Method and device for predicting low-cycle fatigue life of notched part

Abstract

The invention discloses a low-cycle fatigue life prediction method and device for a notched part, and relates to the field of mechanical engineering. The method comprises the following steps: acquiring low-cycle fatigue life data obtained by performing fatigue tests on a notched test piece under different test conditions; performing simulated fatigue tests on the notched test piece under different test conditions to obtain a stress-strain distribution diagram along the dangerous path and a damage parameter value determined along the dangerous path based on a first relational expression; constructing an initial fatigue life prediction model, and determining model parameter values according to the low-cycle fatigue life data and the damage parameter values to obtain a target fatigue life prediction model; determining a second relational expression based on the low-cycle fatigue life data and the value of the critical distance corresponding to the dangerous path; the second relational expression is constructed based on geometric structure characteristics of the notched test piece; and according to the target fatigue life prediction model, the first relational expression and the second relational expression, adopting a critical distance iteration method to perform low-cycle fatigue life prediction of the to-be-tested notched part. The problem that the low-cycle fatigue life prediction accuracy of an existing notched part is low is solved.

Description

Technical Field

[0001] The present disclosure relates to the field of mechanical engineering technology, and in particular to a method and device for predicting the low-cycle fatigue life of a notched part, a storage medium, and an electronic device. Background Art

[0002] There are a large number of discontinuous parts (i.e., notches) in engineering structures, such as oil holes, slots, or air film holes on turbine blades of aircraft engines. These notches often become failure sites under cyclic loads, directly affecting the life of the entire specimen. Therefore, the life prediction of notched parts has important engineering application significance.

[0003] At present, the critical distance method (TCD, theory of critical distance) is generally used to solve the problem of component fatigue under stress concentration, which mainly combines linear elastic fracture mechanics with the empirical method of life prediction. However, this method performs well in high-cycle fatigue life prediction, but has low accuracy in predicting low-cycle fatigue life.

[0004] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0005] The purpose of the embodiments of the present disclosure is to provide a method for predicting the low-cycle fatigue life of a notch part, a device for predicting the low-cycle fatigue life of a notch part, a computer-readable storage medium and an electronic device, thereby solving the problem of low accuracy of low-cycle fatigue life prediction of existing notch parts to a certain extent.

[0006] According to a first aspect of the present disclosure, a method for predicting low cycle fatigue life of a notched component is provided, comprising:

[0007] Obtain low cycle fatigue life data from fatigue tests on notched specimens under different test conditions;

[0008] By performing a simulated fatigue test on the notched specimen under different test conditions, a stress-strain distribution diagram along the dangerous path and a damage parameter value along the dangerous path determined based on a first relationship are obtained; the first relationship is a damage parameter calculation formula determined based on crystal plasticity theory;

[0009] Based on the damage parameter and the Manson-Coffin formula, an initial fatigue life prediction model is constructed; according to the low-cycle fatigue life data and the damage parameter value, the model parameter value of the initial fatigue life prediction model is determined to obtain a target fatigue life prediction model;

[0010] Based on the low cycle fatigue life data and the value of the critical distance corresponding to the dangerous path, determining a second relationship between the low cycle fatigue life and the critical distance; the second relationship is constructed based on the geometric structure characteristics of the notched specimen;

[0011] According to the target fatigue life prediction model, the first relationship and the second relationship, a critical distance iteration method is used to predict the low cycle fatigue life of the notched part to be tested.

[0012] Optionally, the low-cycle fatigue life data includes a fracture macrograph of the notched specimen, and a stress-strain distribution graph along a dangerous path is obtained by performing simulated fatigue tests on the notched specimen under different test conditions, including:

[0013] Performing simulated fatigue tests on the notched specimen under different test conditions through finite element analysis to obtain corresponding stress-strain distribution diagrams;

[0014] According to the stress-strain distribution diagram and the fracture macro-diagram, a dangerous path for indicating the crack propagation direction and a stress-strain curve along the dangerous path are determined.

[0015] Optionally, the damage parameter value along the dangerous path determined based on the first relationship includes:

[0016] Based on the crystal plasticity theory, the damage parameter calculation formula under the crystal plasticity framework is determined;

[0017] According to the damage parameter calculation formula under the crystal plasticity framework and the stress-strain curve along the dangerous path, the damage parameter value along the dangerous path is determined.

[0018] Optionally, an initial fatigue life prediction model is constructed based on damage parameters and the Manson-Coffin formula, including:

[0019] The damage parameters are combined with the Manson-Coffin formula to construct an initial fatigue life prediction model, which is:

[0020]

[0021] Where E is the elastic modulus of the material, N f is the low cycle fatigue life, σ' f , ε' f , b' and c' are model parameters.

[0022] Optionally, the determining of the second relationship between the low cycle fatigue life and the critical distance comprises:

[0023] Based on the dangerous path, determining a value of a corresponding critical distance;

[0024] Determining a stress concentration factor of the notched specimen based on geometrical features in the notched specimen;

[0025] Based on the stress concentration factor, an initial relationship between low cycle fatigue life and critical distance is constructed;

[0026] Determining a target parameter value in the initial relationship based on the low cycle fatigue life data and the corresponding value of the critical distance;

[0027] Substitute the target parameter value into the initial relational expression to obtain the second relational expression.

[0028] Optionally, the step of using a critical distance iteration method to predict the low cycle fatigue life of the notched component to be tested according to the target fatigue life prediction model, the first relationship and the second relationship includes:

[0029] Determine the value of the critical distance corresponding to the current number of iterations according to the low cycle fatigue life value of the current number of iterations and the second relationship;

[0030] Determine the damage parameter value at the target position of the notched part to be tested according to the first relational expression and the value of the critical distance; the target position is the critical distance perpendicular to the loading direction;

[0031] Determining a low cycle fatigue life value for the next iteration number according to the damage parameter value and the target fatigue life prediction model;

[0032] The above iteration process is repeated until the low cycle fatigue life values ​​corresponding to two adjacent iteration processes are equal, and the low cycle fatigue life value at the end of the iteration is used as the low cycle fatigue life prediction value of the notched part to be tested.

