Tension-torsion synchronous and asynchronous loading Hopkinson rod experimental device capable of accurately controlling tension-torsion wave time difference

Abstract

The invention belongs to the field of high-strain-rate composite impact loading test of materials, and discloses a tension-torsion synchronous / asynchronous loading Hopkinson rod experimental device capable of accurately controlling a tension-torsion wave time difference. The tension-torsion synchronous / asynchronous loading Hopkinson rod experimental device can be used for testing the mechanical property of a material under a high-strain-rate tension-torsion composite loading condition. Specifically, a dual-energy release mechanism clamp and a longitudinal clamp on an incident bar are used for releasing torsional waves and tensile waves respectively, accurate control of the time difference of the tensile waves and the torsional waves is achieved through a limiting mechanism and a specific load applying position, namely synchronous / asynchronous arrival is achieved, and the problems that in a traditional measuring mode, tension-torsion synchronous loading is not easy to achieve, and the measuring precision is high are solved. The problem that the strain of the sample cannot be directly calculated due to superposition of stress waveforms is solved, and the experiment difficulty and cost are greatly reduced.

Description

Technical Field

[0001] The invention belongs to the field of high strain rate composite impact loading test of materials, and in particular relates to a tension-torsion synchronous and asynchronous loading Hopkinson bar experimental device for accurately controlling the time difference of tension-torsion waves. Background Art

[0002] In practical engineering applications such as aerospace, shipbuilding and oceanography, weapons and armaments, bridges, and automobiles, structures or components are usually subjected to multi-axial stress states when subjected to impact loads, and the stress state will affect the mechanical response of the material. Therefore, it is particularly important to determine the dynamic mechanical properties of materials under various stress states (especially composite loading). At present, the dynamic mechanical properties of materials under composite loading conditions have become a closely watched issue in engineering applications, but there are still many difficulties that need to be solved in loading and measurement methods. For example, it is difficult to achieve simultaneous tension and torsion loading in traditional measurement methods, and it is impossible to directly calculate the strain of the specimen due to the superposition of stress waveforms, resulting in high experimental difficulty and cost.

[0003] Document 1 "Gilat A,Cheng C S.Modeling torsional split Hopkinson bar testsat strain rates above 10,000s -1 [J]. International Journal of Plasticity, 2002, 18(2-6): 789-799. DOI: 10.1016 / S0749-6419(01)00055-9." discloses an experimental device for torsion testing of materials based on the Hopkinson bar principle, which can perform high strain rate pure torsion experiments on thin-walled tubular specimens. Figure 7 As shown, when this experimental device conducts a pure torsion experiment, the incident rod 1 is first clamped by the clamp 3. A torque is applied to the end of the incident rod to cause the incident rod 1 to elastically deform and store energy. The deformation of the rod is measured using the strain gauge 2 between the torque and the clamp 3. When the clamp 3 is released, the incident rod 1 elastically recovers, and a torsional unloading wave is released to the left and a torsional loading wave is released to the right along the incident rod 1 from the position of the clamp 3 to load the sample 4. The strain gauge 2 located between the clamp 3 and the sample 4 is used to measure the strain signals of the incident wave and the reflected wave, and the strain gauge 2 located on the transmission rod 5 is used to measure the strain signal of the transmitted wave. The response curve of the sample under high strain rate pure torsion loading can be obtained through calculation. However, this only involves experiments in the pure torsion loading state and cannot achieve combined tension and torsion loading.

[0004] To address this issue, the paper 2 "Xu Y, Lopez MA, Zhou J, et al. Experimental analysis of the multiaxial failure stress locus of commercially pure titanium at low and high rates of strain [J]. International Journal of Impact Engineering, 2022, 170: 104341. DOI: 10.1016 / j.ijimpeng.2022." added a tensile load to the Hopkinson torsion bar to achieve a combined tension-torsion loading of the specimen. Figure 8As shown, the apparatus comprises: an incident rod 1, a strain gauge 2 for measuring shear strain, a fixture 3, a specimen 4, a transmission rod 5, a strain gauge 6 for measuring tensile strain, and a high-speed camera 7. The fixture 3 consists of a rolling bearing 8, a slot 9, a pin 10, a nut 11, jaws 12, a frame 13, a notched pin 14, and a hydraulic cylinder 15. Similar to pure torsion experiments, the apparatus first clamps the incident rod 1 using the fixture 3. A simplified model of the fixture 3 is shown in the enlarged partial view below. The notched pin 14 has threads on both ends, and the jaws 12 and notched pin 14 are connected together by a nut 11. Pin 10 passes through slot 9 and a hole in the bottom of jaws 12, connecting jaws 12 to the base of the fixture 3. A pair of symmetrical horizontal pressures are applied below jaws 12 by a hydraulic cylinder 15, pushing the two jaws of jaws 12 toward each other to clamp the rod. At this stage, the clamping force is set slightly below the threshold that causes notched pin 14 to break. A tensile-torsional load is then applied to the incident rod end, causing elastic deformation of the energy storage section from the incident rod end to the clamp 3. Strain gauges 2 and 6 on the incident rod 1 measure the pre-stored torque and tension, respectively. The horizontal pressure on the clamp 3 is further increased via hydraulic cylinder 15, causing the notched pin 14 to fracture, releasing the stress wave. Although the generated torsional wave velocity is lower than the tensile wave velocity, the clamp 3 is sufficiently close to the specimen 4 that the torsional and tensile waves can be considered to arrive at and load the specimen 4 synchronously. After the stress release, the strain gauges 2 and 6 on the incident rod 1 record the strain signals of the torsional and tensile energy storage sections, respectively, as well as the strain signal resulting from the superposition of the incident and reflected waves. The strain gauges 2 and 6 on the transmission rod 5 record the strain signals of the torsional and tensile transmitted waves, respectively. A high-speed camera 7 records the full-field strain generated by the specimen 4 during the loading process. This loading method utilizes the close proximity of the clamp 3 to the specimen to approximate the synchronization of the tensile and torsional pulses. However, strictly speaking, the tensile and torsional waves do not arrive at the specimen synchronously to load it. In addition, due to the relative position of the clamp 3 on the incident rod, the loading wave pulse width is very long, which is approximately close to the length of the incident rod. Ultimately, the incident wave and the reflected wave collected by the strain gauge on the incident rod are not independent of each other, and the reflected wave cannot be used to calculate the strain of the sample.

