A wheel disc crack propagation life calculation method based on stress intensity factor critical value
By obtaining the stress intensity factor distribution and crack propagation plan on the wheel, and combining the constrained load condition and the Class I cyclic peak load condition, the problem of inaccurate prediction of crack propagation life of the wheel in the prior art is solved, and more conservative and safer prediction results are achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- AECC SHENYANG ENGINE RES INST
- Filing Date
- 2022-12-16
- Publication Date
- 2026-05-15
AI Technical Summary
Existing technologies fail to accurately consider limiting load conditions when predicting the crack propagation life of aero-engine rotor discs, resulting in insufficiently conservative predictions. This could lead to an overestimation of the rotor disc's load-bearing capacity, posing a safety hazard.
By obtaining the stress or strain distribution of the disk under limited load conditions, an initial crack is pre-formed, and the stress intensity factor distribution is calculated. Combined with the crack propagation plan, the material fracture toughness is reached when the propagation is terminated, and the crack propagation life under Class I cyclic peak load conditions is calculated.
It provides a more conservative and safer prediction of disc crack propagation life, taking into account the actual maximum limiting load conditions, thus improving the accuracy and safety of the prediction.
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Figure CN115935547B_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of fatigue life calculation, and specifically relates to a method for calculating the crack propagation life of a disc based on the critical value of the stress intensity factor. Background Technology
[0002] The engine rotor disk is one of the most critical components in an aero-engine structure. The primary failure mode for the rotor disk is low-cycle fatigue damage. Failure during operation can lead to non-containment consequences, jeopardizing aircraft safety. Therefore, in aero-engine design, the rotor disk is generally designed as a life-limiting component. The design process must consider the impact of defects or cracks arising from material preparation, blank forming, manufacturing, assembly, transportation, and use on the rotor disk's service life. This necessitates conducting fatigue crack propagation analysis under typical mission conditions to determine whether the crack propagation life from the initial defect to the critical crack size meets the aero-engine maintenance interval requirements.
[0003] Currently, in the analysis and verification of crack propagation in domestic aero-engine rotor discs, analysis based on mission profiles is used to obtain Category I (0 to maximum to 0), Category III (idle to maximum to idle), and Category IV (cruise to maximum to cruise) cycles and their cycle numbers. The equivalent cycle number for the corresponding Category I cycle is obtained using the equal damage method or a 1:4:40 conversion method. Fatigue crack propagation analysis of the rotor disc under Category I cyclic loads is then performed to obtain the fatigue crack propagation cycle life, which is compared with the converted equivalent cycle number to verify whether the requirements are met.
[0004] In practical applications, due to initial defects or cracks in the characteristic parts of the wheel, these defects or cracks begin to propagate under cyclic loading, weakening the wheel's load-bearing capacity. This causes the wheel's residual strength to gradually decrease as the crack grows. When the crack length in the characteristic part of the wheel extends to a certain size (generally called the critical crack size), under the maximum limiting load of the wheel, when the stress intensity factor at the crack tip reaches the material's fracture toughness, the crack in the characteristic part will undergo unstable propagation, causing the wheel to disintegrate and fail. Therefore, the maximum limiting load condition of the wheel during use is the most important load factor determining the allowable crack propagation length in the characteristic parts of the wheel. Given a fixed initial crack size and a fixed material propagation rate, the allowable crack propagation length is the decisive factor in determining the crack propagation life. In actual use, the peak load condition corresponding to Type I cycle is often smaller than the maximum limiting load condition that the wheel may experience in the mission profile (including over-rotation considering the impact of control system accuracy). This makes the critical crack size determined solely by the peak load of Type I cycle longer than the actual situation, and the estimated crack propagation cycle life is also longer than the actual propagation cycle life, thus leading to unreliable prediction results.
[0005] Therefore, it is desirable to have a technical solution to overcome or at least mitigate one of the aforementioned defects of the prior art. Summary of the Invention
[0006] The purpose of this application is to provide a method for calculating the crack propagation life of a disc based on the critical value of the stress intensity factor, so as to solve at least one problem existing in the prior art.