[0033] Optionally, before determining the value of the critical distance corresponding to the current number of iterations, the method further includes:

[0034] Determining a target stress concentration factor according to the geometric structural characteristics of the notched part to be tested;

[0035] According to the target stress concentration factor, a second relationship corresponding to the notched part to be tested is determined.

[0036] According to a second aspect of the present disclosure, there is provided a low cycle fatigue life prediction device for a notched component, comprising:

[0037] A test data acquisition module is used to obtain low-cycle fatigue life data obtained by fatigue tests on notched specimens under different test conditions;

[0038] A simulation data acquisition module, used for obtaining a stress-strain distribution diagram along a dangerous path and a damage parameter value along the dangerous path determined based on a first relationship by performing a simulated fatigue test on the notched specimen under different test conditions; the first relationship is a damage parameter calculation formula determined based on crystal plasticity theory;

[0039] A model determination module is used to construct an initial fatigue life prediction model based on damage parameters and the Manson-Coffin formula; determine model parameter values ​​of the initial fatigue life prediction model according to the low-cycle fatigue life data and the damage parameter values ​​to obtain a target fatigue life prediction model;

[0040] A relationship determination module, used to determine a second relationship between low cycle fatigue life and critical distance based on the low cycle fatigue life data and the value of the critical distance corresponding to the dangerous path; the second relationship is constructed based on the geometric structure characteristics of the notched specimen;

[0041] A prediction module is used to predict the low cycle fatigue life of the notched part to be tested by using a critical distance iteration method according to the target fatigue life prediction model, the first relationship and the second relationship.

[0042] According to a third aspect of the present disclosure, there is provided a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the method for predicting the low-cycle fatigue life of a notched part as described in any one of the above is implemented.

[0043] According to a fourth aspect of the present disclosure, there is provided an electronic device, comprising: a processor; and a memory for storing executable instructions of the processor; wherein the processor is configured to execute any one of the above-mentioned methods for predicting the low-cycle fatigue life of a notched part by executing the executable instructions.

[0044] The exemplary embodiments of the present disclosure may have some or all of the following beneficial effects:

[0045] In the low-cycle fatigue life prediction method for notched parts provided in the disclosed example implementation method, the geometric structural characteristics of the notched parts are introduced into the second relationship between fatigue life and critical distance, thereby realizing life prediction taking into account the geometric structural characteristics of the structural parts and improving the prediction accuracy of low-cycle fatigue life. On the other hand, based on the crystal plasticity theory, a damage parameter calculation formula combining the maximum shear stress and the maximum shear strain is proposed, and at the same time, a fatigue life prediction model for notched parts is constructed by using the damage parameters in combination with the Manson-Coffin formula, further improving the accuracy of the prediction results.

[0046] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification are used to explain the principles of the present disclosure. Obviously, the accompanying drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0048] Figure 1 A schematic flow chart of a method for predicting low cycle fatigue life of a notched component to which an embodiment of the present disclosure can be applied is shown;

[0049] Figure 2 (a) schematically shows a schematic diagram of a single-hole specimen model constructed by finite element analysis according to an embodiment of the present disclosure;

[0050] Figure 2 (b) schematically shows a schematic diagram of a porous specimen model constructed by finite element analysis according to an embodiment of the present disclosure;

[0051] Figure 3 A schematic diagram of a stress amplitude distribution cloud diagram of a single-hole specimen according to an embodiment of the present disclosure is shown;

[0052] Figure 4 A macroscopic cross-sectional view of a single-hole specimen after fatigue test according to an embodiment of the present disclosure is schematically shown;

[0053] Figure 5 A schematic diagram of a stress amplitude distribution cloud diagram of a porous specimen according to an embodiment of the present disclosure is shown;

[0054] Figure 6 A schematic diagram of a critical distance according to an embodiment of the present disclosure is schematically shown;

[0055] Figure 7 A schematic diagram of a determination process of a second relationship according to an embodiment of the present disclosure is schematically shown;

[0056] Figure 8 A schematic diagram of an iterative process of a critical distance iteration method according to an embodiment of the present disclosure is schematically shown;

[0057] Fig. 9 Schematically shows the distribution diagram of the maximum shear stress of a single-hole 0.4 mm specimen along the dangerous path according to an embodiment of the present disclosure;

[0058] Fig.10 The maximum shear strain distribution diagram of a single-hole 0.4 mm specimen along a dangerous path is schematically shown according to an embodiment of the present disclosure;

[0059] Fig.11 Schematically shows the distribution diagram of damage parameters of a single-hole 0.4 mm specimen along a dangerous path according to an embodiment of the present disclosure;

[0060] Fig.12 The maximum shear stress distribution diagram along the dangerous path of a specimen containing 14 air film holes according to an embodiment of the present disclosure is schematically shown;

[0061] Fig.13 The maximum shear strain distribution diagram along the dangerous path of a specimen containing 14 air film holes according to an embodiment of the present disclosure is schematically shown;

[0062] Fig.14 A schematic diagram showing the distribution of damage parameters along a dangerous path of a specimen containing 14 air film holes according to an embodiment of the present disclosure;

[0063] Fig.15 The fitted relationship curve between the modified critical distance and the failure life according to one embodiment of the present disclosure is schematically shown;

[0064] Fig.16 A diagram schematically showing a comparison between the fatigue prediction life and the experimental life of an air film hole structure according to an embodiment of the present disclosure;

[0065] Fig.17 A structural block diagram of a low cycle fatigue life prediction device for a notched component to which the embodiment of the present disclosure can be applied is shown;

[0066] Fig.18 A schematic diagram of the structure of a computer system suitable for implementing an electronic device of an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0067] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in a variety of forms and should not be construed as being limited to the examples set forth herein; on the contrary, these embodiments are provided so that the present disclosure will be more comprehensive and complete, and the concepts of the example embodiments are fully conveyed to those skilled in the art. The described features, structures, or characteristics may be combined in one or more embodiments in any suitable manner. 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 while omitting one or more of the specific details, or other methods, components, devices, steps, etc. may be adopted. In other cases, known technical solutions are not shown or described in detail to avoid obscuring various aspects of the present disclosure.

