Pore water pressure testing device for one-dimensional SHPB (split Hopkinson pressure bar) test of discrete material

Abstract

The utility model discloses a pore water pressure testing device for a one-dimensional SHPB (split Hopkinson pressure bar) test of a discrete material. The pore water pressure testing device comprises an undrained boundary device and a pore water pressure gauge, a discrete material placing area is arranged in the middle of the undrained boundary device, the two ends of the undrained boundary device are oppositely connected with a shooting rod and a reflecting rod respectively, a radial threaded hole is formed in the side wall of the middle of the corresponding placing area, and a stainless steel filter screen is arranged at the bottom of the threaded hole; the pore water pressure gauge comprises a sensor shell, a conversion cylinder, a sensor pressure head and a cable, the cable is located at one end of the sensor shell and integrally connected with the sensor shell, the sensor pressure head is arranged at the other end of the sensor shell, the interior of the sensor pressure head is of an internal thread structure, the outer wall of the conversion cylinder is of an internal thread structure, and one end of the conversion cylinder is connected with the sensor pressure head in a matched mode. And the other end is matched and connected with the threaded hole to press the stainless steel filter screen on the discrete material. The one-dimensional impact loading device can be used for researching the mechanical property of a discrete material in a saturated state in a one-dimensional impact loading process.

Description

Technical Field

[0001] This utility model relates to the field of geotechnical engineering, and in particular to a pore water pressure testing device for one-dimensional SHPB tests of granular materials. Background Technology

[0002] Currently, the Hopkinson pressure bar (SHPB) apparatus, with its unique advantages, has been widely used by numerous scholars both domestically and internationally to study the mechanical properties of materials under medium to high strain rates, capable of achieving strain rates ranging from 10... 2 ~10 4 s -1 Loading tests. With the continuous development and improvement of SHPB testing equipment and technology, its application scope has gradually expanded from traditional block materials such as concrete and rock to the field of granular materials such as sand and soil.

[0003] However, measuring pore water pressure in SHPB tests of saturated granular materials faces numerous challenges. Because the impact process is instantaneous, traditional pore water pressure gauges have excessively low response frequencies and significant hysteresis, making it difficult to accurately reflect the instantaneous changes in pore water pressure during the test. Furthermore, during high-speed impacts, the permeable stone in traditional pore water pressure gauges has low strength and stiffness, making it prone to deformation under impact loads (MPa levels), thus affecting measurement accuracy.

[0004] The moisture content significantly affects the mechanical properties of granular materials; as the moisture content increases, the material's mechanical response changes accordingly. Especially in the saturated state, the mechanical properties of granular materials exhibit significant deterioration. At this point, the material's cohesion decreases substantially, and the internal friction angle also decreases, leading to a significant reduction in its overall strength. Furthermore, saturated granular materials are also affected by pore water pressure. During impact or rapid loading, the instantaneous changes in pore water pressure have a significant impact on the material's mechanical response. Under quasi-static loads, existing pore pressure sensor testing technology meets the requirements for accurate and stable pore pressure testing. However, under high-frequency, instantaneous dynamic loads, when the external pore pressure changes dynamically, the stress wave needs time to propagate through permeable stones, cavities, etc. If the propagation time is greater than the rate of change of the external pore pressure, it will inevitably affect the amplitude and accuracy of the pore pressure. In the performance testing of pore water pressure gauges, traditional pore water pressure gauges typically use thick permeable stones as key components. However, this design has certain limitations. On the one hand, the greater thickness of the permeable stone results in a slower water permeation rate, potentially causing a lag in the measured pore water pressure, thus affecting the accuracy and real-time nature of the test results. On the other hand, during SHPB impact testing, the relatively low stiffness of the permeable stone makes it difficult to withstand rapid impacts, leading to easy damage and impacting the reliability and repeatability of the test. Furthermore, the cavity thickness of the pore water pressure gauge significantly affects its response rate and sampling frequency during high-speed impacts. Summary of the Invention

[0005] Purpose of the utility model: In order to overcome the shortcomings of the prior art, this utility model discloses a pore water pressure testing device for one-dimensional SHPB test of granular materials, which can study the mechanical properties of granular materials under saturation state during one-dimensional impact loading.

