Uniaxial stretching dog bone test piece as well as matched clamp and mold

Abstract

The utility model discloses a uniaxial stretching dog bone test piece and a matched clamp and mold, and belongs to the technical field of strength test methods and the application field of cement-based building materials. The dog bone test piece is uniaxially stretched, the total length of the dog bone test piece is constant, and a stretching section is located in the middle of the dog bone test piece; the left side of the stretching section is connected with a first transition section, and the right side of the stretching section is connected with a second transition section; the left side of the first transition section is connected with a first fixed section, and the right side of the second transition section is connected with a second fixed section; an included angle theta is formed between the extension line of the stretching section and the first transition section or between the extension line of the stretching section and the second transition section, and the range of the included angle theta is 8-15 degrees. Compared with a traditional test piece, the dog bone test piece has the advantages that the length of the transition section is increased, and the length of the fixed section is reduced, so that the included angle between the transition section and the tensile section is reduced, the stress concentration phenomenon of the test piece in a tensile test is reduced, and the accuracy of a test result is improved.

Description

Technical Field

[0001] The utility model discloses a uniaxial tensile dog bone test piece and a matching fixture and a mold, and relates to the technical field of strength test methods and the application field of cement-based building materials. Background Art

[0002] In the strength test of cement-based building materials, in order to obtain the tensile strength of concrete materials, the commonly used method is uniaxial tensile test, which can also obtain the stress-strain relationship. There are many shapes of specimens for uniaxial tests, mainly dog-bone, cylinder, prism, etc. In the actual test process, it is easy to have the problem of stress misalignment or it is difficult to control the tensile force line to completely overlap with the specimen axis when biting the steel bars / aluminum sheets at both ends; secondly, it is easy to cause steel bar slippage during the stretching process. Once steel bar slippage occurs, it will seriously affect the tensile strain test results and even damage the specimen.

[0003] The shape and size of the specimen have a great influence on the success rate of the test. At present, the shape and size of the specimen are not uniform. Considering the different factors of the test, the dog bone specimen is widely recognized. The dog bone specimen commonly used in traditional test methods, such as Figure 1 As shown, the dog-bone specimen is symmetrical along the axial and radial directions, including a tensile section with a smaller width in the middle, a transition section, and fixed sections with a larger width at both ends of the transition section, wherein the angle formed between the transition section and the fixed end is 21°. The area between the two fixed parts is trapezoidal. Due to the sudden change in the cross section, when the dog-bone specimen is subjected to a tensile test, a large stress concentration phenomenon is likely to occur at the connection between the tensile section and the fixed section. The short uniform stress section leads to the failure of the tensile test, and the success rate of the test cannot be guaranteed. In addition, the production of the relevant mold has certain processing difficulties due to the short transition section and large chamfer.

[0004] The related fixtures are another major factor affecting the success rate of the experiment. Some existing instrument manufacturers provide wedge-shaped fixtures that use the bevel locking principle. To ensure versatility, the clamping surface is very wide. Although the specimen is fixed in the up and down directions, it can still move in the front, back, left and right directions. It is easy to be disturbed and eccentric. The angle between the transition section and the stretching section is too large, which causes the chuck to move during the bite, which is easy to damage the specimen, resulting in stress concentration. Most of the existing fixture clamping points are metal contacts, which can easily cause the specimen to break and crack during the test operation, which in turn causes stress concentration and damage to the specimen, affecting the success rate of the test. Utility Model Content

[0005] In view of the shortcomings of the prior art, the utility model proposes a uniaxial tensile dog-bone specimen and a matching fixture and mold to solve the problems of specimen eccentricity and stress concentration, in which the action line and the specimen axis are easily offset and cannot be aligned during the stretching process, and the specimen breaks prematurely due to excessive local stress at the contact point with the fixture.

