Elastomer material dynamic stretching cyclic loading device based on Hopkinson pull rod and method thereof

Abstract

The invention discloses a Hopkinson pull rod-based elastomer material dynamic stretching cyclic loading device and a method thereof. The device comprises a high-pressure cylinder, an impact tube, an incident bar resistance strain gauge, a high-precision data collector, a transmission tube resistance strain gauge, and a pulse shaper, an incident bar, a sample and a transmission tube which are coaxially and sequentially connected. During loading, stress waves generated when the impact tube impacts the incident rod are shaped and reflected by the pulse shaper and continue to spread and act on the sample, so that the sample is uniformly deformed, at the moment, most of the incident waves are reflected, the other part of the incident waves enter the transmission tube to form transmission waves, the sample is unloaded, and the sample is restored and deformed; when the reflected wave is propagated from the left end of the incident rod to the rightmost end again, the sample is loaded, and then the reflected wave and the transmitted wave are generated again, so that loading-unloading-cyclic loading of the sample is realized. The device can be used for testing the dynamic mechanical property of an elastomer material, and high-precision acquisition and recording of load data in the loading-unloading deformation process of the sample.

Description

Technical Field

[0001] The invention relates to a dynamic mechanical property testing technology for elastomeric materials, and in particular to a dynamic stretching cycle loading device and method thereof based on a Hopkinson pull rod for performing a controllable dynamic tensile cycle loading on elastomeric materials in a wide strain rate range, a number of loading cycles and a time interval between two adjacent loadings. Background Art

[0002] Elastomeric materials such as rubber and polyurethane have always been important components in engineering applications. They are widely used in the aerospace field because they can exhibit large elastic deformation and strong deformation recovery ability. However, in the cyclic deformation process of practical applications, such as the extreme conditions of dynamic high strain rate cyclic loading that tire rubber materials undergo during aircraft takeoff and landing, the loading time is in the millisecond or even sub-millisecond level. In this process, it is found that the mechanical properties of rubber and other elastomeric materials will change after multiple loading and unloading cycles. This is due to the evolution of the internal microstructure of the material, including the breakage and rearrangement of molecular chains and the change of the cross-linking state between molecules. These microscopic changes lead to the irreversible loss of the macroscopic properties of the material, often showing obvious stress softening, which causes the material's stiffness, strength and elastic properties to degrade or change in multiple tensile loading cycles. This phenomenon is called the Mullins effect. Therefore, the study of the Mullins effect is not only of practical significance for the engineering application of elastic materials, but also of great significance for understanding behaviors such as mechanical loss during cyclic deformation.

[0003] The traditional method for determining the Mullins effect of materials is to load-unload-reload-reload cycles on the specimens through a quasi-static mechanical testing machine program control to obtain the stress-strain curve of the material under cyclic loading-unloading, and to analyze and study the mechanical response and damage evolution characteristics of the material by combining the hysteresis loop in the curve. However, in the dynamic cyclic loading environment of the real service environment, the strain rate involved in rubber and other elastomeric materials is 10 1 s -1 ~10 3 s -1 The loading time is in the order of milliseconds or even sub-milliseconds, which is impossible to achieve with a quasi-static mechanical testing machine. The existing traditional Hopkinson rod test equipment and loading technology can only load the sample once to obtain a stress-strain curve of the material at a certain high strain rate, and cannot achieve controllable multiple continuous high strain rate cyclic loading of the material. Therefore, it is necessary to improve the traditional Hopkinson rod device and principle to make it more suitable for the mechanical property test of the Mullins effect of elastomeric materials. Summary of the invention

[0004] The present invention is based on the improvement of the traditional Hopkinson pull rod and proposes a dynamic stretching cyclic loading device and method for elastomeric materials to solve the problem in the prior art that the elastomeric materials cannot be subjected to controllable multiple continuous high strain rate cyclic loading.

[0005] The present invention is achieved through the following technical solutions:

[0006] The dynamic tensile cyclic loading device for elastic materials based on the Hopkinson tension rod is characterized by comprising a high-pressure cylinder 2, an impact tube 3, an incident rod resistance strain gauge 4, a high-precision data acquisition device 6, a transmission tube resistance strain gauge 8, and a pulse shaper 1, an incident rod 5, a sample 7 and a transmission tube 9 connected in a coaxial sequence;

[0007] The transmission tube 9 is a plexiglass tube with a groove on one end;

[0008] The incident rod 5 is a long straight metal cylindrical rod, with a flange on one end and a groove on the other end, and is a carrier for stress wave propagation.

