External field critical current test sample rod under axial strain of superconducting tape

Abstract

The invention belongs to the field of superconducting material measurement, and discloses an external field critical current test sample rod under axial strain of a superconducting tape, which comprises a mechanical transmission device, a worm vertical to a left-right rotation trapezoidal screw rod, and a worm gear connected with the middle part of the left-right rotation trapezoidal screw rod through an optical axis key; the axial strain loading platform and the nut seat are respectively screwed into a left thread part and a right thread part of the left-handed and right-handed trapezoidal screw rod, the sample holder is supported and fixed through convex parts at two sides of the nut seat, the copper current terminals are respectively fixed at two ends of a platform part of the sample holder, and the strain gauge is used for being fixed on a middle shaft in the middle of a superconducting tape to be tested; and the electric signal transmission device is electrically connected with the strain gauge. According to the invention, the left-handed and right-handed trapezoidal screw rods are driven to rotate, so that the pair of nut seats with opposite threads are linearly opened and closed, the superconducting tape to be measured on the sample holder tape welding platform is driven to generate axial strain, and the critical current of the superconducting tape under the axial strain in a background magnetic field is measured.

Description

Technical Field

[0001] The present invention belongs to the technical field of superconducting material measurement, and more specifically, relates to a test sample rod for measuring the critical current of a superconducting tape under axial strain in an external magnetic field. Background Art

[0002] During the processes of winding superconducting tapes into coils, magnet operation, cryogenic cooling, quenching, etc., the current-carrying capacity of superconducting tapes fluctuates greatly with changes in external loads and electromagnetic environments. Various variables in the external environment should be fully considered during operation. Since superconducting tapes are composed of different materials with significantly different mechanical and thermal properties, the composite structure of different materials has a significant impact on the critical current decay of superconducting tapes under mechanical behavior. High-temperature superconducting tapes often work in environments with strong magnetic fields and large currents, and will bear huge electromagnetic forces. Excessive stress and strain will cause irreversible degradation of the current-carrying capacity of the tapes. Therefore, studying the variation law of the critical current of superconducting tapes under different mechanical loads in a background magnetic field is an important topic related to the stable operation of the entire system, and important references for tape design and magnet performance analysis can be provided by determining the critical stress and strain.

[0003] Currently, most devices capable of applying axial strain to superconducting tapes in a magnetic field change the axial strain of the tapes by fixing one end of the tape and applying a tensile force to the other end of the tape by a tensile machine. This method can only apply axial tensile strain to the superconducting tape in a magnetic field and cannot apply axial compressive strain; and due to the simple mechanical structure, it can only apply strain to the tape in the vertical direction, and is suitable for experiments in expensive split magnets that can provide a horizontal background magnetic field, but cannot be used in experiments with a vertical magnetic field. Summary of the Invention

[0004] Aiming at the above defects or improvement requirements of the prior art, the present invention provides a test sample rod for measuring the critical current of a superconducting tape under axial strain in an external magnetic field. The purpose is to drive the left and right trapezoidal lead screws to rotate to make a pair of nut seats with opposite threads move linearly and open and close, driving the superconducting tape to be measured on the tape welding platform of the sample holder to generate axial strain, so as to measure the critical current of the superconducting tape under axial tensile / compressive strain in a background magnetic field.

[0005] To achieve the above object, in the first aspect of the present invention, there is provided a test sample rod for measuring the critical current of a superconducting tape under axial strain in an external magnetic field, including a mechanical transmission device, an axial strain loading platform, and an electrical signal transmission device;

[0006] The mechanical transmission device includes a worm and worm gear transmission group and a left - and - right - hand trapezoidal lead screw; the worm and the worm gear in the worm and worm gear transmission group are meshed with each other, the worm is perpendicular to the left - and - right - hand trapezoidal lead screw, and the worm gear is connected to the middle part of the left - and - right - hand trapezoidal lead screw through a key on a smooth shaft; wherein, on both sides of the middle part of the left - and - right - hand trapezoidal lead screw are a left - hand thread part and a right - hand thread part respectively;

[0007] The axial strain loading platform includes a sample holder, copper current terminals, nut seats and strain gauges; the nut seats are respectively screwed into the left - hand thread part and the right - hand thread part of the left - and - right - hand trapezoidal lead screw, the sample holder is supported and fixed by the protruding parts on both sides of the nut seats, the copper current terminals are respectively arranged at both ends of the platform part of the sample holder, and the strain gauges are used to be fixed on the central axis of the middle part of the superconducting tape to be measured;

[0008] The electrical signal transmission device is electrically connected to the strain gauges.

