A test device and test method for a biaxial tensile test of a specimen

Abstract

The present invention relates to the technical field of material performance detection, and provides a test device and a test method for a biaxial tensile test of a specimen, wherein an upper positioning component is arranged below an upper base plate, and a lower positioning component is arranged above a lower base plate, and the upper positioning component and the lower positioning component are arranged coaxially up and down, and cooperate with each other for center positioning of the specimen; a four-gear rack component is arranged in an annular array between the upper base plate and the lower base plate with the axis of the upper positioning component and the lower positioning component as the center, and the gear rack component is provided with a clamping end for applying tension to a tensile fin, and during the test, a biaxial tensile force parallel to the plane where the specimen is located is applied to the specimen through the gear rack component; a strain collection component collects the strain of the specimen; and a stress collection component collects the stress magnitude applied to the specimen by the clamping end. The upper and lower positioning components can realize rapid positioning of the specimen, and the positioning accuracy is high, and the use of a gear rack mechanism can ensure the consistency of four-axis motion and ensure the force balance of the tensile test on the specimen.

Description

Technical Field

[0001] The invention relates to the technical field of material performance detection, and in particular to a test device and a test method for a specimen biaxial tensile test. Background Art

[0002] Before materials are applied to engineering, the performance of the materials needs to be tested to determine whether they meet the application requirements. Among them, the ability of the material to withstand axial tensile and fatigue loads is a relatively critical performance. In the prior art, special testing machines are required, such as four-axis hydraulic testing machines, biaxial testing machines (CN107271287), etc., which are expensive and cumbersome to use. When using a universal testing machine, due to the lack of center positioning of the specimen and the non-simultaneous movement of the four axes, problems such as eccentric loading will occur, affecting the test results; factors such as the lack of guide devices on the upper and lower fixtures may result in poor repeatability of the test results. Summary of the invention

[0003] The technical problem to be solved by the present invention is: in order to overcome the deficiencies in the prior art, the present invention provides a test device and a test method for a specimen biaxial tensile test.

[0004] The technical solution adopted by the present invention to solve the technical problem is: a test device for a biaxial tensile test of a specimen, wherein the specimen is cross-shaped and comprises four tensile fins, wherein a positioning groove is respectively arranged on the upper and lower sides of the common connecting end of the four tensile fins, and a concave clamping surface is arranged on the two side surfaces of each tensile fin close to the connecting end, and a speckle that can be recognized by a camera is arranged in the positioning groove below the specimen;

[0005] The testing device comprises an upper base plate, a lower base plate, an upper positioning assembly, a lower positioning assembly, four gear rack assemblies, a strain collection assembly and a stress collection assembly, wherein the upper base plate and the lower base plate are arranged in parallel up and down for supporting other assemblies and connecting with the testing machine; the upper positioning assembly is arranged below the upper base plate, the lower positioning assembly is arranged above the lower base plate, and the upper positioning assembly and the lower positioning assembly are arranged coaxially up and down, and cooperate with each other for center positioning of the specimen; the four gear rack assemblies are arranged in an annular array between the upper base plate and the lower base plate with the axis of the upper positioning assembly and the lower positioning assembly as the center, the gear rack assembly is provided with a clamping end for applying tension to the tensile fin of the specimen, and during the test, a bidirectional tensile force parallel to the plane where the specimen is located is applied to the specimen through the four gear rack assemblies; the collection end of the strain collection assembly is arranged above or below the specimen for collecting the strain of the specimen; the stress collection assembly is arranged on the clamping end of the gear rack assembly for collecting the stress applied to the specimen by the clamping end.

[0006] Furthermore, in order to achieve the synchronous action of the tensile force on the specimen, the gear rack assembly includes a base, a base, a gear, a vertical rack, a horizontal rack and a clamping block, wherein the bottom of the base is fixedly mounted in the limiting groove of the lower base plate by fixing screws, the base is mounted on the upper end of the base, and can radially approach or move away from the central axis of the test device on the base, a horizontal rack mounting portion is provided at the upper end of the base, a T-shaped sliding groove is provided on the horizontal rack mounting portion, the extension direction of the sliding groove is parallel to the movement direction of the base, the horizontal rack is slidably mounted in the sliding groove, and the tooth surface of the horizontal rack faces upward, and one end of the horizontal rack close to the central axis is fixedly connected to the clamping block for clamping the specimen, and the clamping block is provided with a clamping groove whose shape matches the shape of the tensile fin of the specimen; side plate support platforms extending in the same direction as the sliding groove are provided on both sides of the horizontal rack mounting portion, and a A side plate is installed, and the side plates on both sides are parallel to each other, the gear is rotatably connected between the two side plates through a gear shaft, and the two ends of the gear shaft are rotatably connected to the side plates through bearings, and the gear is arranged above the horizontal rack and meshes with the horizontal rack; a vertical rack is provided on the side of the gear close to the central axis, the vertical rack and the horizontal rack are perpendicular to each other, and the vertical rack meshes with the gear; the upper end of the vertical rack is connected to the upper base plate by a fixing screw, and the connection position with the upper base plate can be adjusted; the lower end is movably connected to the guide column mounting hole on the base through a rack guide rod, and the rack guide rod can move up and down with the vertical rack in the guide column mounting hole, and the rack guide rod plays a guiding role when the vertical rack moves up and down, ensuring the position of the vertical rack in the vertical direction, thereby ensuring the accuracy of torque transmission between the gear and rack; when the vertical rack moves downward, the horizontal rack is driven radially away from the central axis through the gear. Thus, the vertical rack is driven to move downward by the downward pressure between the upper bottom plate and the lower bottom plate, thereby achieving the stretching of the test piece by the clamping block.

