Method and device for predicting full life of gas turbine blade

Abstract

The invention provides a gas turbine blade full-life prediction method and device, and belongs to the technical field of engineering machinery fatigue tests.The gas turbine blade full-life prediction method comprises the steps that integration is conducted on a chboche model, and a residual life expression is obtained; introducing an elastic strain weighting factor and a plastic strain weighting factor into an average stress item in the residual life expression to obtain a nonlinear damage formula; the effective crack length of Hadad is introduced into a Walker crack propagation expression, and a crack propagation formula is obtained; correcting the crack propagation formula based on the crack closure coefficient; and combining the corrected crack propagation formula and the nonlinear damage formula, and sorting to obtain a final blade fatigue life prediction model. The method effectively solves the technical problem that in the prior art, the influence of plastic strain generated under high stress on the fatigue life is not considered, and the whole life from crack initiation to fracture and the residual life in the macroscopic crack propagation stage are not predicted at the same time, so that the maintenance cost is too high.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of engineering machinery fatigue test, and particularly relates to a full-life prediction method and device for a gas turbine blade. BACKGROUND

[0002] During the operation of a gas turbine, the pressure on the pressure surface of the compressor blade is greater than the pressure on the suction surface in a non-instability state, and the periodic aerodynamic load on the blade is always greater than zero. At this time, the periodic load acting on the blade is asymmetric. Unlike symmetric loading, the maximum stress value of the cyclic load causing material fatigue failure is relatively higher under asymmetric loading. Local plastic deformation of the blade material occurs under the action of higher stress, which further changes the fatigue damage accumulation law. For the gas turbine compressor blade, TC4 and TC11 blades are commonly used for fatigue tests, and 2 times dispersion band and 5 times dispersion band are used to represent the error between the model prediction value and the test data. The accuracy of the model prediction is described by combining qualitative and quantitative methods.

[0003] When the stress ratio R = -1, the Chaboche model and the test data agree well. 60.5% of the predicted life of TC4 titanium alloy is distributed in the 2 times dispersion band of the test life, and 88.4% of the predicted life of TC4 titanium alloy is distributed in the 5 times dispersion band of the test life. 87.5% of the predicted life of TC11 titanium alloy is distributed in the 2 times dispersion band of the test life, and the predicted life of TC11 titanium alloy is all distributed in the 5 times dispersion band of the test life. When the stress ratio R = 0.1, under the action of low stress cyclic load (TC4 titanium alloy : 540MPa~630MPa; TC11 titanium alloy : 820MPa~850MPa), the Chaboche model and the test data agree well, but under the action of high stress cyclic load (TC4 titanium alloy : 650MPa~834MPa; TC11 titanium alloy : 900MPa~1079MPa), the Chaboche model prediction value is lower than the test value. For TC4 titanium alloy, 50% of the Chaboche model prediction life is distributed in the 2 times dispersion band of the test life, and 84.4% of the Chaboche model prediction life is distributed in the 5 times dispersion band of the test life. For TC11 titanium alloy, 28.3% of the Chaboche model prediction life is distributed in the 2 times dispersion band of the test life, and 54.3% of the Chaboche model prediction life is distributed in the 5 times dispersion band of the test life. When the stress ratio R = 0.5, under the action of low stress cyclic load (TC4 titanium alloy : 713 MPa ~ 730 MPa; TC11 titanium alloy : 955 MPa ~ 970 MPa), the Chaboche model and the test data are in good agreement, but under the action of high stress cyclic load (TC4 titanium alloy : 760 MPa ~ 912 MPa; TC11 titanium alloy : 980 MPa ~ 1079 MPa), the Chaboche model prediction value is significantly smaller than the test value. For TC4 titanium alloy, 15% of the Chaboche model predicted life is distributed in the 2 times dispersion band of the test life, and 42.5% of the Chaboche model predicted life is distributed in the 5 times dispersion band of the test life; for TC11 titanium alloy, 21.7% of the Chaboche model predicted life is distributed in the 2 times dispersion band of the test life, and 43.5% of the Chaboche model predicted life is distributed in the 5 times dispersion band of the test life.

[0004] When the blade is subjected to high stress asymmetric loading, the greater the stress ratio, the more obvious the difference between the Chaboche model prediction value and the test value. This is because under asymmetric loading, the maximum stress value of the cycle load leading to material fatigue failure is relatively higher, and local plastic deformation of the material under the action of higher stress will further affect the fatigue life. The prediction results of the traditional life prediction model have large errors, which affect the reliability and safety of the structure.

[0005] Although the Walker model considers the change of the stress ratio, the prediction accuracy of the model is better when the stress ratio is 0, and the residual life prediction accuracy decreases under asymmetric loading, which leads to a large prediction error of the crack propagation law of the engineering machinery, and consumes maintenance cost.

[0006] Crack initiation life and crack propagation life are usually studied separately, and there are few theories that can predict the full life of crack initiation to fracture and the residual life of the macroscopic crack propagation stage at the same time. In the crack initiation stage, when the stress borne by the crack body is greater than 0, the crack surface opens; when the stress is less than 0, the crack surface closes. But for the crack in the actual blade, under cyclic loading, a plastic zone will be generated at the crack tip, which will further cause the upper and lower surfaces of the crack to contact each other before complete unloading, resulting in crack closure phenomenon. The traditional model does not consider the influence of this phenomenon when making prediction, and the prediction is often conservative, which leads to an increase in maintenance cost. SUMMARY

[0007] In view of this, it is necessary to provide a method and device for predicting the full life of gas turbine blades, so as to solve the technical problem that the existing technology neither considers the influence of plastic strain generated under high stress on fatigue life, nor simultaneously predicts the full life from crack initiation to fracture and the remaining life of macroscopic crack propagation stage, resulting in excessively high maintenance costs.

