Self-resetting high-low cycle composite fatigue test clamp adaptive to size of notched test piece

Abstract

The invention relates to the technical field of mechanical engineering, in particular to a self-resetting high-low cycle composite fatigue test fixture adaptive to the size of a notched test piece, which comprises a base, a force bearing arm, a swing arm, a limiting screw, a bearing, an upper fixture, an upper clamping plate, a lower fixture, a lower clamping plate, an adjusting bolt, a spring seat and a spring column, the two sides of the base are connected with force bearing arms respectively, the force bearing arms are connected with swing arms through bearings, and the two sides of the lower clamp are connected with the swing arms respectively. A spring column is fixed to the force bearing arm through a spring seat, connected with the swing arm and provided with a reset spring. The lower clamp and the lower clamping plate clamp one end of the notched test piece, and the upper clamp and the upper clamping plate clamp the other end of the notched test piece; a limiting screw is fixed to the force bearing arm, relative rotation of the swing arm and the force bearing arm can be limited, the fatigue test clamp can adapt to different high-low cycle load requirements, and the accuracy and reliability of a test result are improved.

Description

Technical Field

[0001] The invention relates to the technical field of mechanical engineering, and in particular to a self-resetting high-low cycle composite fatigue test fixture adapted to the size of a notched test piece. Background Art

[0002] As one of the key rotating parts of aircraft engines, the turbine shaft works in a complex environment of high temperature, high pressure, and high speed. It is subjected to high and low cycle composite fatigue loads during service, which is prone to fatigue cracks and failure. Therefore, when analyzing the fatigue life of the turbine shaft, it is necessary to consider the coupling effect of multiple loads in different directions at the same time. Due to the large size of the shaft, it is generally impossible to clamp it directly for fatigue crack initiation and expansion tests. The method of designing notched simulation parts is often used to simulate the actual stress conditions of the turbine shaft. At present, typical fatigue testing machines only support unidirectional loading, and cannot apply lateral high cycle loads while applying low cycle large loads. In addition, notched specimens are more sensitive to strain. In order to make the specimens achieve the required deformation mode, the fixtures with fixed structures often need to calculate and iterate the component dimensions using tools such as finite element simulation. The overall process is time-consuming, and there is still a large error between the simulation calculation results of the complex fixture and the actual situation. Therefore, a high and low cycle composite fatigue test fixture is needed that can perform biaxial non-interference loading on notched specimens of specific sizes and ensure long-term stable operation.

[0003] There are relatively few effective designs for biaxial non-interference high-low cycle composite fatigue fixtures in the prior art. The Chinese invention patent application with publication number CN103076246A discloses a biaxial high-low cycle composite fatigue test device, which is a high-low cycle composite fatigue test system design for plate-shaped specimens. The system fixture is connected to the specimen by bolts. The bolts may be disengaged during the vibration test, and the specimen cannot be heated by an induction coil. There is still interference between the high and low cycle loads, and the stress state in the middle of the specimen is somewhat different from the stress state of the actual blade.

[0004] The Chinese invention patent application with publication number CN109470468A discloses a high- and low-cycle composite fatigue test fixture for the tenon joint structure of an aircraft engine turbine. The fatigue machine clamps one end of the test piece through the fixture and the connecting rod, and the other end is connected to the drive shaft through a force transmission rod. The drive shaft is equipped with ball bearings to form a roller structure that can move along the guide groove to release the constraint in the direction of the high-cycle load. The top of the mounting box is clamped by the fatigue machine. The fatigue machine applies a low-cycle load, and the external exciter and the inductive heating copper coil apply a high-cycle load and a thermal load respectively. In this technical solution, when the low-cycle load is large, the bearing cannot roll in the guide groove, and thus the high-cycle load cannot be transmitted.