[0009] The incident rod 5 and the transmission tube 9 only retain the translational freedom in the axial direction;

[0010] The sample 7 is fixed in the grooves of the incident rod 5 and the transmission tube 9;

[0011] The impact tube 3 is a metal annular tube, placed in the high-pressure cylinder 2, and glued to the flange of the incident rod 5;

[0012] The incident rod resistance strain gauge 4 is a metal strain gauge, which is pasted in the middle of the incident rod 5;

[0013] The transmission tube resistance strain gauge 8 is a semiconductor strain gauge, which is pasted on one end close to the slotted end face of the transmission tube 9;

[0014] The incident rod resistance strain gauge 4 and the transmission tube resistance strain gauge 8 are respectively connected to the high-precision data acquisition device 6 through wires.

[0015] Furthermore,

[0016] The density and elastic modulus of the incident rod 5 are greater than the density and elastic modulus of the transmission tube 9;

[0017] The length of the incident rod 5 is more than twice the length of the impact tube 3 , and has the same inner diameter and wave impedance as the impact tube 3 .

[0018] Furthermore, the sample 7 is a dumbbell-shaped sample made of an elastomeric material.

[0019] Furthermore, the impact tube 3 slides on the flange end of the incident rod 5 without friction.

[0020] Furthermore, the pulse shaper 1 is made of a soft material such as plasticine or solder, and filters and shapes the incident stress wave generated by the impact tube 3 hitting the flange flange on the incident rod 5 to prevent the incident stress wave signal collected by the incident rod resistance strain gauge 4 from oscillating.

[0021] Furthermore,

[0022] The incident rod resistance strain gauge 4 and the transmission tube resistance strain gauge 8 convert the strain change in the rod into its own resistance change, and then convert it into the output voltage change of the two bridge arms of the Wheatstone half bridge;

[0023] The incident rod resistance strain gauge 4 and the high-precision data collector 6 are used to measure and collect stress wave signals on the incident rod 5;

[0024] The transmission tube resistance strain gauge 8 and the high-precision data collector 6 are used to measure and collect stress wave signals on the transmission tube 9 .

[0025] The present invention also provides a dynamic stretching cyclic loading method for an elastomeric material based on a Hopkinson pull rod, characterized in that the loading is performed using the above-mentioned device, and the specific steps include:

[0026] Step 1: Arrange the experimental device:

[0027] 1) Select the impact tube 3 and place it in the high-pressure cylinder 2, stick it on the flange of the incident rod 5, and then coaxially connect the pulse shaper 1, the incident rod 5, the sample 7, and the transmission tube 9 in sequence along the loading direction, so that the incident rod 5 and the transmission tube 9 only retain the translational freedom in the axial direction;

[0028] 2) Paste the incident rod resistance strain gauge 4 in the middle of the incident rod 5, weld wires on the pins of the incident rod resistance strain gauge 4, connect them to two opposite bridge arms of the Wheatstone half bridge, and connect the other two bridge arms of the Wheatstone to fixed resistors;

[0029] 3) Paste the transmission tube resistance strain gauge 8 on the end of the transmission tube 9 close to the slot, weld wires on the pins of the transmission tube resistance strain gauge 8, and connect them to two opposite bridge arms of the Wheatstone half bridge, and connect the other two bridge arms of the Wheatstone to fixed resistors;

[0030] 4) Connect the output port of the Wheatstone bridge to the high-precision data acquisition device 6 via a BNC line;

[0031] Step 2: Bonding the sample:

[0032] Fully bond the transition section of the sample 7 into the grooves of the incident rod 5 and the transmission tube 9, only keep the gauge section loaded, and adjust the angle of the sample 7 to meet the expected experimental requirements;

[0033] Step 3: Experimental parameter setting:

[0034] Select the length of the impact tube 3 and the initial speed of the high pressure cylinder 2 pushing the impact tube 3 to impact the flange of the incident rod 5;

