Blade gap type foreign object damage available limit prediction method based on worst gap method

Abstract

The invention discloses a blade notch type foreign object damage available limit prediction method based on a worst notch method. The method comprises the following steps: acquiring a stress ratio and a stress amplitude of a target position; obtaining the high cycle fatigue strength and the crack threshold value of the blade material; gapped foreign object damages with different depths are respectively inserted into target positions, and blade stress distribution is obtained through simulation; respectively inserting cracks with different lengths at the maximum stress position of the notch type foreign object damage, and calculating to obtain the maximum stress intensity factor of the tip of the crack; fitting the maximum stress intensity factor of the crack tip and the crack length, and substituting a fitting function into the worst-nick method model to obtain a change relation of the non-expansion threshold load along with the crack length; and the maximum value of the non-expansion threshold load and the notch type foreign object damage depth are fitted, the fitting function is the allowable load boundary of the target position, and the available limit of the blade after being damaged by the notch type foreign object is determined. According to the invention, the specific value of the damage available limit of the notched foreign object can be accurately given.

Description

Technical Field

[0001] The invention belongs to the technical field of foreign object damage tolerance design and maintenance of aircraft engine blades, and in particular relates to a method for predicting the available limit of blade notch-type foreign object damage based on a worst notch method. Background Art

[0002] Foreign object damage is one of the most common failures of aircraft engines. During takeoff, landing and low-altitude flight, aircraft engines will inevitably inhale hard objects such as stones, gravel, metal, and debris. These hard objects will impact the high-speed rotating blades, causing damage such as notches, pits, tears, scratches, and material loss. When the blades are damaged by foreign objects, severe stress concentration and residual stress will occur, which will in turn cause high-cycle fatigue failure of the blades, causing the fatigue strength of the blades to decline and the fatigue life to shorten, which will endanger the safety and economy of the aircraft engine. Therefore, it is necessary to predict and evaluate the usable limit of the damaged blades.

[0003] In response to the problem of foreign object damage to aircraft engine blades, engine manufacturers usually provide detailed maintenance manuals to guide users on how to deal with foreign object damage to blades during actual use and maintenance. Engine manufacturers provide reference specifications such as usable limit, maximum continued service limit (cycles / hour), repairable limit and repair standard in the maintenance manual. Among them, the usable limit is an important reference for measuring whether the blade can continue to serve without repair after being damaged.

[0004] At present, engine manufacturers have not developed a standardized process for determining the usable limit of blades after foreign object damage. For newly designed engine blades, the formulation of their usable limit after foreign object damage often relies on the revision of the maintenance manual, field inspection conditions, and maintenance experience of existing engines, and lacks a standardized process. However, with the continuous development and improvement of aircraft engine blade design technology, this empirical speculation method is no longer suitable for the formulation of the usable limit of foreign object damage for new engine blades. Therefore, it is necessary to study and develop a prediction method for the usable limit of foreign object damage for blades.

[0005] The invention patent with application publication number CN109374449A discloses a method for determining the usable limit of crack-type hard object damage on the leading and trailing edges of blades considering high and low cycle fatigue. First, high cycle fatigue loads and low cycle fatigue loads are extracted from the high and low cycle composite loads borne by the blade, and a series of crack-type hard object damage crack non-extension isovalue curves related to stress ratios under high cycle fatigue loads and low cycle fatigue loads are established. Then, the static stress and dynamic stress at each point on the leading and trailing edges of the blade are determined by the finite element analysis method. Finally, the crack size corresponding to the isovalue curve is determined by comparing the positions of the static stress and dynamic stress in the crack non-extension isovalue curve, which is the usable limit of crack-type hard object damage at the leading and trailing edges of the blade. This technical solution is aimed at predicting the usable limit of blades with crack-type foreign object damage, and is not suitable for predicting the usable limit of blades with notch-type foreign object damage. If this technical solution is directly used to predict the usable limit of blades with notch-type foreign object damage, the prediction result is relatively conservative, and blades that can continue to serve may be excluded, resulting in a waste of resources.