[0008] To achieve the above-mentioned technical effects, in a first aspect, the present invention provides a method for predicting the entire lifespan of gas turbine blades, comprising: By integrating the Chaboche model, with the integration range from 0 to 1 for the damage variable, the remaining lifetime expression is obtained. By introducing the elastic strain weighting factor and the plastic strain weighting factor into the average stress term in the remaining life expression, a nonlinear damage formula is obtained, wherein the elastic strain weighting factor is the proportion of elastic strain in the total strain, and the plastic strain weighting factor is the proportion of plastic strain in the total strain. By incorporating Haddad's effective crack length into the Walker crack propagation expression, we obtain the crack propagation formula. The crack propagation formula is modified based on the crack closure coefficient, which is determined according to the crack opening stress, and the crack opening stress is determined according to a preset empirical formula and a shape boundary correction factor. By combining the modified crack propagation formula and the nonlinear damage formula, the final blade fatigue life prediction model is obtained, which is used to calculate the final blade fatigue life based on material parameters. Based on the Abaqus analysis environment; Load the preset 3D blade model into Franc3D and set the blade's material parameters; Set unilateral constraints; Insert a crack into the three-dimensional model of the blade; Calculate crack propagation and obtain blade working stress intensity factor and fatigue life data; The blade's working stress intensity factor and fatigue life data are substituted into the blade fatigue life prediction model to obtain the blade's fatigue life.

[0009] In some embodiments of the present invention, the chaboche model includes:

[0010] In the formula, Represents the loss variable. This indicates that no damage has begun. This indicates the end of the material's remaining lifespan. Indicates the number of loops. Indicates the stress amplitude of cyclic load. This represents the average stress under cyclic loading. , , Indicates parameters related to materials; parameter Determined by the following formula:

[0011] In the formula, the symbol Indicates if but ,like but ; Indicates material parameters, The maximum stress; Tensile strength; parameter The fatigue limit under asymmetric loading is determined by the following formula:

[0012] In the formula, The fatigue limit under symmetrical cyclic loading; right Integrating, we obtain the remaining lifetime formula:

[0013] In the formula, Indicates remaining lifespan.

[0014] In some embodiments of the present invention, the step of introducing the elastic strain weighting factor and the plastic strain weighting factor into the average stress term in the remaining life expression to obtain a nonlinear damage formula includes: Based on the MC model, expressions for elastic strain weighting factors and plastic strain weighting factors are introduced, and the fatigue correction factor is obtained by combining them simultaneously. Substituting the fatigue correction factor into the mean stress term of the remaining life expression yields the nonlinear damage formula.

[0015] In some embodiments of the present invention, the expressions for the elastic strain weighting factor and the plastic strain weighting factor include:

[0016] In the formula, This represents the plastic strain weighting factor. This represents the elastic strain weighting factor. Represents the plastic strain modulus. Represents the elastic strain modulus. Indicates stress amplitude. Indicates the elastic modulus. Indicates the cyclic strength coefficient. Indicates the cyclic strain hardening index; The expressions of the MC model include:

[0017] In the formula, The fatigue strength coefficient, The fatigue strength index. The fatigue ductility coefficient, It is the fatigue ductility index; Combining the expressions for the MC model with those for the elastic strain weighting factor and the plastic strain weighting factor, we obtain the fatigue correction factor used to define the elastic-plastic strain weighting effect, expressed as:

[0018] In the formula, This represents the fatigue correction factor. Indicates constant coefficients.

[0019] In some embodiments of the present invention, substituting the fatigue correction factor into the remaining life expression to obtain the nonlinear damage formula includes: The fatigue correction factor is incorporated into the mean stress term of the remaining life expression; The nonlinear loss formula includes: .

[0020] In some embodiments of the present invention, the Walker crack propagation relation is as follows:

[0021] In the formula, Indicates the crack size. , and All of these are material-related parameters; Indicates the stress ratio; The stress intensity factor can be determined by the following formula:

[0022] In the formula, This is a shape boundary correction factor; The crack size; The stress range; The method of incorporating Haddad's effective crack length into the Walker crack propagation expression to obtain the crack propagation formula includes: Introducing Haddad's effective crack length into the crack size term of the stress intensity factor expression, we obtain the crack propagation formula shown below:

[0023] In the formula, Indicates the effective crack length.

[0024] In some embodiments of the present invention, the modification of the crack propagation formula based on the crack closure coefficient includes: The effective stress intensity factor, taking into account the crack closure effect, is defined as follows:

[0025] In the formula, Indicates the effective stress intensity factor. Represents the maximum stress intensity factor. The stress intensity factor represents the stress intensity factor at which a crack opens. Indicates the crack closure factor; The expression for the crack closure coefficient is constructed based on the relationship between stress and stress intensity factor:

[0026] In the formula, Indicates the maximum stress. Indicates minimum stress. This represents the crack opening stress. Indicates the stress ratio; Among them, crack opening stress It is obtained from empirical formulas, which include:

[0027] In the formula, , , , Determined by the following formula:

[0028] In the formula, Indicates the shape boundary correction factor; Indicates the stress state constraint coefficient. , Indicates Poisson's ratio; Represents rheological stress; Wherein, the rheological stress The expression is:

[0029] In the formula, For tensile strength, Yield strength; By replacing the stress intensity factor in the crack propagation formula with the effective stress intensity factor determined based on the crack closure coefficient, we obtain the modified crack propagation formula: .