[0035] Step 4: Start the loading device:

[0036] Fill the high-pressure cylinder 2 with high-pressure nitrogen, and after the air pressure stabilizes, quickly open the launch device, so that the nitrogen in the high-pressure cylinder 2 pushes the impact tube 3 to hit the flange on the incident rod 5 to generate an incident stress wave;

[0037] After being shaped by the pulse shaper 1, the incident stress wave generates a compressive stress wave in the incident rod 5, which is then reflected at the flange end of the incident rod 5 to form a tensile stress wave of equal amplitude, which then continues to propagate along the incident rod 5 until it acts on the sample 7. At this time, the sample 7 is uniformly deformed under the action of the tensile stress wave.

[0038] Most of the incident wave is reflected to form a reflected wave in the incident rod 5, and the other part is transmitted through the sample 7 into the transmission tube 9 to form a transmitted wave, unloading the sample 7. At this time, the sample 7 recovers its deformation during the unloading process;

[0039] When the reflected wave propagates to the flange end of the incident rod 5, it is completely reflected by the end face as a tensile stress wave and then continues to propagate along the incident rod 5. When the tensile stress wave reaches the rightmost end of the incident rod 5, the sample 7 is loaded again, thereby generating reflected waves and transmitted waves again.

[0040] Repeat the above steps, and the stress wave propagates repeatedly in the incident rod 5, thereby realizing the loading-unloading-cyclic loading of the sample 7;

[0041] Step 5: Experimental data collection and processing:

[0042] 1) Calculate the strain signals of the incident rod and the transmission tube;

[0043] 2) Calculate the engineering stress of the specimen;

[0044] 3) Calculate the time interval between two adjacent loadings;

[0045] 4) Calculate the maximum number of cycles.

[0046] Furthermore, the diffusion effect is ignored during the propagation of stress waves, and the incident rod 5 moves forward at the same speed and distance under the action of each stress wave, so that the strain magnitude generated by the sample 7 under the loading of each stress wave is the same.

[0047] Furthermore,

[0048] The number of tensile cycle loading of the sample 7 is controlled by adjusting the length of the incident rod 5, the transmission tube 9 and the impact tube 3;

[0049] The deformation size of the sample 7 after a single loading is determined by the length of the impact tube 3 and the impact speed;

[0050] The deformation recovery size of the sample 7 after a single load is determined by the length of the incident rod 5 and the mass of the transmission tube 9;

[0051] The interval between two adjacent loadings of the sample 7 is determined by the length of the incident rod 5 .

[0052] Furthermore, in step 5:

[0053] 1) The strain signal expression of the incident rod and the transmission tube is:

[0054]

[0055] In the formula,

[0056] ε is the strain in the incident rod and the transmission tube; U is the voltage value of the DC power supply; ΔU is the change of the bridge arm voltage of the Wheatstone half bridge over time; R is the resistance value of the incident rod resistance strain gauge and the transmission tube resistance strain gauge; K is the sensitivity coefficient of the incident rod resistance strain gauge and the transmission tube resistance strain gauge;

[0057] 2) The engineering stress expression of the sample is:

[0058]

[0059] In the formula,

[0060] σ eng is the engineering stress of the specimen; A inc is the cross-sectional area of ​​the incident rod; E inc is the elastic modulus of the incident rod; ε inc is the incident strain signal; A tra is the cross-sectional area of ​​the transmission rod; E tra is the elastic modulus of the transmission rod; ε tra is the strain signal of the transmission rod; A s is the cross-sectional area of ​​the specimen;

[0061] 3) The expression of the time interval between two adjacent loadings is:

[0062]

[0063] In the formula,

[0064] T is the time interval between two adjacent loadings; L1 is the length of the incident rod; C is the wave velocity of the incident rod;

[0065] 4) The expression of the maximum number of cycles is:

[0066]

[0067] In the formula,

[0068] N is the maximum number of cycles, which is an integer; L2 is the length of the transmission tube; C1 is the wave velocity of the transmission tube.

[0069] The technical solution according to the present invention has at least one of the following effects:

[0070] 1. This application is based on the Hopkinson tension rod experimental technology and one-dimensional stress wave propagation theory. Through a single impact on the incident rod, the elastomeric material can be subjected to tensile cyclic loading without stress wave attenuation, and can be used for dynamic mechanical property testing of the Mullins effect of the elastomeric material.