[0009] As a preference of the present invention, the mechanical transmission device includes a servo motor and a connecting rod; the motor shaft of the servo motor is fixed to one end of the connecting rod, and the other end of the connecting rod is connected to the worm through an internal thread.

[0010] As a preference of the present invention, the axial strain loading platform further includes a support member, a first guide rail and a second guide rail; the support member is arranged inside the sample rod and is used to fix the first guide rail and the second guide rail; the first guide rail and the second guide rail are respectively passed through the protruding parts on both sides of the nut seat and are slidably connected to the nut seat, and the first guide rail and the second guide rail are kept parallel to each other.

[0011] As a preference of the present invention, one end of the twisted - pair signal wire is electrically connected to the aviation plug, and the other end is used to connect the strain gauges and to connect the superconducting tape to be measured for strain testing; the silver - plated copper braid is used to connect the copper current terminals for conducting electricity.

[0012] As a preference of the present invention, the electrical signal transmission device further includes a first copper terminal, a first copper lead post, a second copper terminal, a second copper lead post, a first welding post and a second welding post; the upper end of the first copper lead post is fixedly connected to the first copper terminal, the lower end is fixedly connected to the first welding post, and the first welding post is connected to the second copper current terminal through a silver - plated copper braid; the upper end of the second copper lead post is fixedly connected to the second copper terminal, the lower end is fixedly connected to the second welding post, and the second welding post is connected to the first copper current terminal through a silver - plated copper braid.

[0013] Preferably, the electrical signal transmission device further includes a hollow pipe for guiding the leads of the strain gauge and the superconducting strip to be measured to pass through its interior and connect to the aviation plug.

[0014] Preferably, the test sample rod further includes a cover plate and an epoxy fixing plate; the cover plate is arranged at the upper end of the sample rod, and the epoxy fixing plate is arranged between the cover plate and the support member for limiting the position when the sample rod is lifted into the cryostat.

[0015] Preferably, the thread profile angle of the external thread of the left - hand and right - hand trapezoidal lead screw is 30°, the pitch is 1.5 mm, and the nominal diameter is 6 mm.

[0016] Generally speaking, compared with the prior art by the above - mentioned technical solution conceived by the present invention, the following technical advantages are mainly possessed:

[0017] 1. In the present invention, the worm - and - wormwheel transmission group in the mechanical transmission device drives the left - hand and right - hand trapezoidal lead screw to rotate, so that the left - hand and right - hand trapezoidal lead screw rotates to make a pair of nut seats with opposite threads perform a linear opening and closing movement, thereby driving the strip welding platform of the sample rack to generate axial strain, especially under tensile strain or compressive strain. At the same time, by fixing the strain gauge on the superconducting strip, the strain value of the superconducting strip when it undergoes axial tensile / compressive deformation can be accurately measured, so as to realize the measurement of the critical current of the superconducting strip under tensile strain or compressive strain in the vertical background magnetic field.

[0018] 2. In the present invention, double self - locking can be realized by assembling the worm - and - wormwheel and the left - hand and right - hand trapezoidal lead screw. When the sample rack undergoes any deformation, the mechanical device can maintain the mechanical load without falling back, ensuring that the strain of the superconducting strip remains stable during the measurement of the critical current.

