High-cycle fatigue strength evaluation method based on damage influence

Abstract

The invention provides a high-cycle fatigue strength evaluation method based on damage influence, and belongs to the technical field of aero-engines. The method comprises the following steps: performing a high-cycle fatigue test on a to-be-tested material to obtain first high-cycle fatigue strength, and performing a damage fracture test corresponding to a damage type to obtain a damage life, the damage type comprising creep damage and low-cycle damage; determining interruption time on the basis of the damage life, performing a damage fracture test on the basis of different interruption time, then performing a high-cycle fatigue strength test to obtain second high-cycle fatigue strength, and constructing a damage model; constructing a crystal plasticity constitutive model based on the damage model to perform simulation calculation on the to-be-tested material to obtain a simulation damage value; and correcting the first high-cycle fatigue strength based on the second high-cycle fatigue strength and the simulated damage value to obtain an evaluation result of the to-be-tested material. According to the method, deformation mechanisms of different damage types are clearly distinguished, the method is more flexible, interruption time setting refers to influences of different damage degrees, and the method is more accurate, safer and more reliable.

Description

Technical Field

[0001] The present disclosure relates to the technical field of aero-engines, and in particular to a high-cycle fatigue strength assessment method based on damage effects. Background Art

[0002] Turbine blades in aircraft engines are critical components that withstand complex and demanding operating conditions, including high temperatures, high-velocity airflow, and frequent loading. During actual operation, turbine blades are exposed to high-temperature, high-pressure airflow, which can lead to creep damage or, through frequent starts and stops, introduce low-cycle damage. These potential damages, such as creep and low-cycle damage, can further impact the high-cycle fatigue performance of components.

[0003] In traditional high-cycle fatigue assessment, only high-cycle loading is usually considered, and the actual state of components under complex working conditions cannot be restored, resulting in large deviations in component design and maintenance; or, the interaction of creep fatigue and low-cycle fatigue on high-cycle fatigue is mainly studied by applying interactive loads of creep high-cycle fatigue and low-cycle high-cycle fatigue, focusing on the comprehensive impact of creep fatigue, low-cycle fatigue, etc. on high-cycle fatigue life, and often ignoring the creep and low-cycle damage effects of components under long-term and high-stress conditions, resulting in low reliability of the assessed structure, which in turn affects the safety and accuracy of engineering structure design, operation and maintenance.

[0004] The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the Invention

[0005] The purpose of the present disclosure is to provide a high-cycle fatigue strength assessment method based on damage effects, which can specifically make corrections based on the effects of different damages on high-cycle fatigue strength, effectively improve the accuracy of high-cycle fatigue strength assessment of materials, and improve the safety and reliability of corresponding materials in engineering structure design, operation and maintenance.

[0006] To achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0007] According to one aspect of the present disclosure, a high-cycle fatigue strength assessment method based on damage effects is provided, wherein the method may include: performing a high-cycle fatigue strength test on a material to be tested to obtain a first high-cycle fatigue strength; performing a damage fracture test corresponding to at least one damage type on the material to be tested to obtain a damage life corresponding to the damage type, wherein the damage types include creep damage and low-cycle damage; determining at least one interruption time based on the damage life, and performing a damage fracture experiment corresponding to the damage type on the material to be tested based on different interruption times, and then performing a high-cycle fatigue strength test to obtain a second high-cycle fatigue strength, and constructing a damage model; constructing a crystal plasticity constitutive model based on the damage model, and performing simulation calculation on the material to be tested based on the crystal plasticity constitutive model to obtain a simulated damage value corresponding to the damage type; correcting the first high-cycle fatigue strength based on the second high-cycle fatigue strength and the simulated damage value to obtain an assessment result of the high-cycle fatigue strength of the material to be tested.

[0008] Optionally, the damage type is creep damage, the damage fracture test is a creep fracture test, the interruption time is a creep interruption time, the damage model includes a microstructure rafting damage model, and constructing the damage model includes: statistically calculating the matrix phase width of the material to be tested at different creep interruption times in the creep fracture test; constructing a microstructure rafting damage model based on the creep interruption time and the matrix phase width, and the microstructure rafting damage model is used to characterize the creep damage caused by microstructure rafting in the material to be tested.

[0009] Optionally, the damage model also includes a creep continuum damage model, and constructing the damage model also includes: extracting a first strain parameter of the material to be tested from the creep rupture test; constructing a creep continuum damage model corresponding to the material to be tested based on the first strain parameter, and the creep continuum damage model is used to characterize the creep damage formed by the evolution of holes and microcracks caused by creep in the material to be tested.

[0010] Optionally, the damage type is low-cycle damage, the damage fracture test includes a low-cycle fracture test, the damage model includes a low-cycle continuous damage model, and constructing the damage model includes: extracting a second strain parameter of the material to be tested from the low-cycle fracture test; constructing a low-cycle continuous damage model corresponding to the material to be tested based on the second strain parameter, and the low-cycle continuous damage model is used to characterize the low-cycle damage formed by the evolution of holes and microcracks caused by low-cycle fatigue in the material to be tested.

[0011] Optionally, the damage type is creep damage, the damage life is creep rupture life, the damage rupture test is a creep rupture test, at least one interruption time is determined based on the damage life, and a damage rupture test corresponding to the damage type is performed on the material to be tested based on different interruption times, and then a high-cycle fatigue strength test is performed to obtain a second high-cycle fatigue strength, including: determining at least one creep interruption time within the creep rupture life; performing a creep rupture test on the material to be tested at the creep interruption time, and then performing a high-cycle fatigue strength test to obtain a second high-cycle fatigue strength corresponding to the creep damage.

