Clamping device for hopkinson bar test
By using a clamping device that combines circumferential and radial clamping, the problem of clamp detachment from the specimen in the Hopkinson bar test was solved, thereby improving the accuracy and efficiency of high strain rate tests on composite material structures.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- AECC COMML AIRCRAFT ENGINE CO LTD
- Filing Date
- 2025-05-21
- Publication Date
- 2026-06-19
Smart Images
Figure CN224382965U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to a Hopkinson bar test device for composite material structures, and more particularly to a clamping device for the Hopkinson bar test. Background Technology
[0002] The Hopkinson pull bar test is based on stress wave theory to study the mechanical properties of materials under high strain rate tension. An impact bar is given an initial velocity through a launch chamber, and this velocity causes the impact bar to strike an incident bar. The strain, stress, and strain rate are derived from the incident, reflected, and projected pulse signals.
[0003] In the Hopkinson bar test, the sample needs to be securely clamped to ensure the acquisition of complete and accurate transmitted waves, thus enabling the calculation of reliable test results. Generally, Hopkinson bar specimens can be divided into cylindrical and plate-shaped samples. The bar specimen typically consists of two parts: the test section and the clamping section. The test section is smaller than the clamping section to ensure that only the test section deforms during the tensile process, and failure occurs within the test section. There is usually a rounded transition between the test section and the clamping section to reduce the impact of stress concentration on the sample.
[0004] Currently, in Hopkinson bar testing, the clamping section is typically fixed to the incident and transmission rods using threaded clamps, strong adhesive clamps, or snap-fit clamps. The specimen and clamps must be securely fixed to prevent slippage during loading. The clamps and incident / transmission rods are usually securely connected using bolts.
[0005] However, whether the entire specimen detaches before the clamping section depends on the shear strength of the specimen in the clamping section. Due to the small surface area of the clamping section, using strong adhesive to bond the fixture is ineffective. Fixing the specimen to the clamping device with adhesive requires high-strength adhesive and a stable curing process, which easily leads to low testing efficiency. Furthermore, situations often arise where the adhesive layer's properties fail to meet testing requirements, causing the specimen to fail before the test due to detachment from the clamping section. Threaded connections require drilling holes in the tie rod specimen and connecting it to the fixture with bolts to secure the clamping section. This method damages the drilled holes in the tie rod specimen, affecting the strength of the specimen and the obtained test data. Simultaneously, composite material specimens cannot be further machined or welded, making it difficult to use threaded or snap-fit fixtures. Utility Model Content
[0006] The purpose of this invention is to provide a clamping device for the Hopkinson bar test, which can ensure the accuracy of test data and test efficiency without damaging the bar specimen.
[0007] One aspect of this utility model provides a clamping device for the Hopkinson bar test, used to clamp a pull rod specimen, the pull rod specimen being a composite material structure; the pull rod specimen includes a test section and clamping sections on both sides of the test section; the clamping device includes clamps; there are two clamps, each used to clamp the clamping sections on both sides of the pull rod specimen; the clamps include a sleeve, a first fastening structure, and a second fastening structure; wherein, the sleeve has a clamping groove for placing the pull rod specimen, the clamping groove extending along the axial direction of the sleeve; the first fastening structure is disposed on the outer periphery of the sleeve, and the second fastening structure is disposed in the radial direction of the sleeve; the first fastening structure and the second fastening structure together apply a preload force to the pull rod specimen placed in the clamping groove to clamp the pull rod specimen.
[0008] In one embodiment, the clamping groove extends radially through the sleeve; the first fastening structure includes a plurality of hoops; the plurality of hoops are sleeved on the sleeve and spaced apart axially along the sleeve.
[0009] In one embodiment, a plurality of the hoops are uniformly arranged along the axial direction of the sleeve; or the distance between adjacent hoops gradually increases from the opening of the clamping groove.
[0010] In one embodiment, the second fastening structure includes a plurality of push rods; the sleeve has a plurality of openings adapted to the push rods, the plurality of openings being spaced apart axially on the sleeve; the push rods pass through the openings and thereby apply a radial preload to the pull rod sample placed in the clamping groove.