[0006] The invention patent with application publication number CN112733398A discloses a method for determining the repair-free limit of pit-type hard object impact damage, including: extracting the steady-state stress of the blade and at least the first six modal vibration stresses; determining the most dangerous shape of pit-type hard object damage; adding pit-type damage at a specified position on the blade basin or blade back, calculating the stress distribution at the bottom of the pit damage, and calculating the range of stress intensity factors at the bottom of the pit damage under steady-state stress and vibration stress; establishing a pit-type damage crack non-extension model related to stress ratio under high-cycle fatigue load, and obtaining the repair-free limit of pit-type damage at a specified position; repeating the above operations until the repair-free limit of pit-type damage at all positions is obtained. This technical solution uses a general weight function method to predict the repair-free limit of blades with pit-type hard object damage. If this technical solution is directly used to predict the usable limit of blades with notch-type foreign object damage, the prediction result is relatively dangerous, and an incorrect prediction may be made for blades that cannot continue to serve, thereby affecting flight safety.

[0007] Based on the above analysis, in order to make up for the lack of available limit prediction methods for foreign object damage of aircraft engine blades, it is urgent to develop an available limit prediction method for blade notch type foreign object damage based on the worst notch method to obtain more accurate prediction results. Summary of the invention

[0008] In order to solve the problems existing in the prior art, the present invention provides a method for predicting the available limit of blade notch-type foreign object damage based on the worst notch method. The prediction method comprises the following steps in chronological order:

[0009] Step 1: using the blade material to make a uniaxial tensile specimen, and performing a uniaxial tensile test on the uniaxial tensile specimen to obtain the elastic modulus of the blade material;

[0010] Step 2: Use finite element simulation software to establish a blade model, and apply load to the blade model for dynamic simulation to obtain dynamic simulation results; according to the obtained dynamic simulation results, calculate the stress ratio and stress amplitude of the target position of the notch-type foreign object damage;

[0011] Step 3: Use blade materials to make high cycle fatigue specimens and fatigue crack extension specimens, and perform high cycle fatigue tests and fatigue crack extension tests on the high cycle fatigue specimens and fatigue crack extension specimens according to the determined stress ratio of the target position of notch-type foreign object damage, so as to obtain the high cycle fatigue strength and crack threshold value of the blade material;

[0012] Step 4: In the blade model, a number of notch-type foreign object damages of the same notch type and different depths are inserted at the determined notch-type foreign object damage target positions to obtain a set of blade models containing the same notch-type foreign object damage target positions, the same notch type, and notch-type foreign object damages of different depths, and loads are applied to the blade models for dynamic simulation to obtain the stress distribution of the blade after the notch-type foreign object damages of the same notch type and different depths are inserted at the same notch-type foreign object damage target positions;

[0013] Step 5: In each blade model containing the same notch-type foreign object damage target position, the same notch type, and notch-type foreign object damage of different depths, a number of cracks of the same crack type and different lengths are respectively inserted at the maximum stress of the inserted notch-type foreign object damage to obtain a group of blade models containing the same depth of notch-type foreign object damage, the same crack type, and cracks of different lengths, and the maximum stress intensity factors of the same crack type and different lengths at the crack tip under the same depth of notch-type foreign object damage are respectively calculated;

[0014] Step 6: In each blade model with the same notch-type foreign object damage target position, the same notch type, and different depths of notch-type foreign object damage, select a suitable functional relationship to fit the maximum stress intensity factor of the crack tip with the same crack type and different lengths and the corresponding crack length, and obtain the fitting function between the maximum stress intensity factor of the crack tip and the crack length under the notch-type foreign object damage with the depth;

[0015] Step 7: In each blade model containing the same notch-type foreign object damage target position, the same notch type, and different depths of notch-type foreign object damage, substitute the obtained fitting function between the maximum stress intensity factor at the crack tip and the crack length under the notch-type foreign object damage of the depth into the worst notch method model, obtain the relationship between the non-extension threshold load and the crack length under the notch-type foreign object damage of the depth, and determine the maximum value of the non-extension threshold load under the notch-type foreign object damage of the depth;

[0016] Step 8: In the obtained blade model containing the same notch-type foreign object damage target position, the same notch type, and notch-type foreign object damage of different depths, select a suitable functional relationship to fit the maximum value of the non-expansion threshold load and the corresponding notch-type foreign object damage depth under the same notch type and notch-type foreign object damage of different depths, and obtain a fitting function between the maximum value of the non-expansion threshold load and the notch-type foreign object damage depth under the notch-type foreign object damage target position. The fitting function is the allowable load boundary of the blade under the notch-type foreign object damage target position and its stress ratio;

[0017] Step nine: Based on the high cycle fatigue stress requirements and allowable load boundaries of the blade at the notch type foreign object damage target position, the specific value of the notch type foreign object damage usable limit of the blade at the notch type foreign object damage target position can be determined.

