Device and method for measuring tensile strength of small-size test piece

Abstract

The invention discloses a device and a method for measuring the tensile strength of a small-size test piece. The device comprises an upper clamp, a limiting guide rail, a lower clamp, a connecting sleeve, a connecting rod, an auxiliary tool and a baffle, the upper clamp and the lower clamp are connected through the limiting guide rail, and the combination face is provided with an arc-shaped groove in mirror symmetry. And the lower clamp, the connecting rod and the connecting sleeve form a ball sleeve structure for ensuring load centering. The method comprises the following steps: spraying black and white speckles on a test piece; standing the prepared test piece in the arc-shaped groove of the lower clamp by utilizing auxiliary work, and adjusting the upper clamp until the groove is in contact with the test piece; removing the auxiliary tool, debugging the DIC, and loosening the connecting sleeve; applying a pressing load until the test piece is damaged; analyzing and processing data, and calculating the tensile strength of the test piece. The centering device solves the problem of centering of small-size test pieces when loads are applied, is simple in structure, facilitates collection of damaged test pieces and facilitates follow-up fracture analysis.

Description

Technical Field

[0001] The present application relates to the field of material mechanical property testing, and in particular to a device and method for measuring the tensile strength of a small-sized test piece. Background Art

[0002] Tensile strength reflects the maximum ability of a material to resist tensile failure and is one of the important mechanical properties of a material. At present, the main testing methods for tensile strength are axial tension, bending and Brazilian splitting. The axial tension method has high accuracy and is a direct measurement method, but it requires a large test piece and complex preparation. It is generally used for tensile tests on plastic materials and is not suitable for brittle small-sized metal rings. The bending method uses three-point bending or four-point bending to apply a bending failure load to the test piece. The tensile strength of the material is obtained by analyzing the failure load of the test piece. The test piece is generally a round bar or a rectangular structure. The Brazilian splitting method applies radial pressure to generate tensile stress along the loading surface of the test piece. The tensile strength of the material is obtained by analyzing the failure load. The test piece is generally a cylinder. The eccentricity of the applied load has a great influence on the test results, and may even obtain erroneous test results.

[0003] Existing mechanical property testing methods cannot meet the tensile strength testing requirements of small-sized test pieces. Some brittle material test pieces, such as metal hydride structural parts, are difficult to process into standard-sized test pieces due to their special material structure and complex processing technology. On existing test fixtures, it is very difficult to assemble small-sized test pieces, and it is difficult to ensure good centering, which has a great impact on the test results. Therefore, it is of great significance to obtain a tensile strength measurement device and method for small-sized test pieces. Summary of the invention

[0004] In view of this, an object of the present invention is to provide a small-sized test piece tensile strength measurement device and method for carrying out a tensile strength test of a small-sized test piece.

[0005] The present invention adopts the following technical solution:

[0006] A device for measuring the tensile strength of a small-sized test piece, the device comprising an upper fixture, a limit guide rail, a lower fixture, a connecting sleeve, a connecting rod, an auxiliary tooling and a baffle, the upper end of the upper fixture is connected to a material testing machine, a groove is provided at the midline of the lower end surface, the limit guide rail constrains the upper fixture to move along the limit guide rail, the lower end of the limit guide rail is connected to the lower fixture, a groove is provided at the midline of the upper end surface of the lower fixture, and the connecting rod is assembled with the lower end of the lower fixture through the connecting sleeve to form a ball sleeve structure.

[0007] Furthermore, the plane size of the upper clamp is smaller than the plane size formed by the continuous center lines of the upper limit guide rail mounting holes of the lower clamp.

[0008] Furthermore, grooves with a radius consistent with the radius of the limiting guide rail are processed on the four corners of the upper fixture plane, and form a limiting structure with the limiting guide rail.

[0009] Furthermore, the grooves on the lower end surface of the upper clamp and the upper end surface of the lower clamp are distributed in mirror symmetry.

[0010] Furthermore, the groove is processed according to the size of the test piece.

[0011] Furthermore, the ball sleeve structure formed by assembling the connecting rod, the connecting sleeve and the lower end of the lower clamp can adjust the movable angle and tightness through the connecting sleeve.

[0012] Furthermore, the limiting guide rail and the upper end surface of the lower clamp are provided with grooves for installing the baffle.

[0013] Furthermore, the auxiliary tooling is of clip-type, with two symmetrical pieces, and a groove is provided in the middle of the symmetrical surfaces.

[0014] A method for measuring the tensile strength of a small-sized test piece, the method comprising the following steps:

[0015] (1) preparing a test piece, and uniformly spraying black and white speckles on the surface of the test piece;

[0016] (2) Tighten the connecting sleeve to tighten the ball sleeve structure, then place the device in the material testing machine and clamp the upper and lower ends with the material testing machine;

[0017] (3) Place the test piece in the groove of the auxiliary fixture, clamp the auxiliary fixture, and stand the test piece in the middle of the groove of the lower fixture;

[0018] (4) Control the material testing machine to move the upper fixture downward until it is about to contact the test piece. At this time, the test piece is located between the grooves of the upper fixture and the lower fixture, and a baffle is inserted into the groove of the limit guide rail;

[0019] (5) Remove the auxiliary tooling that fixes the test piece and place the DIC camera;

[0020] (6) Completely loosen the connecting sleeve;

[0021] (7) The material testing machine applies a downward pressure load to the upper clamp to complete the tensile strength test of the test piece. After the test piece is destroyed, the loading is terminated;

[0022] (8) Analyze and process the collected data and calculate the tensile strength of the test piece.

