A fatigue test piece simulating a structure having a plurality of identical notched features
By designing fatigue test specimens with multiple identical notch features to simulate the fatigue behavior of multiple stress concentration points in the structure of an aero-engine wheel disk, the problem of the inability of existing technologies to fully simulate the fatigue behavior of these stress concentration points was solved. This enabled efficient and reliable fatigue life testing, provided multiple sets of data samples, and met engineering requirements.
Patent Information
- Application Number
- CN202411948443.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-27
- Publication Date
- 2025-11-07
- Estimated Expiration
- 2044-12-27
AI Technical Summary
Existing technologies cannot effectively simulate the fatigue behavior of multiple stress concentration points in the rotor disc structure of aero engines, resulting in insufficient reliability and accuracy of test results, low test efficiency, and difficulty in obtaining multiple fatigue data sample points.
Design a fatigue test specimen with multiple identical notch features to simulate a structure. Use a plate-like structure with n pairs of notches of the same shape and size evenly distributed to ensure that the stress concentration factor difference is less than 1%. Use the same or similar material as the actual structural component and optimize the design through finite element analysis to ensure the consistency and independence of stress distribution.
It improves the efficiency of fatigue testing, ensures the reliability and consistency of test data, and enables the acquisition of multiple sets of fatigue life data in a single test, meeting practical engineering needs and providing a basis for fatigue life prediction and life dispersion research.
Smart Images
Figure CN119845699B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of aero-engine, and particularly relates to a fatigue test piece simulating a structure having multiple identical notch features. The fatigue performance of typical stress concentration positions such as tenon grooves, eccentric holes and mounting holes of flange edges of a wheel disc structure is simulated, and the life dispersion is reflected. BACKGROUND
[0002] In the wheel disc structure of an aero-engine, positions such as tenon grooves, eccentric holes and mounting holes of flange edges are stress concentration regions, which are potential positions for fatigue crack initiation. In order to accurately evaluate the fatigue performance and life dispersion of these key positions, it is necessary to design a suitable test piece for fatigue test. However, the conventional fatigue test usually adopts a test piece containing only one pair of notches, which cannot comprehensively simulate the fatigue behavior caused by multiple identical stress concentration positions in the actual structure, and it is 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 the stress levels at the notches cannot be ensured to be consistent, which affects the reliability and accuracy of the test results. In addition, the interaction of notch size, spacing and stress distribution cannot be comprehensively considered to guide the design of the multi-notch test piece, so that the test piece is difficult to meet the engineering requirements.
[0004] Therefore, there is an urgent need for a new test piece for simulating the fatigue performance of the notch positions of the wheel disc structure, which can obtain multiple fatigue data sample points in one test, improve the test efficiency and the 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, so as to truly simulate the characteristics of the actual structure and provide strong technical support for fatigue life prediction and life dispersion research. SUMMARY
[0005] In order to solve the problems that the existing technology cannot effectively simulate the fatigue behavior caused by multiple stress concentration positions in the actual structure, and the test efficiency is low and the data dispersion is difficult to obtain, the present application provides a fatigue test piece simulating a structure having multiple identical notch features.
[0006] The test piece is a plate-shaped structure, which includes a test section and clamping sections located at both ends of the test section. The test section uniformly distributes n pairs of notches along the length direction. The notches are identical in shape and size, and the notch spacing is equal.
[0007] The notch is a structure capable of generating stress concentration, including but not limited to semicircular, circular arc, semi-elliptical, U-shaped, V-shaped, hyperbolic, rectangular or other shaped notches.
[0008] The key dimensions include: total length L, width W, thickness T of the test section; notch spacing s; size parameters of the notch: including notch radius p, notch depth a, and other necessary parameters to determine the shape of the notch. For semi-elliptical notch, the length of semi-major axis or semi-minor axis is also needed; for V-shaped notch, the notch included angle is also needed; for rectangular notch, the notch width is also needed.
[0009] The design of the notch spacing s meets the requirement that the difference of stress concentration coefficient at each notch is less than 1%, and the mutual influence of the stress field of each notch can be ignored. The design of the width W meets the requirement that the mutual influence of the stress field between any pair of opposite two notches can be ignored. The design of the thickness T meets the requirement that after crack initiation, the crack can quickly expand in the thickness direction to penetrate, thereby realizing effective observation of the notch fatigue crack.