[0018] Preferably, in step 2, the finite element simulation software is Abaqus and / or Ansys; a load is applied to the blade model, and the load is the constraint and load of the blade under actual working conditions or the constraint and load under test conditions.

[0019] In any of the above schemes, preferably, in step four, at least five notch-type foreign object damages of the same notch type and different depths are respectively inserted at the determined target position of notch-type foreign object damage; the depth range of notch-type foreign object damage that may occur on the blade is estimated according to the type of blade, and the depths of the at least five inserted notch-type foreign object damages are uniformly distributed within the depth range; and a load is applied to the blade model, which load is the constraint and load of the blade under actual working conditions or the constraint and load under test conditions.

[0020] In any of the above schemes, it is preferred that in step four, the shapes of the at least five notch-type foreign object damages inserted are all C-shaped or all V-shaped; if a C-shaped foreign object damage is inserted, the depths of the at least five C-shaped foreign object damages inserted are different and the root curvature radius is the same; if a V-shaped foreign object damage is inserted, the depths of the at least five V-shaped foreign object damages inserted are different, the root curvature radius is the same, and the opening angle is the same.

[0021] In any of the above schemes, it is preferred that in step five, at least five cracks of the same crack type and different lengths are inserted at the maximum stress of the inserted notch-type foreign object damage; the possible crack length range of the blade is estimated based on the type of blade and the shape of the notch-type foreign object damage, and the lengths of the at least five inserted cracks are uniformly distributed within the length range; and the at least five inserted cracks of different lengths have the same geometric characteristics.

[0022] In any of the above schemes, preferably, in step six, the functional relationship can be selected from any one of a polynomial function, a linear function, an exponential function, and a logarithmic function; the fitting function between the maximum stress intensity factor at the crack tip and the crack length can also be obtained by crack extension; the fitting function between the maximum stress intensity factor at the crack tip and the crack length is ΔK(α), where,

[0023] ΔK——maximum stress intensity factor at crack tip,

[0024] α——crack length, mm.

[0025] In any of the above schemes, preferably, in step 7, the worst gap method model is in In the formula,

[0026] ΔS th (α)——Relationship between the non-extension threshold load and crack length, MPa;

[0027] ΔK th — the crack threshold of the blade material obtained by fatigue crack growth test,

[0028] Δσ——stress amplitude at the target position of notch-type foreign object damage obtained by calculation, MPa;

[0029] ΔK(α)——The fitting function between the maximum stress intensity factor at the crack tip and the crack length,

[0030] α——crack length, mm;

[0031] α 0 ——small crack parameter, mm;

[0032] ΔS——High cycle fatigue strength of blade material obtained through high cycle fatigue test, MPa;

[0033] F is the geometric correction factor for the inserted crack form, dimensionless.

[0034] In any of the above schemes, it is preferred that in step seven, when the relationship between the non-extension threshold load and the crack length takes a maximum value, if the crack length is smaller than the minimum crack length among the several cracks inserted in step five, it is necessary to reinsert the crack and perform calculations until the length range of the inserted cracks covers the crack length corresponding to the maximum value of the relationship between the non-extension threshold load and the crack length.

[0035] In any of the above schemes, preferably, in step eight, the functional relationship can be selected from any one of a polynomial function, a linear function, an exponential function, and a logarithmic function; the fitting function between the maximum value of the non-expanded threshold load and the notch-type foreign object damage depth is: In the formula,

[0036] ——maximum value of non-extended threshold load, MPa;

[0037] d——depth of notch-type foreign object damage, mm.

[0038] In any of the above schemes, preferably, the prediction method can also be used to predict the usable limit of the blade after it is damaged by pit-type foreign object damage, that is, the notch-type foreign object damage is replaced by pit-type foreign object damage; the at least five inserted pit-type foreign object damages have different depths and the same root curvature radius, and the at least five inserted cracks of different lengths are all surface semi-elliptical cracks.

[0039] In the present invention, uniaxial tensile tests, high cycle fatigue tests, fatigue crack growth tests, etc. are all carried out in accordance with relevant test specifications, the specimens used in each test are all made in accordance with relevant test specifications, and the test equipment used in each test is traditional equipment, with no special requirements for the equipment model.