[0068] In addition, the accompanying drawings are only schematic illustrations of the present disclosure and are not necessarily drawn to scale. The same reference numerals in the figures represent the same or similar parts, and their repeated description will be omitted. Some of the block diagrams shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software form, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontroller devices.

[0069] The performance of aircraft engines is an important indicator of a country's comprehensive national strength, military strength and international scientific and technological level. Improving the turbine inlet temperature (TET) is one of the key technologies to improve the power and efficiency of aircraft engines, but the improvement of TET is severely limited by the high-pressure turbine cooling blade technology. Therefore, it is particularly important to improve the high-temperature mechanical properties of turbine blades by cooling the blades.

[0070] At present, film cooling is a widely used thermal protection technology for turbine blade cooling. It uses air film to isolate the blade from high-temperature combustion gas. However, the introduction of film cooling technology will destroy the structural integrity of the turbine blade, seriously affecting the strength and life of the turbine blade, and becoming an important factor affecting the safe service of aircraft engines. Due to the small aperture and large number of film holes, the temperature field and stress-strain field at the hole edge are very complex, which is the crack initiation site under the engine service environment. The study of the crack mechanism at the edge of the film hole is attributed to the performance research such as thermomechanical fatigue creep with temperature gradient. At the same time, due to the porous interference effect caused by small aperture and dense arrangement, the film holes become a frequent site of blade failure and fracture. Therefore, it is particularly important to perform fatigue life prediction analysis on structural parts with film holes.

[0071] In related technologies, the presence of structural notches (such as air film hole structures) will destroy the geometric continuity of the blade structure, and stress concentration will occur at the discontinuities of the structure. At present, the critical distance method (TCD) that combines linear elastic fracture mechanics with empirical methods for life prediction is mainly used for components with stress concentration. TCD is based on the linear elastic theory and uses the average stress method for prediction under high-cycle conditions. When it is used to predict LCF (low-circle-fatigue) fatigue life, the accuracy is low. And due to the limitations of the linear elastic theory, the prediction results are relatively conservative under low-cycle conditions, and the deviation of the prediction results will increase as the sharpness of the notch groove increases.

[0072] In view of the above problems, the present invention proposes a method for predicting the low cycle fatigue life of a notched component.

[0073] The technical solution of the embodiment of the present disclosure is described in detail below:

[0074] refer to Figure 1 As shown, a method for predicting the low cycle fatigue life of a notched component according to an exemplary embodiment of the present disclosure may include the following steps:

[0075] Step S110, obtaining low cycle fatigue life data obtained by performing fatigue tests on notched specimens under different test conditions;

[0076] Step S120, by performing a simulated fatigue test on the notched specimen under different test conditions, a stress-strain distribution diagram along the dangerous path and a damage parameter value along the dangerous path determined based on a first relationship formula are obtained; the first relationship formula is a damage parameter calculation formula determined based on crystal plasticity theory;

[0077] Step S130, constructing an initial fatigue life prediction model based on the damage parameter and the Manson-Coffin formula; determining the model parameter values ​​of the initial fatigue life prediction model according to the low-cycle fatigue life data and the damage parameter value, so as to obtain a target fatigue life prediction model;

[0078] Step S140, determining a second relationship between the low cycle fatigue life and the critical distance based on the low cycle fatigue life data and the value of the critical distance corresponding to the dangerous path; the second relationship is constructed based on the geometric structure characteristics of the notched specimen;

[0079] Step S150, predicting the low cycle fatigue life of the notched component to be tested by using a critical distance iteration method according to the target fatigue life prediction model, the first relationship and the second relationship.

[0080] In the low-cycle fatigue life prediction method for notched parts provided in the disclosed example implementation method, the geometric structural characteristics of the notched parts are introduced into the second relationship between fatigue life and critical distance, thereby realizing life prediction taking into account the geometric structural characteristics of the structural parts and improving the prediction accuracy of low-cycle fatigue life. On the other hand, based on the crystal plasticity theory, a damage parameter calculation formula combining the maximum shear stress and the maximum shear strain is proposed, and at the same time, a fatigue life prediction model for notched parts is constructed by using the damage parameters in combination with the Manson-Coffin formula, further improving the accuracy of the prediction results.

[0081] Next, in another embodiment, the above steps are described in more detail.

[0082] Step S110, obtaining low cycle fatigue life data obtained by performing fatigue tests on notched specimens under different test conditions.

[0083] In this example embodiment, the notched specimen refers to a specimen with a discontinuous part in the structure. The specimen can be a directional solidification alloy specimen, for example, a nickel-based single crystal alloy specimen with an air film pore structure. The notched specimen can be a thin-walled flat specimen with one or more air film pore structures. The test conditions can include temperature, stress ratio, frequency, and average stress of the minimum cross section loaded along the loading direction, etc. Different test conditions are formed by combining different test parameters. Fatigue tests can be performed on notched specimens according to corresponding test standards. For example, fatigue tests can be performed under the conditions of a test temperature of 900°C, a fatigue test for stress loading control, an average stress of 400MPa, 540MPa, 640MPa and 830MPa on the minimum cross section in the loading direction, a stress ratio of 0.1, and a loading frequency of 3Hz. The test equipment can be a high-temperature hydraulic servo fatigue testing machine. The test temperature is controlled by a temperature control box, and the test is kept warm for half an hour. The specific process of the fatigue test can be performed in accordance with the national standard GB / T 3075-2008. The experimental conditions and test results are shown in Table 1.