[0030] In some embodiments of the present invention, the combined modified crack propagation formula and the nonlinear damage formula are rearranged to obtain the final blade fatigue life prediction model for calculating the blade fatigue life based on material parameters, including: Integrating the modified crack propagation formula over a range from the initial crack size to the final crack size, we obtain the expression for the crack propagation life:

[0031] Substituting the nonlinear loss formula into the left side of the expression for crack propagation life, the integration interval is... Divided into equal parts m each interval We obtain the following simultaneous equations:

[0032] when m Large enough, assuming In the interval Since is a constant, solving the simultaneous equations yields:

[0033] The final solution yields the effective crack length. for:

[0034] The expression for the blade fatigue life prediction model is obtained by refining the formula as follows:

[0035] In the formula, This represents the predicted fatigue life of the blade.

[0036] In some embodiments of the present invention, the unilateral constraint includes: tenon fixing constraint, blade rotation speed and aerodynamic load.

[0037] Secondly, the present invention also provides a device for predicting the entire lifespan of gas turbine blades, comprising: The life prediction model building module is used to integrate the Chaboche model, with the integration range from 0 to 1 for the damage variable, to obtain the remaining life expression. Elastic strain weighting factors and plastic strain weighting factors are introduced into the average stress term of the remaining life expression to obtain a nonlinear damage formula, where the elastic strain weighting factor is the proportion of elastic strain in the total strain, and the plastic strain weighting factor is the proportion of plastic strain in the total strain. Haddad's effective crack length is introduced into the Walker crack propagation expression to obtain the crack propagation formula. The crack propagation formula is modified based on the crack closure coefficient, which is determined according to the crack opening stress, and the crack opening stress is determined according to a preset empirical formula and a shape boundary correction factor. The modified crack propagation formula and the nonlinear damage formula are combined to obtain the final blade fatigue life prediction model used to calculate the final blade fatigue life based on material parameters. The life prediction module is used in the Abaqus analysis environment. It loads a preset three-dimensional blade model into Franc3D and sets the blade's material parameters. It sets unilateral constraints, inserts cracks into the three-dimensional blade model, calculates crack propagation, and obtains the blade's working stress intensity factor and fatigue life data. It substitutes the blade's working stress intensity factor and fatigue life data into the blade fatigue life prediction model to obtain the blade's fatigue life.

[0038] The beneficial effects of this invention are as follows: This invention provides a method for predicting the full life of gas turbine blades. It introduces the Chaboche model with an elastoplastic factor to correct the problem that under asymmetric loading, materials undergo localized plastic deformation under high stress, which alters the cyclic stress during fatigue damage accumulation. Combined with the crack propagation formula, it incorporates the effective crack length proposed by Haddad theory to establish a preliminary comprehensive life model. Finally, considering the crack closure phenomenon in actual conditions, a closure coefficient is proposed for correction, establishing a comprehensive life model that considers the crack closure effect. This comprehensive life model is then applied to life prediction, effectively solving the technical problem of existing technologies that neither consider the impact of plastic strain generated under high stress on fatigue life nor simultaneously predict the full life from crack initiation to fracture and the remaining life during the macroscopic crack propagation stage, leading to excessively high maintenance costs. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 A flowchart illustrating an embodiment of the gas turbine blade life prediction method provided by the present invention; Figure 2 for Figure 1 A flowchart illustrating an embodiment of step S102; Figure 3 A schematic diagram showing the prediction effect of the Chaboche model with the introduction of elastoplastic strain factor and the original Chaboche model on TC4 titanium alloy provided by the present invention. Figure 4 A schematic diagram showing the prediction effect of the Chaboche model with the introduction of elastoplastic strain factor and the original Chaboche model on TC11 titanium alloy provided by the present invention. Figure 5 The blade fatigue life prediction model based on Walker's crack propagation formula and Haddad's effective crack length provided by this invention is applied to the curves of fatigue life prediction with the maximum stress of cyclic load for TC4 and TC11 titanium alloys, respectively. Figure 6 The blade fatigue life prediction model based on Walker's crack propagation formula and Haddad's effective crack length provided by this invention is used to predict the life versus the test life curves of TC4 and TC11 titanium alloys, respectively. Figure 7 The curve showing the relationship between the small crack propagation length and the number of load cycles in TC4 titanium alloy predicted by the blade fatigue life prediction model based on the Walker crack propagation formula and Haddad effective crack length provided by this invention. Figure 8 The final blade fatigue life prediction model provided by this invention is applied to the fatigue life and maximum stress curves predicted for TC4 titanium alloy and TC11 titanium alloy, respectively. Figure 9 The final blade fatigue life prediction model provided by this invention is applied to the curves of predicted life versus test life for TC4 titanium alloy and TC11 titanium alloy, respectively. Figure 10 The final blade fatigue life prediction model provided by this invention predicts the relationship between the small crack propagation length and the number of load cycles in TC4 titanium alloy. Figure 11 This invention provides Abaqus analysis boundary condition settings and stress cloud diagrams. Figure 12 A schematic diagram of the three-dimensional model of the blade after the insertion of a crack, provided by the present invention; Figure 13 This is a schematic diagram illustrating the parameter changes and lifetime calculation during crack propagation provided by the present invention. Figure 14 This is a schematic diagram of an embodiment of the gas turbine blade life prediction device provided by the present invention. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0042] In the description of the embodiments of the present invention, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0043] The terms "first," "second," etc., used in the embodiments of this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a technical feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0044] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0045] This invention provides a method and apparatus for predicting the entire lifespan of gas turbine blades, which will be described below.

