CN114034586A

CN114034586A - Low-temperature fatigue test system for micro sample

Info

Publication number: CN114034586A
Application number: CN202111334723.1A
Authority: CN
Inventors: 张显程; 谢煜; 谈建平; 赵鹏程
Original assignee: East China University of Science and Technology
Current assignee: East China University of Science and Technology
Priority date: 2021-11-11
Filing date: 2021-11-11
Publication date: 2022-02-11

Abstract

The invention relates to a low-temperature fatigue test system for a micro sample, which comprises a fatigue test device and a low-temperature device, wherein the fatigue test device comprises an actuating shaft and an upper extension rod, a load sensor is arranged on the upper extension rod, an environment box is supported in the fatigue test device, the low-temperature device conveys low-temperature liquid into the environment box, the upper surface and the lower surface of the environment box are provided with openings, and the upper extension rod and the actuating shaft extend into the environment box through the openings; an upper clamp and a lower clamp are symmetrically arranged in the environment box and are respectively connected with the upper extension rod and the actuating shaft, and two ends of the micro sample are respectively connected with the upper clamp and the lower clamp; an extensometer is fixed on the micro sample, and a temperature compensation device is arranged on the load sensor. According to the low-temperature fatigue test system for the micro sample, the load is transferred in a mode that the grooves formed in the upper clamp and the lower clamp lift the micro sample, so that the sizes of two ends of the sample are reduced, the consumption of materials is reduced, the installation space of the extensometer is enlarged, and the extensometer can be used for the micro sample.

Description

Low-temperature fatigue test system for micro sample

Technical Field

The invention relates to the technical field of low-temperature fatigue tests, in particular to a low-temperature fatigue test system for a micro sample.

Background

With the development and progress of science and technology, the field related to low-temperature engineering is more extensive, and the demand for corresponding equipment is continuously increased. For example, polar region scientific research stations, icebreakers, liquefied natural gas storage and transportation, critical components of superconducting generators, and some components related to liquid fuels in aerospace engineering need to be in service under low-temperature or even ultra-low-temperature working conditions, and the reduction of the working temperature often affects various properties of materials, for example, as the temperature is reduced, the strength of some materials is increased, the elongation is reduced, and the fracture form is changed from ductile to brittle fracture. Therefore, along with the continuous rising of the demand of low-temperature materials, the testing of various properties of the materials at low temperature is indispensable, and the occurrence of serious accidents such as accidental failure of the materials at low temperature can be better avoided only by accurately mastering the change trend of the properties of the materials along with the reduction of the temperature.

According to statistics, more than 80% of engineering structure failure and failure are related to fatigue, so the low-temperature fatigue performance test of the material is particularly important for the research and development of low-temperature materials. Due to the problems that the manufacturing cost and the processing and production process of new materials are not mature, nonstandard micro samples are often adopted to carry out test work in the stage of scientific research and development. At present, tests on low-temperature fatigue performance of a micro sample are mostly carried out in a stress control mode, the mode is more suitable for related tests on high-cycle fatigue, but for low-cycle fatigue, particularly related tests with cyclic stress amplitude exceeding material yield strength, tests carried out in a strain control mode are more reasonable and accord with actual use working conditions, and experimental data obtained by the low-cycle fatigue are relatively richer. However, if a strain control mode is adopted for fatigue test, the strain value of the material must be accurately collected in real time, so that the strain value must be fed back to a control system of the fatigue testing machine in real time by adopting an extensometer for control, and if the extensometer is not installed, the strain value can be obtained only by an indirect means, which affects the actual strain value of the material, so that the test control is inaccurate, and the test result is inaccurate.

However, due to the structural problem of the physical extensometer, a larger space is often needed for installation than a gauge length section, for example, if the gauge length section of the extensometer is 10mm, a space of at least 15mm is needed for installing the physical extensometer, the clamping of the extensometer is difficult due to the undersize of a tiny sample, and the application of technologies such as video extensometer and Digital Image Correlation (DIC) is limited by the interference of a low-temperature environment, which brings a lot of difficulties for the fatigue test of a small sample under low-temperature development strain control.

