Rotor bolt fatigue strength reserve evaluation method considering centrifugal bending

Abstract

The application provides a rotor bolt fatigue strength reserve evaluation method considering centrifugal bending, and belongs to the technical field of aero-engines. The method comprises the following steps: determining an overhanging position of a rotor bolt, setting a boundary surface of the overhanging position on the rotor bolt as a section O; setting a point with the maximum bending stress of the section O of the rotor bolt under the action of a centrifugal bending moment as a key point, and calculating the bending stress of the key point; calculating the axial stress of the section O of the rotor bolt under the action of a pre-tightening force load and an external axial tensile load; obtaining the stress of the rotor bolt based on the bending stress and the axial stress; and substituting the pre-tightening force load peak value, the rotor speed peak value, the pre-tightening force load valley value and the rotor speed valley value in a typical state into the above steps to obtain a peak stress and a valley stress, and obtaining the fatigue strength reserve of the rotor bolt based on the peak stress and the valley stress. The application considers the additional bending effect of the overhanging position caused by the centrifugal force when the rotor rotates at high speed, and improves the calculation accuracy of the fatigue strength reserve.

Description

Technical Field

[0001] This application relates to the field of aero-engine technology, and in particular to a method for evaluating the fatigue strength reserve of rotor bolts considering centrifugal bending. Background Technology

[0002] In the high-pressure compressor of an aero-engine, the multi-stage discs (such as turbine discs and compressor discs) are usually connected in series by bolts to form an integral rotor. As a key fastener, the bolts undertake multiple functions such as structural connection, load transfer and sealing, and their reliability is directly related to the overall safety and performance of the engine.

[0003] When designing and evaluating connecting bolts for aero-engines, in addition to the conventional considerations of ensuring reliable rotor connection, effective sealing, and reliable frictional torque transmission, the bending moment caused by rotor speed loads on the bolt head and nut protruding from the connected structure must also be considered for rotor bolts. This is because at rotor speeds exceeding 10,000 rpm and with the bolt's relatively high radius of rotation relative to the axis of rotation, the bolt head and nut protruding from the connected structure will cause bending deformation of the bolt shank under centrifugal force, resulting in additional bending moments on the bolt shank. This leads to uneven stress distribution on both the inner and outer sides of the bolt along the radius of the rotor disc, generating alternating stress under different engine speed cycles, which needs to be considered separately in the low-cycle life assessment of the bolts.

[0004] Currently available information does not include a method for assessing the impact of bending stress caused by bolt rotation speed on bolt life. Summary of the Invention

[0005] In view of this, the present application provides a method for evaluating the fatigue strength reserve of rotor bolts that takes centrifugal bending into account, which at least partially solves the problem in the prior art that the influence of centrifugal bending on the fatigue strength reserve of rotor bolts is not considered.

[0006] This application provides a method for evaluating the fatigue strength reserve of rotor bolts considering centrifugal bending, including:

[0007] Step 1: Determine the extended portion of the rotor bolt. The extended portion includes the bolt head and nut portion of the rotor bolt that extend beyond section O. Section O is the clamping boundary surface of the parts connected by the rotor bolt. Step 2: For the bolt head or nut portion that extends beyond section O, designate the point at section O where the bending stress is greatest under centrifugal bending moment as the key point, and calculate the bending stress at that key point. Step 3: Calculate the axial stress at section O of the rotor bolt under the action of preload and external axial tensile load; Step 4: Based on the bending stress and axial stress at key points, obtain the stress expression for the rotor bolts; Step 5: Substitute the peak value of the preload and the peak value of the rotor speed under typical large conditions into steps 1 to 4 to obtain the peak stress of the rotor bolts. Substitute the valley value of the preload and the valley value of the rotor speed under typical valley conditions into steps 1 to 4 to obtain the valley stress of the rotor bolts. Step 6: Obtain the fatigue strength reserve of the rotor bolts based on the peak stress and valley stress of the rotor bolts.