[0046] like Figure 1 As shown, in a first aspect, the present invention provides a method for predicting the entire lifespan of gas turbine blades, comprising: S101. Integrate the Chaboche model, with the integration range from 0 to 1 for the damage variable, to obtain the remaining lifetime expression.

[0047] In some embodiments of the present invention, the chaboche model includes: (1) In equation (1), Represents the loss variable. This indicates that no damage has begun. This indicates the end of the material's remaining lifespan. Indicates the number of loops. Indicates the stress amplitude of cyclic load. This represents the average stress under cyclic loading. , , Indicates parameters related to materials.

[0048] Among them, parameters Determined by the following formula: (2) In equation (2), the symbol Indicates if but ,like but ; Indicates material parameters, The maximum stress; This refers to tensile strength.

[0049] parameter The fatigue limit under asymmetric loading is determined by the following formula: (3) In equation (3), This represents the fatigue limit under symmetrical cyclic loading.

[0050] According to equation (1), we can obtain: (4) right Perform by arrive Integrating this equation yields the remaining lifetime formula: (5) In equation (5), Indicates remaining lifespan.

[0051] It should be noted that when the materials are intact, When the material fails, Therefore, it is easy to know the damage variable. The process from 0 to 1 is the remaining life of the material.

[0052] S102. By introducing the elastic strain weighting factor and the plastic strain weighting factor into the average stress term in the remaining life expression, a nonlinear damage formula is obtained, where the elastic strain weighting factor is the proportion of elastic strain in the total strain, and the plastic strain weighting factor is the proportion of plastic strain in the total strain.

[0053] like Figure 2In some embodiments of the present invention, step S102 includes: S201. Based on the MC model, the expressions for the elastic strain weighting factor and the plastic strain weighting factor are introduced, and the fatigue correction factor is obtained by combining them.

[0054] Specifically, the expressions for the elastic strain weighting factor and the plastic strain weighting factor include: (6) In equation (6), This represents the plastic strain weighting factor. This represents the elastic strain weighting factor. Represents the plastic strain modulus. Represents the elastic strain modulus. Indicates stress amplitude. Indicates the elastic modulus. Indicates the cyclic strength coefficient. Indicates the cyclic strain hardening index; The expressions for the MC model include: (7) In equation (7), The fatigue strength coefficient, The fatigue strength index. The fatigue ductility coefficient, It is the fatigue ductility index.

[0055] By combining the expressions for the MC model, the elastic strain weighting factor, and the plastic strain weighting factor, and simplifying them, we obtain the fatigue correction factor used to define the elastic-plastic strain weighting effect, expressed as: (8) In equation (8), This represents the fatigue correction factor. Indicates constant coefficients.

[0056] S202. Substituting the fatigue correction factor into the mean stress term of the remaining life expression, we obtain the nonlinear damage formula: (9) After considering the mean stress effect under asymmetric loading and the local plastic deformation in the high-stress zone, the improved Chaboche model is applied to predict fatigue life. The relationship between fatigue life and maximum stress is as follows: Figure 3 As shown. Figure 4 To compare the predicted and experimental values ​​of the improved Chaboche model, Table 1 shows the Chaboche model parameters for titanium alloys.

[0057] Table 1. Parameters of Titanium Alloy Chaboche

[0058] Depend on Figure 3 (Left: Predicted data for TC4 titanium alloy; Right: Predicted data for TC11 titanium alloy) It can be seen that in the high-stress region of asymmetric loading, the improved model matches the experimental data better than the original Chaboche model. Figure 4 (Left: TC4 titanium alloy prediction data; Right: TC11 titanium alloy prediction data) It can be seen that when... R When the coefficient of performance (COP) is 0.1, for TC4 titanium alloy, 62.5% of the predicted lifetimes from the improved Chaboche model fall within a dispersion band twice the experimental lifetime, and 75% fall within a dispersion band five times the experimental lifetime; for TC11 titanium alloy, 43.5% of the predicted lifetimes from the improved Chaboche model fall within a dispersion band twice the experimental lifetime, and 67.4% fall within a dispersion band five times the experimental lifetime. R When the value is 0.5, for TC4 titanium alloy, 47.5% of the predicted lifetimes of the improved Chaboche model are distributed within the dispersion band of twice the test lifetime, and 87.5% of the predicted lifetimes of the improved Chaboche model are distributed within the dispersion band of five times the test lifetime; for TC11 titanium alloy, 26.1% of the predicted lifetimes of the improved Chaboche model are distributed within the dispersion band of twice the test lifetime, and 47.8% of the predicted lifetimes of the improved Chaboche model are distributed within the dispersion band of five times the test lifetime.

[0059] Compared with the original Chaboche model, the improved Chaboche model, which considers the average stress effect under asymmetric loading and the influence of local plastic deformation in high-stress areas, has better prediction accuracy.

[0060] S103. By introducing Haddad's effective crack length into the Walker crack propagation expression, the crack propagation formula is obtained.

[0061] It should be noted that fatigue failure of blade materials involves three stages: crack initiation, stable propagation, and instantaneous fracture. During the instantaneous fracture stage, crack propagation is extremely rapid, and the lifespan of this stage is typically not considered.