[0007] The technical solution of this application is:
[0008] A method for calculating the crack propagation life of a wheel disk based on the critical value of the stress intensity factor includes:
[0009] Step 1: Obtain the limiting load condition and the stress or strain distribution of the wheel under the limiting load condition;
[0010] Step 2: Pre-create initial cracks at characteristic locations on the wheel disk and calculate the stress intensity factor distribution curve at the leading edge of the initial crack under the aforementioned limiting load conditions.
[0011] Step 3: Obtain the first crack propagation plan, and according to the first crack propagation plan, carry out crack propagation under the limiting load condition. When the stress intensity factor at the crack tip reaches the fracture toughness Kc of the material, the propagation is terminated, and the crack propagation morphology at the time of crack termination and the stress intensity factor distribution curve at the corresponding crack tip are obtained.
[0012] Step 4: Obtain the Class I cyclic peak load condition and the stress or strain distribution of the disk under the Class I cyclic peak load condition;
[0013] Step 5: Calculate the stress intensity factor distribution curve at the crack tip corresponding to the crack propagation morphology under the Class I cyclic peak load condition, and obtain the maximum stress intensity factor K′ at the crack tip. C ;
[0014] Step Six: Obtain a second crack propagation plan, and according to the second crack propagation plan, perform crack propagation under the Class I cyclic peak load condition. When the stress intensity factor at the crack tip reaches K′... C The crack propagation is terminated at a certain time, and the relationship curve between the crack propagation length and the corresponding stress intensity factor under the specified crack propagation path is obtained. Combined with the crack propagation rate model, the crack propagation length versus propagation life curve is calculated. Based on the crack propagation life curve, the crack propagation life is obtained.
[0015] In at least one embodiment of this application, step one, namely obtaining the limited load condition and the stress or strain distribution of the wheel under the limited load condition, includes:
[0016] Obtain the limiting load conditions: rotational speed n = 15000 r / min, and the centrifugal tensile stress on the rim of the blade is 450 MPa;
[0017] The circumferential stress distribution in the center region of the wheel disk under the aforementioned restricted load condition was obtained using the linear elastic finite element method.
[0018] In at least one embodiment of this application, in step two, the size of the initial crack is:
[0019] For surface cracks, the initial crack size is: length × depth = 0.76 mm × 0.38 mm;
[0020] For the corner crack, the initial crack size is: length × depth = 0.38mm × 0.38mm.
[0021] In at least one embodiment of this application, in step two, the pre-fabrication of the initial crack at the characteristic part of the wheel specifically means: pre-fabrication of the initial crack at the center of the wheel, wherein the initial crack is a surface crack with a crack length of 0.76 mm and a crack depth of 0.38 mm.
[0022] In at least one embodiment of this application, step three, the first crack propagation plan includes:
[0023] The p% of the crack propagation length corresponding to the midpoint of the stress intensity factor at the previous crack tip is taken as the crack propagation increment at the midpoint of the stress intensity factor at the next crack tip:
[0024] Δa median =a medeian ×p%
[0025] The crack propagation increment at other points along the crack front is calculated using the following formula:
[0026] Δa i =Δa median ×(K i / K median ) 2
[0027] Among them, a medeian Δa represents the crack propagation length at the point where the stress intensity factor at the crack tip is located. median K represents the crack propagation increment at the midpoint of the stress intensity factor at the next crack lead. i K represents the stress intensity factor value at the i-th point of the crack front. median This represents the median value of the stress intensity factor at the crack tip.
[0028] In at least one embodiment of this application, p% is 15%.
[0029] In at least one embodiment of this application, step four, which involves obtaining the Class I cyclic peak load condition and the stress or strain distribution of the disk under the Class I cyclic peak load condition, includes:
[0030] Obtain the Class I cyclic peak load condition: rotational speed n = 13500 r / min, and the centrifugal tensile stress on the rim of the blade is 364.5 MPa;
[0031] The circumferential stress distribution in the center region of the disk under the type I cyclic peak load condition was obtained using the linear elastic finite element method.
