CN204718885U - Material Micro Mechanical Properties is biaxial stretch-formed-fatigue test system - Google Patents

Abstract

The utility model relates to a biaxial tension-fatigue test system for the micromechanical properties of materials, which belongs to the field of precision scientific instruments. By applying orthogonal tensile loads to the specimens, there are two mutually perpendicular tensile stresses on a plane, and at the same time, fatigue loads can also be applied to the specimens on the basis of tensile loads to study different loads The micromechanical properties of materials under the form and load conditions. The system consists of precision loading-transmission unit, fatigue unit, mechanical and deformation signal detection unit, specimen clamping unit and other parts. The advantages are: the testing system is novel and compact in structure, and can respectively realize uniaxial tensile testing, biaxial tensile testing, uniaxial tensile-fatigue testing, and biaxial tensile-fatigue testing, and has good compatibility with optical microscopes. Dynamically study the correlation law between the microstructure of materials and the mechanism of deformation and damage under the action of tensile-fatigue loads.

Description

Biaxial tensile-fatigue test system for material micromechanical properties

technical field

The utility model relates to the field of precision scientific instruments, in particular to a biaxial stretching-fatigue testing system for the microscopic mechanical properties of materials. It can be used as a test platform for uniaxial tension, biaxial tension, single-cycle tension-fatigue, and biaxial tension-fatigue material micromechanical properties, and it can also be used as a biaxial tension-fatigue material micromechanical property test. Axial co-frequency fatigue and biaxial non-coherent frequency fatigue tests. Moreover, the system can perform the above-mentioned micro-mechanical performance tests of various materials under some optical microscopes, so as to realize real-time observation of the micro-mechanical behavior and deformation damage process of the tested materials. At the same time, the quasi-static loading technology in the stretching process is realized through the reducer and the worm gear with a large reduction ratio; through the mechanical and deformation signal detection unit, the tensile force and tensile deformation of the specimen during the test process are measured. The signal collection can fit the stress-strain history of the measured material under the corresponding load, and can analyze the micro-mechanical properties of the material; through the processing software, the force and deformation signals collected by the mechanical and deformation signal detection unit are analyzed and processed. It is also possible to implement closed-loop control of the test system.

Background technique

In the process of testing the mechanical properties of materials, the whole process of dynamic monitoring of the microscopic deformation and damage of materials under load can be carried out through optical microscopes and other instruments, which can reveal more deeply the microscopic mechanical behaviors, damage mechanisms and The correlation law between its material properties and the load it receives.

In order to measure important parameters such as elastic modulus, hardness, fracture limit, and shear modulus of materials and their products, a variety of testing methods have been proposed based on micro-nano mechanical testing. Among them, the testing methods related to tensile mainly include uniaxial tensile stretching, uniaxial tension-fatigue, biaxial tension, etc. However, in practice, materials and their products are often subjected to non-single-mode loads, such as tension/compression-bending composite load mode, tension/compression-fatigue composite load mode, shear-torsion composite load mode, etc. Therefore, analyzing the mechanical properties of materials and their denatured damage mechanisms under the combined load mode has practical significance that cannot be ignored for the development of materials science.

In addition, most of the plate and shell structural components in actual engineering are subjected to two-way loads, including single crystal metals, concrete, and some anisotropic composite materials. Only the mechanical properties of their single bearings under tensile loads are studied, and not objective. Therefore, the development of a biaxial tension-fatigue test system is of great significance to the study of the mechanical properties of materials under biaxial tension and fatigue loads and the deformation and damage mechanism of materials.

Contents of the invention

The purpose of the utility model is to provide a biaxial tension-fatigue test system for the micromechanical properties of materials, which solves the above-mentioned problems existing in the prior art. The utility model can respectively realize uniaxial tensile mechanical test, biaxial tensile mechanical test, uniaxial tensile-fatigue mechanical test, biaxial tensile-fatigue mechanical test, wherein for biaxial tensile-fatigue mechanical test, this The system can also realize biaxial co-frequency fatigue loading and biaxial non-coherent frequency fatigue loading and other modes. The biaxial tension-fatigue material micro-mechanical performance testing system can also be compatible with some optical microscopes, and the micro-mechanical performance testing of materials Real-time observation of the process, such as in-situ monitoring of crack initiation, crack propagation, and material failure and damage process; in addition, the tensile force and tensile force of the specimen during the test are monitored through the mechanical and deformation signal detection unit. The acquisition of signals such as elongation and deformation can fit the stress-strain history of the measured material under the corresponding load, and then conduct in-depth research on the micro-mechanical behavior and deformation damage mechanism of the material under the action of biaxial tension-fatigue load.