[0006] Technical solution: The pore water pressure testing device for one-dimensional SHPB test of granular materials disclosed in this utility model includes an undrained boundary device and a pore water pressure gauge.

[0007] The non-drainage boundary device has a bulk material placement area in the middle, with a shooting rod and a reflective rod connected to both ends respectively. A radial threaded hole is opened on the middle side wall of the placement area, and a stainless steel filter screen is provided at the bottom of the threaded hole.

[0008] The pore water pressure gauge includes a sensor housing, a conversion cylinder, a sensor head, and a cable. The cable is located at one end of the sensor housing and is integrally connected to it. The sensor head is located at the other end of the sensor housing and has an internal thread structure. The outer wall of the conversion cylinder has an internal thread structure. One end of the cylinder is matched and connected to the sensor head, and the other end is matched and connected to the threaded hole to press the stainless steel filter screen onto the bulk material.

[0009] Furthermore, the non-drainage boundary device includes a stepped sleeve, a first water-stop sealing ring, a pad, and a collar pressure head; the center position of the stepped sleeve corresponds to the inner diameter of the bulk material decreasing to form a stepped structure, and the inner walls at both ends are internally threaded structures. The first water-stop sealing ring is located on the end face of the stepped structure, and the end face of the first water-stop sealing ring has the same size as the end face of the stepped structure. The pad is located at both ends of the bulk material, and its outer diameter is the same as the inner diameter of the first water-stop sealing ring. The collar pressure head is a through structure, and its inner diameter of the pressure head is the same as the outer diameter of the pad. Its outer surface is an externally threaded structure that matches the stepped sleeve. The first water-stop sealing ring is axially pressurized by axially tightening the threads.

[0010] Furthermore, the pad material is the same as the Hopkinson pressure bar material.

[0011] Furthermore, a second water-stop sealing ring is provided between the conversion cylinder and the stainless steel filter screen.

[0012] Furthermore, the stainless steel filter screen has a cylindrical fine-pore structure and is pressed onto the bulk material by a conversion cylinder.

[0013] Furthermore, the pore size of the stainless steel filter screen is smaller than the minimum particle size of the bulk material.

[0014] Correspondingly, the test method for the pore water pressure testing device used in the one-dimensional SHPB test of granular materials is disclosed, including the following steps:

[0015] S1. Install a pad, a first water-stop sealing ring and a collar pressure head at one end of the stepped sleeve, and load the sample from the other end. After loading the sample, place all the components of the pore water pressure gauge into the vacuum saturation cylinder.

[0016] S2. Connect the top valve of the vacuum saturation cylinder to the vacuum pump to perform vacuuming;

[0017] S3. Connect the valve on the side wall of the vacuum saturation cylinder to the airless water preparation machine. While maintaining the vacuum state, introduce airless water until it completely submerges the stepped sleeve and the pore water pressure gauge.

[0018] S4. Open the top cover of the vacuum saturation cylinder, lead out the cable, assemble the pore water pressure gauge in the airless water inside the cylinder, and then take it out.

[0019] S5. Assemble the pore water pressure gauge and connect it to the stepped sleeve. Then assemble the mounting pad, the first water-stop sealing ring and the collar pressure head at the other end of the stepped sleeve.

[0020] S6. Place the entire device on the Hopkinson pressure bar device to realize the mechanical response test of granular materials under impact load in a saturated state.

[0021] Beneficial effects: Compared with existing technologies:

[0022] This invention provides a solution for pore water pressure testing of saturated bulk materials under Hopkinson pressure during impact tests. It employs a stepped sleeve, stepped surface, and threaded holes on the side wall of the stepped sleeve, using pads made of the same material as the pressure bar to connect the bulk material to the incident and reflecting rods to ensure the one-dimensional assumption. By installing a stainless steel filter screen and a water-stop sealing ring on the side wall of the stepped sleeve, it effectively ensures that the bulk material does not overflow or drain during sample loading and saturation. Furthermore, by using a stainless steel filter screen instead of the permeable stone in traditional pore water pressure gauges, it addresses the hysteresis and low stiffness issues in pore water pressure testing during the SHPB test.

