Double-shear experimental method and experimental device under ultrahigh strain rate
By canceling the incident rod in the Hopkinson rod experimental device, directly impacting the double shear sample and using an optical extensometer to measure the deformation, the problem of difficult maintenance of the strain rate platform segment in the traditional method is solved, and the ultra-high strain rate is achieved Experimental accuracy and stability.
Patent Information
- Application Number
- CN202411290503.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-14
- Publication Date
- 2024-12-20
AI Technical Summary
The traditional Hopkinson rod experimental device is difficult to maintain a constant strain rate platform section under ultra-high strain rate, resulting in conflicting experimental results, mainly due to the unsatisfactory loading of the incident wave, which leads to stress waveform distortion and oscillation, and cannot be loaded stably into the sample. .
Using the double shear experimental method, the incident rod was cancelled, the bullet directly hit the double shear sample, the deformation was obtained through an optical extensometer, and the load was obtained in combination with the strain collector, the relationship between stress and strain was determined, the rise time of the incident wave was eliminated, and only the Platform segment.
The experimental accuracy at ultra-high strain rate is improved, the stability of strain rate is ensured, stress waveform distortion is avoided, and the reliability of experimental results is enhanced.
Smart Images
Figure CN119164795A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of material mechanical property research, and in particular relates to a double shearing test method and an experimental device for ultra-high strain rate. Background Art
[0002] In the past, there have been many research methods for the mechanical properties of metal materials under quasi-static conditions. After the invention of the Hopkinson bar experimental device, there have been many reports on the mechanical behavior of metal materials under high strain rate conditions. The Hopkinson bar experimental technology is currently the most important and reliable experimental method for the mechanical properties of materials under ultra-high strain rates. With the research on materials under ultra-high strain rates (strain rate range of 10 4 s~10 6 s －1 As the research on mechanics under the condition of high strain rate deepens, the Hopkinson bar experimental technology has also encountered some bottlenecks. For example, some of the experimental results under ultra-high strain rate are contradictory, especially when the strain rate reaches 10 3 When the above happens, the contradictory results become more obvious.
[0003] The reason for the contradictory experimental results is that in the traditional Hopkinson pressure bar device, in order to make the material have a higher strain rate, the impact speed of the bullet (short rod) needs to be continuously increased. Figure 1 As shown in Figures (a), (b) and (c) in Figure 3, as the impact velocity increases, it becomes increasingly difficult to maintain a constant strain rate platform segment, and this changing platform segment can no longer represent the actual loading conditions.
[0004] As the impact velocity increases, the strain rate plateau becomes more difficult to maintain constant, mainly due to the non-ideal loading incident wave. Figure 2 According to the one-dimensional stress wave theory, in the traditional Hopkinson pressure bar test device, the bullet (short rod) first hits the incident rod (long rod). At this time, the loading waveform is a strong discontinuous wave. The waveform inside the long rod should be a rectangular square wave, but due to the influence of the lateral inertia effect, geometric dispersion occurs. The actual waveform has a rise time and oscillates in the platform section. When the square wave loads the sample later, the incident rod will load this distorted square wave to the sample. Moreover, as the loading speed of the bullet increases, the width of the square wave in the incident rod will not change much, the wavelength is always about twice the length of the loaded bullet, and the wave speed is also constant. As the loading speed increases, the speed of the incident rod will also increase, which will result in the loading wave in the incident rod not being fully input into the sample, and the collision process between the incident rod and the sample will end, that is, the incident rod and the sample are no longer in contact, and the loading process ends, which makes the subsequent stress wave not loaded into the sample, which leads to a decrease in the proportion of the stress wave platform section loaded on the sample, and it is impossible to achieve a stable high strain rate in the sample. Summary of the invention
[0005] In view of this, the present invention provides a double shear test method and experimental device for ultra-high strain rate. The method eliminates the incident rod in the Hopkinson pressure bar device, allows the bullet to directly hit the sample, and directly obtains the deformation of the double shear sample through an optical extensometer, thereby improving the experimental accuracy at ultra-high strain rate.