In addition, at present, a traditional electromagnetic servo fatigue testing machine is usually adopted to carry out fatigue test on a micro sample, the load applied to the micro sample is monitored in real time through a load sensor, but the temperature lower than the normal working temperature interval of the load sensor may cause the problems of inaccurate reading of the load sensor and the like, so that accurate fatigue load cannot be applied to the micro sample, the low-temperature fatigue test result is inaccurate, and therefore the low-temperature fatigue testing machine cannot be directly used for carrying out test work at various low temperatures.

Disclosure of Invention

The invention aims to provide a micro sample low-temperature fatigue test system, which is used for carrying out accurate low-temperature fatigue test on a micro sample in a strain control mode.

The invention provides a low-temperature fatigue test system for a micro sample, which is used for carrying out a fatigue test on the micro sample and comprises a fatigue test device and a low-temperature device, wherein the fatigue test device comprises an actuating shaft and an upper extension rod, a load sensor is arranged on the upper extension rod, an environment box is supported in the fatigue test device, the low-temperature device conveys low-temperature liquid into the environment box through a guide pipe, the upper surface and the lower surface of the environment box are respectively provided with a hole, and the upper extension rod and the actuating shaft respectively extend into the environment box through the holes;

an upper clamp and a lower clamp are symmetrically arranged in the environment box, the lower clamp is fixedly connected with the actuating shaft, the upper clamp is fixedly connected with the upper extension rod, and two ends of the micro sample are respectively fixedly connected with the upper clamp and the lower clamp;

an extensometer is fixed on the micro sample, and a temperature compensation device is arranged on the load sensor.

Furthermore, the upper clamp and the lower clamp are both provided with grooves matched with the micro samples.

Further, the depth of the groove is slightly smaller than the thickness of the tiny sample.

Furthermore, cover plates are arranged on the upper clamp and the lower clamp respectively, and cover plates cover the grooves.

Furthermore, the upper clamp and the lower clamp are both provided with a step structure.

Furthermore, the temperature compensation device comprises a heat exchanger, a circulating water pump and a water circulation device with a hollow interior, a circulating water conduit is arranged in the water circulation device, two ends of the circulating water conduit are respectively connected with the circulating water pump and the heat exchanger, the circulating water pump is connected with the heat exchanger, and the water circulation device is tightly attached to the load sensor.

Further, the environment box is connected with the fatigue test device through a walking bracket, and the environment box can be conveniently disassembled and assembled.

Further, the environment box comprises a box door and a box body which are hinged to each other, the box door and the box body are made of heat-insulating materials, and sealing rubber gaskets are arranged on the periphery of the box door.

Further, an observation window is arranged on the box door.

Furthermore, a temperature equalizing fan and a thermocouple are arranged in the box body, a PID controller and a motor are arranged outside the box body, the PID controller is respectively electrically connected with the motor and the thermocouple, and a driving shaft of the motor is connected with the temperature equalizing fan.

Furthermore, a pressure release pipe communicated with the inside and the outside is arranged on the box body.

Furthermore, a sealing slide block is arranged between the box body and the actuating shaft as well as between the box body and the upper extension rod.

According to the low-temperature fatigue test system for the micro sample, the upper clamp and the lower clamp special for the micro sample are designed, and the load is transferred by utilizing the way that the micro sample is lifted by the grooves formed in the upper clamp and the lower clamp, so that the sizes of two ends of the sample are further reduced, the consumption of materials is reduced, the installation space of the extensometer is enlarged, and the application of the extensometer to the micro sample in a low-temperature environment is possible; the temperature compensation device is arranged on the load sensor, so that the influence of low temperature on the load sensor can be reduced or eliminated, and the accuracy of a test result is ensured.