[0005] To address the issues of simultaneous loading and pulse width control, reference 3, "Zhou J, Xu Y, et al. The mechanical response of commercially pure copper under multiaxial loading at low and high strain rates [J]. International Journal of Impact Engineering, 2022. DOI: 10.1016 / j.ijmecsci.2022.107340," proposes a dual-clamp design. The clamps are placed on two rods, and tensile and torsional loads are applied to the ends of the two rods, respectively. The clamp positions are calculated to ensure that the tensile and torsional waves simultaneously reach the specimen end face. It should be noted that in this device, the incident rod also serves as the "transmission rod," and the transmission rod also serves as the "incident rod." As shown in Figure 9, the device also includes a strain gauge 6 for measuring tensile strain, a clamp 3, a strain gauge 2 for measuring shear strain, a high-speed camera 7, and a piezoelectric clamp 16. The piezoelectric clamp 16 consists of a piezoelectric device 17, a piezoelectric clamp jaw 18, a frame 13, and a hydraulic cylinder 15. The structure and usage of the clamp 3 in this device are similar to those of the clamp 3 described in Reference 2. During the experiment, the clamp 3 first clamps the incident rod 1, applying a tensile load at the end of the incident rod. The strain gauge 6 on the left side of the clamp on the incident rod 1 measures the pre-stored tensile force. The jaws 18 of the piezoelectric clamp 16 are clamped between a set of rolling bearings, allowing only horizontal movement. Before applying torque, the piezoelectric device 17 is in its maximum extension state (stage 1). The hydraulic cylinder 15 in the piezoelectric clamp 16 pushes the jaws 18 until they clamp the transmission rod 5, then applies torque (stage 2). The strain gauge 2 on the transmission rod 5 measures the pre-stored torque. The pressure applied by the hydraulic cylinder 15 in the clamp 3 is further increased, causing the notched pin 14 to fracture. At this point, a tensile loading wave propagates along the incident rod 1 toward the specimen 4. When the strain gauge 6-a on the leftmost side of the clamp 3 on the incident rod 1 receives a signal, the piezoelectric clamp 16 is released (stage 3), triggering the torsional loading wave to propagate along the transmission rod 5 toward the specimen 4. Strain gauge 2 on incident rod 1 captures the torsional transmission wave, while strain gauge 6-c on transmission rod 5 captures the tensile transmission wave. The incident, reflected, and transmitted wave signals are then used to directly calculate the specimen's mechanical response under high-strain-rate tensile loading. However, since the device cannot directly capture the complete torsional incident and reflected waves, high-speed photography is still required to measure the specimen's strain. The gap between the contraction of the piezoelectric clamp and the rod generating sufficient time for the torsional wave to propagate requires 35-40 μs. Based on available data from the literature, the rising edge of the torsional wave is approximately 100 μs, which is longer than that in typical dynamic pure torsion experiments.Furthermore, torque is applied by an electrodynamic harmonic drive, and the tensile signal collected by the strain gauge on the incident rod 1 is used as a trigger condition to open the piezoelectric clamp 16 and generate a torsional loading wave along the transmission rod 5. The dynamic curve on the right side of Figure 9(b) shows that the torsional wave released in this way is more violent than the oscillation of the clamp release method using the traditional notched pin brittle fracture method. Figure 9(b) shows. Figure 8 Comparison of the dynamic time history curves obtained by the single-clamp and double-clamp Hopkinson bar test apparatus in Figure 9(a).

