A split hopkinson pressure bar and sample alignment and support device

Abstract

The application is a kind of alignment and support device for split Hopkinson pressure bar and sample, which comprises a main frame for containing sample, the side of the main frame is hollowed out, respectively used for horizontal abutting of incident bar and transmission bar from both sides of the hollowed-out part, and a plurality of frame connecting columns are embedded in the bottom of the main frame for supporting the lower part of the sample. The support device effectively improves the misalignment of the pressure bar and sample caused by the weight of the sample, greatly reduces the required steps of the test, and helps the auxiliary support of the sample with heavy weight.

Description

Technical Field

[0001] This invention relates to the field of materials testing technology, specifically to a device for aligning and supporting a split Hopkinson bar with a specimen. Background Technology

[0002] The SHPB device originated from a pressure bar designed by Hopkinson in 1914, known as the Hopkinson bar (HPB). In 1949, Kolsky successfully developed a split Hopkinson bar. In 1963, Lindholm replaced the previous capacitive sensors with strain gauges bonded to two bars, fundamentally changing the Hopkinson bar testing method. By the 1970s, the SHPB testing technique had become a standard method for testing the mechanical properties of materials at high strain rates and was widely used.

[0003] In the SHPB dynamic uniaxial compression test, the bullet impact velocity is controlled by adjusting the nitrogen pressure in the high-pressure control box and the depth of the bullet in the firing chamber. The bullet collides head-on with the incident rod at a certain velocity. After passing through the waveform shaping plate attached to the head of the incident rod, an incident stress wave is generated in the incident rod. Upon propagating to the interface between the incident rod and the specimen, due to the difference in wave impedance between the rod and the specimen, transmission and reflection occur. That is, part of the stress pulse is reflected back to the incident rod to form a reflected stress wave, while the other part of the stress pulse propagates into the interior of the specimen. When it reaches the interface between the specimen and the transmission rod, transmission and reflection also occur. That is, part of the stress pulse forms a transmitted stress wave in the transmission rod, while the rest is reflected back into the interior of the specimen.

[0004] When conducting dynamic uniaxial compressive strength tests on rock samples using the SHPB apparatus, a crucial step is connecting the rock sample to the incident and transmission rods. Typically, sufficient grease is applied to both ends of the rock sample, and then the incident and transmission rods are pressed firmly against the sample to ensure a secure bond, while also maintaining that all three are on the same horizontal plane. This pressing also aims to minimize air gaps between the incident rod and the sample, and between the sample and the transmission rod, allowing the stress wave to propagate along a straight horizontal line within the solid. However, rock samples are often quite heavy, and the tangential frictional resistance generated by the grease is often less than the sample's own weight. Therefore, the rock sample may slowly slide downwards over time. Safety regulations require that the apparatus be inflated only after it is securely fixed. Thus, when the bullet impacts the compression rod and propagates the stress wave, the incident rod, sample, and transmission rod may no longer be aligned. This could cause the sample to fail before reaching stress equilibrium, leading to test failure.

[0005] Therefore, it is necessary to support the rock samples during the experiment to ensure that the center of the sample is aligned with the incident and transmitted rods when receiving stress waves propagating from the incident rod. Currently, the mainstream sample support method is a support structure consisting of wooden blocks and plastic foam (see...). Figure 1 The principle behind using plastic foam in direct contact with the sample is that foam has low stiffness and also possesses sound insulation and shock absorption properties, so stress waves will basically not propagate through the plastic foam. However, it is worth noting that the low stiffness of the foam also means that it will produce large deformations under small forces, thus the support provided to the sample is relatively weak, and the resulting waveform is usually not very favorable. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems existing in the prior art and provide a separate Hopkinson bar alignment and support device for the specimen, so as to effectively prevent the center of the bar and the center of the specimen from not being on the same horizontal line due to the weight of the specimen, and at the same time greatly reduce the time required for the test.

[0007] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0008] A separate Hopkinson pressure bar alignment and support device for a specimen includes a main frame for holding the specimen. The sides of the main frame are hollowed out to allow an incident rod and a transmission rod to extend from the hollowed-out sides and horizontally abut against the specimen. Several frame connecting columns are embedded in the bottom of the main frame to support the lower part of the specimen.

[0009] Furthermore, the main frame consists of a pair of vertically arranged and oppositely positioned polygonal frames. The space between the two polygonal frames is used to accommodate the sample. Multiple sides of each polygonal frame form a hollow structure in the middle, which facilitates the insertion of the incident rod and the transmission rod. The bottom of the pair of polygonal frames is provided with at least one pair of protrusions extending horizontally towards the opposite polygonal frame. The two ends of the frame connecting column are respectively embedded in the protrusions of the opposite polygonal frames.

