Fatigue test piece with simulation structure having multiple same notch characteristics

Abstract

The invention belongs to the technical field of aero-engines, and discloses a fatigue test piece with a simulation structure having a plurality of same notch characteristics, the test piece is a plate-shaped structure, and comprises a test section and clamping sections located at two ends of the test section; n pairs of notches are uniformly distributed in the test section, the shapes and sizes of the notches are the same, and the intervals of the notches are equal. The theoretical stress concentration coefficient difference at each notch is less than 1%, and the fatigue life dispersion condition of typical stress concentration parts such as mortises and eccentric holes of a wheel disc structure and mounting holes of a flange edge can be simulated. By adopting the method provided by the invention, multiple groups of fatigue life data can be obtained by one fatigue test, the test efficiency is improved, the method is suitable for fatigue life test and life dispersibility research, and the fatigue performance of the aero-engine structural member can be evaluated more accurately, so that the overall reliability of the engine is improved.

Description

Technical Field

[0001] The present application belongs to the field of aero-engine technology, and particularly relates to a fatigue test piece having a simulated structure with multiple identical notch features, which simulates fatigue performance of typical stress concentration locations such as the mortise and tenon structure, eccentric holes, and mounting holes on the flange edge, and reflects life dispersion. Background Art

[0002] In the wheel structure of an aircraft engine, the mortise and tenon, eccentric hole, and mounting hole on the flange are stress concentration areas and potential locations for fatigue crack initiation. In order to accurately evaluate the fatigue performance and life dispersion of these key parts, it is necessary to design appropriate test pieces for fatigue testing. However, traditional fatigue tests usually use test pieces containing only a pair of notches, which cannot fully simulate the fatigue behavior caused by multiple identical stress concentration locations in the actual structure, making it difficult to effectively evaluate the fatigue performance and life dispersion of the actual structure.

[0003] In the existing multi-notch test design, the stress fields between the notches may interfere with each other, and it is impossible to ensure that the stress levels at each notch are consistent, which affects the reliability and accuracy of the test results. In addition, it is impossible to comprehensively consider the interaction between notch size, spacing and stress distribution to guide the design of multi-notch test pieces, making it difficult for the test pieces to meet engineering requirements.

[0004] Therefore, a new test piece is urgently needed to simulate the fatigue performance of the notch part of the wheel structure, which can obtain multiple fatigue data sample points in one test to improve the test efficiency and statistical reliability of the data. The test piece should ensure that the stress distribution of each notch has little influence on each other, and the difference is controlled within an acceptable range, truly simulate the characteristics of the actual structure, and provide strong technical support for fatigue life prediction and life dispersion research. Summary of the invention

[0005] In order to solve the problems in the prior art that the fatigue behavior caused by multiple stress concentration locations in the actual structure cannot be effectively simulated, as well as the low test efficiency and difficulty in obtaining data dispersion, the present invention provides a fatigue test piece with a simulated structure having multiple identical notch features.

[0006] The test piece is a plate-like structure, including a test section and clamping sections located at both ends of the test section. The test section has n pairs of notches evenly distributed along the length direction. The notches have the same shape and size, and the notches have equal spacing.

[0007] The notch is a structure that can generate stress concentration, including but not limited to notches in semicircular, arc-shaped, semi-elliptical, U-shaped, V-shaped, hyperbolic, rectangular or other shapes.

[0008] The key dimensions include: total length L, width W, thickness T of the test section; notch spacing s; notch size parameters: including notch radius ρ, notch depth a, and other necessary parameters to determine the notch shape. For a semi-elliptical notch, the semi-major axis or semi-minor axis length is also required; for a V-shaped notch, the notch angle is also required; for a rectangular notch, the notch width is also required.

[0009] The notch spacing s is designed to satisfy the difference in stress concentration coefficients at each notch being less than 1%, and the mutual influence of stress fields of each notch can be ignored. The width W is designed to satisfy the mutual influence of stress fields between any pair of opposite notches can be ignored. The thickness T is designed to satisfy the ability of cracks to rapidly expand along the thickness direction to penetrate after initiation, thereby achieving effective observation of notch fatigue cracks.

[0010] The test piece is made of the same or similar material as the actual structural part to ensure the reliability and comparability of the test results. In addition, the geometric shape and notch distribution of the test piece are highly symmetrical to ensure that the stress distribution and fatigue behavior at each notch are consistent. By loading the test piece with a fatigue testing machine, the dispersion of fatigue life of multiple notch parts of the wheel disc structure can be reflected. After loading to a certain number of cycles, multiple cracks can be observed.