[0071] 2. The controllable multiple continuous high strain rate cyclic loading device based on the Hopkinson pull rod constructed in this application can achieve dozens of loading cycles by reasonably adjusting the length of the incident rod, the transmission tube and the impact tube, which makes the study of the Mullins effect of elastomeric materials more comprehensive.

[0072] 3. The multi-jet rain erosion device constructed in this application can achieve better control over the deformation size of the sample after a single loading, the deformation recovery size of the sample after a single loading, and the interval time between two adjacent loadings of the sample, and can comprehensively consider the influence of various factors on the Mullins effect of the elastomeric material.

[0073] 4. This application does not restrict the size and shape of the sample used to study the Mullins effect. By reasonably designing the sample, the Mullins effect cyclic loading experiment can be carried out on elastic samples of different materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0075] Figure 1 It is a schematic structural diagram of a dynamic stretching cycle loading device for elastic materials based on a Hopkinson pull rod established according to the present invention;

[0076] Figure 2 It is a typical original stress wave waveform diagram collected by the incident rod strain gauge and the transmission tube strain gauge in the device of the present invention;

[0077] Figure 3 is a strain-time diagram obtained by testing a typical sample using the device of the present invention;

[0078] Figure 4is a stress-strain diagram obtained by testing a typical sample using the device of the present invention;

[0079] Description of reference numerals:

[0080] 1- pulse shaper; 2- high pressure cylinder; 3- impact tube; 4- incident rod resistance strain gauge; 5- incident rod; 6- high precision data acquisition device; 7- sample; 8- transmission tube resistance strain gauge; 9- transmission tube. DETAILED DESCRIPTION

[0081] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0082] The following is combined with Figure 1-4 , describes in detail the technical solutions provided by each embodiment of the present invention.

[0083] According to an embodiment of the present invention, a dynamic tensile cyclic loading device for elastic materials based on a Hopkinson pull rod is provided, which can be used to test the dynamic mechanical properties of elastic materials such as rubber, and in particular, can collect and record load data during the loading-unloading deformation process of the sample with high precision in milliseconds or even sub-milliseconds. Figure 1 As shown, it includes a pulse shaper 1, a high-pressure cylinder 2, an impact tube 3, an incident rod resistance strain gauge 4, an incident rod 5, a high-precision data collector 6, a sample 7, a transmission tube resistance strain gauge 8, and a transmission tube 9; wherein the pulse shaper 1, the incident rod 5, the sample 7, and the transmission tube 9 are coaxially connected in sequence, and the incident rod 5 and the transmission tube 9 only retain the translational freedom in the axial direction.

[0084] The following describes the specific requirements of each part of the device and the device principle:

[0085] The transmission tube 9 is a plexiglass tube of a certain length, with a groove on one end surface;

[0086] The incident rod 5 is a long straight metal cylindrical rod, whose density and elastic modulus are greater than those of the transmission tube 9, and whose length is more than twice that of the impact tube 3, and whose inner diameter and wave impedance are the same as those of the impact tube 3 (wave impedance is defined as the product of density, elastic wave velocity and cross-sectional area), with a flange plate on the side wall at one end and a groove on the end face at the other end, and is a carrier for the propagation of stress waves;

[0087] The sample 7 is a dumbbell-shaped sample made of an elastomeric material, which is bonded into the grooves of the incident rod 5 and the transmission tube 9 by using a high-strength adhesive;

[0088] The impact tube 3 is a metal annular tube of a certain length, which is glued to the flange of the incident rod 5 and moves without friction. The high-pressure cylinder 2 can compress the air to accelerate and impact the flange on the incident rod 5, and generate tensile stress waves to load the sample 7.