[0011] In one embodiment, the push rod has an external thread and the opening has an internal thread; the internal thread of the opening and the external thread of the push rod engage to allow the push rod to rotate within the opening, thereby adjusting the radial preload applied to the pull rod specimen.
[0012] In one embodiment, the clamping groove includes a first clamping surface and a second clamping surface opposite to each other; both the first clamping surface and the second clamping surface are provided with a pad; the pad is in contact with the pull rod sample, one end of the top rod is in contact with the pad, and the radial preload is transmitted to the pull rod sample through the pad.
[0013] In one embodiment, the first clamping surface and the second clamping surface are provided with mounting grooves; the pad is disposed in the mounting groove, and the pad and the mounting groove are fitted with a clearance fit.
[0014] In one embodiment, the opening is located within the mounting groove, and the distance between adjacent openings is the same.
[0015] In one embodiment, the surface of the pad opposite to the tie rod sample is polished to form a rough surface.
[0016] In one embodiment, the fixture further includes a protective structure disposed on the surface of the pad opposite to the pull rod sample.
[0017] This invention relates to a clamping device for the Hopkinson bar test. Through the combined action of a first circumferentially positioned fastening structure and a second radially positioned fastening structure, a pre-tightening force is applied to the bar specimen within the clamping groove, effectively clamping the specimen. This solves the problem of insufficient shear force in the adhesive layer and premature detachment of the clamp from the specimen caused by adhesive bonding. Compared to adhesive bonding, this clamping device is less expensive, allows for better control of the clamping force, prevents specimen detachment during clamping, improves the first-pass yield, and saves the curing time required by adhesive bonding, thus increasing test efficiency. Furthermore, this clamping device eliminates the need for drilling holes in the bar specimen, ensuring accurate test results and data without damaging the specimen. Attached Figure Description
[0018] The above and other features, properties and advantages of this utility model will become more apparent from the following description taken in conjunction with the accompanying drawings and embodiments, wherein:
[0019] Figure 1 This is a schematic diagram of an embodiment of the clamping device for the Hopkinson's pull rod test according to the present invention.
[0020] Figure 2 yes Figure 1 A cross-sectional view of the clamping device shown;
[0021] Figure 3 yes Figure 2 A partial enlarged view of the clamping device shown. Detailed Implementation
[0022] For composite material structural specimens, conventional clamping methods cannot stably hold them on tie rods, which makes it difficult to conduct tests on the dynamic mechanical behavior of composite structures under high strain rates. Furthermore, existing technologies often require the disposal of other devices fixedly connected to the clamp when the clamp fails, increasing economic costs.
[0023] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided to explain the present invention and not to limit it. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made to the present invention without departing from the scope or spirit thereof. For example, features shown or described as part of one embodiment may be used with another embodiment to produce yet another embodiment. Therefore, the present invention is intended to cover these modifications and variations that fall within the scope of the appended claims and their equivalents.
[0024] As used herein, the term “axial” refers to the central axis of the sleeve or the direction parallel to the central axis of the sleeve, the term “radial” refers to the direction perpendicular to the “axial”, and the term “circumferential” refers to the direction about the “axial”.
[0025] High strain rate refers to the linear strain or shear strain that occurs per unit time. Strain rate is a measure of the deformation rate of a material and is the derivative of strain with respect to time. High strain rate is generally between 100 / s and 10000 / s.
[0026] The Hopkinson pull bar test is primarily used to test the mechanical properties of materials under high strain rates. It involves using a launch chamber to impart an initial velocity to an impact bar, which then strikes an incident bar at this velocity. The strain, stress, and strain rate are derived from the incident, reflected, and projected pulse signals.
[0027] Figure 1 The structure of one embodiment of the clamping device for the Hopkinson's tie rod test of this invention is shown. The clamping device for the Hopkinson's tie rod test of this invention is used to clamp a tie rod specimen 1, which is a composite material structure. A composite material structure refers to a structure made of a multiphase material formed from two or more materials through appropriate processing methods. Due to the special characteristics of composite material structures, the tie rod specimen 1 with a composite material structure cannot be further machined or welded, making it difficult to clamp using threaded or snap-fit clamps 10.