[0012] Optionally, the damage type is low-cycle damage, the damage life is the number of low-cycle fracture cycles, the damage fracture test is a low-cycle fracture test, at least one interruption time is determined based on the damage life, and a damage fracture test corresponding to the damage type is performed on the material to be tested based on different interruption times, and then a high-cycle fatigue strength test is performed to obtain a second high-cycle fatigue strength, including: determining at least one low-cycle interruption time within the number of low-cycle fracture cycles; performing a low-cycle fracture test on the material to be tested under the low-cycle interruption time, and then performing a high-cycle fatigue strength test to obtain a second high-cycle fatigue strength corresponding to the low-cycle damage.

[0013] Optionally, the damage type is creep damage, the damage fracture test includes a creep fracture test, the damage value includes a creep damage simulation value, a crystal plasticity constitutive model is constructed based on the damage model, and simulation calculations are performed on the material to be tested based on the crystal plasticity constitutive model to obtain a simulated damage value corresponding to the damage type, including: constructing a crystal plasticity constitutive model based on the damage model corresponding to creep damage; establishing a finite element model for the material to be tested, and applying the test conditions of the creep fracture test; simulating and calculating the finite element model based on the crystal plasticity constitutive model of creep damage to obtain the creep simulation damage value corresponding to the material to be tested.

[0014] Optionally, the damage type is low-cycle damage, the damage fracture test includes a low-cycle fracture test, the simulated damage value includes a low-cycle simulated damage value, a crystal plasticity constitutive model is constructed based on the damage model, and the material to be tested is simulated and calculated based on the crystal plasticity constitutive model to obtain the simulated damage value corresponding to the damage type, including: constructing a crystal plasticity constitutive model based on the damage model corresponding to low-cycle damage; establishing a finite element model for the material to be tested, and applying the test conditions of the low-cycle fracture test; simulating and calculating the finite element model based on the crystal plasticity constitutive model of low-cycle damage to obtain the low-cycle simulated damage value corresponding to the material to be tested.

[0015] Optionally, the first high cycle fatigue strength is corrected based on the second high cycle fatigue strength and the simulated damage value to obtain an evaluation result of the high cycle fatigue strength of the material to be tested, including: fitting the second high cycle fatigue strength and the simulated damage value to obtain correction parameters of the material to be tested; and correcting the first high cycle fatigue strength based on the correction parameters to obtain an evaluation result of the high cycle fatigue strength of the material to be tested.

[0016] Optionally, a high cycle fatigue strength test is performed on the material to be tested to obtain a first high cycle fatigue strength, including: using a lifting method to perform a stress-controlled high cycle fatigue strength test on the material to be tested at a target temperature; and drawing a high cycle fatigue life curve of the material to be tested, thereby obtaining the first high cycle fatigue strength of the material to be tested.

[0017] The present disclosure provides a high-cycle fatigue strength evaluation method based on damage influence, which first performs a high-cycle fatigue test on the material to be tested to obtain a first high-cycle fatigue strength, then performs a damage fracture test corresponding to at least one damage type on the material to be tested to obtain a damage life corresponding to the damage type, and the damage type may include creep damage and low-cycle damage; then, at least one interruption time is determined based on the obtained damage life, and based on different interruption times, a damage fracture test corresponding to the damage type is first performed on the material to be tested, and then a high-cycle fatigue strength test is performed to obtain a second high-cycle fatigue strength, and a damage model is constructed; based on the damage model, a crystal plasticity constitutive model is constructed to simulate and calculate the material to be tested to obtain a simulated damage value; and, based on the second high-cycle fatigue strength and the simulated damage value, the first high-cycle fatigue strength is corrected to obtain an evaluation result of the high-cycle fatigue strength of the material to be tested. This method can be modified based on the impact of different damages on high-cycle fatigue strength according to actual assessment needs. By distinguishing different damage types, the impact of different damage types can be evaluated separately, the deformation mechanisms of different damage types can be clearly distinguished, and the comprehensive impact of the combination of two or more damage types can be evaluated, so that the assessment of high-cycle fatigue strength can be more flexibly adapted to actual assessment needs and the assessment accuracy under various working conditions can be improved. In addition, by setting the interruption time, the impact of different damage degrees on the high-cycle fatigue strength assessment results is referenced, which effectively improves the accuracy of the high-cycle fatigue strength assessment of materials under long-term and high-stress conditions, and ensures the safety and reliability of the corresponding materials in engineering structure design, operation and maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments or the conventional technology descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1One of the step flow charts of the high cycle fatigue strength assessment method based on damage influence provided by an embodiment of the present disclosure is shown.

[0020] Figure 2 The second step flow chart of the high cycle fatigue strength assessment method based on damage influence provided by an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0021] Example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be more comprehensive and complete and will fully convey the concepts of the example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to provide a thorough understanding of the embodiments of the present disclosure.

[0022] The described features, structures or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced without one or more of the specific details, or other methods, components, materials, etc. may be employed. In other cases, well-known structures, materials or operations are not shown or described in detail to avoid obscuring the main technical ideas of the present disclosure.

[0023] When a structure is “on” another structure, it may mean that the structure is integrally formed on the other structure, or that the structure is “directly” disposed on the other structure, or that the structure is “indirectly” disposed on the other structure via another structure.

[0024] The terms "a," "an," and "" are used to indicate that there are one or more elements / components / etc.; the terms "including" and "having" are used to indicate an open-ended inclusive meaning and mean that there may be additional elements / components / etc. in addition to the listed elements / components / etc. The terms "first," "second," etc. are used only as labels and do not limit the quantity of their objects.

