CN108931440A - A kind of small sample is uniaxially stretched creep test fixture - Google Patents

Abstract

The invention belongs to the technical field of testing tensile and creep mechanical properties, in particular to a fixture for uniaxial tensile creep testing of small samples. The fixture of the present invention comprises: an upper bracket, an upper clamp, a universal clamp block, a clamp pin, a lower bracket, a lower clamp, an outer extension rod, a lower rod, an inner extension rod, a guide frame, a measuring foot, a nut, a displacement measuring device and extension frame. The present invention mainly solves the problem that the existing small sample test fixture generally has the problem of slipping during the sample stretching stage when the sample is clamped. The tilt, distortion and slippage caused by the process ensure that the sample will not affect the coaxiality of the measurement during the stretching process; the thermocouple is inserted into the test sample fixture to directly and accurately test the real test temperature of the sample; the quartz rod is used to connect The linear variable differential transformer (LVDT) can be applied to the high-temperature mechanical performance test of samples in an environment up to 1200°C.

Description

A Fixture for Uniaxial Tensile Creep Test of Small Samples

technical field

The invention belongs to the technical field of testing tensile and creep mechanical properties, in particular to a fixture for uniaxial tensile creep testing of small samples.

Background technique

The small sample testing technology is to save test materials to a great extent on the premise of meeting the relevant test requirements, and is suitable for the experimental environment with strict size requirements. For example, in the limited experimental space in the irradiation experiment, it can It makes great use of the irradiation space, and is also very suitable for small samples such as treasures and thin films. At the same time, countries around the world are also actively establishing small sample testing standards, and various types of small sample testing equipment have gradually begun to develop. Therefore, it is necessary to provide a fixture that can overcome the above sample testing problems.

Contents of the invention

The technical problem to be solved in the present invention is: the existing small sample test fixture generally has the problem of slippage in the sample stretching stage when the sample is clamped.

Technical scheme of the present invention is as follows:

A fixture for uniaxial tensile creep test of small samples, including: upper bracket, upper clamp, universal clamp block, clamp pin, lower bracket, lower clamp, outer extension rod, lower rod, inner extension rod, guide frame, Measuring feet, nuts, displacement measuring devices and extension frames; wherein, the upper fixture is in the shape of a cuboid, and its lower end is provided with clamp pins for positioning; one of the universal clamps is fixed on the lower end of the upper fixture by screws. The clamping block is provided with a clamping pin hole, and the setting position of the clamping pin hole matches the spatial position of the clamping pin arranged at the lower end of the upper fixture, and the clamping pin hole and the clamping pin cooperate to position the universal clamping block at the lower end of the upper fixture The installation position of the universal clamp block is fixed on the lower end of the upper fixture by screws; on the two contacting surfaces of the universal clamp block and the lower end of the upper fixture, there are also several horizontal lines, which are used to increase the stability of the sample. clamping force;

The lower clamp is in the shape of a cuboid, and its upper end is also provided with a clamp pin for positioning; another universal clamp is fixed on the upper end of the lower clamp by screws, and the universal clamp is provided with a clamp pin hole and a clamp pin hole. The setting position of the clamping block matches the spatial position of the clamping block pin arranged at the upper end of the lower fixture, and the clamping block pin hole and the clamping block pin cooperate to locate the installation position of the universal clamping block at the lower end of the upper clamping fixture; the upper end of the universal clamping block and the lower clamping There are also several horizontal lines on the two contacting surfaces, which are used to increase the clamping force of the sample;

Both the upper bracket and the lower bracket are strip-shaped, the upper clamp is fixed on the upper bracket by screws, and the lower clamp is fixed on the lower bracket by screws;

There is a pair of outer extension rods and inner extension rods; the upper ends of the two outer extension rods are fixedly installed on the two ends of the upper bracket respectively, and the two outer extension rods are arranged along the vertical direction, and the two outer extension rods are parallel; The upper ends of the inner extension rods are respectively fixedly installed on the two ends of the lower bracket, the two inner extension rods are arranged along the vertical direction, and the two inner extension rods are parallel, and the two inner extension rods are located between the two outer extension rods;