[0028] According to the specifications for tension bar testing, the tension bar specimen 1 is cylindrical or plate-shaped. The tension bar specimen 1 includes a test section and clamping sections on both sides of the test section. The test section is smaller than the clamping sections to ensure that only the test section deforms during the tensile process and that failure occurs within the test section. There is generally a rounded transition between the test section and the clamping sections to reduce the impact of stress concentration on the tension bar specimen 1.
[0029] like Figure 1As shown, the clamping device of this utility model is a detachable type, including two clamps 10. The two clamps 10 have the same configuration. Each clamp 10 includes a first end 11 and a second end 12 opposite to each other. The first end 11 of the clamp 10 is used to clamp the clamping sections on both sides of the pull rod sample 1, and the second end 12 of the clamp 10 is used to connect with an incident rod (not shown) or a transmission rod (not shown), which can be bolted. Figure 1 One of the two clamps 10 shown is connected to the incident rod, and the other is connected to the transmission rod.
[0030] The clamp 10 includes a sleeve 100, a first fastening structure 200, and a second fastening structure (not shown). The sleeve 100 has a clamping groove 110 for placing the pull rod sample 1, which extends axially from the first end 11 of the clamp 10 along the sleeve 100. The first fastening structure 200 is disposed on the outer periphery of the sleeve 100, and the second fastening structure is disposed radially on the sleeve 100. The first and second fastening structures together apply a preload force to the pull rod sample 1 placed in the clamping groove 110 to clamp the pull rod sample 1.
[0031] The clamping device for the Hopkinson's pull rod test of this utility model applies a pre-tightening force to the pull rod specimen 1 in the clamping groove 110 through the cooperation of the first fastening structure 200 arranged in the circumferential direction and the second fastening structure arranged in the radial direction. This can clamp the pull rod specimen 1 and effectively solve the problem that the shear force of the adhesive layer cannot meet the test requirements due to the use of adhesive curing method, and the clamp 10 and the pull rod specimen 1 are pulled apart first.
[0032] Compared to adhesive bonding, the clamping device of this invention is less expensive, can better control the clamping force, prevents the sample from being pulled out in the clamping section, improves the first-pass yield, saves the curing time required by adhesive bonding, and thus improves the testing efficiency.
[0033] Meanwhile, the clamping device of this utility model does not require drilling holes in the tie rod sample 1, which can ensure the accuracy of the test results and test data without damaging the tie rod sample 1.
[0034] Continue to refer to Figure 1 The clamping groove 110 extends radially through the sleeve 100, and the first clamping surface 111 and the second clamping surface 112 opposite to each other in the clamping groove 110 clamp the tie rod sample 1 under the action of the pre-tightening force applied by the first fastening structure 200.
[0035] In one embodiment, the first fastening structure 200 includes a plurality of clamps 210. The clamps 210 are made of metal. The clamps 210 are a single ring structure, and the plurality of clamps 210 are sleeved on the sleeve 100 and spaced apart along the axial direction of the sleeve 100 to distribute the preload.
[0036] According to experimental verification, the number of hoop rings 210 is at least six. Figure 1 The diagram shows seven hoops 210. Of course, the number of hoops 210 can be eight or more, depending on the magnitude of the preload force required.
[0037] The opening 113 of the clamping groove 110 allows the pull rod sample 1 to be inserted. When the hoop 210 is fitted onto the sleeve 100, the opening 113 of the clamping groove 110 also allows the pull rod sample 1 to be inserted.
[0038] In one embodiment, multiple clamps 210 are evenly arranged along the axial direction of the sleeve 100 to avoid the preload applied by the multiple clamps 210 being too concentrated.
[0039] In another embodiment, the distance between adjacent clamping rings 210 gradually increases from the opening 113 of the clamping groove 110. This results in a greater preload applied at the opening 113 of the clamping groove 110, leading to better clamping of the tie rod sample 1.
[0040] By setting the hoop 210, the clamping force applied to the sample can be increased, effectively solving the problem that the shear force of the adhesive layer caused by the adhesive curing method cannot meet the test requirements.
