verified respectively. As Figure 4 shown is the schematic diagram of the creep strain simulation and fitting results of the standard test bar simulated by the coupled creep constitutive model of the embodiment of the present invention under a stress level of 500 MPa; as Figure 5 shown is the schematic diagram of the creep strain simulation and fitting results of the standard test bar simulated by the coupled creep constitutive model of the embodiment of the present invention under a stress level of 700 MPa.

[0048] Step 4: Establish a three-dimensional finite element model of the turbine disk in ABAQUS, apply the working load and temperature field on the established model, and obtain the stress, strain, and temperature of each integration point of the three-dimensional finite element model of the turbine disk through numerical simulation;

[0049] In this step, specifically, a three-dimensional finite element model of the turbine disk is established in ABAQUS. The material properties of the finite element model are defined according to the superalloy material used for the turbine disk. The hexahedral mesh is used for division, and the working load and working temperature field are applied; the total creep analysis step time is defined. To make the calculation process fast and convergent, it is necessary to adjust the time increment step size not to be too large or too small, so as to simulate the stress distribution of the turbine disk under long-term working load. Specifically, by establishing a static analysis step one and a viscous analysis step two, where:

[0050] In static analysis step one, apply working loads including centrifugal load and aerodynamic load, and the working temperature field is the working environment temperature of the turbine disk; for example, apply body forces rotating around the axial direction to all element nodes with an amplitude of 27,000 r / min, add axial displacement constraints to the upper and lower end faces at the core of the turbine disk, and set the working temperature field to 650 °C;

[0051] In viscous analysis step two, set the total creep duration, adjust the time increment step and the automatic stabilization method to enable the rapid convergence of creep strain and its creep stress calculation; for example, define the total creep time as 300 h. To make the calculation process fast and convergent, adjust the initial increment step size to 1E-2, the minimum increment step to 1E-4, the maximum increment step to 3600, and the creep strain error tolerance to 1E-4. This is used to simulate the stress distribution of the turbine disk under long-term working loads.

[0052] Step 5: Use the CREEP user subroutine provided by the finite element software ABAQUS to calculate the creep strain, creep deformation, and relaxation stress at each integration point within each time increment step, and predict the creep deformation of the turbine disk under different stresses.

[0053] In this step, specifically, call the CREEP user subroutine in ABAQUS to perform iterative calculations of the creep strain and deformation of the turbine disk. Within the time increment step of each iteration, calculate the creep rate and creep increment at each stage of creep for all integration points according to the current creep time, temperature, and stress conditions.

[0054] If the result converges, update the stress strain and total creep and increase the increment step to continue the iterative calculation;

[0055] Finally, feedback the calculation results to the ABAQUS main program to obtain the creep strain and creep deformation of the turbine disk under the total creep duration.

[0056] It should be noted that the content not described in detail in the embodiments of the present invention belongs to the prior art well-known to those skilled in the art.

[0057] In summary, the method described in the embodiments of the present invention aims at the creep deformation of the turbine disk under complex multi-stress fields. By fitting and regressing the uniaxial creep test bar tensile test data to obtain the material creep characteristic parameters, compared with a single constitutive model, multiple constitutive models are coupled according to their applicable stress ranges and creep stages, which can more accurately predict the creep deformation behavior of the turbine disk under different stresses and different creep stages in the ABAQUS finite element simulation, and has important guiding significance for the study of the creep deformation behavior of the actual turbine disk in the working environment.

[0058] In addition, those of ordinary skill in the art can understand that all or part of the steps in implementing the methods of the above embodiments can be completed by instructing relevant hardware through a program, and the corresponding program can be stored in a computer-readable storage medium. The storage medium mentioned above can be a read-only memory, a magnetic disk, an optical disk, or the like.

[0059] As described above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims. The information disclosed in the background art part of this article is only intended to deepen the understanding of the overall background art of the present invention, and should not be regarded as an admission or any form of implication that this information constitutes the prior art already known to those skilled in the art.