The pull-down rod is a cylindrical rod, and the lower fixture is fixedly installed on the top of the pull-down rod through a bolt; at the middle and lower part of the pull-down rod, a guide frame is also fixed; the middle part of the guide frame is provided with a large through-hole, and the pull-down rod passes through the large through-hole. There are two small through-holes on both sides of the guide frame, the two outer extension rods pass through the two small through-holes relatively to the outer side, and the two inner extension rods pass through the two relatively inner through-holes respectively. Two small through holes are pierced; the two outer extension rods are relatively fixed to the guide frame, and the two inner extension rods can slide back and forth axially in the small through holes through which they pass;

The extension frame is arranged at the lower part of the extension frame; the extension frame is a strip shape, and a large through hole is also arranged in the middle of the extension frame, and the pull rod passes through the large through hole of the extension frame, and can be inserted into the large through hole of the extension frame. The hole slides back and forth along its own axial direction; on the extension frame, at the positions on both sides of the large through hole, there is also a small through hole, and the lower ends of the two inner extension rods are respectively inserted into the two small holes on the extension frame. and fixed in the hole; at both ends of the extension frame, there are also through holes respectively, and the displacement measuring device is fixedly installed in the through holes at both ends of the extension frame;

The displacement measuring device has a housing and a probe, and the housing is fixedly installed in the through holes at both ends of the extension frame;

There are two measuring feet, the measuring feet are sheet-like structures, which are respectively arranged on both sides of the pull-down rod; one end of the two measuring feet is respectively fixedly connected to the lower ends of the two external extension rods, and the other ends of the two measuring feet are all set There is a through hole, the probe of the displacement measuring device passes through the through hole of the measuring foot upwards, and is connected by nut locking; the nut is a knurled thin nut with a large outer diameter, which can prevent the downward displacement of the probe .

Preferably, the furniture of the present invention also includes a thermocouple probe, and a hole is arranged on the side of the upper clamp, and a thermocouple probe is installed in the hole. When the sample is clamped, the thermocouple probe directly contacts the sample. It can measure the true temperature of the sample to the greatest extent possible while ensuring the strength of the fixture.

Preferably, there are three clamping pins arranged at the lower end of the upper fixture, arranged in an inverted triangle in space, and the height line of the inverted triangle is located in the vertical direction.

Preferably, pins are also provided on the upper clamp for connecting the entire clamp system with the tensile system of the test equipment for tensile creep testing.

Preferably, there are three clamping pins arranged at the upper end of the lower fixture, arranged in a triangle in space, and the height line of the triangle is located in the vertical direction.

Preferably, both the outer extension rod and the inner extension rod are made of quartz material to ensure rigidity at high temperature.

Preferably, the upper ends of the two outer extension rods are respectively fixed and installed on the two ends of the upper bracket by two heat-resistant screws.

Preferably, the upper ends of the two inner extension rods are respectively fixed and installed on the two ends of the lower bracket by two heat-resistant screws.

Preferably, the fixture of the present invention also includes split sleeves, and the two split sleeves are respectively installed in the two through holes at both ends of the extension frame; each split sleeve is clamped with a displacement measuring device; on the side of each end of the extension frame, Both are equipped with adjusting bolts, and rotating the adjusting bolts can adjust the clamping force of the split sleeve on the displacement measuring device.

Preferably, the displacement measuring device is a linear variable differential transformer.

The beneficial effects of the present invention are:

(1) The present invention adopts pin positioning, uses four upper and lower bolts to lock the sample, and sets horizontal lines on the contact surface, which avoids the inclination, distortion and slippage of the sample during the clamping process, and at the same time ensures that the sample is stretched during the stretching process. It will not affect the coaxiality of the sample measurement;

(2) Insert the thermocouple into the test sample fixture to directly and accurately test the real test temperature of the sample;

(3) The linear variable differential transformer (LVDT) is connected by quartz rods, which can be applied to the high-temperature mechanical performance test of samples under the environment of up to 1200°C.

Description of drawings

Fig. 1 is a schematic diagram of the overall composition of the fixture of the present invention;

Fig. 2 is an enlarged schematic view of the upper part of the fixture of the present invention;

Fig. 3 is the side view of fixture of the present invention;

Among them, 1-upper bracket, 2-piercing pin, 3-upper clamp, 4-heat-resistant screw, 5-sample, 6-general clamp block, 7-clamp pin, 8-lower bracket, 9-lower clamp, 10-pin, 11-outer extension rod, 12-down rod, 13-inner extension rod, 14-guide frame, 15-measuring foot, 16-nut, 17-displacement measuring device, 18-split sleeve, 19-extension frame , 20-adjusting bolt, 21-thermocouple probe.

