Method for determining dangerous damage section of foreign object based on steady-state stress and vibration stress

Abstract

The invention discloses a method for determining a foreign object damage dangerous section based on steady-state stress and vibration stress. The method comprises the following steps that the actual vibration stress of the front edge of a blade and the steady-state stress of the corresponding position of the front edge of the blade are obtained; calculating an equivalent fatigue load of the blade according to the steady-state stress and the actual vibration stress; and according to the equivalent fatigue load and the material fatigue limit of the blade, calculating the fatigue reserve coefficient of each stage of the blade, and determining the dangerous section of the blade. According to the technical scheme, the most dangerous cross section of the blade can be directly and accurately determined, damage prefabrication is only performed on the cross section after the dangerous cross section of the blade is determined, repeated work of a traditional method during dangerous cross section determination is avoided, the purpose of dangerous cross section assessment can be achieved, and the working efficiency is improved. And resource waste caused by non-dangerous cross section examination can be avoided, and convenience is provided for external object damage test of the whole engine.

Description

Technical Field

[0001] The invention relates to the field of aeroengine design, and in particular to a method for determining a dangerous section of a blade caused by foreign object damage based on steady-state stress and vibration stress. Background Art

[0002] When an aircraft is flying near the ground, foreign objects (such as stones, rivets, nuts, screws, aircraft parts, shells and tools, excluding sand, birds, ice, etc.) hit the engine fan blades, which will cause damage to the blades such as notches, tears, pits, deformation, corner loss or fracture (notches are the most important form of blade foreign object damage), causing foreign object damage to the engine blades. In severe cases, it will cause fatigue fracture of the blades, thus endangering the flight safety of the aircraft. In recent years, the incidence of foreign object damage on active aircraft is 8 to 14 times per 100,000 flight hours, resulting in high maintenance costs. Due to the prominent problem of foreign object damage in the field use of aircraft engines, more and more engines are required to conduct foreign object damage resistance tests during design to simulate and assess the ability of engine blades to resist foreign object damage when used in the field.

[0003] According to the design standards, during the FOD test, it is necessary to prefabricate damage on the dangerous section of the leading edge of the fan blade, and install the blade with prefabricated damage on the engine to complete the FOD simulation test. Therefore, how to determine the dangerous section of the blade and prefabricate damage on the dangerous section is directly related to the success or failure of the FOD test.

[0004] At present, most of the foreign object damage tests consider the simple superposition of steady-state stress and vibration stress, and at the same time, the sections where the maximum steady-state stress and the maximum vibration stress are located are selected as dangerous sections. When the blade is working, the two sections where the maximum steady-state stress or the maximum vibration stress is located are not the most dangerous sections of the blade. Prefabrication of notches in these two sections cannot achieve the purpose of assessing the most dangerous sections. At the same time, if notches are also prefabricated in these two sections, unnecessary assessments and waste of resources will result. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for determining a dangerous section of a blade due to foreign object damage based on steady-state stress and vibration stress, comprising the following steps:

[0006] Obtaining the actual vibration stress at the leading edge of the blade and the steady-state stress at the corresponding position of the leading edge of the blade;

[0007] Calculating the equivalent fatigue load of the blade according to the steady-state stress and the actual vibration stress;

[0008] According to the equivalent fatigue load and material fatigue limit of the blade, fatigue reserve coefficients of each order of the blade are calculated to determine the dangerous section of the blade.

[0009] When calculating the fatigue reserve coefficient of each order of the blade, the steady-state stress and vibration stress at the corresponding position of each order of the blade are superimposed and converted into the equivalent fatigue load of the blade.

[0010] Furthermore, when determining the dangerous section of the blade, the fatigue reserve coefficient of each order of blades is calculated according to the fatigue limit value and equivalent fatigue load of the blade material;

[0011] The section with the lowest coefficient is defined as the most dangerous section of the blade leading edge.

[0012] Among them, the actual vibration stress of the leading edge of the blade is generated by converting the vibration stress of the measuring point in the finite element analysis software.