[0023] A small-size test piece tensile strength measurement device and method of the present invention can obtain the effective tensile strength of the small-size test piece, is not restricted by the size of the test piece, is particularly suitable for small-size test pieces that cannot be measured by traditional methods, and aims to obtain the tensile strength of the test piece, which helps to better understand the properties of the test piece.

[0024] In view of the deficiencies and defects in the prior art, the present invention provides a device for measuring the tensile strength of a small-sized test piece, which solves the problem of centering the load applied to the small-sized test piece.

[0025] The arc of the arc groove designed in the present invention is designed according to the diameter of the test piece to ensure that the test piece undergoes tensile rupture and avoids yield fracture.

[0026] The invention has a simple structure and utilizes an ingenious baffle installation to facilitate the collection of the destroyed test pieces and facilitate subsequent fracture analysis.

[0027] The invention is easy to operate, and can obtain the deformation amount of the test piece through DIC and assist in judging the fracture mode of the test piece. Combined with the calculation formula, the tensile strength of the test piece can be obtained more accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of a device for measuring the tensile strength of a small-sized test piece according to an embodiment of the present invention; Figure 2 It is a schematic diagram of the assembly of the lower clamp, the spherical connecting rod and the connecting sleeve according to an embodiment of the present invention; Figure 3 The following is a schematic diagram of the assembly of the upper fixture, the test piece, the auxiliary tooling and the lower fixture of the embodiment of the present invention: 1-upper fixture, 2-limiting guide rail, 3-lower fixture, 4-connecting sleeve, 5-spherical connecting rod, 6-test piece, 7-auxiliary tooling, 8-baffle; DETAILED DESCRIPTION

[0029] Example 1

[0030] The present invention provides a small-size test piece tensile strength measuring device, such as Figure 1 As shown, it is composed of an upper fixture 1, a limiting guide rail 2, a lower fixture 3, a connecting sleeve 4, a spherical connecting rod 5, an auxiliary tooling 7, and a baffle 8. The upper end of the upper fixture 1 can be connected to a material testing machine, and the bottom surface of the lower end is a rectangular plane with a circular arc groove at the center line of the plane; the upper end of the limiting guide rail 2 is conical, and the lower end is fixedly connected to the lower fixture by bolts; the upper end surface of the lower fixture 3 is a rectangular plane with a circular arc groove at the center line of the plane, and the end surface of the connecting rod below the lower fixture 3 has a spherical groove; the spherical connecting rod 5 is assembled with the lower end of the lower fixture 3 through the connecting sleeve 4 to form a ball sleeve structure; the auxiliary tooling 6 is a clip type, two symmetrical, and a rectangular groove is opened in the middle of the symmetrical surface.

[0031] Furthermore, the rectangular plane size of the upper fixture 1 is slightly smaller than the plane size formed by the center lines of the limiting guide rail installation holes of the lower fixture 3.

[0032] Furthermore, grooves with a radius consistent with the radius of the limiting guide rail 2 are processed at the four corners of the rectangular plane of the upper clamp 1, forming a limiting structure with the limiting guide rail 2. The limiting guide rail 2 passes through the constraint position of the upper clamp 1 to constrain the upper clamp 1 to move along the limiting guide rail 2.

[0033] Furthermore, the arc-shaped grooves on the lower end surface of the upper fixture 1 and the upper end surface of the lower fixture 3 are distributed in a mirror-symmetrical manner.

[0034] Furthermore, the arc of the arc-shaped groove is processed according to the size of the test piece.

[0035] Furthermore, the ball sleeve structure formed by assembling the spherical connecting rod 5, the connecting sleeve 4 and the lower end of the lower clamp 3 can adjust the movable angle and tightness through the connecting sleeve.

[0036] Furthermore, grooves are formed on the upper end surfaces of the position limiting guide rail 2 and the lower clamp 3 for installing the baffle 8 .

[0037] A method for testing the tensile strength of a small-sized test piece, using the small-sized test piece tensile strength testing device, comprises the following steps:

[0038] Step 1: Prepare a test piece 6, and evenly spray black and white speckles on the surface of the test piece 6; in this embodiment, the test piece is a ring with an outer diameter of φ8 mm, an inner diameter of φ4 mm, and a thickness of 2 mm;

[0039] Step 2: Tighten the connecting sleeve 4 to tighten the ball sleeve structure, then place the device in the material testing machine, and clamp the upper and lower ends with the material testing machine;

[0040] Step 3: Place the test piece 6 in the groove of the auxiliary tooling 7, clamp the auxiliary tooling 7, and stand the test piece 6 in the middle of the arc-shaped groove of the lower fixture 3; in this embodiment, the groove size of the auxiliary tooling is 8mm×2mm×3mm, and the diameter of the arc-shaped groove of the upper fixture and the lower fixture is φ12mm;