Detailed ways

The jig for uniaxial tensile creep test of small samples of the present invention will be described in detail below with reference to the accompanying drawings and examples.

As shown in FIGS. 1 and 2 , the jig of the present invention includes an upper jig 3 and a lower jig 9 . The upper fixture 3 is in the shape of a cuboid, and its lower end is provided with a clamp pin 7 for positioning. There are three clamp pins 7 arranged at the lower end of the upper fixture 3, which are arranged in an inverted triangle in space, and the height line of the inverted triangle in the vertical direction. The lower end of the upper clamp 3 is also provided with a universal clamp 6, the universal clamp 6 is provided with a clamp pin hole, and the location of the clamp pin hole is the same as the spatial position of the clamp pin 7 arranged at the lower end of the upper clamp 3. Matching, the clip pin hole cooperates with the clip pin 7 to locate the installation position of the universal clip 6 at the lower end of the upper fixture 3 . The universal clamping block 6 is fixedly mounted on the lower end of the upper clamp 3 by screws. On the two contacting surfaces of the universal clamp block 6 and the lower end of the upper clamp 3 , there are also several horizontal lines, which are used to increase the clamping force on the sample 5 .

On the upper clamp 3, there is also a pin 2, which is used to connect the entire clamp system with the tensile system of the test equipment for tensile creep testing.

The lower clamp 9 is in the shape of a cuboid, and its upper end is provided with a clamp pin 7 for positioning. There are three clamp pins 7 arranged at the upper end of the lower clamp 9, which are arranged in a triangle in space, and the triangular high line is located in the vertical position. direction. The upper end of lower fixture 9 is provided with another universal clamping block 6, and this universal clamping block 6 is provided with clamping block pin hole, and the setting position of clamping block pin hole is arranged on the space position of clamping block pin 7 that is arranged on lower clamp 9 upper ends. Matching, the clip pin hole cooperates with the clip pin 7 to locate the installation position of the universal clip 6 at the lower end of the upper fixture 3 . The universal clamping block 6 is fixedly mounted on the lower end of the upper clamp 3 by screws. On the two contacting surfaces of the upper end of the universal clamp block 6 and the lower clamp 9 , there are also several horizontal lines for increasing the clamping force on the sample 5 .

The fixture of the present invention also includes an upper bracket 1 and a lower bracket 8, the upper bracket 1 and the lower bracket 8 are strip-shaped, the upper clamp 3 is fixed on the upper bracket 1 by screws, and the lower clamp 9 is fixed on the lower bracket by screws. on the bracket 8.

The clamp of the present invention also includes an outer extension rod 11 and an inner extension rod 13 . Each of the outer extension rods 11 and the inner extension rods 13 has a pair, and is made of quartz material to ensure rigidity under high temperature. The upper ends of the two outer extension rods 11 are fixedly installed on the two ends of the upper bracket 1 by two heat-resistant screws 4 respectively, and the two outer extension rods 11 are arranged vertically, and the two outer extension rods 11 are parallel. The upper ends of the two inner extension rods 13 are also fixedly installed on the two ends of the lower bracket 8 by two heat-resistant screws 4 respectively. The two inner extension rods 13 are arranged in the vertical direction, and the two inner extension rods 13 are parallel. The inner extension rod 13 is located between the two outer extension rods 11 .

The clamp of the present invention also includes a pull-down rod 12, which is a cylindrical rod. The lower clamp 9 is fixedly installed on the top of the pull-down rod 12 through the latch 10 . A guide frame 14 is also fixed at the middle and lower part of the pull down rod 12 . The middle part of the guide frame 14 is provided with a large through hole, and the lower rod 12 passes through the large through hole. There are also two small through-holes on both sides of the guide frame 14, two outer extension rods 11 pass through the two small through-holes at positions relatively on the outside respectively, and two inner extension rods 13 pass from the positions relatively on the inside respectively. through two small through-holes. The positions of the two outer extension rods 11 and the guide frame 14 are relatively fixed, and the two inner extension rods 13 can slide back and forth axially in the small through holes through which they pass.