[0084] Table 1 Low cycle fatigue test results of nickel-based single crystal alloy DD6 flat plate specimen with air film hole

[0085]

[0086] Low-cycle fatigue life data under different test conditions can be obtained through experiments, and the electronic device executing this method can obtain low-cycle fatigue life data from a testing machine or other equipment storing test results. Low-cycle fatigue life data may include stress-strain data, stress-life data, etc., and may also include macroscopic data such as fracture macrographs of notched specimens, crack length, and crack direction, and may also include other data obtainable from experiments, which is not limited in this example.

[0087] In step S120, by performing simulated fatigue tests on the notched specimen under different test conditions, a stress-strain distribution diagram along the dangerous path and a damage parameter value along the dangerous path determined based on the first relationship are obtained.

[0088] In this example implementation, the simulated fatigue test can be implemented by finite element analysis, and the test conditions of the simulated fatigue test can be the same as the fatigue test in step S110, so as to combine the simulated test results with the real test results to predict the life. The dangerous path refers to the crack propagation path of the specimen, and the dangerous path can be determined based on the simulated stress-strain distribution cloud map and / or the macroscopic section of the specimen of the fatigue test. The first relationship is a damage parameter calculation formula determined based on the crystal plasticity theory.

[0089] Exemplarily, the low-cycle fatigue life data includes a fracture macrograph of a notched specimen, and finite element analysis can be used to perform simulated fatigue tests on the notched specimen under different test conditions to obtain a corresponding stress-strain distribution diagram; based on the stress-strain distribution diagram and the fracture macrograph, a dangerous path for indicating the direction of crack propagation and a stress-strain curve along the dangerous path are determined.

[0090] In this example implementation, a notched specimen can be constructed by finite element analysis ABAQUS and a simulated fatigue test can be performed. For example, a three-dimensional eight-node (C3D8) unit can be used for meshing. The single-hole model has 1092 units and the multi-hole model has 7008 units. The constructed single-hole air film hole specimen model and multi-hole air film hole specimen model are as follows: Figure 2 (a) and 2(b), the figure shows the diagram of 1 / 4 specimen. Four different stresses can be used for simulation calculation, and the test conditions are the same as those in S110. The stress distribution cloud diagram of the single-hole specimen model constructed by finite element analysis is shown in Figure 3 As shown in the figure, the cross-sectional macroscopic image of the actual specimen after fatigue test is as follows Figure 4 As shown, combined Figure 3 and Figure 4 It can be seen that the fracture of the specimens with a single air film hole all started from the direction perpendicular to the stress axis, and the initial stage of the crack extension direction was also perpendicular to the stress axis. Therefore, the dangerous path of the specimen with a single air film hole is determined to be perpendicular to the stress loading axis. Figure 5 As shown, from Figure 5 It can be seen that the dangerous path of the sample with multiple air film holes is the crack path between two holes. After determining the dangerous path, the stress-strain curve along the dangerous path can be obtained from the stress-strain distribution cloud map.

[0091] Exemplarily, the process of determining the damage parameter value along the dangerous path includes the following steps:

[0092] Based on the crystal plasticity theory, the damage parameter calculation formula under the crystal plasticity framework is determined;

[0093] According to the damage parameter calculation formula under the crystal plasticity framework and the stress-strain curve along the dangerous path, the damage parameter value along the dangerous path is determined.

[0094] In this exemplary embodiment, a crystal plastic slip constitutive model can be constructed based on the crystal plastic slip theory, and a damage parameter D under the crystal plasticity framework can be defined according to the idea of ​​SWT parameters (Smith-Watson-Topper). η

[0095]

[0096] In the above formula, τ(α) is the shear stress amplitude of each slip system, γ (α) is the shear strain amplitude of each slip system, S f is the Schmid factor, is the conversion coefficient between shear strain and axial strain. Figure 6 The figure shows a schematic diagram of the stress at a point (r, θ) on the specimen. In the figure, σ represents the tensile stress on both sides of the specimen, r represents the distance from the point to the notch root / crack starting point, θ represents the direction of the point, that is, the angle between the point and the polar axis of the predefined polar coordinates, and L represents the critical distance, which usually refers to a distance at the tip of the notch. Beyond this distance, it is assumed that the stress field distribution is uniform and the stress concentration effect at the tip is ignored. In this example, r=L, θ=0 is the correction condition of the critical distance method, which means that the distance along the notch bisector and from the crack starting point is the critical distance, where the direction for a single-hole specimen should be perpendicular to the loading direction. On the dangerous path, it is generally believed that D η The maximum value of the parameter is the location where the crack initiates, and this value can be obtained by performing finite element calculations on the structure under fixed working conditions.

[0097] In step S130, an initial fatigue life prediction model is constructed based on the damage parameters and the Manson-Coffin formula; model parameter values ​​of the initial fatigue life prediction model are determined according to the low-cycle fatigue life data and the damage parameter values ​​to obtain a target fatigue life prediction model.

[0098] In this example implementation, the damage parameter can be combined with the Manson-Coffin formula to construct an initial fatigue life prediction model. The initial fatigue life prediction model is specifically as follows:

[0099]

[0100] Where E is the elastic modulus of the material, N f is the low cycle fatigue life, σ' f , ε' f , b' and c' are model parameters, and their values ​​are constants.

[0101] The damage parameter value of the notched specimen at r = L can be determined by finite element analysis and formula (1), and then based on the obtained multiple groups of damage parameter values ​​D η And the corresponding low cycle fatigue life data N f The functional relationship between the two is fitted to obtain the model parameter values ​​in formula (2). The target fatigue life prediction model can be obtained by substituting the model parameter values ​​into formula (2).