[0005] The Chinese invention patent application with publication number CN107421984A discloses a thermomechanical fatigue test fixture for hollow turbine blades with superimposed high-frequency vibration, which realizes the application of high and low-frequency loads through a load-bearing arm and a swing arm, and controls the swing amplitude of the swing arm through a limit plate to adjust the high-frequency load. When the swing angle is too large, the torque generated by the low-frequency load is too large, and the excitation rod cannot pull the swing arm back, and fatigue testing under large high-frequency loads cannot be achieved; and when high-frequency loading is applied, the swing arm and the limit plate constantly collide to generate a large noise, which requires a high strength of the limit plate and poses a safety hazard. Summary of the invention

[0006] In view of the above problems, the present invention provides a self-resetting high- and low-cycle composite fatigue test fixture that adapts to the size of notched specimens, solving the problem of how to adapt to different high- and low-cycle load requirements in the prior art.

[0007] The present invention provides a self-resetting high-low cycle composite fatigue test fixture adapted to the size of a notched specimen, comprising: a base 1, a load-bearing arm 2, a swing arm 3, a limit screw 4, a sleeve 5, a bearing 6, an upper fixture 7, an upper clamping plate 8, a lower fixture 9, a lower clamping plate 10, an adjusting bolt 11, a spring seat 12, a reset spring 13, and a spring column 14;

[0008] The base 1 is connected to a load-bearing arm 2 on both sides, and the load-bearing arm 2 is connected to the swing arm 3 through a bearing 6, and the lower clamp 9 is connected to the swing arm 3 on both sides; spring seats 12 are fixed on both sides of the load-bearing arm 2, and spring columns 14 are fixed on both sides of the swing arm 3. One end of a return spring 13 is sleeved on the spring column 14 fixed on one side of the swing arm 3, and the other end of the return spring 13 is sleeved on the spring column 14 fixed on the spring seat 12 on the same side; the lower clamp 9 and the lower clamp 10 clamp one end of the notched specimen 15, and the upper clamp 7 and the upper clamp 8 clamp the other end of the notched specimen 15; a limiting screw 4 is fixed on the load-bearing arm 2, which can limit the relative rotation of the swing arm 3 and the load-bearing arm 2.

[0009] Preferably, the spring seat 12 is fixed to the load-bearing arm 2 through a screw hole; one end of the spring column 14 is fixed to the screw hole of the spring seat 12 , and the other end of the spring column 14 is embedded in the groove of the swing arm 3 .

[0010] Preferably, the load-bearing arm 2 is provided with a circular through hole, a bearing 6 is arranged in the circular through hole, a sleeve 5 is arranged between the bearing 6 and the swing arm 3, and the bearing 6 is respectively connected to the swing arm 3 and the load-bearing arm 2; a fine groove is arranged on one side of the circular through hole, the load-bearing arm 2 is provided with a through hole perpendicular to the direction of the fine groove, an adjusting bolt 11 is arranged in the through hole perpendicular to the direction of the fine groove, and the adjusting bolt 11 can adjust the tightness of the bearing 6.

[0011] Preferably, the lower end of the lower fixture 9 has a boss, and the boss has a plurality of threaded holes at different heights for connecting the exciting rod;

[0012] The upper end of the upper fixture 7 has a boss, and the lower end of the base 1 has a boss. The fatigue machine clamps the bosses of the upper fixture 7 and the base 1 respectively.

[0013] Preferably, the axial extension line of the bearing 6 passes through the test section of the notched test piece 15 .

[0014] Preferably, pins are provided on both sides of the base 1, and the ends of the pins are threaded. Through holes are opened at the corresponding positions of the load-bearing arm 2 and the pins of the base 1. The pins of the base 1 pass through the through holes, and the base 1 is connected to the load-bearing arm 2 by tightening bolts.

[0015] Preferably, the swing arm 3 is provided with a hexagonal hole, and the lower clamp 9 has hexagonal columns on both sides. The hexagonal columns of the lower clamp 9 are embedded in the hexagonal holes of the swing arm 3 and are connected to the swing arm 3.

[0016] Preferably, the upper clamp 7, the upper clamp plate 8, the lower clamp 9 and the lower clamp plate 10 all have wedge-shaped surfaces matching the specimen, the lower clamp 9 and the lower clamp plate 10 clamp one end of the notched specimen 15 through fixing bolts, and the upper clamp 7 and the upper clamp plate 8 clamp the other end of the notched specimen 15 through fixing bolts.