[0032] In at least one embodiment of this application, in step six, the second crack propagation plan is the same as the first crack propagation plan.
[0033] The invention has at least the following beneficial technical effects:
[0034] The method for calculating the crack propagation life of a disk based on the critical value of the stress intensity factor in this application can predict the crack propagation life of a disk under Class I cyclic peak load based on the working envelope of the aero-engine and the disk's limited load conditions determined by its usage. Attached Figure Description
[0035] Figure 1 This is a flowchart of a method for calculating the crack propagation life of a wheel based on the critical value of the stress intensity factor according to one embodiment of this application;
[0036] Figure 2 This is a schematic diagram of the circumferential stress distribution at the center of the wheel disk under a limited load condition according to one embodiment of this application;
[0037] Figure 3 This is a schematic diagram of a wheel with an initial crack pre-formed at the center of the wheel according to one embodiment of this application;
[0038] Figure 4 This is the stress intensity factor distribution curve of the initial crack tip under the limited load condition according to one embodiment of this application;
[0039] Figure 5 This is a schematic diagram of the crack propagation morphology during crack termination propagation according to one embodiment of this application.
[0040] Figure 6 This is the stress intensity factor distribution curve of the crack front under the limited load condition according to one embodiment of this application;
[0041] Figure 7 This is a schematic diagram of the circumferential stress distribution at the center of the disk under a Class I cyclic peak load condition according to one embodiment of this application;
[0042] Figure 8 This is the corresponding Class I cyclic peak load condition in one embodiment of this application. Figure 5 The stress intensity factor distribution curve at the crack front under the crack propagation morphology is shown.
[0043] Figure 9 This is a curve showing the relationship between the length of the deepest point of crack propagation and the number of lifetime cycles in one embodiment of this application. Detailed Implementation
[0044] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.
[0045] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this application.
[0046] The following is in conjunction with the appendix Figures 1 to 9 This application will be described in further detail.
[0047] This application provides a method for calculating the crack propagation life of a wheel disk based on the critical value of the stress intensity factor. (See also...) Figure 1 This includes the following steps:
[0048] Step 1: Obtain the limiting load conditions and the stress or strain distribution of the wheel under the limiting load conditions;
[0049] Step 2: Pre-create initial cracks at characteristic locations on the wheel disk and calculate the stress intensity factor distribution curve at the initial crack tip under constrained load conditions.
[0050] Step 3: Obtain the first crack propagation plan, and according to the first crack propagation plan, carry out crack propagation under the condition of limiting load. When the stress intensity factor at the crack tip reaches the fracture toughness Kc of the material, the propagation is terminated, and the crack propagation morphology at the time of crack termination and the stress intensity factor distribution curve at the corresponding crack tip are obtained.
[0051] Step 4: Obtain the Class I cyclic peak load condition and the stress or strain distribution of the disk under the Class I cyclic peak load condition;
[0052] Step 5: Calculate the stress intensity factor distribution curve at the crack tip under the corresponding crack propagation morphology under Class I cyclic peak load conditions, and obtain the maximum stress intensity factor K′ at the crack tip. C ;
[0053] Step 6: Obtain the second crack propagation plan, and according to the second crack propagation plan, carry out crack propagation under Class I cyclic peak load conditions. When the stress intensity factor at the crack tip reaches K′... C The crack propagation is terminated at a certain time, and the relationship curve between the crack propagation length and the corresponding stress intensity factor under the specified crack propagation path is obtained. Combined with the crack propagation rate model, the crack propagation length versus propagation life curve is calculated. Based on the crack propagation life curve, the crack propagation life is obtained.
[0054] The method for calculating the crack propagation life of a wheel disk based on the critical value of the stress intensity factor in this application firstly involves obtaining the limited load condition of the wheel disk in step one. Under the limited load condition, the stress or strain distribution of the wheel disk is obtained using the linear elastic finite element method. In this embodiment, the limited load condition is: rotational speed n = 15000 r / min, and the centrifugal tensile stress on the rim of the wheel disk is 450 MPa. The circumferential stress distribution in the center region of the wheel disk, where the stress is greatest and most dangerous under this load, is obtained using the linear elastic finite element method as follows: Figure 2 As shown.