Drawings

FIG. 1 is a schematic structural diagram of a low-temperature fatigue test system for a micro sample according to an embodiment of the present invention;

FIG. 2 is a perspective view of a lower clamp provided in accordance with an embodiment of the present invention;

FIG. 3 is a front view of FIG. 2;

FIG. 4 is a side view of FIG. 2;

FIG. 5 is a top view of FIG. 2;

FIG. 6 is a schematic view of an angle after the upper and lower clamps, the micro-sample and the extensometer are installed according to the embodiment of the present invention;

FIG. 7 is a schematic view of another angle after the upper and lower clamps, the micro-sample and the extensometer are installed according to the embodiment of the present invention;

FIG. 8 is a schematic structural diagram of an environmental chamber according to an embodiment of the present invention;

FIG. 9 is a cross-sectional view A-A of FIG. 6;

fig. 10 is a sectional view B-B of fig. 7.

Detailed Description

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in fig. 1, the embodiment of the present invention provides a micro sample low temperature fatigue test system, which is used for performing a low temperature fatigue test on a micro sample 5, and includes a fatigue test apparatus 1 and a low temperature apparatus 3 located at one side of the fatigue test apparatus, where the fatigue test apparatus 1 includes a rack, the rack includes a base 11 and pillars 12 mounted on the base 11, the number of the pillars 12 is at least 2, so as to ensure the stability of the fatigue test apparatus, in this embodiment, the pillars 12 are preferably four, and enclose a rectangular parallelepiped region, the upper ends of the pillars 12 are connected by a cross beam 13, and the cross beam 13 may be movably connected with the pillars 12, for example, fastened by bolts, so as to achieve greater compatibility for samples of different sizes.

The base 11 is a hollow structure, a servo mechanism 14 is installed in the hollow part and used for applying a cyclic load to the micro sample 5 and supporting the base 11, an actuating shaft 15 is connected to a driving shaft of the servo mechanism 14, an upper extension rod 16 is arranged on the cross beam 13, the actuating shaft 15 and the lower extension rod 16 are coaxially arranged, an upper chuck 18 and a lower chuck 19 for fixing a standard sample are respectively arranged at the lower end of the upper extension rod 16 and the upper end of the actuating shaft 15, an upper clamp 41 is fixed at the lower end of the upper chuck 18, a lower clamp 42 is fixed at the upper end of the lower chuck 19, the upper clamp 41 and the lower clamp 42 are symmetrically arranged, and two ends of the micro sample 5 are respectively clamped and fixed by the upper clamp 41 and the lower clamp 42. The actuating shaft 15 moves up and down under the driving of the servo mechanism 14, so that a cyclic load is applied to the micro sample 5, and a load sensor 17 is arranged between the upper extension rod 16 and the cross beam 13, can monitor the cyclic load in the fatigue test process in real time and send the cyclic load to a control system (not shown in the figure) of the fatigue test device.

The servo 14 may be a motor drive, an electromagnetic drive, or a hydraulic drive.

Be provided with environment case 2 in the cuboid region that pillar 12 encloses, its upper surface and lower surface all are provided with the trompil, and inside being acted as trompil 21 of axle 15 through environment case 2 lower surface stretched into environment case 2, it stretched into inside environment case 2 to go up the trompil of extension rod 16 through environment case 2 upper surface, and it is inside that last anchor clamps 41, lower anchor clamps 42 and small sample 5 all are located environment case 2. The bottom of the environment box 2 can be provided with a walking bracket 200, and the walking bracket 200 can freely move on the base 11 of the fatigue test device, so that the environment box 2 is driven to freely move, and the upper clamp, the lower clamp, the micro sample and other accessories can be conveniently disassembled and assembled. The specific structure of the walking frame 200 can be found in the patent with the publication number CN211599955U, and is not described in detail here.