[0017] Preferably, the stiffness coefficient K of the return spring 13 satisfies:

[0018] K=P / 2L

[0019] Wherein, P is the low cycle load, and L is the vertical distance between the notch of the notch specimen 15 and the return spring 13 .

[0020] Preferably, a heating coil is provided outside the notched test piece 15 .

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] (1) The present invention can apply a high-cycle load to the specimen while applying a low-cycle large load through the relative rotation of the swing arm and the load-bearing arm, thereby realizing a tension-bending composite fatigue state of the notched specimen, which helps to more realistically simulate the stress conditions of the specimen under actual working conditions and improve the accuracy and reliability of the test results.

[0023] (2) The present invention provides a variety of mechanisms to balance harmful torque and inertia, including the bending stress of the specimen, the friction of the bearing, the tension of the excitation rod, and the elastic force of the reset spring, so as to ensure that the notched specimen test section reaches the specified stress state. The present invention is provided with a reset spring, and the elastic force generated when the reset spring is compressed by the deflected lower clamp can make the clamp return to a stable position, thereby achieving the specified working state.

[0024] (3) Compared with the flat specimen, the wedge-shaped specimen of the present invention is easier to clamp and has a higher load-bearing capacity. It can ensure the stability of the clamping during long-term testing. At the same time, it is not easy for the bolts to loosen or the specimen to fall off due to vibration. The clamp is not easy to wear and damage after a long-term test, avoiding harmful stress concentration, ensuring that the deformation mode of the specimen is in line with expectations, and reducing the risk of specimen fracture in the non-test section. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings are only for the purpose of illustrating particular embodiments and are not to be construed as limiting the invention.

[0026] Figure 1 This is an overall schematic diagram of the installation of the clamp provided by the present invention.

[0027] Figure 2 Schematic diagram of the base provided by the present invention, wherein (a) is an appearance view, (b) is a front view, (c) is a top view, and (d) is a left view.

[0028] Figure 3 Schematic diagram of the load-bearing arm provided by the present invention, wherein (a) is an appearance diagram, (b) is a front view, (c) is a top view, and (d) is a right side view.

[0029] Figure 4 Schematic diagram of the swing arm provided by the present invention, wherein (a) is an appearance diagram, (b) is a top view, (c) is a front view, and (d) is a right view.

[0030] Figure 5 Schematic diagram of the lower clamp provided by the present invention, wherein (a) is an appearance diagram, (b) is a front view, (c) is a top view, and (d) is a right side view.

[0031] Figure 6 Schematic diagram of the lower splint provided by the present invention, wherein (a) is an appearance diagram, (b) is a front view, (c) is a top view, and (d) is a left view.

[0032] Figure 7 Schematic diagram of the upper clamp provided by the present invention, wherein (a) is an appearance diagram, (b) is a front view, (c) is a top view, and (d) is a left view.

[0033] Figure 8 Schematic diagram of the upper splint provided by the present invention, wherein (a) is an appearance diagram, (b) is a front view, (c) is a top view, and (d) is a left view.

[0034] Fig. 9 Schematic diagram of the spring seat provided by the present invention, wherein (a) is an appearance diagram, (b) is a front view, (c) is a top view, and (d) is a left view.

[0035] Fig.10 This is an appearance diagram of the spring column provided by the present invention.

[0036] Fig.11 This is an appearance diagram of the limit screw provided by the present invention.

[0037] Fig.12 Schematic diagram of the test piece provided by the present invention, wherein (a) is an appearance diagram, (b) is a front view, (c) is a top view, and (d) is a left view.

[0038] Figure markings: 1-base, 2-load-bearing arm, 3-swing arm, 4-limit screw, 5-sleeve, 6-bearing, 7-upper clamp, 8-upper clamp, 9-lower clamp, 10-lower clamp, 11-adjusting bolt, 12-spring seat, 13-reset spring, 14-spring column, 15-notched specimen. DETAILED DESCRIPTION

[0039] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. In addition, the present invention can also be implemented in other ways different from those described herein, and therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0040] The present invention is mainly aimed at high- and low-cycle composite fatigue tests of notch fatigue simulation specimens.