[0010] Furthermore, a sample support ring is fitted onto the frame connecting column for elastic auxiliary support of the sample.

[0011] Furthermore, the top of the polygonal frame is provided with a pressure rod fitting arc segment, which facilitates the fitting of the incident rod and the transmission rod.

[0012] Furthermore, frame support columns are connected at the included angles between adjacent sides of the polygonal frame to serve as reinforcing ribs.

[0013] Furthermore, the adjacent sides of the polygonal frame are chamfered.

[0014] Furthermore, the polygonal frame is made of aluminum alloy or rigid polyurethane foam.

[0015] Furthermore, the sample support ring is made of polyurethane foam as an elastic replacement.

[0016] Furthermore, the arc of the pressure rod fitting the arc segment is between 30° and 150°.

[0017] The beneficial effects of this invention are:

[0018] The support device of this invention effectively improves the situation where the pressure bar specimen cannot be aligned due to the specimen's own weight, and also greatly reduces the steps required for the test, which is helpful for auxiliary support of specimens with heavy mass. Attached Figure Description

[0019] Figure 1 The existing test specimen support structure is made of wood blocks and plastic foam.

[0020] Figure 2 This is a front view of the support device of the present invention;

[0021] Figure 3 This is a side view of the support device of the present invention;

[0022] Figure 4 This is a bottom view of the support device of the present invention;

[0023] Figure 5 For the present invention Figure 2 Enlarged schematic diagram of the structure at point II;

[0024] Figure 6 This is a schematic diagram of the axial and transverse sections of the support ring of the present invention;

[0025] Figure 7 This is a diagram showing the support device of the present invention without a sample placed in it.

[0026] Figure 8 This is a diagram showing the state of the support device of the present invention placed in the sample;

[0027] Figure 9 This is a diagram showing the usage state of the support device of the present invention.

[0028] The following are the labels in the diagram: 1. Incident rod, 2. Transmission rod, 3. Main frame, 31. Protrusion, 32. Pressure rod fitting arc segment, 4. Frame support column, 5. Sample, 6. Frame connecting column, 7. Support ring, 8. Level. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] like Figure 2 As shown, a separate Hopkinson pressure bar alignment and support device for a specimen is provided. The device includes a main frame 3 for accommodating the specimen 5. The sides of the main frame 3 are hollowed out, allowing the incident rod 1 and the transmission rod 2 to extend from the hollowed-out sides to horizontally abut against the specimen 5. Several frame connecting columns 6 are embedded at the bottom of the main frame 3 to support the lower part of the specimen 5.

[0031] The main frame 3 consists of a pair of vertically arranged, opposite polygonal frames. The space between the two polygonal frames is used to accommodate the sample 5. Multiple sides of each polygonal frame form a central hollow structure, facilitating the insertion of the incident rod 1 and the transmission rod 2. The bottom of the pair of polygonal frames has at least one pair of protrusions 31 extending horizontally towards the opposite polygonal frame. The two ends of the frame connecting column 6 are respectively embedded in the protrusions 31 of the opposite polygonal frames. In this embodiment, the polygonal frames are rectangular frames. If the sample 5 is a cylinder, then the incident rod 1 and the transmission rod 2 are also cylindrical rods. A pair of protrusions 31 are provided on the bottom edge of each rectangular frame. Figure 3 and Figure 4 As shown, a notch is left on the bottom edge, and protrusions 31 extend horizontally from the two edges of the notch. After the frame connecting column 6 is embedded, a gap is formed between the two frame connecting columns 6. The sample 5 is placed horizontally on the two frame connecting columns 6. At this time, the bottom arc of the sample 5 is exposed downwards in the gap, making it more stable. At the same time, it prevents the sample 5 from shifting downwards due to its own weight, which would lead to test failure. The center of gravity of the sample 5 and the frame connecting column 6 is low, and it is not easy to overturn. Furthermore, the gap can be adjusted for samples 5 of different diameters, so that the incident rod 1, samples 5 of different diameters, and transmission rod 2 are kept on the same horizontal line.

[0032] like Figure 5 As shown, a sample support ring 7 is sleeved on the frame connecting column 6 for elastic auxiliary support of the sample 5.

[0033] A pressure bar is provided at the top of the polygonal frame to fit the arc segment 32, such as... Figure 3 As shown, it is convenient to fit the incident rod 1 and the transmission rod 2. Its main function is to evenly transfer the weight of the entire main frame 3 and the sample 5 to the incident rod 1 and the transmission rod 2. For a rectangular frame, the pressure rod fitting arc segment 32 is set on the top edge.