[0010] The test piece is made of the same or similar material as the actual structure, to ensure the reliability and comparability of the test results. And the geometry and notch distribution of the test piece have high symmetry, to ensure the consistency of the stress distribution and fatigue behavior at each notch. Through the loading of the fatigue testing machine on the test piece, the dispersion of the fatigue life of the multiple notch parts of the wheel disc structure can be reflected, and multiple cracks can be observed after loading to a certain number of cycles.
[0011] The advantages of the present application include:
[0012] 1. The test piece proposed by the present application can simulate multiple stress concentration regions of the structure, improve the efficiency of the fatigue test, and save the test time and cost.
[0013] 2. Through optimization design, the stress distribution at each notch is similar and independent, with a difference of less than 1%, ensuring the reliability of the test data.
[0014] 3. Multiple sets of fatigue life data can be obtained by one test, which is beneficial to study the dispersion of fatigue life and meets the actual engineering needs. BRIEF DESCRIPTION OF DRAWINGS
[0015] Figure 1 It is a perspective view of the multi-notch test piece of the present application.
[0016] Figure 2 It is an overall size diagram of the multi-notch test piece of the present application.
[0017] Figure 3 It is a notch size diagram of the multi-notch test piece of the present application.
[0018] Figure 4 It is a finite element analysis result diagram of the multi-notch test piece of the present application.
[0019] Figure 5This is a crack distribution diagram after fatigue testing of the multi-notch test specimen of the present invention. Detailed Implementation
[0020] To make the technical solution and advantages of this application clearer, the technical solution of this application will be described in a clearer and more complete manner below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only some embodiments of this application, and are only used to explain this application, not to limit this application. It should be noted that, for ease of description, only the parts related to this application are shown in the accompanying drawings. Other related parts can be referred to the general design. In the absence of conflict, the embodiments and technical features in the embodiments of this application can be combined with each other to obtain new embodiments.
[0021] This embodiment provides a multi-notch test specimen for fatigue testing, including a test section and clamping sections located at both ends of the test section, such as... Figure 1 As shown. The material was cut from a titanium alloy wheel disc of an aircraft engine.
[0022] Test specimen design drawings as follows Figure 2 As shown, a semi-circular notch is present. The test section has a length L = 30ρ, a width W = 20ρ / 3, and a thickness T = 2ρ, where ρ is the notch radius. To simulate multiple eccentric holes in the rotor disc structure of an aero-engine, four pairs of semi-circular notches are evenly distributed on the test section. The notch shape is as follows... Figure 3 As shown, the notches are semi-circular with equal radius ρ and depth a, and a notch spacing s = 6ρ. The notches are symmetrically distributed along the length of the test section, with identical shape and size, equal spacing, and theoretical stress concentration factors at each notch differing by less than 1%.
[0023] During the design of the test specimen, linear elastic stress analysis was performed using the finite element method to ensure the rationality of the design. Considering that the test specimen is a symmetrical structure with three symmetry planes, 1 / 8 of the structure was selected for mesh generation. Displacement constraints in the z-direction were applied on the xy symmetry plane, displacement constraints in the x-direction were applied on the yz symmetry plane, and displacement constraints in the y-direction were applied on the zx symmetry plane. A tensile load P was applied at the edge of the pin hole to ensure that the net cross-sectional stress was 600 MPa.
[0024] Stress distribution in the tensile direction as follows Figure 4 As shown, the maximum stress values at each notch are basically the same, with differences of less than 1%. Meanwhile, the stress distribution cloud map shows that the stress fields at each notch are independent of each other, with no significant stress interference between them. This proves that the design of the notch spacing 's' is reasonable and meets the requirement of stress field independence.
[0025] According to the design size, the test piece is precisely machined. During the machining process, the notch size and shape are strictly controlled, and a high-precision numerical control drilling machine is used to machine the semicircular notch. After machining, the test piece is subjected to size inspection and surface quality inspection. The notch size parameters meet the IT7 precision requirements in GB / T 1800.1-2020, the tolerance level is 7, the size range is determined according to the basic size, and the notch surface roughness meets Ra≤0.8μm.