Above-mentioned purpose of the utility model is realized through the following technical solutions:

Biaxial tensile-fatigue test system for material micromechanical properties, including precision loading-transmission unit, fatigue unit, mechanical and deformation signal detection unit, specimen clamping unit, etc.; wherein, the precision loading-transmission unit is fixed on the bottom plate 5 by screws Above, the fatigue unit is installed on the precision loading-transmission unit through two symmetrical guide rails Ia32, slider Ia31, guide rail Ib36, and slider Ib35, and the fatigue unit is connected to the specimen clamping unit through four identical connecting rods 17, The mechanical and deformation signal detection unit is installed on the specimen clamping unit.

The precision loading-transmission unit provides the preloading force of the test system and the force required for adjusting the position of the specimen clamping unit. It is powered by the DC motor 1 and drives the two-way through the reducer 2, the worm wheel 25 and the worm 24. The ball screw 11 rotates; the output shaft of the DC motor 1 is connected to the worm shaft 48 through the coupling 3, the worm wheel 25 is installed on the bidirectional ball screw 11, and the worm wheel 25 and the worm 24 play the role of speed reduction and torque increase The bidirectional ball screw 11 is fixed on the bottom plate 5 through the guide rail IIa9, slider IIa8, slider II29, guide rail IIb12, slider IIb13, slider II49e and screw support seat 28, and the bidirectional ball screw 11 Two identical lead screw nuts I, II10, 50 are installed, respectively connected to two identical nut seats I, II14, 30; said nut seats I, II14, 30 are divided into upper and lower parts, connected by screws, In this way, the difficulty of installation is reduced; the guide rail Ia32, the slider Ia31, the guide rail Ib36, and the slider Ib35 are respectively installed on the nut seats I, II14, and 30, and the two sliders Ia, b31, and 35 are all installed on the lower support plate 34 , the support column 33 is connected with the upper support plate 44 by screws, and the upper support plate 44 is fixedly connected to the flexible hinge 15; the screw nuts I, II 10, 50, nut seats I, II 14, 30, guide rails Ia, b32, 36 and The sliders Ia, b31, 35 are arranged symmetrically; the guide rails Ia, b32, 36 form an angle of 20° with the horizontal plane, therefore, when the sliders a, bI31, 35 move along the guide rails Ia, b32, 36 respectively , will drive the support column 33 to move up and down while keeping its horizontal position unchanged.

The fatigue unit includes a flexible hinge 15, four identical piezoelectric stacks 16 and four identical connecting rods 17, wherein the flexible hinge 15 has a symmetrical structure and is mounted on the lower support plate 44 by screws; the four The same piezoelectric stacks 16 are respectively installed in the flexible hinge 15, and are pre-tensioned by copper sheets; one end of the connecting rod 17 is connected to the flexible hinge 15 through the pin shaft I42, and the other end is connected to the sensor holder 19 through the pin shaft II45. Connected, the sensor holder 19 is installed on the slider Ⅳ 38 by screws.

The mechanical and deformation signal detection unit includes four identical tension sensors 21 and two displacement sensors I, II 41, 18, and the tension sensors 21 are connected between the clamp body I 43 and the sensor holder 19 through threads; the displacement sensor II 18 is installed Between the two opposite clamp bodies I, II43, 51, the displacement sensor I41 and the displacement sensor II18 are vertically arranged; the tensile force borne by the test piece 40 is on a straight line with the axis of the corresponding tensile sensor.

The specimen clamping unit is composed of four clamping bodies I43 and one-to-one corresponding pressing plates 39, the test piece is placed between the clamping bodies I43 and the pressing plates 39, and the clamping bodies I43 and the pressing plates 39 are connected by screws, And clamp the test piece 40 by tightening the screws; the clamp body I43 is installed on the slider IV38, and the slider IIc20 and the slider IV38 are installed on the same guide rail IIIa37; guide rails IIIb, c, d52, 53, 54 is the same as the guide rail IIIa37; knurling is processed on the clamp body I43 and the pressure plate 39 to ensure the reliability of clamping.