[0089] The pulse shaper 1 is made of a soft material such as plasticine or solder, and filters and shapes the incident stress wave generated by the impact tube 3 hitting the flange flange on the incident rod 5, thereby filtering out high-frequency waves and preventing the incident stress wave signal collected by the incident rod resistance strain gauge 4 from oscillating;

[0090] The incident rod resistance strain gauge 4 is a metal strain gauge and is pasted in the middle of the incident rod 5;

[0091] The transmission tube resistance strain gauge 8 is a semiconductor strain gauge with a high sensitivity coefficient. It is pasted on one end close to the slotted end face of the transmission tube 9. It can convert the strain change in the rod into its own resistance change, and then convert it into the output voltage change of the two bridge arms of the Wheatstone half bridge, and then use the high-precision data collector 6 to collect data.

[0092] The specific loading test process of the embodiment of the present invention is described in detail below.

[0093] Step 1: Arrange the experimental setup.

[0094] 1) Select an impact tube 3 of appropriate length and place it in the high-pressure cylinder 2, stick it on the flange of the incident rod 5, and then coaxially connect the pulse shaper 1, the incident rod 5, the sample 7, and the transmission tube 9 in sequence along the loading direction, so that the incident rod 5 and the transmission tube 9 only retain the translational freedom in the axial direction;

[0095] 2) Paste the incident rod resistance strain gauge 4 in the middle of the incident rod 5, weld wires on the pins of the incident rod resistance strain gauge 4, connect them to two opposite bridge arms of the Wheatstone half bridge, and connect the other two bridge arms of the Wheatstone to fixed resistors;

[0096] 3) Paste the transmission tube resistance strain gauge 8 on one end of the transmission tube 9 close to the slotted end surface, weld wires on the pins of the transmission tube resistance strain gauge 8, and connect them to two opposite bridge arms of the Wheatstone half bridge, and connect the other two bridge arms of the Wheatstone to fixed resistors;

[0097] 4) Connect the output port of the Wheatstone bridge to the high-precision data collector 6 via a BNC line.

[0098] In this embodiment,

[0099] The materials of the impact tube 3 and the incident rod 5 are both titanium alloy, the elastic modulus E is 113500MPa, the wave velocity C is 4966m / s, and the inner diameter of the impact tube 3 is equal to the diameter of the incident rod 5, both are 19mm, the impact tube 3 is 0.6m long, and the incident rod 5 is 2.5m long; the transmission tube 9 uses a plexiglass tube with a length of 4m and a diameter of 19mm, which can realize a transmission stress wave with a pulse width of up to 3.8ms;

[0100] An incident rod resistance strain gauge 4 is pasted in the middle of the incident rod 5, wherein the resistance value of the incident rod resistance strain gauge 4 is 1000Ω and the sensitivity coefficient is 1.92. A wire is welded on the pin of the incident rod resistance strain gauge 4 and connected to two opposite bridge arms of the Wheatstone half bridge. The other two bridge arms of the Wheatstone are connected to a fixed resistor with a resistance value of 1000Ω, and the power supply voltage is a 30V DC voltage;

[0101] A transmission tube resistance strain gauge 8 is attached to one end of the transmission tube 9 near the slotted end surface. The resistance value of the transmission tube resistance strain gauge 8 is 120Ω and the sensitivity coefficient is 110. Similarly, wires are welded on the pins of the transmission tube resistance strain gauge 8 and connected to two opposite bridge arms of the Wheatstone half bridge. The other two bridge arms of the Wheatstone are connected to fixed resistors with a resistance value of 120Ω. The power supply voltage is a 5V DC voltage.

[0102] Then, the output port of the Wheatstone bridge is connected to the high-precision data collector 6 via a BNC line.

[0103] Step 2: Bonding the sample

[0104] Sample 7 is a dumbbell-shaped sample made of elastomeric material. Its transition section is completely bonded to the grooves of the incident rod 5 and the transmission tube 9 using high-strength glue. Only the gauge section is loaded, and the angle of sample 7 is adjusted to meet the expected experimental requirements.

[0105] Step 3: Experimental parameter setting

[0106] Select a suitable length of the impact tube 3 and the initial speed at which the high-pressure cylinder 2 pushes the impact tube 3 to impact the flange disk of the incident rod 5.