[0040] The worst notch method in the present invention is a modified damage tolerance method based on the expansion and stagnation behavior of small cracks. This method first obtains a small crack expansion threshold value related to the crack size, and then establishes a functional relationship between the crack expansion threshold stress and the crack size, stress ratio, notch geometry, and crack shape to obtain the maximum value of the crack expansion threshold stress to determine the high cycle fatigue strength.

[0041] The blade notch type foreign object damage available limit prediction method based on the worst notch method of the present invention has the following beneficial effects:

[0042] (1) The present invention proposes for the first time a method based on the worst notch method to predict the usable limit of a blade after it suffers from notch-type foreign object damage, and can accurately give the allowable load boundary and specific values ​​of the usable limit after foreign object damage, thus solving the problem of the lack of a reasonable and standardized usable limit formulation process for notch-type foreign object damage.

[0043] (2) The present invention provides a reasonable and standardized usable limit prediction method for aircraft engine blades that suffer notch-type foreign object damage during use, and the prediction results are accurate, and there is no situation where the prediction results are overly conservative or dangerous.

[0044] (3) The prediction method of the present invention is also applicable to the prediction of the usable limit of a blade after it suffers pit-type foreign object damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a flow chart of a preferred embodiment of a method for predicting the available limit of blade notch type foreign object damage based on the worst notch method according to the present invention;

[0046] Figure 2 for Figure 1 A cross-sectional view of a simulated blade in the illustrated embodiment;

[0047] Figure 3 for Figure 1 A finite element model diagram of a simulated blade in the illustrated embodiment;

[0048] Figure 4 for Figure 1 Schematic diagram of notch-type foreign object damage at different insertion depths in the illustrated embodiment;

[0049] Figure 5 for Figure 1 Schematic diagram of inserting a through crack at the maximum stress of a notch-type foreign object damage with a depth of 0.4 mm in the embodiment shown, wherein: (a) a finite element model before inserting the through crack, (b) a finite element model after inserting the through crack, (c) a finite element model of the through crack;

[0050] Figure 6 for Figure 1 The relationship between the non-extending threshold load and the crack length under the 0.4mm depth notch type foreign object damage in the embodiment shown;

[0051] Figure 7 for Figure 1 Fitting results of the allowable load boundaries in the illustrated embodiment. DETAILED DESCRIPTION

[0052] In order to further understand the content of the present invention, the present invention will be described in detail below in conjunction with specific embodiments.

[0053] like Figure 1 As shown, according to a preferred embodiment of the method for predicting the available limit of blade notch type foreign object damage based on the worst notch method of the present invention, the prediction method includes the following steps in chronological order:

[0054] Step 1: using the blade material to make a uniaxial tensile specimen, and performing a uniaxial tensile test on the uniaxial tensile specimen to obtain the elastic modulus of the blade material;

[0055] Step 2: Use finite element simulation software to establish a blade model, and apply load to the blade model for dynamic simulation to obtain dynamic simulation results; according to the obtained dynamic simulation results, calculate the stress ratio and stress amplitude of the target position of the notch-type foreign object damage;

[0056] Step 3: Use blade materials to make high cycle fatigue specimens and fatigue crack extension specimens, and perform high cycle fatigue tests and fatigue crack extension tests on the high cycle fatigue specimens and fatigue crack extension specimens according to the determined stress ratio of the target position of notch-type foreign object damage, so as to obtain the high cycle fatigue strength and crack threshold value of the blade material;

[0057] Step 4: In the blade model, a number of notch-type foreign object damages of the same notch type and different depths are inserted at the determined notch-type foreign object damage target positions to obtain a set of blade models containing the same notch-type foreign object damage target positions, the same notch type, and notch-type foreign object damages of different depths, and loads are applied to the blade models for dynamic simulation to obtain the stress distribution of the blade after the notch-type foreign object damages of the same notch type and different depths are inserted at the same notch-type foreign object damage target positions;

[0058] Step 5: In each blade model containing the same notch-type foreign object damage target position, the same notch type, and notch-type foreign object damage of different depths, a number of cracks of the same crack type and different lengths are respectively inserted at the maximum stress of the inserted notch-type foreign object damage to obtain a group of blade models containing the same depth of notch-type foreign object damage, the same crack type, and cracks of different lengths, and the maximum stress intensity factors of the same crack type and different lengths at the crack tip under the same depth of notch-type foreign object damage are respectively calculated;

