A deep cold cross tensile test device and test method

Abstract

The present application discloses a cryogenic cross tensile test device and test method, including a bidirectional cross tensile device, a sealing box, an observation device and a liquid nitrogen supply device, characterized in that a sealing box is provided in the bidirectional cross tensile device, the liquid nitrogen supply device supplies liquid nitrogen to the center of the sealing box, the bidirectional cross tensile device includes a tensile chuck, the sealing box and the tensile chuck are sealed and lubricated by a packing sealing device, the packing in the packing sealing device is impregnated with graphite, and the packing sealing device includes a gland, a sealing cavity and a packing; a double-layer glass observation window is provided at the bottom of the sealing box, a heating device and a lighting device are provided in the two layers of glass, and the observation device includes an optical reflector installed at a 45° angle below the sealing box and a CCD camera. The device and method of the present application can improve the sealing performance of the sealing box, improve the uniformity of low temperature distribution and the temperature control accuracy.

Description

Technical Field

[0001] The invention belongs to the field of material tensile performance testing devices, in particular to a deep cold cross tensile testing device and a testing method. Background Art

[0002] The existing cross-tensile test devices are all used in normal temperature or high temperature environments. There are few reports and literature on cross-tensile test devices and test methods under cryogenic conditions. How to improve the sealing performance of cross-tensile test devices under cryogenic conditions, how to maintain the uniformity and stability of temperature distribution under cryogenic conditions, and how to measure strain in real time under cryogenic conditions are the difficulties faced at this stage.

[0003] Patent document CN114397191A discloses a multi-factor composite environment bidirectional loading test system. Although the scheme discloses a bidirectional loading test device under cryogenic conditions, the use of the key component in the device, the seal, is not discussed, and the method for maintaining the uniformity of the low-temperature environment provided by liquid nitrogen is not described. Moreover, the observation window used is set on the cabin door, that is, on the side wall of the test environment. Due to the low-temperature characteristics of liquid nitrogen, liquid nitrogen and nitrogen are easily accumulated on the surface of the test piece, which will block the line of sight. Without other safeguards, the observation window is set on the side of the test piece, which is not conducive to observation. The temperature difference on both sides of the observation window is large and fogging is easy. In addition, the test is carried out in a closed space. Using the observation window in the patent document, it is actually impossible to observe a clear image, and real-time strain measurement cannot be performed through the DIC system (three-dimensional digital speckle strain measurement system). On the other hand, the general test requires spraying white matte paint on the test piece first, and then spraying black speckle for identification and calculation of strain. Under cryogenic conditions, due to the different expansion coefficients of the test piece and the paint layer, the primer on the surface of the test piece will fall off during the deformation process, resulting in the inability of the DIC system to identify the speckle. There is no solution to the above problems in the prior art. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a deep cold cross tensile test device and a test method.

[0005] A cryogenic cross tensile test device comprises a bidirectional cross tensile device, a sealing box, an observation device and a liquid nitrogen supply device, wherein a sealing box is arranged in the bidirectional cross tensile device, the liquid nitrogen supply device supplies liquid nitrogen to the center of the sealing box, the bidirectional cross tensile device comprises a tensile chuck, the tensile chuck penetrates into the sealing box and is connected with a test piece in the sealing box, the sealing box and the tensile chuck are sealed and lubricated by a packing sealing device, the packing in the packing sealing device is impregnated with graphite, the packing sealing device comprises a gland, a sealing cavity and a packing, the packing is arranged between the sealing box and the tensile chuck, the gland is sleeved outside the tensile chuck and applies axial compression to the packing, and a sealing cavity is formed between the radial outer side of the packing and the sealing box; a double-layer glass observation window is arranged at the bottom of the sealing box, a heating device and a lighting device are arranged in the two layers of glass, and the observation device comprises an optical reflector and a CCD camera installed at a 45° angle below the sealing box.

[0006] Furthermore, a guide structure is arranged on the side wall of the sealing box, and the guide structure includes two layers of guide chambers from the inside to the outside, the opening of the inner guide chamber is arranged at the bottom of the side wall, the opening of the guide chamber is arranged as a flared portion, the flared portion extends upward and is connected with the closed portion, an air supply device is arranged in the closed portion, the closed portion is connected with the outer guide chamber, the inner structure of the outer guide chamber is the same as that of the inner guide chamber, and a controllable sealing door is arranged at the flared portion of the outer guide chamber, and the guide structure can guide the low-temperature medium in the sealing box to flow evenly from the center of the specimen to the surrounding area.

