Constant-amplitude impact fatigue device based on Hopkinson rod three-point bending sample

Abstract

The invention belongs to the technical field of impact fatigue performance detection, and particularly relates to a Hopkinson rod three-point bending sample-based constant-amplitude impact fatigue device, which comprises a dynamic indentation system, an energy absorption system, a strain measurement system and a pressure data acquisition system, and is characterized in that the dynamic indentation system comprises kinetic energy application equipment, an impact rod, an incident rod and a three-point bending test bed; the strain measurement system comprises a strain gauge and a dynamic strain acquisition instrument which are electrically connected, the pressure data acquisition system comprises a force transducer and a data acquisition instrument which are electrically connected, and the energy absorption system comprises a flange, a sleeve and a mass block. The device depends on the Hopkinson rod technology, the momentum well design is ingeniously fused, the problem of secondary loading is effectively avoided, constant-amplitude impact fatigue loading is achieved, key parameters such as the yield point, the elastic limit and the breaking strength of the material are accurately measured, and the reliability and safety of the material are comprehensively evaluated.

Description

Technical Field

[0001] The invention belongs to the technical field of impact fatigue performance detection, and in particular relates to a constant amplitude impact fatigue device based on a Hopkinson rod three-point bending specimen. Background Art

[0002] In key engineering fields such as aerospace, modern weapons, and energy mining, many structural components, such as arresting hooks of carrier-based aircraft, aircraft landing gear, artillery barrels, automatic machines in firearms, drill bits, drill rods, and cold working dies in oil production, are often subjected to repeated impacts of small loads (small energy). This loading mode is different from single impact fractures with large energy and conventional quasi-static fatigue. It is caused by the accumulation of damage caused by repeated impact loads, which leads to crack initiation, expansion, and final failure. This phenomenon is called impact fatigue. The particularity of the impact fatigue problem lies in the fact that the effect of strain rate on fatigue damage and life cannot be ignored. The strain rate may cause some materials to yield or even reach the ultimate strength, especially the change of fracture toughness, which may lead to premature failure of engineering components. Engineering practice has proved that most of the failure and damage of these structural parts are caused by impact fatigue. If only the test results of a single impact fracture are used to evaluate the impact fatigue performance, it often leads to too high requirements for material toughness and too conservative evaluation standards. Conventional quasi-static fatigue tests do not consider the decrease in toughness caused by the strain rate effect, so it is difficult to predict the premature failure of materials caused by impact fatigue.

[0003] Therefore, it is crucial to accurately evaluate the impact fatigue performance, which requires scientific impact fatigue test results. These test results can provide a deeper understanding of the behavior of materials under actual working conditions, provide key data for engineering design and life prediction, and thus reduce the risk of structural failure. Faced with the impact fatigue challenges faced by important facility components, the engineering community is constantly exploring and realizing the innovation and improvement of related devices. Among these innovations, the drop hammer and pendulum impact fatigue test methods in the energy method are particularly prominent. They use a motor to lift the pendulum to a certain height, release the pendulum to impact the yoke-type force transmission mechanism, and apply a tensile impact load to the tensile specimen to obtain experimental data; the impact fatigue device driven by the crank-connecting rod mechanism developed by Krimo Azouaoui et al. is used to perform multiple small-energy impacts on composite plate specimens to study their impact fatigue performance and damage mechanism; the drop hammer test bench designed by Sun Qianwen et al. uses a three-point bending specimen with a notch, and records the strain time history of the notch front edge through a strain gauge attached to the notch, so as to evaluate the degree of plastic deformation caused by each impact and determine the number of cycles of crack initiation. These innovative methods and improvements not only demonstrate the continuous progress of related industries in the field of impact fatigue research, but also reflect the engineering community's unremitting efforts to improve the reliability and durability of key components.

[0004] Although the engineering community has achieved some innovative results in solving the impact fatigue problem of important components, these solutions still need to be further improved in practical applications. Specifically, the pendulum impact fatigue test method is mainly suitable for low-cycle impact fatigue with a short fatigue life due to the low frequency of applied loads. The impact fatigue device driven by the crank-connecting rod mechanism developed by Krimo Azouaoui and others, although technically innovative, also faces the problem of frequency limitation, and measures need to be taken to prevent secondary impacts to avoid affecting the accuracy of the experimental results. Although the drop hammer test bench designed by Sun Qianwen and others has been improved by using a three-point bending specimen, its test frequency is still not high, and it is difficult to completely avoid the problem of secondary impacts.

