A fretting fatigue test specimen structure with controllable micro-slippage

Abstract

This invention discloses a fretting fatigue test specimen structure with controllable micro-slippage, comprising a cyclic tensile structure and a fretting block. The two ends of the cyclic tensile section are connected to a tensile testing machine via threaded sections to provide a load F. Simultaneously, symmetrical strip-shaped protrusions are designed on opposite sides, respectively engaging with the front groove on the contact surface of the fretting block, and applying pressure P to press the fretting block against the sidewall of the cyclic tensile section. A groove is also designed at the rear of the fretting block contact surface, dividing the fretting block into a front contact area and a rear contact area. Under the combined action of F and P, a controllable micro-slippage occurs in the rear contact area of ​​the tensile test specimen in the rear contact area of ​​the fretting block, and this micro-slippage increases as F increases or P decreases. This invention can control the micro-slippage during the fretting fatigue test, improving the control accuracy of the fretting fatigue test and thus improving the accuracy of life prediction.

Description

Technical Field

[0001] This invention belongs to the technical field of mechanical structure strength assessment and simulation component design, and specifically relates to a micro-motion fatigue test component structure with controllable micro-slippage, which is suitable for uniaxial fatigue testing machines. Background Technology

[0002] Currently, a significant number of connecting components in aero-engines exhibit fretting fatigue, such as the tenon joints between the compressor and turbine, the bolted structure of the casing, and the connections between the disc and shaft. To ensure the operational safety of these component connections, strength testing is typically conducted, especially fatigue strength testing under fretting conditions. However, for these connecting components, life prediction requires supporting fundamental data. Fretting fatigue testing involves many uncontrollable factors, and quantitatively describing the impact of fretting is a crucial aspect of fretting fatigue life prediction.

[0003] Taking the tenon joint structure of an aero-engine bladed disk as an example, during takeoff or landing, changes in rotational speed lead to changes in centrifugal force. These changes in centrifugal force cause relative micro-slippage between the tenon and the mortise. Therefore, the study of fatigue life of this type of tenon joint structure is essentially a fretting fatigue problem, and its basic experimental data should be obtained through fretting fatigue test specimens. Through reasonable design, the stress components, stress gradients, and micro-slippage at the critical points of the fretting fatigue test specimens can reflect the contact and fretting states under specific fretting conditions. These basic data can then be used to predict the fretting fatigue life of the tenon joint structure.

[0004] Traditional bridge-plate fretting fatigue test specimens require additional pressure application equipment and loading at both ends to observe micro-slippage and conduct fretting fatigue tests. A significant drawback is the uncontrollable magnitude of this micro-slippage. To facilitate loading and operation of fretting fatigue test specimens, enabling fretting fatigue testing on uniaxial tensile testing equipment, the specimen needs to be rationally designed so that a controllable micro-slippage occurs at the test point under uniaxial tensile conditions. Furthermore, fatigue tests are conducted on the fretting fatigue test specimens on a uniaxial fatigue testing machine, recording the number of load cycles required for fatigue crack formation. The fatigue life of the tenon-and-mortise joint structure is predicted based on the test data. Moreover, by adjusting the geometry and load of the fretting fatigue test specimen, the stress state and micro-slippage at the test point can be made consistent with those of the tenon-and-mortise joint structure, thus designing a fretting fatigue simulation of the tenon-and-mortise joint structure. Summary of the Invention

[0005] In response to the typical fretting phenomenon between components in aero-engines, this invention proposes a test specimen structure that controls the fretting amount through geometric structure and bidirectional loading. The purpose is to obtain basic data on fretting fatigue through this fretting fatigue test specimen and to predict the fretting fatigue life of tenon joint structures.

[0006] The present invention relates to a micro-motion fatigue test specimen structure with controllable micro-slippage, comprising a cyclic tensile structure and a micro-motion pressure block.

[0007] The cyclic stretching structure is connected to threaded sections at both ends; symmetrical strip-shaped protrusions are designed on both sides along the left and right directions.

