Clamping device for thin-wall whole pipe fatigue test and test method

Abstract

The invention provides a clamping device for a thin-wall whole pipe fatigue test and a test method, and belongs to the technical field of clamping devices. The device comprises clamping cushion blocks which are fixedly connected to two ends of a thin-wall whole tube sample main body and are used for transmitting test force; the high polymer material film adhesive tape is wound on a transition area of the clamping cushion block and the thin-wall whole pipe sample main body; the chock plugs are used for being plugged into the two ends of the thin-wall whole-tube sample main body, and packing paper is installed between the chock plugs and the inner wall of the thin-wall whole-tube sample main body and used for supporting the inner wall of the sample and evenly transmitting test force. The clamping cushion blocks are fixedly connected to the two ends of the sample and matched with the high polymer material film adhesive tape to reduce friction, the chock plugs are wound around the packing paper to support the inner wall, a stable clamping structure is formed, and it is ensured that fatigue fracture occurs in the working section. The problems of clamping stress concentration and fracture of a non-working section can be effectively avoided, the accuracy of a fatigue life evaluation result of the whole thin-wall pipe is improved, and the method can be widely applied to high-cycle and low-cycle fatigue performance tests under different conditions.

Description

Technical Field

[0001] This invention relates to the field of clamping device technology, and particularly to a clamping device and testing method for fatigue testing of thin-walled tubes, which is suitable for low-cycle and high-cycle fatigue performance testing of thin-walled tubes. Background Technology

[0002] In existing technologies, fatigue is an important mechanical property parameter of materials. Testing the fatigue performance of thin-walled tube materials is of great significance for predicting the service performance of structural components. Currently, the main difficulties in tensile and compressive fatigue testing of tubes lie in: (1) The clamping system of the testing machine is prone to stress concentration and friction in the clamping section of the thin-walled tube specimen, which leads to the specimen breaking in the clamping section and makes it impossible to obtain the true fatigue life and stress / strain level. (2) Excessive clamping force of the fixture can easily cause the sample to deform, while insufficient clamping force can easily cause it to fall off during the test; (3) Currently, conventional testing equipment and clamping methods make it difficult to achieve tensile and compressive fatigue testing of thin-walled tubes, especially for long-life applications. N f ≥10 7 The experiment. Summary of the Invention

[0003] In view of this, in order to solve the technical problems of clamping section failure, clamping force runaway and difficulty in long-life testing in the existing testing machine clamping system, the present invention provides a clamping device for fatigue testing of thin-walled tubes, which can effectively avoid clamping stress concentration and non-working section fracture, improve the accuracy of fatigue life assessment results of thin-walled tubes, and can be widely used in high-cycle and low-cycle fatigue performance testing under different conditions.

[0004] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a clamping device for fatigue testing of thin-walled tubes, comprising: Clamping pads are fixedly connected to both ends of the thin-walled tube sample body to transmit test force; A polymer film tape is wrapped around the transition area between the clamping pad and the thin-walled tube sample body; A plug is used to insert into both ends of the thin-walled tubular specimen body, and a pad is installed between the plug and the inner wall of the thin-walled tubular specimen body to support the inner wall of the specimen and uniformly transmit the test force.

[0005] Preferably, the clamping pad is bonded to the thin-walled tube sample body using a two-component reactive adhesive.

[0006] Preferably, the edges inside the clamping pad are rounded to avoid stress on the thin-walled tube sample body.

[0007] Preferably, the inner diameter of the clamping pad is 0.2-0.4 mm larger than the outer diameter of the thin-walled tube sample body.

[0008] Preferably, the diameter of the plug is 0.2-0.4 mm smaller than the inner diameter of the thin-walled tube sample body.

[0009] Preferably, the length of the plug is 10-20 mm less than the height of the testing machine clamp.

[0010] Preferably, the end of the plug is larger than the diameter of the working part of the plug and smaller than the outer diameter of the thin-walled tube sample body.

[0011] Preferably, the height of the clamping pad is lower than the height of the testing machine clamping block, and is consistent with the length of the plug.