The cryogenic device 3 is used for providing low temperature for the inside of the environment box 2, including the cryogenic liquid tank 31, the below of cryogenic liquid tank 31 is provided with support 32 to support it, cryogenic liquid is stored to the inside storage of cryogenic liquid tank 31, and communicate with the inside of environment box 2 through supply liquid pipe 33, cryogenic liquid can be one of the nontoxic no explosion danger liquid such as liquid nitrogen or liquid helium, through letting in cryogenic liquid to the inside of environment box 2, cryogenic liquid gasification heat absorption, thereby make the inside low temperature state that is in of environment box 2, specifically, the inside temperature of environment box 2 can reach 4.2K-300K.

A temperature compensation device 6 is disposed below the load cell 17 for keeping the temperature of the load cell 17 around room temperature so that it can operate normally. Preferably, the temperature compensation device 6 can adopt a water circulation device with a hollow inner part, a circulating water guide pipe is arranged in the water circulation device, the circulating water guide pipe is connected with a circulating water pump, the water circulation device is tightly attached to the load sensor 17, the circulating water pump feeds circulating water into the circulating water guide pipe, the circulating water takes away cold from the surface of the load sensor 17, then the circulating water is pumped into a heat exchanger to exchange heat with the environment, the temperature is recovered, and the circulating water is recirculated to the load sensor 17 to take away the cold, and the steps are repeated.

As shown in fig. 2-5, one side of the lower fixture 42 is provided with a groove 421 matching with the end of the small sample 5, the end of the small sample 5 is inserted into the groove 421 to be fixed, preferably, the size of the groove 421 is slightly larger than the size of the end of the small sample 5, so as to reduce the processing difficulty, facilitate installation of the small sample 5, and after the installation is completed, the gap between the small sample 5 and the fixture can be eliminated by applying a smaller pre-tightening force to the fixture. The groove 421 includes a first vertical section 4211, an inclined section 4212 and a second vertical section 4213 which are sequentially arranged, wherein the surface of the inclined section 4212 is attached to the side surface of the micro sample 5, and the side surface of the micro sample 5 is lifted by the inclined section 4212, so that the load is transferred; the first vertical section 4211 can be lengthened a little, so that the stress state of the lower clamp 42 can be improved, and the lower clamp is not easy to damage and deform.

The lower clamp 42 is further provided with a stepped structure (i.e., shoulder) 422 along its length that cooperates with the upper surface of the lower jaw 19 to facilitate centering and leveling of the lower clamp and the lower jaw 19. Specifically, when the lower fixture 42 is installed, the lower surface of the stepped structure 422 abuts against the upper surface of the lower chuck 19, so as to ensure the horizontal and centering performance of the lower fixture 42.

The side of the lower clamp 42 opposite to the groove 421 can be processed into a flat plate with anti-slip lines 424, the front and back surfaces of the flat plate are provided with the anti-slip lines 424, the flat plate is clamped by a lower chuck 19 (usually a wedge) of the fatigue testing device and then connected with the fatigue testing device, and the anti-slip lines 424 are arranged, so that the friction force between the lower clamp 42 and the lower chuck 19 can be increased, and the flat plate and the fatigue testing device are tightly fixed. The clamping principle of a standard clamp of a fatigue testing device belongs to the prior art and is not described in detail herein.

The upper clamp 41 and the lower clamp 42 are symmetrically arranged, and the structure thereof is the same as that of the lower clamp 42, and the description thereof is omitted.

As shown in fig. 6 and 7, both ends of the micro sample 5 are respectively put into the grooves of the upper and

lower jigs

41 and 42 to be fixed. The micro sample 5 is provided with an extensometer 7 so as to accurately acquire the strain value of the micro sample 5 in real time. The depth of the grooves of the upper and

lower jigs

41 and 42 is preferably slightly shallower than the thickness of the micro-sample 5, so that the surface of the micro-sample 5 is protruded, so that the extensometer is not blocked by the upper and lower jigs at the time of installation, thereby allowing the extensometer to be smoothly installed. In addition, when a test with a large load is carried out, the stress condition of the upper clamp and the lower clamp is often required to be improved by increasing the thickness of the upper clamp and the lower clamp, at the moment, the thickness difference between the micro sample 5 and the groove is equivalent to leave a little redundancy, and the situation that the micro sample 5 is blocked by the upper clamp and the lower clamp due to the increase of the thickness of the upper clamp and the lower clamp to cause that the extensometer cannot be installed is avoided.