[0008] According to a specific implementation of an embodiment of this application, calculating the bending stress at the key point includes: Obtain the mass and centroid radius of the extended portion, and calculate the centrifugal force of the extended portion; Calculate the centrifugal bending moment of the extended part based on the centrifugal force and bending lever arm of the extended part; Calculate the bending stress at this critical point based on the centrifugal bending moment.

[0009] According to a specific implementation of this application, the formula for calculating the centrifugal force is as follows: F W =mrω 2 , The formula for calculating the centrifugal bending moment is: M=F W L, The formula for calculating the bending stress is: σ w =M / W=mrLω 2 / W, W=πd 3 / 32, Among them, F W Let m be the mass of the extended part, r be the radius of the centrifugal center of mass of the extended part, ω be the rotor speed, M be the centrifugal bending moment, L be the bending moment arm of the extended part, and σ be the centrifugal force. w Where is the bending stress, W is the section modulus of the bolt section, and d is the effective diameter at section O.

[0010] According to a specific implementation of this application, the formula for calculating the axial stress is as follows: , σ z Let P be the axial stress, S be the preload load on the rotor bolt under working load, S be the area at section O, and F be the axial tensile load on the rotor bolt. The stiffness coefficient of the connected parts. This is the rotor bolt stiffness coefficient.

[0011] According to a specific implementation of this application, the formula for calculating the stiffness coefficient of the connected components is as follows: , The formula for calculating the rotor bolt stiffness coefficient is as follows: , Where P0 is the initial preload applied to the rotor bolt, x1 is the compression of the connected parts obtained by substituting P0 into the finite element model, and x2 is the bolt elongation obtained by substituting P0 into the finite element model.

[0012] According to a specific implementation of an embodiment of this application, the stress expression of the rotor bolt is as follows: , Where σ is the stress of the rotor bolt.

[0013] According to a specific implementation of an embodiment of this application, obtaining the fatigue strength reserve of the rotor bolt based on the peak stress and valley stress of the rotor bolt includes: Based on the peak stress and valley stress of the rotor bolts, the alternating stress and average stress of the rotor bolts are obtained. The fatigue strength reserve of the rotor bolts is obtained based on the alternating stress and average stress of the rotor bolts.

[0014] According to a specific implementation of this application, the formula for calculating the alternating stress is as follows: , The formula for calculating the average stress is: , in, For alternating stress, For average stress, The peak stress of the rotor bolts, This represents the valley stress of the rotor bolts.

[0015] According to a specific implementation of this application, the formula for calculating the fatigue strength reserve is as follows: , Where n is the fatigue strength reserve, This represents the measured tensile strength limit of the bolt. This represents the measured fatigue limit of the bolt.

[0016] Beneficial effects: The rotor bolt fatigue strength reserve assessment method considering centrifugal bending in this application embodiment can quickly assess the alternating stress generated by the protruding part of the rotor connecting bolt under engine load and the corresponding high-cycle fatigue strength reserve of the bolt during the design phase. This provides a rapid analysis method for selecting bolt and nut models and designing non-standard bolt head and nut structural dimensions during the design phase. By clearly defining the protruding part of the bolt and the key stress section, and combining the stress superposition under the combined action of the bending effect generated by centrifugal force, preload, and axial load, the method systematically calculates the peak and valley stresses under different working conditions, and then assesses the fatigue strength reserve based on alternating stress and average stress. This effectively fills the gap in the prior art that ignores the influence of centrifugal bending on the fatigue strength of rotor bolts, improves the accuracy and comprehensiveness of the assessment results, and provides important technical support for the design optimization and safety and reliability verification of aero-engine rotor bolts. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart of a method for evaluating the fatigue strength reserve of rotor bolts considering centrifugal bending according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the rotor bolt extension portion according to an embodiment of the present invention. Detailed Implementation