[0107] In this embodiment, a high-pressure cylinder 2 is used to push the impact tube 3 to impact the incident rod 5. A suitable length L of the impact tube 3 is selected according to the experimental purpose. Then, according to the stress wave theory, the high-pressure cylinder 2 pushes the impact tube 3 with a length of L to impact the flange flange disk on the incident rod 5 with an initial velocity v0, and a compression wave with a wavelength of 2L / C and a particle velocity of v0 / 2 is formed inside the incident rod 5, where C is the wave velocity of the incident rod. When the compression wave propagates to the left end face of the incident rod 5, the compression wave is completely reflected into a tensile wave. When the tensile wave propagates in the incident rod 5 to the rightmost end of the incident rod 5, since the wave impedance of the sample 7 is much smaller than that of the incident rod 5, the particle velocity at the rod end doubles to v0.

[0108] Step 4: Start the loader

[0109] After the experimental parameters are set, high-pressure nitrogen gas of the required pressure value is filled into the high-pressure cylinder 2. After the pressure is stable, the launch device is quickly turned on. The nitrogen gas in the high-pressure cylinder 2 pushes the impact tube 3 to hit the flange flange on the incident rod 5 at a certain speed to generate an incident stress wave.

[0110] After being shaped by the pulse shaper 1, the incident stress wave generates a compression stress wave of a certain amplitude and pulse width in the incident rod 5, and then reflects at the flange end of the incident rod 5 to form a tensile stress wave of equal amplitude, which then continues to propagate along the incident rod 5 until it acts on the sample 7. At this time, the sample 7 is uniformly deformed under the action of the tensile stress wave;

[0111] Since the wave impedance of the incident rod 5 is much greater than that of the sample 7, most of the incident wave is reflected to form a reflected wave in the incident rod 5, and the other part is transmitted through the sample 7 into the transmission tube 9 to form a transmitted wave, unloading the sample 7. At this time, the sample 7 will recover its deformation during the unloading process;

[0112] When the reflected wave propagates to the flange end of the incident rod 5, it is completely reflected by the end face as a tensile stress wave and then continues to propagate along the incident rod 5. When the tensile stress wave reaches the rightmost end of the incident rod 5, the sample 7 is loaded again, thereby generating reflected waves and transmitted waves again.

[0113] According to the stress wave propagation theory and ignoring the wave diffusion effect, the stress wave can propagate repeatedly in the incident rod 5, thereby realizing the loading-unloading-cyclic loading of the sample 7.

[0114] Step 5: Experimental data collection and processing

[0115] 1) According to the voltage information collected by the incident rod resistance strain gauge and the transmission tube resistance strain gauge, such as Figure 2 As shown in the figure, using the Wheatstone bridge formula, the strain signals of the incident rod and the transmission tube can be calculated as:

[0116]

[0117] Where ε is the strain in the incident rod and the transmission tube, U is the voltage of the DC power supply, ΔU is the change of the bridge arm voltage of the Wheatstone half bridge over time, R is the resistance value of the incident rod resistance strain gauge and the transmission tube resistance strain gauge, and K is the sensitivity coefficient of the incident rod resistance strain gauge and the transmission tube resistance strain gauge.

[0118] 2) According to the one-dimensional stress wave theory, the stress of the sample can be calculated by formula (2):

[0119]

[0120] In the formula, σeng is the engineering stress of the specimen, A inc is the cross-sectional area of ​​the incident rod, E inc is the elastic modulus of the incident rod, ε inc is the incident strain signal, A tra is the cross-sectional area of ​​the transmission rod, E tra is the elastic modulus of the transmission rod, ε tra is the transmission rod strain signal, A s is the cross-sectional area of ​​the specimen.

[0121] 3) The time interval T between two adjacent loadings can be calculated by formula (3):

[0122]

[0123] Where L1 is the length of the incident rod and C is the wave velocity of the incident rod.

[0124] 4) The maximum number of cycles N is calculated by formula (4):

[0125]

[0126] Where T is the time interval between two adjacent loadings, L2 is the length of the transmission tube, C1 is the wave velocity of the transmission tube, and N is an integer.

[0127] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the claims of the present invention.