[0026] After inspection, the test is carried out on the LF5105 type electro-hydraulic servo fatigue test system. During the test, a long-focus lens combined with a CCD image sensor is used to monitor the crack initiation and propagation at each notch in real time. The test results are shown in Figure 5 After loading to a certain number of cycles, crack initiation is observed at 4 notches, and the crack propagates perpendicular to the load direction. Multiple tests can be performed to obtain multiple fatigue life values of the material at different temperatures and stresses, and further statistical methods can be used to examine the life dispersion, such as calculating the coefficient of variation of each group of data, which can reflect the dispersion degree of different groups of data, providing an important basis for fatigue life prediction and reliability analysis.
[0027] The present embodiment realizes the following effects by designing a multi-notch test piece:
[0028] 1. Improve test efficiency: multiple sets of fatigue life data are obtained at one time, 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%, ensuring the consistency of the test data.
[0030] 3. Verify the effectiveness of the design method: through finite element analysis, it is found that each notch has undergone consistent fatigue load spectrum, and multiple cracks may be observed. In the test process, 4 cracks were observed, verifying the feasibility of the multi-notch test piece design method proposed in the present 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 sites, providing an effective means for fatigue life test and life dispersion research. This method improves test efficiency and reduces cost, and has important significance for the fatigue performance research of key structural components such as turbine disks of aero-engines.
[0032] In addition, the following points need to be noted during implementation:
[0033] First, ensure the machining accuracy of the notch size and shape to avoid inconsistent stress distribution caused by size deviation.
[0034] Second, using high-precision loading device (the embodiment adopts force test LF5105 type electro-hydraulic servo fatigue test system), strictly control the load, frequency and environmental conditions of fatigue test, ensure the reliability of test data.
[0035] Third, using high-precision monitoring equipment, real-time acquisition of crack initiation and propagation data, facilitate subsequent analysis.
Claims
1. A fatigue test piece simulating a structure having a plurality of identical notched features, characterized by: The test piece is a plate structure, including a test section and clamping sections at both ends of the test section, the test section uniformly distributes n pairs of notches along the length direction, the notches are of the same shape and size, and the notch spacing is equal; the design of the notch spacing meets the requirement that the stress concentration coefficient difference at each notch is less than 1%, and the influence of the stress field of each notch on each other is negligible; the design of the width of the test section meets the requirement that the mutual influence of the stress field between any pair of opposite notches is negligible; the design of the thickness of the test section needs to meet the requirement that the crack can rapidly expand to the through-thickness after crack initiation, so as to realize effective observation of the notch fatigue crack.
2. A fatigue test piece simulating a structure having a plurality of identical notched features according to claim 1, characterized in that: The notch is a structure capable of generating stress concentration, including semicircular, circular arc, semi-elliptical, U-shaped, V-shaped, hyperbolic or rectangular notches.
3. A fatigue test piece simulating a structure having a plurality of identical notched features according to claim 1, characterized in that: The key dimensions include: total length, width, thickness and notch spacing of the test section; size parameters of the notch: including notch radius, notch depth; for semi-elliptical notches, the length of the semi-major axis or semi-minor axis is also required; for V-shaped notches, the notch included angle is also required; for rectangular notches, the notch width is also required.
4. A fatigue test piece simulating a structure having a plurality of identical notched features according to claim 1 or 2, characterized in that: Through the loading of the test piece by the fatigue testing machine, the dispersion of the fatigue life of multiple notch positions of the structural part is reflected, and multiple cracks are observed after being loaded to a certain number of cycles.
5. The fatigue test piece of claim 1, wherein the plurality of identical notched features are simulated structures. The geometry and notch distribution of the test piece have symmetry, which ensures that the stress distribution and fatigue behavior at each notch are consistent.
6. A fatigue test piece simulating a structure having a plurality of identical notched features according to claim 1, wherein: During the processing of the test piece, the notch size and shape are strictly controlled; after processing, the test piece is subjected to size inspection and surface quality inspection; the notch size parameters meet the IT7 precision requirement in GB / T 1800.1—2020, the tolerance grade is 7, and the notch surface roughness Ra is ≤0.8 μm.