[0062] The stress intensity factor range is a key parameter for fatigue crack propagation. During the steady-state propagation stage, the relationship between the crack propagation rate and the stress intensity factor range is as follows: (10) In equation (10), and All of these are material-related parameters; The range of stress intensity factors can be determined by the following formula: (11) In equation (11), This is a shape boundary correction factor; The crack size; This represents the stress range.

[0063] Extensive experimental studies on crack propagation have demonstrated that stress ratio has a significant impact on crack propagation rate. Therefore, Walker further investigated the effect of stress ratio on crack propagation rate and proposed a new crack propagation law (i.e., the Walker crack propagation relation), the expression of which is: (12) In equation (12), Indicates the crack size. , and All of these are material-related parameters; Indicates the stress ratio.

[0064] The propagation of small cracks is complex, and its propagation law differs from that of long cracks. The main difference lies in the fact that, under the same stress intensity factor range, the propagation rate of small cracks is significantly faster than that of long cracks. Therefore, Haddad et al. defined the concept of effective crack length for calculating the stress intensity factor of small cracks: (13) Therefore, Haddad's effective crack length By introducing the crack size term into the stress intensity factor expression, we obtain the crack propagation formula shown below: (14) Furthermore, integrating equation (14), the integration range is from the initial size of the crack. To the end size The expression for crack propagation life is obtained as follows: (15) Substitute equation (9) into the left side of equation (14), and then define the integration interval. Divided into equal parts m each interval ,get: (16) It should be noted that it is generally believed that when At this time, the small crack propagation life can be approximated. This refers to the fatigue life of materials. .

[0065] whenm Large enough, i.e., interval Small enough, assuming In the interval If is a constant, then: (17) The final solution yields the effective crack length. for: (18) The expression for the integrated life prediction model is obtained by refining the formula as follows: (19) In equation (19), This represents the predicted fatigue life of the blade.

[0066] Taking a smooth bar specimen as an example, the shape boundary correction factor for the smooth bar specimen is: (20) In equation (20), d 0 represents the diameter of the bar. a The crack length is given.

[0067] Depend on Figure 5 (Left: Predicted data for TC4 titanium alloy; Right: Predicted data for TC11 titanium alloy) It can be seen that under asymmetric loading, the fatigue life predicted by the comprehensive prediction model varies with the maximum stress of the cyclic load, consistent with the distribution of experimental data. From... Figure 6 (Left: TC4 titanium alloy prediction data; Right: TC11 titanium alloy prediction data) It can be seen that when... R When the coefficient of performance (COP) is 0.1, for TC4 titanium alloy, 62.5% of the comprehensive model predicted lifetime falls within a dispersion band twice the experimental lifetime, and 75% falls within a dispersion band five times the experimental lifetime; for TC11 titanium alloy, 48.8% of the comprehensive model predicted lifetime falls within a dispersion band twice the experimental lifetime, and 67.4% falls within a dispersion band five times the experimental lifetime. R When the coefficient of performance is 0.5, for TC4 titanium alloy, 47.5% of the comprehensive model predicted lifetime is distributed within a dispersion band of 2 times the test lifetime, and 87.5% of the comprehensive model predicted lifetime is distributed within a dispersion band of 5 times the test lifetime.

[0068] In addition to predicting the overall fatigue life of the specimen, the comprehensive fatigue life prediction model can also predict the small crack propagation life during the crack initiation stage. The comprehensive model was used to predict the small crack propagation life of TC4 titanium alloy specimens at stress ratios of 0.1 and 0.3, for example... Figure 7(The left side shows the predicted data when the stress ratio is 0.1, and the right side shows the predicted data when the stress ratio is 0.3.) Under asymmetric loading, the prediction model of the small crack propagation law of the TC4 titanium alloy single-sided notch tensile specimen is in good agreement with the distribution of experimental data, indicating that the comprehensive model is suitable for predicting the small crack propagation life of TC4 titanium alloy under asymmetric cyclic loading.

[0069] S104. The crack propagation formula is modified based on the crack closure coefficient. The crack closure coefficient is determined based on the crack opening stress, which is determined based on a preset empirical formula and a shape boundary correction factor.

[0070] It should be noted that the physical quantity affecting the propagation of small cracks exhibiting closure phenomena is the effective stress intensity factor range, and its expression is: (twenty one) In equation (21), Indicates the effective stress intensity factor. Represents the maximum stress intensity factor. The stress intensity factor represents the stress intensity factor at which a crack opens. This represents the crack closure coefficient.

[0071] Furthermore, a crack closure factor is constructed based on the relationship between stress and stress intensity factor. The expression: (twenty two) In equation (22), Indicates the maximum stress. Indicates minimum stress. This represents the crack opening stress. Indicates the stress ratio.

[0072] Among them, crack opening stress It is obtained from empirical formulas, which include: (twenty three) In equation (23), , , , Determined by the following formula: (twenty four) In equation (24), Indicates the shape boundary correction factor; Indicates the stress state constraint coefficient. , Indicates Poisson's ratio; This represents rheological stress.

[0073] Among them, rheological stress The expression is: (25) In equation (25), For tensile strength, Yield strength; By replacing the stress intensity factor in the crack propagation formula with the effective stress intensity factor determined based on the crack closure coefficient, we obtain the modified crack propagation formula: (26).