At the lower position of the pull down rod 12, an extension frame 19 is provided. The extension frame 19 is strip-shaped, and a large through hole is also arranged in the middle of the extension frame 19. The pull-down rod 12 passes through the large through hole of the extension frame 19, and can slide back and forth in the large through hole of the extension frame 19 along its own axis. . On the extension frame 19, a small through hole is respectively arranged at the positions on both sides of the large through hole, and the lower ends of the two inner extension rods 13 are respectively inserted into the two small through holes on the extension frame 19 and fixed. The two ends of the extension frame 19 are respectively provided with through holes, and the two open sleeves 18 are respectively installed in the two through holes at the two ends of the extension frame 19 . Each split sleeve 18 also clamps a displacement measuring device 17, and the displacement measuring device is a linear variable differential transformer. On the side of each end of the extension frame 19 , an adjusting bolt 20 is installed, and the rotating adjusting bolt 20 can adjust the clamping force of the open sleeve 18 on the movement measuring device 17 .

The displacement measuring device 17 has a housing and a probe, and the housing is clamped in the open sleeve 18 .

The fixture of the present invention also includes two measuring feet 15 , the measuring feet 15 are sheet-like structures and are respectively arranged on both sides of the pull-down rod 12 . One end of the two measuring feet 15 is respectively fixedly connected to the lower ends of the two outer extension rods 11, the other ends of the two measuring feet 15 are provided with through holes, and the probe of the displacement measuring device 17 passes through the through holes of the measuring feet 15 upwards. Out, and through the nut 16 locking connection. The nut 16 is a knurled thin nut with a large outer diameter, which can prevent the downward displacement of the probe.

As shown in Figure 3, a hole is also provided on the side of the upper clamp 3, and a thermocouple probe 21 is installed in the hole. When the sample 5 is clamped, the thermocouple probe 21 is directly in contact with the sample 5, which can be While ensuring the strength of the fixture, measure the real temperature of sample 5 to the greatest possible extent.

The jig for uniaxial tensile creep test of small samples of the present invention, when in use, the materials to be tested are processed and prepared according to the size requirements of small samples, and then loaded into relevant equipment suitable for testing the mechanical properties of small samples, then the tensile test can be carried out. Mechanical performance tests such as elongation and creep.

Taking the vanadium alloy, the structural material of the fusion reactor, as the room temperature tensile test as an example, the use process of the fixture of the present invention is as follows:

1) Process a small vanadium alloy sample according to the small sample standard, and perforate both ends of the small sample. Put the small sample on the upper clamp 3 and the lower clamp 9 on the clamp block pin 7 located in the middle. By preloading a certain small force value, adjust the coaxiality of the connecting rod, so that the sample and the connecting rod of the fixture are in a straight line, and pass the other two clamp pins 7 on the upper fixture 3 and the lower fixture 9 respectively. 9 Position and install the universal clamp 6, so that the universal clamp 6 is close to the surface of the sample, and fixed by screws, so that the horizontal lines on the surface of the clamp bite the surface of the sample;

2) Adjust the loading force of the tensile testing equipment, pre-clamp the sample, eliminate the gap of the entire fixture system, and then unload the force value to zero, and return the deformation and displacement data to zero at the same time;

3) Set the sample and tensile data parameters on the software side, and start the tensile test until the sample breaks. After the test, the stress-strain curve of the material can be drawn using the force value and deformation data, and the tensile strength, yield strength and elongation and other data parameters.

Taking the high-temperature tensile experiment of vanadium alloy, the structural material of the fusion reactor, as an example, the use process of the fixture of the present invention is as follows:

1) Small sample processing, installation and clamping are as described in steps 1 and 2 of the above example;

2) Insert the thermocouple into the design position of the fixture, and at the same time add zirconium foil to the outside of the small sample to surround it for a week to absorb oxygen under high temperature conditions. in a vacuum device;

3) Turn on the mechanical pump for preliminary vacuuming, and at the same time turn on the cooling device. When the pressure in the vacuum chamber is lower than 20Pa, turn on the molecular pump. When the vacuum degree of the entire chamber reaches 1×10 ^-4 Pa level, turn on the heating. Set the 5-10 Newton pre-tightening force to load and maintain it through the program to prevent the sample from compressing and deforming when the fixture expands during the heating process;

4) The heating process is controlled by adjusting the power of the heating wire to ensure that the vacuum degree is better than 1×10 ^-3 Pa during the entire heating process;