[0006] In order to solve the above technical problems, the technical solution of the utility model is as follows:

[0007] Uniaxial tension dog bone specimen, the total length of the constant dog bone specimen a remains unchanged, such as Figure 2 As shown, the stretching section 5 is located in the middle of the dog-bone specimen a; the first transition section 6-1 is connected to the left side of the stretching section 5, and the second transition section 6-2 is connected to the right side of the stretching section 5. The first transition section 6-1 and the second transition section 6-2 on the left and right sides of the stretching section 5 are of the same length and are symmetrically distributed along the longitudinal center line; the first fixed section 7-1 is connected to the left side of the first transition section 6-1, and the second fixed section 7-2 is connected to the right side of the second transition section 6-2. The first fixed section 7-1 and the second fixed section 7-2 are of the same length and are symmetrically distributed along the longitudinal center line of the stretching section 5; an angle θ is formed between the extension line of the stretching section 5 and the first transition section 6-1 or between the extension line of the stretching section 5 and the second transition section 6-2. The size of the angle θ is adjusted by simultaneously adjusting the lengths of the first transition section 6-1 and the second transition section 6-2 and simultaneously adjusting the lengths of the first fixed section 7-1 and the second fixed section 7-2, wherein the range of the angle θ is 8° to 15°.

[0008] Uniaxial tension dog bone specimen supporting fixture, such as Figure 3 to Figure 5 As shown, it includes an upper splint 9 and a lower splint 12, both of which are square steel plates of the same size, and the upper splint 9 and the lower splint 12 are symmetrically distributed along the transverse center line; a circular through hole 14 is opened in the middle position of the top of the upper splint 9, and the upper splint 9 and the threaded pull rod 13 are hinged by a pin passing through the circular through hole 14; two positioning blocks 11 are fixedly installed at the lower end of the circular through hole 14, and the two positioning blocks 11 are symmetrically distributed along the longitudinal center line of the upper splint 9; a rubber fixing plate 10 is installed below the circular through hole 14 and above the two positioning blocks 11, and a rubber fixing plate 10 is also installed below the two positioning blocks 11.

[0009] A circular through hole 14 is opened in the middle position of the bottom of the lower clamping plate 12, and the lower clamping plate 12 and the threaded pull rod 13 are hinged by a pin passing through the circular through hole 14; two positioning blocks 11 are fixedly installed at the upper end of the circular through hole 14, and the two positioning blocks 11 are symmetrically distributed along the longitudinal center line of the lower clamping plate 12; a rubber fixing plate 10 is installed above the circular through hole 14 and below the two positioning blocks 11, and a rubber fixing plate 10 is also installed above the two positioning blocks 11.

[0010] Uniaxial tensile dog bone specimen matching mold, such as Figure 6 to Figure 8As shown, it includes a base plate 17 and a cover plate 15; 4 threaded holes 17-1 are evenly distributed on the base plate 17; a cover plate 15 is arranged on the base plate 17, and a cast through groove 18 is arranged inside the cover plate 15; the cover plate 15 comprises two L-shaped cover plate assemblies 16, and a threaded through hole 16-5 opposite to the threaded hole 17-1 on the base plate 17 is arranged on the surface of the L-shaped cover plate assembly 16; a protrusion block 16-4 is arranged at the tail of the inner side surface of the long side of the L-shaped cover plate assembly 16, and a first threaded through hole 16-1 is arranged on the right side of the protrusion block 16-4; a groove 16-3 is arranged at the cross-sectional joint surface of the short side of the L-shaped cover plate assembly 16, and a first threaded hole 16-2 is arranged on the left side of the groove 16-3, and the groove 16-3 and the first threaded hole 16-2 are matched with the protrusion block 16-4 and the first threaded through hole 16-1 arranged at the tail of the long side of the L-shaped cover plate assembly 16.