[0074] S105, combined with the modified crack propagation formula and the nonlinear damage formula, yields the final blade fatigue life prediction model used to calculate the final blade fatigue life based on material parameters.

[0075] Specifically, the modified crack propagation formula is integrated, and the integration range is from the initial size of the crack. To the end size The expression for crack propagation life is obtained as follows: (27) Substituting the nonlinear loss formula into the left-hand side of the expression for crack propagation life, the integration interval is... Divided into equal parts m each interval We obtain the following simultaneous equations: (28) when m Large enough, assuming In the interval Since is a constant, solving the simultaneous equations yields: (29) The final solution yields the effective crack length. for: (30) The expression for the blade fatigue life prediction model is obtained by refining the formula as follows: (31) In equation (29), This represents the predicted fatigue life of the blade.

[0076] A comprehensive fatigue life prediction model considering the closure effect was applied to predict the fatigue life of smooth TC4 and TC11 titanium alloy bar specimens under asymmetric loading, and a comparative analysis was conducted. The relationship between fatigue life and maximum stress is shown below. Figure 8 (Left: Predicted data for TC4 titanium alloy; Right: Predicted data for TC11 titanium alloy) The comparison between test life and predicted life is shown below.Figure 9 As shown. By Figure 9 (Left: TC4 titanium alloy prediction data; Right: TC11 titanium alloy prediction data) It can be seen that when... R When the coefficient of performance (COP) is 0.1, for TC4 titanium alloy, 62.5% of the comprehensive model predicted lifetime falls within a dispersion band twice the experimental lifetime, and 75% falls within a dispersion band five times the experimental lifetime; for TC11 titanium alloy, 48.8% of the comprehensive model predicted lifetime falls within a dispersion band twice the experimental lifetime, and 67.4% falls within a dispersion band five times the experimental lifetime. R When the coefficient of performance is 0.5, for TC4 titanium alloy, 47.5% of the comprehensive model predicted lifetime is distributed within a dispersion band of 2 times the test lifetime, and 87.5% of the comprehensive model predicted lifetime is distributed within a dispersion band of 5 times the test lifetime.

[0077] A comprehensive fatigue life model considering the closure effect was applied to predict the small crack propagation life of TC4 titanium alloy single-sided notched tensile specimens at stress ratios of 0.1 and 0.3, with experimental values ​​compared. The relationship between the predicted small crack propagation length and the number of cycles is shown in the comprehensive model considering the closure effect. Figure 10 (The left image shows predicted data when the stress ratio is 0.1, and the right image shows predicted data when the stress ratio is 0.3.) Figure 10 It is evident that, under asymmetric loading, the comprehensive prediction model considering the closure effect predicts the small crack propagation law of the TC4 titanium alloy single-sided notch tensile specimen in good agreement with the experimental data distribution, and the prediction accuracy is high. This indicates that the comprehensive model considering the closure effect is suitable for the study of small crack propagation under asymmetric cyclic loading.

[0078] In summary, compared with existing technologies, the present invention provides a method for predicting the full life of gas turbine blades. This method incorporates the Chaboche model with an elastoplastic factor to correct the problem that local plastic deformation occurs under high stress during asymmetric loading, altering the cyclic stress in the fatigue damage accumulation process. Combined with the crack propagation formula, the effective crack length proposed by Haddad theory is introduced to establish a preliminary comprehensive life model. Finally, considering the crack closure phenomenon in actual conditions, a closure coefficient is proposed for correction, establishing a comprehensive life model that considers the crack closure effect. This effectively solves the technical problems of existing technologies that neither consider the impact of plastic strain generated under high stress on fatigue life, nor simultaneously predict the full life from crack initiation to fracture and the remaining life during the macroscopic crack propagation stage, leading to excessively high maintenance costs.

[0079] Specifically, the present invention also has the following advantages: (1) Considering the average stress effect and the influence of plastic deformation in the high stress zone under asymmetric loading, the stress ratio factor and the elastic-plastic fatigue correction factor are introduced to improve the Chaboche model. The improved Chaboche model is more consistent with the experimental data and has higher prediction accuracy.

[0080] (2) Based on the theory of effective crack length, combined with the Walker crack propagation formula and the improved Chaboche model, a fatigue life prediction model suitable for asymmetric loading was established. The application analysis of smooth titanium alloy specimens under asymmetric cyclic loading confirmed that the comprehensive prediction model is suitable for predicting the fatigue life of titanium alloys under asymmetric cyclic loading. In the high stress level region of asymmetric loading, the prediction accuracy of the comprehensive prediction model is higher than that of the improved Chaboche model. The application analysis of crack propagation in TC4 titanium alloy single-sided notched tensile specimens showed that the comprehensive prediction model is suitable for calculating the small crack propagation life under asymmetric cyclic loading, and it agrees well with the experimental data.

[0081] (3) Under the same cyclic load, the occurrence of small crack closure phenomenon reduces the effective driving force for crack propagation. Therefore, the fatigue life prediction value obtained by the comprehensive fatigue life prediction model considering the closure effect is greater than the prediction value of the comprehensive model that does not consider the closure effect, and is more accurate.

[0082] (4) The proposed comprehensive life model considering crack closure effect provides a theoretical basis for damage analysis and life prediction of TC4 titanium alloy compressor blades.

[0083] S106, Based on the Abaqus analysis environment.

[0084] S107. Load the preset 3D model of the blade into franc3d and set the material parameters of the blade.

[0085] S108. Set unilateral constraints.