[0059] Step 6: In each blade model with the same notch-type foreign object damage target position, the same notch type, and different depths of notch-type foreign object damage, select a suitable functional relationship to fit the maximum stress intensity factor of the crack tip with the same crack type and different lengths and the corresponding crack length, and obtain the fitting function between the maximum stress intensity factor of the crack tip and the crack length under the notch-type foreign object damage with the depth;

[0060] Step 7: In each blade model containing the same notch-type foreign object damage target position, the same notch type, and different depths of notch-type foreign object damage, substitute the obtained fitting function between the maximum stress intensity factor at the crack tip and the crack length under the notch-type foreign object damage of the depth into the worst notch method model, obtain the relationship between the non-extension threshold load and the crack length under the notch-type foreign object damage of the depth, and determine the maximum value of the non-extension threshold load under the notch-type foreign object damage of the depth;

[0061] Step 8: In the obtained blade model containing the same notch-type foreign object damage target position, the same notch type, and notch-type foreign object damage of different depths, select a suitable functional relationship to fit the maximum value of the non-expansion threshold load and the corresponding notch-type foreign object damage depth under the same notch type and notch-type foreign object damage of different depths, and obtain a fitting function between the maximum value of the non-expansion threshold load and the notch-type foreign object damage depth under the notch-type foreign object damage target position. The fitting function is the allowable load boundary of the blade under the notch-type foreign object damage target position and its stress ratio;

[0062] Step nine: Based on the high cycle fatigue stress requirements and allowable load boundaries of the blade at the notch type foreign object damage target position, the specific value of the notch type foreign object damage usable limit of the blade at the notch type foreign object damage target position can be determined.

[0063] In step 1, the blade material is GH4169, and the elastic modulus of the blade material obtained by uniaxial tensile test is 162.7 GPa; the type of simulated blade is a straight blade, and its blade section is as follows Figure 2 shown.

[0064] In step 2, the finite element simulation software is Abaqus and / or Ansys, and the finite element model of the blade is simulated as follows: Figure 3 As shown; a load is applied to the blade model, which load is the constraint and load of the blade under actual working conditions or the constraint and load under test conditions.

[0065] In this embodiment, the applied tensile fatigue stress ratio is -1, and the stress amplitude is 1 MPa. Therefore, the stress ratio of the straight section of the blade is -1, and the stress amplitude is 2 MPa.

[0066] In step 3, when the stress ratio is -1, the high cycle fatigue strength of the GH4169 blade material is 267.74MPa (expressed as the maximum cycle stress), and the crack threshold is

[0067] In step 4, nine notch-type foreign object damages of the same notch type and different depths are inserted into the determined notch-type foreign object damage target positions. The depths of the notch-type foreign object damages are 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm and 1.2 mm, respectively. Figure 4 As shown; the possible depth range of notch-type foreign object damage of the blade is estimated according to the type of blade, and the depths of the nine inserted notch-type foreign object damages are evenly distributed within the depth range; a load is applied to the blade model, and the load is the constraint and load of the blade under actual working conditions or the constraint and load under test conditions.

[0068] In this embodiment, the shapes of the nine inserted notch-shaped foreign object injuries are all C-shaped, and the nine C-shaped foreign object injuries have different depths and the same root curvature radius.

[0069] In step five, five cracks of the same crack type and different lengths are inserted at the maximum stress of the inserted notch-type foreign object damage, and the lengths of the cracks are 0.01mm, 0.02mm, 0.03mm, 0.04mm and 0.06mm respectively. The five cracks of different lengths have the same geometric characteristics, and in this embodiment, they are all penetrating cracks. The possible crack length range of the blade is estimated according to the type of blade and the shape of the notch-type foreign object damage, and the lengths of the five inserted cracks are evenly distributed within this length range.

[0070] In this embodiment, taking the notch-type foreign object damage with a depth of 0.4 mm as an example, a through crack is inserted at the maximum stress of the notch-type foreign object damage with a depth of 0.4 mm, such as Figure 5 As shown in Table 1, (a) finite element model before insertion of penetration crack, (b) finite element model after insertion of penetration crack, (c) finite element model of penetration crack. The maximum stress intensity factors of five different lengths of crack tips under 0.4 mm deep notch type foreign object damage are calculated, as shown in Table 1.