[0023] This invention further eliminates gas interference by introducing an airless water saturation test, and significantly reduces the propagation time of stress waves in the cavity by shortening the cavity thickness of the pore water pressure gauge. This greatly improves the response speed and data acquisition frequency of the pore water pressure gauge, enabling it to more accurately capture instantaneous changes in pore water pressure and provide more reliable measurement results for high-speed impact tests. Attached Figure Description

[0024] Figure 1 This is a diagram of the split structure of this utility model;

[0025] Figure 2 This is a structural diagram of the present utility model;

[0026] Figure 3 This is an overall sectional view of the present invention;

[0027] Figure 4 This is a structural diagram of the pore water pressure gauge of this utility model;

[0028] Figure 5 This is a structural diagram of the threaded hole of this utility model. Detailed Implementation

[0029] The technical solution of this utility model will be further described below with reference to the accompanying drawings and embodiments.

[0030] like Figure 1-5 The pore water pressure testing apparatus shown for one-dimensional SHPB tests of granular materials includes an undrained boundary device 1 and a pore water pressure gauge 2.

[0031] The non-drainage boundary device 1 has a placement area for bulk material 3 in the middle, and the two ends are respectively connected to the shooting rod and the reflector rod. A radial threaded hole 4 is opened on the middle side wall of the placement area, and a stainless steel filter screen 5 is provided at the bottom of the threaded hole 4.

[0032] The pore water pressure gauge 2 includes a sensor housing 201, a conversion cylinder 202, a sensor pressure head 203, and a cable 204. The cable 204 is located at one end of the sensor housing 201 and is integrally connected to it. The sensor pressure head 203 is located at the other end of the sensor housing 201 and has an internal thread structure. The outer wall of the conversion cylinder 202 has an internal thread structure. One end is matched and connected to the sensor pressure head 203, and the other end is matched and connected to the threaded hole 4 to press the stainless steel filter screen 5 onto the bulk material 3.

[0033] The non-drainage boundary device 1 includes a stepped sleeve 101, a first water-stop sealing ring 102, a pad 103, and a collar pressure head 104. The stepped sleeve 101 forms a stepped structure with the inner diameter of the bulk material 3 decreasing at its center position. The inner walls at both ends are internally threaded. The first water-stop sealing ring 102 is located on the end face of the stepped structure, and the end face of the first water-stop sealing ring 102 has the same size as the end face of the stepped structure. The pad 103 is located at both ends of the bulk material 3, and its outer diameter is the same as the inner diameter of the first water-stop sealing ring 102. The collar pressure head 104 is a through structure, and its inner diameter of the pressure head is the same as the outer diameter of the pad 103. Its outer surface is an externally threaded structure that matches the stepped sleeve 101. The first water-stop sealing ring 102 is axially pressurized by axially tightening the threads.

[0034] The pad 103 is made of the same material as the Hopkinson pressure bar, 60Si2MnA, which ensures the accuracy of the one-dimensional elastic wave assumption during the impact process.

[0035] A second water-stop sealing ring 6 is provided between the conversion cylinder 202 and the stainless steel filter screen 5.

[0036] The stainless steel filter screen 5 has a cylindrical fine pore structure and is pressed onto the bulk material 3 by the conversion cylinder 202. Its thickness is much smaller than that of the permeable stone in the traditional pore pressure gauge, and its permeability is better than that of the permeable stone, which can effectively reduce the hysteresis of pore water pressure testing. At the same time, the rigidity of stainless steel is much greater than that of permeable stone, making it more suitable for testing under high-speed impact conditions.

[0037] The stainless steel filter screen 5 has a pore size of 0.074 mm, which is smaller than the minimum particle size of the bulk material 3.