[0011] The utility model has achieved the expected technical effects: 1. The uniaxial tensile dog-bone specimen and the matching fixture and mold provided by the utility model are suitable for direct tensile tests of cement-based building materials such as concrete, mortar and ECC. Figure 2 As shown, when the total length of the dog-bone specimen a remains unchanged, by simultaneously reducing the lengths of the first fixed section 7-1 and the second fixed section 7-2 at both ends of the dog-bone specimen a and increasing the lengths of the first transition section 6-1 and the second transition section 6-2, the included angle θ formed between the extension line of the stretching section 5 and the first transition section 6-1 or between the extension line of the stretching section 5 and the second transition section 6-2 is reduced. Compared with the prior art, the included angle θ is reduced from the original 21° to 9°, which greatly reduces the stress concentration phenomenon at the first fixed section 7-1 and the second fixed section 7-2 fixed by the matching fixture, thereby improving the success rate of the test; the matching fixture of the uniaxial tension dog-bone specimen adopts a rubber fixing plate 10, as shown in FIG. Figure 3 As shown, on the one hand, the damage to the dog-bone specimen a caused by the contact between the upper clamping plate 9 and the lower clamping plate 12 made of metal and the dog-bone specimen a can be reduced, and the stress concentration phenomenon caused by the contact of the metal contacts can be significantly reduced, which can effectively ensure that the specimen breaks in the tensile section 5; on the other hand, the problem that the dog-bone specimen a is not easy to fit with the matching fixture is overcome, wherein the threaded pull rod 13 can be clamped by the universal testing machine, and can automatically adjust the force direction during the test and keep it in a coincident state with the axis of the dog-bone specimen a, allowing the threaded pull rod 13 undergoes minor deformation during repeated use; at the same time, the rubber fixing plate 10 can avoid the destruction of the dog-bone specimen a caused by the extrusion force during stretching, so that the stress is better transmitted to the stretching section 5 of the dog-bone specimen a, thereby better controlling the tensile fracture position of the dog-bone specimen a within the length range of the stretching section 5, thereby improving the accuracy and reliability of the test; the mold of the uniaxial tensile dog-bone specimen adopts a combination of a bottom plate 17 and a cover plate 15, and the cover plate 15 is assembled by two detachable L-shaped cover plate assemblies 16, such as Figure 6 to Figure 8As shown, the shape of the casting groove 18 is exactly the same as that of the dog-bone specimen a, so that the preparation operation of the dog-bone specimen a is simple and the casting is convenient; the cover plate 15 includes two L-shaped cover plate assemblies 16, and the shapes and structures of the two L-shaped cover plate assemblies 16 are exactly the same. The cover plate 15 with a split design is convenient for demoulding the dog-bone specimen a from the cover plate 15 after solidification, reducing the damage to the dog-bone specimen a during demoulding and reducing the production cost. Through the mutual cooperation of the protruding block 16-4 and the groove 16-3, the two L-shaped cover plate assemblies 16 can be accurately positioned during the splicing of the long side and the short side to form a complete cover plate 15, while also reducing the assembly deviation caused by the positioning error during the splicing process.

[0012] 2. The technical effects achieved by this utility model can be verified by experiments. The experimental items are as follows:

[0013] When the total length and width of the dog-bone specimen a are constant, the lengths of the first transition section 6-1, the second transition section 6-2, the first fixed section 7-1 and the second fixed section 7-2 are adjusted to prepare the following dog-bone specimen a:

[0014]

[0015] The dog-bone specimen a made by the matching mold is installed in the matching fixture and subjected to a tensile test. The dog-bone specimens 1, 2 and 3 of the utility model are tested and analyzed, and the data are as follows:

[0016] Dog bone specimen σv(MPa) σm(MPa) Concentration Factor 1 2.703 3.19 1.18 2 2.005 2.117 1.05 3 2.868 3.47 1.21

[0017] It can be seen from the data that as the angle θ decreases, the maximum stress value appears more obviously in the tensile section 5, and when the angle is 9°, the uniformly distributed stress value σv of the tensile section 5 is the smallest compared with the maximum stress concentration value σm, and the concentration coefficient is the smallest, which can significantly reduce the stress concentration phenomenon in the tensile section 5, making the probability of the fracture surface occurring in the tensile section higher and the test success rate higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a front view schematic diagram of a dog-bone test piece in the background technology of the present utility model.

[0019] Figure 2 This is a schematic front view of the uniaxial tension dog-bone specimen of the present invention, and this figure also serves as an abstract drawing.

[0020] Figure 3 It is a three-dimensional schematic diagram of the overall structure of the fixture for the uniaxial tension dog-bone specimen of the present invention.

[0021] Figure 4 It is a structural schematic diagram of the upper splint of the utility model.

[0022] Figure 5 The utility model is a three-dimensional schematic diagram of the overall structure of the uniaxial tension dog-bone specimen and its matching fixture when in use.

[0023] Figure 6 It is a structural schematic diagram of a mold base plate supporting a uniaxial tensile dog-bone specimen of the utility model.