The testing system of the utility model can perform in-situ testing of the microscopic mechanical properties of materials under the dynamic monitoring of an optical microscope. Depending on the purpose of in-situ observation, an optical microscope can be selected to monitor the crack initiation, propagation, and fracture process of the test piece under load; a Raman spectrometer can be selected to detect the micro-area on the surface of the test piece and perform tensile/fatigue loading Phase structure research, grain and grain boundary changes, crack initiation, etc.; X-ray diffractometer can also be used to analyze the phase of the specimen, determine the grain size and stress distribution, and study the special properties of the material and its atomic arrangement. , the relationship between crystal phase changes, etc.; some observation equipment can be used together, such as optical microscopes and Raman spectrometers.

The guide rails IIIa, b37, and 52 are installed on the top plate I22, the guide rails IIIc, d53, and 54 are installed on the top plate II23, and the column 6 is connected with the top plate II23 and the bottom plate 5 through threads; the connection mode of the top plate I22 is connected with the connection mode of the top plate II23 The same; the column 6 conducts the tension on the top plate II 23 to the bottom plate 5 .

Among the four identical piezoelectric stacks 16, the output of the two piezoelectric stacks on the same tensile axis is consistent, so as to keep the cross center of the test piece fixed during the test.

The four tensile-fatigue ends of the specimen are on a plane, and the tensile loads of the four ends are uniformly loaded by a loading unit, and the application of fatigue loads is independent of each other, that is, the four tensile-fatigue ends can be Fatigue loads are applied separately. During the test, due to the symmetry of the device structure, the center of the test piece remained basically unchanged, which was conducive to the realization of in-situ observation. Defects such as indentations can be prefabricated at the cross center of the test piece, that is, the main observation area of the test piece, so as to facilitate the exploration of the microscopic mechanical properties of the material and its deformation and damage mechanisms under different load forms and load sizes.

The utility model applies tensile load to the four tensile ends of the test piece at the same time, so that there are two mutually perpendicular tensile stresses in the cross center of the test piece on a plane, and at the same time, the test piece can also be adjusted on the basis of the tensile load. Fatigue loads are applied to the four tensile ends of the tester to study the micromechanical properties of materials under different load forms and load sizes; based on the symmetry of the test system structure, the four tensile ends are completely symmetrical and share a loading unit Preloading is carried out so that the cross center of the specimen remains stationary while the specimen clamping unit pulls the specimen to move in the opposite direction at the same speed, which is convenient for dynamic monitoring of the material testing process using an optical microscope; in addition, the four biaxial stretching Each stretching end uses a piezoelectric stack for fatigue loading, that is, the fatigue loading of each stretching end is independent of each other, which makes the selection of fatigue loading schemes more diverse.

The beneficial effect of the utility model lies in that the testing system is novel and compact in structure and light in weight, and can perform in-situ testing of the microscopic mechanical properties of materials under the dynamic monitoring of an optical microscope, and can perform uniaxial tensile testing, biaxial tensile testing, and single-axis tensile testing. Axial tension-fatigue test, biaxial tension-fatigue test, and for biaxial tension-fatigue test, two low-cycle fatigue tests of biaxial co-frequency and non-coherent frequency can be realized, which can test materials and their products in two directions The micromechanical properties and degenerative damage mechanism under the tension-fatigue loading mode can be accurately evaluated; the test system can use some optical microscopes to observe the test process in real time and realize in-situ observation. The symmetry of the test system structure is fully utilized, and only one loading unit is used for preloading, which ensures the symmetry and synchronization of the two coaxial tensile ends during the test, and also ensures the cross center of the specimen during the test. stability. In summary, the utility model not only has good application and development prospects, but also has great significance for the development of in-situ testing technology and devices, and the progress of research on the microscopic mechanical properties of materials.

Description of drawings

The accompanying drawings described here are used to provide a further understanding of the utility model and constitute a part of the application. The schematic examples and descriptions of the utility model are used to explain the utility model and do not constitute improper limitations to the utility model.