[0055] In a preferred embodiment of this application, in step two, initial defects are pre-formed at characteristic locations of the wheel. For surface cracks, the initial crack size is generally: length × depth = 0.76mm × 0.38mm; for corner cracks, the initial crack size is generally: length × depth = 0.38mm × 0.38mm. In this embodiment, as... Figure 3 As shown, an initial surface crack was pre-induced at the center of the disk, with a crack length of 0.76 mm and a crack depth of 0.38 mm. The stress intensity factor distribution curve corresponding to the initial crack morphology at the crack tip under constrained load conditions was obtained (see [reference]). Figure 4 .
[0056] In a preferred embodiment of this application, step three, the first crack propagation plan, includes:
[0057] The p% of the crack propagation length corresponding to the stress intensity factor at the previous crack tip is used as the crack propagation increment at the stress intensity factor at the next crack tip. The recommended p% value is 15%.
[0058] Δa median =a medeian ×p%
[0059] The crack propagation increment at other points along the crack front is calculated using the following formula:
[0060] Δa i =Δa median ×(K i / K median ) 2
[0061] Among them, a medeian Δa represents the crack propagation length at the point where the stress intensity factor at the crack tip is located. median K represents the crack propagation increment at the midpoint of the stress intensity factor at the next crack lead. i K represents the stress intensity factor value at the i-th point of the crack front. median This represents the median value of the stress intensity factor at the crack tip.
[0062] In this embodiment, a crack propagation plan is formulated at the point in the stress intensity factor at the crack tip based on the initial crack size. Each crack propagation increment is 15% of the crack propagation length, resulting in the crack propagation length and propagation increment plan shown in Table 1.
[0063] Table 1
[0064] Crack propagation increment step Crack size (mm) Crack propagation increment (mm) 0 0.380 0.0 1 0.437 0.057 2 0.503 0.066 3 0.578 0.075 … … … 31 28.935 3.774 32 33.275 4.340 33 38.266 4.991
[0065] Based on the above crack propagation plan, under limited load conditions, when the crack propagation occurs and the stress intensity factor at the crack tip reaches the fracture toughness Kc of the material (Kc is [value missing] in this embodiment), the crack propagation continues. ), terminate the propagation, and obtain the critical crack size and morphology under the limited load condition (such as Figure 5 (as shown) and the stress intensity factor distribution curve at the crack tip (as shown) Figure 6 (As shown).
[0066] Furthermore, in a preferred embodiment of this application, step four, obtaining the Class I cyclic peak load condition and the stress or strain distribution of the disk under the Class I cyclic peak load condition, includes:
[0067] Obtain the Class I cyclic peak load condition: rotational speed n = 13500 r / min, and the centrifugal tensile stress on the rim of the blade is 364.5 MPa;
[0068] The circumferential stress distribution in the disk center region under type I cyclic peak load conditions was obtained using the linear elastic finite element method, such as... Figure 7 As shown.
[0069] In this embodiment, in step five, under the action of type I cyclic peak load condition, the stress intensity factor distribution curve of the crack front corresponding to the crack propagation morphology in step three is as follows: Figure 8 As shown, the corresponding maximum stress intensity factor K′ C =97.5MPa.
[0070] Finally, following the first crack propagation plan in step three, a second crack propagation plan is formulated, and the critical value of the crack propagation stress intensity factor is set to K′ obtained in step five. C = 97.5 MPa. When the crack propagation is carried out according to the propagation plan, the stress intensity factor at the crack tip reaches K′. C When the crack propagation terminates, the relationship curve between the crack propagation length and the corresponding stress intensity factor is obtained. Combined with the crack propagation rate model, the crack propagation life curve at this crack propagation length is calculated. This process is implemented using existing life calculation software. The final crack propagation life curve is shown below. Figure 9 As shown, the cycle life corresponding to the expansion from the initial crack to the required critical stress intensity factor is 20,480 cycles.