[0041] Simulation parts are test pieces designed and manufactured according to specific test requirements and actual application conditions. They are used to simulate the actual use environment and loads under laboratory conditions to obtain the mechanical and physical performance data of materials or structures under real conditions.

[0042] The notched specimen in the present invention is a specimen with an artificial notch introduced into a standard specimen, which is used to study the mechanical behavior of the material under stress concentration conditions. The introduction of the notch forms a stress concentration area at a specific location of the specimen, which helps to evaluate the performance of the material in the presence of cracks or defects that may exist in actual applications.

[0043] High- and low-cycle loads are terms in the industry. Low-cycle loads are generally large-amplitude, low-frequency loads with an amplitude generally greater than 5kN and a frequency generally less than 1Hz; high-cycle loads are generally small-amplitude, high-frequency loads with a displacement amplitude generally less than 1.5mm and a frequency generally greater than 10Hz.

[0044] In order to illustrate the effectiveness of the method proposed in the present invention, the above technical solution of the present invention is described in detail below through a specific embodiment. Figure 1As shown, a self-resetting high-low cycle composite fatigue test fixture that adapts to the size of a notched specimen is disclosed, specifically comprising: a base 1, a load-bearing arm 2, a swing arm 3, a limit screw 4, a sleeve 5, a bearing 6, an upper fixture 7, an upper clamp 8, a lower fixture 9, a lower clamp 10, an adjusting bolt 11, a spring seat 12, a reset spring 13 and a spring column 14, and a clamping notched specimen 15.

[0045] The base 1 is connected to a load-bearing arm 2 on both sides, and the load-bearing arm 2 is connected to the swing arm 3 through a bearing 6, and the lower clamp 9 is connected to the swing arm 3 on both sides; spring seats 12 are fixed on both sides of the load-bearing arm 2, and spring columns 14 are fixed on both sides of the swing arm 3. One end of a return spring 13 is sleeved on the spring column 14 fixed on one side of the swing arm 3, and the other end of the return spring 13 is sleeved on the spring column 14 fixed on the spring seat 12 on the same side; the lower clamp 9 and the lower clamp 10 clamp one end of the notched specimen 15, and the upper clamp 7 and the upper clamp 8 clamp the other end of the notched specimen 15; a limiting screw 4 is fixed on the load-bearing arm 2, which can limit the relative rotation of the swing arm 3 and the load-bearing arm 2.

[0046] In some embodiments, longitudinal through holes are opened at positions corresponding to the base 1 and the load-bearing arm 2 and are connected by fastening bolts. There are pins on both sides of the base 1, and the ends of the pins are threaded. Through holes are opened at positions corresponding to the pins of the load-bearing arm 2 and the base 1. The pins of the base 1 pass through the through holes, and the base 1 is connected to the load-bearing arm 2 by fastening bolts. The positioning and fixation between the load-bearing arm 2 and the base 1 are ensured by the two-way connection; the load-bearing arm 2 is opened with a circular through hole, and a bearing 6 is arranged in the circular through hole. A sleeve 5 is arranged between the bearing 6 and the swing arm 3, and the bearing 6 is respectively connected to the swing arm 3 and the load-bearing arm 2; a limit screw 4 is installed on the surface of the load-bearing arm 2 connected to the swing arm 3 through a screw hole to prevent excessive relative rotation between the swing arm 3 and the load-bearing arm 2.

[0047] The two sides of the load-bearing arm 2 are respectively fixed with spring seats 12 by bolts, and the two sides of the swing arm 3 are respectively provided with circular grooves, and the center of the circular groove of the swing arm 3 is fixed with a spring column 14 through a screw hole, and one end of the spring column 14 is provided with a thread, which is matched with the screw hole in the center of the circular groove of the swing arm 3 for fixing, and the other end of the spring column 14 is located in the circular groove to form a cylindrical protrusion, and the height of the cylindrical protrusion is consistent with the depth of the circular groove to form a circular groove. The outer diameter of the reset spring 13 is consistent with the diameter of the circular groove, and the inner diameter of the reset spring 13 is consistent with the diameter of the spring column 14, and one end of the reset spring 13 is sleeved on the spring column 14 in the circular groove of the swing arm 3.