[0006] The present invention adopts a double shear test method for ultra-high strain rate using the following technical scheme:
[0007] A double shear test method for ultra-high strain rate, characterized in that the test method comprises:
[0008] The bullet is fired through the loading device to directly impact the double shear specimen installed at one end of the transmission tube;
[0009] The deformation of the double shear specimen in the axial direction of the transmission tube is obtained by an optical extensometer, and the load on the double shear specimen in the axial direction of the transmission tube is obtained by a strain collector;
[0010] The relationship between the stress and strain of the double shear specimen at an ultra-high strain rate is determined according to the deformation of the double shear specimen in the axial direction of the transmission tube and the load applied to the double shear specimen in the axial direction of the transmission tube.
[0011] Furthermore, taking time as a reference, the deformation of the double shear specimen in the axial direction of the transmission tube and the load applied to the double shear specimen in the axial direction of the transmission tube are combined to obtain a deformation-load curve, and then the deformation-load curve is derived to obtain a stress-strain curve of the double shear specimen.
[0012] The present invention provides a double shear test device for ultra-high strain rate using the following technical solutions:
[0013] A double shear test device for ultra-high strain rate, comprising a loading device, a transmission tube, an optical extensometer, a strain gauge, a strain acquisition instrument, and a digital processing device;
[0014] The loading device is used to fire a bullet to directly impact the double shear specimen installed at one end of the transmission tube;
[0015] The optical extensometer is used to measure the deformation of the double shear specimen in the axial direction of the transmission tube after being hit by the bullet;
[0016] The strain gauge is attached to the transmission tube and is connected to the signal of the strain collector, so as to obtain the load on the double shear specimen in the axial direction of the transmission tube after being hit by the bullet;
[0017] The digital processing device is connected to the optical extensometer and the strain collector for obtaining the relationship between the stress and strain of the double shear specimen.
[0018] Furthermore, it also includes a speed measuring device;
[0019] The speed measuring device is used to measure the speed of the bullet.
[0020] Furthermore, the digital processing device includes an oscilloscope and a computer;
[0021] The input end of the digital oscilloscope is connected to the optical extensometer and the strain collector for displaying the relationship between the deformation of the double shear specimen in the direction of the transmission tube axis and time in a graphical manner, and the relationship between the load on the double shear specimen in the direction of the transmission tube axis and time in a graphical manner;
[0022] The computer is connected to the output terminal signal of the digital oscilloscope to obtain the relationship between the stress and strain of the double shear specimen at an ultra-high strain rate.
[0023] Furthermore, the bullet is rod-shaped, and its diameter is smaller than the inner diameter of the transmission tube.
[0024] Furthermore, an energy absorbing and buffering structure is provided in the transmission tube cavity and / or at the other end of the transmission tube.
[0025] Furthermore, the speed measuring device is a laser speed measuring system.
[0026] Further, the double shear specimen includes a loading section, two supporting sections and two testing sections;
[0027] The loading section is in the shape of a rectangular column;
[0028] The two support sections are rectangular column-shaped and symmetrically arranged on both sides of the loading section;
[0029] The test section is in the shape of a rectangular column and is arranged between the loading section and the supporting section, and the cross-sectional area of the test section is smaller than the cross-sectional area of the supporting section.
[0030] Furthermore, rounded corners are used between the test section and the loading section, and between the test section and the supporting section.
[0031] Beneficial effects:
[0032] 1. A bullet is fired through a loading device to directly impact a double shear specimen installed at one end of a transmission tube; the deformation of the double shear specimen in the axial direction of the transmission tube is obtained through an optical extensometer, and the load on the double shear specimen in the axial direction of the transmission tube is obtained through a strain collector, and the strain collector is connected to the signal of the strain gauge pasted on the transmission tube; the relationship between the stress and strain of the double shear specimen at an ultra-high strain rate is determined based on the deformation of the double shear specimen in the axial direction of the transmission tube and the load on the double shear specimen in the axial direction of the transmission tube.
[0033] This method eliminates the rise time of the incident wave, leaving only a platform segment in the waveform, thereby stabilizing the strain rate in the sample and improving the experimental accuracy at ultra-high strain rates.