[0071] Table 1 Maximum stress intensity factors at crack tips of different lengths under 0.4 mm deep notch-type foreign object damage

[0072]

[0073] In step 6, the functional relationship is a polynomial function; the fitting function between the maximum stress intensity factor at the crack tip and the crack length is ΔK(α), where:

[0074] ΔK——maximum stress intensity factor at crack tip,

[0075] α——crack length, mm.

[0076] In this embodiment, taking the notch-type foreign object damage with a depth of 0.4 mm as an example, the maximum stress intensity factor at the crack tip under the notch-type foreign object damage with a depth of 0.4 mm and the crack length are fitted, and the fitting function relationship obtained is ΔK 0.4 =1804.3α 3 -286.2α 2 +22.295α+0.1876.

[0077] In step 7, the worst gap method model is in

[0078] In the formula,

[0079] ΔS th (α)——Relationship between the non-extension threshold load and crack length, MPa;

[0080] ΔK th — the crack threshold of the blade material obtained by fatigue crack growth test,

[0081] Δσ——stress amplitude at the target position of notch-type foreign object damage obtained by calculation, MPa;

[0082] ΔK(α)——The fitting function between the maximum stress intensity factor at the crack tip and the crack length,

[0083] α——crack length, mm;

[0084] α 0 ——small crack parameter, mm;

[0085] ΔS——High cycle fatigue strength of blade material obtained through high cycle fatigue test, MPa;

[0086] F is the geometric correction factor for the inserted crack form, dimensionless.

[0087] When the relationship between the non-extension threshold load and the crack length reaches the maximum value, if the crack length is less than the minimum crack length of the five cracks inserted in step 5, it is necessary to reinsert the crack and perform the calculation until the length range of the inserted crack covers the crack length corresponding to the maximum value of the relationship between the non-extension threshold load and the crack length.

[0088] In this embodiment, taking the notch-type foreign object damage with a depth of 0.4 mm as an example, the relationship between the non-extending threshold load and the crack length under the notch-type foreign object damage with a depth of 0.4 mm is obtained as follows: Figure 6 The maximum values ​​of the non-extending threshold loads under nine deep notch-type foreign object damages are calculated and shown in Table 2.

[0089] Table 2 Maximum values ​​of non-extended threshold loads under notch-type foreign object damage of different depths

[0090]

[0091] In step eight, the functional relationship is a polynomial function; the fitting function between the maximum value of the unextended threshold load and the depth of the notch-type foreign object damage is: In the formula,

[0092] ——maximum value of non-extended threshold load, MPa;

[0093] d——depth of notch-type foreign object damage, mm.

[0094] The allowable load boundary obtained by fitting in this embodiment is Draw a curve like Figure 7 shown.

[0095] In step nine, taking the vibration stress not exceeding 40% of the fatigue strength as the standard, the usable limit of the blade notch-type foreign object damage is calculated to be 1.077 mm.

[0096] In this embodiment, uniaxial tensile tests, high cycle fatigue tests, fatigue crack growth tests, etc. are all carried out in accordance with relevant test specifications, the specimens used in each test are all made in accordance with relevant test specifications, and the test equipment used in each test is traditional equipment, with no special requirements for the equipment model.

[0097] The worst notch method in this embodiment is a modified damage tolerance method based on the expansion and stagnation behavior of small cracks. This method first obtains a small crack expansion threshold value related to the crack size, and then establishes a functional relationship between the crack expansion threshold stress and the crack size, stress ratio, notch geometry, and crack shape to obtain the maximum value of the crack expansion threshold stress to determine the high cycle fatigue strength.

[0098] The blade notch type foreign object damage available limit prediction method based on the worst notch method in this embodiment has the following beneficial effects:

[0099] (1) For the first time, the worst notch method is proposed to predict the usable limit of blades after notch-type foreign object damage, and the allowable load boundary and specific values ​​of the usable limit after foreign object damage can be accurately given, solving the problem of the lack of a reasonable and standardized usable limit formulation process for notch-type foreign object damage. (2) It provides a reasonable and standardized usable limit prediction method for aircraft engine blades that suffer notch-type foreign object damage during use, and the prediction results are accurate, without the situation where the prediction results are too conservative or dangerous. (3) It is also applicable to predicting the usable limit of blades after pit-type foreign object damage, that is, replacing notch-type foreign object damage with pit-type foreign object damage, and the inserted pit-type foreign object damages have different depths and the same root curvature radius, and the inserted cracks of different lengths are all surface semi-elliptical cracks.

