A boundary control device for one-dimensional SHPB test of granular materials

Abstract

The application discloses a boundary control device for one-dimensional SHPB test of bulk materials, which comprises an inner stepped sleeve, a cushion block, a waterproof silica gel ring and a sleeve ring pressure head; the middle part of the inner stepped sleeve is a placing area, and both ends are connecting areas; the inner diameter of the connecting area is larger than that of the placing area to form a stepped structure; the stepped structure is provided with a convex groove in the axial and circumferential directions; the connecting area is provided with an internal thread and a through screw hole; the cushion block extends from the connecting area to the placing area; the waterproof silica gel ring is arranged at the stepped structure and located between the cushion block and the connecting area; the sleeve ring pressure head is arranged on the outer wall of the cushion block and is provided with an external thread; and the waterproof silica gel ring is pressed to radial deformation by screwing the sleeve ring pressure head to the inside. The application provides a solution for one-dimensional drainage boundary control of bulk materials in different water content states under the Hopkinson confining pressure during impact test; the stepped sleeve and the convex groove at the stepped surface are designed; and the cushion block with the same material as the pressure rod is adopted to connect the bulk materials with the incident and reflected rods to ensure the one-dimensional assumption.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering, and in particular to a boundary control device for one-dimensional SHPB tests of granular materials. Background Technology

[0002] Currently, many scholars both domestically and internationally regard the Hopkinson bar apparatus as one of the important methods for studying the mechanical properties of materials under medium to high strain rates. It can achieve 10... 2 ~10 4 s -1 Strain rate loading tests are conducted. With the maturity and development of the SHPB testing apparatus and technology, its application has expanded beyond bulk materials such as concrete and rock to include granular materials like sand. Due to the low inherent wave impedance of granular materials, acquiring transmitted wave signals is difficult. Therefore, specially designed sleeves are needed to add confining pressure to constrain the lateral deformation of the granular material and improve its overall strength. Currently, commonly performed one-dimensional laterally confined impact tests all use sleeves as constraints. The granular material needs to be prepared in advance, and the prepared sample is placed between the incident and reflecting rods before the impact test. To meet the test requirements, the sleeve diameter must be slightly larger than the pad diameter; therefore, this apparatus cannot be used for one-dimensional impact compression tests on water-containing granular materials.

[0003] The moisture content significantly affects the mechanical properties of granular materials; as the moisture content increases, the material's mechanical response changes accordingly. However, because the commonly used sleeve size is slightly larger than the diameter of the pad, the current SHPB one-dimensional impact testing apparatus for granular materials cannot account for the characteristics of hydrated granular materials. This is because when the moisture content of the granular material exceeds 20%, free water will flow out from the gaps in the sleeve during sample loading, making it impossible to control the drainage and venting boundaries of the hydrated sample. Therefore, one-dimensional drainage boundary control is crucial for granular materials with different moisture contents in SHPB impact testing. Zhao Zhangyong and Tianrui Li studied the effect of moisture content on the impact characteristics of unsaturated calcareous sand and unsaturated sand, respectively, but their testing apparatuses could not meet the requirements for granular materials with a moisture content exceeding 30%. Zhao Futian invented a Hopkinson confining pressure control and testing system for soil dynamics, which used permeable stone as a pad between the granular material and the incident rod, but could not guarantee the assumption of uniformity in the test. Summary of the Invention

[0004] Purpose of the invention: In order to overcome the shortcomings of the prior art, the present invention discloses a boundary control device for one-dimensional SHPB test of granular materials. By using a built-in water-stopping silicone ring, the device tightens the pad block after being compressed and forms a sealed sample chamber, thereby realizing the non-drained and non-vented boundary of granular materials under one-dimensional impact, filling the gap in the SHPB impact test of hydrated granular materials.

[0005] Technical solution: The boundary control device for one-dimensional SHPB test of granular materials disclosed in this invention includes an inner stepped sleeve and pads, water-stop silicone rings and collar pressure heads respectively provided at both ends of the inner stepped sleeve;

[0006] The inner stepped sleeve has a bulk material placement area in the middle and connection areas at both ends. The inner diameter of the connection area is larger than that of the placement area, forming a stepped structure. The stepped structure has convex grooves in both the axial and circumferential directions at the step. The connection area has internal threads and through screw holes.

[0007] The pad extends from the connection area of ​​the inner stepped sleeve to the placement area;

[0008] The water-stop silicone ring is placed at the step of the inner stepped sleeve, between the pad and the connecting area;

[0009] The collar pressure head is sleeved on the outer wall of the pad and has an external thread corresponding to the internal thread. It is screwed inward through the thread structure. The inner axial end of the collar pressure head presses the water-stop silicone ring onto the step until it undergoes radial deformation.

[0010] Furthermore, the grooves provided at the steps of the inner stepped sleeve include a first groove provided at the axial end of the placement area and a second groove provided on the inner wall of the connection area.

[0011] Furthermore, the water-stopping silicone ring is pressed onto the first and second protrusions, and its inner wall is provided with a third protrusion that presses against the pad.

[0012] Furthermore, the pad is made of the same material as the Hopkinson pressure bar.

[0013] Furthermore, the collar pressure head has a through groove at the position corresponding to the screw hole, and the screw passes through the screw and the groove to fix the pad.

[0014] Beneficial effects: Compared with the prior art, the present invention: (1) provides a solution for one-dimensional drainage boundary control of granular materials with different water content under Hopkinson pressure during impact test. By designing stepped sleeves and grooves at the stepped surfaces, and using pads of the same material as the pressure bar to connect the granular materials with the incident and reflection bars, the one-dimensional assumption is guaranteed; (2) the axial force is applied to the water-stop silicone ring by the collar pressure head to make it hold the pad, and at the same time, the simulation of no drainage and no air leakage is achieved; (3) the mechanical properties of granular materials under different water content states can be studied during one-dimensional impact loading. Attached Figure Description

[0015] Figure 1 This is a diagram of the split structure of the present invention;

[0016] Figure 2 This is a sectional view of the invention.