[0006] Reference 4 "Ren Q, Zhang Y, Hu L, et al. Achieving synchronous compression-shear loading on SHPB by utilizing mechanical metamaterial [J]. International Journal of Impact Engineering, 2024" eliminated the use of fixtures and no longer used the strain of the rod itself to store deformation energy. Instead, it used impact-type combined metamaterials to achieve compression-torsion composite loading of the sample. Figure 10 As shown, the device comprises: an incident rod 1, a strain gauge 6 for measuring tensile strain, a metamaterial 19, a specimen 4, a strain gauge 2 for measuring shear strain, a high-speed camera 7, and a transmission rod 5. The device operates as follows: the impact of the impact rod on the incident rod 1 generates a compression wave. Because the unit-cell compression-torsion metamaterial 19, composed of spatially chiral oblique rods, is used, the compression wave is converted into a compression wave and a torsional wave when it passes through the metamaterial 19, thereby generating a synchronous compression-torsion composite loading on the specimen 4. The strain gauge 6 on the incident rod 1 measures the incident and reflected compressive wave signals, the strain gauge 6 on the transmission rod 5 measures the transmitted compressive wave signal, and the strain gauge 2 measures the transmitted torsional wave signal. The high-speed camera 7 monitors the specimen strain to verify the synchronization of the tensile and torsional loading processes. This experimental setup eliminates the use of fixtures and instead uses metamaterials to apply combined compression and torsion to the specimen, ensuring the synchronization of tensile and torsional waves. However, limitations remain. Achieving combined loading with varying ratios of shear and tensile stress requires replacing metamaterials with different structures, which makes it difficult to achieve the desired ratio of torque and tension, leading to high experimental costs. Furthermore, epoxy glue is required to connect the rod, metamaterial, and specimen during the experiment, ensuring that the applied shear stress is within the epoxy's tolerance and that the metamaterial does not undergo plastic deformation, further complicating the experimental operation. Furthermore, while the metamaterial's wave impedance is on the same order of magnitude as the rod's, it still does not fully match the impedance, which can affect the measurement results.

[0007] In view of this, designing an experimental device that can realize synchronous or asynchronous tension-torsion combined loading has important academic and engineering value. Summary of the Invention

[0008] This invention aims to develop a Hopkinson bar experimental apparatus capable of testing the mechanical properties of materials under high-strain-rate combined tension-torsion loading conditions. Specifically, it utilizes a dual-energy release mechanism fixture and a longitudinal fixture on the incident bar to release torsional and tensile waves, respectively. A limit mechanism and specific load application positions are used to precisely control the time difference between the tensile and torsional waves (synchronous / asynchronous arrival). This solves the problems of traditional measurement methods, such as the difficulty in achieving simultaneous tension-torsion loading and the inability to directly calculate specimen strain due to the superposition of stress waveforms.

[0009] In order to achieve the above object, the present invention provides the following technical solutions:

[0010] A tensile-torsion synchronous-asynchronous loading Hopkinson bar experimental device for precisely controlling the time difference between tensile and torsion waves comprises: an incident rod, a strain gauge for measuring tensile strain, a fixture, a specimen, a transmission rod, a strain gauge for measuring shear strain, a support, a torsional actuator, a tensile actuator, and a platform. The device is characterized in that it further comprises: a screw, a first baffle, a first screw nut, a baffle, a longitudinal fixture, a second baffle, a second screw nut, a torsion limit support, a third baffle, a third screw nut, and a bracket.

[0011] The two brackets are respectively installed at both ends of the platform to support the screw rod. Along the X-axis direction, the two screw rods pass through the bracket, the first baffle, the first screw nut, the second baffle, the second screw nut, the third screw nut, and the third baffle in sequence; the incident rod passes through the support, the clamp, the first baffle, the longitudinal fixture, the second baffle, the torsion actuator, the torsion limit support, the third baffle and the tensile actuator in sequence, and the axes of each component are consistent; the clamp, the longitudinal fixture, the torsion actuator and the tensile actuator are fixed to the platform, and the strain gauge for measuring tensile strain and the strain gauge for measuring shear strain are respectively attached to the incident rod and the transmission rod, wherein the clamp and the longitudinal clamp are used as a dual energy release mechanism, and the torsion limit support is used as a limiting mechanism. The clamp first releases the circumferential strain restriction and releases the torsion wave. When the torsion wave is released and reaches the longitudinal clamp, the baffle rotates a relative angle and passes through the longitudinal clamp. The longitudinal strain of the incident rod is no longer restricted and the tensile wave is released.

[0012] The torsion actuator is located between the second baffle and the torsion limit support; the torsion actuator is clearance-matched with the outer contour of the octagonal prism on the incident rod;

[0013] The tensile actuator is located between the third baffle and the bracket, is fixedly connected to the third baffle, and is further fixedly connected to the platform. The tail of the incident rod passes through the third baffle and cooperates with the tensile actuator to achieve the application of the tensile load.