[0005] Therefore, although the existing technology can deal with the impact fatigue problem of components to a certain extent, it is still necessary to make the impact frequency closer to the actual engineering application environment of the material. During the test, secondary impact should be avoided to improve the accuracy of the device, thereby providing more critical data for engineering design and life prediction, and effectively reducing the risk of structural failure. At the same time, considering the cost-effectiveness, it is particularly important to design an impact fatigue device that is both economical and reliable. This can not only improve the accuracy of the test, but also ensure a comprehensive evaluation of the fatigue performance of the component within the budget constraints, providing solid technical support for engineering safety and reliability. Summary of the invention

[0006] The purpose of the present invention is to provide a constant amplitude impact fatigue device based on a Hopkinson bar three-point bending specimen, which relies on the Hopkinson bar technology and cleverly integrates the momentum well design, effectively avoids the problem of secondary loading, realizes constant amplitude impact fatigue loading, accurately determines key parameters such as the yield point, elastic limit and breaking strength of the material, and comprehensively evaluates the reliability and safety of the material.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A constant amplitude impact fatigue device based on a Hopkinson bar three-point bending specimen, comprising a dynamic indentation system, an energy absorption system, a strain measurement system and a pressure data acquisition system;

[0009] The dynamic indentation system comprises a kinetic energy application device, an impact rod, an incident rod and a three-point bending test bench, wherein the impact rod and the three-point bending test bench are respectively opposite to two ends of the incident rod, and the impact rod and the kinetic energy application device are opposite;

[0010] The strain measurement system includes an electrically connected strain gauge and a dynamic strain acquisition instrument, wherein the strain gauge is mounted on the incident rod;

[0011] The pressure data acquisition system includes an electrically connected force sensor and a data acquisition instrument, and the three-point bending test bench is fixedly connected to the force sensor;

[0012] The energy absorption system includes a momentum trap unit assembled on the outside of the incident rod, the momentum trap unit includes a flange, a sleeve and a mass block, the sleeve and the mass block are slidably connected to the outside of the incident rod, and the flange is nested and connected to one end of the incident rod close to the impact rod.

[0013] Furthermore, the kinetic energy applying device comprises an impact cylinder, a front end of which is fixedly connected to a gun barrel, and the impact rod is slidably connected to the inside of the gun barrel.

[0014] Furthermore, the strain gauge is bonded to the middle position of the incident rod.

[0015] Furthermore, one end of the incident rod is fixedly connected to a pressure head portion.

[0016] Furthermore, the pressure head portion comprises a connecting block, both ends of which are respectively fixedly connected with a threaded rod and a conical pressure head, one end of the incident rod is provided with a threaded hole, and the threaded rod is threadedly connected inside the threaded hole.

[0017] Furthermore, the bottom radius of the conical indenter is r 2 =2.02mm, and the semi-cone angle of the tip of the conical indenter is 70.3°.

[0018] Furthermore, the impact rod and the incident rod are both cylindrical rods, the cylindrical rods are made of 45# steel, and the radius of the cylindrical rod is r 1 =5mm, and the pressing head is made of diamond.

[0019] A constant amplitude impact fatigue test method based on a Hopkinson bar three-point bending specimen comprises the following steps:

[0020] Step 1: Build a constant amplitude impact fatigue device;

[0021] Step 2: Fix the sample on the three-point bending test bench according to the three-point bending method;

[0022] Step 3: Push the impact rod to make it impact the incident rod once, so that the incident rod drives the indenter head to press into the sample to produce an indentation;

[0023] Step 4: Collect data through strain gauges and force sensors.

[0024] The technical effects achieved by the present invention are:

[0025] A constant amplitude impact fatigue device based on a Hopkinson bar three-point bending specimen of the present invention relies on the Hopkinson bar technology and cleverly integrates the momentum well design, effectively avoiding the problem of secondary loading and realizing constant amplitude impact fatigue loading. The device adopts a three-point bending test method, which not only ensures the stability of the specimen, but also can obtain the load-displacement curve, and then accurately determine the key parameters of the material such as the yield point, elastic limit and breaking strength, and comprehensively evaluate the reliability and safety of the material. These precise test results deepen our understanding of the behavior of materials in actual working environments, provide crucial data support for engineering design and life prediction, and effectively reduce the risk of structural failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the structure of the present invention;

[0027] Figure 2 It is a partial structural schematic diagram of the present invention;

[0028] Figure 3 It is a schematic diagram of a local explosion structure of the present invention;

[0029] Figure 4 It is a schematic structural diagram of the pressure head of the present invention;

[0030] Figure 5 The present invention Figure 1 The schematic diagram at A in the middle;

[0031] Figure 6 It is a waveform propagation schematic diagram of the present invention.