[0019] 3. The sample rack of the present invention is made of beryllium copper alloy. Preferably, through the design of the size of the sample rack, an axial strain uniform area is generated by the deformation of the strip welding platform under the linear movement of the first nut seat and the second nut seat, so that the axial strain change range is - 1% - 1%. Thus, it is ensured that there is a long axial strain uniform area when applying mechanical power to deform the sample rack, increasing the length of the superconducting strip welded. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the overall appearance structure of the test sample rod for the external - field critical current of the superconducting strip under axial strain in the present invention;

[0021] Figure 2 It is a schematic diagram of the partial structure of the test sample rod for the external - field critical current of the superconducting strip under axial strain in the present invention;

[0022] Figure 3 Schematic diagram of the local structure of the test sample rod for the critical current of the external magnetic field under axial strain of the superconducting tape exemplified in the present invention;

[0023] Figure 4 In the present invention Figure 3 Schematic diagram of the structure from another perspective.

[0024] In all the drawings, the same reference numerals are used to represent the same elements or structures, where: 1 - aviation plug, 2 - cover plate, 3 - transmission rod, 4 - epoxy fixing plate, 5 - support, 6 - gas return interface, 7 - hollow pipe, 8 - first copper terminal, 9 - first copper lead column, 10 - servo motor, 11 - second copper terminal, 12 - second copper lead column, 13 - first welding post, 14 - connecting rod, 15 - worm gear, 16 - first guide rail, 17 - first nut seat, 18 - second welding post, 19 - worm, 20 - second nut seat, 21 - first copper current terminal, 22 - sample holder, 23 - left - right hand trapezoidal lead screw, 24 - strain gauge, 25 - second copper current terminal, 26 - second guide rail. Detailed implementation manners

[0025] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] As Figure 1As shown, in this embodiment, a test sample rod for measuring the critical current of a superconducting tape under axial tensile / compressive strain particularly includes a mechanical transmission device, an axial strain loading platform, and an electrical signal transmission device under tensile strain or compressive strain. The mechanical transmission device includes a worm and worm gear transmission group and a left and right hand trapezoidal lead screw 23. The worm 19 in the worm and worm gear transmission group meshes with the worm gear 15. The worm 19 is perpendicular to the left and right hand trapezoidal lead screw 23, and the worm gear 15 is key-connected to the middle of the left and right hand trapezoidal lead screw 23 through a smooth shaft. Among them, one side of the middle of the left and right hand trapezoidal lead screw 23 is a left-handed thread part, and the other side is a right-handed thread part. The axial strain loading platform includes a sample holder 22, copper current terminals, nut seats, and strain gauges 24. The nut seats are respectively screwed into the left-handed thread part and the right-handed thread part of the left and right hand trapezoidal lead screw 23. The sample holder 22 is supported and fixed by the protruding parts on both sides of the nut seats. The first copper current terminal 21 and the second copper current terminal 25 are respectively fixed at both ends of the platform part of the sample holder 22. The strain gauge 24 is used to be fixed on the central axis of the middle of the superconducting tape to be measured. And the electrical signal transmission device is electrically connected to the strain gauge 24. Thus, under the cooperation of the worm 19 and the worm gear 15, as the worm gear 15 rotates in the vertical direction, it drives the left and right hand trapezoidal lead screw 23 to rotate clockwise or counterclockwise in the horizontal direction. As the rotation direction of the left and right hand trapezoidal lead screw 23 is different, the nut seats undergo axial displacements of approaching or separating from each other, thereby driving the platform part of the sample holder 22 to perform a linear opening and closing movement and deformation. The axial strain loading platform is electrically connected to the electrical signal transmission device to complete the measurement of the critical current and axial strain of the superconducting tape.

[0027] In some embodiments, as Figures 2 - 4 shown, the mechanical transmission device includes a servo motor 10, a connecting rod 14, a worm gear 15, a worm 19, and a left and right hand trapezoidal lead screw 23. The motor shaft of the servo motor 10 is fixed to one end of the connecting rod 14, and the other end of the connecting rod 14 is connected to the worm 19 through an internal thread. The worm 19 meshes with the worm gear 15. The worm 19 is perpendicular to the left and right hand trapezoidal lead screw 23, and the worm gear 15 is key-connected to the middle of the left and right hand trapezoidal lead screw 23 through a smooth shaft. Thus, by controlling the rotation of the motor shaft of the servo motor 10, it drives the connecting rod 14 and the worm 19 to rotate. The worm gear 15 rotates because it meshes with the worm 19, and then drives the left and right hand trapezoidal lead screw 23 to rotate. In some embodiments, there is also a connecting rod 3 added between the servo motor 10 and the connecting rod 14 for connection. Specifically, the motor shaft of the servo motor 10 is fixed to one end of the connecting rod 14 to ensure smooth and stable rotation.