[0007] Furthermore, in order to make the center of the specimen located on the central axis of the testing machine, an adjustment mechanism is also included, and the adjustment mechanism is used to realize that the base on the base is radially close to or away from the central axis of the testing device. The adjustment mechanism includes a boss mounting groove arranged on the top of the base, an adjustment boss arranged on the bottom of the base, and an adjustment screw, wherein the adjustment boss is arranged in the boss mounting groove, and the boss mounting groove is provided with an opening facing the central axis, and a through hole is provided on the base on the side opposite to the opening, and the adjustment screw passes through the through hole and is threadedly connected with the adjustment boss in the boss mounting groove. The movement of the adjustment boss in the boss mounting groove is achieved by rotating the adjustment screw, so that the base drives the upper components of the base to radially approach or move away from the central axis of the testing device, that is, to adjust the position of the center of the specimen. The center of the specimen is located on the central axis of the testing machine, which can ensure the balance of the force applied by the testing machine to the specimen and improve the precision and accuracy of the test.

[0008] Furthermore, in order to record and observe the strain of the specimen during the test, a strain collection component is added. Therefore, the strain collection component includes a reflector and a camera. The reflector is tilted on the lower base plate below the specimen and the angle between the reflector and the lower base plate is 45°. The camera is arranged on the periphery of the reflector and the camera is facing the direction of the reflected light of the reflector. During the stretching process, the area with speckles on the bottom of the specimen is reflected to the camera through the reflector, and the deformation of the specimen due to the stretching is photographed by the camera, so as to obtain the strain of the specimen during the stretching process.

[0009] Furthermore, in order to determine the corresponding relationship between strain and stress, the stress collection assembly includes a strain gauge, which is attached to the clamping block between the horizontal rack and the clamping groove, and the strain gauge collects the stress on the clamping block acting on the specimen. When collecting stress and strain, the collection should be performed at the same time, so that the performance of the specimen material can be judged by the corresponding situation of stress and strain.

[0010] Furthermore, in order to ensure that the center of the test piece is located on the central axis of the testing machine, the upper positioning assembly includes an upper positioning ring and an upper positioning rod, the upper end of the upper positioning ring is fixed below the upper base plate, an upper positioning cavity is provided inside the upper positioning ring, the upper end of the upper positioning rod is inserted into the upper positioning cavity and can move axially along the upper positioning cavity, and the lower end of the upper positioning rod is provided with a positioning end matching the shape of the positioning groove; a locking mechanism for locking the upper positioning rod in the upper positioning cavity is provided on the side of the upper positioning ring;

[0011] The lower positioning assembly comprises a lower positioning ring and a lower positioning rod, the lower positioning ring is detachably connected to the upper surface of the lower base plate, and the lower positioning ring and the lower base plate can be connected by threads; or they can be directly connected by plugging and pulling, and the matching accuracy between the apertures can ensure that the lower positioning ring can be stably connected to the lower base plate and can be easily removed; a lower positioning cavity is provided in the lower positioning ring, the lower end of the lower positioning rod is inserted in the lower positioning cavity and can move axially along the lower positioning cavity, and the upper end of the lower positioning rod is provided with a positioning end matching the shape of the positioning groove; and the lower positioning assembly meets the following conditions:

[0012] (1) In order to realize the positioning function of the lower positioning rod, after the top of the lower positioning rod is embedded in the positioning groove of the specimen, the height H1 from the top of the lower positioning rod to the bottom of the lower positioning ring is less than the sum of the heights of the lower positioning rod and the lower positioning ring, that is, H1

[0013] (2) After the lower positioning rod is inserted into the bottom of the lower positioning cavity, the height H3 from the top of the lower positioning rod to the bottom of the lower positioning ring is less than the height H2 from the upper surface of the lower bottom plate to the lower surface of the test piece.

[0014] ​Furthermore, in order to ensure the stability during the downward pressing of the upper base plate, at least one group of guide components is also included, each group of the guide components includes a guide post and a guide sleeve, an axial guide cavity is provided in the guide sleeve, and the guide cavity can be a through hole opened on the guide sleeve, and can also be a blind hole. One end of the guide post is inserted into the guide cavity and can move along the axial direction in the guide cavity, and the other end of the guide post is fixed on one of the upper base plate and the lower base plate, and the other end of the guide sleeve is fixed on the other of the upper base plate and the lower base plate. The connection relationship between the guide post and the guide sleeve of the positioning assembly and the upper base plate and the lower base plate is not unique, and can be determined according to design habits and actual conditions. Preferably, the guide components are in two groups, symmetrically arranged between the upper base plate and the lower base plate on both sides of the specimen.

[0015] Furthermore, in order to ensure the stability of the connection between the guide column and the guide sleeve, a first limiting ring is provided at the connection between the guide column and the upper base plate or the lower base plate, and the first limiting ring is clamped on the upper base plate or the lower base plate; and / or a second limiting ring is provided at the connection between the guide sleeve and the upper base plate or the lower base plate, and the second limiting ring is clamped on the upper base plate or the lower base plate.

[0016] Furthermore, in order to achieve rapid positioning and connection with the testing machine, an upper connecting rod is provided above the upper base plate, and the upper connecting rod is fixedly connected to the upper base plate through an upper connecting rod positioning ring, and the upper end of the upper connecting rod is connected to the testing machine; a lower connecting rod is provided below the lower base plate, and the lower connecting rod is fixedly connected to the lower base plate through a lower connecting rod positioning ring, and the lower end of the lower connecting rod is connected to the testing machine; and the upper connecting rod and the lower connecting rod are coaxially arranged.