[0013] Furthermore, before generating the actual vibration stress of the leading edge of the blade, the first ten modal vibration stresses of the blade are measured, and the first ten modal relative vibration stress distributions are calculated through modal analysis.

[0014] The step of obtaining the steady-state stress at a position corresponding to the leading edge of the blade comprises:

[0015] Calculate the stress of the blade at the maximum speed. The radial stress is the maximum steady-state stress caused by the centrifugal force.

[0016] According to the position of the maximum point of vibration stress on the leading edge of the blade, the steady-state stress of the blade at the same position is read.

[0017] Furthermore, the conversion into an equivalent fatigue load of the blade is achieved using the Goodman equation.

[0018] Based on the maximum steady-state stress and maximum vibration stress of the blade during operation, the present invention proposes an intuitive, specific and easy-to-operate method for determining the dangerous section of the blade. The method uses the Goodman equation to convert the maximum steady-state stress and vibration stress borne by the blade during operation into the stress at the leading edge of the blade. At the same time, the fatigue reserve coefficient of each section is calculated using the fatigue limit of the material. The section with the lowest reserve coefficient is the most dangerous section of the leading edge of the blade. Through the present invention, the most dangerous section of the blade can be calculated quickly and accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a step diagram of a method for determining a dangerous section of a blade based on steady-state stress and vibration stress provided in an embodiment of the present invention;

[0020] Figure 2 is a schematic diagram of the tenth-order vibration stress distribution of a blade provided according to an embodiment of the present invention;

[0021] Figure 3 It is a schematic diagram of a dangerous cross section of a blade provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to simulate the damage of foreign objects on the engine fan blades, it is necessary to preform damage on the dangerous section of the leading edge of the blade. Therefore, the determination of the dangerous section and the preformation of damage are the key to the success of the test. According to the definition in the relevant standards: "The damage position is at the most dangerous position with the highest speed and the highest vibration stress", that is, the position of the maximum steady-state stress and the position of the highest vibration stress generated by the highest speed. Therefore, the position where the maximum steady-state stress and the highest vibration stress of the leading edge of the blade are superimposed is determined, and the section where the stress is the largest is the dangerous section of the blade.

[0023] The present application can determine the dangerous section of the leading edge of the blade based on the steady-state stress and vibration stress of the blade.

[0024] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings.

[0025] Figure 1 The present invention provides a method for determining a dangerous section of a blade based on steady-state stress and vibration stress, as shown in the figure, including the following steps:

[0026] Step S110: obtaining the actual vibration stress of the leading edge of the blade and the steady-state stress at a corresponding position of the leading edge of the blade;

[0027] 1) Obtain the actual vibration stress of the blade leading edge:

[0028] In this step, the vibration stress of the engine blade is first measured to measure the vibration stress value corresponding to each mode of the blade. Generally, the vibration stress values ​​of the first ten modes of the blade are measured;

[0029] The relative vibration stress distribution of the first ten modes is calculated through modal analysis, and the position of the maximum vibration stress point on the leading edge of the blade can be obtained from this;

[0030] At the same time, finite element modal analysis is used to calculate the relative vibration stress at the blade measuring point and the relative vibration stress at the corresponding blade leading edge under each mode, and the proportional relationship between the relative vibration stresses of the two parts can be obtained. The vibration stress measurement results at the measuring point can be converted into the actual vibration stress value at the leading edge of the blade using this proportional relationship.

[0031] 2) Obtain the steady-state stress at the corresponding position of the blade leading edge:

[0032] On the other hand, the steady-state stress of the blade at the maximum speed is calculated by finite element analysis software. Among the steady-state stress of the blade (including radial stress, circumferential stress, etc.), the radial stress caused by centrifugal force is the most important component of the steady-state stress of the blade;

[0033] According to the position of the maximum point of vibration stress on the leading edge of the blade, the steady-state stress of the blade at the same position is read.

[0034] Step S120: calculating the equivalent fatigue load value of the blade according to the steady-state stress and the actual vibration stress at the leading edge of the blade;

[0035] In this step, the steady-state stress and vibration stress at the corresponding position of each order of the blade are superimposed, which can be realized by using the Goodman equation to calculate the equivalent fatigue load of the blade.

