Pore water pressure testing device and method for discrete material one-dimensional SHPB test
By using stainless steel filters and optimized pore water pressure gauge design in SHPB tests, the problem of response hysteresis and low stiffness in saturated dispersion material tests is solved, achieving more efficient and reliable pore water pressure measurements.
Patent Information
- Application Number
- CN202510300907.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-14
- Publication Date
- 2025-06-24
AI Technical Summary
In the SHPB test of saturated dispersion materials, the response frequency of the traditional pore water pressure gauge is too low, and there is a large hysteresis, which is difficult to accurately reflect the instantaneous changes in pore water pressure during the test. At the same time, during the high-speed impact process, the low stiffness and easy deformation of permeate affect the measurement accuracy.
A pore water pressure testing device for one-dimensional SHPB test of dispersible materials was designed, and a stainless steel filter was used to replace traditional permeable stone, and the cavity thickness of the pore water pressure gauge was shortened to improve its response speed and data acquisition frequency.
It significantly reduces the hysteresis and low stiffness problems of pore water pressure testing, improves the accuracy and real-time measurement, and can more accurately capture the instantaneous changes in pore water pressure, providing more reliable measurement results for high-speed impact tests.
Smart Images
Figure CN120195035A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of geotechnical engineering, and particularly relates to a pore water pressure testing device and a testing method for one-dimensional SHPB tests of granular materials. Background Art
[0002] At present, due to its unique advantages, the Split Hopkinson Pressure Bar (SHPB) device has been widely used by many scholars at home and abroad to study the mechanical properties of materials at medium and high strain rates, and can achieve loading tests with a strain rate range of 10 2 ~10 4 s -1 . With the continuous development and improvement of the SHPB test device 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.
[0003] However, in the SHPB test of saturated granular materials, the measurement of pore water pressure faces many challenges. Since the impact process is instantaneous, the response frequency of traditional pore water pressure gauges is too low, with a large lag, and it is difficult to accurately reflect the instantaneous change of pore water pressure during the test. In addition, during the high-speed impact process, the strength and stiffness of the permeable stones of traditional pore water pressure gauges are relatively low, and they are prone to deformation under the action of impact loads (MPa level), thus affecting the measurement accuracy.
[0004] The water content state has a great influence on the mechanical properties of granular materials. As the water content increases, the mechanical response of the materials changes accordingly. Especially in the saturated state, the mechanical properties of granular materials will show significant deterioration. At this time, the cohesion of the materials decreases significantly, and the internal friction angle also decreases accordingly, resulting in a significant reduction in its overall strength. In addition, the granular materials in the saturated state are also affected by pore water pressure. During the impact or rapid loading process, the instantaneous change of pore water pressure will have an important impact on the mechanical response of the materials. Under quasi-static loads, the existing pore pressure sensor testing technology has met the requirements for accurate and stable pore pressure testing. However, under high-frequency and instantaneous dynamic loads, when the external pore pressure is dynamically changing, the stress wave needs to transmit through the permeable stone, cavity, etc. If the transmission time is greater than the change speed of the external pore pressure, it will inevitably affect the pore pressure amplitude and accuracy. In the performance test of the pore pressure gauge, traditional pore pressure gauges usually use a relatively thick permeable stone as a key component. However, this design has certain limitations. On the one hand, the large thickness of the permeable stone results in a slow water penetration speed, so that the measured pore water pressure may have a lag, affecting the accuracy and real-time nature of the test results. On the other hand, during the SHPB impact test, the stiffness of the permeable stone is relatively low, making it difficult to withstand rapid impacts and prone to damage, thus affecting the reliability and repeatability of the test. In addition, the cavity thickness of the pore pressure gauge has an important impact on its response rate and acquisition frequency during the high-speed impact process. Summary of the Invention
[0005] Object of the Invention: In order to overcome the deficiencies of the background technology, the first object of the present invention is to disclose a pore water pressure testing device for one-dimensional SHPB tests of granular materials; The second object is to disclose a testing method based on the above-mentioned pore water pressure testing device for one-dimensional SHPB tests of granular materials, which can study the mechanical properties of granular materials in the saturated state during the one-dimensional impact loading process.