[0034] 2. The loading device is used to fire a bullet to directly impact the double shear specimen installed at one end of the transmission tube; the optical extensometer is used to measure the deformation of the double shear specimen in the axial direction of the transmission tube after being hit by the bullet; the strain gauge is pasted on the transmission tube and connected to the signal of the strain collector to obtain the load on the double shear specimen in the axial direction of the transmission tube after being hit by the bullet; the digital processing device is connected to the optical extensometer and the strain collector signal to obtain the relationship between the stress and strain of the double shear specimen.
[0035] In this way, there is no incident rod in the experimental device, and there is no incident wave in the traditional scheme, so there is no rise time of the incident wave, leaving only a platform segment in the waveform, so that the strain rate in the sample can be stabilized, improving the experimental accuracy under ultra-high strain rates.
[0036] 3. The speed measuring device is used to measure the speed of the bullet. In this way, the relationship between the stress and strain of the double shear specimen under different set conditions such as bullet speed, bullet diameter, bullet weight (bullet diameter and bullet weight can be selected according to experimental requirements) can be obtained.
[0037] 4. The bullet is rod-shaped and its diameter is smaller than the inner diameter of the transmission tube. In this way, after the double shear specimen is broken by impact, the bullet can continue to fly in the tube, thus avoiding damage to the transmission tube.
[0038] 5. An energy-absorbing buffer structure is provided inside the transmission tube or at the other end of the transmission tube. In this way, the remaining kinetic energy of the bullet after hitting the double shear specimen can be absorbed by the buffer mechanism, thus avoiding plastic deformation of the incident tube and reducing experimental errors.
[0039] 6. The support section is a rectangular column and is symmetrically arranged on both sides of the loading section; the test section is a rectangular column arranged between the loading section and the support section, and the cross-sectional area of the test section is smaller than the cross-sectional area of the support section; the double shear specimen is supported on the wall of the transmission tube through the support section.
[0040] In this way, when the loading section of the sample is subjected to high-speed impact, the test section can form a shear stress state in the shear regions on its left and right sides, thereby achieving the purpose of studying the relationship between stress and strain of metal materials under the shear stress state.
[0041] 7. The test section and the loading section, as well as the test section and the support section are all provided with rounded corners. This can prevent stress concentration at the connection between the test section and the loading section, as well as the test section and the support section, so that the stress is distributed in the test section as much as possible, thereby improving the reliability of the experimental results. BRIEF DESCRIPTION OF THE DRAWINGS
[0042] Figure 1 These are the stress-strain curves obtained with increasing impact speed in the traditional Hopkinson bar device, where (a) to (c) the impact speed is continuously increased;
[0043] Figure 2 The stress-strain curves between elementary theory and actual measurements when using the traditional Hopkinson pressure bar apparatus for experiments;
[0044] Figure 3 A double shear test device for ultra-high strain rate provided in an embodiment of the present invention;
[0045] Figure 4 A double shear specimen for use at ultra-high strain rates provided by an embodiment of the present invention, wherein (a) is a main view, (b) is a left view, and (c) is a schematic diagram of a three-dimensional structure;
[0046] Figure 5 A schematic diagram of the three-dimensional structure of another double shear specimen used at an ultra-high strain rate provided in an embodiment of the present invention.
[0047] Among them, 1-bullet, 2-speed measuring device, 3-double shear specimen, 301-support section, 302-test section, 303-loading section, 4-strain gauge, 5-transmission tube, 6-strain acquisition instrument, 7-digital oscilloscope, 8-optical extensometer, 9-computer. DETAILED DESCRIPTION
[0048] The present invention is described in detail below with reference to the accompanying drawings and embodiments.
[0049] Embodiment 1:
[0050] Reference Figure 1 to Figure 3 , this embodiment provides a double shear test method for ultra-high strain rate, the test method is:
[0051] The bullet is fired by the loading device to directly impact the double shear specimen 3 installed at one end of the transmission tube 5;
[0052] The deformation of the double shear specimen 3 in the axial direction of the transmission tube is obtained by the optical extensometer 8, and the load on the double shear specimen 3 in the axial direction of the transmission tube 5 is obtained by the strain collector 6. The strain collector 6 is connected to the strain gauge 4 bonded to the transmission tube 5.