Fig. 1 is the overall structure schematic diagram of the testing system of the present utility model;

Fig. 2 is the control principle block diagram of the utility model;

Fig. 3 is the structure schematic diagram of precision loading-transmission unit of the present utility model;

Fig. 4 is a structural schematic diagram of the fatigue unit, the specimen clamping unit and the mechanics and deformation signal detection unit of the present invention;

Fig. 5 is a structural schematic diagram of the fatigue unit and the specimen clamping unit of the present invention;

Fig. 6 is a structural schematic diagram of a mechanical and deformation signal detection unit of the present invention;

Figure 7 is a schematic diagram of the in-situ observation principle of the present invention (the solid line represents the position of the observation area A and the microscope lens before the test, during the test, the observation area A gradually changes to the dotted line position, and at the same time, the lens follows the movement of the specimen observation area Make adjustments to ensure the whole dynamic monitoring of the microscopic deformation damage of the material).

In the figure: In the figure: 1. DC motor; 2. Reducer; 3. Coupling; 4. Motor seat; 5. Base plate; 6. Column; 7. Column platform; 8. Slider Ⅱa; ;10. Lead screw nut Ⅰ; 11. Two-way ball screw; 12. Guide rail Ⅱb; 13. Slider Ⅱb; 14. Nut seat Ⅰ; 15. Flexible hinge; 16. Piezoelectric stack; 17. Connecting rod; 18 Displacement sensor II; 19, sensor fixing seat; 20, slider IIc; 21, tension sensor; 22, top plate I; 23, top plate II; 24, worm; 25, worm wheel; 26, bearing; 27, bearing seat; 28, Screw support seat; 29, slider IId; 30, nut seat II; 31, slider Ia; 32, guide rail Ia; 33, support column; 34, lower support plate; 35, slider Ib; 36, guide rail Ib; 37. Guide rail Ⅲa; 38. Slider Ⅳ; 39. Press plate; 40. Test piece; 41. Displacement sensor Ⅰ; 42. Pin shaft Ⅰ; 43. Clamp body Ⅰ; 44. Upper support plate; 45. Pin shaft Ⅱ; 46. Fixed plate; 47. Stop plate; 48. Worm shaft; 49. Slider IIe; 50. Screw nut II; 51. Clamp body II; 52. Guide rail IIIb; 53. Guide rail IIIc; 54. Guide rail IIId; , Clamping film.

Detailed ways

Further illustrate the detailed content of the utility model and its specific implementation below in conjunction with accompanying drawing.

Referring to Fig. 1 to Fig. 7, the biaxial tension-fatigue test system for material micromechanical properties of the present invention includes a precision loading-transmission unit, a fatigue unit, a mechanical and deformation signal detection unit, a specimen clamping unit, etc., wherein , the precision loading-transmission unit is fixed on the bottom plate 5 by screws, the fatigue unit is installed on the precision loading-transmission unit through two symmetrical guide rails Ia32, slider Ia31, guide rail Ib36, and slider Ib35, and the fatigue unit is installed on the precision loading-transmission unit through four identical The connecting rods 17 are respectively connected with the specimen clamping unit, and the mechanical and deformation signal detection unit is installed on the specimen clamping unit; using the symmetry of the test system structure, the specimen clamping unit pulls the specimen to move in the opposite direction, The cross center of the specimen remains static, which is convenient for in-situ observation with an optical microscope; the test system can respectively realize uniaxial tensile test, biaxial tensile test, uniaxial tensile-fatigue test, biaxial tensile-fatigue test, It has good compatibility with the optical microscope, and can dynamically study the correlation law between the microstructure of the material and the deformation damage mechanism under the action of tensile-fatigue load.