[0014] The blocking rod is located between the fixture and the longitudinal fixture and close to one side of the longitudinal fixture, and is clamped on the incident rod; the sample is placed between the incident rod and the transmission rod.

[0015] Furthermore, the longitudinal clamp includes: a spring, a pawl, a pin, a one-way ratchet, and a fan-shaped opening groove. The one-way ratchet is embedded in the opening of the vertical plate of the longitudinal clamp and can rotate relative to the vertical plate of the longitudinal clamp; the pawl is connected to the vertical plate of the longitudinal clamp by a pin, and is pressed against the tangential edge of the one-way ratchet under the action of the spring.

[0016] Furthermore, a triangular armature is provided at the bottom of the bracket, which is used to make the tension-torsion synchronous and asynchronous loading Hopkinson bar experimental device symmetrically distributed about the center line of the platform.

[0017] Furthermore, the incident rod is divided into two sections, one section is a cylinder and the other section is an octagonal prism. The torsional actuator is loosely matched with the outer contour of the octagonal prism on the incident rod to achieve torque application without increasing longitudinal friction.

[0018] Furthermore, the cross-sectional area of the octagonal prism is 90% of the cross-sectional area of the cylinder.

[0019] Furthermore, the screw rod cooperates with the baffle plate and the nut to form a self-balancing frame for limiting the relative positions of various components on the platform.

[0020] Furthermore, the tensile and torsional reflected waves generated by the sample are collected by the strain gauges for measuring tensile strain and shear strain attached to the incident rod.

[0021] Furthermore, the thread at the tail of the incident rod passes through the third baffle and cooperates with the internal thread of the tensile actuator to achieve the application of the tensile load.

[0022] Furthermore, the transmission wave signal is collected by a strain gauge for measuring tensile strain and a strain gauge for measuring shear strain attached to the transmission rod.

[0023] Furthermore, the position of the torsion limiting support can be moved independently to change the length of the torsion energy storage section.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) By designing a dual energy release mechanism on the incident rod, it is possible to achieve both synchronous loading of the sample with the same pulse width and asynchronous loading with different pulse widths, which is suitable for the complex stress state that the material may be subjected to in actual engineering;

[0026] 2) By changing the position where torque is applied on the traditional incident rod end, and combining it with a torsion limit support and the arrangement of the relative positions of the fixture and strain gauge on the incident rod, the stress-strain curve of the specimen after composite loading can be obtained using only strain gauge measurement, eliminating the need for high-speed photography technology and simplifying the measurement process.

[0027] 3) While achieving synchronous or asynchronous tension-torsion combined loading, it overcomes the experimental difficulty and high cost caused by the inability to directly calculate the sample strain due to the superposition of stress waveforms, greatly reducing the experimental difficulty and cost, with a high success rate and good repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the relative arrangement of the strain gauges and fixtures of the device of the present invention.

[0029] Figure 2 It is a three-dimensional wireframe and detailed structural diagram of the incident rod of the device of the present invention.

[0030] Figure 3 The specific style diagram of the clamp designed for other equipment is referenced for this invention.

[0031] Figure 4 Schematic diagram of the longitudinal fixture of the device of the present invention.

[0032] Figure 5 Schematic diagram of the incident rod of the device of the present invention.

[0033] Figure 6 Schematic diagram of the torsion limiting support of the device of the present invention.

[0034] Figure 7 This is a test device proposed in Reference 1 that can perform pure torsion tests on materials based on the Hopkinson bar principle.

[0035] Figure 8 This is a test device proposed in reference 2 that uses a single fixture to achieve combined tension-torsion loading of a Hopkinson bar.

[0036] Figure 9(a) shows the Hopkinson tension-torsion bar test apparatus proposed in Reference 3, which uses a double fixture to improve the accuracy of wave synchronous loading.

[0037] Figure 9(b) shows Figure 8 Dynamic time history curves obtained by the single-clamp Hopkinson bar test device in Figure 9(a) and the double-clamp Hopkinson bar test device in Figure 9(a).

[0038] Figure 10 This is the Hopkinson experimental device proposed in reference 4 that uses metamaterials to achieve synchronous compression and torsion composite loading of the sample.

[0039] In the figure, 1-incident rod, 2-strain gauge for measuring shear strain, 3-fixture, 4-sample, 5-transmission rod, 6-strain gauge for measuring tensile strain, 7-high-speed camera, 8-ball bearing, 9-slot, 10-pin, 11-nut, 12-jaw, 13-frame, 14-notch pin, 15-hydraulic cylinder, 16-piezoelectric fixture, 17-piezoelectric device, 18-piezoelectric fixture jaw, 19-metamaterial, 20-support, 21-screw, 2 2-first baffle, 23-first screw nut, 24-baffle, 25-longitudinal clamp, 26-torsion actuator, 27-torsion limit support, 28-tension actuator, 29-aluminum seat bracket, 30-spring, 31-pawl, 32-pin, 33-one-way ratchet, 34-fan-shaped opening groove, 35-octagonal hole sleeve, 36-second baffle, 37-second screw nut, 38-third baffle, 39-third screw nut, 40-platform. DETAILED DESCRIPTION