[0053] The relationship between the stress and strain of the double shear specimen 3 at an ultra-high strain rate is determined based on the deformation of the double shear specimen 3 in the axial direction of the transmission tube and the load received in the axial direction of the transmission tube 5 .
[0054] This method eliminates the incident rod and the rise time of the incident wave, leaving only the platform section of the stress-strain curve of the double shear specimen, thereby stabilizing the strain rate in the double shear specimen 3 and improving the experimental accuracy at ultra-high strain rates. Moreover, this experimental scheme, when used in conjunction with the double shear specimen 3, can more accurately obtain the dynamic plasticity of the material, and can allow the nominal strain rate to vary over a wide range, and obtain the axial deformation and deformation history during the development of the adiabatic shear band, which has more accurate test results and flexibility for material testing at high strain rates and the study of adiabatic shear bands.
[0055] In this method, the deformation of the double shear specimen 3 in the axial direction of the transmission tube 5 and the load on the double shear specimen 3 in the axial direction of the transmission tube 5 are both functions of time. In the subsequent data processing, the time is used as a reference to combine the two to obtain a deformation-load curve. Through the deformation-load curve, the stress-strain curve can be calculated by derivation of the deformation-load relationship. In addition, the stress-strain relationship of the double shear specimen 3 under different loading conditions can be obtained by changing the speed, diameter (the bullet 1 in this embodiment is rod-shaped), weight, etc. of the bullet 1.
[0056] It should be pointed out that the Hopkinson bar experimental device is based on the one-dimensional stress wave theory, and obtains the stress-strain relationship of the sample material by measuring the strain on the incident rod and the transmission rod, thereby successfully avoiding the difficulty of simultaneously measuring the stress and strain that change with time at the same position of the sample. The device has a simple structure and low cost. However, based on the technical problems recorded in the background technology, the present invention eliminates the incident rod and directly obtains the strain of the sample through an optical extensometer, which can avoid the technical problems existing in the Hopkinson bar experimental device at ultra-high strain rates.
[0057] Embodiment 2:
[0058] Reference Figure 3 This embodiment provides a double shear test device for ultra-high strain rate, which includes a loading device (not shown in the figure), a transmission tube 5, an optical extensometer 8, a strain gauge 4, a strain acquisition instrument 6, and a digital processing device, wherein:
[0059] The loading device is used to launch a bullet 1 to directly impact the double shear specimen 3 installed at one end of the transmission tube 5; the optical extensometer 8 is used to measure the deformation of the double shear specimen 3 in the axial direction of the transmission tube 5 after the bullet hits; the strain gauge 4 is pasted on the transmission tube 5 and is connected to the strain collector 6 for signal, and the strain collector 6 obtains the load on the double shear specimen 3 in the axial direction of the transmission tube 5 through the strain gauge 4; the digital processing device is connected to the strain collector 6 and the optical extensometer 8 for signal processing and measuring the deformation of the double shear specimen 3 in the axial direction of the transmission tube 5 after the bullet hits, and the load data on the double shear specimen 3 in the axial direction of the transmission tube 5, so as to obtain the relationship between the stress and strain of the double shear specimen 3 at an ultra-high strain rate.
[0060] There is no incident rod in this experimental device, so there is no incident wave in the traditional scheme, so there is no rise time of the incident wave, so that the stress-strain curve of double shear specimen 3 only has a platform segment, and the strain rate in double shear specimen 3 can be stabilized, which solves the problem of contradictory double shear test results under ultra-high strain rates and improves the experimental accuracy under ultra-high strain rates.
[0061] Specifically, in the present embodiment, the digital processing device comprises a digital oscilloscope 7 and a computer 9, wherein the signal input end of the digital oscilloscope 7 is signal-connected to the strain collector 6 and the optical extensometer 8, and the output end of the digital oscilloscope 7 is signal-connected to the computer 9. The digital oscilloscope 7 can display the relationship between the deformation of the double shear specimen 3 in the axial direction of the transmission tube 5 and time in a graphical manner, and can display the relationship between the load and time received by the double shear specimen 3 in the axial direction of the transmission tube 5 in a graphical manner. Moreover, the relationship between the deformation of the double shear specimen 3 in the axial direction of the transmission tube 5 and time, and the relationship between the load and time received by the double shear specimen 3 in the axial direction of the transmission tube 5 are summarized to the computer 9 through the digital oscilloscope 7. The computer 9 uses time as a reference, combines the two to obtain the deformation-load relationship, and calculates the stress-strain curve of the double shear specimen 3 through the deformation-load relationship.