[0007] Furthermore, the liquid nitrogen supply device includes a PLC control system, a temperature sensor connected to the PLC control system, a self-pressurized liquid nitrogen tank, a solenoid valve, a flow meter, an opening valve, and a liquid nitrogen delivery pipe with an air supply system, the temperature sensor is arranged on the tensile chuck and the specimen, the self-pressurized liquid nitrogen tank is connected to the solenoid valve, the solenoid valve is connected to the flow meter, the flow meter is connected to the opening valve, the opening valve is connected to the liquid nitrogen delivery pipe with the air supply system, and the air supply system delivers the liquid nitrogen to the center of the specimen in the sealed box.

[0008] Furthermore, the side wall and the bottom of the sealing box are double-layer stainless steel structures, and the interior is filled with ceramic fiber blanket insulation material.

[0009] A cryogenic cross tensile test method, using the cryogenic cross tensile test device, comprises the following steps:

[0010] S1. The specimen is first treated with matte blackening, then sprayed with white speckles, the specimen is connected to a temperature sensor and then placed in a sealed box, the tensile chuck is connected, and the bidirectional cross tensile device is operated for centering;

[0011] S2. Fix the upper cover of the sealing box and insert the liquid nitrogen delivery tube;

[0012] S3, the temperature sensor is arranged on the outer end of the stretching chuck equipped with the force sensor, and an antifreeze sleeve is put on the middle part of the stretching chuck to perform real-time temperature control of the stretching chuck;

[0013] S4, PLC control system controls the liquid nitrogen supply device to introduce liquid nitrogen to start cooling;

[0014] S5. The PLC control system detects that the test piece reaches the specified temperature and then closes the opening valve. After the temperature of the test piece rises, the opening valve is opened again to continue cooling down, so as to control the test piece at the specified temperature.

[0015] S6. After the temperature of the specimen is stable, operate the bidirectional cross tensile device to carry out the tensile test;

[0016] S7. Use DIC system for real-time strain measurement.

[0017] Furthermore, in step S5, the PLC control system first closes the controllable sealing door, and then opens the opening valve and the controllable sealing door after the temperature of the specimen rises, and turns on the air supply device in the guide structure to control the low-temperature medium in the sealing box to flow from the center of the specimen to the surrounding area and out of the sealing box through the guide structure.

[0018] Compared with the prior art, the present invention adopts a packing sealing device to seal between the tensile chuck and the sealing box. After the packing is installed in the sealing cavity, it is axially compressed through the pressure cover. Due to the plasticity of the packing, it generates radial force and is in close contact with the polished rod to achieve sealing. At the same time, the graphite impregnated in the packing plays a lubricating role between the contact surfaces.

[0019] In addition, in this application, the specimen is first subjected to matte blackening treatment, and then sprayed with white speckles to solve the problem of primer detachment under deep cold conditions. The observation window is set at the bottom of the specimen, which can reduce the impact of the accumulation and vaporization of the low-temperature medium in the sealed box on the bottom field of view. The observation window is directly opposite the center of the specimen. A heating device is set in the double-layer glass, which can significantly improve the problem of glass fogging. Due to the limitation of the device space, the CCD camera cannot directly photograph the surface of the specimen. Therefore, an optical reflector is installed at a 45° angle under the sealed box. The camera uses the mirror to take real-time photos of the speckles on the lower surface of the specimen in the observation window; an internal lighting device is set under the sealed box for easy observation. By setting the observation window and heating device at the bottom of the sealed box, combined with the adjustment of the sequence of matte blackening treatment and white speckles, real-time observation of the biaxial tensile test specimen under deep cold conditions can be achieved, so that real-time strain measurement of the DIC system can be performed, solving the problem that only offline strain measurement of the DIC system can be performed in a sealed environment.