[0024] Figure 7 It is a structural schematic diagram of a mold cover plate and an L-shaped cover plate assembly of a uniaxial tensile dog-bone specimen of the present invention.

[0025] Figure 8 It is a schematic cross-sectional structure diagram of a matching mold for a uniaxial tensile dog-bone specimen of the present invention. DETAILED DESCRIPTION

[0026] The utility model needs to be further limited as follows.

[0027] The first fixed section 7 - 1 is connected to the left side of the first transition section 6 - 1 , and the second fixed section 7 - 2 is connected to the right side of the second transition section 6 - 2 . The widths of the first fixed section 7 - 1 and the second fixed section 7 - 2 are both greater than the width of the stretching section 5 .

[0028] The included angle θ formed between the extension line of the stretching section 5 and the first transition section 6 - 1 or between the extension line of the stretching section 5 and the second transition section 6 - 2 is 9°.

[0029] During the test, the dog-bone specimen a is installed in the positioning blocks 11 of the upper and lower clamping plates, and its first fixing section 7-1 is just completely exposed to the top of the two positioning blocks 11 in the upper clamping plate 9, and the second fixing section 7-2 is just completely exposed to the bottom of the two positioning blocks 11 in the lower clamping plate 12, and the rubber fixing plate 10 is placed on the outer surface of the first fixing section 7-1, and the rubber fixing plate 10 is fastened to the upper clamping plate 9 by bolts, and the dog-bone specimen a is clamped and fixed by the mutual cooperation between the positioning blocks 11, the rubber fixing plate 10 and the upper clamping plate 9. During the test, the installation and fixing method of the dog-bone specimen a on the lower clamping plate 12 is the same as that on the upper clamping plate 9, which will not be repeated here.

[0030] The bottom ends of the two positioning blocks 11 in the upper clamping plate 9 are inclined inward, and the angle formed by the positioning block 11 and the longitudinal center line is consistent with the angle θ formed between the extension line of the stretching section 5 and the first transition section 6-1 or the extension line of the stretching section 5 and the second transition section 6-2.

[0031] The top ends of the two positioning blocks 11 in the lower clamping plate 12 are both inclined inwards, and the angle formed by the positioning blocks 11 and the longitudinal center line is consistent with the angle θ formed between the extension line of the stretching section 5 and the first transition section 6-1 or between the extension line of the stretching section 5 and the second transition section 6-2.

[0032] The bottom plate 17 is a flat plate, and the bottom plate 17 and the cover plate 15 are fastened by bolts.

[0033] The two L-shaped cover plate assemblies are positioned using the protruding block 16 - 4 and the groove 16 - 3 , and the two L-shaped cover plate assemblies 16 are fastened and connected to form the cover plate 15 .

[0034] The two L-shaped cover plate assemblies 16 are assembled into the cover plate 15 by bolts, bonding or by putting a locking ring matching the shape of the outer side of the cover plate 15 on the two L-shaped cover plate assemblies 16 .

[0035] The length, width and depth of the casting through slot 18 are the same as those of the dog-bone specimen a.

Claims

1. Uniaxial tension dog bone specimen, constant dog bone specimen (a) has a constant total length, characterized in that: The stretching section (5) is located in the middle of the dog bone specimen (a); the first transition section (6-1) is connected to the left side of the stretching section (5), and the second transition section (6-2) is connected to the right side of the stretching section (5); the first transition section (6-1) and the second transition section (6-2) on the left and right sides of the stretching section (5) are of the same length and are symmetrically distributed along the longitudinal center line; the first fixed section (7-1) is connected to the left side of the first transition section (6-1), and the second fixed section (7-2) is connected to the right side of the second transition section (6-2); the first fixed section (7 -1) and the second fixed section (7-2) are of the same length and are symmetrically distributed along the longitudinal center line of the stretching section (5); an angle (θ) is formed between an extension line of the stretching section (5) and the first transition section (6-1) or an extension line of the stretching section (5) and the second transition section (6-2); the angle (θ) is adjusted by simultaneously adjusting the length of the first transition section (6-1) and the second transition section (6-2) and simultaneously adjusting the length of the first fixed section (7-1) and the second fixed section (7-2), wherein the range of the angle (θ) is 8° to 15°.