[0071] The method for calculating the crack propagation life of a wheel based on the critical value of the stress intensity factor in this application, considering the requirements of the limited load condition, predicts a crack propagation life of 20,480 cycles; while without considering the limited load condition, the predicted crack propagation life is 24,886 cycles. It is evident that the crack propagation life given in this application is more conservative and offers higher safety.
[0072] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.
Claims
1. A method for calculating the crack propagation life of a disc based on the critical value of the stress intensity factor, characterized in that, include: Step 1: Obtain the limiting load condition and the stress or strain distribution of the wheel under the limiting load condition; Limiting load conditions: rotational speed n = 15000 r / min, centrifugal tensile stress on the rim of the blade is 450 MPa; Step 2: Pre-create initial cracks at characteristic locations on the wheel disk and calculate the stress intensity factor distribution curve at the leading edge of the initial crack under the aforementioned limiting load conditions. Step 3: Obtain the first crack propagation plan, and according to the first crack propagation plan, carry out crack propagation under the limiting load condition. When the stress intensity factor at the crack tip reaches the fracture toughness Kc of the material, the propagation is terminated, and the crack propagation morphology at the time of crack termination and the stress intensity factor distribution curve at the corresponding crack tip are obtained. The first crack propagation plan includes: The crack propagation length corresponding to the location in the stress intensity factor at the crack tip above. % represents the crack propagation increment at the midpoint of the stress intensity factor at the next crack tip: ； The crack propagation increment at other points along the crack front is calculated using the following formula: ； in, This represents the crack propagation length at the midpoint of the stress intensity factor at the crack tip. This represents the crack propagation increment at the midpoint of the stress intensity factor at the next crack tip. Let i be the stress intensity factor value at the i-th point of the crack tip. This represents the median value of the stress intensity factor at the crack tip. Step 4: Obtain the Class I cyclic peak load condition and the stress or strain distribution of the disk under the Class I cyclic peak load condition; Type I cyclic peak load condition: rotational speed n = 13500 r / min, centrifugal tensile stress on the rim of the blade is 364.5 MPa; Step 5: Calculate the stress intensity factor distribution curve at the crack tip corresponding to the crack propagation morphology under the Class I cyclic peak load condition, and obtain the maximum stress intensity factor at the crack tip. ; Step Six: Obtain a second crack propagation plan, and according to the second crack propagation plan, perform crack propagation under the Class I cyclic peak load condition. When the stress intensity factor at the crack tip reaches... The crack propagation is terminated at a certain time, and the relationship curve between the crack propagation length and the corresponding stress intensity factor under the specified crack propagation path is obtained. Combined with the crack propagation rate model, the crack propagation length versus propagation life curve is calculated. Based on the crack propagation life curve, the crack propagation life is obtained. The second crack propagation plan is the same as the first crack propagation plan.
2. The method for calculating the crack propagation life of a wheel based on the critical value of the stress intensity factor according to claim 1, characterized in that, In step one, the circumferential stress distribution in the center region of the wheel disk under the condition of the restricted load is obtained using the linear elastic finite element method.
3. The method for calculating the crack propagation life of a wheel based on the critical value of the stress intensity factor according to claim 2, characterized in that, In step two, the size of the initial crack is: For surface cracks, the initial crack size is: length × depth = 0.76 mm × 0.38 mm; For the corner crack, the initial crack size is: length × depth = 0.38mm × 0.38mm.
4. The method for calculating the crack propagation life of a wheel based on the critical value of the stress intensity factor according to claim 3, characterized in that, In step two, the pre-fabrication of initial cracks at the characteristic parts of the wheel specifically involves pre-fabricating initial cracks at the center of the wheel. These initial cracks are surface cracks with a length of 0.76 mm and a depth of 0.38 mm.
5. The method for calculating the crack propagation life of a wheel based on the critical value of the stress intensity factor according to claim 4, characterized in that, The %for %.
6. The method for calculating the crack propagation life of a wheel based on the critical value of the stress intensity factor according to claim 5, characterized in that, In step four, the circumferential stress distribution in the disk center region under the action of the type I cyclic peak load condition is obtained using the linear elastic finite element method.