[0048] A circular groove is provided at a position corresponding to the spring seat 12 on the same side as the spring column 14 on the swing arm 3, and a screw hole is provided at the center of the circular groove. Similarly, for the spring column 14 on the spring seat 12, the thread at one end of the spring column 14 is matched with the screw hole at the center of the circular groove of the spring seat 12 for fixing, and the other end of the spring column 14 forms a cylindrical protrusion in the circular groove of the spring seat 12, and the other end of the return spring 13 is sleeved on the spring column 14 in the circular groove of the spring seat 12. In this way, the spring column 14, the spring seat 12, and the groove of the swing arm 3 jointly control the return spring from lateral displacement.

[0049] In some embodiments, a fine groove is opened in the vertical direction on one side of the through hole of the load-bearing arm 2 where the bearing 6 is located, and a through hole is opened in the front and rear directions of the load-bearing arm 2. An adjusting bolt 11 is provided in the through hole. The adjusting bolt 11 can adjust the tightness of the bearing 6, and then adjust the magnitude of the relative rotational friction between the swing arm 3 and the load-bearing arm 2.

[0050] In some embodiments, the swing arm 3 is provided with a hexagonal hole, and the lower clamp 9 has hexagonal columns on both sides, and the hexagonal columns of the lower clamp 9 are connected to the swing arm 3 by being embedded in the hexagonal holes of the swing arm 3. The upper clamp 7, the upper clamp plate 8, the lower clamp 9 and the lower clamp plate 10 all have wedge-shaped surfaces that match the specimen, and the lower clamp 9 and the lower clamp plate 10 clamp one end of the notched specimen 15 by fixing bolts, and the upper clamp 7 and the upper clamp plate 8 clamp the other end of the notched specimen 15 by fixing bolts.

[0051] In some embodiments, the lower end of the lower fixture 9 has a boss, and the boss has multiple threaded holes at different heights for connecting the excitation rod. Compared with the direct excitation of one end of the specimen, the length of the excitation arm is increased, which is conducive to the application of high-cycle loads. The upper end of the upper fixture 7 has a boss, and the lower end of the base 1 has a boss. The fatigue machine clamps the bosses of the upper fixture 7 and the base 1 respectively to transmit low-cycle large loads.

[0052] Through the above structure, while applying low-cycle large load, high-cycle load is applied to the specimen through the relative rotation of the swing arm and the load-bearing arm, thereby realizing the tension-bending composite fatigue state of the notched specimen; when the swing arm and the load-bearing arm rotate relative to each other through a certain angle, the low-cycle load will generate a large torque at the bearing, thereby hindering the application of high-cycle load. At this time, the harmful torque and inertia are mainly balanced by the bending stress of the specimen, the friction force of the bearing, the tension of the excitation rod and the elastic force of the reset spring to ensure that the test section of the notched specimen reaches the specified stress state.

[0053] When the relative rotation angle between the swing arm and the load-bearing arm is too large, the hindering torque increases. Since the bending stress of the specimen is limited to a given value due to the strain state and cannot be adjusted, it can be known through mechanical analysis that the bearing tightness can be adjusted by adjusting the bolt to generate different friction forces or the elastic force generated when the return spring is compressed by the deflected lower clamp, so that the clamp can return to a stable position, thereby achieving the specified working state. The approximate range of the spring stiffness coefficient can be given: when the specimen has an ideal deformation mode, the vertical distance between the specimen rotation center (test section) and the return spring is L, the low-cycle load is P, and when the rotation angle of the lower clamp is θ, the harmful torque is approximately PLθ. When the initial state of the return spring is a natural extension state, the elastic moment generated by the single return spring on the compression side at the rotation center of the specimen is KL 2 θ, according to the equilibrium relationship, we get K=P / 2L, where K is the spring constant.

[0054] In some embodiments, based on the size of the clamp and the maximum load requirement, a spring constant of not less than 86 N / mm can be obtained.

[0055] The limit screw of the present invention only plays a safety role to prevent the swing arm from swinging excessively due to excessive low-cycle load torque. The swing arm will not collide with the limit screw under normal working conditions, and the noise is relatively small.