[0019] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0020] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0022] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The illustrations only show the components related to this application and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0023] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0024] This application provides a method for evaluating the fatigue strength reserve of rotor bolts considering centrifugal bending, as described below. Figure 1 and Figure 2 A detailed description is provided, including the following steps: Step 1: Determine the extended portion of the rotor bolt. The extended portion includes the bolt head and nut portion of the rotor bolt that extend beyond section O. Section O is the clamping boundary surface of the parts connected by the rotor bolt. Step 2: For the bolt head or nut portion that extends beyond section O, designate the point at section O where the bending stress is greatest under centrifugal bending moment as the key point, and calculate the bending stress at that key point. Step 3: Calculate the axial stress at section O of the rotor bolt under the action of preload and external axial tensile load; Step 4: Based on the bending stress and axial stress at key points, obtain the stress expression for the rotor bolts; Step 5: Substitute the peak value of the preload and the peak value of the rotor speed under typical large conditions into steps 1 to 4 to obtain the peak stress of the rotor bolts. Substitute the valley value of the preload and the valley value of the rotor speed under typical valley conditions into steps 1 to 4 to obtain the valley stress of the rotor bolts. Step 6: Obtain the fatigue strength reserve of the rotor bolts based on the peak stress and valley stress of the rotor bolts.

[0025] In practical implementation, for the extended portion, without considering the contact and tightening of the bolt head and nut against the mounting edge end face, and assuming that only the contact portion of the bolt hole wall bears the centrifugal force of the rotor bolt, the specific location of the extended portion, where the bolt does not contact the surface of the bolt hole of the connected component, can be referred to... Figure 2 The determination of the boundary section O at location A needs to be combined with the actual installation conditions of the bolts to ensure that it accurately reflects the stress state when the centrifugal force is borne only by the contact area between the bolt hole wall and the bolt. For the selection of key points in step 2, in addition to considering the point with the maximum bending stress at section O, it is also necessary to analyze the stress change trend at this point throughout the rotor's operation to ensure the representativeness of subsequent stress calculations. In step 3, when calculating axial stress, the values ​​of the preload and external axial tensile load should be based on the working parameters of the rotor bolts in actual engineering. At the same time, the loss and uneven distribution of load during the load transfer process must be considered. The finite element analysis method should be used to accurately solve for the axial stress at section O. In step 4, when obtaining the stress of the rotor bolts based on bending stress and axial stress, a combined calculation according to the fourth strength theory is required. The two values ​​are vector-superimposed to obtain the comprehensive stress value. Step 5 selects the peak and valley values ​​of the preload and rotor speed under typical conditions to simulate the extreme stress conditions of the rotor under different operating conditions. Comprehensive stress data is obtained by repeatedly substituting values ​​into the calculation processes of steps 1 to 4. Step 6: When calculating the fatigue strength reserve based on the peak stress and valley stress, it is necessary to refer to the relevant fatigue strength design specifications, combine the fatigue performance parameters of the rotor bolt material, adopt an appropriate fatigue strength evaluation model, and finally determine whether the fatigue strength reserve of the rotor bolt under the condition of centrifugal bending meets the design requirements.

[0026] In one embodiment, calculating the bending stress at the critical point includes: Obtain the mass and centroid radius of the extended portion, and calculate the centrifugal force of the extended portion; Calculate the centrifugal bending moment of the extended part based on the centrifugal force and bending lever arm of the extended part; Calculate the bending stress at this critical point based on the centrifugal bending moment.

[0027] Furthermore, the formula for calculating the centrifugal force is as follows: F W =mrω 2 (1), The formula for calculating the centrifugal bending moment is: M=F W L(2), The formula for calculating the bending stress is: σ w =M / W=mrLω 2 / W(3) W=πd 3 / 32(4) Among them, F W Let m be the mass of the extended portion, r be the radius of the center of mass of the extended portion, ω be the rotor speed, M be the centrifugal bending moment, L be the bending moment arm of the extended portion (i.e., L is the distance from the center of mass of the extended portion to section O), and σ be the centrifugal force. w Where W is the bending stress, W is the section modulus of the bolt section, and d is the effective diameter at section O. The effective diameter is either the diameter of the smooth rod (when the section is at the smooth rod) or the minor diameter of the thread (when the section is at the threaded section).

[0028] In practice, the bolt extension portion is divided along section O in the 3D solid modeling software to obtain the bolt extension portion A, which has no bolt holes to bear the centrifugal force after assembly. The mass m and centroid radius r of the extension portion A are obtained, and the centrifugal force F of the extension portion A is calculated. W And the centrifugal bending moment M, and the bending stress σ at the key point w .