[0020] Finally, in the present application, the structure of the side wall of the sealed box is improved by setting an inner and outer double-layer guide cavity, and setting an expanding portion and a closing portion in the guide cavity to guide the flow direction of the low-temperature medium in the sealed box. First, the sealed box is filled with the low-temperature medium. When the temperature drops to the specified temperature, the temperature will rise. At this time, the sealing door of the guide cavity and the opening valve of the liquid nitrogen supply device are opened, and the air supply device set in the closing portion of the guide cavity is opened. The low-temperature medium accumulated in the center of the sealed box can be drained to the surrounding areas to avoid the accumulation of the low-temperature medium under the test piece, causing the temperature of the observation window to rise. The temperature of the heating device is too low, which increases the difficulty of defogging the heating device. In addition, the guide cavity is arranged with an expanded opening at the bottom and a closed opening at the top, which can form a fluid movement with low-speed flow at the bottom and high-speed flow at the top. The low-speed flow at the bottom can reduce the circulation speed of the cryogenic medium and improve the utilization rate of liquid nitrogen. The fast flow at the top can reduce the cross-sectional area required for the closed opening, reduce the time for the cryogenic medium to stay at the upper part of the sealing box, and reduce the heat exchange between the cryogenic liquid newly flowing into the sealing box and the medium with slightly higher temperature in the guide cavity, thereby improving the uniformity of temperature distribution in the sealing box and the accuracy of temperature control. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of the deep cold cross tensile test device

[0022] Figure 2 Schematic diagram of the packing seal structure

[0023] Figure 3 Schematic diagram of the partial structure of the cross-stretching device

[0024] Figure 4 Schematic diagram of diversion structure

[0025] Figure 5 Schematic diagram of the longitudinal section of the diversion cavity

[0026] Figure 6 Schematic diagram of the temperature measurement points of the test piece

[0027] Figure 7 Schematic diagram of the specimen after being blackened and sprayed with white speckle

[0028] Reference numerals

[0029] 1. Sealing box, 2. Stretching chuck, 3. Packing sealing device, 3.1. Pressure cover, 3.2. Packing, 3.3. Sealing chamber, 4. Observation window, 5. Heating device, 6. Optical reflector, 7. CCD camera, 8. PLC control system, 9. Temperature sensor, 10. Self-pressurized liquid nitrogen tank, 11. Solenoid valve, 12. Flow meter, 13. Opening valve, 14. Liquid nitrogen delivery pipe with air supply system, 15. Test piece, 16. Ceramic fiber blanket insulation material; A. Temperature measuring point, B. Temperature measuring point, C. Temperature measuring point DETAILED DESCRIPTION

[0030] Example

[0031] like Figure 1-3 As shown, a cryogenic cross-tension test device includes a bidirectional cross-tension device, a sealing box 1, an observation device and a liquid nitrogen supply device, wherein the bidirectional cross-tension device can adopt the bidirectional cross-tension test device disclosed in the patent application number 201710187880.1, a sealing box 1 is arranged in the bidirectional cross-tension device, and the liquid nitrogen supply device supplies liquid nitrogen to the center of the sealing box 1, and the bidirectional cross-tension device includes a stretching chuck 2, the stretching chuck 2 penetrates the sealing box 1 and is connected to the test piece 15 in the sealing box 1, and the sealing box 1 and the stretching chuck 2 are sealed by a packing sealing device 3 and lubrication, the packing in the packing sealing device 3 is impregnated with graphite, the packing sealing device comprises a gland 3.1, a sealing cavity 3.3 and a packing 3.2, the packing 3.2 is arranged between the sealing box 1 and the stretching chuck 2, the gland 3.1 is sleeved outside the stretching chuck 2, and applies axial compression to the packing 3.2, and a sealing cavity 3.3 is formed between the radial outer side of the packing 3.2 and the sealing box 1; a double-layer glass observation window 4 is arranged at the bottom of the sealing box 1, a heating device 5 and a lighting device are arranged in the two layers of glass, and the observation device comprises an optical reflector 6 and a CCD camera 7 installed at a 45° angle below the sealing box.