[0017] Figure 3 This is an overall external view of the invention;

[0018] Figure 4 This is an overall sectional view of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] like Figure 1-4 The boundary control device shown for one-dimensional SHPB test of granular materials includes an inner stepped sleeve 1 and pads 2, a water-stop silicone ring 3 and a collar pressure head 4 respectively set at both ends of the inner stepped sleeve 1, with the granular material 5 located between the two pads.

[0021] like Figure 2 As shown, the inner stepped sleeve 1 has a middle section for placing bulk material 5 and two ends for connecting sections. The inner diameter of the connecting section is larger than that of the placement section, forming a stepped structure. The stepped sections of this structure have grooves in both the axial and circumferential directions. The connecting sections have internal threads 101 and through screw holes 102. The grooves provided at the steps of the inner stepped sleeve 1 include a first groove 103 provided at the axial end of the placement section and a second groove 104 provided on the inner wall of the connecting section.

[0022] The pad 2 extends from the connecting area of ​​the inner stepped sleeve 1 to the placement area, and its diameter is slightly smaller than the inner diameter of the placement area. It is made of 60Si2MnA material, the same material as the Hopkinson pressure bar, to ensure the accuracy of the one-dimensional elastic wave assumption during the impact process.

[0023] The water-stop silicone ring 3 is placed at the step of the inner stepped sleeve 1, between the pad 2 and the connecting area, and presses on the first convex groove 103 and the second convex groove 104. Its inner wall is provided with a third convex groove 301 that presses on the pad 2.

[0024] The collar pressure head 4 is sleeved on the outer wall of the pad 2 and has an external thread 401 corresponding to the internal thread 101. It is screwed inwards through the threaded structure, and the axial inner end of the collar pressure head 4 presses the water-stop silicone ring 3 against the step until it undergoes radial deformation. The collar pressure head 4 has a through-hole annular groove 402 corresponding to the screw hole 102, and a screw passes through the screw hole 102 and the annular groove 402 to fix the pad 2.

[0025] In use, first insert the pad 2 from one end of the inner stepped sleeve 1, then insert the water-stop silicone ring 3 and the collar pressure head 4. Continuously rotate the collar pressure head 4 to squeeze the water-stop silicone ring 3. After the water-stop silicone ring 3 hugs the pad 2, screws are screwed into the reserved screw hole 102 of the sleeve to fix the pad 2. Then start loading the sample. After loading the sample, place the device on the Hopkinson pressure bar device to realize the mechanical response test of granular materials with different water content under impact load.

[0026] Implementation examples: Figure 4 As shown, taking a one-dimensional SHPB impact test of water-bearing sand as an example, first, place the pad block 2 inside the sample chamber of the inner stepped sleeve 1. Then, put the water-stop silicone ring 3 on the pad block 2. Start by screwing the collar pressure head 4 into the stepped sleeve to apply axial pressure to the water-stop silicone ring 3 so that it grips the pad block 2 tightly. Then, insert screws to fix the pad block at the pre-drilled screw holes in the inner stepped sleeve. After loading the sample into the sample chamber and compacting it, put in another pad block 2. Then, put in the water-stop silicone ring 3 and collar pressure head 4 in sequence. Tighten the collar pressure head 4 to apply axial stress to the water-stop silicone ring so that it grips the pad block to form a sealed chamber. Similarly, tighten the screws to fix the pad block. Finally, place the entire device between the incident rod and the reflector rod to carry out the impact test.

Claims

1. A boundary control device for one-dimensional SHPB test of granular materials, characterized in that: It comprises an inner stepped sleeve (1), a cushion block (2), a water-stopping silica gel ring (3) and a sleeve ring pressure head (4) arranged at both ends of the inner stepped sleeve (1) respectively. The middle part of the inner stepped sleeve (1) is a placement area of bulk material (5), and both ends are connecting areas, the inner diameter of the connecting area is larger than that of the placement area, forming a stepped structure, the stepped structure is provided with a convex groove in the axial and circumferential directions, and the connecting area is provided with an internal thread (101) and a through screw hole (102); The cushion block (2) extends from the connecting area to the placement area of the inner stepped sleeve (1); The water-stopping silica gel ring (3) is arranged at the stepped part of the inner stepped sleeve (1) and located between the cushion block (2) and the connecting area; The sleeve ring pressure head (4) is sleeved on the outer wall of the cushion block (2) and is provided with an external thread (401) corresponding to the internal thread (101), and is screwed inwardly, the axial inner end of the sleeve ring pressure head (4) presses the water-stopping silica gel ring (3) at the stepped part to cause radial deformation; The convex groove arranged at the stepped part of the inner stepped sleeve (1) comprises a first convex groove (103) arranged at the axial end of the placement area and a second convex groove (104) arranged on the inner wall of the connecting area; The water-stopping silica gel ring (3) is pressed on the first convex groove (103) and the second convex groove (104), and the inner wall is provided with a third convex groove (301) for pressing the cushion block (2); The sleeve ring pressure head (4) is provided with a through annular groove (402) corresponding to the position of the screw hole (102), and the screw passes through the screw hole (102) and the annular groove (402) to fix the cushion block (2).

2. The boundary control device for one-dimensional SHPB test of granular materials according to claim 1, characterized in that: The cushion block (2) is made of the same material as the Hopkinson pressure bar.

Images