[0038] The testing method based on the above-mentioned testing device includes the following steps:

[0039] S1. Install pad 103, first water-stop sealing ring 102 and collar pressure head 104 at one end of stepped sleeve 101, and load the sample from the other end. After loading the sample, place all components of pore water pressure gauge 2 into vacuum saturation cylinder.

[0040] S2. Connect the top valve of the vacuum saturation cylinder to the vacuum pump to perform vacuuming;

[0041] S3. Connect the valve on the side wall of the vacuum saturation cylinder to the airless water preparation machine. While maintaining the vacuum state, introduce airless water until it completely submerges the stepped sleeve 101 and the pore water pressure gauge 2.

[0042] S4. Open the top cover of the vacuum saturation cylinder, lead out the cable 204, and assemble the pore water pressure gauge 2 in the airless water inside the cylinder before taking it out.

[0043] S5. Connect the assembled pore water pressure gauge 2 to the stepped sleeve 101, and then assemble the mounting pad 103, the first water-stop sealing ring 102, and the collar pressure head 104 at the other end of the stepped sleeve 101.

[0044] S6. Place the entire device on the Hopkinson pressure bar device to realize the mechanical response test of the granular material 3 under impact load in the saturated state.

Claims

1. A pore water pressure testing device for one-dimensional SHPB test of granular materials, characterized in that: It comprises a non-draining boundary device (1) and a pore water pressure gauge (2); The non-draining boundary device (1) has a placement area of granular material (3) in the middle, and the two ends are respectively connected to an incident rod and a reflection rod; a radial threaded hole (4) is arranged in the middle side wall corresponding to the placement area; a stainless steel filter screen (5) is arranged at the bottom of the threaded hole (4). The pore water pressure gauge (2) comprises a sensor shell (201), a conversion cylinder (202), a sensor pressure head (203), and a cable (204); the cable (204) is located at one end of the sensor shell (201) and is integrally connected thereto; the sensor pressure head (203) is arranged at the other end of the sensor shell (201), and the inside thereof is an internal thread structure; the outer wall of the conversion cylinder (202) is an internal thread structure, one end of which is matched and connected with the sensor pressure head (203), and the other end is matched and connected with the threaded hole (4), and the stainless steel filter screen (5) is pressed on the granular material (3).

2. The pore water pressure testing device for one-dimensional SHPB test of granular materials according to claim 1, characterized in that: The non-draining boundary device (1) comprises a stepped sleeve (101), a first water stop sealing ring (102), a pad (103), and a sleeve ring pressure head (104); the stepped sleeve (101) has a stepped structure corresponding to the smaller inner diameter of the granular material (3) in the center position, and the inner walls of the two ends are internal thread structures; the first water stop sealing ring (102) is located at the end face of the stepped structure, and the end face of the first water stop sealing ring (102) is consistent in size with the end face of the stepped structure; the pad (103) is located at the two ends of the granular material (3), and the outer diameter thereof is consistent with the inner diameter of the first water stop sealing ring (102); the sleeve ring pressure head (104) is a through structure, the inner diameter of the pressure head thereof is consistent with the outer diameter of the pad (103), and the outside thereof is an external thread structure matched with the stepped sleeve (101); the first water stop sealing ring (102) is axially pressed by screwing the thread in the axial direction.

3. The pore water pressure testing device for one-dimensional SHPB test of granular materials according to claim 2, characterized in that: The material of the pad (103) is consistent with the material of the Hopkinson pressure bar.

4. The pore water pressure testing device for one-dimensional SHPB test of granular materials according to claim 1, characterized in that: A second water stop sealing ring (6) is arranged between the conversion cylinder (202) and the stainless steel filter screen (5).

5. The pore water pressure testing device for one-dimensional SHPB test of granular materials according to claim 1, characterized in that: The stainless steel filter screen (5) is a cylindrical fine hole structure, which is pressed on the granular material (3) by the conversion cylinder (202).

6. The pore water pressure testing device for one-dimensional SHPB test of granular materials according to claim 5, characterized in that: The pore diameter of the stainless steel filter screen (5) is smaller than the smallest particle size of the granular material (3).

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