[0025] Figure 1 FIG1 shows one of the flow charts of the steps of the high cycle fatigue strength evaluation method based on damage effect provided by the embodiment of the present disclosure. Figure 1 As shown, the method may include steps 101 to 105.

[0026] As shown below:

[0027] Step 101: Perform a high cycle fatigue strength test on the material to be tested to obtain a first high cycle fatigue strength.

[0028] In the embodiment of the present disclosure, high cycle fatigue refers to the material to be tested undergoing 10 cycles of stress below its yield strength. 5 Fatigue caused by the above number of cycles is also called stress fatigue. High-cycle fatigue strength can reflect the strength of local structural changes and internal defect development caused by high-cycle fatigue in the material to be tested. The first high-cycle fatigue strength of the material to be tested can be measured by a high-cycle fatigue strength test without other damage intervention. The high-cycle fatigue strength test is based on a standard test piece for high-cycle fatigue. Those skilled in the art can design a standard test piece for high-cycle fatigue according to experimental conditions, application requirements, etc., including size, shape, etc., and set the test conditions of the high-cycle fatigue strength test, such as stress application, number of cycles, etc.

[0029] Step 102: Perform a damage fracture test corresponding to at least one damage type on the material to be tested to obtain a damage life corresponding to the damage type, where the damage types include creep damage and low-cycle damage.

[0030] In the disclosed embodiments, damage refers to irreversible defects that arise and develop in the internal microstructure of the material to be tested under external influences. The damage type can be obtained by classifying the external causes of the damage, the microstructural manifestations of the damage, etc. Different damage types may be caused by different external conditions, and thus the mechanisms of material deformation and denaturation are also different. Therefore, corresponding damage fracture tests can be designed for different damage types to study the process of the standard test piece of the damage fracture test from microstructural defects to macroscopic mechanical property degradation and fracture, thereby determining the damage life of the material to be tested that fractures under the corresponding damage type.

[0031] For example, the damage types may include creep damage, low-cycle damage, etc., wherein creep damage refers to the plastic deformation of the material to be tested slowly under constant temperature and constant load; low-cycle damage refers to the plastic deformation of the material to be tested under cyclic stress close to or higher than its yield strength, which occurs after 10 4 to 10 5 The following number of cycles produces plastic deformation, and damage fracture testing can be used to characterize the accumulation of plastic deformation caused by the corresponding damage type and determine the fracture life. Those skilled in the art may also select other damage types based on actual application requirements and test conditions, and the present disclosure does not impose specific limitations on this.

[0032] Step 103: Determine at least one interruption time based on the damage life, and perform damage fracture experiments corresponding to the damage type on the material to be tested based on different interruption times, then perform a high cycle fatigue strength test to obtain the second high cycle fatigue strength, and construct a damage model.

[0033] In the disclosed embodiment, at least one interruption time can be determined within the damage lifespan, and damage fracture tests corresponding to the damage types can be performed on the test material based on the different interruption times, thereby simulating different degrees of damage accumulation on the test material. High-cycle fatigue strength tests can then be performed to obtain characterization data of high-cycle fatigue based on different levels of damage accumulation. The damage fracture test utilizes the same damage interruption test as in step 102, and the high-cycle fatigue strength test utilizes the same high-cycle fatigue strength test as in step 101.

[0034] Furthermore, damage models corresponding to different damage types can be established based on the results of damage fracture tests, so as to characterize the initiation and expansion characteristics of damage of different causes and forms in the material to be tested through the damage model, so as to perform damage simulation calculations based on the damage model in the future.

[0035] Step 104: construct a crystal plasticity constitutive model based on the damage model, and perform simulation calculations on the material to be tested based on the crystal plasticity constitutive model to obtain a simulated damage value corresponding to the damage type.

[0036] In the disclosed embodiment, one or more damage models constructed based on the framework of crystal plasticity theory can be introduced to establish a crystal plasticity constitutive model that takes into account the corresponding damage type. Furthermore, a finite element model can be established for the test piece of the material to be tested, and the same temperature, stress and boundary constraints as those in the damage fracture test can be applied to the finite element model, so as to use the constructed crystal plasticity constitutive model to perform numerical simulation on the aforementioned finite element model to calculate different damage types that meet the application and test requirements, or simulate damage values ​​under different conditions corresponding to the same damage type.

[0037] Step 105: Correct the first high cycle fatigue strength based on the second high cycle fatigue strength and the simulated damage value to obtain an evaluation result of the high cycle fatigue strength of the material to be tested.

[0038] In the disclosed embodiment, the second high-cycle fatigue strength is determined by conducting high-cycle fatigue strength tests after damage-fracture tests with different interruption times. The simulated damage value is then used to construct a crystal plasticity constitutive model using the corresponding damage model, and then a finite element simulation is performed on the material under test. On this basis, the disclosed embodiment uses the second high-cycle fatigue strength and the simulated damage value to correct the first high-cycle fatigue strength. This allows the evaluation of the high-cycle fatigue strength of the material under test to also consider the impact of different degrees of damage under long-term, high-stress conditions on the performance of the material under high-cycle fatigue loading. It also allows for separate or combined evaluation of different damage types, ensuring accuracy and flexibility.

[0039] Figure 2 The second step flow chart of the high cycle fatigue strength assessment method based on damage effect provided by the embodiment of the present disclosure is shown. It should be noted that, Figure 2 The steps shown are for illustration only. Those skilled in the art can select some of the steps shown in 2 to perform high cycle fatigue strength assessment based on actual application requirements, or based on Figure 2 The step process shown is expanded to other damage types or test schemes. The execution order and combination of the step process can be flexibly adjusted based on test conditions, test requirements, etc. when feasible. This embodiment does not impose specific restrictions on this.