[0041] In one embodiment, the second fastening structure includes a plurality of push rods. The sleeve 100 has a plurality of openings 120 adapted to the push rods, the openings 120 being spaced apart axially in the sleeve 100. The push rods pass through the openings 120, thereby applying a radial preload to the pull rod sample 1 placed in the clamping groove 110. By fixing the clamp 10 to the pull rod sample 1 with the push rods and applying a preload to clamp the pull rod sample 1, the problem of the clamp 10 pulling off the sample first due to the use of adhesive bonding and curing can be effectively solved.
[0042] Furthermore, the push rod has external threads, and the opening 120 has internal threads. That is, the push rod is a bolt. The opening 120 is a threaded hole. The internal thread of the opening 120 and the external thread of the push rod engage, allowing the push rod to rotate within the opening 120, thereby adjusting the radial preload applied to the tie rod specimen 1. This allows for flexible control of the preload applied by the push rod to the tie rod specimen 1.
[0043] like Figure 1 As shown, the opening 120 is designed with axisymmetry, that is, the opening 120 is arranged symmetrically about the central axis of the sleeve 100, and the push rod can apply a symmetrical preload to the pull rod sample 1. Figure 1 For example, the sleeve 100 has four sets of openings 120 arranged symmetrically, for a total of eight openings 120.
[0044] The sleeve 100 has at least four 120-sized openings, such as... Figure 2As shown; the number of openings 120 can also be five or more, and this utility model does not impose any limitation. A larger number of openings 120 avoids damage to the test piece caused by the concentration of preload.
[0045] Both the first clamping surface 111 and the second clamping surface 112 of the clamping groove 110 are provided with pads 400. The pads 400 are in contact with the tie rod specimen 1, and one end of the push rod is in contact with the pads 400. The radial preload is transmitted to the tie rod specimen 1 through the pads 400. The pads 400 can be made of metal. Using the pads 400 to contact the tie rod specimen 1 can avoid the risk of the specimen being locally crushed due to the large contact force caused by the metal push rod directly contacting the tie rod specimen 1. At the same time, the fixing groove of the fixture 10 plays a good centering role, ensuring the coaxiality of the specimen, fixture 10 and testing device during the test.
[0046] After one end of the push rod presses against the pad block inside the sleeve 100, it achieves stable clamping and reduces damage to the tie rod specimen 1, which is beneficial for testing the dynamic mechanical behavior of composite material structures.
[0047] The 400 pad can be made of metal. The pad block has a rectangular cross-section and a relatively small thickness, which can be selected from 2.5mm to 3mm.
[0048] The first clamping surface 111 and the second clamping surface 112 are provided with mounting grooves 114. The bottom surface of the mounting groove 114 is rectangular, and the pad 400 is disposed in the mounting groove 114 with a clearance fit between the pad 400 and the mounting groove 114. The surfaces of the pad 400 and the tie rod sample 1 opposite each other are basically flush with the first clamping surface 111 or the second clamping surface 112.
[0049] like Figure 2 As shown, the mounting groove 114 is not a through-hole design, and the opening 120 is located within the mounting groove 114. Furthermore, the distance between adjacent openings 120 is the same to avoid excessive concentration of preload applied to the tie rod specimen 1.
[0050] In one embodiment, the surface of the pad 400 opposite to the pull rod sample 1 is polished to form a rough surface. Polishing and roughening can increase the friction between the pad 400 and the pull rod sample 1, thereby reducing the risk of the pull rod sample 1 falling off the clamping device to a certain extent.
[0051] In one embodiment, the clamping device further includes a protective structure 500, such as... Figure 3 As shown. The protective structure 500 is disposed between the pad 400 and the tie rod specimen 1, that is, between the rough surface of the pad 400 and the tie rod specimen 1 in the above embodiment. The protective structure 500 is mainly used to protect the specimen from being crushed by the steel pad 400. Because the tensile strength of the tie rod specimen 1 is relatively large, it may be crushed during the application of the tightening force.
[0052] The protective structure 500 can be made of aluminum plate, with the same length and width as the pad 400. The thickness of the protective structure 500 can be 2mm. Because aluminum plate is relatively soft, it can avoid hard contact between the steel pad 400 and the tie rod specimen 1, reducing the risk of the tie rod specimen 1 being crushed.