[0032] In an optional embodiment, if Figure 4 , 5 As shown, a guide structure is arranged on the side wall of the sealing box 1. For example, a guide structure is arranged in the side walls on both sides of each stretching chuck 2. The guide structure includes two layers of guide cavities from the inside to the outside. The opening of the inner guide cavity is arranged at the bottom of the side wall. The opening of the guide cavity is arranged as a flared portion. The flared portion extends upward and is connected with the closed portion. An air supply device is arranged in the closed portion. The closed portion is connected with the outer guide cavity. The structure inside the outer guide cavity is the same as that of the inner guide cavity. A controllable sealing door is arranged at the junction of the flared portion and the closed portion of the outer guide cavity. The guide structure can guide the low-temperature medium in the sealing box to flow evenly from the center of the specimen to the surrounding area. Among them, in the inner guide cavity, the setting of the expansion part can form a slight negative pressure at the bottom of the sealing box 1, so that the low-temperature medium accumulated around the test piece 15 in the sealing box 1 slowly flows to the side wall of the stretching chuck 2, and then enters the guide structure under the suction of negative pressure, so that the low-temperature medium in the sealing box 1 forms a circulating flow, and can reduce the low-temperature medium accumulated near the stretching chuck 2, and reduce the impact of the deep cold environment on the stretching chuck 2. The setting of the closing part can increase the flow speed of the low-temperature medium in the closing part. Preferably, the vertical height of the expansion part is greater than the vertical height of the closing part, so that the low-temperature medium can stay in the sealing box 1 as much as possible, and make full use of the low-temperature residual temperature of the low-temperature medium; in the outer guide cavity, the structural setting is consistent with the inner guide cavity, and a double-layer sandwich structure can be formed to form an insulation structure for the low-temperature medium in the sealing box 1, further improving the utilization rate of liquid nitrogen.

[0033] In an optional embodiment, the liquid nitrogen supply device includes a PLC control system 8, a temperature sensor 9 connected to the PLC control system 8, a self-pressurizing liquid nitrogen tank 10, a solenoid valve 11, a flow meter 12, an opening valve 13, and a liquid nitrogen delivery pipe 14 with an air supply system. The temperature sensor 9 can be set on the tensile chuck 2 and the test piece 15, the self-pressurizing liquid nitrogen tank 10 is connected to the solenoid valve 11, the solenoid valve 11 is connected to the flow meter 12, the flow meter 12 is connected to the opening valve 13, and the opening valve 13 is connected to the liquid nitrogen delivery pipe 14 with an air supply system, and the air supply system delivers liquid nitrogen to the center of the test piece 15 in the sealed box 1. Preferably, the temperature sensor is a low-temperature thermocouple wire.

[0034] In an optional embodiment, the side wall and the bottom of the sealing box 1 are double-layer stainless steel structures, and the interior is filled with ceramic fiber blanket insulation material 16.

[0035] A cryogenic cross tensile test method, using the cryogenic cross tensile test device, comprises the following steps:

[0036] S1, specimen 15 was first treated with matte blackening, and then sprayed with white speckles (such as Figure 7 As shown), the low-temperature thermocouple wire is welded on the specimen 15 and then placed in the sealing box 1, the stretching chuck is connected, and the bidirectional cross stretching device is operated for centering. Among them, three low-temperature thermocouple wires can be set and welded to the temperature measuring points A, B, and C on the specimen 15 respectively (as shown in FIG. Figure 6 shown),

[0037] S2, fix the upper cover of the sealing box 1 and insert the liquid nitrogen delivery tube;

[0038] S3, a low-temperature thermocouple wire is welded to the outer end of the tensile chuck 2 equipped with the force sensor, and an antifreeze sleeve is put on the middle part of the tensile chuck 2 to perform real-time temperature control of the tensile chuck 2 to prevent the force sensor from being frozen;

[0039] S4, PLC control system controls the liquid nitrogen supply device to introduce liquid nitrogen to start cooling;

[0040] S5, the PLC control system 8 closes the opening valve 13 after the test piece 15 reaches the specified temperature, and then opens the opening valve 13 to continue cooling down after the temperature of the test piece 15 rises, so as to control the test piece 13 to be at the specified temperature;

[0041] S6. After the temperature of the specimen 15 is stable, operate the bidirectional cross tensile device to perform a tensile test;

[0042] S7. Use DIC system for real-time strain measurement.

[0043] In an optional embodiment, in step S5, the PLC control system first closes the controllable sealing door, and then opens the opening valve and the controllable sealing door after the temperature of the specimen rises, and turns on the air supply device in the guide structure to control the low-temperature medium in the sealing box 1 to flow from the center of the specimen to the surrounding area and flow out of the sealing box 1 through the guide structure.

[0044] Wherein, the air supply device can be a fan.