[0029] Furthermore, the formula for calculating the axial stress is as follows: (5), σ z Let P be the axial stress, S be the preload load on the rotor bolt under working load, S be the area at section O, and F be the axial tensile load on the rotor bolt. The stiffness coefficient of the connected parts. This is the rotor bolt stiffness coefficient.

[0030] Furthermore, the formula for calculating the stiffness coefficient of the connected components is as follows: (6), The formula for calculating the rotor bolt stiffness coefficient is as follows: (7), Where P0 is the initial preload applied to the rotor bolt, x1 is the compression of the connected parts obtained by substituting P0 into the finite element model, and x2 is the bolt elongation obtained by substituting P0 into the finite element model.

[0031] In specific implementation, the methods for determining the stiffness coefficient of the connected parts and the stiffness coefficient of the bolt include: constructing a finite element model of the connected parts and the connecting parts, applying an initial preload load P0 to the bolt, inputting P0 into the finite element model to obtain the compression amount of the connected parts as x1 and the elongation amount of the bolt as x2, and then calculating the stiffness coefficient according to the above formula.

[0032] Furthermore, the stress expression for the rotor bolt during operation is as follows: (8), Where σ is the stress of the rotor bolt.

[0033] According to a specific implementation of an embodiment of this application, obtaining the fatigue strength reserve of the rotor bolt based on the peak stress and valley stress of the rotor bolt includes: Based on the peak stress and valley stress of the rotor bolts, the alternating stress and average stress of the rotor bolts are obtained. The fatigue strength reserve of the rotor bolts is obtained based on the alternating stress and average stress of the rotor bolts.

[0034] In practice, since the preload P and rotor speed ω of the bolt under working load both change with the engine state, corresponding to peak and trough loads for various cycles, the peak value of the preload load under typical conditions (specific working conditions required by the design) is taken. and The peak stress of the bolt is calculated by substituting it into formulas (1) to (8). Similarly, the valley value of the preload is taken. and Substituting these values ​​into formulas (1) through (8), the valley stress of the calculated bolt is obtained. .

[0035] Furthermore, the formula for calculating the alternating stress is as follows: (9), The formula for calculating the average stress is: (10) in, For alternating stress, For average stress, The peak stress of the rotor bolts, This represents the valley stress of the rotor bolts.

[0036] Furthermore, the formula for calculating the fatigue strength reserve is as follows: (11), Where n is the fatigue strength reserve, This represents the measured tensile strength limit of the bolt. This represents the measured fatigue limit of the bolt.

[0037] The embodiments provided by this invention can quickly assess the alternating stress generated by the protruding portion of the rotor connecting bolt under engine load and the corresponding high-cycle fatigue strength reserve of the bolt during the design phase. This provides a rapid analysis method for selecting bolt and nut models and designing the structural dimensions of non-standard bolt heads and nuts during the design phase. Compared to traditional evaluation methods that only consider preload and axial load, this method incorporates the centrifugal bending effect, integrating the dynamic stress characteristics of the protruding bolt portion into the analysis system, making the stress calculation results more consistent with actual working conditions. In engineering applications, designers can use this evaluation method to compare multiple schemes for different types of rotor bolts. By adjusting parameters such as bolt protrusion length and cross-sectional dimensions, the bolt structure can be optimized to reduce stress concentration, thereby achieving lightweight bolt design while meeting strength reserve requirements and improving the overall performance of the aero-engine. Furthermore, the method's streamlined and formulaic nature facilitates rapid mastery and application by engineers to actual projects, effectively shortening the design cycle and reducing R&D costs.