5) When the temperature reaches 750°C, keep it warm for 15 minutes, then set the tensile rate to 0.2mm/min, start the tensile test until the sample breaks, and the software system will record the temperature, vacuum degree and stress and strain during the whole experiment in real time and other experimental parameters;

6) After the experiment is over, the data will be automatically saved for analysis. Turn off the heating system. When the temperature drops below 300°C, close the baffle valve to isolate the side of the molecular pump. At the same time, turn off the molecular pump. After the molecular pump stops completely, the temperature drops simultaneously. Turn off the mechanical pump when the temperature is below 100°C. When the temperature of the vacuum chamber drops below 80°C, the bolts can be loosened, the sealing flange can be opened, and the test sample can be taken out to complete the experiment.

Taking the high-temperature creep experiment of vanadium alloy, the structural material of fusion reactor, as an example, the use process of the fixture of the present invention is as follows:

1) The steps of sample installation, vacuuming and heating are as described in steps 1-4 of the above example;

2) When the temperature reaches 750°C, keep it warm for 6 hours to completely release the clamp and the high-temperature expansion deformation of the sample. During the process, maintain the pre-tightening force until the deformation data curve tends to be completely stable, adjust the loading stress to the target value of the creep test and maintain it. Start the creep experiment.

3) After the test, use the deformation data and test time data to draw the creep test curve, and then analyze and obtain data parameters such as the minimum creep rate of the material.

Claims (10)

1. a kind of small sample is uniaxially stretched creep test fixture, including：Upper bracket (1), upper fixture (3), general fixture block (6), Fixture block pin (7), lower bracket (8), lower fixture (9), bar (11) of extending outside, lower pull rod (12), interior bar of extending (13), saddle (14), Measure foot (15), nut (16), displacement measuring device (17) and frame of extending (19)；It is characterized in that：

The upper fixture (3) is rectangular shape, and lower end is provided with fixture block pin (7) used for positioning；One universal clamp Block (6) is fixedly installed on the lower end of upper fixture (3) by screw, is provided with fixture block pin hole on general fixture block (6), fixture block pin hole Position and the spatial position for the fixture block pin (7) for being set to upper fixture (3) lower end is arranged to match, fixture block pin hole and fixture block pin (7) Cooperation positions general fixture block (6) in the installation site of upper fixture (3) lower end；General fixture block (6) is fixedly installed in by screw The lower end of fixture (3)；On two faces being in contact of the general fixture block (6) and upper fixture (3) lower end, also it is provided with several Band, for increasing the chucking power to sample (5)；

The lower fixture (9) is rectangular shape, and the upper end is also equipped with fixture block pin (7) used for positioning；In lower fixture (9) Upper end is fixedly installed another general fixture block (6) by screw, is provided with fixture block pin hole, fixture block pin hole on general fixture block (6) Setting position and the spatial position of the fixture block pin (7) for being set to lower fixture (9) upper end match, fixture block pin hole and fixture block pin (7) cooperation positions general fixture block (6) in the installation site of upper fixture (3) lower end；On the general fixture block (6) and lower fixture (9) On two faces being in contact at end, several bands are also provided with, for increasing the chucking power to sample (5)；

The upper bracket (1) and lower bracket (8) are streaky shape, and upper fixture (3) is fixedly installed in the upper branch by screw On frame (1), lower fixture (9) is fixedly installed on the lower bracket (8) by screw；

It is described outer to extend bar (11) and interior bar of extending (13) respectively has a pair；The upper end of two bars (11) of extending outside is fixedly mounted respectively It is arranged along the vertical direction in bar (11) of extending outside the both ends of upper bracket (1), two, and bar (11) of extending outside two is parallel；Two Extend in the root upper end of bar (13) is fixedly installed in the both ends of lower bracket (8) respectively, extends bar (13) along the vertical direction in two Setting, and extends bar (13) in parallel in two, extend in two bar (13) extended between bar (11) outside two；

The lower pull rod (12) is cylindric bar, and lower fixture (9) is fixedly installed in the top of lower pull rod (12) by bolt (10)； At the middle and lower part position of lower pull rod (12), it is further fixed on saddle (14)；Large through-hole, lower pull rod are provided in the middle part of saddle (14) (12) it is passed through from large through-hole；The two sides of saddle (14) are also each there are two small through hole, and two are extended bar (11) respectively from position outside It is pierced by two small through hole relatively in the outer part, two small through hole of the bar (13) respectively from position relatively in the inner part of extending in two In be pierced by；Wherein extend outside two bar (11) and saddle (14) position it is relatively fixed, bar (13) of extending in two can be worn at it It slidably reciprocates in the small through hole crossed along axial direction；