[0012] Preferably, the clamping pad is made of aluminum alloy or copper alloy.

[0013] Secondly, the present invention provides a fatigue testing method for a thin-walled tube sample body using the above-mentioned clamping device, comprising the following steps: Step (1): Clean the contact surfaces of the thin-walled tube sample body with the clamping pad and plug; Step (2): Wrap a polymer film tape around the transition area between the thin-walled tube sample body and the clamping pad; Step (3): Insert the plug wrapped with padding paper into the inside of both ends of the thin-walled whole tube sample body; Step (4): Fix the clamping pads to both ends of the thin-walled tube sample body and ensure coaxiality; Step (5): Install the clamped specimen onto the testing machine for fatigue testing.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention optimizes the clamping structure design to ensure that fatigue fracture occurs in the working section (load section) of the thin-walled tube, guaranteeing the authenticity of fatigue data and the accuracy of evaluation results. The clamping pads are made of relatively soft materials such as aluminum alloy or copper alloy, and the internal edges are rounded. The clamping pads are fixedly connected to both ends of the thin-walled tube sample body. The strong adhesion and coaxiality control are preferably achieved through a two-component reactive adhesive, avoiding clamping stress concentration and sample slippage. The polymer film tape wrapped around the transition area reduces the interference of friction on fatigue life. The plug is made of a similar material and wrapped with padding paper and embedded in the tube to prevent deformation of the thin-walled tube. This solution can be widely used for high-cycle and low-cycle fatigue performance testing of thin-walled tubes under different stress and strain conditions, effectively solving the problems of non-working section fracture, sample deformation or detachment caused by traditional clamping. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a partially enlarged schematic diagram of the clamping transition section of the present invention; Figure 3 A three-dimensional schematic diagram of the main body of the thin-walled tube fatigue test specimen. Figure 4 This is a schematic diagram of the clamping pad structure; Figure 5 This is a schematic diagram of the plug's structure; Figure 6 High-cycle fatigue-life curve of the thin-walled tube sample body; In the figure, 101 is the main body of the thin-walled tube sample; 201 is the clamping pad; 202 is the two-component reactive adhesive; 203 is the polymer film tape; 301 is the stopper; 302 is the pad paper; and 401 is the testing machine clamping block. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0017] In the description of this invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0018] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "sleeved / connected," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0019] like Figure 1-3 As shown, the present invention provides a clamping device for fatigue testing of thin-walled tubes, comprising: The clamping pad 201 is fixedly connected to both ends of the thin-walled tube sample body 101 and is used to transmit the test force.

[0020] A polymer film tape 203 is wrapped around the transition area between the clamping pad 201 and the thin-walled tube sample body 101 to avoid friction in the clamping transition area.

[0021] The plug 301 is used to insert into both ends of the thin-walled tube sample body 101, and a pad 302 is installed between the plug 301 and the inner wall of the thin-walled tube sample body 101 to support the inner wall of the sample and uniformly transmit the test force.

[0022] In this invention, the clamping pad 201 is made of a relatively soft material such as aluminum alloy or copper alloy to reduce hard contact damage to the sample, prevent deformation or breakage due to excessively hard clamping material, and protect the original properties of the sample. The inner diameter of the clamping pad 201 depends on the outer diameter of the thin-walled tube; it is recommended to be 0.2-0.4 mm larger than the outer diameter of the thin-walled tube to allow for installation clearance, preventing the thin-walled sample from being squeezed and deformed by clamping force and ensuring the original shape of the sample. The height of the clamping pad 201 is lower than the height of the testing machine clamp 401 and is consistent with the length of the plug 301. This ensures a matching force transmission path, stable transmission of test force, avoids local stress concentration, and reduces sample damage.

[0023] like Figure 4 As shown, the clamping pad 201 and the thin-walled tube sample body 101 are preferably bonded together using a two-component reactive adhesive 202. This, combined with the hydraulic clamps of the testing machine, ensures coaxiality and guarantees a firm connection between the plug 301 and the thin-walled tube during testing, preventing relative slippage or separation and avoiding clamping failure. This ensures stable and accurate force transmission. Before bonding, the bonding surfaces of the plug 301 and the thin-walled tube must be cleaned to remove oil, dust, and other impurities, improving bonding strength. During installation, the entire area of ​​the clamping pad 201 should be completely within the testing machine clamp 401.