[0011] Advantages of the present invention include:

[0012] 1. The test piece proposed in the present invention can simulate multiple stress concentration areas of a structural component, thereby improving the efficiency of fatigue testing and saving testing time and cost.

[0013] 2. Through optimized design, the stress distribution at each notch is ensured to be similar and independent of each other, with a difference of less than 1%, thus ensuring the reliability of the test data.

[0014] 3. Multiple sets of fatigue life data can be obtained in one test, which is conducive to studying the dispersion of fatigue life and meeting the actual needs of engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a three-dimensional diagram of the multi-notch test piece of the present invention.

[0016] Figure 2 It is the overall dimension diagram of the multi-notch test piece of the present invention.

[0017] Figure 3 This is a diagram of the notch dimensions of the multi-notch test piece of the present invention.

[0018] Figure 4 This is a diagram showing the finite element analysis results of the multi-notch test piece of the present invention.

[0019] Figure 5This is a crack distribution diagram of the multi-notch test piece after fatigue test of the present invention. DETAILED DESCRIPTION

[0020] In order to make the technical solution and advantages of the present application clearer, the technical solution of the present application will be further described in detail in detail and in detail in conjunction with the accompanying drawings. It can be understood that the specific embodiments described here are only partial embodiments of the present application, which are only used to explain the present application, not to limit the present application. It should be noted that, for the convenience of description, only the parts related to the present application are shown in the accompanying drawings, and other related parts can refer to the general design. In the absence of conflict, the embodiments in the present application and the technical features in the embodiments can be combined with each other to obtain new embodiments.

[0021] This embodiment provides a multi-notch test piece for fatigue testing, including a test section and clamping sections located at both ends of the test section. Figure 1 As shown. The material is cut from a titanium alloy wheel disc of an aircraft engine.

[0022] The design drawing of the test piece is as follows: Figure 2 As shown, it is a semicircular notch, the test section length L = 30ρ, width W = 20ρ / 3, thickness T = 2ρ, ρ is the notch radius. In order to simulate the multiple eccentric holes in the aircraft engine wheel structure, 4 pairs of semicircular notches are evenly distributed on the test section. The notch shape is as follows Figure 3 As shown, it is a semicircular notch, the radius ρ and the notch depth a are equal, and the notch spacing s = 6ρ. The notches are symmetrically distributed along the length of the test section, the shape and size of the notches are exactly the same, the notch spacing is equal, and the difference in the theoretical stress concentration coefficient at each notch is less than 1%.

[0023] During the design of the test piece, the finite element method was used to perform linear elastic stress analysis on the test piece to ensure the rationality of the design. Considering that the test piece is a symmetrical structure with three symmetry planes, 1 / 8 of the structure was selected for meshing, and a displacement constraint in the z direction was applied on the xy symmetry plane, a displacement constraint in the x direction was applied on the yz symmetry plane, and a displacement constraint in the y direction was applied on the zx symmetry plane. A tensile load P was applied to the pin hole edge to ensure that the net section stress was 600MPa.

[0024] The stress distribution in the tensile direction is as follows Figure 4 As shown, it can be seen that the maximum stress values ​​at each notch are basically the same, with a difference of less than 1%. At the same time, the stress distribution cloud diagram shows that the stress fields of each notch are independent of each other, and there is no obvious stress interference between them. This proves that the design of the notch spacing s is reasonable and meets the requirements of stress field independence.

[0025] According to the design dimensions, the test piece is precision machined. During the machining process, the size and shape of the notch are strictly controlled, and a high-precision CNC drilling machine is used to machine the semicircular notch. After machining, the test piece is inspected for size and surface quality. The notch size parameters meet the IT7 precision requirements in GB / T 1800.1-2020, the tolerance grade is grade 7, the size range is determined according to the basic size, and the notch surface roughness meets Ra≤0.8μm.

[0026] After passing the inspection, the test was carried out on the LF5105 electro-hydraulic servo fatigue test system. During the test, a telephoto lens combined with a CCD image sensor was used to monitor the crack initiation and expansion at each notch in real time. The test results are as follows: Figure 5 As shown in the figure, after loading to a certain number of cycles, crack initiation was observed in 4 notches, and the cracks expanded perpendicular to the load direction. By performing multiple tests, multiple fatigue life values ​​of the material at different temperatures and stresses can be obtained. Further, statistical methods can be used to examine the life dispersion. For example, calculating the coefficient of variation of each group of data can reflect the degree of dispersion of different groups of data, which provides an important basis for fatigue life prediction and reliability analysis.