[0056] The wedge-shaped specimen of the present invention is easier to clamp than a flat specimen, and there will be no loosening of bolts due to vibration, which will cause the specimen to fall off. It has a higher load-bearing capacity, can ensure the stability of the clamping of the fixture during long-term testing, and the fixture is not prone to wear and damage after a long-term test. However, in addition to the large stress concentration at the notch of the wedge-shaped specimen, there will also be a certain stress concentration at the transition between the wedge surface and the parallel section. If the deformation mode of the wedge-shaped specimen does not meet expectations, it is very likely that the specimen will break in the non-test section. In order to meet the deformation requirements of wedge-shaped specimens of specific sizes and keep the rotation center of the specimen at the test position as much as possible, the axial extension lines of the two bearings must pass through the test section of the specimen, thereby meeting the deformation requirements of the notched specimen and avoiding the influence of harmful stress concentration.

[0057] A certain distance is left between the two swing arms of the present invention, and a heating coil can be added outside the test piece to carry out a high-temperature fatigue test.

[0058] In some embodiments, the clamp provided by the present invention can work stably under the conditions of low-cycle load reaching 15kN and high-cycle load displacement reaching ±7mm.

[0059] The present invention also provides a debugging method for the self-resetting high-low cycle composite fatigue test fixture that adapts to the size of the notched specimen, which specifically includes:

[0060] Strain gauges are pasted on the test section of the notched specimen 15 to detect its strain state through the strain gauge. The notched specimen 15 is clamped between the upper fixture 7, the upper clamp 8 and the lower fixture 9, the lower clamp 10. The fatigue machine transmits low-cycle large loads by clamping the upper fixture 7 and the base 1. The exciter is connected to the threaded hole of the lower fixture 9 through the excitation rod to transmit high-cycle loads. The strain gauge is used to determine whether the strain state of the current test section meets the requirements. If the swing arm 3 is close to the limit screw 4 and cannot swing freely, the tightness of the bearing 6 is adjusted by adjusting the bolt 11 to increase the friction force, or the reset spring 13 with a larger stiffness coefficient is replaced, so as to balance the harmful torque caused by the low-cycle load and realize the application of high-cycle load.

[0061] The beneficial effects of the present invention are as follows: the fatigue machine clamps the upper fixture and the base to transmit low-frequency large loads; the vibrator is connected to the screw hole of the lower fixture through the vibration rod to transmit high-frequency vibration loads; the swing arm and the load-bearing arm of the clamped specimen are relatively rotated through the bearing structure to realize the transmission of the bending load of the notched specimen; the friction force of the swing arm rotation is controlled by adjusting the adjusting bolt of the bearing at the connection between the swing arm and the load-bearing arm, and the swing amplitude of the swing arm is actively controlled; the reset spring provides a certain rebound force to the swing arm to balance the harmful torque and avoid instability.

[0062] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0063] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0064] In the present invention, the terms "first", "second", "third", "fourth" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance. The term "plurality" refers to two or more, unless otherwise clearly defined.

[0065] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A self-resetting high-low cycle composite fatigue test fixture adapted to the size of notched specimens, characterized in that: include: A base (1), a load-bearing arm (2), a swing arm (3), a limit screw (4), a sleeve (5), a bearing (6), an upper clamp (7), an upper clamping plate (8), a lower clamp (9), a lower clamping plate (10), an adjusting bolt (11), a spring seat (12), a return spring (13) and a spring column (14); The base (1) is connected to a load-bearing arm (2) on both sides, the load-bearing arm (2) is connected to the swing arm (3) through a bearing (6), and the lower clamp (9) is connected to the swing arm (3) on both sides; spring seats (12) are fixed on both sides of the load-bearing arm (2), and spring columns (14) are fixed on both sides of the swing arm (3); one end of a return spring (13) is sleeved on the spring column (14) fixed on one side of the swing arm (3), and the other end of the return spring (13) is sleeved on the spring column (14) fixed on the spring seat (12) on the same side; the lower clamp (9) and the lower clamp (10) clamp one end of the notched test piece (15), and the upper clamp (7) and the upper clamp (8) clamp the other end of the notched test piece (15); a limit screw (4) is fixed on the load-bearing arm (2) to limit the relative rotation of the swing arm (3) and the load-bearing arm (2).