In a possible embodiment, the upper and

lower clamps

41 and 42 may be provided with a cover plate 43, the cover plate 43 being disposed in a lateral direction of the upper and lower clamps and covering the groove. Specifically, after the two ends of the micro sample 5 are mounted in the grooves, the cover plate 43 covers the grooves and the micro sample 5, and is fastened and connected with the upper and lower clamps through the bolts 44. Because the depth of the groove is slightly smaller than the thickness of the micro sample 5, the cover plate 43 can slightly apply pressure to the micro sample 5, so that when the micro sample 5 is cut into two sections from the middle, the cover plates 43 at the two ends can fix the micro sample 5, and the phenomenon that the two ends of the micro sample 5 fly out due to uneven stress or shaking and the like when the micro sample 5 is instantaneously broken is avoided, and the safety of operators and equipment is damaged.

Screw holes are arranged on the upper clamp and the lower clamp to be matched with the bolts 44 to realize fastening. As shown in fig. 3, the lower clamp 42 is provided with two screw holes 423, and both ends of the cover plate 43 are respectively engaged with the two screw holes 423 and the bolts 44, thereby being tightly coupled with the lower clamp 42.

Because the conventional upper and lower chucks are locked mechanically or hydraulically, the two larger surfaces (namely two end surfaces) of the sample are clamped by the two wedge-shaped blocks and the load is transmitted by the friction force between the two surfaces, so that a larger clamping surface is needed when a test for providing a large load is needed, namely, the two ends of the sample are larger so as to provide enough friction force, the size of the upper and lower chucks needs to be larger and occupy more space, for a small sample, the length of the middle section of the sample is reduced, the extensometer is usually arranged at the middle section, because one side of the extensometer is provided with mechanical structures such as a sensor and a knife edge, if the middle section is too small, the mechanical structures collide with the upper and lower chucks at the two ends of the small sample 5, the extensometer cannot be arranged, and in order to ensure that the extensometer cannot sway left and right in the test process to influence the measurement, the knife edge of the sample gauge length needs to be contacted on a large surface of the sample gauge length (not on a side surface with a smaller area), so that the conventional upper and lower clamping heads inevitably occupy the installation space of the extensometer. The grooves are formed in the upper clamp and the lower clamp, the mode of applying load is changed from a mode of clamping a large surface of a sample and relying on friction force into a mode of lifting the sample through two sides of the groove, and therefore the surfaces related to loading and strain measurement are separated, the installation space of the extensometer is released better, and therefore the extensometer can be applied to low-temperature fatigue tests of small samples.

As shown in fig. 8-10, the environmental chamber 2 includes a chamber door 21 and a chamber body 22 hinged to each other, a guide rail (or a slider) and a universal wheel are disposed on the chamber body 22 so as to be engaged with the base 11 and the column of the fatigue test device, the small test sample 5 is disposed inside the chamber body 22, the chamber body 22 is communicated with a low temperature liquid tank 31 of the low temperature device through a liquid supply conduit 33 so as to realize low temperature inside the chamber body 22, the chamber door 21 and the chamber body 22 are made of heat insulating material, and a sealing rubber gasket (not shown) is disposed around the chamber door 21, so that when the chamber door 21 is closed, a sealed space is formed between the chamber door 21 and the chamber body 22 to maintain the low temperature inside the chamber body 22. The door 21 is provided with an observation window 211, and when the door 21 is closed, the deformation of the micro-sample 5 inside the casing 22 can be observed through the observation window 211.