[0008] One side of the micro-motion block is a contact surface that mates with the side wall of the cyclic stretching structure. Two grooves are designed on it from front to back. The front groove mates with the strip-shaped protrusion; the rear groove divides the micro-motion block into a front contact area and a rear contact area.

[0009] The aforementioned micro-motion blocks consist of two parts. They engage with the strip-shaped protrusions on the cyclic tensile structure via a front groove, allowing the contact surfaces of the micro-motion blocks to contact the sidewalls of the cyclic tensile structure and providing pressure P to both blocks. The tensile test specimen is threadedly connected to the uniaxial fatigue testing machine via threaded sections at both ends. The uniaxial fatigue testing machine applies a load F to one end of the tensile test specimen. Under the combined action of F and P, a controllable micro-slippage occurs in the contact area of ​​the rear contact section of the tensile test specimen in the rear contact zone of the micro-motion blocks. This micro-slippage increases as F increases or P decreases.

[0010] The advantages of this invention are:

[0011] (1) The present invention provides a micro-motion fatigue test piece structure with controllable micro-slip amount, which can realize the control of micro-slip amount in the micro-motion fatigue test process, improve the control accuracy of micro-motion fatigue test, and thus improve the accuracy of life prediction.

[0012] (2) The test piece structure of the present invention can achieve micro-slippage control only under the conditions of stress ring and single-sided uniaxial loading, which improves the dependence on test equipment and reduces the difficulty and cost of testing. Attached Figure Description

[0013] Figure 1 This is a front view schematic diagram of the cyclic tensile structure in the fretting fatigue test specimen with controllable micro-slip amount according to the present invention;

[0014] Figure 2 This is a front view schematic diagram of the micro-motion pressure block structure in the micro-motion fatigue test specimen with controllable micro-slip amount according to the present invention;

[0015] Figure 3 This is a top view schematic diagram of the cyclic tensile structure in the fretting fatigue test specimen with controllable micro-slip amount according to the present invention;

[0016] Figure 4 This is a side cross-sectional view of the cyclic tensile structure in the fretting fatigue test specimen with controllable micro-slip amount according to the present invention;

[0017] Figure 5 This is a bottom view of the micro-motion pressure block in the micro-motion fatigue test specimen with controllable micro-slip amount according to the present invention;

[0018] Figure 6 This is a side cross-sectional view of the micro-motion pressure block in the micro-motion fatigue test specimen with controllable micro-slip amount according to the present invention;

[0019] Figure 7 This is a front view of the assembled fretting fatigue test piece with controllable micro-slip amount according to the present invention;

[0020] Figure 8 This is a top view of the assembled micro-motion fatigue test piece with controllable micro-slip amount according to the present invention;

[0021] Figure 9 This is a diagram showing the force distribution in the contact area of ​​the rear contact section of the micro-motion pressure block.

[0022] Figure 10 a is the curve of the contact area edge displacement of the micro-motion fatigue test specimen with controllable micro-slip amount of the present invention as a function of tensile load under a 500MPa cyclic load;

[0023] Figure 10 b is the curve of the edge displacement of the contact area of ​​the rear contact section as a function of tensile load on the micro-motion fatigue test specimen with controllable micro-slip amount of the present invention under a 600MPa cyclic load.

[0024] Figure 10 c is the curve of the edge displacement of the contact area of ​​the rear contact section as a function of tensile load on the micro-motion fatigue test piece with controllable micro-slip amount of the present invention under a 700MPa cyclic load.

[0025] Figure 10 d represents the curve of the edge displacement of the contact area of ​​the rear contact section of the fretting fatigue test specimen with controllable micro-slip amount of the present invention as a function of tensile load under 800MPa cyclic load.

[0026] In the picture:

[0027] 1-Circulating tension structure; 2-Micro-motion pressure block; 3-Transition section

[0028] 4-Threaded connection end 101-Front end 102-Middle section

[0029] 103-Rear section 104-Strip-shaped protrusion 201-Groove A

[0030] 202-Groove B 203-Front contact section 204-Middle contact section

[0031] 205-Post-contact segment Detailed Implementation

[0032] The present invention will now be described in further detail with reference to the accompanying drawings.