[0062] In this embodiment, the bullet 1 is in the shape of a rod with a diameter of 10 mm, and the material is martensite, and the ejection speed is between 1 and 200 m / s. Moreover, the diameter of the rod-shaped bullet 1 is smaller than the inner diameter of the transmission tube 5. In this way, after the double shear specimen 3 is broken by impact, the bullet 1 can continue to fly in the transmission tube 5, thereby avoiding damage to the transmission tube 5. If a transmission rod is selected instead of the transmission tube 5, the bullet 1 will rebound after hitting the double shear specimen 3, and all the kinetic energy will be loaded into the transmission rod in a very short time, which will cause damage to the transmission rod. Furthermore, in this embodiment, an energy absorbing buffer structure is provided in the cavity of the transmission tube 5 or at the other end of the transmission tube 5 (the end opposite to the installation of the double shear specimen 3). In this way, the remaining kinetic energy of the bullet 1 after hitting the double shear specimen 3 can be absorbed by the buffer mechanism, avoiding plastic deformation of the transmission tube 5 and reducing experimental errors.
[0063] As an improvement, the experimental device also includes a speed measuring device 2, which is arranged between the loading device and the double shear sample 3, and is used to measure the speed of the bullet 1 (the speed can be the speed at any time after the bullet 1 is fired and before it hits the double shear sample 3, or the average speed of the bullet 1 from the time it is fired to the time it hits the double shear sample 3, or the speed processed by other mathematical methods, the core of which is to reduce the error in the speed calculation when the bullet 1 hits the double shear sample 3). In this way, the relationship between the stress and strain of the double shear sample 3 under different set conditions such as the speed of the bullet 1, the diameter of the bullet 1, and the weight of the bullet 1 (the diameter of the bullet 1 and the weight of the bullet 1 can be selected according to the experimental requirements) can be obtained. Specifically, in this embodiment, the speed measuring device 2 is composed of three light sources and three independent photodiodes, which are arranged between the loading device and the transmission tube 5.
[0064] Embodiment three:
[0065] Reference Figure 3~Figure 4 On the basis of the second embodiment, a double shear specimen 3 for ultra-high strain rate is provided, the double shear specimen 3 comprises a loading section 303, two supporting sections 301 and two testing sections 302, wherein:
[0066] The loading section 303 is in the shape of a rectangular column; the two supporting sections 301 are in the shape of rectangular columns and are symmetrically arranged at both ends of the height direction of the loading section 303; the test section 302 is in the shape of a rectangular column arranged between the loading section 303 and the supporting section 301, and the cross-sectional area of the test section 302 is smaller than the cross-sectional area of the supporting section 301; the double shear specimen is supported on the tube wall of the transmission tube 5 by the supporting section 301.
[0067] Specifically, in this embodiment, the length of the cross section of the test section 302 is 6 mm, the width is 5 mm, and the height is 2 mm; the length of the cross section of the support section 301 is 10 mm, the width is 10 mm, and the height is 8 mm; the length of the cross section of the loading section 303 is 10 mm, the width is 6 mm, and the height is 10 mm. Moreover, the test section 302 and the loading section 303, as well as the connection between the test section 302 and the support section 301 are all provided with fillets with a radius of 0.2 mm, so that stress concentration can be prevented at the connection between the test section 302 and the loading section 303, as well as the connection between the test section 302 and the support section 301, so that the stress is distributed as much as possible in the test section 302, thereby improving the reliability of the experimental results.
[0068] The double shear specimen 3 can be manufactured by the following steps:
[0069] (i) Using wire-cutting electric discharge, cut the specimen from a 12 mm diameter low-carbon steel bar, and then further finish the specimen according to the drawing;
[0070] (ii) Keep the processed samples in a vacuum environment at 800°C for 1.5 hours and cool them in a furnace.
[0071] (III) Polish the sample so that its surface roughness reaches the Ra1.6 standard, then clean it with alcohol and dry it for later use.