[0040] like Figure 2 As shown, the method may include the following steps 201 to 221.

[0041] Step 201: Using the lifting method, perform a stress-controlled high cycle fatigue strength test on the material to be tested at a target temperature.

[0042] In the embodiment of the present disclosure, the test piece corresponding to the material to be tested can be subjected to a high cycle fatigue strength test under stress control at a target temperature based on the test requirements. By adopting the lifting and lowering method to test at multiple stress levels, if the test piece breaks before reaching the number of cycles, the stress level is reduced, and if the test piece reaches the number of cycles without breaking, the stress level is increased, thereby obtaining the high cycle fatigue strength of the test piece under the predetermined number of cycles. The number of cycles can be 10 5 Above, such as 10 5 , 10 7 The embodiments of the present disclosure do not impose any specific limitations on this.

[0043] Step 202: draw a high cycle fatigue life curve of the material to be tested, thereby obtaining a first high cycle fatigue strength of the material to be tested.

[0044] Furthermore, based on the high-cycle fatigue strength test, a high-cycle fatigue life-strength curve (SN curve) can be plotted for the material under test. This high-cycle fatigue life-strength curve uses the logarithm of fatigue life as the horizontal axis and fatigue strength as the vertical axis. The curve represents the changing relationship between fatigue strength and fatigue life of the standard component under high-cycle cyclic characteristics, thereby determining the first high-cycle fatigue strength of the material under test. The first high-cycle fatigue strength is obtained by directly conducting high-cycle fatigue strength tests on the test piece.

[0045] Step 203: Perform a damage fracture test corresponding to at least one damage type on the material to be tested to obtain a damage life corresponding to the damage type.

[0046] In the disclosed embodiment, step 203 corresponds to the description of step 102, and will not be repeated here to avoid repetition. The damage fracture test should also be conducted at the target temperature. Different test pieces and test conditions can be designed based on the formation and development of different damage types to obtain the damage life of the material under test under the corresponding damage fracture test.

[0047] In an optional method embodiment of the present disclosure, the damage type may include creep damage, the damage life corresponds to the creep rupture life, the damage rupture test corresponds to the creep rupture test, and the following steps 204 to 212 may be performed for creep damage.

[0048] Step 204: Determine at least one creep interruption time within the creep rupture life.

[0049] In the embodiment of the present disclosure, at least one arbitrary creep interruption time is determined within the creep rupture life, that is, during the process in which creep damage initiates and develops to a certain extent in the material to be tested but has not yet led to fracture. For example, 10%, 30%, 50%, 70%... of the creep rupture life can be used as the creep interruption time. The embodiment of the present disclosure does not impose any specific restrictions on the specific size and number of the creep interruption time.

[0050] Step 205 : Perform a creep rupture test on the material to be tested at the creep interruption time, and then perform a high cycle fatigue strength test to obtain a second high cycle fatigue strength corresponding to the creep damage.

[0051] Furthermore, based on the determined creep interruption time, creep rupture tests are conducted on the specimens undergoing the creep rupture test at different creep interruption times. Specifically, the creep rupture test is terminated when the creep interruption time is reached, and a high-cycle fatigue strength test is then conducted. This high-cycle fatigue strength test can correspond to steps 101 or 201 to 202 described above. By conducting a high-cycle fatigue strength test based on pre-creep, the high-cycle fatigue strength of the specimens after different creep interruption times can be obtained using the lift-and-fall method, thereby incorporating the effects of varying degrees of creep damage on the high-cycle fatigue strength into the assessment.

[0052] Furthermore, based on relevant experiments on creep damage, a damage model of creep damage can be constructed. In an optional method embodiment of the present disclosure, the damage model of creep damage can include a microstructure rafting damage model.

[0053] Step 206: Count the widths of the matrix phase of the material to be tested at different creep interruption times in the creep rupture test.

[0054] Step 207 : constructing a microstructure rafting damage model based on the creep interruption time and the matrix phase width. The microstructure rafting damage model is used to characterize creep damage caused by microstructure rafting in the material to be tested.

[0055] Microstructural rafting refers to the microstructural change in which the γ′ phase undergoes directional coarsening during the initiation and development of creep damage, and is also one of the primary deformation mechanisms of creep damage. In the disclosed embodiments, the matrix phase width of the material under test at different creep interruption times during a creep rupture test can be statistically analyzed. Based on the relationship between the matrix phase width and the creep interruption time, a creep damage expression that considers microstructural rafting is established, as shown in the following formula (1), thereby constructing a microstructural rafting damage model.

[0056]

[0057] Among them, ω r represents the creep damage caused by microstructural rafting, θ represents the matrix phase width corresponding to different creep interruption times, and θ0 is the initial matrix phase width before creep initiation; the rest are material parameters, which are obtained by fitting the experimental data collected from creep rupture experiments at different creep interruption times.

[0058] Because microstructural rafting primarily occurs during creep, while low-cycle damage typically lacks significant rafting, the microstructural rafting damage model can be considered only when constructing a damage model for creep damage. Based on the different damage deformation mechanisms, those skilled in the art can select the appropriate damage model.

[0059] In an optional method embodiment of the present disclosure, the damage model of creep damage may include a creep continuum damage model.

[0060] Step 208: extract the first strain parameter of the material to be tested from the creep rupture test.