Claims

1. A dynamic tensile cyclic loading device for elastic materials based on a Hopkinson pull rod, characterized in that: It comprises a high-pressure cylinder (2), an impact tube (3), an incident rod resistance strain gauge (4), a high-precision data acquisition device (6), a transmission tube resistance strain gauge (8), and a pulse shaper (1), an incident rod (5), a sample (7) and a transmission tube (9) which are coaxially connected in sequence; The transmission tube (9) is a plexiglass tube, one end of which is grooved; The incident rod (5) is a long straight metal cylindrical rod, with a flange plate on the side wall at one end and a groove on the end surface at the other end, and is a carrier for stress wave propagation; The incident rod (5) and the transmission tube (9) only retain the degree of freedom of translation in the axial direction; The sample (7) is fixed in the grooves of the incident rod (5) and the transmission tube (9); The impact tube (3) is a metal annular tube, placed in the high-pressure cylinder (2) and glued to the flange of the incident rod (5); The incident rod resistance strain gauge (4) is a metal strain gauge and is pasted in the middle of the incident rod (5); The transmission tube resistance strain gauge (8) is a semiconductor strain gauge and is pasted on one end close to the slotted end face of the transmission tube (9); The incident rod resistance strain gauge (4) and the transmission tube resistance strain gauge (8) are respectively connected to a high-precision data acquisition device (6) via wires.

2. The dynamic tensile cyclic loading device for elastic materials based on the Hopkinson pull rod according to claim 1, characterized in that: The density and elastic modulus of the incident rod (5) are greater than the density and elastic modulus of the transmission tube (9); The length of the incident rod (5) is more than twice the length of the impact tube (3), and has the same inner diameter and wave impedance as the impact tube (3).

3. The dynamic tensile cyclic loading device for elastic materials based on the Hopkinson pull rod according to claim 1, characterized in that: The sample (7) is a dumbbell-shaped sample of an elastomeric material.

4. The dynamic tensile cyclic loading device for elastic materials based on the Hopkinson pull rod according to claim 1, characterized in that: The impact tube (3) slides frictionlessly on the flange end of the incident rod (5).

5. The dynamic tensile cyclic loading device for elastic materials based on the Hopkinson pull rod according to claim 1, characterized in that: The pulse shaper (1) is made of a relatively soft material such as plasticine or solder, and filters and shapes the incident stress wave generated by the impact tube (3) impacting the flange disk on the incident rod (5), thereby preventing the incident stress wave signal collected by the incident rod resistance strain gauge (4) from oscillating.

6. The dynamic tensile cyclic loading device for elastic materials based on the Hopkinson pull rod according to claim 1, characterized in that: The incident rod resistance strain gauge (4) and the transmission tube resistance strain gauge (8) convert the strain change in the rod into its own resistance change, and then convert it into the output voltage change of the two bridge arms of the Wheatstone half bridge; The incident rod resistance strain gauge (4) and the high-precision data collector (6) are used to measure and collect stress wave signals on the incident rod (5); The transmission tube resistance strain gauge (8) and the high-precision data collector (6) are used to measure and collect stress wave signals on the transmission tube (9).