[0024] In this invention, the two-component reactive adhesive 202 is made of epoxy resin, which can be cured at room temperature and can withstand high temperatures up to 200°C. It is mainly suitable for bonding metal materials such as stainless steel and cast iron. After curing, its service life can reach 8-10 years. A ring of two-component reactive adhesive 202 is evenly applied to the clamping part of the thin-walled tube body to bond the thin-walled tube body and the clamping pad 201 together. It is then clamped by the hydraulic chuck of the testing machine to ensure the coaxiality of the thin-walled tube sample body 101 and the clamping pad 201. After standing for 24 hours, the two-component reactive adhesive 202 is completely cured, and fatigue tests can be carried out.

[0025] The edges inside the clamping pad 201 are rounded to further eliminate stress concentration points, avoid stress on the thin-walled tube sample body 101, prevent the sample from failing prematurely due to stress concentration or breaking in the non-working section (breaking outside the gauge length), and extend the effective test life of the sample.

[0026] In this invention, the polymer film tape 203 uses pure polytetrafluoroethylene film as the substrate, with an extremely smooth surface, a coefficient of friction as low as 0.04, and almost no adhesion to any substance. It also possesses good flexibility, allowing it to conform to complex curved surfaces. A single loop is applied to the transition area between the thin-walled tube sample body 101 and the clamping pad 201 (e.g., ...). Figure 3 As shown in the figure, this can avoid the impact of friction on fatigue life.

[0027] like Figure 5 As shown, in this invention, the material of the plug 301 should preferably be similar to that of the thin-walled tube. The diameter of the plug 301 is recommended to be 0.2-0.4 mm smaller than the inner diameter of the thin-walled tube to achieve a clearance fit. This avoids damage to the inner wall when the plug 301 is inserted, ensures uniform force transmission, and prevents sample deformation. The length of the plug 301 can be determined based on the height of the testing machine clamp 401, and is recommended to be 10-20 mm shorter than the height of the clamp 401 to avoid interference with the clamping pad 201. This ensures that the plug 301 does not exceed the clamping block range during clamping and does not affect the force transmission path. The end of the plug 301 should be slightly larger than the diameter of its working part and smaller than the outer diameter of the fatigue sample of the thin-walled tube. This is so that even after wrapping a layer of paper around the plug 301, it can be stably inserted into the tube during installation, while ensuring uniform force transmission during the test and preventing additional damage to the tube. The end of the plug 301 is designed to be slightly larger than the diameter of the plug 301 in order to provide a certain guiding effect during installation and facilitate accurate alignment; while it is smaller than the outer diameter of the thin-walled whole tube fatigue sample in order to avoid interference with the clamping device during the test and affect the accuracy of the test results.

[0028] Secondly, the present invention provides a fatigue testing method for a thin-walled tube sample body 101 using the above-mentioned clamping device, comprising the following steps: Step (1): Clean the contact surfaces of the thin-walled tube sample body 101 with the clamping pad 201 and the plug 301; Step (2): Wrap polymer film tape 203 around the transition area between the thin-walled tube sample body 101 and the clamping pad 201; Step (3): Insert the plug 301 wrapped with padding paper 302 into the interior of both ends of the thin-walled whole tube sample body 101; Step (4): Fix the clamping pad 201 to both ends of the thin-walled tube sample body 101 and ensure coaxiality; Step (5): Install the clamped specimen onto the testing machine for fatigue testing.

[0029] Based on the above testing methods, this invention conducts high-cycle fatigue performance tests on high-strength stainless steel thin-walled tubes (wall thickness ≤ 1.0 mm, D / t ≥ 20). High-strength stainless steel tubes possess high strength, corrosion resistance, high pressure resistance, high-temperature oxidation resistance, and easily meet engineering requirements for lightweighting, toughness, and low consumption, and are widely used in high-tech fields such as aviation, aerospace, and automotive.