[0045] Through the test device and test method of the present application, real-time observation of the cross tensile test under cryogenic conditions and real-time strain measurement of the DIC system can be achieved, which is of great significance for accurately measuring the mechanical properties of materials, modeling, measuring strain paths, etc. In addition, by setting the guide structure in the side wall of the sealed box, the uniformity of temperature distribution and the accuracy of temperature control can be significantly improved, the utilization rate of liquid nitrogen can be improved, and the accumulation of low-temperature media near the observation window can be reduced, providing a clearer field of view, reducing the power required for the heating device, and saving costs.

[0046] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0047] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it 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 it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0048] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0049] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A cryogenic cross tensile test device, comprising a bidirectional cross tensile device, a sealing box, an observation device and a liquid nitrogen supply device, characterized in that: A sealing box is arranged in the bidirectional cross-stretching device, and a liquid nitrogen supply device supplies liquid nitrogen to the center of the sealing box. The bidirectional cross-stretching device includes a stretching chuck. The sealing box and the stretching chuck are sealed and lubricated by a packing sealing device. The packing in the packing sealing device is impregnated with graphite. The packing sealing device includes a gland, a sealing cavity and packing. The packing is arranged between the sealing box and the stretching chuck. The gland is sleeved outside the stretching chuck and applies axial compression to the packing. A sealing cavity is formed between the radial outer side of the packing and the sealing box; a double-layer glass observation window is arranged at the bottom of the sealing box, and a heating device and a lighting device are arranged in the two layers of glass. The observation device includes an optical reflector installed at a 45° angle below the sealing box and a CCD camera; A guide structure is arranged on the side wall of the sealing box, and the guide structure includes two layers of guide chambers from the inside to the outside. The opening of the inner guide chamber is arranged at the bottom of the side wall, and the opening of the guide chamber is arranged as a flared portion. The flared portion extends upward and is connected with the closed portion. An air supply device is arranged in the closed portion, and the closed portion is connected with the outer guide chamber. The inner structure of the outer guide chamber is the same as that of the inner guide chamber. A controllable sealing door is arranged at the flared portion of the outer guide chamber. The guide structure can guide the low-temperature medium in the sealing box to flow evenly from the center of the specimen to the surrounding area.

2. The deep cold cross tensile test device according to claim 1, characterized in that: The liquid nitrogen supply device includes a PLC control system, a temperature sensor connected to the PLC control system, a self-pressurized liquid nitrogen tank, a solenoid valve, a flow meter, an opening valve, and a liquid nitrogen delivery pipe with an air supply system. The temperature sensor is arranged on the tensile chuck and the test piece, the self-pressurized liquid nitrogen tank is connected to the solenoid valve, the solenoid valve is connected to the flow meter, the flow meter is connected to the opening valve, the opening valve is connected to the liquid nitrogen delivery pipe with the air supply system, and the air supply system delivers the liquid nitrogen to the center of the test piece in the sealed box.

3. The deep cold cross tensile test device according to claim 1, characterized in that: The side walls and bottom of the sealed box are double-layer stainless steel structures, and the interior is filled with ceramic fiber blanket insulation material.

4. A cryogenic cross tensile test method, using the cryogenic cross tensile test device described in claim 2 or 3, characterized in that: The following steps are involved: S1. The specimen is first treated with matte blackening, then sprayed with white speckles, the specimen is connected to a temperature sensor and then placed in a sealed box, the tensile chuck is connected, and the bidirectional cross tensile device is operated for centering; S2. Fix the upper cover of the sealing box and insert the liquid nitrogen delivery tube; S3, the temperature sensor is arranged on the outer end of the stretching chuck equipped with the force sensor, and an antifreeze sleeve is put on the middle part of the stretching chuck to perform real-time temperature control of the stretching chuck; S4, controlling the liquid nitrogen supply device to introduce liquid nitrogen to start cooling; S5. The PLC control system detects that the test piece reaches the specified temperature and then closes the opening valve. After the temperature of the test piece rises, the opening valve is opened again to continue cooling down, so as to control the test piece at the specified temperature. S6. After the temperature of the specimen is stable, operate the bidirectional cross tensile device to carry out the tensile test; S7. Use DIC system for real-time strain measurement.

5. A deep cold cross tensile test method according to claim 4, characterized in that: In step S5, the PLC control system first closes the controllable sealing door, and then opens the opening valve and the controllable sealing door after the temperature of the specimen rises, turns on the air supply device in the guide structure, and controls the low-temperature medium in the sealing box to flow from the center of the specimen to the surroundings and out of the sealing box through the guide structure.

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