7. A dynamic tensile cyclic loading method for elastomeric materials based on a Hopkinson pull rod, characterized in that: The method of loading using the device according to any one of claims 1 to 6 comprises the following specific steps: Step 1: Arrange the experimental device: 1) An impact tube (3) is selected and placed in a high-pressure cylinder (2), and glued to the flange of the incident rod (5). Then, along the loading direction, the pulse shaper (1), the incident rod (5), the sample (7), and the transmission tube (9) are coaxially connected in sequence, so that the incident rod (5) and the transmission tube (9) only retain the translational freedom degree in the axial direction; 2) The incident rod resistance strain gauge (4) is pasted in the middle of the incident rod (5), and wires are welded to the pins of the incident rod resistance strain gauge (4) and connected to two opposite bridge arms of the Wheatstone half bridge, and the other two bridge arms of the Wheatstone are connected to fixed resistors; 3) A transmission tube resistance strain gauge (8) is attached to one end of the transmission tube (9) near the slot, and a wire is welded to the pin of the transmission tube resistance strain gauge (8) and connected to two opposite bridge arms of a Wheatstone half bridge, and the other two bridge arms of the Wheatstone are connected to fixed resistors; 4) Connect the output port of the Wheatstone bridge to a high-precision data acquisition device (6) via a BNC line; Step 2: Bonding the sample: The transition section of the sample (7) is completely bonded into the grooves of the incident rod (5) and the transmission tube (9), only the gauge section is loaded, and the angle of the sample (7) is adjusted to meet the expected experimental requirements; Step 3: Experimental parameter setting: Selecting the length of the impact tube (3) and the initial speed at which the high-pressure cylinder (2) pushes the impact tube (3) to impact the flange of the incident rod (5); Step 4: Start the loading device: High-pressure nitrogen is filled into the high-pressure cylinder (2), and after the gas pressure is stabilized, the launch device is quickly opened, so that the nitrogen in the high-pressure cylinder (2) pushes the impact tube (3) to impact the flange plate on the incident rod (5) to generate an incident stress wave; After being shaped by the pulse shaper (1), the incident stress wave generates a compressive stress wave in the incident rod (5), which is then reflected at the flange end of the incident rod (5) to form a tensile stress wave of equal amplitude, which then continues to propagate along the incident rod (5) until it acts on the sample (7). At this time, the sample (7) is uniformly deformed under the action of the tensile stress wave; Most of the incident wave is reflected to form a reflected wave in the incident rod (5), and the other part is transmitted through the sample (7) into the transmission tube (9) to form a transmitted wave, thereby unloading the sample (7). At this time, the sample (7) recovers its deformation during the unloading process; When the reflected wave propagates to the flange end of the incident rod (5), it is completely reflected by the end face as a tensile stress wave and then continues to propagate along the incident rod (5). When the tensile stress wave reaches the rightmost end of the incident rod (5), the sample (7) is loaded again, thereby generating reflected waves and transmitted waves again. Repeating the above steps, the stress wave propagates repeatedly in the incident rod (5), thereby achieving loading-unloading-cyclic loading of the sample (7); Step 5: Experimental data collection and processing: 1) Calculate the strain signals of the incident rod and the transmission tube; 2) Calculate the engineering stress of the specimen; 3) Calculate the time interval between two adjacent loadings; 4) Calculate the maximum number of cycles.

8. The method for dynamic tensile cyclic loading of elastomeric materials based on Hopkinson pull rod according to claim 7, characterized in that: The diffusion effect is ignored during the propagation of stress waves, and the incident rod (5) moves forward at the same speed and distance under the action of each stress wave, so that the strain generated by the sample (7) under the loading of each stress wave is the same.

9. The method for dynamic tensile cyclic loading of elastomeric materials based on Hopkinson tie rod according to claim 7, characterized in that: The number of tensile cycle loadings of the sample (7) is controlled by adjusting the lengths of the incident rod (5), the transmission tube (9) and the impact tube (3); The deformation size of the sample (7) after a single load is determined by the length of the impact tube (3) and the impact speed; The deformation recovery size of the sample (7) after a single load is determined by the length of the incident rod (5) and the mass of the transmission tube (9); The interval between two adjacent loadings of the sample (7) is determined by the length of the incident rod (5).

10. The dynamic tensile cyclic loading method for elastomeric materials based on the Hopkinson pull rod according to claim 7, characterized in that: In step 5: 1) The strain signal expression of the incident rod and the transmission tube is: In the formula, ε is the strain in the incident rod and the transmission tube; U is the voltage value of the DC power supply; ΔU is the change of the bridge arm voltage of the Wheatstone half bridge over time; R is the resistance value of the incident rod resistance strain gauge and the transmission tube resistance strain gauge; K is the sensitivity coefficient of the incident rod resistance strain gauge and the transmission tube resistance strain gauge; 2) The engineering stress expression of the sample is: In the formula, σ eng is the engineering stress of the specimen; A inc is the cross-sectional area of ​​the incident rod; E inc is the elastic modulus of the incident rod; ε inc is the incident strain signal; A tra is the cross-sectional area of ​​the transmission rod; E tra is the elastic modulus of the transmission rod; ε tra is the strain signal of the transmission rod; A s is the cross-sectional area of ​​the specimen; 3) The expression of the time interval between two adjacent loadings is: In the formula, T is the time interval between two adjacent loadings; L1 is the length of the incident rod; C is the wave velocity of the incident rod; 4) The expression of the maximum number of cycles is: In the formula, N is the maximum number of cycles, which is an integer; L2 is the length of the transmission tube; C1 is the wave velocity of the transmission tube.

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