[0102] In step S140 , a second relationship between the low cycle fatigue life and the critical distance is determined based on the low cycle fatigue life data and the value of the critical distance corresponding to the dangerous path.

[0103] In this example embodiment, the second relationship is constructed based on the geometrical structural characteristics of the notched specimen. The value of the critical distance is determined using the critical distance method based on the stress-strain curve along the critical path and the low-cycle fatigue life data.

[0104] In some embodiments, Figure 7 As shown, the second relationship between the low cycle fatigue life and the critical distance can be determined by the following steps S710-S750:

[0105] Step S710, determining a corresponding critical distance value based on the dangerous path;

[0106] In this example implementation, the value of the critical distance may be the distance between a point on the dangerous path and the starting point of the path (i.e., a distance at the tip of the notch). This distance indicates that after exceeding this distance, the stress field distribution is uniform, i.e., the stress concentration effect at the tip is ignored. In other words, beyond this distance, the notched structural member may be treated as an ideal material without a notch. Specifically, the value of the critical distance corresponding to the dangerous path and the maximum shear stress and maximum shear strain at the critical distance may be determined by finite element analysis to obtain a relationship diagram between the critical distance and the maximum shear stress, and between the critical distance and the maximum shear strain. For example, a relationship diagram between the critical distance and the maximum shear stress and the maximum shear strain of a single-hole specimen is shown in FIG. Fig. 9 and 10 shown.

[0107] Step S720, determining the stress concentration factor of the notched specimen based on the geometric structure characteristics in the notched specimen.

[0108] In this example implementation, different geometric features in the notched specimens will result in different stress concentration factors for the notched specimens. The geometric features may include specimen size, number of notches, hole diameter, hole center spacing, etc. Specifically, for a single-hole flat specimen, its corresponding stress concentration factor can be obtained by looking up a table. For example, the stress concentration factor K of a 0.4 mm single-hole specimen is t About 3, the stress concentration factor K of the 0.8mm single hole specimen t About 3.1.

[0109] For porous flat plate specimens, the circular holes are arranged in an equilateral triangle. Assuming the plate width is B, the thickness is t, the hole diameter is d, and the center spacing of the circular holes is b, the stress concentration factor can be determined according to the range of d / b: When d / b < 0.5, the maximum tensile stress σ maxNot on the line connecting the center points of the two holes; when d / b>0.5, the maximum tensile stress moves toward the line connecting the center points of the two holes as d / b increases. Finally, the corresponding stress concentration factor can be determined by looking up the table. For example, when According to the d / b value, the stress concentration factor K can be obtained t =4.0.

[0110] Step S730: constructing an initial relationship between low cycle fatigue life and critical distance based on the stress concentration factor.

[0111] In this example implementation, the functional relationship between the fatigue life of the structural member and the critical distance is:

[0112] Among them, A and B are material parameters. Different materials and stress ratios R will correspond to different A and B values.

[0113] Based on the above formula (3), the initial relationship between low cycle fatigue life and critical distance is constructed as follows:

[0114]

[0115] The above formula (4) combines the stress concentration factor that characterizes the geometric structure characteristics of the specimen.

[0116] Step S740: determining the target parameter value in the initial relationship based on the low cycle fatigue life data and the corresponding critical distance value.

[0117] In this example embodiment, the values ​​of parameters A and B in the formula (target parameter values) may be determined by mathematical fitting based on the low cycle fatigue life data in S110 and the corresponding critical distance value.

[0118] Step S750, substituting the target parameter value into the initial relational expression to obtain a second relational expression.

[0119] In this example implementation, the values ​​of A and B determined in S740 are substituted into equation (4) to obtain the second relational equation.

[0120] Above Figure 7 The second relationship determined in the illustrated embodiment relates both the critical distance and the geometrical structure characteristics, thereby improving the accuracy of low cycle fatigue life prediction of notched specimens with specific geometrical structure characteristics.

[0121] In step S150, based on the target fatigue life prediction model, the first relationship and the second relationship, a critical distance iteration method is used to predict the low cycle fatigue life of the notched component to be tested.

[0122] In this example implementation, the notched piece to be tested can be a test piece with the same notch type and material constitutive properties as the notched test piece in each of the above steps. For example, the notched test piece and the test piece to be tested are both nickel-based single crystal alloy test pieces with air film holes, or they can be test pieces with different geometric structures, which is not limited in this example. The critical distance iteration method can be used to predict the low-cycle fatigue life of the notched piece to be tested. The critical distance iteration method is to give an initial life value, based on the initial value, calculate the corresponding critical distance and damage parameters, and obtain the final life prediction value through continuous iteration.

[0123] For example, when the geometric structure characteristics of the notched part to be tested are different from those in the above steps, the target stress concentration factor can be determined according to the geometric structure characteristics of the notched part to be tested; and the second relationship corresponding to the notched part to be tested can be determined according to the target stress concentration factor. The specific process can refer to the second relationship determination process of the notched test piece, which will not be described here.

[0124] For example, refer to Figure 8 , the low cycle fatigue life prediction process based on iteration can be carried out through the following steps:

[0125] The first step is to determine the critical distance value corresponding to the current iteration number according to the low cycle fatigue life value of the current iteration number and the second relationship;

[0126] The second step is to determine the damage parameter value at the target position of the notched part to be tested according to the first relational expression and the value of the critical distance; the target position is the critical distance perpendicular to the loading direction;

[0127] The third step is to determine the low-cycle fatigue life value of the next iteration number according to the damage parameter value and the target fatigue life prediction model;

[0128] The fourth step is to repeat the above iterative process until the low-cycle fatigue life values ​​corresponding to two adjacent iterative processes are equal, and the low-cycle fatigue life value at the end of the iteration is used as the low-cycle fatigue life prediction value of the notched part to be tested.