[0040] To make the objectives, technical solutions, and advantages of the present invention more clear, the present invention will be described in more detail below with reference to theoretical formulas, accompanying drawings, and specific embodiments. It should be noted that the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0042] This invention proposes a Hopkinson bar experimental apparatus that implements simultaneous or asynchronous tensile-torsion loading of a specimen by providing a dual-energy release mechanism on the incident rod and designing a method to remove the restriction that torque loads can only be applied at the end of the incident rod. Regarding stress wave acquisition, to avoid the superposition of collected waves, which would prevent direct strain calculation of the specimen from reflected waves, the dual-energy release mechanism is provided on the incident rod. The relative positions of the two fixtures and the specimen are determined based on the calculated distance relationship required for the tensile and torsional waves to reach the specimen simultaneously. The relative positions of the fixtures, strain gauges, and applied load on the incident rod are determined by taking into account the required pulse width and the length required for acquisition integrity.

[0043] like Figure 1 and 2 As shown, the tensile / torsion synchronous / asynchronous loading Hopkinson bar experimental device provided in an embodiment of the present invention includes: an incident rod 1, a strain gauge 2 for measuring tensile strain, a fixture 3, a sample 4, a transmission rod 5, a strain gauge 6 for measuring shear strain, a support 20, a torsional actuator 26, a tensile actuator 28, a bracket 29 and a platform 40, and also includes: a screw 21, a first baffle 22, a first screw nut 23, a baffle 24, a longitudinal fixture 25, a second baffle 36, a second screw nut 37, a torsion limit support 27, a third baffle 38, and a third screw nut 39; wherein, two brackets 29 are respectively installed at both ends of the platform 40 for supporting the screw 21, and along the X-axis direction, the two screws 21 pass through the bracket 29, the first baffle 22, the first screw nut 23, the second baffle 36, the second screw nut 37, the third baffle 38, The third screw nut 39; the incident rod 1 passes through the support 20, the clamp 3, the first baffle 22, the longitudinal fixture 25, the second baffle 36, the torsional actuator 26, the torsional limit support 27, the third baffle 38 and the tensile actuator 28 in sequence, and the axes of each component are consistent; the clamp 3, the longitudinal clamp 25, the torsional actuator 26 and the tensile actuator 28 are fixed to the mounting platform, and the strain gauge 2 for measuring tensile strain and the strain gauge 6 for measuring shear strain are respectively attached to the incident rod 1 and the transmission rod 5, wherein the clamp 3 and the longitudinal clamp 25 are used as a dual energy release mechanism, and the torsional limit support 27 is used as a limiting mechanism. The clamp 3 first releases the circumferential strain restriction and releases the torsional wave. When the torsional wave is released and reaches the longitudinal clamp 25, the baffle 24 rotates a relative angle and passes through the longitudinal clamp 25. The longitudinal strain of the incident rod 1 is no longer restricted and the tensile wave is released;

[0044] The torsion actuator 26 is located between the second baffle 36 and the torsion limit support 27, and is spaced apart from the longitudinal fixture 25. The incident rod 1 is divided into two sections, one cylindrical and the other octagonal. The torsion actuator 26 is loosely matched with the outer contour of the octagonal prism on the incident rod 1 to achieve torque application without increasing longitudinal friction.

[0045] The tensile actuator 28 is located between the third baffle 38 and the bracket 29, and is fixedly connected to the third baffle 38 and then to the platform 40. The thread at the tail of the incident rod 1 passes through the third baffle 38 and cooperates with the internal thread of the tensile actuator 28 to achieve the application of the tensile load;

[0046] The blocking rod 24 is located between the clamp 3 and the longitudinal fixture 25 and close to the longitudinal fixture 25, and is clamped on the incident rod 1; the sample 4 is placed between the incident rod 1 and the transmission rod 5. Figure 4 As shown, the longitudinal fixture 25 includes a spring 30, a pawl 31, a pin 32, a one-way ratchet 33, and a fan-shaped opening 34. The one-way ratchet 33 is embedded in an opening in the vertical plate of the longitudinal fixture 25 and can rotate relative to it. The pawl 31 is connected to the vertical plate via a pin 32 and, under the action of the spring 30, presses against the tangential edge of the one-way ratchet 33. Figure 2 Detailed description is given of the three-dimensional wireframe and detailed structural diagram of the incident rod portion of the device of the present invention.