[0017] A test method for a biaxial tensile test of a specimen comprises the following steps:

[0018] S1: Install the upper connecting rod on the upper base plate and the lower connecting rod on the lower base plate on the testing machine respectively, so that the vertical rack and gear of each set of gear rack assembly are meshed with each other;

[0019] S2: insert the upper positioning rod into the upper positioning ring, and the position of the upper positioning rod in the upper positioning ring can be adjusted up and down, and at the same time insert the lower positioning rod into the lower positioning ring, and the lower positioning ring with the lower positioning rod inserted is detachably connected to the lower base plate, and the position of the lower positioning rod in the lower positioning ring can be adjusted up and down;

[0020] S3: placing the specimen on the clamping block, placing the four tensile fins of the specimen in the clamping grooves of the clamping block respectively, and clamping them with the clamping grooves;

[0021] S4: Adjust the adjusting screws of the gear rack assembly, and slowly move the base on the base so that the positioning groove on the upper end face of the specimen is aligned with the positioning end of the upper positioning rod, and the positioning groove on the lower end face of the specimen is aligned with the positioning end of the lower positioning rod; at the same time, adjust the heights of the upper positioning rod and the lower positioning rod until the positioning ends of the upper positioning rod and the lower positioning rod are fully inserted into the positioning grooves on both sides of the specimen respectively;

[0022] S5: Since the base moves relative to the base, the bottom of the vertical rack is connected to the base, so it will move synchronously with the base, and the upper end of the vertical rack is connected to the upper base plate, so a torque will be generated at the connection between the vertical rack and the upper base plate, causing the vertical rack to deform or bend, affecting the meshing accuracy and transmission accuracy of the vertical rack and the gear. Therefore, after adjusting the position of the base, it is necessary to adjust the fixing screws connecting the upper end of the vertical rack and the upper base plate to release the torque on the vertical rack, and then lock the vertical rack with the upper base plate through the fixing screws;

[0023] S5: insert the lower positioning rod into the bottom of the lower positioning ring, then remove the lower positioning assembly from the lower base plate, and at the same time, insert the upper positioning rod into the top of the upper positioning ring, and fix the upper positioning rod in the upper positioning ring through the locking mechanism on the side wall of the upper positioning ring;

[0024] S6: Install the reflector on the lower base plate directly below the specimen at an angle of 45° between the reflector and the lower base plate, and the reflected light of the reflector faces the camera lens;

[0025] S7: Start the testing machine, bring the upper base plate and the lower base plate closer to each other, and the vertical rack moves in the vertical direction relative to the gear, driving the gear to rotate, thereby driving the horizontal rack meshing with the gear to move outward, and applying tensile forces in two directions to the specimen simultaneously through the clamping block connected to the horizontal rack; and during the stretching process, the camera captures the strain information of the bottom surface of the specimen in real time through the reflector, and transmits the strain information to the data processing unit; at the same time, the strain gauge on the clamping block measures the stress information applied to the specimen, and transmits the stress information to the data processing unit, completing the tensile test of the specimen.

[0026] The beneficial effects of the present invention are as follows: the present invention provides a test device for a biaxial tensile test of a specimen,

[0027] (1) The upper positioning assembly and the lower positioning assembly are used to assist in positioning the specimen, thereby realizing rapid center positioning of the specimen;

[0028] (2) The test device can be used to perform the test on a universal testing machine or a compression testing machine, which reduces the requirements for the testing machine;

[0029] (3) A gear rack mechanism is used, and the upper and lower base plates are driven synchronously through relative movement to ensure that the tensile forces applied to the four tensile fins on the specimen act synchronously, thereby ensuring the consistency of movement in the four directions;

[0030] (4) A guide assembly consisting of a guide column and a guide sleeve is added between the upper base plate and the lower base plate to ensure smooth and accurate guidance during the relative movement of the upper base plate and the lower base plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0032] Figure 1 It is a schematic diagram of the three-dimensional structure of the specimen.

[0033] Figure 2 It is a schematic diagram of the bottom structure of the specimen.

[0034] Figure 3 It is a structural schematic diagram of a test device for a biaxial tensile test of a specimen according to the present invention.

[0035] Figure 4 It is a structural schematic diagram of a test device for a biaxial tensile test of a specimen according to the present invention.

[0036] Figure 5 yes Figure 4 Schematic diagram of the axial cross-section structure.

[0037] Figure 6 It is a structural diagram of the gear rack assembly.

[0038] Figure 7 It is a structural diagram of the gear rack assembly.

[0039] Figure 8 It is a structural diagram of a horizontal rack.

[0040] Fig. 9 It is a schematic diagram of the structure of the base.

[0041] Fig.10 It is a schematic diagram of the structure of the base.

[0042] Fig.11 It is a structural schematic diagram of the upper positioning rod / lower positioning rod.

[0043] Fig.12 It is a schematic diagram of the working principle of the strain acquisition component.

[0044] Fig.13 is a schematic diagram of the position of the reflector.

[0045] Fig.14 It is a schematic diagram of the dimensional relationship between the lower positioning component and the test piece.

[0046] In the figure: 1-upper positioning ring, 2-upper positioning rod, 2-1-positioning end, 3-guide column, 4-gear rack assembly, 4-1-fixing screw, 4-2-vertical rack, 4-3-connecting pin, 4-4-clamping block, 4-5-horizontal rack, 4-51-tooth surface, 4-52-connecting hole, 4-53-rack slide, 4-54-groove, 4-55-U-shaped bayonet; 4-6-rack guide rod, 4-7-fixing screw, 4-8-base, 4-9-adjusting screw; 4-10-base, 4-101-slide, 4-102-side plate support platform, 4-103-adjusting boss, 4-104-adjusting threaded hole, 4-105-side plate mounting hole, 4 -106-guide column mounting hole; 4-107-locating pin hole, 4-11-locating pin, 4-12-fixing screw, 4-13-side plate, 4-14-bearing, 4-15-gear shaft, 4-16-gear, 4-17-clamping groove; 5-test piece, 5-1-stretching fin, 5-2-connecting end, 5-3-locating groove, 5-4-clamping surface, 5-5-speckle; 6-lower locating rod, 7-guide sleeve, 8-lower locating ring, 9a-upper connecting rod, 9b-lower connecting rod, 10a-upper connecting rod locating ring, 10b-lower connecting rod locating ring, 11-lower base plate, 12-locating screw, 13-upper base plate, 14-fixing screw, 15-reflector, 16-camera. DETAILED DESCRIPTION

[0047] The present invention will now be described in detail with reference to the accompanying drawings. This figure is a simplified schematic diagram, which only illustrates the basic structure of the present invention in a schematic manner, and therefore only shows the components related to the present invention.