[0129] In this example implementation, a fatigue life initial value N can be given first f,0 , and perform an iterative calculation process based on this initial value. For one iteration process, the low-cycle fatigue life value N based on the current number of iterations f,i And formula (9) to determine the corresponding critical distance L (N f,i ), and then based on formula (1) calculate the f,i ) at the damage parameter D η , and then based on Dη and formula (2), we can infer N f,i+1 Repeat the above process until N f,i+1 =N f,i The predicted life span value can be obtained.

[0130] The test results of the single-hole 0.4 mm sample and the 14-hole sample under the test conditions in Table 1 are analyzed. Figure 9-11 They are the maximum shear stress distribution diagram, maximum shear strain distribution diagram and damage parameter distribution diagram of the single hole 0.4mm sample, respectively. Figure 9-11 It can be seen that no matter what the working conditions are, the maximum value is at the edge of the hole and gradually decreases along the path. This shows that for the flat plate structure containing a single air film hole, the crack initiates at the maximum shear stress at the edge of the hole, which is also the maximum shear strain, which is consistent with the fracture morphology after the test.

[0131] like Figure 12-14 They are the distribution of the maximum shear stress along the dangerous path with 14 air film holes, the distribution of the maximum shear strain along the dangerous path with 14 air film holes, and the distribution of the damage parameters along the dangerous path with 14 air film holes. Fig.12 , 13 It can be seen that, unlike the stress-strain distribution of the single-hole specimen, the maximum shear stress distribution of the porous specimen on the dangerous path is not uniform due to the influence of the porous interference effect, but is generally symmetrical along the 0.43 mm point. The farther away from the center row of holes, the smaller the shear stress and strain. Fig.14 It can be seen that the overall distribution of damage parameters also shows a certain degree of symmetry, but larger damage parameters appear in the area closer to the center row of holes, which further shows that the cracks are generated near the center row of holes. Higher damage parameters are also distributed near the holes on both sides, indicating that cracks are also easily generated there. From the shear stress strain and damage parameter distribution, it can be seen that under smaller stress conditions, the distribution of strain and damage parameters is more uniform, while the larger stress (830MPa) is enhanced due to the porous interference effect, and the material is more likely to produce micro-voids under high temperature and high stress. The stress field around the hole becomes more complicated, so the strain distribution does not show obvious symmetry, reaching the maximum near the center row of holes and gradually decreasing along the path, indicating that the initial crack under high stress is generated at the edge of the middle row of holes and quickly extends to the holes on both sides.

[0132] like Fig.15 As shown, based on The obtained single hole and 14-hole arrangement of air film holes K t L(N f ) and failure life N f From the simulation relationship diagram, it can be seen that the relationship curves of different hole arrangements are different.

[0133] According to the disclosed method, the life of a single-hole flat plate at two radii and a triangular flat plate with 8 holes and 14 holes with dense air film holes is predicted. The prediction results are as follows: Fig.16As shown in the comparison diagram, it can be seen that the low cycle fatigue life prediction values ​​of the disclosed method are basically within the double error dispersion band, which proves the effectiveness of the disclosed method.

[0134] The present invention performs finite element simulation on the air film hole structure to obtain the stress-strain distribution diagram of the structure around the hole, determine the dangerous path of the structure, and obtain the stress-strain curve along the dangerous path; establishes a fatigue life prediction model in combination with damage parameters; uses a modified critical distance method improved based on crystal plasticity theory to perform curve fitting on the test results, determine the model parameter values, and achieve accurate prediction of the high-temperature fatigue life of notched parts (such as turbine blade air film hole structures) under low-cycle fatigue cycles.

[0135] Furthermore, in this exemplary embodiment, a low-cycle fatigue life prediction device 1700 for a notched component is also provided. The low-cycle fatigue life prediction device 1700 for a notched component can be applied to a server or a terminal device. Fig.17 As shown, the low cycle fatigue life prediction device 1700 of the notched component may include:

[0136] The test data acquisition module 1710 is used to obtain low cycle fatigue life data obtained by performing fatigue tests on notched specimens under different test conditions;

[0137] The simulation data acquisition module 1720 is used to obtain a stress-strain distribution diagram along a dangerous path and a damage parameter value along the dangerous path determined based on a first relationship by performing a simulated fatigue test on the notched specimen under different test conditions; the first relationship is a damage parameter calculation formula determined based on crystal plasticity theory;

[0138] The model determination module 1730 is used to construct an initial fatigue life prediction model based on the damage parameter and the Manson-Coffin formula; determine the model parameter values ​​of the initial fatigue life prediction model according to the low-cycle fatigue life data and the damage parameter value to obtain a target fatigue life prediction model;

[0139] A relational expression determination module 1740 is used to determine a second relational expression between low cycle fatigue life and critical distance based on low cycle fatigue life data and a value of a critical distance corresponding to a dangerous path; the second relational expression is constructed based on geometric structural characteristics of a notched specimen;

[0140] The prediction module 1750 is used to predict the low cycle fatigue life of the notched component to be tested by using the critical distance method according to the target fatigue life prediction model, the first relationship and the second relationship.

[0141] In an exemplary embodiment of the present disclosure, the low cycle fatigue life data includes a fracture macrograph of a notched specimen, and the simulation data acquisition module 1720 is further used to:

[0142] Through finite element analysis, simulated fatigue tests were carried out on notched specimens under different test conditions to obtain the corresponding stress-strain distribution diagram;

[0143] According to the stress-strain distribution diagram and the fracture macrograph, the dangerous path indicating the crack propagation direction and the stress-strain curve along the dangerous path are determined.

[0144] In an exemplary embodiment of the present disclosure, the simulation data acquisition module 1720 is further used to:

[0145] The damage parameter values ​​along the dangerous path determined based on the first relationship include:

[0146] Based on the crystal plasticity theory, the damage parameter calculation formula under the crystal plasticity framework is determined;

[0147] According to the damage parameter calculation formula under the crystal plasticity framework and the stress-strain curve along the dangerous path, the damage parameter value along the dangerous path is determined.