[0047] During the assembly process, first install the aluminum base bracket 29, tensile actuator 28, torsion limit support 27, torsion actuator 26, support 20 and screw 21 from right to left (after the two screws 21 pass through the aluminum base bracket 29, then install the baffle and screw nut according to the Figure 2 After completing the previous installation, fix the clamp 3 and the longitudinal fixture 25 to the position and fix them to the platform with bolts. Then, pass the incident rod 1 through the support 20, the clamp 3, the first baffle 22, the longitudinal fixture 25, the second baffle 36, the torsion actuator 26, the torsion limit support 27, the third baffle 38 and the tensile actuator 28 from left to right. Figure 5 As shown in the figure, the torsion actuator 26 is loosely fitted and connected to the tension actuator 28 via a threaded connection. Finally, the blocking rod 24 is clamped on the incident rod 1. The inner octagonal hole and the rod head are transitionally fitted and fixed together via external threads. Each time an experiment is performed, three pairs of strain gauges 2 for measuring tensile strain and three pairs of strain gauges 6 for measuring shear strain are attached to the Figure 1 As shown in the position, the specimen 4 and the left end of the incident rod 1 (as shown in Figure 5 As shown) polygonal fit and connected with bolts.

[0048] A simplified schematic diagram of the relative positions of the above components is shown in Figure 1 As shown, L1, L " Indicates the length of the tensile and torsional energy storage segments; Δl1, Δl " Respectively represent the clamp 3 (energy release mechanism 1, such as Figure 3 As shown) to the longitudinal fixture 25 (energy release mechanism 2, as Figure 4 As shown in the figure, the distance from the clamp 3 to the sample 4 and the distance from the clamp 3 to the sample 4 can be determined by calculating the above conditions and the actual length of the incident rod. First, it is necessary to ensure that the sample 4 is always in a composite loading state (synchronous loading with the same pulse width) during the loading process. Taking into account the difference in the velocity of the tensile wave and the torsional wave, the length of the energy storage section of the tensile and torsional waves needs to satisfy the relationship of formula (1); the moment when the clamp (3) is released is taken as the initial moment, and the time t1 required for the tensile wave to reach the sample 4 is calculated by formula (2). It should be noted that this period of time also needs to consider the time when the torsional unloading wave reaches the longitudinal clamp 25 to trigger the tensile wave; the time t1 required for the torsional wave to reach the sample 4 is calculated by formula (3). " .

[0049]

[0050] If t1=t " If the condition is met, it is assumed that the time when the tensile wave and the torsional wave reach the sample 4 is the same, that is, the sample 4 is loaded synchronously. " The length relationship between them should satisfy formula (4):

[0051]

[0052] In Δl " The premise for ensuring that the complete incident wave and reflected wave can be collected within the segment is that the distance from the strain gauge to the sample 4 is at least greater than 1 times the length of the energy storage segment: Δl " >L2,Δl " >L1; the above relationship can be uniformly described as formula (5):

[0053] Δl " =aL1(a>1) (5)

[0054] Another geometric condition that needs to be met is that Δl1 must be contained in L " In the paragraph, combining equations (4) and (5) yields equation (6):

[0055]

[0056] By combining equations (1) and (6), we can find the value range of a, as shown in equation (7):

[0057]

[0058] The calculation formula for the length of the incident rod 1 is shown in formula (8). According to the length of the incident rod 1 selected for the actual equipment, a suitable value in the value range of a can be selected to determine the actual length of each part.

[0059]

[0060] Where C1 and C2 represent the tensile wave velocity and the torsional wave velocity, respectively.