2. The uniaxial tension dog-bone specimen according to claim 1, characterized in that: The included angle (θ) is 9°.

3. Uniaxial tension dog bone specimen supporting fixture, characterized in that: It comprises an upper clamping plate (9) and a lower clamping plate (12), both of which are square steel plates of the same size, and are symmetrically distributed along the transverse center line; a circular through hole (14) is provided at the middle position of the top of the upper clamping plate (9), and the upper clamping plate (9) and the threaded pull rod (13) are hinged by a pin passing through the circular through hole (14); two positioning blocks (11) are fixedly installed at the lower end of the circular through hole (14), and the two positioning blocks (11) are symmetrically distributed along the longitudinal center line of the upper clamping plate (9); a rubber fixing plate (10) is installed below the circular through hole (14) and above the two positioning blocks (11), and a rubber fixing plate (10) is also installed below the two positioning blocks (11); A circular through hole (14) is provided at the middle position of the bottom of the lower clamping plate (12), and the lower clamping plate (12) and the threaded pull rod (13) are hingedly connected by a pin passing through the circular through hole (14); two positioning blocks (11) are fixedly installed at the upper end of the circular through hole (14), and the two positioning blocks (11) are symmetrically distributed along the longitudinal center line of the lower clamping plate (12); a rubber fixing plate (10) is installed above the circular through hole (14) and below the two positioning blocks (11), and a rubber fixing plate (10) is also installed above the two positioning blocks (11).

4. The uniaxial tension dog-bone specimen supporting fixture according to claim 3, characterized in that: The bottom ends of the two positioning blocks (11) in the upper clamping plate (9) are both inclined inwardly, and the angle formed by the positioning blocks (11) and the longitudinal center line is consistent with the angle (θ) formed between the extension line of the stretching section (5) and the first transition section (6-1) or the extension line of the stretching section (5) and the second transition section (6-2).

5. The uniaxial tension dog-bone specimen supporting fixture according to claim 3, characterized in that: The top ends of the two positioning blocks (11) in the lower clamping plate (12) are both inclined inwards, and the angle formed by the positioning blocks (11) and the longitudinal center line is consistent with the angle (θ) formed by the extension line of the stretching section (5) and the first transition section (6-1) or the extension line of the stretching section (5) and the second transition section (6-2).

6. The matching mold for uniaxial tensile dog-bone specimen is characterized by: The invention comprises a bottom plate (17) and a cover plate (15); four threaded holes (17-1) are evenly distributed on the bottom plate (17); a cover plate (15) is arranged on the bottom plate (17); a casting through groove (18) is arranged inside the cover plate (15); the shape of the casting through groove (18) is completely the same as the shape of the dog bone specimen (a); the cover plate (15) comprises two L-shaped cover plate assemblies (16); threaded through holes (16-5) are arranged on the surface of the L-shaped cover plate assemblies (16) and are opposite to the threaded holes (17-1) on the bottom plate (17); A protruding block (16-4) is provided at the tail of the inner side surface of the long side of the component (16), and a first threaded through hole (16-1) is provided on the right side of the protruding block (16-4); a groove (16-3) is provided at the cross-sectional joint surface of the short side of the L-shaped cover component (16), and a first threaded hole (16-2) is provided on the left side of the groove (16-3), and the groove (16-3) and the first threaded hole (16-2) are matched with the protruding block (16-4) and the first threaded through hole (16-1) provided at the tail of the long side of the L-shaped cover component (16).

7. The uniaxial tension dog-bone specimen matching mold according to claim 6, characterized in that: The two L-shaped cover plate assemblies (16) are positioned using the protruding blocks (16-4) and the grooves (16-3), and the two L-shaped cover plate assemblies (16) are fastened and connected to form a cover plate (15).

8. The uniaxial tension dog-bone specimen matching mold according to claim 6, characterized in that: The two L-shaped cover plate assemblies (16) are assembled into a cover plate (15) by bolting, bonding or by putting a locking ring matching the shape of the outer side of the cover plate (15) on the two L-shaped cover plate assemblies (16).

9. The uniaxial tension dog-bone specimen matching mold according to claim 6, characterized in that: The length, width and depth of the casting slot (18) are the same as those of the dog bone specimen (a).

Images