[0148] In an exemplary embodiment of the present disclosure, the model determination module 1730 is further configured to:

[0149] The damage parameters are combined with the Manson-Coffin formula to construct the initial fatigue life prediction model. The initial fatigue life prediction model is:

[0150]

[0151] Where E is the elastic modulus of the material, N f is the low cycle fatigue life, σ' f , ε' f , b' and c' are model parameters.

[0152] In an exemplary embodiment of the present disclosure, the relationship determination module 1740 is further configured to:

[0153] Based on the dangerous path, determine the value of the corresponding critical distance;

[0154] Based on the geometric structure characteristics of the notched specimen, the stress concentration factor of the notched specimen is determined;

[0155] Based on the stress concentration factor, the initial relationship between low-cycle fatigue life and critical distance is constructed;

[0156] Determine the target parameter value in the initial relationship based on the low cycle fatigue life data and the corresponding critical distance value;

[0157] Substituting the target parameter value into the initial relational expression, a second relational expression is obtained.

[0158] In an exemplary embodiment of the present disclosure, the prediction module 1750 is further configured to:

[0159] According to the low cycle fatigue life value of the current iteration number and the second relationship, the value of the critical distance corresponding to the current iteration number is determined;

[0160] According to the first relational expression and the value of the critical distance, the damage parameter value at the target position of the notched part to be tested is determined; the target position is a position perpendicular to the loading direction and corresponding to the value of the critical distance at a distance from the crack starting point;

[0161] According to the damage parameter value and the target fatigue life prediction model, the low cycle fatigue life value of the next iteration is determined;

[0162] Repeat the above iterative process until the low-cycle fatigue life values ​​corresponding to two adjacent iterative processes are equal, and use the low-cycle fatigue life value at the end of the iteration as the low-cycle fatigue life prediction value of the notched part to be tested.

[0163] The specific details of each module or unit in the above-mentioned low-cycle fatigue life prediction device for notched parts have been described in detail in the corresponding low-cycle fatigue life prediction method for notched parts, so they will not be repeated here.

[0164] As another aspect, the present application also provides a computer-readable medium, which may be included in the electronic device described in the above embodiment; or may exist independently without being assembled into the electronic device. The above computer-readable medium carries one or more programs, and when the above one or more programs are executed by an electronic device, the electronic device implements the method in the following embodiment. For example, the electronic device may implement the following Figure 1 The various steps shown, etc.

[0165] It should be noted that the computer-readable medium shown in the present disclosure may be a computer-readable signal medium or a computer-readable storage medium or any combination of the above two. The computer-readable storage medium may be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device or device, or any combination of the above. More specific examples of computer-readable storage media may include, but are not limited to: an electrical connection with one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In the present disclosure, a computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in combination with an instruction execution system, device or device. In the present disclosure, a computer-readable signal medium may include a data signal propagated in a baseband or as part of a carrier wave, in which a computer-readable program code is carried. This propagated data signal may take a variety of forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. Computer-readable signal media may also be any computer-readable medium other than computer-readable storage media, which may send, propagate or transmit a program for use by or in conjunction with an instruction execution system, apparatus or device. The program code contained on the computer-readable medium may be transmitted using any appropriate medium, including but not limited to: wireless, wire, optical cable, RF, etc., or any suitable combination of the above.

[0166] Fig.18 A schematic diagram of the structure of a computer system suitable for implementing an electronic device of an embodiment of the present disclosure is shown.

[0167] It should be noted that Fig.18 The computer system 1800 of the electronic device shown is only an example and should not bring any limitation to the functions and scope of use of the embodiments of the present disclosure.

[0168] like Fig.18 As shown, the computer system 1800 includes a central processing unit (CPU) 1801, which can perform various appropriate actions and processes according to the program stored in the read-only memory (ROM) 1802 or the program loaded from the storage part 1808 to the random access memory (RAM) 1803. In the RAM 1803, various programs and data required for system operation are also stored. The CPU 1801, the ROM 1802, and the RAM 1803 are connected to each other through a bus 1804. An input / output (I / O) interface 1805 is also connected to the bus 1804.

[0169] The following components are connected to the I / O interface 1805: an input section 1806 including a keyboard, a mouse, etc.; an output section 1807 including a cathode ray tube (CRT), a liquid crystal display (LCD), etc., and a speaker, etc.; a storage section 1808 including a hard disk, etc.; and a communication section 1809 including a network interface card such as a LAN card, a modem, etc. The communication section 1809 performs communication processing via a network such as the Internet. A drive 1810 is also connected to the I / O interface 1805 as needed. A removable medium 1818, such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, etc., is installed on the drive 1810 as needed, so that a computer program read therefrom is installed into the storage section 1808 as needed.

[0170] In particular, according to an embodiment of the present disclosure, the process described below with reference to the flowchart can be implemented as a computer software program. For example, an embodiment of the present disclosure includes a computer program product, which includes a computer program carried on a computer-readable medium, and the computer program contains program code for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from a network through a communication part 1809, and / or installed from a removable medium 1818. When the computer program is executed by a central processing unit (CPU) 1801, various functions defined in the method and apparatus of the present application are executed.

[0171] The flow charts and block diagrams in the accompanying drawings illustrate the possible architecture, functions and operations of the systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each box in the flow chart or block diagram can represent a module, a program segment, or a part of a code, and the above-mentioned module, program segment, or a part of a code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order from the order marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram or flow chart, and the combination of the boxes in the block diagram or flow chart can be implemented with a dedicated hardware-based system that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0172] It should be noted that, although the steps of the method in the present disclosure are described in a specific order in the drawings, this does not require or imply that the steps must be performed in the specific order, or that all the steps shown must be performed to achieve the desired results. Additionally or alternatively, some steps may be omitted, multiple steps may be combined into one step, and / or one step may be decomposed into multiple steps, etc., which shall all be considered as part of the present disclosure.