[0041] Step 4: Control the material testing machine to move the upper fixture 1 downward until it is about to contact the test piece 6. At this time, the test piece 6 is located between the arc-shaped grooves of the upper fixture 1 and the lower fixture 3, and a baffle 8 is inserted into the groove of the limit guide rail 2;

[0042] Step 5: Remove the auxiliary tooling 7 that fixes the test piece 6 and place the DIC camera;

[0043] Step 6: Completely loosen the connecting sleeve 4;

[0044] Step 7: The material testing machine applies a downward pressure load to the upper fixture 1 to complete the tensile strength test of the test piece 6. After the test piece 6 is destroyed, the loading is terminated. In this embodiment, the material testing machine is set to a test speed of 0.01 mm / min, and the camera acquisition frequency is set to 3 frames.

[0045] Step 8: Analyze and process the collected data to calculate the tensile strength of the test piece 6. The specific calculation formula is σ T =KP / (πbt), where σ T is the tensile strength of specimen 6, K is the stress concentration factor, P is the maximum load applied, b is the outer radius of specimen 1, and t is the thickness of specimen 1. In addition, observe the split specimen 1 and combine the DIC photos to determine whether the test process meets the requirements. The standard is that the splitting method of specimen 1 is radial splitting.

[0046] The present invention is described in detail above in combination with specific implementation methods and exemplary examples. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments; the above description cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, the technical solution of the present invention and its implementation methods may be subjected to a variety of equivalent substitutions, modifications or improvements, all of which fall within the scope of the present invention; the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A device for measuring the tensile strength of a small-size test piece, characterized in that: The device comprises an upper fixture (1), a limiting guide rail (2), a lower fixture (3), a connecting sleeve (4), a connecting rod (5), an auxiliary tooling (7) and a baffle (8); the upper end of the upper fixture (1) is connected to a material testing machine, and a groove is provided at the center line of the lower end surface; the limiting guide rail (2) constrains the upper fixture (1) to move along the limiting guide rail (2); the lower end of the limiting guide rail (2) is connected to the lower fixture (3), and a groove is provided at the center line of the upper end surface of the lower fixture (3); the connecting rod (5) is assembled with the lower end of the lower fixture (3) through the connecting sleeve (4) to form a ball sleeve structure.

2. A small-size test piece tensile strength measuring device according to claim 1, characterized in that: The plane size of the upper clamp (1) is smaller than the plane size formed by the continuous center line of the installation hole of the upper limit guide rail (2) of the lower clamp (3).

3. A small-size test piece tensile strength measuring device according to claim 1, characterized in that: The four corners of the plane of the upper clamp (1) are machined with grooves whose radius is consistent with the radius of the limiting guide rail (2), and the limiting guide rail (2) forms a limiting structure.

4. The small-size test piece tensile strength measuring device according to claim 1, characterized in that: The grooves on the lower end surface of the upper clamp (1) and the upper end surface of the lower clamp (3) are distributed in a mirror-symmetrical manner.

5. The small-size test piece tensile strength measuring device according to claim 1, characterized in that: The groove is machined according to the size of the test piece.

6. The small-size test piece tensile strength measuring device according to claim 1, characterized in that: The ball sleeve structure formed by assembling the connecting rod (5), the connecting sleeve (4) and the lower end of the lower clamp (3) can adjust the movable angle and tightness through the connecting sleeve.

7. The small-size test piece tensile strength measuring device according to claim 1, characterized in that: The upper end surfaces of the limiting guide rail (2) and the lower clamp (3) are provided with grooves for mounting the baffle (8).

8. The small-size test piece tensile strength measuring device according to claim 1, characterized in that: The auxiliary tooling (7) is of a clip-type, with two symmetrical pieces, and a groove is provided in the middle of the symmetrical surfaces.

9. A method for measuring the tensile strength of a small-sized test piece, the method being based on the small-sized test piece tensile strength measuring device according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: (1) preparing a test piece (6), and uniformly spraying black and white speckles on the surface of the test piece (6); (2) Tighten the connecting sleeve (4) to tighten the ball sleeve structure, and then place the device in a material testing machine, and clamp the upper and lower ends of the device with the material testing machine; (3) placing the test piece (6) in the groove of the auxiliary fixture (7), clamping the auxiliary fixture (7), and standing the test piece (6) in the middle of the groove of the lower fixture (3); (4) controlling the material testing machine to move the upper fixture (1) downward until it is about to contact the test piece (6), at which time the test piece (6) is located between the grooves of the upper fixture (1) and the lower fixture (3), and inserting a baffle into the groove of the limit guide rail (2); (5) Remove the auxiliary tooling (7) that fixes the test piece (6) and place the DIC camera; (6) Completely loosen the connecting sleeve (4); (7) applying a downward pressure load to the upper clamp (1) by a material testing machine to complete the tensile strength test of the test piece (6), and the loading is terminated after the test piece is destroyed; (8) Analyze and process the collected data and calculate the tensile strength of the test piece.

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