[0030] The specific testing method is as follows: Step (1): The bonding surfaces of the plug 301 and the thin-walled tube need to be cleaned to remove oil, dust and other impurities. Step (2): Wrap a layer of polymer film tape 203 around the transition position between the gauge length and clamping of the thin-walled tube; Step (3): Wrap a ring of padding paper 302 around the surface of the plug 301 and embed it smoothly into the tube; Step (4): Apply the two-component reactive adhesive 202 evenly to the inner wall of the clamping pad 201 and the outer surface of the thin-walled tube sample. Then, attach the clamping pad 201 to both ends of the thin-walled tube sample, ensuring that the gaps between the upper and lower clamping blocks face the same direction. Clamp the sample with the hydraulic clamps of the testing machine to ensure the coaxiality of the thin-walled tube body and the clamping pad 201. After standing for 24 hours, the two-component reactive adhesive 202 is fully cured to ensure a firm connection between the plug 301 and the thin-walled tube during the test, preventing relative sliding or separation. Step (5): Assemble the sample onto the fatigue testing machine and perform the corresponding fatigue test.

[0031] Finally, based on the test results, the fatigue-life curve of the thin-walled pipe was plotted, as follows: Figure 6 As shown.

[0032] The above description is merely a preferred embodiment of the present invention. However, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention should be covered within the scope of protection of the present invention.

Claims

1. A clamping device for fatigue testing of thin-walled tubes, characterized in that, include: Clamping pads are fixedly connected to both ends of the thin-walled tube sample body to transmit test force; A polymer film tape is wrapped around the transition area between the clamping pad and the thin-walled tube sample body; A plug is used to insert into both ends of the thin-walled tubular specimen body, and a pad is installed between the plug and the inner wall of the thin-walled tubular specimen body to support the inner wall of the specimen and uniformly transmit the test force.

2. The clamping device for fatigue testing of thin-walled tubes according to claim 1, characterized in that, The clamping pad is bonded to the thin-walled tube sample body using a two-component reactive adhesive.

3. The clamping device for fatigue testing of thin-walled tubes according to claim 1, characterized in that, The edges inside the clamping pad are rounded to avoid stress on the thin-walled tube sample body.

4. The clamping device for fatigue testing of thin-walled tubes according to claim 1, characterized in that, The inner diameter of the clamping pad is 0.2-0.4 mm larger than the outer diameter of the thin-walled tube sample body.

5. The clamping device for fatigue testing of thin-walled tubes according to claim 1, characterized in that, The diameter of the plug is 0.2-0.4 mm smaller than the inner diameter of the thin-walled tube sample body.

6. The clamping device for fatigue testing of thin-walled tubes according to claim 1, characterized in that, The length of the plug is 10-20mm less than the height of the clamping block of the testing machine.

7. A clamping device for fatigue testing of thin-walled tubes according to claim 1, characterized in that, The end of the plug is larger than the diameter of the working part of the plug, but smaller than the outer diameter of the thin-walled tube sample body.

8. A clamping device for fatigue testing of thin-walled tubes according to claim 1, characterized in that, The height of the clamping pad is lower than the height of the testing machine clamping block, and is consistent with the length of the plug.

9. A clamping device for fatigue testing of thin-walled tubes according to any one of claims 1-8, characterized in that, The clamping pad is made of aluminum alloy or copper alloy.

10. A fatigue testing method for a thin-walled tube specimen using the clamping device according to any one of claims 1-9, characterized in that, Includes the following steps: Step (1): Clean the contact surfaces of the thin-walled tube sample body with the clamping pad and plug; Step (2): Wrap a polymer film tape around the transition area between the thin-walled tube sample body and the clamping pad; Step (3): Insert the plug wrapped with padding paper into the inside of both ends of the thin-walled tube sample body; Step (4): Fix the clamping pads to both ends of the thin-walled tube sample body and ensure coaxiality; Step (5): Install the clamped specimen onto the testing machine for fatigue testing.

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