[0032] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0033] 1. Impact rod; 2. Flange; 3. Sleeve; 4. Mass block; 5. Incident rod; 6. Pressure head; 7. Strain gauge; 8. Sample unit; 9. Force sensor; 10. Three-point bending test bench; 11. Threaded rod; 12. Conical pressure head; 13. Threaded hole; 14. Impact cylinder; 15. Gun barrel; 16. Connecting block. DETAILED DESCRIPTION

[0034] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or several specific embodiments of the present invention, and does not strictly limit the scope of protection of the specific claims of the present invention.

[0035] Embodiment 1:

[0036] like Figure 1-Figure 6As shown, a constant amplitude impact fatigue device based on a Hopkinson bar three-point bending specimen includes a dynamic indentation system, an energy absorption system, a strain measurement system and a pressure data acquisition system;

[0037] Among them, the dynamic indentation system includes a kinetic energy application device, an impact rod 1, an incident rod 5 and a three-point bending test bench 10. The impact rod 1 and the three-point bending test bench 10 are respectively opposite to the two ends of the incident rod 5. When the impact rod 1 moves, it can perform a single impact on the incident rod 5. The sample unit 8 is assembled on the three-point bending test bench 10, so that the sample unit 8 forms a three-point bending. A three-point bending specimen is selected and tested using the two-wave method, so that the mechanical properties data of the material can be obtained more accurately; using a three-point bending specimen, conventional experiments use static three-point bending tests, and dynamic three-point bending tests are closer to engineering practice and can better simulate the load conditions of components in engineering application environments. This is achieved here by this device. By using this device to conduct experiments, key parameters such as the yield point, elastic limit and breaking strength of the material can be accurately determined, and the reliability and safety of the material can be evaluated.

[0038] The impact rod 1 and the kinetic energy applying device are opposite to each other, and the impact rod 1 can be pushed by the kinetic energy applying device;

[0039] The kinetic energy applying device includes an impact cylinder 14, the front end of which is fixedly connected to a gun barrel 15, and an impact rod 1 is slidably connected to the inside of the gun barrel 15. At this time, the impact rod 1 can be pushed by starting the impact cylinder 14, thereby pushing the impact rod 1 relatively simply.

[0040] The strain measurement system includes an electrically connected strain gauge 7 and a dynamic strain collector, which are responsible for accurately measuring displacement data. The strain gauge 7 is mounted on the incident rod 5, and the strain gauge 7 is preferably bonded to the middle position of the incident rod 5. The displacement curve of the incident rod 5 is monitored by the strain gauge 7.

[0041] The pressure data acquisition system includes an electrically connected force sensor 9 and a data acquisition instrument, which can accurately capture the pressure load on the sample unit 8. The three-point bending test bench 10 is fixedly connected to the force sensor 9. Through the coordinated work of these systems, the device can accurately evaluate the mechanical properties of the material under impact fatigue conditions.

[0042] The energy absorption system includes a momentum trap unit installed on the outside of the incident rod 5, which is used to reduce the secondary impact loading of the incident rod 5 and ensure the accuracy of the experiment.

[0043] Specifically, the momentum trap unit includes a flange 2, a sleeve 3 and a mass block 4. The sleeve 3 and the mass block 4 are slidably connected to the outside of the incident rod 5. The flange 2 is fixedly connected to one end of the incident rod 5 close to the impact rod 1. The fixing method can be a nested connection. When the incident rod 5 is pushed by the impact rod 1, the secondary impact of the incident rod 5 can be reduced by the flange 2, the sleeve 3 and the mass block 4.

[0044] Here, the sleeve 3 , the mass 4 and the incident rod 5 are connected by sliding friction, which is as smooth as possible to reduce the friction between the sleeve 3 , the mass 4 and the incident rod 5 .

[0045] The impact rod 1 and the incident rod 5 are both cylindrical rods made of 45 steel (E = 210 GPa), and the radius is r 1 =5mm, the designed length of the incident rod 5 is L 2 =500mm.