[0034] The polygonal frame is connected to a frame support column 4 at the included angle between adjacent sides as a reinforcing rib to prevent the main frame 3 from deforming under stress, which could lead to the failure of the entire structure. In this embodiment, both the main frame 3 and the frame support column 4 are made of rigid polyurethane foam, which is easy to directly injection mold. The frame connecting column 6 is made of a different material than the main frame 3. For example, the frame connecting column 6 is made of aluminum alloy, which is not only lighter and more rigid, but also less prone to deformation. It is also easy to embed and connect with the protrusion 31 of the main frame 3 (metal and plastic are easier to embed).

[0035] The adjacent sides of the polygonal frame are chamfered.

[0036] The polygonal frame is made of aluminum alloy or rigid polyurethane foam.

[0037] The sample support ring 7 is made of polyurethane foam, which will only produce a small amount of elastic deformation when squeezed. This ensures that the center of the sample 5 is on the same horizontal line as the center of the pressure bar (incident bar 1 and transmission bar 2), serving as an elastic replacement part. Since the contact area between the sample support ring 7 and the sample 5 is small, it ensures that the sample 5 will not be affected by confining pressure when impacted. In addition, the sample support ring 7 can be easily replaced after it undergoes large deformation.

[0038] The arc of the pressure bar fitting arc segment 32 is between 30° and 150°.

[0039] Usage of the device of the present invention

[0040] A simplified schematic diagram of the installation of the support device and the placement of sample 5 is shown below. Figure 7 and Figure 8 As shown, the process mainly consists of two steps. First, the support device is placed on the incident rod 1 and transmission rod 2 with their ends aligned (or the incident rod 1 and transmission rod 2 partially extend into the support device). Then, the sample 5, with both ends coated with sufficient grease (grease is sticky and can act as an adhesive and isolate air at the joint), is placed horizontally inside the support device. Finally, the incident rod 1 and transmission rod 2 at both ends are pressed forcefully towards the sample 5 to complete the installation process of the sample 5. Figure 9 As shown, before the impact test, a level 8 can be inserted into the top of the main frame 3 to flexibly adjust the positions of the incident rod 1, the transmission rod 2 and the sample 5, ensuring that the tops of the incident rod 1, the transmission rod 2 and the sample 5 are on the same horizontal plane.

[0041] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A device for aligning and supporting a split Hopkinson bar and a specimen, characterized in that, The device includes a main frame (3) for holding a sample (5). The sides of the main frame (3) are hollowed out, allowing the incident rod (1) and the transmission rod (2) to extend from the hollowed-out sides to horizontally abut against the sample (5). Several frame connecting columns (6) are embedded in the bottom of the main frame (3) to support the lower part of the sample (5). The main frame (3) is composed of a pair of vertically arranged and oppositely arranged polygonal frames. The space between the two polygonal frames is used to accommodate the sample (5). Multiple sides of each polygonal frame form a hollowed-out structure in the middle, which facilitates the insertion of the incident rod (1) and the transmission rod (2). The bottom of the pair of polygonal frames is provided with at least a pair of protrusions (31) extending horizontally towards the opposite polygonal frame. The two ends of the frame connecting columns (6) are respectively embedded in the protrusions (31) of the opposite polygonal frames.

2. The alignment and support device for the split Hopkinson bar and the specimen according to claim 1, characterized in that, The frame connecting column (6) is fitted with a sample support ring (7) for elastic auxiliary support of the sample (5).

3. The alignment and support device for the split Hopkinson pressure bar and the specimen according to claim 1, characterized in that, The top of the polygonal frame is provided with a pressure rod fitting arc segment (32) to facilitate fitting of the incident rod (1) and the transmission rod (2).

4. The alignment and support device for the split Hopkinson bar and the specimen according to claim 1, characterized in that, The polygonal frame is connected to a frame support column (4) at the included angle between adjacent sides, which serves as a reinforcing rib.

5. The alignment and support device for the split Hopkinson bar and the specimen according to claim 1 or 4, characterized in that, The adjacent sides of the polygonal frame are chamfered.

6. The alignment and support device for the split Hopkinson pressure bar and the specimen according to claim 1, characterized in that, The polygonal frame is made of aluminum alloy or rigid polyurethane foam.

7. The alignment and support device for the split Hopkinson pressure bar and the specimen according to claim 2, characterized in that, The sample support ring (7) is made of polyurethane foam as an elastic replacement.

8. The alignment and support device for the split Hopkinson bar and the specimen according to claim 3, characterized in that, The arc of the pressure bar fitting arc segment (32) is between 30° and 150°.

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