[0048] like Figure 1 and Figure 2 As shown, it is a schematic diagram of the structure of the specimen 5. The specimen 5 is cross-shaped and includes four stretching fins 5-1. A positioning groove 5-3 is respectively provided on the upper and lower sides of the common connection end 5-2 of the four stretching fins 5-1. The shape of the positioning groove 5-3 includes but is not limited to a circle, an ellipse, a polygon, etc., as long as it can achieve positioning in the horizontal plane and the vertical plane at the same time, that is, to achieve center positioning. In this embodiment, the positioning groove 5-3 is preferably rectangular, and the side wall is an inclined surface, which is convenient for the positioning end 2-1 on the upper positioning rod 2 and the lower positioning rod 6 to be inserted, and the side wall of the front end of the positioning end 2-1 is also an inclined surface; each stretching fin 5-1 is provided with a concave clamping surface 5-4 on both sides of the side close to the connection end 5-2, and a speckle 5-5 that can be recognized by the camera 16 is provided in the positioning groove 5-3 below the specimen 5. In the figure, F1 and F2 represent stretching in two orthogonal (mutually perpendicular) directions.

[0049] like Figure 3-Figure 5As shown, a test device for a biaxial tensile test of a specimen of the present invention comprises an upper base plate 13, a lower base plate 11, an upper positioning assembly, a lower positioning assembly, four sets of gear rack assemblies 4, a strain collection assembly and a stress collection assembly, wherein the upper base plate 13 and the lower base plate 11 are arranged in parallel up and down for supporting other components and connecting with the testing machine; the upper positioning assembly is arranged below the upper base plate 13, the lower positioning assembly is arranged above the lower base plate 11, and the upper positioning assembly and the lower positioning assembly are arranged coaxially up and down, and cooperate with each other for center positioning of the specimen 5; the four sets of gear rack assemblies The rack and pinion assembly 4 is arranged in a circular array between the upper base plate 13 and the lower base plate 11 with the axes of the upper positioning assembly and the lower positioning assembly as the center. The gear rack assembly 4 is provided with a clamping end for applying tension to the tensile fin 5-1 of the specimen 5. During the test, a bidirectional tensile force parallel to the plane where the specimen 5 is located is applied to the specimen 5 through four groups of gear rack assemblies 4; the collection end of the strain collection assembly is arranged above or below the specimen 5, and is used to collect the strain of the specimen 5; the stress collection assembly is arranged on the clamping end of the gear rack assembly 4, and is used to collect the stress applied to the specimen 5 by the clamping end.

[0050] In order to ensure the stability of the upper base plate 13 during the downward pressing process, at least one group of guide components is also included, each group of the guide components includes a guide column 3 and a guide sleeve 7, an axial guide cavity is provided in the guide sleeve 7, and the guide cavity can be a through hole opened on the guide sleeve 7, or a blind hole, one end of the guide column 3 is inserted into the guide cavity, and can move along the axial direction in the guide cavity, the other end of the guide column 3 is fixed on one of the upper base plate 13 and the lower base plate 11, and the other end of the guide sleeve 7 is fixed on the other of the upper base plate 13 and the lower base plate 11. The connection relationship between the guide column 3 and the guide sleeve 7 of the positioning component and the upper base plate 13 and the lower base plate 11 is not unique, and can be determined according to design habits and actual conditions. As a preference, there are two groups of guide components in this embodiment, which are symmetrically arranged between the upper base plate 13 and the lower base plate 11 on both sides of the test piece 5, and the guide column 3 is connected to the upper base plate 13, and the guide sleeve 7 is connected to the lower base plate 11. In order to ensure the stability of the connection between the guide column 3 and the guide sleeve 7, a first limit ring is provided at the connection between the guide column 3 and the upper base plate 13, and the first limit ring is clamped on the upper base plate 13; a second limit ring is provided at the connection between the guide sleeve 7 and the lower base plate 11, and the second limit ring is clamped on the lower base plate 11.

[0051] In order to achieve rapid positioning and connection with the testing machine, an upper connecting rod 9a is further provided above the upper base plate 13, and the upper connecting rod 9a is fixedly connected to the upper base plate 13 by an upper connecting rod positioning ring 10a and a fixing screw 14, and the upper end of the upper connecting rod 9a is connected to the testing machine; a lower connecting rod 9b is further provided below the lower base plate 11, and the lower connecting rod 9b is fixedly connected to the lower base plate 11 by a lower connecting rod positioning ring 10b and a fixing screw, and the lower end of the lower connecting rod 9b is connected to the testing machine; and the upper connecting rod 9a and the lower connecting rod 9b are coaxially arranged.