[0028] In some embodiments, as Figures 3 - 4As shown, the axial strain loading platform includes a sample holder 22, a first copper current terminal 21, a second copper current terminal 25, a first nut seat 17, a second nut seat 20, and a strain gauge 24. The first nut seat 17 and the second nut seat 20 are respectively screwed into both sides of the left and right hand trapezoidal lead screw 23 (the left threaded part and the right threaded part of the left and right hand trapezoidal lead screw 23), and are connected to the two side legs of the sample holder 22 through the protruding parts on both sides to fixedly support the sample holder 22; the first copper current terminal 21 and the second copper current terminal 25 are fixedly arranged at both ends of the platform part of the sample holder 22; the strain gauge 24 is fixed on the central axis of the middle section of the superconducting tape to be measured. Thus, the superconducting tape to be measured is welded to the first copper current terminal 21, the second copper current terminal 25, and the sample holder 22 by low-temperature solder; due to the opposite threads, the first nut seat 17 and the second nut seat 20 move axially closer to or away from each other as the rotation direction of the left and right hand trapezoidal lead screw 23 is different, thereby driving the platform part of the sample holder 22 to generate axial tensile strain or axial compressive strain.

[0029] In some embodiments, the first copper current terminal 21 and the second copper current terminal 25 are in the same plane as the tape welding platform of the sample holder 22 to avoid stress concentration.

[0030] In some embodiments, referring to Figures 3 - 4 As shown, the axial strain loading platform further includes a support member 5, a first guide rail 16, and a second guide rail 26; the support member 5 is arranged inside the entire sample rod and is used to fix the first guide rail 16 and the second guide rail 26; the first guide rail 16 and the second guide rail 26 are respectively fixed between the support members 5, respectively pass through the protruding parts on both sides of the first nut seat 17 and the second nut seat 20, are slidably connected to the nut seats, and are kept parallel to each other; the first nut seat 17 and the second nut seat 20 are respectively screwed into both sides of the left and right hand trapezoidal lead screw 23 (the left threaded part and the right threaded part of the left and right hand trapezoidal lead screw 23), and the protruding parts on both sides thereof respectively pass through the first guide rail 16 and the second guide rail 26 to limit their radial displacement.

[0031] In some embodiments, the electrical signal transmission device includes an aviation plug, a silver-plated copper braid, and a twisted pair signal line. The silver-plated copper braid is used to connect the copper current terminals for conducting electricity. One end of the twisted pair signal line is electrically connected to the aviation plug 1, and the other end is used to connect the strain gauge 24 and the superconducting tape to be measured for strain testing. When in use, a current is applied to the superconducting tape to be measured through the silver-plated copper braid, and the aviation plug 1 is connected to a nanovoltmeter and a strain gauge to measure the voltage node voltage and axial strain of the superconducting tape to be measured.

[0032] In some embodiments, specifically as Figures 2 - 4As shown in the figure, the electrical signal transmission device further includes a hollow pipe 7, a first copper terminal 8, a first copper lead post 9, a second copper terminal 11, a second copper lead post 12, a first welding post 13, a second welding post 18, a silver-plated copper braid, and a twisted signal wire; the first copper terminal 8 and the second copper terminal 11 are insulated from the cover plate 2 by black glue treatment and are fixedly connected to the upper ends of the first copper lead post 9 and the second copper lead post 12 respectively; the lower ends of the first copper lead post 9 and the second copper lead post 12 are fixedly connected to the first welding post 13 and the second welding post 18 respectively; the first welding post 13 is connected to the second copper current terminal 25 through a silver-plated copper braid, and the second welding post 18 is connected to the first copper current terminal 21 through a silver-plated copper braid; the leads of the strain gauge 24 and the voltage leads of the superconducting strip to be measured are connected to the aviation plug 1 through the hollow pipe 7. During use, the first copper terminal 8 and the second copper terminal 11 are connected to a DC current source to apply current to the superconducting strip to be measured, and the aviation plug 1 is connected to a nanovoltmeter and a strain gauge to measure the voltage node voltage and axial strain of the superconducting strip to be measured.