[0061] Step 209: construct a creep continuum damage model corresponding to the material to be tested based on the first strain parameter. The creep continuum damage model is used to characterize creep damage formed in the material to be tested after evolution of pores and microcracks caused by creep.

[0062] In the disclosed embodiment, the first strain parameter of the material to be tested can also be extracted in the creep rupture test based on the continuous damage model created by Kachanov and Rabotnov. For example, the first strain parameter can include the critical shear stress, creep strain rate, initial damage rate, and other temperature parameters, material parameters, etc. Based on the first strain parameter, a creep damage expression that takes into account the evolution of holes and cracks can be established, as shown in the following formula (2), thereby constructing a creep continuous damage model. The creep continuous damage model takes into account the creep damage caused by the evolution of holes and microcracks caused by creep in the material to be tested under creep damage.

[0063]

[0064] Among them, τ s(α) =βτ c τ c is the critical shear stress, β and C are material parameters, is the creep strain rate, is the steady-state creep rate, χ and φ are temperature parameters, is the initial damage rate.

[0065] It should be noted that the above creep damage models are only used as examples. Those skilled in the art can select one or more different damage models based on the deformation mechanism of creep damage to characterize the creep damage that may occur in the material to be tested in actual applications. Based on the selection of the microstructure rafting damage model and the creep continuum damage model, the creep damage of the material to be tested can be the sum of the microstructure rafting damage and the creep continuum damage, as shown in the following formula (3):

[0066] ω=ω r +ω c (3)

[0067] Among them, ω r is the microstructure rafting damage model, ω c It is a creep continuum damage model.

[0068] Furthermore, a simulation calculation can be performed based on a damage model of creep damage to determine a creep simulation damage value corresponding to the creep damage.

[0069] Step 210: Construct a crystal plasticity constitutive model based on the damage model corresponding to creep damage.

[0070] Step 211: Establish a finite element model for the material to be tested, and apply test conditions of the creep rupture test.

[0071] Step 212: Perform simulation calculation on the finite element model based on the crystal plastic constitutive model of creep damage to obtain a creep simulation damage value corresponding to the material to be tested.

[0072] In the disclosed embodiment, the damage model corresponding to creep damage may include a microstructure rafting damage model, a creep continuous damage model, etc., and a finite element model of the test piece corresponding to the material to be tested is further established, and the simulated damage value of creep damage is calculated on the corresponding finite element model.

[0073] In the simulation calculation of creep damage, the macroscopic plastic deformation of the material to be tested can be characterized by the microscopic slip system, thereby establishing a crystal plastic constitutive model that takes creep damage into account. On this basis, creep damage is caused by the shear strain on the slip plane of the octahedral slip system. The shear strain rate of the slip system α is expressed as follows (4):

[0074]

[0075] Among them, A and n are Norton parameters, which can be obtained according to the slope of the steady-state creep stage.

[0076] Then the shear stress τ of slip system α is (α) It is expressed as follows:

[0077] τ (α) =σ:P (α)

[0078]

[0079] Among them, P (α) is the orientation factor, σ is the stress tensor, m (α) is the slip direction of the slip system α, n (α) is the unit normal vector of the slip surface of slip system α.

[0080] Furthermore, the macro creep strain rate Can be divided into elastic part With non-elastic part It is expressed as the following formula (6):

[0081]

[0082] in, According to the knowledge of elastic mechanics, The shear strain rate of the slip system is obtained by the following formula (7):

[0083]

[0084] Then, the macro creep strain rate is calculated based on the following formula (8): To break it down:

[0085]

[0086] Among them, Oct1 is the octahedral slip family, Oct2 is the dodecahedral slip family, and Cub is the hexahedral slip family.

[0087] On this basis, assuming and The two parts do not affect each other, so the creep strain rate It can be expressed as the following formula (9):

[0088]

[0089] Among them, C e is the anisotropic elastic tensor, C e The matrix can be expressed as follows:

[0090]

[0091] Where C 11 , C 12 , C 44 Related to the elastic modulus E, shear modulus G and Poisson's ratio μ.

[0092] When performing finite element calculations, if the required coordinate system is different from the

[001] crystal axis system, such as

[011] or

[111] crystal axis system, the C e The coordinate transformation is performed using the following formula (11):

[0093] C XYZ =DC e D T

[0094]

[0095] Among them, l, m, n are the direction cosines of the model coordinate axis OXXZ axis in the crystal axis oxyz.

[0096] Furthermore, the shear strain rate can be expressed by the damage evolution as shown in the following formula (12):

[0097]

[0098] in, is the initial shear strain rate, ω (α) is the plastic strain damage, S (α) is the degradation of the material to be tested along the slip system α, is a function of temperature and stress, ω (α) is ω as shown in the above formula (3).

[0099] It can be expressed as the following formula (13):

[0100]

[0101] Where A and n are temperature-dependent creep parameters, R is the gas constant, T is the absolute temperature, and Q is the activation energy. oct =6.97E-19J / atom, hexahedral slip system Q cube =7.30E-19J / atom.

[0102] On this basis, the damage model of the above formulas (1) and (2) is introduced to simulate the creep damage and obtain the creep simulation damage value.

[0103] In an optional method embodiment of the present disclosure, the damage type may include low-cycle damage, the damage life corresponds to the number of low-cycle cycles, and the damage fracture test corresponds to the low-cycle fracture test. For low-cycle damage, the following steps 213 to 219 may be included.

[0104] Step 213: Determine at least one low-cycle interruption time within the low-cycle fracture cycle number.