[0052] like Figure 6-Figure 10As shown, the gear rack assembly 4 includes a base 4-8, a pedestal 4-10, a gear 4-16, a vertical rack 4-2, a horizontal rack 4-5 and a clamping block 4-4, wherein the bottom of the base 4-8 is fixedly mounted in the limiting groove of the lower base plate 11 by fixing screws 4-7. In this embodiment, there are four fixing screws 4-7, and arc-shaped avoidance grooves are provided at the four corners of the limiting groove to facilitate the rectangular base 4-8 to be smoothly embedded in the limiting groove; the base 4-10 is installed at the upper end of the base 4-8, and can radially approach or move away from the central axis of the test device on the base 4-8. After the test device is installed on the testing machine, the central axes of the two coincide. A horizontal rack 4-5 mounting portion is provided at the upper end of the base 4-10, and a T-shaped slide groove 4-101 is provided on the horizontal rack 4-5 mounting portion. The extension direction of the slide groove 4-101 is parallel to the movement direction of the base 4-10. The horizontal rack 4-5 is slidably installed in the slide groove 4-101, and the rack slide 4-53 of the horizontal rack 4-5 is embedded in the T-shaped slide groove 4-101, and the tooth surface 4-51 of the horizontal rack 4-5 faces upward. In order to reduce the resistance during sliding, a groove 4-54 is provided on the bottom surface of the horizontal rack 4-5 to reduce the contact area with the slide groove 4-101 and reduce friction; the horizontal rack 4-5 is provided with a U-shaped bayonet 4-55 at one end close to the central axis, and the upper and lower side walls of the U-shaped bayonet 4-55 are provided with opposite connecting holes 4-52. The end of the clamping block 4-4 is inserted into the U-shaped bayonet 4-55, and then the connecting pin 4-3 is inserted into the connecting hole 4-52 to fix the clamping block 4-4 for clamping the specimen 5 in the U-shaped bayonet 4-55; the clamping block 4-4 is provided with a clamping groove 4-17 whose shape matches the shape of the stretching fin 5-1 of the specimen 5. Both sides of the horizontal rack mounting portion are provided with side panel support platforms 4-102 extending in the same direction as the slide groove 4-101, and a side panel 4-13 is installed on the side panel support platforms 4-102 on each side, and the side panels 4-13 on both sides are parallel to each other and sandwich the horizontal rack mounting portion in the middle, and the side panels 4-13 are provided with side panel mounting holes 4-105 for fixing the side panels 4-13 on the sides where the horizontal rack mounting portion and the side panels 4-13 are in contact, and the side panels 4-13 and the horizontal rack mounting portion are fixed by fixing screws 4-12 threadedly connected in the side panel mounting holes 4-105, and the bottom of the side panel 4-13 is supported on the side panel support platform 4-102.A locating pin 4-11 is also provided on the side panel 4-13 on one side, and a locating pin hole 4-107 is also provided between the two side panel mounting holes 4-105. When the side panel 4-13 is installed, the locating pin 4-11 is inserted into the locating pin hole 4-107, and the positioning between the base 4-10 and the side panel 4-13 can be achieved by the locating pin 4-11; the gear 4-16 is rotatably connected between the two side panels 4-13 through the gear shaft 4-15, and the two ends of the gear shaft 4-15 are rotatably connected to the side panels 4-13 through bearings 4-14 respectively, and the gear 4-16 is arranged above the horizontal rack 4-5 and meshed with the horizontal rack 4-5; a vertical rack 4-2 is provided on the side of the gear 4-16 close to the central axis, and the vertical rack 4-2 is perpendicular to the horizontal rack 4-5, and the vertical rack 4-2 is meshed with the gear 4-16; the upper end of the vertical rack 4-2 is connected to the The upper base plate 13 is connected, and the connection position with the upper base plate 13 can be adjusted; when positioning the upper and lower positioning components, the fixing screw 4-1 can be in a locked state, and the torque on the vertical rack 4-2 is released after the positioning is completed, or it can be directly loosened, and the torque is synchronously released directly during the positioning adjustment process, and then locked after the positioning is completed; the lower end is movably connected to the guide column mounting hole 4-106 on the base 4-10 through the rack guide rod 4-6, and the rack guide rod 4-6 can move up and down in the guide column mounting hole 4-106 with the vertical rack 4-2. When the vertical rack 4-2 moves up and down, the rack guide rod 4-6 plays a guiding role to ensure the vertical position of the vertical rack 4-2 in the vertical direction, thereby ensuring the accuracy of torque transmission between the gear 4-16 rack; when the vertical rack 4-2 moves downward, the horizontal rack 4-5 is driven radially away from the central axis through the gear 4-16. Thus, the vertical rack 4 - 2 is driven to move downward by the downward pressure between the upper bottom plate 13 and the lower bottom plate 11 , thereby achieving the stretching of the test piece 5 by the clamping block 4 - 4 .

[0053] It should be noted that during the use of the test device, the movement distance and stroke in the four directions must be kept consistent. Therefore, the gear 4-16 and the horizontal rack 4-5 and the vertical rack 4-2 in the gear rack assembly 4 have certain requirements for the tooth side clearance during design and assembly. The tooth side clearance requires zero side clearance or extremely small side clearance to eliminate the synchronization error of the movement distance in the four directions. In this embodiment, the preferred maximum tooth side clearance is 0.02mm.

[0054] like Figure 6 , Figure 7 , Fig. 9 and Fig.10As shown, the gear rack assembly 4 also includes an adjustment mechanism, which is used to realize the base 4-10 on the base 4-8 to move radially close to or away from the central axis of the test device. The adjustment mechanism includes a boss mounting groove (not shown in the figure) arranged on the top of the base 4-8, an adjustment boss 4-103 arranged at the bottom of the base 4-10, and an adjustment screw 4-9, wherein the adjustment boss 4-103 is arranged in the boss mounting groove, the boss mounting groove is provided with an opening facing the central axis, and the base 4-10 on the side opposite to the opening is provided with a through hole, and the adjustment screw 4-9 passes through the through hole and is threadedly connected with the adjustment threaded hole 4-104 on the adjustment boss 4-103. By rotating the adjustment screw 4-9 to rotate in the adjustment threaded hole 4-104, the movement of the adjustment boss 4-103 in the boss mounting groove is realized, so that the base 4-10 drives the components on the base 4-10 to move radially close to or away from the central axis of the test device, that is, the position of the center of the test piece 5 is adjusted. The center of the test piece 5 is located on the central axis of the testing machine, which can ensure the balance of the force applied by the testing machine to the test piece 5 and improve the precision and accuracy of the test.

[0055] like Fig.12 and Fig.13 As shown, the strain collection assembly includes a reflector 15 and a camera 16, wherein the reflector 15 is tiltedly arranged on the lower base plate 11 below the specimen 5, and the angle between the reflector 15 and the lower base plate 11 is 45°, and the camera 16 is arranged on the periphery of the reflector 15, and the camera 16 is directly facing the direction of the reflected light of the reflector 15; during the stretching process, the area with speckles 5-5 at the bottom of the specimen 5 is reflected to the camera 16 through the reflector 15, and the deformation of the specimen 5 due to the stretching is photographed by the camera 16, so as to obtain the strain of the specimen 5 during the stretching process.