Referring to Fig. 3, the described precision loading-transmission unit provides the preloading force of the in-situ testing system and the force required for adjusting the position of the specimen clamping unit, and is fixed on the motor base 4 by the DC motor 1 Power is provided, and the two-way ball screw 11 is driven to rotate through the reducer 2, the worm wheel 25, and the worm 24; Above, the worm wheel 25 and the worm 24 play the role of reducing speed and increasing torque; the bidirectional ball screw 11 passes through guide rail IIa9, slider IIa8, slider IId29, guide rail IIb12, slider IIb13, slider IIe49, and screw The support seat 28 is fixed on the bottom plate 5, and two identical screw nuts I, II 10, 50 are installed on the bidirectional ball screw 11, which are respectively connected with two identical nut seats I, II 14, 30; the nuts Seats I, II14, 30 are divided into upper and lower parts, which are connected by screws to reduce the difficulty of installation; the nut seats I, II14, 30 are respectively installed with guide rail Ia32, slider Ia31, guide rail Ib36, slider Ib35, The two sliders Ia, b31, 35 are installed on the lower support plate 34, the support column 33 is connected with the upper support plate 44 by screws, and the upper support plate 44 is used to fix and connect the flexible hinge 15; the screw nut I, Ⅱ10, 50, nut seats Ⅰ, Ⅱ14, 30, guide rails Ⅰa, b32, 36 and sliders a, bⅠ31, 35 are arranged symmetrically; said guide rail Ⅰa32, guide rail Ⅰb36 form an included angle of 20° with the horizontal plane, therefore, when When the sliders Ia, 31, 35 move along the guide rails Ia, a32, 36 respectively, they will drive the support column 33 to move up and down while keeping its horizontal position unchanged.

4 and 5, the fatigue unit includes a flexible hinge 15, four identical piezoelectric stacks 16 and four identical connecting rods 17, wherein the flexible hinge 15 is a symmetrical structure, and is installed on the lower support by screws. 44 on the board; the four identical piezoelectric stacks 16 are installed in the flexible hinge 15 respectively, and are preloaded by copper sheets; one end of the connecting rod 17 is connected with the flexible hinge 15 through the pin I42, and the other end The sensor fixing seat 19 is connected with the sensor fixing seat 19 through the pin shaft II45, and the sensor fixing seat 19 is installed on the slider IV38 through screws.

The specimen clamping unit is composed of four clamping bodies I43 and one-to-one corresponding pressing plates 39, the test piece is placed between the clamping bodies I43 and the pressing plates 39, and the clamping bodies I43 and the pressing plates 39 are connected by screws, And clamp the test piece 40 by tightening the screws; the clamp body I43 is installed on the slider IV38, and the slider IIc20 and the slider IV38 are installed on the same guide rail IIIa37; the clamp body I43 and the pressure plate 39 There is knurling on the upper processing to ensure the reliability of clamping.

Referring to Fig. 6, the described mechanical and deformation signal detection unit includes four identical tension sensors 21 and two displacement sensors I, II 41, 18, and the tension sensors 21 are connected between the clamp body I 43 and the sensor holder 19 by threads Between; the displacement sensor II18 is installed between the two opposite clamp body I43 and the clamp body II51, and the displacement sensor 41 and the displacement sensor II18 are vertically arranged.

The guide rail IIIa37 and guide rail IIIb52 are installed on the top plate I22, the guide rail IIIc53 and guide rail IIId54 are installed on the top plate II23, one end of the column 6 is connected to the top plate II23 through threads, and the other end is connected to the bottom plate 5 through the column platform 7; the connection of the top plate I22 The connection method is the same as that of the top plate II 23; the column 6 conducts the tension on the top plate II 23 to the bottom plate 5.

One end of the worm shaft 48 is connected with the shaft coupling 3 , and the other end is installed on the bearing seat 27 through the bearing 26 .

The displacement sensor II18 is installed on the clamp body I43 through the fixed plate 46 and the clamping piece 55. The end of the sensor is always in contact with the stop plate 47, and the stop plate 47 is installed on the clamp body II51. Before testing, the displacement sensor II18 In the compressed state, during the test, as the distance between clamp body I43 and clamp body II51 increases, the displacement sensor II18 slowly elongates; the installation and measurement methods of the displacement sensor I41 are the same as those of the displacement sensor II18.

The four identical piezoelectric stacks 16 require that the output of the two piezoelectric stacks on the same tensile axis be consistent, so as to keep the cross center of the specimen in place during the test and facilitate in-situ observation .

The piezoelectric stack 16, connecting rod 17, force sensor 21, clamp body I43, etc. corresponding to the four directions of biaxial stretching are identical, so as to ensure that the cross center of the test piece 40 does not move horizontally during biaxial stretching, which is convenient In situ observation of the testing process by microscope.

The four identical force sensors 21 and the tensile force borne by the test piece 40 are in a straight line, which ensures the accuracy of the measurement results of the force sensors.