[0072] Embodiment 4:
[0073] Reference Figure 3 and Figure 5 On the basis of the second embodiment, another double shear specimen for ultra-high strain rate is provided. The double shear specimen 3 is different from the third embodiment in that the sizes of the support section 301 and the fillet are different. In this embodiment, the support section 301 and the loading section 303 have the same length and width.
[0074] Specifically, in this embodiment, the cross section of the support section 301 has a length of 10 mm, a width of 6 mm, a height of 8 mm, and a fillet radius of 0.2 mm. In addition, the raw material of the double shear specimen 3 is a low-carbon steel plate, and of course, other raw materials may also be selected.
[0075] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.
Claims
1. A double shear test method for ultra-high strain rate, characterized in that: The experimental method includes: The bullet is fired through the loading device to directly impact the double shear specimen installed at one end of the transmission tube; The deformation of the double shear specimen in the axial direction of the transmission tube is obtained by an optical extensometer, and the load on the double shear specimen in the axial direction of the transmission tube is obtained by a strain collector; The relationship between the stress and strain of the double shear specimen at an ultra-high strain rate is determined according to the deformation of the double shear specimen in the axial direction of the transmission tube and the load applied to the double shear specimen in the axial direction of the transmission tube.
2. A double shear test method for ultra-high strain rate, characterized in that: First, with time as a reference, the deformation of the double shear specimen in the axial direction of the transmission tube and the load received by the double shear specimen in the axial direction of the transmission tube are combined to obtain a deformation-load curve, and then the deformation-load curve is derived to obtain a stress-strain curve of the double shear specimen.
3. A double shear test device for ultra-high strain rate, characterized in that: It includes a loading device, a transmission tube, an optical extensometer, a strain gauge, a strain acquisition instrument, and a digital processing device; The loading device is used to fire a bullet to directly impact the double shear specimen installed at one end of the transmission tube; The optical extensometer is used to measure the deformation of the double shear specimen in the axial direction of the transmission tube after being hit by the bullet; The strain gauge is attached to the transmission tube and is connected to the signal of the strain collector, so as to obtain the load on the double shear specimen in the axial direction of the transmission tube after being hit by the bullet; The digital processing device is connected to the optical extensometer and the strain collector for obtaining the relationship between the stress and strain of the double shear specimen.
4. A double shear test device for ultra-high strain rate according to claim 3, characterized in that: Also includes a speed measuring device; The speed measuring device is used to measure the speed of the bullet.
5. A double shear test device for ultra-high strain rate according to claim 3 or 4, characterized in that: The digital processing device includes an oscilloscope and a computer; The input end of the digital oscilloscope is connected to the optical extensometer and the strain collector for displaying the relationship between the deformation of the double shear specimen in the direction of the transmission tube axis and time in a graphical manner, and the relationship between the load on the double shear specimen in the direction of the transmission tube axis and time in a graphical manner; The computer is connected to the output terminal signal of the digital oscilloscope to obtain the relationship between the stress and strain of the double shear specimen at an ultra-high strain rate.
6. A double shear test device for ultra-high strain rate according to claim 3 or 4, characterized in that: The bullet is rod-shaped, and its diameter is smaller than the inner diameter of the transmission tube.
7. A double shear test device for ultra-high strain rate according to claim 3 or 4, characterized in that: An energy absorbing and buffering structure is arranged inside the transmission tube cavity and / or at the other end of the transmission tube.
8. A double shear test device for ultra-high strain rate according to claim 3 or 4, characterized in that: The speed measuring device is a laser speed measuring system.
9. A double shear test device for ultra-high strain rate according to claim 3 or 4, characterized in that: The double shear specimen includes a loading section, two supporting sections and two testing sections; The loading section is in the shape of a rectangular column; The two support sections are rectangular column-shaped and symmetrically arranged on both sides of the loading section; The test section is in the shape of a rectangular column and is arranged between the loading section and the supporting section, and the cross-sectional area of the test section is smaller than the cross-sectional area of the supporting section.
10. A double shear test device for ultra-high strain rate according to claim 9, characterized in that: Rounded corners are used for transition between the test section and the loading section, and between the test section and the supporting section.