On the environment case 2 with make axle 15 and last extension rod 16 complex trompil open and locate on box 22, can set up sealed slider 221 in the trompil, sealed slider 221 can slide around in the trompil, two sealed sliders 221 overlap respectively and establish the outer wall of making axle 15 and last extension rod 16, sealed slider 221 and box 22, it all sets up sealedly between axle 15 and the extension rod 16 down to make, thereby isolated environment case 2 inside and outside intercommunication, keep the inside low temperature state of environment case 2.

The inner wall of the box body 22 is provided with a thermocouple 81 and a temperature equalizing fan 82, the outer wall of the box body 22 is provided with a PID controller (proportional-integral-derivative controller) 83 and a motor 84, and a driving shaft of the motor 84 is connected with the temperature equalizing fan 82 and used for driving the temperature equalizing fan 82 to rotate so as to equalize the temperature inside the box body 22.

The liquid supply conduit 33 is provided with an electromagnetic valve 85, and the amount of the low-temperature liquid introduced into the interior of the tank 22 is controlled by controlling the opening and closing of the electromagnetic valve 85, thereby controlling the temperature of the interior of the tank 22. Specifically, when the electromagnetic valve 85 is completely opened, the introduction amount of the low-temperature liquid is the largest, and the temperature of about 4.2K can be realized after gasification; when the electromagnetic valve 85 is intermittently opened and closed, a small amount of low-temperature liquid is intermittently introduced, and a certain set temperature between 4.2K and 300K can be realized; when the electromagnetic valve 85 is completely closed, no low-temperature liquid is introduced, and the environment temperature of about 300K can be realized.

The PID controller 83 is electrically connected with the thermocouple 81, the motor 84 and the electromagnetic valve 85 respectively, the thermocouple 81 monitors the temperature inside the box body 22 in real time and transmits the temperature to the PID controller 83, and the PID controller 83 can control the temperature inside the box body 22 by controlling the opening and closing of the motor 84 and the electromagnetic valve 85. The PID controller 83 has an operation panel on which a real-time temperature can be displayed, and an operator can set the inside of the cabinet 22 to a desired temperature state through the operation panel.

Preferably, the outer wall of the box 22 is provided with a mounting cavity 9, and the PID controller 83, the motor 84 and the electromagnetic valve 85 are all arranged in the mounting cavity 9, so that on one hand, the structure can be more compact, and on the other hand, the PID controller 83, the motor 84 and the electromagnetic valve 85 can be protected. The operation panel of the PID controller 83 protrudes outside the mounting chamber 9 for easy operation.

The tank 22 is further provided with a pressure release pipe 222 for communicating the inside and the outside, and some gas formed by the gasification of the low-temperature liquid in the tank 22 can be released through the pressure release pipe 222, so that the pressure in the tank 22 is not too high.

The operation process of the fatigue testing system of the invention is as follows:

firstly, an upper clamp 41 and a lower clamp 42 are respectively and rigidly connected with an upper chuck 18 and a lower chuck 19 in a clamping mode, centered and leveled, then an actuating shaft 15 is slowly lifted, so that a micro sample 5 can be just placed into grooves of the upper clamp and the lower clamp at the same time, then a cover plate is covered and locked by bolts, then an extensometer is clamped 7 on the micro sample 5, after the steps are completed, an environment box 2 is pushed to a proper position, and then a sealing sliding block 221 is installed on a box body 22, so that the periphery of the actuating shaft 15 and an upper extension rod 16 is sealed; and then the box door 21 is closed, the low-temperature liquid tank 31 is communicated with the environment box 2 by using the liquid supply conduit 33, the temperature in the environment box 2 is controlled by the PID controller 83, when the required temperature state is reached and the time required by the heat preservation experiment is reached, the fatigue test device starts to operate, the fatigue test is carried out on the micro sample 5, meanwhile, the extensometer 7 transmits the real-time strain of the micro sample 5 to a control system of the fatigue test device, and the result is obtained after the test is finished.