[0033] The present invention relates to a fretting fatigue test specimen structure with controllable micro-slippage, such as... Figure 1 , Figure 2 As shown, it consists of a cyclic stretching structure 1 and a micro-motion pressure block 2.

[0034] like Figure 1 , Figure 3 , Figure 4 As shown, the cyclic stretching structure 1 is a plate-like structure with a rectangular cross-section. The rectangular end faces at both ends are transitioned to circular end faces by transition sections 3 to connect to the threaded connection end 4 with a columnar diameter of φF, forming a dumbbell structure with a total length of L5 in the front-to-back direction.

[0035] The aforementioned cyclic stretching structure 1 is divided into three sections from front to back: front, middle, and rear. The middle section 102 serves as the working section, with widened sides. Its front-to-back length is L3, thickness is H1, and left-to-right width is B1. The increased width on both sides is the same, L2, making the left-to-right width of the middle section 102 greater than the width B1 of the front section 101 and the rear section 103. Simultaneously, symmetrical strip-shaped protrusions 104 are designed in the middle of the upper and lower surfaces of the middle section 102. These protrusions 104 are designed along the left-to-right direction, with both ends flush with the left and right sides of the middle section 102. The front-to-back length of the strip-shaped protrusions 104 is L1, and its height is H2. The edges at the top and back of the strip protrusion 104, as well as the edges at the junction with the middle section 102, are rounded to facilitate assembly. Furthermore, the front section 101 of the cyclic stretching structure 1 is designed to have a shorter front-to-back length than the rear section 103, thereby positioning the strip protrusion 104 on the middle section 102 slightly forward of the center of the cyclic stretching structure 1.

[0036] like Figure 2 , Figure 5 , Figure 6The micro-motion block 2 is used to cooperate with the aforementioned cyclic stretching structure 1. It is a rectangular block structure with a total length of L6 in the front-to-back direction, a thickness of H3, and a width of B3 in the left-to-right direction, equal to the width B1 of the front section 101 and the rear section 102 of the cyclic stretching structure 1. The bottom surface is designed with grooves A201 and B202 from front to back, both along the left-to-right direction and penetrating the left and right sidewalls of the micro-motion block 2. This forms three contact sections on the bottom surface of the micro-motion block 2 from front to back: the front contact section 203 is in front of groove A201, the middle contact section 204 is between groove A201 and groove B202, and the rear contact section 205 is behind groove B202. The edges of the bottom surfaces of the three contact sections in the front-to-back direction are rounded, while the remaining parts are flat, serving as contact surfaces with the surface of the cyclic stretching structure 1. The width of these contact surfaces in the front-to-back direction is L9, and the distance between the bottom contact surfaces of the middle contact section 204 and the rear contact section is L8.

[0037] The groove A201 is used to insert the strip-shaped protrusion 104 on the middle section 102 of the aforementioned cyclic tension structure 1. The width of the groove A201 in the front-to-back direction is L7, and the depth is H4. The depth is slightly greater than the height (H2-H1) / 2 of the strip-shaped protrusion 104 on one side. The specific depth is determined according to the yield strength of the material. In the design, it is advisable to ensure that the bottom rounded corner of the groove A201 does not enter the plastic zone, so as to facilitate the parallel contact between the bottom contact surfaces of the three contact sections and the surface of the cyclic tension structure 1.

[0038] The aforementioned fretting fatigue test specimen structure, through the geometric fit between the groove A201 on the fretting pressure block 2 and the strip protrusion 104 on the cyclic tensile structure 1, and under bidirectional load application, will generate a controllable micro-slip at the contact surface of the rear contact section 204. Since the fretting wear effect is better than under stress R=-1 conditions, the two ends of the test specimen are connected by threads. Simultaneously, the pressure of the fretting pressure block 2 originates from a stress ring or a specially designed hydraulic loading mechanism, and the cyclic tensile load is applied via a uniaxial fatigue testing machine. Through this method, the front part of the fretting pressure head 2 can have the same deformation as the cyclic tensile structure 1, while a relative micro-slip occurs between the rear contact section 205 and the working section of the cyclic tensile structure 1. By widening the working section and the strip protrusion 104, safe operation at the strip protrusion 104 can be ensured, causing cracks to occur at the edge of the contact surface between the cyclic tensile structure 1 and the rear contact section 205 of the fretting pressure block 2.