[0006] Technical Solution: The pore water pressure testing device for one-dimensional SHPB tests of granular materials disclosed by the present invention includes an undrained boundary device and a pore pressure gauge; The middle of the undrained boundary device is a placement area for granular materials, with an incident bar and a reflection bar connected to both ends respectively. A radial threaded hole is opened on the middle side wall corresponding to the placement area, and a stainless steel filter screen is provided at the bottom of the threaded hole; The pore 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 provided at the other end of the sensor housing, and its internal is an internal thread structure. The outer wall of the conversion cylinder is an internal thread structure, and one end is connected to the sensor head in a matching manner, and the other end is connected to the threaded hole in a matching manner, pressing the stainless steel filter screen against the granular materials.
[0007] Further, the undrained boundary device includes a stepped sleeve, a first water-stop sealing ring, a cushion block and a collar press head; a stepped structure is formed at the center position of the stepped sleeve corresponding to the reduced inner diameter of the granular material, and the inner walls at both ends are internal thread structures. The first water-stop sealing ring is located at the end face of the stepped structure, and the end face of the first water-stop sealing ring is the same size as the end face of the stepped structure. The cushion blocks are located at both ends of the granular material, and their outer diameters are the same as the inner diameter of the first water-stop sealing ring. The collar press head is a through structure, the inner diameter of its pressing head is the same as the outer diameter of the cushion block, and its outside is an external thread structure matching the stepped sleeve, and axial pressure is applied to the first water-stop sealing ring by screwing axially.
[0008] Further, the material of the cushion block is the same as that of the Hopkinson bar.
[0009] Further, a second water-stop sealing ring is provided between the conversion cylinder and the stainless steel filter screen.
[0010] Further, the stainless steel filter screen is a cylindrical fine-pore structure and is pressed by the conversion cylinder against the granular material.
[0011] Further, the pore diameter of the stainless steel filter screen is smaller than the minimum particle size of the granular material.
[0012] Correspondingly, a test method for the pore water pressure test device for one-dimensional SHPB test of granular materials is disclosed, including the following steps: S1. Install the cushion block, the first water-stop sealing ring and the collar press head at one end of the stepped sleeve, load the sample from the other end, and place all components of the pore water pressure gauge in the vacuum saturation cylinder together after loading the sample; S2. Connect the valve at the top of the vacuum saturation cylinder to the vacuum pump and evacuate. S3. Connect the valve on the side wall of the vacuum saturation cylinder to the de-aired water preparation machine, and introduce de-aired water under the premise of maintaining the vacuum state until it completely submerges the stepped sleeve and all components of the pore water pressure gauge; S4. Open the top cover of the vacuum saturation cylinder, lead out the cable, assemble the pore water pressure gauge in the de-aired water in the cylinder and then take it out; S5. Connect the assembled pore water pressure gauge to the stepped sleeve, and then assemble the cushion block, the first water-stop sealing ring and the collar press head at the other end of the stepped sleeve; S6. Place the whole device on the Hopkinson bar device to realize the mechanical response test of the granular material under impact load in a saturated state.
[0013] Beneficial effects: Compared with the prior art: The present invention provides a solution for the pore water pressure measurement of granular materials in a saturated state under Hopkinson confining pressure during impact tests. By designing a stepped sleeve and stepped surface, as well as threaded holes on the side wall of the stepped sleeve, pads made of the same material as the pressure bars are used to connect the granular materials to the incident and reflected bars to ensure the one-dimensional assumption. By setting a stainless steel filter screen and a water stop sealing ring on the side wall of the stepped sleeve, it effectively ensures that the granular materials do not overflow and do not drain during the sample loading and saturation processes. By using a stainless steel filter screen instead of the permeable stone of the traditional pore water pressure gauge, the hysteresis and low stiffness problems in pore water pressure measurement during the SHPB test are solved.