[0105] In the embodiment of the present disclosure, at least one arbitrary low-cycle interruption time is determined within the number of low-cycle fracture cycles, that is, during the process in which low-cycle damage initiates and develops to a certain extent in the material to be tested but has not yet led to fracture. For example, 10%, 30%, 50%, 70%... of the number of low-cycle fracture cycles can be used as the low-cycle interruption time. The embodiment of the present disclosure does not impose any specific restrictions on the specific size and number of the low-cycle interruption time.

[0106] Step 214 : Perform a low-cycle fracture test on the material to be tested at a low-cycle interruption time, and then perform a high-cycle fatigue strength test to obtain a second high-cycle fatigue strength corresponding to the low-cycle damage.

[0107] Furthermore, based on the determined low-cycle interruption time, low-cycle fracture tests are conducted on the specimens undergoing the low-cycle fracture test at different low-cycle interruption times. Specifically, the low-cycle fracture test is terminated when the low-cycle interruption time is reached, and a high-cycle fatigue strength test is then conducted. This high-cycle fatigue strength test can correspond to steps 101 or 201 to 202 described above. By conducting a high-cycle fatigue strength test based on the pre-low-cycle test, the high-cycle fatigue strength of the specimens after different low-cycle interruption times can be obtained using the lifting and lowering method, thereby incorporating the effects of varying degrees of low-cycle damage on the high-cycle fatigue strength into the assessment.

[0108] Step 215: extract a second strain parameter of the material to be tested from the low-cycle fracture test.

[0109] Step 216: construct a low-cycle continuous damage model corresponding to the material to be tested based on the second strain parameter. The low-cycle continuous damage model is used to characterize low-cycle damage formed by the evolution of at least one of holes and cracks caused by low-cycle fatigue in the material to be tested.

[0110] In the embodiment of the present disclosure, referring to the relevant description of steps 209 to 210, a second strain parameter of the material to be tested can be extracted in the low-cycle fracture test. For example, the second strain parameter can include the critical shear stress, the critical shear strain rate, etc., and can also include other parameters determined by the low-cycle fracture test. Based on the first strain parameter, a low-cycle damage D expression considering the evolution of holes and cracks can be established, as shown in the following formula (14), thereby constructing a low-cycle continuous damage model. The low-cycle continuous damage model takes into account the low-cycle damage formed by the evolution of holes and microcracks caused by low-cycle fatigue in the material to be tested under low-cycle damage.

[0111]

[0112] in is the maximum shear stress in the cycle, is the maximum shear strain rate in the cycle, s oct Refers to the reference stress and is the scale factor in the expression; Parameters such as m and n are determined by low-cycle fracture tests; Q c is the activation energy (Q c =6.87E-19J / atom), R is the gas constant, and T is the Kelvin temperature.

[0113] Furthermore, a simulation calculation can be performed based on the damage model of the low-frequency damage to determine the low-frequency simulated damage value corresponding to the low-frequency damage.

[0114] Step 217: Construct a crystal plasticity constitutive model based on the damage model corresponding to low-cycle damage.

[0115] Step 218: Establish a finite element model for the material to be tested, and apply test conditions for a low-cycle fracture test.

[0116] Step 219: Perform simulation calculation on the finite element model based on the crystal plasticity constitutive model of low-cycle damage to obtain the low-cycle simulated damage value corresponding to the material to be tested.

[0117] In the disclosed embodiment, the damage model corresponding to low-cycle damage may include a microstructure rafting damage model, a low-cycle continuous damage model, etc., and a finite element model of the test piece corresponding to the material to be tested is further established, and the simulated damage value of the low-cycle damage is calculated on the corresponding finite element model.

[0118] In the simulation calculation of low-cycle damage, the shear strain rate of each slip system is It can be described by a rate-dependent equation, as shown in the following expression (15):

[0119]

[0120] in, is the reference shear strain rate, is the critical shear stress; m is the sensitivity index of strain rate, and m = 0 when it is independent of strain rate, to represent the influence of strain rate on the elastic-plastic behavior of the material.

[0121] Then the plastic macro strain ε p The relationship between the shear strain rate of the slip system can be expressed as follows:

[0122] ε p =∑γ (α) P(α) . (16)

[0123] On this basis, the evolution of the shear stress of the slip system follows the hardening law shown in the following formula (17):

[0124]

[0125] Among them, h αβ It is called the hardening coefficient, which determines the hardening caused by the slip shear in slip system β to slip system α.

[0126] Specifically, h αβ It can be determined by the following formula (18):

[0127] h αβ =q αβ h β , (18)

[0128] Where q αβ is the matrix describing latent hardening, h β is the single slip hardening rate. The hardening rate used in the embodiment of the present disclosure can be expressed as the following formula (19):

[0129]

[0130] Where h0 is the hardening modulus, τ s and p are model parameters.

[0131] On this basis, finite element calculation can be performed to obtain the stress and strain distribution state of the test piece, and the test piece may include an air film hole.

[0132] At this time, for the material to be tested, the material parameters at room temperature may include T = 25 ° C, E = 131500 MPa, G = 155070 MPa, μ = 0.344, m=0.02,h0=1.2τ0,τ s =1.17τ0 and p = 1.3. Therefore, considering the temperature effect and the law of the sliding system activation at the peak temperature, the evolution of the low-cycle fatigue damage D of the material to be tested can be expressed as the aforementioned formula (14). This damage model is introduced to simulate the low-cycle damage and obtain the low-cycle simulated damage value.