[0046] One end of the incident rod 5 is fixedly connected to a pressure head 6, which is made of diamond (E=1100 GPa). The pressure head 6 includes a connecting block 16, and both ends of the connecting block 16 are respectively fixedly connected to a threaded rod 11 and a conical pressure head 12. One end of the incident rod 5 is provided with a threaded hole 13, and the threaded rod 11 is threadedly connected inside the threaded hole 13, so that the pressure head 6 can be replaced more conveniently. Considering the generalized wave impedance matching (ρ 1 c 1 A 1 =ρ 2 c 2 A 2 ), the bottom radius of the conical indenter 12 is designed to be r 2 =2.02mm, the semi-cone angle of the tip of the conical indenter 12 is 70.3°, and since the lengths of the flange 2 and the conical indenter 12 are much smaller than the length of the incident rod 5, their influence on the stress wave can be ignored in theory.

[0047] Among them, one size of the impact rod 1, flange 2, sleeve 3, mass block 4, incident rod 5, and pressure head 6 is disclosed herein, the length of the impact rod 1 is 100 mm, the outer diameter of the impact rod 1 is 5 mm, the diameter of the flange 2 is 7 mm, the length of the flange 2 is 2 mm, the length of the sleeve 3 is 100 mm, the outer diameter of the sleeve 3 is 7 mm, the inner diameter of the sleeve 3 is 5 mm, the length of the mass block 4 is 100 mm, the inner diameter of the mass block 4 is 5 mm, the outer diameter of the mass block 4 is 25 mm, the diameter of the incident rod 5 is 5 mm, the length of the threaded rod 11 is 7 mm, the diameter of the threaded rod 11 is 2.5 mm, the length of the connecting block 16 is 5 mm, and the diameter of the connecting block 16 is 5 mm.

[0048] The working principle of the present invention is as follows: the impact rod 1 impacts the incident rod 5 at an initial speed, generating two compression stress waves: one moves to the left in the impact rod 1, and the other moves to the right in the incident rod 5. The compression wave in the incident rod 5 reaches the flange and is divided into two waves, one enters the sleeve 3, and the other continues to propagate in the incident rod 5. The compression wave in the sleeve 3 reaches the mass block 4. Due to the rigid wall effect of the mass block 4, the transmitted wave can be ignored, and the reflected wave moves to the left back to the sleeve 3. At the same time, the compression wave in the incident rod 5 continues to move to the right. The compression wave in the impact rod 1 is reflected by the free end and becomes a tensile wave that moves to the right. The impact rod 1 slows down until it leaves the incident rod 5. One end of the impact rod 1 mounting flange 2 becomes a free end. The strain gauge 7 records the two wave signals in the incident rod 5. The compression wave first reaches the pressure head 6, driving the pressure head 6 to press into the sample unit 8 to generate an indentation.

[0049] After the compression wave is pressed into the sample unit 8, it is reflected into a tensile wave, driving the pressure head 6 to leave the sample unit 8. The two tensile waves are briefly superimposed and then separated; the tensile wave reflected by the sleeve 3 reaches the pressure head 6. At this time, the pressure head 6 is far away from the sample unit 8, and the tensile wave becomes a compression wave and moves to the left along the incident rod 5. The strain gauge 7 records two stress waves with different waveforms, the tensile wave and the compression wave. At the same time, the incident rod 5 continues to move away from the sample unit 8. The compression wave retained in the sleeve 3 is captured by the dynamic trap unit and gradually disappears. The compression wave is reflected at the free end and propagates toward the pressure head 6 again. Only the tensile wave continues to propagate and is recorded in the incident rod 5. At the same time, the stress wave makes the incident rod 5 move away from the sample unit 8, ensuring the integrity of the surface of the sample unit 8 dynamically pressed once.

[0050] In summary, this technical solution relies on the Hopkinson bar technology and cleverly integrates the momentum well design, effectively avoiding the problem of secondary loading and realizing constant amplitude impact fatigue loading. The device adopts a three-point bending test method, which not only ensures the stability of the specimen, but also can obtain the load-displacement curve, and then accurately determine the key parameters such as the yield point, elastic limit and destructive strength of the material, and comprehensively evaluate the reliability and safety of the material. These precise test results deepen our understanding of the behavior of materials in actual working environments, provide crucial data support for engineering design and life prediction, and effectively reduce the risk of structural failure.

[0051] Compared with the traditional electronic universal testing machine, the invention has achieved a significant reduction in engineering costs and a double leap in economic benefits and technical advantages. This innovation not only reduces the economic burden, but also brings significant positive impacts at both the technical and social levels. It enhances the economic benefits of technology, minimizes the impact on the environment, and plays a positive role in promoting social operation and economic development.