Referring to Figures 1 to 7, before the inventive test system is installed, it is necessary to calibrate and correct four identical force sensors 21 and two displacement sensors II, I18, and 41 used in the test system, and then install, debugging. Before testing the mechanical properties of materials, it is necessary to reset the clamping unit of the specimen, and it is required to adjust the clamping unit of the specimen to a suitable position in order to position and clamp the specimen, and after reset, displacement sensors II, I18, 41 are all under compression, and the allowable elongation is guaranteed to be greater than the tensile length of the specimen.

According to the purpose of the experiment, choose the appropriate measurement method, that is, uniaxial tensile test, biaxial tensile test, uniaxial tensile-fatigue test or biaxial tensile-fatigue test, and the fatigue test involved mainly refers to low cycle fatigue. The test is carried out on the basis that the specimen is stretched, that is, the specimen is pre-deformed or under a certain load condition for medium and low frequency tensile tests. Therefore, the test research conducted with the invented test system mainly analyzes the mechanical performance parameters such as material elastic modulus E, yield strength σ _S , strength limit σ _b , elongation after fracture A, and reduction of area Z. in,

Elastic Modulus $\mathrm{E.}=\frac{\mathrm{\σ}}{\mathrm{\ϵ}},$

Yield Strength ${\mathrm{\σ}}_{\mathrm{the\; s}}=\frac{f_{eL}}{S_0},$

strength limit ${\mathrm{\σ}}_b=\frac{f_b}{S_0},$

elongation after break $A=\frac{L_u-L_0}{L_0}\×100\%,$

rate of reduction in area $Z=\frac{S_0-S_u}{S_0}\×100\%;$

Among them, σ: stress of material, ε: strain of material, F _eL : material load corresponding to lower yield point, F _b : maximum load of material, S ₀ : original cross-sectional area of material, _Su : cross-sectional area of material after fracture, L ₀ : The original gauge length of the material, _Lu : The gauge length after the material breaks.

The mechanical properties of materials are mainly reflected in the deformation and failure properties of materials under load. The elastic modulus, fracture limit, fatigue strength and other parameters of the material are the most important test objects in the mechanical performance test of the material. The elastic modulus, yield strength, strength limit, elongation after fracture and section of the material can be measured through tensile testing. Shrinkage, which measures the mechanical properties of materials when subjected to tensile loads. The yield and failure process of the material under the action of bidirectional tensile load is studied through the load-displacement curve. The alternating stress generated by the cyclic loading force will cause permanent damage to the local material, and induce the initiation, expansion and instability of cracks. The effect of fatigue loading on the mechanical properties of materials can be measured by tensile-fatigue testing.

In the whole process of testing, in order to monitor the crack initiation, propagation and instability of the tested piece in real time, the test piece needs to be polished and corroded before the test, and the optical microscope imaging system is used for dynamic monitoring, and the image can be recorded at the same time. Combined with the debugging software, the engineering stress-strain curve and other mechanical parameters that characterize the mechanical properties of the material can also be obtained in real time.

The above descriptions are only preferred examples of the utility model, and are not intended to limit the utility model. For those skilled in the art, the utility model can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made to the utility model shall be included in the protection scope of the utility model.

Claims (7)

1. A biaxial stretching-fatigue test system for micromechanical property of material is characterized in that: the device comprises a precision loading-transmission unit, a fatigue unit, a mechanical and deformation signal detection unit and a test piece clamping unit; the precision loading-transmission unit is fixed on a bottom plate (5) through screws, the fatigue unit is installed on the precision loading-transmission unit through two symmetrical guide rails I a (32), a sliding block I a (31), a guide rail I b (36) and a sliding block I b (35), the fatigue unit is respectively connected with the test piece clamping unit through four same connecting rods (17), and the mechanics and deformation signal detection unit is installed on the test piece clamping unit.