[0133] In the disclosed embodiments, the aforementioned damage types, such as creep damage and low-cycle damage, are described as examples. Deformation mechanisms for creep damage, low-cycle damage, and the like may be evaluated independently, or interactive load analysis and evaluation may be performed on creep damage and low-cycle damage, as well as fitting of creep simulated damage values ​​and low-cycle simulated damage values. Based on the aforementioned concepts, independent deformation mechanisms for other damages, or combinations of other different damages, may also be evaluated. The disclosed embodiments do not impose specific limitations on this. For at least one damage type, the corresponding second high-cycle fatigue strength and simulated damage value, either individually or in combination, may be obtained, which proceeds to steps 220 and 221.

[0134] Step 220: Fit the second high cycle fatigue strength and the simulated damage value to obtain correction parameters of the material to be tested.

[0135] Step 221: Correct the first high cycle fatigue strength based on the correction parameter to obtain an evaluation result of the high cycle fatigue strength of the material to be tested.

[0136] In the disclosed embodiments, the second high-cycle fatigue strength and simulated damage values ​​are embedded in the first high-cycle fatigue strength assessment to obtain the fatigue performance of the material under test under controllable operating conditions. Specifically, based on the assessment requirements, the second high-cycle fatigue strength and simulated damage values ​​corresponding to the damage type can be fitted to obtain correction parameters. The first high-cycle fatigue strength can then be corrected based on the correction parameters to obtain the high-cycle fatigue strength assessment result of the material under test.

[0137] Taking the damage type including creep damage as an example, the high cycle fatigue strength evaluation result considering creep damage can be expressed as the following formula (20):

[0138]

[0139] in, To consider the evaluation results of high cycle fatigue strength after creep damage, is the first high cycle fatigue strength; It is the correction parameter corresponding to the creep damage of the material to be tested, which is obtained by fitting the creep simulation damage value obtained by the damage model simulation based on creep damage, based on the pre-creep rupture test and the second high-cycle fatigue strength obtained after the high-cycle fatigue strength test.

[0140] Taking the damage type including low-cycle damage as an example, the high-cycle fatigue strength assessment result considering low-cycle damage can be expressed as the following formula (21):

[0141]

[0142] in, In order to consider the evaluation results of high cycle fatigue strength after low cycle damage, is the first high cycle fatigue strength; It is the correction parameter corresponding to the low-cycle damage of the material to be tested. It is obtained by fitting the low-cycle simulated damage value obtained by simulating the damage model based on low-cycle damage, based on the second high-cycle fatigue strength obtained after the pre-low-cycle fracture test and the high-cycle fatigue strength test.

[0143] In the embodiment of the present disclosure, the damage types may also include creep damage and low-cycle damage. The correction parameters are obtained by fitting the second high-cycle fatigue strength and simulated damage values ​​of creep damage and low-cycle damage, and then the first high-cycle fatigue strength is corrected to evaluate the impact of the combination of multiple damage types on high-cycle fatigue.

[0144] The present disclosure provides a high-cycle fatigue strength evaluation method based on damage influence, which first performs a high-cycle fatigue test on the material to be tested to obtain a first high-cycle fatigue strength, then performs a damage fracture test corresponding to at least one damage type on the material to be tested to obtain a damage life corresponding to the damage type, and the damage type may include creep damage and low-cycle damage; then, at least one interruption time is determined based on the obtained damage life, and based on different interruption times, a damage fracture test corresponding to the damage type is first performed on the material to be tested, and then a high-cycle fatigue strength test is performed to obtain a second high-cycle fatigue strength, and a damage model is constructed; based on the damage model, a crystal plasticity constitutive model is constructed to simulate and calculate the material to be tested to obtain a simulated damage value; and, based on the second high-cycle fatigue strength and the simulated damage value, the first high-cycle fatigue strength is corrected to obtain an evaluation result of the high-cycle fatigue strength of the material to be tested. This method can be modified based on the impact of different damages on high-cycle fatigue strength according to actual assessment needs. By distinguishing different damage types, the impact of different damage types can be evaluated separately, the deformation mechanisms of different damage types can be clearly distinguished, and the comprehensive impact of the combination of two or more damage types can be evaluated, so that the assessment of high-cycle fatigue strength can be more flexibly adapted to actual assessment needs and the assessment accuracy under various working conditions can be improved. In addition, by setting the interruption time, the impact of different damage degrees on the high-cycle fatigue strength assessment results is referenced, which effectively improves the accuracy of the high-cycle fatigue strength assessment of materials under long-term and high-stress conditions, and ensures the safety and reliability of the corresponding materials in engineering structure design, operation and maintenance.

[0145] Furthermore, the above-mentioned figures are merely illustrative of the processes included in the methods according to exemplary embodiments of the present disclosure and are not intended to be limiting. It is readily understood that the processes illustrated in the above-mentioned figures do not indicate or limit the temporal order of these processes. Furthermore, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0146] It should be understood that the present disclosure is not limited in its application to the detailed structure and arrangement of the components proposed in this specification. The present disclosure is capable of other embodiments and can be implemented and executed in a variety of ways. The aforementioned variations and modifications fall within the scope of the present disclosure. It should be understood that the present disclosure disclosed and defined in this specification extends to all alternative combinations of two or more individual features mentioned or evident in the text and / or the drawings. All of these different combinations constitute multiple alternative aspects of the present disclosure. The embodiments of this specification illustrate the best mode known for implementing the present disclosure and will enable those skilled in the art to utilize the present disclosure.