[0052] Embodiment 2:

[0053] This embodiment discloses a constant amplitude impact fatigue test method based on a Hopkinson bar three-point bending specimen on the basis of embodiment 1, and the method comprises the following steps:

[0054] Step 1: Build Figure 1 The constant amplitude impact fatigue device shown in the figure has a strain gauge 7 pasted in the middle of the incident rod;

[0055] Step 2: Fix the sample unit 8 on the three-point bending test bench 10 according to the three-point bending method;

[0056] Step 3: Adjust the required air pressure according to the experiment, inflate, and after reaching the required threshold, start the impact cylinder 14 to conduct the experiment, push the impact rod 1, and let the impact rod 1 impact the incident rod 5 once, so that the incident rod 5 drives the pressure head 6 to press into the sample unit 8 to produce an indentation;

[0057] In the third step, the distance between the impact rod 1 and the impact cylinder 14 is adjusted to about 2 cm, the computer is reset, and the minimum distance between the two is maintained, so that the impact rod 1 can obtain initial power in the most direct way under the power drive provided by the impact cylinder 14.

[0058] Step 4: Collect data through strain gauge 7 and force sensor 9, and the experiment is completed.

[0059] The above is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered as the protection scope of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention shall be implemented according to the conventional means in the art unless otherwise specified and limited.

Claims

1. A constant amplitude impact fatigue device based on a Hopkinson bar three-point bending specimen, characterized in that: It includes dynamic indentation system, energy absorption system, strain measurement system and pressure data acquisition system; The dynamic indentation system comprises a kinetic energy application device, an impact rod (1), an incident rod (5) and a three-point bending test bench (10), wherein the impact rod (1) and the three-point bending test bench (10) are respectively opposite to two ends of the incident rod (5), and the impact rod (1) and the kinetic energy application device are opposite to each other; The strain measurement system comprises an electrically connected strain gauge (7) and a dynamic strain acquisition instrument, wherein the strain gauge (7) is mounted on the incident rod (5); The pressure data acquisition system comprises an electrically connected force sensor (9) and a data acquisition instrument, and the three-point bending test bench (10) is fixedly connected to the force sensor (9); The energy absorption system comprises a momentum trap unit mounted on the outside of an incident rod (5), the momentum trap unit comprising a flange (2), a sleeve (3) and a mass block (4), the sleeve (3) and the mass block (4) being slidably connected to the outside of the incident rod (5), and the flange (2) being fixedly connected to one end of the incident rod (5) close to the impact rod (1).

2. The constant amplitude impact fatigue device based on the Hopkinson bar three-point bending specimen according to claim 1, characterized in that: The kinetic energy application device comprises an impact cylinder (14), the front end of which is fixedly connected to a gun barrel (15), and the impact rod (1) is slidably connected inside the gun barrel (15).

3. The constant amplitude impact fatigue device based on the Hopkinson bar three-point bending specimen according to claim 1, characterized in that: The strain gauge (7) is bonded to the middle position of the incident rod (5).

4. The constant amplitude impact fatigue device based on the Hopkinson bar three-point bending specimen according to claim 1, characterized in that: One end of the incident rod (5) is fixedly connected to a pressure head (6).

5. The constant amplitude impact fatigue device based on the Hopkinson bar three-point bending specimen according to claim 4, characterized in that: The pressure head (6) comprises a connecting block (16), the two ends of which are respectively fixedly connected with a threaded rod (11) and a conical pressure head (12), one end of the incident rod (5) is provided with a threaded hole (13), and the threaded rod (11) is threadedly connected inside the threaded hole (13).

6. The constant amplitude impact fatigue device based on the Hopkinson bar three-point bending specimen according to claim 5, characterized in that: The bottom radius of the conical indenter (12) is r2=2.02 mm, and the semi-cone angle of the tip of the conical indenter (12) is 70.3°.

7. The constant amplitude impact fatigue device based on the Hopkinson bar three-point bending specimen according to claim 4, characterized in that: The impact rod (1) and the incident rod (5) are both cylindrical rods, the cylindrical rods are made of 45 steel, the radius of the cylindrical rod is r1=5 mm, and the pressure head (6) is made of diamond.

8. A constant amplitude impact fatigue test method based on a Hopkinson bar three-point bending specimen, using a constant amplitude impact fatigue device based on a Hopkinson bar three-point bending specimen according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: Build a constant amplitude impact fatigue device; Step 2: Fix the sample (8) on a three-point bending test bench (10) by a three-point bending method; Step 3: Push the impact rod (1) to allow the impact rod (1) to impact the incident rod (5) once, so that the incident rod (5) drives the pressure head (6) to press into the sample (8) to generate an indentation; Step 4: Collect data through the strain gauge (7) and the force sensor (9).

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