[0039] like Figure 7 , Figure 8As shown, two micro-motion blocks 2 are respectively engaged with the strip-shaped protrusions 104 on opposite sides of the cyclic tensile structure 1 through grooves A201, and pressure P is provided to the two micro-motion blocks 2 through stress rings or other devices (such as a special hydraulic mechanism). At this time, the entire assembly is symmetrical along the centerline both vertically and horizontally. The tensile test specimen is threadedly connected to the uniaxial fatigue testing machine through the threaded connection ends 4 at both ends, and the uniaxial fatigue testing machine applies a load F to one end of the tensile test specimen. Under the combined action of tensile force F and pressure P, a controllable micro-slippage is generated in the contact area between the rear contact section 205 of the micro-motion block 2 and the cyclic tensile structure 1, and this micro-slippage increases as F increases or P decreases.

[0040] like Figure 9 As shown, the force distribution diagram of the contact area of ​​the rear contact section 205 of the micro-motion pressure block 2 can be seen. It can be seen that there is stress concentration and high stress gradient at the boundary of the contact area of ​​the present invention, which can realize the simulation of micro-motion stress in the contact area of ​​the tenon connection structure.

[0041] Figure 10 a~ Figure 10 d represents the displacement curves of the contact area edge of the rear contact section 205 under four cyclic loads of 500, 600, 700, and 800 MPa, respectively, as a function of tensile load (the displacement difference is the sliding amount). Table 1 shows the specific values ​​of the micro-slippage under different loads. Figure 10 a~ Figure 10 As can be seen from d and Table 1, the micro-slip amount also increases with the increase of tensile load. The micro-slip amount can be controlled by the special geometry of the present invention and the control of bidirectional load.

[0042] Table 1. Microslip Displacement under Various Loads

[0043]

[0044]

[0045] Therefore, this invention designs a fretting fatigue test specimen structure that can control micro-slippage through a special geometric structure and bidirectional loading adjustment. This specimen can be used to conduct fretting fatigue tests, providing fundamental experimental data for establishing a more accurate method for predicting fretting fatigue life.

Claims

1. A fretting fatigue test specimen structure with controllable micro-slippage, characterized in that: It includes a cyclic stretching structure and a micro-motion pressure block; the cyclic stretching structure is a rectangular plate structure, with the rectangular end faces at both ends transitioning to circular end faces and connecting to columnar threaded connection ends through transition sections to form a dumbbell structure; the cyclic stretching structure has symmetrical strip-shaped protrusions along the left and right directions on both sides; at the same time, the cyclic stretching structure is divided into three sections from front to back: front, middle and back; among which, the width of the middle section is greater than that of the front and back sections. One side of the micro-motion block is a contact surface that mates with the side wall of the cyclic stretching structure. Two grooves are designed on it from front to back. The front groove mates with the strip protrusion, and the rear groove divides the micro-motion block into a front contact area and a rear contact area. The aforementioned micro-motion blocks consist of two parts. They engage with the strip-shaped protrusions on the cyclic tensile structure via a front groove, allowing the contact surface of the micro-motion blocks to contact the sidewall of the cyclic tensile structure and providing pressure P to the two micro-motion blocks. The cyclic tensile structure is connected to the uniaxial fatigue testing machine via threaded sections at both ends, and the uniaxial fatigue testing machine applies a load F to one end of the cyclic tensile structure. Under the combined action of F and P, a controllable micro-slippage occurs between the rear contact area of ​​the micro-motion blocks and the rear contact area of ​​the cyclic tensile structure, and this micro-slippage increases as F increases or P decreases.

2. The fretting fatigue test specimen structure with controllable micro-slippage as described in claim 1, characterized in that: The strip-shaped protrusion is located slightly forward of the center of the cyclic stretching structure.

3. The fretting fatigue test specimen structure with controllable micro-slippage as described in claim 1, characterized in that: The depth of the front groove on the micro-motion pressure block is greater than the height of the strip protrusion.

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