[0173] It should be understood that the 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 accompanying drawings. All these different combinations constitute multiple alternative aspects of the disclosure. The embodiments of this specification illustrate the best mode known for implementing the disclosure and will enable those skilled in the art to utilize the disclosure.

Claims

1. A method for predicting the low cycle fatigue life of a notched component, characterized in that: include: Obtain low cycle fatigue life data from fatigue tests on notched specimens under different test conditions; By performing a simulated fatigue test on the notched specimen under different test conditions, a stress-strain distribution diagram along the dangerous path and a damage parameter value along the dangerous path determined based on a first relationship are obtained; the first relationship is a damage parameter calculation formula determined based on crystal plasticity theory; Based on the damage parameter and the Manson-Coffin formula, an initial fatigue life prediction model is constructed; according to the low-cycle fatigue life data and the damage parameter value, the model parameter value of the initial fatigue life prediction model is determined to obtain a target fatigue life prediction model; Based on the low cycle fatigue life data and the value of the critical distance corresponding to the dangerous path, determining a second relationship between the low cycle fatigue life and the critical distance; the second relationship is constructed based on the geometric structure characteristics of the notched specimen; According to the target fatigue life prediction model, the first relationship and the second relationship, a critical distance iteration method is used to predict the low cycle fatigue life of the notched part to be tested.

2. The method according to claim 1, characterized in that The low-cycle fatigue life data includes a fracture macrograph of the notched specimen, and a stress-strain distribution graph along a dangerous path is obtained by performing simulated fatigue tests on the notched specimen under different test conditions, including: Performing simulated fatigue tests on the notched specimen under different test conditions through finite element analysis to obtain corresponding stress-strain distribution diagrams; According to the stress-strain distribution diagram and the fracture macro-diagram, a dangerous path for indicating the crack propagation direction and a stress-strain curve along the dangerous path are determined.

3. The method according to claim 1, characterized in that The damage parameter values ​​along the dangerous path determined based on the first relationship include: Based on the crystal plasticity theory, the damage parameter calculation formula under the crystal plasticity framework is determined; According to the damage parameter calculation formula under the crystal plasticity framework and the stress-strain curve along the dangerous path, the damage parameter value along the dangerous path is determined.

4. The method according to claim 1, characterized in that: Based on the damage parameters and Manson-Coffin formula, an initial fatigue life prediction model is constructed, including: The damage parameters are combined with the Manson-Coffin formula to construct an initial fatigue life prediction model, which is: Where E is the elastic modulus of the material, N f is the low cycle fatigue life, σ' f , ε' f , b' and c' are model parameters.

5. The method according to claim 1, characterized in that The second relationship between the low cycle fatigue life and the critical distance is determined, including: Based on the dangerous path, determining a value of a corresponding critical distance; Determining a stress concentration factor of the notched specimen based on geometrical features in the notched specimen; Based on the stress concentration factor, an initial relationship between low cycle fatigue life and critical distance is constructed; Determining a target parameter value in the initial relationship based on the low cycle fatigue life data and the corresponding value of the critical distance; Substitute the target parameter value into the initial relational expression to obtain the second relational expression.

6. The method according to any one of claims 1 to 5, characterized in that: The method of using a critical distance iteration method to predict the low cycle fatigue life of the notched part to be tested according to the target fatigue life prediction model, the first relationship and the second relationship includes: Determine the value of the critical distance corresponding to the current number of iterations according to the low cycle fatigue life value of the current number of iterations and the second relationship; Determine the damage parameter value at the target position of the notched part to be tested according to the first relational expression and the value of the critical distance; the target position is the critical distance perpendicular to the loading direction; Determining a low cycle fatigue life value for the next iteration number according to the damage parameter value and the target fatigue life prediction model; The above iteration process is repeated until the low cycle fatigue life values ​​corresponding to two adjacent iteration processes are equal, and the low cycle fatigue life value at the end of the iteration is used as the low cycle fatigue life prediction value of the notched part to be tested.

7. The method according to claim 5, characterized in that Before determining the value of the critical distance corresponding to the current number of iterations, the method further includes: Determining a target stress concentration factor according to the geometric structural characteristics of the notched part to be tested; According to the target stress concentration factor, a second relationship corresponding to the notched part to be tested is determined.

8. A low cycle fatigue life prediction device for notched parts, characterized in that: include: A test data acquisition module, used to acquire low cycle fatigue life data obtained by fatigue tests on notched specimens under different test conditions; A simulation data acquisition module, used for obtaining a stress-strain distribution diagram along a dangerous path and a damage parameter value along the dangerous path determined based on a first relationship by performing a simulated fatigue test on the notched specimen under different test conditions; the first relationship is a damage parameter calculation formula determined based on crystal plasticity theory; A model determination module is used to construct an initial fatigue life prediction model based on damage parameters and the Manson-Coffin formula; determine model parameter values ​​of the initial fatigue life prediction model according to the low-cycle fatigue life data and the damage parameter values ​​to obtain a target fatigue life prediction model; A relationship determination module, used to determine a second relationship between low cycle fatigue life and critical distance based on the low cycle fatigue life data and the value of the critical distance corresponding to the dangerous path; the second relationship is constructed based on the geometric structure characteristics of the notched specimen; A prediction module is used to predict the low cycle fatigue life of the notched part to be tested by using a critical distance iteration method according to the target fatigue life prediction model, the first relationship and the second relationship.

9. A computer readable medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the method according to any one of claims 1 to 7 is implemented.

10. An electronic device, characterized in that: include: one or more processors; A storage device, used to store one or more programs, when the one or more programs are executed by the one or more processors, enables the one or more processors to implement the method according to any one of claims 1 to 7.

Images