[0056] In order to determine the correspondence between strain and stress, the stress collection assembly includes a strain gauge, which is attached to the clamping block 4-4 between the horizontal rack 4-5 and the clamping groove 4-17. The strain gauge collects the stress on the clamping block 4-4 acting on the specimen 5. When collecting stress and strain, the collection should be carried out at the same time, so that the performance of the material of the specimen 5 can be judged by the correspondence between stress and strain. The specific position of the strain gauge is not shown in the figure.

[0057] like Figure 2 and Fig.11As shown, in order to ensure that the center of the test piece 5 is located on the central axis of the testing machine, the upper positioning assembly includes an upper positioning ring 1 and an upper positioning rod 2. The upper end of the upper positioning ring 1 is fixed below the upper base plate 13. An upper positioning cavity is provided inside the upper positioning ring 1. The upper end of the upper positioning rod 2 is inserted into the upper positioning cavity and can move axially along the upper positioning cavity. The lower end of the upper positioning rod 2 is provided with a positioning end 2-1 that matches the shape of the positioning groove 5-3; a locking mechanism for locking the upper positioning rod 2 in the upper positioning cavity is provided on the side of the upper positioning ring 1; the locking mechanism includes a positioning screw 12 threadedly connected to the side wall of the upper positioning ring 1. When locking, the positioning screw 1 2 is screwed inwards and pressed against the upper positioning rod 2; the lower positioning assembly includes a lower positioning ring 8 and a lower positioning rod 6, the lower positioning ring 8 is detachably connected to the upper surface of the lower base plate 11, and the lower positioning ring 8 and the lower base plate 11 can be connected by threads; they can also be directly connected by plugging and pulling, and the matching accuracy between the apertures can ensure that the lower positioning ring 8 can be stably connected to the lower base plate 11 and can be easily removed; a lower positioning cavity is provided in the lower positioning ring 8, and the lower end of the lower positioning rod 6 is inserted in the lower positioning cavity and can move axially along the lower positioning cavity, and the upper end of the lower positioning rod 6 is provided with a positioning end 2-1 that matches the shape of the positioning groove 5-3.

[0058] like Fig.14 As shown, the lower positioning component meets the following conditions:

[0059] (1) In order to realize the positioning function of the lower positioning rod 6, after the top of the lower positioning rod 6 is embedded in the positioning groove 5-3 of the test piece 5, the height H1 from the top of the lower positioning rod 6 to the bottom of the lower positioning ring 8 is less than the sum of the heights of the lower positioning rod 6 and the lower positioning ring 8, that is, H1

[0060] (2) After the lower positioning rod 6 is inserted into the bottom of the lower positioning cavity, the height H3 from the top of the lower positioning rod 6 to the bottom of the lower positioning ring 8 is smaller than the height H2 from the upper surface of the lower bottom plate 11 to the lower surface of the test piece 5.

[0061] In this embodiment, the lower positioning cavity in the lower positioning ring 8 is a through hole, and therefore, H3 is also the height of the lower positioning rod 6. It should be noted that when the lower positioning cavity is a blind hole, H3 is greater than the height of the lower positioning rod 6; H2 represents the height from the lower surface of the specimen 5 to the lower base plate 11 after adjustment; H3 < H2 must be satisfied before the lower positioning rod 6 and the lower positioning ring 8 can be removed from the lower base plate 11 after adjustment.

[0062] A test method for a biaxial tensile test of a specimen comprises the following steps:

[0063] ​S1: Install the upper connecting rod 9a on the upper base plate 13 and the lower connecting rod 9b on the lower base plate 11 on the testing machine, respectively, so that the vertical rack 4-2 of each set of gear rack assembly 4 is meshed with the gear 4-16;

[0064] S2: insert the upper positioning rod 2 into the upper positioning ring 1, and the position of the upper positioning rod 2 in the upper positioning ring 1 can be adjusted up and down, and at the same time insert the lower positioning rod 6 into the lower positioning ring 8, and the lower positioning ring 8 with the lower positioning rod 6 inserted is detachably connected to the lower base plate 11, and the position of the lower positioning rod 6 in the lower positioning ring 8 can be adjusted up and down;

[0065] S3: Place the specimen 5 on the clamping block 4-4, so that the four stretched fins 5-1 of the specimen 5 are respectively placed in the clamping grooves 4-17 of the clamping block 4-4, and clamped by the clamping grooves 4-17;

[0066] S4: Adjust the adjusting screw 4-9 of the rack and pinion assembly 4, and slowly move the base 4-10 on the base 4-8 so that the positioning groove 5-3 on the upper end face of the specimen 5 is opposite to the positioning end 2-1 of the upper positioning rod 2, and the positioning groove 5-3 on the lower end face of the specimen 5 is opposite to the positioning end 2-1 of the lower positioning rod 6; at the same time, adjust the heights of the upper positioning rod 2 and the lower positioning rod 6 until the positioning ends 2-1 of the upper positioning rod 2 and the lower positioning rod 6 are fully inserted into the positioning grooves 5-3 on both sides of the specimen 5 respectively; the adjusting screw 4-9 is used to fine-tune the test device.