2. The material micromechanical property biaxial tension-fatigue test system according to claim 1, characterized in that: the precision loading-transmission unit provides a preloading force and a force required by adjusting the position of the test piece clamping unit, the direct current motor (1) provides power, and the bidirectional ball screw (11) is driven to rotate by the speed reducer (2), the worm wheel (25) and the worm (24); an output shaft of the direct current motor (1) is connected with a worm shaft (48) through a coupler (3), a worm wheel (25) is installed on the bidirectional ball screw (11), and the worm wheel (25) and the worm (24) play roles in reducing speed and increasing torque; the bidirectional ball screw (11) is fixedly arranged on the bottom plate (5) through a guide rail IIa (9), a slide block IIa (8), a slide block II (29), a guide rail IIb (12), a slide block IIb (13), a slide block II (49) e and a screw support seat (28), and two identical screw nuts I, II (10, 50) are arranged on the bidirectional ball screw (11) and are respectively connected with two identical nut seats I, II (14, 30); the nut seats I and II (14 and 30) are divided into an upper part and a lower part which are connected through screws, so that the mounting difficulty is reduced; the nut seats I and II (14 and 30) are respectively provided with a guide rail Ia (32), a slide block Ia (31), a guide rail Ib (36) and a slide block Ib (35), the two slide blocks Ia and b (31 and 35) are arranged on a lower supporting plate (34), a supporting column (33) is connected with an upper supporting plate (44) through screws, and the upper supporting plate (44) is fixedly connected with a flexible hinge (15); the screw rod nuts I and II (10 and 50), the nut seats I and II (14 and 30), the guide rails I a and b (32 and 36) and the slide blocks I a and b (31 and 35) are symmetrically arranged; the guide rails Ia and b (32 and 36) form an included angle of 20 degrees with the horizontal plane, so that when the sliding blocks a and bi (31 and 35) move along the guide rails Ia and b (32 and 36) respectively, the supporting column (33) is driven to move up and down to keep the horizontal position of the supporting column unchanged.

3. The material micromechanical property biaxial tension-fatigue test system according to claim 1, characterized in that: the fatigue unit comprises a flexible hinge (15), four identical piezoelectric stacks (16) and four identical connecting rods (17), wherein the flexible hinge (15) is of a symmetrical structure and is mounted on the lower support plate (44) through screws; the four same piezoelectric stacks (16) are respectively arranged in the flexible hinges (15) and are pre-tightened through copper sheets; one end of the connecting rod (17) is connected with the flexible hinge (15) through a pin shaft I (42), the other end of the connecting rod is connected with the sensor fixing seat (19) through a pin shaft II (45), and the sensor fixing seat (19) is installed on the sliding block IV (38) through a screw.

4. The material micromechanical property biaxial tension-fatigue test system according to claim 1, characterized in that: the mechanical and deformation signal detection unit comprises four identical tension sensors (21) and two displacement sensors I and II (41 and 18), wherein the tension sensors (21) are connected between the clamp body I (43) and the sensor fixing seat (19) through threads; the displacement sensor II (18) is arranged between the two opposite clamp bodies I and II (43 and 51), and the displacement sensor I (41) and the displacement sensor II (18) are vertically arranged; the tensile force borne by the test piece (40) is aligned with the axis of the corresponding tension sensor.

5. The material micromechanical property biaxial tension-fatigue test system according to claim 1, characterized in that: the test piece clamping unit consists of four clamp bodies I (43) and pressing plates (39) corresponding to the clamp bodies I (43) one by one, a test piece is placed between the clamp bodies I (43) and the pressing plates (39), the clamp bodies I (43) and the pressing plates (39) are connected through screws, and the test piece (40) is clamped through screwing the screws; the clamp body I (43) is arranged on a sliding block IV (38), and the sliding block IIc (20) and the sliding block IV (38) are arranged on the same guide rail IIIa (37); the guide rails IIIb, c, d (52, 53, 54) are the same as the guide rail IIIa (37); knurling is processed on the clamp body I (43) and the pressing plate (39) so as to ensure the clamping reliability.

6. The material micromechanical property biaxial tension-fatigue test system according to claim 5, characterized in that: the guide rails IIIa and b (37 and 52) are installed on the top plate I (22), the guide rails IIIc and d (53 and 54) are installed on the top plate II (23), and the upright post (6) is connected with the top plate II (23) and the bottom plate (5) through threads; the connection mode of the top plate I (22) is the same as that of the top plate II (23); the upright post (6) transmits the pulling force applied to the top plate II (23) to the bottom plate (5).

7. The material micromechanical property biaxial tension-fatigue test system according to claim 3, characterized in that: the output of the four same piezoelectric stacks (16) in the same stretching axial direction is consistent, so that the cross center of the test piece is kept fixed in position during the test.