[0061] The device first determines the distance Δl of the fixture 3 on the incident rod 1 according to the experimental requirements. " , the distance Δl1 between the longitudinal fixture 25, and the relative positions of the distance L2 between the torsional actuator 26 and the distance L1 between the tensile actuator 28. The bracket 29 is preferably an aluminum base bracket, which is used to support the screw 21, and the triangular armature at the bottom is used to ensure that the experimental device is symmetrically distributed about the center line of the platform. The first baffle 22, the first screw nut 23, the third nut 39 and the third baffle 38 on the screw 21 form a rectangular self-balancing frame to limit the distance between the clamp 3 and the tensile actuator 28, ensuring that the clamp 3 does not slide when the tensile load is applied. The structure and use method of the clamp 3 are similar to those of the clamp 3 in the above-mentioned document 2. The clamp 3 is used to clamp the incident rod 1 to limit the circumferential rotation of the incident rod 1. According to the calculation, the distance L between the torsional actuator 26 and the clamp 3 is obtained. " The position where the torque is applied is the position where the incident rod 1 is applied, and the strain gauge 6 on the right side of the clamp 3 can measure the pre-stored torque. At this time, the position where the torque is applied to the incident rod 1 and the clamp 3 are elastically deformed as the torque energy storage section. The blocking rod 24 clamped on the incident rod 1 rotates a certain angle along with the energy storage section. At this time, there is no force between the blocking rod 24 and the longitudinal clamp 25. According to the angle after the blocking rod 24 is rotated, the longitudinal clamp 25 ( Figure 4The angle of the one-way ratchet 33 (as shown) is adjusted to bring the edge of the fan-shaped opening slot 34 sufficiently close to the retaining rod 24. A tensile load is then applied to the incident rod end via the tensile actuator 28, forcing the retaining rod 24 into close contact with the longitudinal fixture 25. This limits the axial displacement of the energy storage section between the longitudinal fixture 25 and the tensile actuator, causing elastic deformation of the energy storage section. The strain gauge 2 on the right side of the longitudinal fixture 25 can then measure the pre-stored tensile force. The load on the fixture 3 is further increased via the hydraulic cylinder 15, causing the notched pin 9 to fracture. A rightward torsional unloading wave and a leftward torsional loading wave simultaneously occur from the fixture 3. The strain gauge 6 located between the fixture 3 and the specimen 4 records the torsional incident wave signal. This type of fixture coordination can use the emitted torsional unloading wave as a trigger signal for the longitudinal fixture 25. When the torsional unloading wave propagates to the longitudinal fixture 25, the incident rod 1 drives the blocking rod 24 to rotate a certain angle. When the blocking rod 24 enters the opening slot 34, the longitudinal fixture 25 releases the axial restriction on the energy storage section, and the tensile loading wave is released to catch up with the torsional loading wave. The signal of the tensile incident wave is recorded by the strain gauge 2 between the fixture 3 and the sample 4. Since the shape of the opening slot 35 is fan-shaped, it can be found through calculation that when the torsional unloading wave triggers the release of the tensile loading wave, it does not affect the propagation of the torsional unloading wave. Finally, the torsional loading wave and the tensile loading wave simultaneously reach the connecting end face of the incident rod 1 and the sample 4 to complete the synchronous loading. The tensile and torsional reflected waves generated by the sample 4 are collected by the strain gauges 2 and 6 on the left side of the fixture 3 on the incident rod. The dual energy release mechanism realizes the precise control of the time difference between the tensile wave and the torsional wave. The selected a value only needs to be within the value range of a in the above calculation to realize that the strain gauges 2 and 6 on the incident rod 1 can collect the complete incident wave and reflected wave signals, which can be directly used to calculate the strain of the sample 4; similarly, the strain gauges 2 and 6 on the transmission rod 5 can also collect the complete transmitted wave signals, which can directly calculate the stress of the sample, solving the problem of Figure 8 , 9, and 10. In the Hopkinson tension-torsion bar, the pulse width is too long, which causes the incident wave signal and the reflected wave signal to be superimposed together and the limitation of being unable to decouple the real complete waveform signal. It is worth mentioning that the shape of the incident rod 1 is as follows. Figure 5 As shown, the left end of the incident rod 1 is cylindrical and the right end is octagonal, which can ensure the torsion actuator 26 and the torsion limit support 27 ( Figure 6 The combination of the torsion limiting support 27 and the cylindrical section 24 can also ensure that the deformation of this section and the cylindrical section is substantially uniform when subjected to a tensile load, satisfying the one-dimensional stress wave assumption. The length of the torsion energy storage section can be changed by adjusting the position of the torsion limiting support 27 and moving it independently.

[0062] The present invention's tensile-torsion synchronous / asynchronous loading Hopkinson bar experimental device controls the relative positions of the stored tensile and torsional strains on the incident rod, as well as the position of the limiting mechanism and the specific applied load. The torsional wave release process triggers the release of the tensile wave, causing the tensile wave to pursue the torsional wave toward the specimen, ultimately arriving synchronously at the specimen, completing synchronous loading of the specimen. This approach can also achieve asynchronous loading of the specimen by adjusting the position to achieve asynchronous arrival of the tensile and torsional waves. Furthermore, based on the above approach, by designing the energy storage section length based on the actual incident rod length, it is possible to determine that strain gauges attached to a certain length range on the incident and transmission rods can capture complete waveforms, which can be directly used to calculate physical quantities such as stress, strain, and strain rate of the specimen.

[0063] It should be noted that the above-described embodiments are merely preferred embodiments of the present invention. Persons skilled in the art will appreciate that various modifications, improvements, and equivalent substitutions may be made to the present invention without departing from the principles of the present invention, and such modifications, improvements, and equivalent substitutions are deemed to fall within the scope of protection of the claims of the present invention.