According to the low-temperature fatigue test system for the micro sample, provided by the embodiment of the invention, the upper clamp and the lower clamp special for the micro sample 5 are designed, and the load is transferred by utilizing the way that the grooves formed by the upper clamp and the lower clamp lift the micro sample 5, so that the sizes of two ends of the sample 5 are reduced, the consumption of materials is reduced, the installation space of the extensometer is increased, the extensometer can be possibly applied to the micro sample in a low-temperature environment, the installation space of the extensometer is increased, and the extensometer can be smoothly installed; by arranging the temperature compensation device 6 on the load sensor 17, the influence of low temperature on the load sensor 17 can be reduced or eliminated, and the accuracy of the test result is ensured.

The above embodiments are merely preferred embodiments of the present invention, which are not intended to limit the scope of the present invention, and various changes may be made in the above embodiments of the present invention. All simple and equivalent changes and modifications made according to the claims and the content of the specification of the present application fall within the scope of the claims of the present patent application. The invention has not been described in detail in order to avoid obscuring the invention.

Claims

1. A micro sample low-temperature fatigue test system is used for carrying out fatigue test on a micro sample, and comprises a fatigue test device and a low-temperature device, wherein the fatigue test device comprises an actuating shaft and an upper extension rod, a load sensor is arranged on the upper extension rod, an environment box is supported in the fatigue test device, and the low-temperature device conveys low-temperature liquid into the environment box through a conduit,

the upper surface and the lower surface of the environment box are respectively provided with an opening, and the upper extension rod and the actuating shaft respectively extend into the environment box through the openings;

an upper clamp and a lower clamp are symmetrically arranged in the environment box, the upper clamp is fixedly connected with the upper extension rod, the lower clamp is fixedly connected with the actuating shaft, and two ends of a micro sample are respectively fixedly connected with the upper clamp and the lower clamp;

2. The micro-sample low-temperature fatigue testing system according to claim 1, wherein grooves matched with the micro-samples are arranged on the upper clamp and the lower clamp.

3. A micro-coupon low temperature fatigue testing system of claim 2, wherein the depth of said groove is slightly less than the thickness of said micro-coupon.

4. The low-temperature fatigue test system for the micro-samples according to claim 2, wherein the upper clamp and the lower clamp are both provided with cover plates, and the cover plates cover the grooves.

5. The low-temperature fatigue test system for the micro-samples according to claim 1, wherein a step structure is arranged on each of the upper clamp and the lower clamp.

6. The system for testing the low-temperature fatigue of the micro-sample according to claim 1, wherein the temperature compensation device comprises a heat exchanger, a circulating water pump and a water circulation device with a hollow interior, a circulating water conduit is arranged in the water circulation device, two ends of the circulating water conduit are respectively connected with the circulating water pump and the heat exchanger, the circulating water pump is connected with the heat exchanger, and the water circulation device is tightly attached to the load sensor.

7. The micro-specimen low-temperature fatigue testing system according to claim 1, wherein the environmental chamber and the fatigue testing device are connected through a walking bracket.

8. The system for testing the low-temperature fatigue of the micro-samples according to any one of claims 1 to 7, wherein the environmental chamber comprises a chamber door and a chamber body which are hinged with each other, the chamber door and the chamber body are both made of heat insulation materials, and the circumference of the chamber door is provided with a sealing rubber gasket.

9. The system for testing the low-temperature fatigue of the micro-sample according to claim 8, wherein the box door is provided with an observation window.

10. The micro-sample low-temperature fatigue testing system according to claim 8, wherein a temperature equalizing fan and a thermocouple are arranged in the box body, a PID controller and a motor are arranged outside the box body, the PID controller is electrically connected with the motor and the thermocouple respectively, and a driving shaft of the motor is connected with the temperature equalizing fan.

11. A micro-sample low-temperature fatigue test system according to claim 8, wherein the box body is provided with a pressure release pipe communicating the inside and the outside.

12. A small sample low-temperature fatigue test system according to claim 8, wherein a sealing slider is arranged between the box body and the actuating shaft and between the box body and the upper extension rod.