[0027] This embodiment achieves the following effects by designing a multi-notch test piece:

[0028] 1. Improve test efficiency: Multiple sets of fatigue life data can be obtained in one test, saving test time and resources.

[0029] 2. High data reliability: The stress distribution of each notch is consistent, and the stress difference is less than 1%, which ensures the consistency of the test data.

[0030] 3. Verify the validity of the design method: Through finite element analysis, it can be seen that each notch undergoes a consistent fatigue load spectrum, and it is possible to observe multiple cracks. During the test, 4 cracks were observed, which verifies the feasibility of the multi-notch test piece design method proposed in this invention.

[0031] The multi-notch test piece and its design method provided by the present invention successfully simulate the fatigue behavior caused by multiple stress concentration locations, providing an effective means for fatigue life testing and life dispersion research. The method improves test efficiency and reduces costs, and is of great significance for fatigue performance research of key structural parts such as the wheel of an aircraft engine.

[0032] In addition, during implementation, the following points should be noted:

[0033] First, ensure the processing accuracy of the notch size and shape to avoid inconsistent stress distribution caused by dimensional deviation.

[0034] Second, use a high-precision loading device (this embodiment uses the LF5105 electro-hydraulic servo fatigue test system of Lishi) to strictly control the load, frequency and environmental conditions of the fatigue test to ensure the reliability of the test data.

[0035] Third, use high-precision monitoring equipment to obtain real-time crack initiation and expansion data for subsequent analysis.

Claims

1. A fatigue test piece having a plurality of identical notch features in a simulated structure, characterized in that: The test piece is a plate-like structure, including a test section and clamping sections located at both ends of the test section. The test section has n pairs of notches evenly distributed along the length direction. The notches have the same shape and size, and the notches have equal spacing.

2. A fatigue test piece having a plurality of identical notch features in a simulated structure according to claim 1, characterized in that: The notch is a structure capable of generating stress concentration, including but not limited to a semicircular, arc-shaped, semi-elliptical, U-shaped, V-shaped, hyperbolic or rectangular notch.

3. A fatigue test piece having a plurality of identical notch features in a simulated structure according to claim 1, characterized in that: The key dimensions include: the total length, width, thickness and notch spacing of the test section; the size parameters of the notch: including the notch radius and notch depth; for a semi-elliptical notch, the semi-major axis or semi-minor axis length is also required; for a V-shaped notch, the notch angle is also required; for a rectangular notch, the notch width is also required.

4. A fatigue test piece having a plurality of identical notch features in a simulated structure according to claim 1 or 3, characterized in that: The notch spacing is designed to ensure that the difference in stress concentration coefficients at each notch is less than 1%, and the influence of stress fields of each notch on each other is negligible.

5. A fatigue test piece having a plurality of identical notch features in a simulated structure according to claim 3, characterized in that: The width is designed to ensure that the mutual influence of stress fields between any pair of opposite notches is negligible.

6. A fatigue test piece having a plurality of identical notch features in a simulated structure according to claim 3, characterized in that: The thickness should be designed to ensure that after the crack initiates, it can quickly expand along the thickness direction to penetrate through the crack, so as to achieve effective observation of the notch fatigue crack.

7. A fatigue test piece with a simulated structure having multiple identical notch features according to claim 1 or 2, characterized in that: The fatigue testing machine is used to load the test piece, which reflects the dispersion of fatigue life at multiple notch locations of the structural component. After loading to a certain number of cycles, multiple cracks are observed.

8. The fatigue test piece having a plurality of identical notch features in a simulated structure according to claim 1, characterized in that: The geometric shape and notch distribution of the test piece are symmetrical, ensuring that the stress distribution and fatigue behavior at each notch are consistent.

9. A fatigue test piece having a plurality of identical notch features in a simulated structure according to claim 1, characterized in that: During the processing of the test piece, the notch size and shape are strictly controlled; after processing, the test piece is subjected to dimensional inspection and surface quality inspection; the notch size parameters meet the IT7 precision requirements in GB / T1800.1-2020, the tolerance grade is 7, and the notch surface roughness Ra≤0.8μm.

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