[0067] S5: Since the base 4-10 moves relative to the base 4-8, the bottom of the vertical rack 4-2 is connected to the base 4-10, and therefore, it will move synchronously with the base 4-10, and the upper end of the vertical rack 4-2 is connected to the upper base plate 13, therefore, a torque will be generated at the connection between the vertical rack 4-2 and the upper base plate 13, causing the vertical rack 4-2 to deform or bend, affecting the meshing accuracy and transmission accuracy of the vertical rack 4-2 and the gear 4-16. Therefore, after adjusting the position of the base 4-10, it is necessary to adjust the fixing screw 4-1 connecting the upper end of the vertical rack 4-2 and the upper base plate 13 to release the torque on the vertical rack 4-2, and then, lock the vertical rack 4-2 with the upper base plate 13 by the fixing screw 4-1;

[0068] S5: Insert the lower positioning rod 6 into the bottom of the lower positioning ring 8, then remove the lower positioning assembly from the lower base plate 11, and at the same time, insert the upper positioning rod 2 into the top of the upper positioning ring 1, and fix the upper positioning rod 2 in the upper positioning ring 1 through the locking mechanism on the side wall of the upper positioning ring 1;

[0069] S6: Install the reflector 15 obliquely on the lower base plate 11 directly below the test piece 5, and make the angle between the reflector 15 and the lower base plate 11 be 45°, so that the reflected light of the reflector 15 faces the lens of the camera 16;

[0070] S7: Start the testing machine, so that the upper base plate 13 and the lower base plate 11 are close to each other, and the vertical rack 4-2 moves in the vertical direction relative to the gear 4-16, driving the gear 4-16 to rotate, thereby driving the horizontal rack 4-5 meshing with the gear 4-16 to move outward, and the clamping block 4-4 connected to the horizontal rack 4-5 applies tensile forces in two directions to the specimen 5 at the same time; and during the stretching process, the camera 16 captures the strain information of the bottom surface of the specimen 5 in real time through the reflector 15, and transmits the strain information to the data processing unit; at the same time, the strain gauge on the clamping block 4-4 measures the stress information applied to the specimen 5, and transmits the stress information to the data processing unit, completing the tensile test of the specimen 5.

[0071] The testing machine performs the biaxial tensile test at a compression speed of less than 10 mm / min until the specimen 5 obviously yields or breaks. Preferably, the biaxial tensile test is performed at a compression speed of less than 5 mm / min. The material of the specimen 5 to be tested is determined according to the actual test parts, and the rest are made of Unimax die steel (hardness> HRC 52) to ensure rigidity.

[0072] The data processing unit may be a single chip microcomputer, a DSP, or a computer to realize data processing and storage. Since data processing is irrelevant to the technical problem solved by the present invention, it will not be described in detail here.

[0073] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the scope of the present invention through the above description. The technical scope of this invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A test device for a specimen biaxial tensile test, characterized in that: The test piece is cross-shaped and includes four stretched fins. A positioning groove is provided on the upper and lower sides of the common connection end of the four stretched fins, respectively. A concave clamping surface is provided on the two side surfaces of each stretched fin close to the connection end. A speckle that can be recognized by a camera is provided in the positioning groove below the test piece. The testing device comprises an upper base plate, a lower base plate, an upper positioning assembly, a lower positioning assembly, four gear rack assemblies, a strain collection assembly and a stress collection assembly, wherein the upper base plate and the lower base plate are arranged in parallel up and down for supporting other assemblies and connecting with the testing machine; the upper positioning assembly is arranged below the upper base plate, the lower positioning assembly is arranged above the lower base plate, and the upper positioning assembly and the lower positioning assembly are arranged coaxially up and down, and cooperate with each other for center positioning of the specimen; the four gear rack assemblies are arranged in an annular array between the upper base plate and the lower base plate with the axis of the upper positioning assembly and the lower positioning assembly as the center, and the gear rack assembly is provided with a clamping end for applying tension to the tensile fin of the specimen. During the test, a bidirectional tensile force parallel to the plane where the specimen is located is applied to the specimen through the four gear rack assemblies; the collection end of the strain collection assembly is arranged above or below the specimen for collecting the strain of the specimen; the stress collection assembly is arranged on the clamping end of the gear rack assembly for collecting the stress applied to the specimen by the clamping end; The upper positioning assembly comprises an upper positioning ring and an upper positioning rod, the upper end of the upper positioning ring is fixed below the upper base plate, an upper positioning cavity is provided inside the upper positioning ring, the upper end of the upper positioning rod is inserted into the upper positioning cavity and can move axially along the upper positioning cavity, and the lower end of the upper positioning rod is provided with a positioning end matching the shape of the positioning groove; a locking mechanism for locking the upper positioning rod in the upper positioning cavity is provided on the side of the upper positioning ring; The lower positioning assembly includes a lower positioning ring and a lower positioning rod. The lower positioning ring is detachably connected to the upper surface of the lower base plate. A lower positioning cavity is provided in the lower positioning ring. The lower end of the lower positioning rod is inserted in the lower positioning cavity and can move axially along the lower positioning cavity. The upper end of the lower positioning rod is provided with a positioning end that matches the shape of the positioning groove.

2. The test device for the biaxial tensile test of a specimen according to claim 1, characterized in that: The gear rack assembly comprises a base, a pedestal, a gear, a vertical rack, a horizontal rack and a clamping block, wherein the base is fixedly mounted on the lower bottom plate, the base is mounted on the upper end of the base and can radially approach or move away from the central axis of the test device on the base, a horizontal rack mounting portion is provided at the upper end of the base, a T-shaped slide groove is provided on the horizontal rack mounting portion, the extension direction of the slide groove is parallel to the movement direction of the base, the horizontal rack is slidably mounted in the slide groove, and the tooth surface of the horizontal rack faces upward, one end of the horizontal rack close to the central axis is fixedly connected to the clamping block for clamping the specimen, and the clamping block is provided with a clamping groove whose shape matches the shape of the tensile fin of the specimen; both sides of the horizontal rack mounting portion are provided with A side panel support platform extending in the same direction of the slide groove, a side panel is installed on the side panel support platform on each side, the gear is rotatably connected between the two side panels through a gear shaft, and the gear is arranged above the horizontal rack and meshes with the horizontal rack; a vertical rack is provided on the side of the gear close to the central axis, the vertical rack and the horizontal rack are perpendicular to each other, and the vertical rack meshes with the gear; the upper end of the vertical rack is connected to the upper base plate by a fixing screw, and the connection position with the upper base plate can be adjusted; the lower end is movably connected to the guide column mounting hole on the base through a rack guide rod, and the rack guide rod can move up and down in the guide column mounting hole together with the vertical rack; when the vertical rack moves downward, the horizontal rack is driven radially away from the central axis through the gear.