[0086] Specifically, such as Figure 11 As shown, the rotational speed is set to 628.319 rad / s, and the aerodynamic load is introduced, as follows: Figure 11 (a) To set fixed constraints, Figure 11 (b) represents the position and rotational speed. The aerodynamic load is calculated and imported according to actual needs.

[0087] S109. Insert cracks into the three-dimensional model of the blade.

[0088] Specifically, such as Figure 12 As shown on the left, this invention is illustrated by taking an example where a crack with a width of 10mm and a depth of 1mm is set at a position 10% from the bottom of the blade, along the X-axis at a width of 40%, with a twist angle of 41°. Figure 12 right.

[0089] S110. Calculate crack propagation and obtain blade working stress intensity factor and fatigue life data.

[0090] like Figure 13 As shown, the situation after the crack propagation stops in 15 steps is listed, as well as the changes in the three stress intensity factors and J integral during the propagation process.

[0091] S111. Substitute the blade working stress intensity factor and fatigue life data into the blade fatigue life prediction model to obtain the blade fatigue life.

[0092] Specifically, franc3d uses fracture mechanics to predict fatigue life, i.e. the classic Paris criterion. This invention modifies it by using the blade fatigue life prediction model constructed above.

[0093] The life prediction formula of the Paris criterion is: (32) (33) We can obtain: (34) The comprehensive lifetime prediction model of this invention, which considers the closure effect, is as follows: (35) (36) In the At that time, the extended life was considered to be the fatigue life of the blade, therefore: (37) (38) Therefore, the fatigue life is calculated based on franc3d. The fatigue life considering stress ratio and crack closure effect can then be obtained.

[0094] In summary, this invention also provides a method for joint simulation combining franc3d and abaqus. Taking a certain type of blade as an example, simulation was performed, and the basic life prediction model in franc3d was modified. This provides a new method for damage analysis and life prediction of TC4 titanium alloy compressor blades.

[0095] like Figure 14 Secondly, the present invention also provides a gas turbine blade life prediction device 140, comprising: The life prediction model establishment module 1401 is used to integrate the Chaboche model, with the integration range from 0 to 1 for the damage variable, to obtain the remaining life expression. Elastic strain weighting factors and plastic strain weighting factors are introduced into the average stress term in the remaining life expression to obtain a nonlinear damage formula, where the elastic strain weighting factor is the proportion of elastic strain in the total strain, and the plastic strain weighting factor is the proportion of plastic strain in the total strain. Haddad's effective crack length is introduced into the Walker crack propagation expression to obtain a crack propagation formula. The crack propagation formula is modified based on the crack closure coefficient, which is determined according to the crack opening stress, and the crack opening stress is determined according to a preset empirical formula and a shape boundary correction factor. The modified crack propagation formula and the nonlinear damage formula are combined to obtain the final blade fatigue life prediction model used to calculate the final blade fatigue life based on material parameters. The life prediction module 1402 is used in the Abaqus analysis environment to load a preset three-dimensional blade model in Franc3D and set the blade material parameters; set unilateral constraints; insert cracks in the three-dimensional blade model; calculate the crack propagation; obtain the blade working stress intensity factor and fatigue life data; and substitute the blade working stress intensity factor and fatigue life data into the blade fatigue life prediction model to obtain the fatigue life of the blade.

[0096] The above provides a detailed description of the method and apparatus for predicting the full life of gas turbine blades provided by the present invention. Specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for predicting the entire lifespan of gas turbine blades, characterized in that, include: By integrating the Chaboche model, with the integration range from 0 to 1 for the damage variable, the remaining lifetime expression is obtained. By introducing the elastic strain weighting factor and the plastic strain weighting factor into the average stress term in the remaining life expression, a nonlinear damage formula is obtained, wherein the elastic strain weighting factor is the proportion of elastic strain in the total strain, and the plastic strain weighting factor is the proportion of plastic strain in the total strain. By incorporating Haddad's effective crack length into the Walker crack propagation expression, we obtain the crack propagation formula. The crack propagation formula is modified based on the crack closure coefficient, which is determined according to the crack opening stress, and the crack opening stress is determined according to a preset empirical formula and a shape boundary correction factor. By combining the modified crack propagation formula and the nonlinear damage formula, the final blade fatigue life prediction model is obtained, which is used to calculate the final blade fatigue life based on material parameters. Based on the Abaqus analysis environment; Load the preset 3D blade model into Franc3D and set the blade's material parameters; Set unilateral constraints; Insert a crack into the three-dimensional model of the blade; Calculate crack propagation and obtain blade working stress intensity factor and fatigue life data; The blade's working stress intensity factor and fatigue life data are substituted into the blade fatigue life prediction model to obtain the blade's fatigue life.

2. The method for predicting the entire lifespan of gas turbine blades according to claim 1, characterized in that, The chaboche model includes: In the formula, Represents the loss variable. This indicates that no damage has begun. This indicates the end of the material's remaining lifespan. Indicates the number of loops. Indicates the stress amplitude of cyclic load. This represents the average stress under cyclic loading. , , Indicates parameters related to materials; parameter Determined by the following formula: In the formula, the symbol Indicates if but ,like but ; Indicates material parameters, The maximum stress; Tensile strength; parameter The fatigue limit under asymmetric loading is determined by the following formula: In the formula, The fatigue limit under symmetrical cyclic loading; right Integrating, we obtain the remaining lifetime formula: In the formula, Indicates remaining lifespan.