[0033] When the above test sample rod is in use, the superconducting strip to be measured is welded to the first copper current terminal 21, the second copper current terminal 25, and the sample holder 22 by low-temperature solder; by controlling the rotation of the motor shaft of the servo motor 10, the connecting rod 14 and the worm 19 rotate, and the worm wheel 15 rotates because it meshes with the worm 19, and then drives the left-right trapezoidal screw 23 to rotate; the thread directions on both sides of the left-right trapezoidal screw 23 are left-handed and right-handed respectively, the internal thread direction of the first nut seat 17 is right-handed, and the internal thread direction of the second nut seat 20 is left-handed. By controlling the rotation direction of the left-right trapezoidal screw 23, the first nut seat 17 and the second nut seat 20 are controlled to perform a linear movement of simultaneous opening and closing, and then drive the platform part of the sample holder 22 to generate axial tensile strain or axial compressive strain; the axial strain loading platform is connected to the electrical signal transmission device through a silver-plated copper braid and a twisted signal wire to complete the measurement of the critical current and axial strain of the superconducting strip. And the left-right trapezoidal screw 23 is self-locked with the first nut seat 17 and the second nut seat 20, and the worm 19 and the worm wheel 15 are self-locked, and the two sets of devices are combined to keep the load from falling back at any position.

[0034] Based on the sample rod of the present invention, the method for specifically testing the critical current of the superconducting tape under axial tensile / compressive strain of the external field is as follows: The superconducting tape is welded on the central axes of the first copper current terminal 21, the sample holder 22 and the second copper current terminal 25 with low-temperature solder, and the planes of the first copper current terminal 21, the second copper current terminal 25 and the sample stage 21 for fixing the superconducting tape are in the same plane; the strain gauge 24 is fixed on the central axis of the middle section of the superconducting tape to be tested; voltage leads are welded along the central axis in the length direction of the superconducting tape and are located in the middle of the tape; the superconducting tape to be tested is connected to the electrical signal transmission device through the voltage leads, and the strain gauge 24 is connected to the electrical signal transmission device through twisted pairs; the sample rod is hoisted into the cryostat, the gas is replaced and cryogenic liquid is introduced; by controlling the rotation direction of the motor shaft of the servo motor 10, the two side legs of the sample holder 22 are driven to move axially closer to or away from each other, thereby driving the superconducting tape to be tested to undergo axial tensile strain or axial compressive strain; the strain value of the strain gauge 24 is measured by a strain gauge, and the electric field strength on the superconducting tape is determined by a nanovoltmeter. When it reaches 1 μV / cm, the current value applied to the superconducting tape at this time is the critical current in the external field under axial tensile / compressive strain.

[0035] In some embodiments, the thread angle of the external thread of the left and right-handed trapezoidal lead screw is 30°, the pitch is 1.5 mm, and the nominal diameter is 6 mm. The left and right-handed trapezoidal lead screw is used to apply deformation to the superconducting tape to be tested, and its size only needs to be adapted to the design of the sample rod.

[0036] In some embodiments, the sample holder is made of beryllium copper alloy, and its tape welding platform deforms under the linear movement of the first nut seat and the second nut seat to generate a uniform axial strain region, ensuring that the axial strain change range is -1% - 1%. Among them, the length and width of the tape welding platform of the lead screw and the sample holder, and the distance from the center of the circular hole of the leg to the welding platform are matched. For example, the length of the tape welding platform of the sample holder is 48 mm, the width is 10 mm, the thickness is 2 mm, the diameter of the circular hole of the leg is 4 mm, and the distance from its center to the tape welding plane is 10 mm.

[0037] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the protection of the present invention and its equivalent technologies, the present invention also intends to include these changes and modifications. The above-described embodiments are only preferred embodiments given to fully illustrate the present invention, and the scope of protection is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the scope of protection of the present invention.