[0038] 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 evaluating the fatigue strength reserve of rotor bolts considering centrifugal bending, characterized in that, include: Step 1: Determine the extended portion of the rotor bolt. The extended portion includes the bolt head and nut portion of the rotor bolt that extend beyond section O. Section O is the clamping boundary surface of the parts connected by the rotor bolt. Step 2: For the bolt head or nut portion that extends beyond section O, designate the point at section O where the bending stress is greatest under centrifugal bending moment as the key point, and calculate the bending stress at that key point. Step 3: Calculate the axial stress at section O of the rotor bolt under the action of preload and external axial tensile load; Step 4: Based on the bending stress and axial stress at key points, obtain the stress expression for the rotor bolts; Step 5: Substitute the peak value of the preload and the peak value of the rotor speed under typical large conditions into steps 1 to 4 to obtain the peak stress of the rotor bolts. Substitute the valley value of the preload and the valley value of the rotor speed under typical valley conditions into steps 1 to 4 to obtain the valley stress of the rotor bolts. Step 6: Obtain the fatigue strength reserve of the rotor bolts based on the peak stress and valley stress of the rotor bolts.

2. The method for evaluating the fatigue strength reserve of rotor bolts considering centrifugal bending according to claim 1, characterized in that, The calculation of the bending stress at this key point includes: Obtain the mass and centroid radius of the extended portion, and calculate the centrifugal force of the extended portion; Calculate the centrifugal bending moment of the extended part based on the centrifugal force and bending lever arm of the extended part; Calculate the bending stress at this critical point based on the centrifugal bending moment.

3. The method for evaluating the fatigue strength reserve of rotor bolts considering centrifugal bending according to claim 2, characterized in that, The formula for calculating the centrifugal force is: F W =mrω 2 , The formula for calculating the centrifugal bending moment is: M=F W L, The formula for calculating the bending stress is: σ w =M / W=mrLω 2 / IN, W=πd 3 / 32, Among them, F W Let m be the mass of the extended part, r be the radius of the centrifugal center of mass of the extended part, ω be the rotor speed, M be the centrifugal bending moment, L be the bending lever arm of the extended part, and σ be the centrifugal force. w Where is the bending stress, W is the section modulus of the bolt section, and d is the effective diameter at section O.

4. The method for evaluating the fatigue strength reserve of rotor bolts considering centrifugal bending according to claim 3, characterized in that, The formula for calculating the axial stress is: ， σ z Let P be the axial stress, S be the preload load on the rotor bolt under working load, S be the area at section O, and F be the axial tensile load on the rotor bolt. The stiffness coefficient of the connected parts. This is the rotor bolt stiffness coefficient.

5. The method for evaluating the fatigue strength reserve of rotor bolts considering centrifugal bending according to claim 4, characterized in that, The formula for calculating the stiffness coefficient of the connected components is: ， The formula for calculating the rotor bolt stiffness coefficient is as follows: ， Where P0 is the initial preload applied to the rotor bolt, x1 is the compression of the connected parts obtained by substituting P0 into the finite element model, and x2 is the bolt elongation obtained by substituting P0 into the finite element model.

6. The method for evaluating the fatigue strength reserve of rotor bolts considering centrifugal bending according to claim 4, characterized in that, The stress expression for the rotor bolt is: ， Where σ is the stress of the rotor bolt.

7. The method for evaluating the fatigue strength reserve of rotor bolts considering centrifugal bending according to claim 1, characterized in that, The method of obtaining the fatigue strength reserve of the rotor bolts based on the peak stress and valley stress of the rotor bolts includes: Based on the peak stress and valley stress of the rotor bolts, the alternating stress and average stress of the rotor bolts are obtained. The fatigue strength reserve of the rotor bolts is obtained based on the alternating stress and average stress of the rotor bolts.

8. The method for evaluating the fatigue strength reserve of rotor bolts considering centrifugal bending according to claim 7, characterized in that, The formula for calculating the alternating stress is: ， The formula for calculating the average stress is: ， in, For alternating stress, For average stress, The peak stress of the rotor bolts, This represents the valley stress of the rotor bolts.

9. The method for evaluating the fatigue strength reserve of rotor bolts considering centrifugal bending according to claim 8, characterized in that, The formula for calculating the fatigue strength reserve is: ， Where n is the fatigue strength reserve, This represents the measured tensile strength limit of the bolt. This represents the measured fatigue limit of the bolt.

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