Claims

1. A high cycle fatigue strength assessment method based on damage influence, characterized in that: The method comprises: Conduct high cycle fatigue strength test on the material to be tested and obtain the first high cycle fatigue strength; Performing a damage fracture test corresponding to at least one damage type on the material to be tested to obtain a damage life corresponding to the damage type, wherein the damage type includes creep damage and low-cycle damage; Determining at least one interruption time based on the damage life, and performing the damage fracture test corresponding to the damage type on the material to be tested based on different interruption times, then performing the high cycle fatigue strength test to obtain a second high cycle fatigue strength, and constructing a damage model; Constructing a crystal plasticity constitutive model based on the damage model, and performing simulation calculation on the material to be tested based on the crystal plasticity constitutive model to obtain a simulated damage value corresponding to the damage type; The first high cycle fatigue strength is corrected based on the second high cycle fatigue strength and the simulated damage value to obtain an evaluation result of the high cycle fatigue strength of the material to be tested.

2. The method according to claim 1, characterized in that The damage type is creep damage, the damage fracture test is a creep fracture test, the interruption time is a creep interruption time, the damage model includes a microstructure rafting damage model, and constructing the damage model includes: Counting the width of the matrix phase of the material to be tested at different creep interruption times in the creep rupture test; The microstructure rafting damage model is constructed based on the creep interruption time and the matrix phase width. The microstructure rafting damage model is used to characterize the creep damage caused by microstructure rafting in the material to be tested.

3. The method according to any one of claims 1 and 2, characterized in that: The damage model further includes a creep continuum damage model, and the construction of the damage model further includes: Extracting a first strain parameter of the material to be tested from a creep rupture test; The creep continuum damage model corresponding to the material to be tested is constructed based on the first strain parameter, and the creep continuum damage model is used to characterize the creep damage formed by the evolution of pores and microcracks caused by creep in the material to be tested.

4. The method according to claim 1, wherein The damage type is low-cycle damage, the damage fracture test includes a low-cycle fracture test, the damage model includes a low-cycle continuous damage model, and the damage model construction includes: extracting a second strain parameter of the material to be tested from the low-cycle fracture test; The low-cycle continuous damage model corresponding to the material to be tested is constructed based on the second strain parameter, and the low-cycle continuous damage model is used to characterize the low-cycle damage formed by the evolution of holes and microcracks caused by low-cycle fatigue in the material to be tested.

5. The method according to claim 1, wherein The damage type is creep damage, the damage life is creep rupture life, the damage rupture test is a creep rupture test, determining at least one interruption time based on the damage life, performing the damage rupture test corresponding to the damage type on the material to be tested based on different interruption times, and then performing the high cycle fatigue strength test to obtain a second high cycle fatigue strength, including: determining at least one creep interruption time within the creep rupture life; The creep rupture test is performed on the material to be tested at the creep interruption time, and then the high cycle fatigue strength test is performed to obtain the second high cycle fatigue strength corresponding to the creep damage.

6. The method according to claim 1, wherein The damage type is low-cycle damage, the damage life is the number of low-cycle fracture cycles, the damage fracture test is a low-cycle fracture test, determining at least one interruption time based on the damage life, performing the damage fracture test corresponding to the damage type on the material to be tested based on different interruption times, and then performing the high-cycle fatigue strength test to obtain a second high-cycle fatigue strength, including: determining at least one low-cycle interruption time within the number of low-cycle fracture cycles; The low-cycle fracture test is performed on the material to be tested at the low-cycle interruption time, and then the high-cycle fatigue strength test is performed to obtain the second high-cycle fatigue strength corresponding to the low-cycle damage.

7. The method according to claim 1, characterized in that The damage type is creep damage, the damage-fracture test includes a creep-fracture test, the damage value includes a creep damage simulation value, and constructing a crystal plasticity constitutive model based on the damage model, and performing simulation calculation on the material to be tested based on the crystal plasticity constitutive model to obtain a simulated damage value corresponding to the damage type includes: Constructing a crystal plasticity constitutive model based on the damage model corresponding to the creep damage; Establishing a finite element model for the material to be tested and applying the test conditions of the creep rupture test; The finite element model is simulated and calculated based on the crystal plastic constitutive model of the creep damage to obtain a creep simulation damage value corresponding to the material to be tested.

8. The method according to claim 1, characterized in that The damage type is low-cycle damage, the damage fracture test includes a low-cycle fracture test, the simulated damage value includes a low-cycle simulated damage value, and constructing a crystal plasticity constitutive model based on the damage model, and performing simulation calculation on the material to be tested based on the crystal plasticity constitutive model to obtain the simulated damage value corresponding to the damage type includes: Constructing a crystal plasticity constitutive model based on the damage model corresponding to the low-cycle damage; Establishing a finite element model for the material to be tested and applying the test conditions of the low-cycle fracture test; The finite element model is simulated and calculated based on the crystal plastic constitutive model of the low-cycle damage to obtain a low-cycle simulated damage value corresponding to the material to be tested.

9. The method according to claim 1, characterized in that The correcting the first high cycle fatigue strength based on the second high cycle fatigue strength and the simulated damage value to obtain an evaluation result of the high cycle fatigue strength of the material to be tested includes: Fitting the second high cycle fatigue strength and the simulated damage value to obtain correction parameters of the material to be tested; The first high cycle fatigue strength is corrected based on the correction parameter to obtain an evaluation result of the high cycle fatigue strength of the material to be tested.

10. The method according to claim 1, characterized in that The method of performing a high cycle fatigue strength test on the material to be tested to obtain a first high cycle fatigue strength comprises: Performing the stress-controlled high cycle fatigue strength test on the material to be tested at a target temperature using a lifting method; A high cycle fatigue life curve of the material to be tested is drawn to obtain the first high cycle fatigue strength of the material to be tested.

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