Claims

1. A superconducting tape axial strain external field critical current test sample rod, characterized in that: It includes a mechanical transmission device, an axial strain loading platform and an electrical signal transmission device; The mechanical transmission device comprises a worm and worm gear transmission group and a left-handed trapezoidal screw; the worm and the worm gear in the worm and worm gear transmission group are meshed with each other, the worm is perpendicular to the left-handed trapezoidal screw, and the worm gear is connected to the middle part of the left-handed trapezoidal screw through an optical axis key; wherein the two sides of the middle part of the left-handed trapezoidal screw are respectively a left thread part and a right thread part; The axial strain loading platform comprises a sample holder, a copper current terminal, a nut seat and a strain gauge; the nut seat is respectively screwed into the left thread part and the right thread part of the left-handed and right-handed trapezoidal screw rod, the sample holder is supported and fixed by the raised parts on both sides of the nut seat, the copper current terminals are respectively arranged at both ends of the sample holder platform part, and the strain gauge is used to be fixed on the central axis in the middle of the superconducting tape to be tested; The electrical signal transmission device is electrically connected to the strain gauge.

2. The superconducting tape axial strain external field critical current test sample rod according to claim 1, characterized in that: The mechanical transmission device comprises a servo motor and a connecting rod; the motor shaft of the servo motor is fixed to one end of the connecting rod, and the other end of the connecting rod is connected to the worm through an internal thread.

3. The superconducting tape axial strain external field critical current test sample rod according to claim 1, characterized in that: The copper current terminal is in the same plane as the strip welding platform of the sample holder.

4. The superconducting tape axial strain external field critical current test sample rod according to claim 1, characterized in that: The axial strain loading platform also includes a support member, a first guide rail and a second guide rail; the support member is arranged inside the sample rod and is used to fix the first guide rail and the second guide rail; the first guide rail and the second guide rail are respectively passed through the raised parts on both sides of the nut seat, are slidably connected to the nut seat, and keep the first guide rail and the second guide rail parallel to each other.

5. The superconducting tape axial strain external field critical current test sample rod according to claim 1, characterized in that: The electrical signal transmission device includes a silver-plated copper braided belt, a twisted pair signal line and an aviation plug; one end of the twisted pair signal line is electrically connected to the aviation plug, and the other end is used to connect the strain gauge and the superconducting tape to be tested for strain testing; the silver-plated copper braided belt is used to connect the copper current terminal for conduction.

6. The superconducting tape axial strain external field critical current test sample rod as claimed in claim 5, characterized in that: The electrical signal transmission device also includes a first copper terminal, a first copper lead terminal, a second copper terminal, a second copper lead terminal, a first welding terminal and a second welding terminal; the upper end of the first copper lead terminal is fixedly connected to the first copper terminal, and the lower end is fixedly connected to the first welding terminal, and the first welding terminal is connected to the second copper current terminal via a silver-plated copper braid; the upper end of the second copper lead terminal is fixedly connected to the second copper terminal, and the lower end is fixedly connected to the second welding terminal, and the second welding terminal is connected to the first copper current terminal via a silver-plated copper braid.

7. The superconducting tape axial strain external field critical current test sample rod according to claim 6, characterized in that: The electrical signal transmission device also includes a hollow pipe for guiding the lead wires of the strain gauge and the lead wires of the superconducting tape to be tested to pass through the inside thereof and be connected to the aviation plug.

8. The superconducting tape axial strain external field critical current test sample rod as claimed in claim 4, characterized in that: The test sample rod also includes a cover plate and an epoxy fixing plate; the cover plate is arranged at the upper end of the sample rod, and the epoxy fixing plate is arranged between the cover plate and the support member, and is used to limit the position of the sample rod when it is hung into the low-temperature thermostat.

9. The superconducting tape axial strain external field critical current test sample rod according to claim 1, characterized in that: The tooth angle of the left-handed trapezoidal screw external thread is 30°, the pitch is 1.5 mm, and the nominal diameter is 6 mm.

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