3. The method for predicting the entire lifespan of gas turbine blades according to claim 2, characterized in that, The step of incorporating the elastic strain weighting factor and the plastic strain weighting factor into the average stress term in the remaining life expression to obtain the nonlinear damage formula includes: Based on the MC model, expressions for elastic strain weighting factors and plastic strain weighting factors are introduced, and the fatigue correction factor is obtained by combining them simultaneously. Substituting the fatigue correction factor into the mean stress term of the remaining life expression yields the nonlinear damage formula.

4. The method for predicting the full lifespan of gas turbine blades according to claim 3, characterized in that, The expressions for the elastic strain weighting factor and the plastic strain weighting factor include: In the formula, This represents the plastic strain weighting factor. This represents the elastic strain weighting factor. Represents the plastic strain modulus. Represents the elastic strain modulus. Indicates stress amplitude, Indicates the elastic modulus. Indicates the cyclic strength coefficient. Indicates the cyclic strain hardening index; The expressions of the MC model include: In the formula, The fatigue strength coefficient, The fatigue strength index, The fatigue ductility coefficient, It is the fatigue ductility index; Combining the expressions for the MC model with those for the elastic strain weighting factor and the plastic strain weighting factor, we obtain the fatigue correction factor used to define the elastic-plastic strain weighting effect, expressed as: In the formula, This represents the fatigue correction factor. Indicates constant coefficients.

5. The method for predicting the full lifespan of gas turbine blades according to claim 4, characterized in that, The nonlinear loss formula includes: 。 6. The method for predicting the entire lifespan of gas turbine blades according to claim 1, characterized in that, The Walker crack propagation equation is as follows: In the formula, Indicates the crack size. , and All of these are material-related parameters; Indicates the stress ratio; The stress intensity factor can be determined by the following formula: In the formula, This is a shape boundary correction factor; The crack size; The stress range; The method of incorporating Haddad's effective crack length into the Walker crack propagation expression to obtain the crack propagation formula includes: Introducing Haddad's effective crack length into the crack size term of the stress intensity factor expression, we obtain the crack propagation formula shown below: In the formula, Indicates the effective crack length.

7. The method for predicting the full lifespan of gas turbine blades according to claim 6, characterized in that, The modification of the crack propagation formula based on the crack closure coefficient includes: The effective stress intensity factor, taking into account the crack closure effect, is defined as follows: In the formula, Indicates the effective stress intensity factor. Represents the maximum stress intensity factor. The stress intensity factor represents the stress intensity factor at which a crack opens. Indicates the crack closure factor; The expression for the crack closure coefficient is constructed based on the relationship between stress and stress intensity factor: In the formula, Indicates the maximum stress. Indicates minimum stress. This represents the crack opening stress. Indicates the stress ratio; Among them, crack opening stress It is obtained from empirical formulas, which include: In the formula, , , , Determined by the following formula: In the formula, Indicates the shape boundary correction factor; Indicates the stress state constraint coefficient. , Indicates Poisson's ratio; Represents rheological stress; Wherein, the rheological stress The expression is: In the formula, For tensile strength, Yield strength; By replacing the stress intensity factor in the crack propagation formula with the effective stress intensity factor determined based on the crack closure coefficient, we obtain the modified crack propagation formula: 。 8. The method for predicting the full lifespan of gas turbine blades according to any one of claims 5 or 7, characterized in that, The combined modified crack propagation formula and nonlinear damage formula are used to derive the final blade fatigue life prediction model for calculating blade fatigue life based on material parameters, including: Integrating the modified crack propagation formula over a range from the initial crack size to the final crack size, we obtain the expression for the crack propagation life: Substituting the nonlinear loss formula into the left side of the expression for crack propagation life, the integration interval is... Divided into equal parts m each interval We obtain the following simultaneous equations: when m Large enough, assuming In the interval Since is a constant, solving the simultaneous equations yields: The final solution yields the effective crack length. for: The expression for the blade fatigue life prediction model is obtained by refining the formula as follows: In the formula, This represents the predicted fatigue life of the blade.

9. The method for predicting blade fatigue life according to claim 1, characterized in that, The unilateral constraints include: tenon fixing constraints, blade rotation speed, and aerodynamic loads.

10. A device for predicting the entire lifespan of a gas turbine blade, characterized in that, include: The life prediction model building module is used to integrate the Chaboche model, with the integration range from 0 to 1 for the damage variable, to obtain the remaining life expression. Elastic strain weighting factors and plastic strain weighting factors are introduced into the average stress term of the remaining life expression to obtain a nonlinear damage formula, where the elastic strain weighting factor is the proportion of elastic strain in the total strain, and the plastic strain weighting factor is the proportion of plastic strain in the total strain. Haddad's effective crack length is introduced into the Walker crack propagation expression to obtain the crack propagation formula. The crack propagation formula is modified based on the crack closure coefficient, which is determined according to the crack opening stress, and the crack opening stress is determined according to a preset empirical formula and a shape boundary correction factor. The modified crack propagation formula and the nonlinear damage formula are combined to obtain the final blade fatigue life prediction model used to calculate the final blade fatigue life based on material parameters. The life prediction module is used in the Abaqus analysis environment. It loads a preset three-dimensional blade model into Franc3D and sets the blade's material parameters. It sets unilateral constraints, inserts cracks into the three-dimensional blade model, calculates crack propagation, and obtains the blade's working stress intensity factor and fatigue life data. It substitutes the blade's working stress intensity factor and fatigue life data into the blade fatigue life prediction model to obtain the blade's fatigue life.

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