[0036] Step S130: Calculate fatigue reserve coefficients of blades of various orders according to the equivalent fatigue load and material fatigue limit of the blade, and the section with the lowest fatigue reserve coefficient is the most dangerous section of the blade.

[0037] Table 1 provides the calculation results of the fatigue reserve coefficient of the dangerous section of the leading edge of a blade using the method for determining the dangerous section of the blade provided by the present invention. It can be seen from the table that the fatigue reserve coefficient of the tenth-order blade is 6.9, which is the lowest among all the blades of each order. Therefore, the section where the maximum value of the tenth-order vibration stress of the blade is located is the most dangerous section of the blade; wherein, the section where the maximum value of the tenth-order vibration stress of the blade is located is as follows: Figure 2 As shown, the dangerous section of the tenth-order blade is Figure 3 As shown, the damage prefabrication position is determined thereby, and during subsequent damage prefabrication, damage prefabrication can be performed at the leading edge of the tenth-order dangerous section of the blade.

[0038] Table 1 Calculation results of fatigue reserve coefficient of a blade

[0039]

[0040] The present invention is based on the actual conclusion that when determining the dangerous section of the blade, the section where the maximum steady-state stress or the maximum vibration stress is located is not the most dangerous section of the blade. Aiming at the shortcomings of the traditional confirmation method, an intuitive, specific and easy-to-operate method for determining the dangerous section of the blade is proposed. The method uses the Goodman equation to convert the maximum steady-state stress and vibration stress that the blade bears during operation into the stress at the leading edge of the blade. At the same time, combined with the fatigue limit of the material, the most dangerous section of the leading edge of the blade is judged by the fatigue reserve coefficient of each section. Through the method of the present invention, the most dangerous section of the blade can be determined directly and accurately. After determining the dangerous section of the blade, damage prefabrication is only performed on the section, avoiding the repetitive work of the traditional method when determining the dangerous section, which can achieve the purpose of dangerous section assessment and avoid the waste of resources caused by non-dangerous section assessment, providing convenience for the whole engine foreign object damage test.

[0041] The above disclosures are only several specific embodiments of the present invention; however, the present invention is not limited thereto, and any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for determining the dangerous section of foreign object damage based on steady-state stress and vibration stress, It is characterized in that The following steps are involved: Obtaining the actual vibration stress at the leading edge of the blade and the steady-state stress at the corresponding position of the leading edge of the blade; Calculating the equivalent fatigue load of the blade according to the steady-state stress and the actual vibration stress; According to the equivalent fatigue load and material fatigue limit of the blade, fatigue reserve coefficients of each order of the blade are calculated to determine the dangerous section of the blade.

2. The method according to claim 1, It is characterized in that When calculating the fatigue reserve coefficient of each order of the blade, the steady-state stress and the vibration stress at the corresponding position of each order of the blade are superimposed and converted into the equivalent fatigue load of the blade.

3. The method according to claim 2, It is characterized in that When determining the dangerous section of the blade, the fatigue reserve coefficient of each order of blades is calculated according to the fatigue limit value and equivalent fatigue load of the blade material; The section with the lowest coefficient is defined as the most dangerous section of the blade leading edge.

4. The method according to claim 1, It is characterized in that The actual vibration stress of the leading edge of the blade is generated by converting the vibration stress of the measuring point in the finite element analysis software.

5. The method according to claim 4, It is characterized in that Before generating the actual vibration stress of the leading edge of the blade, the first ten modal vibration stresses of the blade are measured, and the first ten modal relative vibration stress distributions are calculated through modal analysis.

6. The method according to claim 1, It is characterized in that Obtaining the steady-state stress at a position corresponding to the leading edge of the blade includes: Calculate the stress of the blade at the maximum speed. The radial stress is the maximum steady-state stress caused by the centrifugal force. According to the position of the maximum point of vibration stress on the leading edge of the blade, the steady-state stress of the blade at the same position is read.

7. The method according to claim 1, It is characterized in that The conversion to the equivalent fatigue load of the blade is achieved using the Goodman equation.

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