[0014] The present invention further eliminates gas interference by introducing a degassed 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, thereby greatly improving the response speed and data acquisition frequency of the pore water pressure gauge, enabling it to more accurately capture the instantaneous changes in pore water pressure and providing more reliable measurement results for high-speed impact tests. Brief Description of the Drawings
[0015] Figure 1 is the split structure diagram of the present invention; Figure 2 is the overall structure diagram of the present invention; Figure 3 is the overall cross-sectional view of the present invention; Figure 4 is the structure diagram of the pore water pressure gauge of the present invention; Figure 5 is the structure diagram of the threaded hole of the present invention. Detailed Embodiments
[0016] The technical solutions of the present invention will be further described below in conjunction with the drawings and embodiments.
[0017] As Figures 1-5 shown, the pore water pressure measurement device for one-dimensional SHPB tests of granular materials includes a non-draining boundary device 1 and a pore water pressure gauge 2.
[0018] The middle of the non-draining boundary device 1 is the placement area for granular materials 3, and the incident bar and the reflected bar are respectively docked at both ends. A radial threaded hole 4 is opened on the middle side wall corresponding to the placement area, and a stainless steel filter screen 5 is provided at the bottom of the threaded hole 4.
[0019] The pore water pressure gauge 2 includes a sensor housing 201, a conversion cylinder 202, a sensor tip 203, and a cable 204. The cable 204 is located at one end of the sensor housing 201 and is integrally connected thereto. The sensor tip 203 is provided at the other end of the sensor housing 201, and its interior is an internal thread structure. The outer wall of the conversion cylinder 202 is an internal thread structure. One end is matingly connected to the sensor tip 203, and the other end is matingly connected to the threaded hole 4, pressing the stainless steel filter screen 5 against the granular material 3.
[0020] The undrained boundary device 1 includes a stepped sleeve 101, a first water stop sealing ring 102, a spacer 103, and a collar press head 104. A stepped structure is formed at the central position of the stepped sleeve 101 corresponding to the reduced inner diameter of the granular material 3, and the inner walls at both 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 the same size as the end face of the stepped structure. The spacer 103 is located at both ends of the granular material 3, and its outer diameter is the same as the inner diameter of the first water stop sealing ring 102. The collar press head 104 is a through structure, the inner diameter of its press head part is the same as the outer diameter of the spacer 103, and its exterior is an external thread structure matching the stepped sleeve 101, axially pressing the first water stop sealing ring 102 by screwing axially.
[0021] The material of the spacer 103 is the same as that of the Hopkinson bar, both being 60Si2MnA, ensuring the accuracy of the one-dimensional elastic wave hypothesis during the impact process.
[0022] A second water stop sealing ring 6 is provided between the conversion cylinder 202 and the stainless steel filter screen 5.
[0023] The stainless steel filter screen 5 has a cylindrical fine pore structure, is pressed against the granular material 3 by the conversion cylinder 202, has a thickness much smaller than that of the permeable stone of the traditional pore pressure gauge, has better permeability than the permeable stone, and can effectively reduce the lag of pore water pressure measurement. At the same time, the stiffness of the stainless steel material is much greater than that of the permeable stone, making it more suitable for tests under high-speed impact conditions.
[0024] The aperture of the stainless steel filter screen 5 is 0.074 mm, which is smaller than the minimum particle size of the granular material 3.
[0025] The testing method based on the above testing device includes the following steps: S1. Install the spacer 103, the first water stop sealing ring 102, and the collar press head 104 at one end of the stepped sleeve 101, load the sample from the other end, and after loading the sample, place the components of the pore water pressure gauge 2 in the vacuum saturation cylinder together. S2. Connect the valve at the top of the vacuum saturation cylinder to the vacuum pump and conduct vacuum pumping. S3. Connect the valve on the side wall of the vacuum saturation cylinder to the degassed water preparation machine. On the premise of maintaining the vacuum state, introduce degassed water until it completely submerges each component of the stepped sleeve 101 and the pore water pressure gauge 2; S4. Open the top cover of the vacuum saturation cylinder, lead out the cable 204, assemble the pore water pressure gauge 2 under the degassed water in the cylinder, and then take it out; 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 seal ring 102 and the collar press head 104 at the other end of the stepped sleeve 101; S6. Place the entire device on the Hopkinson bar device to realize the mechanical response test of the granular material 3 under the impact load in the saturated state.