2. The self-resetting high-low cycle composite fatigue test fixture adapted to the size of the notched specimen according to claim 1 is characterized in that: The two sides of the load-bearing arm (2) are respectively fixed with spring seats (12) by bolts, the two sides of the swing arm (3) are respectively provided with circular grooves, the center of the circular groove of the swing arm (3) is fixed with a spring column (14) through a screw hole, the diameter of the circular groove of the swing arm (3) is consistent with the outer diameter of the return spring (13), the diameter of the spring column (14) is consistent with the inner diameter of the return spring (13), and one end of the return spring (13) is sleeved on the spring column (14) on one side of the swing arm (3); A circular groove is formed on the spring seat (12) on the same side. A spring column (14) is fixed at the center of the circular groove of the spring seat (12) through a screw hole. The diameter of the circular groove of the spring seat (12) is consistent with the outer diameter of the return spring (13). The diameter of the spring column (14) is consistent with the inner diameter of the return spring (13). The other end of the return spring (13) is sleeved on the spring column (14) of the spring seat (12).

3. The self-resetting high-low cycle composite fatigue test fixture adapted to the size of the notched specimen according to claim 2 is characterized in that: The load-bearing arm (2) is provided with a circular through hole, a bearing (6) is provided in the circular through hole, a sleeve (5) is provided between the bearing (6) and the swing arm (3), and the bearing (6) is connected to the swing arm (3) and the load-bearing arm (2) respectively; a fine groove is provided on one side of the circular through hole, and an adjusting bolt (11) for adjusting the width of the fine groove is provided on the load-bearing arm (2).

4. The self-resetting high-low cycle composite fatigue test fixture adapted to the size of the notched specimen according to claim 3 is characterized in that: The lower end of the lower fixture (9) is provided with a boss, and the boss is provided with a plurality of threaded holes at different heights for connecting the exciting rod; The upper end of the upper clamp (7) has a boss, and the lower end of the base (1) has a boss. The fatigue machine clamps the bosses of the upper clamp (7) and the base (1) respectively.

5. The self-resetting high-low cycle composite fatigue test fixture adapted to the size of the notched specimen according to claim 4 is characterized in that: An extended axis of the bearing (6) passes through the notch of the notch test piece (15).

6. The self-resetting high-low cycle composite fatigue test fixture adapted to the size of the notched specimen according to claim 5 is characterized in that: Pins are provided on both sides of the base (1), the ends of the pins are threaded, through holes are opened at positions corresponding to the pins of the load-bearing arm (2) and the base (1), the pins of the base (1) pass through the through holes, and the base (1) is connected to the load-bearing arm (2) by tightening bolts.

7. The self-resetting high-low cycle composite fatigue test fixture adapted to the size of the notched specimen according to claim 6 is characterized in that: The swing arm (3) is provided with a hexagonal hole, and the lower clamp (9) has hexagonal columns on both sides. The hexagonal columns of the lower clamp (9) are embedded in the hexagonal holes of the swing arm (3) and are connected to the swing arm (3).

8. The self-resetting high-low cycle composite fatigue test fixture adapted to the size of the notched specimen according to claim 7 is characterized in that: The upper clamp (7), the upper clamp plate (8), the lower clamp (9) and the lower clamp plate (10) all have wedge-shaped surfaces matching the test piece; the lower clamp (9) and the lower clamp plate (10) clamp one end of the notched test piece (15) via fixing bolts, and the upper clamp (7) and the upper clamp plate (8) clamp the other end of the notched test piece (15) via fixing bolts.

9. The self-resetting high-low cycle composite fatigue test fixture adapted to the size of the notched specimen according to any one of claims 2 to 8, characterized in that: The stiffness coefficient K of the return spring (13) satisfies: K=P / 2L Wherein, P is the low cycle load, and L is the vertical distance between the notch of the notch test piece (15) and the return spring (13).

10. The self-resetting high-low cycle composite fatigue test fixture adapted to the size of the notched specimen according to claim 9, characterized in that: A heating coil is arranged outside the notched test piece (15).

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