[0053] The clamping device of this invention is independent of each other. When any part is damaged, the damaged part can be replaced without replacing all parts of the clamp 10, thus saving economic costs in the testing process.
[0054] By tightening the top rod with a wrench, a tightening force is applied to the tie rod sample 1; at the same time, the hoop 210 is fitted onto the sleeve 100 to prevent the sleeve 100 of the clamp 10 from deforming, thus ensuring that the tightening force meets the test requirements.
[0055] The clamping device of this invention can be used for Hopkinson bar tests on composite material structures under high strain rates. It does not cause pull-out, ensuring the integrity of the test piece and thus ensuring that accurate test data can be obtained. The test results are good and it has promising application prospects.
[0056] It should be noted that during the Hopkinson tensile test, because the test section and clamping section of the composite material tension rod specimen 1 have the same diameter, a portion of the clamping section inevitably remains under high tensile stress. Therefore, some strain exists in the clamping section, leading to an overestimation of the strain value calculated from the strain signal on the Hopkinson rod, requiring additional strain detection technology. If the sample strain is <2%, strain gauges can be directly attached to the sample to measure the accurate strain; if the sample strain is >2%, high-speed photography and existing digital image algorithms can be used to calculate the accurate strain. After the dynamic tensile test, the stress-strain curve is corrected based on the results of the accurate strain detection technology during data processing.
[0057] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible variations and modifications without departing from the spirit and scope of the present invention. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope defined by the claims of the present invention.
Claims
1. A clamping device for the Hopkinson bar test, used to clamp a bar specimen, wherein the bar specimen is a composite material structure; The tie rod specimen includes a test section and clamping sections on both sides of the test section; characterized in that The clamping device includes a clamp; The clamps are two in number, each used to clamp the clamping sections on both sides of the pull rod sample; The clamp includes a sleeve, a first fastening structure, and a second fastening structure; wherein... The sleeve has a clamping groove for placing the tie rod sample, and the clamping groove extends along the axial direction of the sleeve. The first fastening structure is disposed on the outer periphery of the sleeve, and the second fastening structure is disposed on the radial side of the sleeve; The first fastening structure and the second fastening structure together apply a preload force to the pull rod sample placed in the clamping groove to clamp the pull rod sample.
2. The clamping device as described in claim 1, characterized in that, The clamping groove extends radially through the sleeve; The first fastening structure includes multiple clamps; Multiple hoops are fitted onto the sleeve and spaced apart along the axial direction of the sleeve.
3. The clamping device as described in claim 2, characterized in that, The plurality of said hoop rings are evenly arranged along the axial direction of the sleeve; or The distance between adjacent hoop rings gradually increases from the opening of the clamping groove.
4. The clamping device according to any one of claims 1 to 3, characterized in that The second fastening structure includes multiple push rods; The sleeve has multiple openings that are adapted to the push rod, and the multiple openings are spaced apart along the axial direction of the sleeve; The push rod passes through the opening and applies a radial preload to the pull rod sample placed in the clamping groove.
5. The clamping device of claim 4, wherein The push rod has external threads, and the opening has internal threads; The internal thread of the opening and the external thread of the push rod engage to allow the push rod to rotate within the opening, thereby adjusting the radial preload applied to the pull rod specimen.
6. The clamping device of claim 4, wherein The clamping slot includes a first clamping surface and a second clamping surface that are opposite each other; Both the first clamping surface and the second clamping surface are provided with pads; The pad is in contact with the tie rod sample, and one end of the top rod is in contact with the pad. The radial preload is transmitted to the tie rod sample through the pad.
7. The clamping device of claim 6, wherein The first clamping surface and the second clamping surface are provided with mounting grooves; The pad is disposed in the mounting groove, and the pad and the mounting groove are fitted with a clearance fit.
8. The clamping device of claim 7, wherein The opening is located within the mounting groove, and the distance between adjacent openings is the same.
9. The clamping device of claim 6, wherein The surface of the pad that is opposite to the tie rod sample is polished to form a rough surface.
10. The clamping device of claim 6, wherein The clamp also includes a protective structure; The protective structure is disposed on the surface of the pad and the tension rod sample opposite to each other.