Claims

1. A method for predicting creep deformation of a turbine disk based on a coupled creep constitutive model, characterized in that, the method includes: Step 1: For the creep deformation of the turbine disk under a complex multi-stress field, use the uniaxial creep test of a standard test bar to obtain the relationship curve between creep strain and time at different stress levels; Step 2: According to the combined time-hardening creep constitutive model and the θ-parameter method creep constitutive model, fit and regress the test data at different stress levels to obtain the material creep characteristic parameters at different stress levels; In Step 2, analyze the relationship curve between creep strain and time at different stress levels. At low stress levels, the proportion of the first and second stages of creep in the service life of the turbine disk is the largest. As the stress increases, the occurrence time of the third stage of creep gradually advances. In order to ensure that the creep constitutive model accurately describes the steady-state creep behavior of the first and second stages of creep and predicts the occurrence time of the third stage, the θ-parameter method creep constitutive model for the third stage of creep is used to fit and regress the material characteristic parameters. The fitting formula of the θ-parameter method creep constitutive model is shown in the following formulas (1) and (2): lgθ i = a i + b i T + c i σ + d i Tσ(2) Use the combined time-hardening creep constitutive model for the first and second stages of creep to fit and regress the material characteristic parameters. The fitting formula of the combined time-hardening creep constitutive model is shown in the following formula (3): θ in formula (1) 1 , θ 2 , θ 3 , θ 4 are influence coefficients, obtained from formula (2); a i , b i , c i , d i are the creep characteristic parameters of the material in the θ-parameter method creep constitutive model, i = 1, 2, 3, 4; ε cr is the creep strain; t is the time; T is the temperature; σ is the stress, unit MPa; e is the natural constant; C in formula (3) 1 、C 2 、C 3 、C 4 、C 5 、C 6 、C 7 are the creep characteristic parameters of the material in the combined time-hardening creep constitutive model; Step 3: In the CREEP user subroutine provided by the finite element software ABAQUS, couple and calculate the combined time-hardening creep constitutive model and the θ-parameter method creep constitutive model by applying environmental stress to each integration point; Step 4: Establish a three-dimensional finite element model of the turbine disk in ABAQUS, apply the working load and temperature field to the established model, and obtain the stress, strain, and temperature of each integration point of the three-dimensional finite element model of the turbine disk through numerical simulation; Step 5: Use the CREEP user subroutine provided by the finite element software ABAQUS to calculate the creep strain, creep deformation, and relaxation stress of each integration point one by one in each time increment step, and predict the creep deformation of the turbine disk under different stresses.

2. The method for predicting creep deformation of a turbine disk based on a coupled creep constitutive model according to claim 1, characterized in that, in Step 1, first, for the creep deformation of the turbine disk under a complex multi-stress field, conduct a tensile test on a uniaxial creep test bar of GH4169 superalloy with the same material as the turbine disk to obtain the relationship curve between creep strain and time of this material at a working temperature of 650 °C, a service duration of 1600 h, and a working load in the stress range of 300 MPa to 800 MPa; wherein, the stress range in the uniaxial creep test bar tensile test should cover the maximum stress to the minimum stress of the turbine disk.

3. The method for predicting creep deformation of a turbine disk based on a coupled creep constitutive model according to claim 1, characterized in that, In step 3, a CREEP user subroutine is written using the finite element software ABAQUS. In the written CREEP user subroutine, according to the ABAQUS external interface specifications, three variable return values of the combined time hardening creep constitutive model and the θ - parameter method creep constitutive model need to be defined separately according to the explicit and implicit integration methods, which are respectively: The explicit creep integration return value, that is, the creep strain increment DECRA(1); the implicit creep integration return value, that is, the derivative of the creep strain increment with respect to the creep strain DECRA(2); the derivative of the creep strain increment with respect to the equivalent stress DECRA(5); The corresponding formulas for the three variable return values deduced from the combined time hardening creep constitutive model are as follows: The corresponding formulas for the three variable return values deduced from the θ - parameter method creep constitutive model are as follows: In the CREEP user subroutine, the two constitutive models are coupled and calculated by applying the environmental stress to each integration point and defining the variable return values DECRA(1), DECRA(2), and DECRA(5); In ABAQUS, a finite element model of a standard test bar is established, and the CREEP user subroutine is verified by uniaxial creep simulation with the same boundary conditions as the uniaxial creep test of the standard test bar.

4. The method for predicting the creep deformation of a turbine disk based on a coupled creep constitutive model according to claim 1, characterized in that, In step 4, a three - dimensional finite element model of the turbine disk is established in ABAQUS. The material properties of the finite element model are defined according to the superalloy material used for the turbine disk. A hexahedral mesh is used for division, and the working load and working temperature field are applied; the total creep analysis step time is defined. Specifically, by establishing a static analysis step 1 and a viscous analysis step 2, where: In the static analysis step 1, the working load including centrifugal load and aerodynamic load is applied, and the working temperature field is the working environment temperature of the turbine disk; In the viscous analysis step 2, the total creep duration is set, and the time increment step and the automatic stabilization method are adjusted to enable the rapid convergence of the creep strain and its creep stress calculation.

5. The method for predicting the creep deformation of a turbine disk based on a coupled creep constitutive model according to claim 1, characterized in that, In step 5, specifically, the CREEP user subroutine is called in ABAQUS for iterative calculation of the creep strain and deformation of the turbine disk. In each time increment step of each iteration, for all integration points, the creep rate and creep increment of each creep stage are calculated one by one according to the current creep time, temperature, and stress conditions; If the result converges, update the stress - strain and total creep and increase the increment step to continue the iterative calculation; Finally, the calculation result is fed back to the ABAQUS main program to obtain the creep strain and creep deformation of the turbine disk under the total creep duration.

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