3. The test device for the biaxial tensile test of a specimen according to claim 2, characterized in that: It also includes an adjustment mechanism, which is used to enable the base to move radially closer to or farther away from the central axis of the test device on the base. The adjustment mechanism includes a boss mounting groove arranged on the top of the base, an adjustment boss arranged at the bottom of the base, and an adjustment screw. The adjustment boss is arranged in the boss mounting groove, and the boss mounting groove is provided with an opening facing the central axis. A through hole is provided on the base on the side facing away from the opening, and the adjustment screw passes through the through hole and is threadedly connected to the adjustment boss in the boss mounting groove.

4. The test device for the biaxial tensile test of a specimen according to claim 1, characterized in that: The strain collection assembly includes a reflector and a camera. The reflector is tilted on the lower base plate below the specimen, and the angle between the reflector and the lower base plate is 45°. The camera is arranged on the periphery of the reflector, and the camera faces the direction of the reflected light of the reflector.

5. The test device for the biaxial tensile test of a specimen according to claim 1, characterized in that: The stress collection component includes a strain gauge, which is attached to a clamping block between a horizontal rack and a clamping groove, and collects stress on the clamping block acting on the test piece.

6. The test device for the biaxial tensile test of a specimen according to claim 1, characterized in that: The lower positioning assembly meets the following conditions: (1) After the top of the lower positioning rod is embedded in the positioning groove of the specimen, the height H1 from the top of the lower positioning rod to the bottom of the lower positioning ring is less than the sum of the heights of the lower positioning rod and the lower positioning ring, that is, H1<h1+h2, where h1 is the height of the lower positioning rod and h2 is the height of the lower positioning ring; (2) After the lower positioning rod is inserted into the bottom of the lower positioning cavity, the height H3 from the top of the lower positioning rod to the bottom of the lower positioning ring is less than the height H2 from the upper surface of the lower bottom plate to the lower surface of the test piece.

7. The test device for the biaxial tensile test of a specimen according to claim 1, characterized in that: It also includes at least one group of guide components, each group of guide components includes a guide column and a guide sleeve, an axial guide cavity is provided in the guide sleeve, one end of the guide column is inserted into the guide cavity, and can move along the axial direction in the guide cavity, the other end of the guide column is fixed on one of the upper base plate and the lower base plate, and the other end of the guide sleeve is fixed on the other of the upper base plate and the lower base plate.

8. The test device for the biaxial tensile test of a specimen according to claim 7, characterized in that: A first limiting ring is provided at the connection between the guide column and the upper base plate or the lower base plate, and the first limiting ring is clamped on the upper base plate or the lower base plate; And / or a second limiting ring is provided at the connection between the guide sleeve and the upper base plate or the lower base plate, and the second limiting ring is clamped on the upper base plate or the lower base plate.

9. The test device for a specimen biaxial tensile test according to claim 1, characterized in that: An upper connecting rod is also provided above the upper base plate, and the upper connecting rod is fixedly connected to the upper base plate through an upper connecting rod positioning ring, and the upper end of the upper connecting rod is connected to the testing machine; A lower connecting rod is also provided below the lower base plate. The lower connecting rod is fixedly connected to the lower base plate through a lower connecting rod positioning ring, and the lower end of the lower connecting rod is connected to the testing machine; and the upper connecting rod is coaxially arranged with the lower connecting rod.

10. A test method for a specimen biaxial tensile test, characterized in that: The test device for the biaxial tensile test of a specimen according to any one of claims 1 to 9 further comprises the following steps: S1: Install the upper connecting rod on the upper base plate and the lower connecting rod on the lower base plate on the testing machine respectively, so that the vertical rack and gear of each set of gear rack assembly are meshed with each other; S2: insert the upper positioning rod into the upper positioning ring, and the position of the upper positioning rod in the upper positioning ring can be adjusted up and down, and at the same time insert the lower positioning rod into the lower positioning ring, and the lower positioning ring with the lower positioning rod inserted is detachably connected to the lower base plate, and the position of the lower positioning rod in the lower positioning ring can be adjusted up and down; S3: placing the specimen on the clamping block, placing the four tensile fins of the specimen in the clamping grooves of the clamping block respectively, and clamping them with the clamping grooves; S4: Adjust the adjusting screws of the gear rack assembly, and slowly move the base on the base so that the positioning groove on the upper end face of the specimen is aligned with the positioning end of the upper positioning rod, and the positioning groove on the lower end face of the specimen is aligned with the positioning end of the lower positioning rod; at the same time, adjust the heights of the upper positioning rod and the lower positioning rod until the positioning ends of the upper positioning rod and the lower positioning rod are fully inserted into the positioning grooves on both sides of the specimen respectively; S5: Adjust the fixing screws connecting the upper end of the vertical rack and the upper base plate to release the torque on the vertical rack, and then lock the vertical rack and the upper base plate with the fixing screws; S6: insert the lower positioning rod into the bottom of the lower positioning ring, then remove the lower positioning assembly from the lower base plate, and at the same time, insert the upper positioning rod into the top of the upper positioning ring, and fix the upper positioning rod in the upper positioning ring through the locking mechanism on the side wall of the upper positioning ring; S7: Install the reflector on the lower base plate directly below the specimen at an angle of 45°, and the reflected light of the reflector faces the camera lens; S8: Start the testing machine, make the upper base plate and the lower base plate approach each other, and the vertical rack moves in the vertical direction relative to the gear, driving the gear to rotate, thereby driving the horizontal rack meshing with the gear to move outward, and applying tensile forces in two directions to the specimen at the same time through the clamping block connected to the horizontal rack; and during the stretching process, the camera captures the strain information of the bottom surface of the specimen in real time through the reflector, and transmits the strain information to the data processing unit; at the same time, the strain gauge on the clamping block measures the stress information applied to the specimen, and transmits the stress information to the data processing unit, completing the tensile test of the specimen.

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