Claims

1. A Hopkinson bar experimental device with synchronous and asynchronous loading of tension and torsion for precise control of the time difference between tension and torsion waves, comprising: An incident rod (1), a strain gauge (2) for measuring tensile strain, a fixture (3), a sample (4), a transmission rod (5), a strain gauge (6) for measuring shear strain, a support (20), a torsional actuator (26), a tensile actuator (28), and a platform (40), characterized in that it also includes: a screw (21), a first baffle (22), a first screw nut (23), a baffle (24), a longitudinal fixture (25), a second baffle (36), a second screw nut (37), a torsional limit support (27), a third baffle (38), a third screw nut (39), and a bracket (29); The two brackets (29) are respectively installed at the two ends of the platform (40) to support the screw rod (21). Along the X-axis direction, the two screw rods (21) sequentially pass through the bracket (29), the first baffle (22), the first screw nut (23), the second baffle (36), the second screw nut (37), the third baffle (38), and the third screw nut (39); the incident rod (1) sequentially passes through the support (20), the clamp (3), the first baffle (22), the longitudinal clamp (25), the second baffle (42), the torsion actuator (26), the torsion limit support (27), the third baffle (38), and the tensile actuator (28), and the axes of the various components are consistent; the clamp (3), a longitudinal fixture (25), a torsional actuator (26) and a tensile actuator (28) are fixedly connected to a platform (40), the strain gauge (2) for measuring tensile strain and the strain gauge (6) for measuring shear strain are respectively attached to the incident rod (1) and the transmission rod (5), wherein the fixture (3) and the longitudinal fixture (25) are used as a dual energy release mechanism, and the torsional limit support (27) is used as a limit mechanism, the fixture (3) first releases the circumferential strain restriction to release the torsional wave, and when the torsional wave is released and reaches the longitudinal fixture (25), the blocking rod (24) rotates a relative angle and passes through the longitudinal fixture (25), the longitudinal strain of the incident rod (1) is no longer restricted, and the tensile wave is released; The torsion actuator (26) is located between the second baffle (36) and the torsion limit support (27); the torsion actuator (26) is clearance-matched with the outer contour of the incident rod (1); The tensile actuator (28) is located between the third baffle (38) and the bracket (29), is fixedly connected to the third baffle (38), and is further fixedly connected to the platform (40). The tail of the incident rod (1) passes through the third baffle (38) and cooperates with the tensile actuator (28) to achieve the application of the tensile load. The blocking rod (24) is located between the clamp (3) and the longitudinal fixture (25) and close to one side of the longitudinal fixture (25), and is clamped on the incident rod (1); the sample (4) is placed between the incident rod (1) and the transmission rod (5).

2. The tensile-torsion synchronous-asynchronous loading Hopkinson bar experimental device for precisely controlling the time difference of tensile-torsion waves according to claim 1 is characterized in that: The longitudinal fixture (25) comprises: a spring (30), a pawl (31), a pin (32), a one-way ratchet (33), and a fan-shaped opening groove (34); the one-way ratchet (33) is embedded in the opening of the vertical plate of the longitudinal fixture (25) and can generate relative rotation with the vertical plate of the longitudinal fixture (25); the pawl (31) is connected to the vertical plate of the longitudinal fixture (25) by means of the pin (32), and is pressed against the tangential edge of the one-way ratchet (33) under the action of the spring (30).

3. The tensile-torsion synchronous-asynchronous loading Hopkinson bar experimental device for precisely controlling the time difference of tensile-torsion waves according to claim 1 or 2 is characterized in that: A triangular armature is provided at the bottom of the bracket, which is used to make the tension-torsion synchronous and asynchronous loading Hopkinson rod experimental device symmetrically distributed about the center line of the platform (40).

4. The tensile-torsion synchronous-asynchronous loading Hopkinson bar experimental device for precisely controlling the time difference of tensile-torsion waves according to claim 1 is characterized in that: The incident rod (1) is divided into two sections, one section is a cylinder and the other section is an octagonal prism. The torsion actuator (26) is clearance-matched with the outer contour of the octagonal prism on the incident rod (1) to achieve torque application without increasing longitudinal friction.

5. The tensile-torsion synchronous-asynchronous loading Hopkinson bar experimental device for precisely controlling the time difference of tensile-torsion waves according to claim 4 is characterized in that: The cross-sectional area of the octagonal prism is 90% of the cross-sectional area of the cylinder.

6. The tensile-torsion synchronous-asynchronous loading Hopkinson bar experimental device for precisely controlling the time difference of tensile-torsion waves according to claim 1 is characterized in that: The screw (21), baffles (22, 36, 38) and nuts (23, 37, 39) cooperate to form a self-balancing frame for limiting the relative positions of various components on the platform (40).

7. The tensile-torsion synchronous-asynchronous loading Hopkinson bar experimental device for precisely controlling the time difference of tensile-torsion waves according to claim 1 is characterized in that: The tensile and torsional reflected waves generated by the sample (4) are collected by a strain gauge (2) for measuring tensile strain and a strain gauge (6) for measuring shear strain attached to the incident rod (1).

8. The tensile-torsion synchronous-asynchronous loading Hopkinson bar experimental device for precisely controlling the time difference of tensile-torsion waves according to claim 1 is characterized in that: The thread at the tail of the incident rod (1) passes through the third baffle (38) and then matches with the internal thread of the tensile actuator (28) to achieve the application of the tensile load.

9. The tensile-torsion synchronous-asynchronous loading Hopkinson bar experimental device for precisely controlling the time difference of tensile-torsion waves according to claim 1 is characterized in that: Transmission wave signals are collected by a strain gauge (2) for measuring tensile strain and a strain gauge (6) for measuring shear strain attached to a transmission rod (5).

10. The tensile-torsion synchronous-asynchronous loading Hopkinson bar experimental device for precisely controlling the time difference of tensile-torsion waves according to claim 1 is characterized in that: The position of the torsion limiting support (27) can be moved independently to change the length of the torsion energy storage section.

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