[0100] Special note: The technical solution of the present invention involves many parameters, and the synergistic effects between the various parameters need to be comprehensively considered to obtain the beneficial effects and significant progress of the present invention. Moreover, the value ranges of the various parameters in the technical solution are obtained after a large number of experiments. For each parameter and the combination of each parameter, the inventor has recorded a large amount of experimental data. Due to space limitations, the specific experimental data will not be disclosed here.

[0101] It is not difficult for those skilled in the art to understand that the method for predicting the available limit of blade notch-type foreign object damage based on the worst notch method of the present invention includes any combination of the invention content and specific implementation methods of the above-mentioned invention specification and the various parts shown in the drawings. Due to the limited space and to make the specification concise, the various schemes composed of these combinations are not described one by one. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for predicting the available limit of blade notch-type foreign object damage based on the worst notch method, characterized by: The prediction method comprises the following steps in order: Step 1: using the blade material to make a uniaxial tensile specimen, and performing a uniaxial tensile test on the uniaxial tensile specimen to obtain the elastic modulus of the blade material; Step 2: Use finite element simulation software to establish a blade model, and apply load to the blade model for dynamic simulation to obtain dynamic simulation results; according to the obtained dynamic simulation results, calculate the stress ratio and stress amplitude of the target position of the notch-type foreign object damage; Step 3: Use blade materials to make high cycle fatigue specimens and fatigue crack extension specimens, and perform high cycle fatigue tests and fatigue crack extension tests on the high cycle fatigue specimens and fatigue crack extension specimens according to the determined stress ratio of the target position of notch-type foreign object damage, so as to obtain the high cycle fatigue strength and crack threshold value of the blade material; Step 4: In the blade model, a number of notch-type foreign object damages of the same notch type and different depths are inserted at the determined notch-type foreign object damage target positions to obtain a set of blade models containing the same notch-type foreign object damage target positions, the same notch type, and notch-type foreign object damages of different depths, and loads are applied to the blade models for dynamic simulation to obtain the stress distribution of the blade after the notch-type foreign object damages of the same notch type and different depths are inserted at the same notch-type foreign object damage target positions; Step 5: In each blade model containing the same notch-type foreign object damage target position, the same notch type, and notch-type foreign object damage of different depths, a number of cracks of the same crack type and different lengths are respectively inserted at the maximum stress of the inserted notch-type foreign object damage to obtain a group of blade models containing the same depth of notch-type foreign object damage, the same crack type, and cracks of different lengths, and the maximum stress intensity factors of the same crack type and different lengths at the crack tip under the same depth of notch-type foreign object damage are respectively calculated; Step 6: In each blade model with the same notch-type foreign object damage target position, the same notch type, and different depths of notch-type foreign object damage, select a suitable functional relationship to fit the maximum stress intensity factor of the crack tip with the same crack type and different lengths and the corresponding crack length, and obtain the fitting function between the maximum stress intensity factor of the crack tip and the crack length under the notch-type foreign object damage with the depth; Step 7: In each blade model containing the same notch-type foreign object damage target position, the same notch type, and different depths of notch-type foreign object damage, substitute the obtained fitting function between the maximum stress intensity factor at the crack tip and the crack length under the notch-type foreign object damage of the depth into the worst notch method model, obtain the relationship between the non-extension threshold load and the crack length under the notch-type foreign object damage of the depth, and determine the maximum value of the non-extension threshold load under the notch-type foreign object damage of the depth; Step 8: In the obtained blade model containing the same notch-type foreign object damage target position, the same notch type, and notch-type foreign object damage of different depths, select a suitable functional relationship to fit the maximum value of the non-expansion threshold load and the corresponding notch-type foreign object damage depth under the same notch type and notch-type foreign object damage of different depths, and obtain a fitting function between the maximum value of the non-expansion threshold load and the notch-type foreign object damage depth under the notch-type foreign object damage target position. The fitting function is the allowable load boundary of the blade under the notch-type foreign object damage target position and its stress ratio; Step nine: Based on the high cycle fatigue stress requirements and allowable load boundaries of the blade at the notch type foreign object damage target position, the specific value of the notch type foreign object damage usable limit of the blade at the notch type foreign object damage target position can be determined.