Claims
1. A pore water pressure testing device for one-dimensional SHPB test of bulk materials, characterized by: It includes an undrained boundary device (1) and a pore water pressure gauge (2); The middle of the non-drainage boundary device (1) is a placement area for the bulk material (3), and the two ends are respectively connected to the receiving rod and the reflecting rod, and a radial threaded hole (4) is provided on the middle side wall of the corresponding placement area, and a stainless steel filter (5) is provided at the bottom of the threaded hole (4); The pore water pressure gauge (2) comprises 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 thereto; the sensor pressure head (203) is provided at the other end of the sensor housing (201) and has an internal thread structure in its interior; the outer wall of the conversion cylinder (202) has an internal thread structure, one end of which is matched and connected to the sensor pressure head (203) and the other end of which is matched and connected to the threaded hole (4), so that the stainless steel filter (5) is pressed against the bulk material (3).
2. The pore water pressure testing device for one-dimensional SHPB test of bulk materials according to claim 1, characterized in that: The non-drainage boundary device (1) comprises a stepped sleeve (101), a first water-stop sealing ring (102), a cushion block (103) and a collar pressure head (104); the inner diameter of the bulk material (3) at the center of the stepped sleeve (101) is reduced to form a stepped structure, and the inner walls at both 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 cushion block (103) is located at both ends of the bulk material (3), and its outer diameter is consistent with the inner diameter of the first water-stop sealing ring (102); the collar pressure head (104) is a through structure, and the inner diameter of its pressure head is consistent with the outer diameter of the cushion block (103); its outer portion is an external thread structure matching the stepped sleeve (101), and axial pressure is applied to the first water-stop sealing ring (102) by axially tightening the thread.
3. The pore water pressure testing device for one-dimensional SHPB test of bulk materials according to claim 2, characterized in that: The material of the cushion block (103) is consistent with that of the Hopkinson pressure bar.
4. The pore water pressure testing device for one-dimensional SHPB test of bulk materials according to claim 1, characterized in that: A second water-stop sealing ring (6) is provided 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 bulk materials according to claim 1, characterized in that: The stainless steel filter screen (5) is a columnar fine-pore structure and is pressed against the bulk material (3) by the conversion cylinder (202).
6. The pore water pressure testing device for one-dimensional SHPB test of bulk materials according to claim 5, characterized in that: The pore size of the stainless steel filter (5) is smaller than the minimum particle size of the bulk material (3).
7. A testing method based on the pore water pressure testing device for one-dimensional SHPB test of bulk materials according to claim 2, comprising the following steps: S1. Install a spacer (103), a first water-stop seal (102) and a collar pressure head (104) at one end of the stepped sleeve (101), load the sample from the other end, and after the sample is loaded, place the components of the pore water pressure gauge (2) in a vacuum saturation cylinder; S2, connect the top valve of the vacuum saturation cylinder to the vacuum pump to evacuate; S3, connecting the valve on the side wall of the vacuum saturation cylinder to the airless water preparation machine, and introducing airless water while maintaining the vacuum state until the airless water completely submerges the stepped sleeve (101) and the pore water pressure gauge (2); S4, open the top cover of the vacuum saturation cylinder, lead out the cable (204), assemble the pore water pressure gauge (2) in the airless water in the cylinder, and then take it out; S5, connecting the assembled pore water pressure gauge (2) to the stepped sleeve (101), and then assembling the mounting pad (103), the first water stop seal (102) and the collar pressure head (104) at the other end of the stepped sleeve (101); S6. Place the entire device on a Hopkinson pressure bar device to implement a mechanical response test of the bulk material (3) under an impact load in a saturated state.