The frame of extending (19) is set to the lower position of lower pull rod (12)；Frame (19) are extended for streaky shape, in frame of extending (19) large through-hole is also equipped in the middle part of, lower pull rod (12) is pierced by from the large through-hole of frame of extending (19), and can extend It axially slidably reciprocates in the large through-hole of frame (19) along itself；It is also each at the position of large through-hole two sides on frame of extending (19) It is provided with a small through hole, the lower end for bar (13) of extending in two is inserted into this two small through hole on frame of extending (19) simultaneously respectively It is fixed；At the both ends of frame of extending (19), it is also respectively arranged with through-hole, displacement measuring device (17) fixed installation is frame of extending (19) in the through-hole at both ends；

Institute's displacement measurement device (17) has shell and probe, and the through-hole at frame (19) both ends that are to extend is fixedly mounted in shell In；

There are two the measurement feet (15), and measurement foot (15) is laminated structure, is respectively arranged at lower pull rod (12) two sides；Two surveys One end of foot-measuring (15) is respectively fixedly connected with to two bar (11) lower ends of extending outside, is all provided on the other end of two measurements foot (15) It is equipped with through-hole, the probe of displacement measuring device (17) is pierced by upwards from the through-hole of measurement foot (15), and is locked by nut (16) Connection；The nut (16) is annular knurl thin nut, has big outer diameter, the displacement that probe can be prevented downward.

2. small sample as described in claim 1 is uniaxially stretched creep test fixture, it is characterised in that：Furniture of the invention is also Including thermocouple probe (21), it is additionally provided with hole in the side of upper fixture (3), thermocouple probe (21) are installed in hole, are being pressed from both sides When holding sample (5), thermocouple probe (21) is directly in contact with sample (5), can be maximum while guaranteeing fixture intensity The true temperature of sample (5) can be capable of measuring.

3. small sample as claimed in claim 2 is uniaxially stretched creep test fixture, it is characterised in that：It is set to upper fixture (3) it there are three the fixture block pins (7) of lower end, arranges in space in up-side down triangle, and the high line of be in up-side down triangle is located at On vertical direction.

4. small sample as claimed in claim 3 is uniaxially stretched creep test fixture, it is characterised in that：On upper fixture (3), It is additionally provided with and wears pin (2), for entire chucking appliance system to be connected with test equipment tensioning system, carry out tensile creep test.

5. small sample as claimed in claim 4 is uniaxially stretched creep test fixture, it is characterised in that：It is set to lower fixture (9) there are three the fixture block pins (7) of upper end, arrangement triangular in shape in space, and high line triangular in shape is located at vertical direction On.

6. small sample as claimed in claim 5 is uniaxially stretched creep test fixture, it is characterised in that：The outer bar of extending (11) it is made with interior bar of extending (13) of quartz material, to guarantee the rigidity under high temperature.

7. small sample as claimed in claim 6 is uniaxially stretched creep test fixture, it is characterised in that：It extends outside described two The upper end of bar (11) passes through the both ends that two resistance to thermal screws (4) are fixedly installed in upper bracket (1) respectively.

8. small sample as claimed in claim 7 is uniaxially stretched creep test fixture, it is characterised in that：It extends in described two The upper end of bar (13) passes through the both ends that two resistance to thermal screws (4) are fixedly installed in lower bracket (8) respectively.

9. small sample as claimed in claim 8 is uniaxially stretched creep test fixture, it is characterised in that：Fixture of the invention is also Including opening sleeve (18), two opening sleeves (18) are respectively arranged in the two through-holes at frame of extending (19) both ends；Each opening Displacement measuring device (17) are clamped in set (18)；In the side at frame of extending (19) every end, it is mounted on and adjusts bolt (20), Rotation, which adjusts bolt (20), can adjust opening sleeve (18) to the chucking power of displacement measuring device (17).

10. small sample as claimed in claim 9 is uniaxially stretched creep test fixture, it is characterised in that：Institute's displacement measurement Device (17) is linear variable difference transformer.