2. The method for predicting the available limit of blade notch type foreign object damage based on the worst notch method according to claim 1 is characterized in that: In step 2, the finite element simulation software is Abaqus and / or Ansys; a load is applied to the blade model, and the load is the constraint and load of the blade under actual working conditions or the constraint and load under test conditions.

3. The method for predicting the available limit of blade notch type foreign object damage based on the worst notch method according to claim 2 is characterized in that: In step four, at least five notch-type foreign object damages of the same notch type and different depths are respectively inserted at the determined target positions of notch-type foreign object damage; the possible depth range of notch-type foreign object damage on the blade is estimated according to the type of blade, and the depths of the at least five inserted notch-type foreign object damages are uniformly distributed within the depth range; and a load is applied to the blade model, which load is the constraint and load of the blade under actual working conditions or the constraint and load under test conditions.

4. The method for predicting the available limit of blade notch type foreign object damage based on the worst notch method according to claim 3 is characterized in that: In step four, the shapes of the at least five inserted notch-type foreign object damages are all C-shaped or all V-shaped; if a C-shaped foreign object damage is inserted, the depths of the at least five inserted C-shaped foreign object damages are different and the root curvature radius is the same; if a V-shaped foreign object damage is inserted, the depths of the at least five inserted V-shaped foreign object damages are different, the root curvature radius is the same, and the opening angle is the same.

5. The method for predicting the available limit of blade notch type foreign object damage based on the worst notch method according to claim 4 is characterized in that: In step five, at least five cracks of the same crack type and different lengths are inserted at the maximum stress of the inserted notch-type foreign object damage; the possible crack length range of the blade is estimated based on the type of blade and the shape of the notch-type foreign object damage, and the lengths of the at least five inserted cracks are evenly distributed within the length range; the at least five inserted cracks of different lengths have the same geometric characteristics.

6. The method for predicting the available limit of blade notch type foreign object damage based on the worst notch method according to claim 5 is characterized in that: In step six, the functional relationship can be selected from any one of a polynomial function, a linear function, an exponential function, and a logarithmic function; the fitting function between the maximum stress intensity factor at the crack tip and the crack length can also be obtained by crack extension; the fitting function between the maximum stress intensity factor at the crack tip and the crack length is ΔK(α), where, ΔK——maximum stress intensity factor at crack tip, α——crack length, mm.

7. The method for predicting the available limit of blade notch type foreign object damage based on the worst notch method according to claim 6 is characterized in that: In step 7, the worst gap method model is in In the formula, ΔS th (α)——Relationship between the non-extension threshold load and crack length, MPa; ΔK th — the crack threshold of the blade material obtained by fatigue crack growth test, Δσ——stress amplitude at the target position of notch-type foreign object damage obtained by calculation, MPa; ΔK(α)——The fitting function between the maximum stress intensity factor at the crack tip and the crack length, α——crack length, mm; α0——small crack parameter, mm; ΔS——High cycle fatigue strength of blade material obtained through high cycle fatigue test, MPa; F is the geometric correction factor for the inserted crack form, dimensionless.

8. The method for predicting the available limit of blade notch type foreign object damage based on the worst notch method according to claim 7 is characterized in that: In step seven, when the relationship between the non-extension threshold load and the crack length reaches the maximum value, if the crack length is less than the minimum crack length of the several cracks inserted in step five, it is necessary to reinsert the crack and perform the calculation until the length range of the inserted crack covers the crack length corresponding to the maximum value of the relationship between the non-extension threshold load and the crack length.

9. The method for predicting the available limit of blade notch type foreign object damage based on the worst notch method according to claim 8 is characterized in that: In step eight, the functional relationship may be any one of a polynomial function, a linear function, an exponential function, and a logarithmic function; the fitting function between the maximum value of the unextended threshold load and the depth of the notch-type foreign object damage is: In the formula, ——maximum value of non-extended threshold load, MPa; d——depth of notch-type foreign object damage, mm.

10. The method for predicting the available limit of blade notch type foreign object damage based on the worst notch method according to any one of claims 1 to 9, characterized in that: The prediction method can also be used to predict the usable limit of a blade after it is damaged by pit-type foreign object damage, that is, the notch-type foreign object damage is replaced by pit-type foreign object damage; the at least five inserted pit-type foreign object damages have different depths and the same root curvature radius, and the at least five inserted cracks of different lengths are all surface semi-elliptical cracks.

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