JPH04250336A - Device and method for tension test of metallic material - Google Patents

Abstract

PURPOSE:To enable rupture of a test piece at the center portion of gauge length thereof by cooling a mandrel in catch portions provided at both ends of the test piece, while controlling to a specified temperature the surface of the parallel portion of the test piece which is provided between the catch portions, so as to provide the test piece with such a temperature gradient as lowering toward each catch portion. CONSTITUTION:A cooling coil 8 and a temperature sensor 9 are mounted on respective portions of the surface of each of catch portions 3 provided at both ends of a tubular test piece 1 and a heating coil 11 and a temperature sensor 12 are mounted on respective portions of the boundary between each catch portion 3 and a parallel portion 2. While the catch portions 3 are cooled, the temperature of a portion near the boundary between each catch portion 3 and the parallel portion 2 is detected by the sensor 12 and sent to a temperature controller 10. In order to prevent the temperature detected by the sensor 12 from dropping below a preset specific test temperature, the temperature controller 10 controls current transmitted through the coil 11. When the temperature of the end portion of each catch portion 3 being detected by the sensor 9 drops below a predetermined temperature corresponding to the size of the test piece, a cooling device 7 is repeatedly stopped and driven for a fixed time so that the temperature distribution of the test piece 1 is stabilized. Therefore, the rupture position of the test piece due to a tension test can be concentrated at the center portion of the test piece.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tensile testing apparatus and testing method for rod-shaped or tubular metal materials, and in particular to optimization of the fracture position of a test piece.

0002

2. Description of the Related Art When a force is applied to a machine or structure, whether or not the material is being used appropriately can be determined by knowing the mechanical properties of the material. A tensile test is a typical mechanical test for testing mechanical properties. A tensile test measures various mechanical properties by gradually applying tensile force to a test piece, and measures the material's yield point, yield strength, tensile strength, yield elongation, elongation at break, and area of area. Also,
In addition, proportional limits, elastic limits, elastic modulus, load-elongation diagrams, etc. can also be determined. These properties are used not only as standards for designing structures, etc., but also as representative quality characteristics for material manufacturing control.

[0003] When the relationship between tensile stress σ and strain ε in a steel tensile test is drawn as a diagram, the stress-strain diagram shown in FIG. 5 is obtained. As a load is applied to the test piece, the elongation increases linearly in proportion to the load up to point P in the figure. From point P to point E, this elongation increases somewhat with respect to the load, deviating from the straight line and bending somewhat, but the elasticity is maintained, and when the load is removed, the elongation ceases and it returns to its original shape. When the load is increased above point E, elongation remains even after the load is removed, resulting in permanent elongation. If the load is further increased after point E, it enters the region of plastic deformation and the permanent elongation gradually increases, and when it reaches point S, there is a slight decrease in load, and the elongation increases rapidly under the reduced almost constant load. A yield elongation occurs. When this yielding ends, work hardening occurs in the material, and the load increases again. As the load increases, the elongation also increases, reaching the maximum load at point M, and local elongation appears along with a local reduction in cross section at a certain location of the test piece. As this reduction in cross section becomes even greater, the load decreases until the point Z is reached and the material breaks.

[0004] In order to compare the results of the tensile test that measures the various mechanical properties shown in this stress-strain diagram with other published results, and to give authority to the test results, test pieces are used depending on the type of material. The shape and dimensions are specified in JISZ2201. As shown in FIG. 6, a test piece 21 such as a steel plate or flat steel is provided with a parallel part 22 having the same cross section at the center of the test piece 21 and at both ends of the parallel part 22, and is gripped by a chuck of a testing machine. In order to uniformly distribute stress to the gripping portion 23 and the parallel portion 22, the parallel portion 22 and the gripping portion 23 are
and a shoulder portion 24 formed of a circular arc provided between. In addition, as shown in Fig. 7, the cross section of test piece 1 such as No. 2, No. 3, No. 11, etc. used in the tensile test of rod-shaped or tubular metal materials was cut from the original material, and In the case of a piece, a mandrel 4 is inserted into the gripping part 3 or it is hammered into a flat plate.

When performing a tensile test using these test pieces, gauge points 5 and 6 are marked on the parallel parts 22 and 2 of the test piece, separated by a predetermined gauge distance L, to serve as a reference for elongation measurement. After measuring the original cross-sectional area of the parallel parts 22, 2, the test piece is mounted on a testing machine, and a load is applied at a speed within a specified range until the test piece breaks. Then, the load corresponding to each characteristic value such as yield point and tensile strength is read from changes in the load appearing on the tube, and the stress value thereof is calculated. Furthermore, the fractured parts of the fractured test pieces are compared to measure the amount of elongation and the minimum area of the fractured part, and the elongation at break and the area of area are calculated. In addition, when measuring characteristic values such as yield strength and yield elongation that are obtained by mutual changes in elongation and load, an extensometer is attached to the test.

When a steel material is subjected to a tensile test, local shrinkage occurs as shown in FIG. 8(a), and the steel material breaks at that location. In order to check the elongation of each part, we divide the space between gauge points 5 and 6 into equal lengths and mark them in advance, and when we plot the elongation between each scale as a line, we can see that the local shrinkage is shown in Figure 8(b). It has grown significantly in and around the area. The true value of elongation is obtained when the position where this local shrinkage occurs and the breakage occurs is in the center of the gauge points 5 and 6, and the elongation can be measured accurately. Therefore, as shown in Figure 9, if the fracture position of the test piece is within 1/4 of the gauge distance L from the center between gauge marks 5 and 6, it is an A fracture, and the fracture position is from the center between gauge marks 5 and 6 to the gauge distance L. When the break exceeds 1/4 of the distance L and is within the gauge points 5 and 6, it is distinguished as a B fracture, and when it breaks outside the gauge points 5 and 6, it is distinguished as a C fracture. In cases other than A fracture, if the elongation at break does not satisfy the specified value, it is stipulated that the test at that time can be invalidated and a retest can be conducted (JIS G0303 General Rules for Inspection of Steel Materials).

[0007]

[Problem to be Solved by the Invention] As mentioned above, since the true value of elongation is obtained at the A fracture, the test piece 21 of steel plate, flat steel, etc. has a parallel part 22 with a small cross-sectional area in the center. A
This makes it easy for breakage to occur. However, the rod-shaped or tubular test piece 1 is still cut from the original material, and does not have a parallel portion 22 with a reduced cross-sectional area, unlike a test piece 21 such as a steel plate. Therefore, it breaks at any position between the chucks of the testing machine. Therefore, as shown in FIG.
a, 6a to 5n, 6n are provided overlappingly so that the breakage position is likely to be A breakage.

However, since this test piece 1 breaks at an arbitrary position, it may break near the chuck of the testing machine resulting in a B break, or the test piece 1 may break in an automatic testing machine.
In many cases, the fracture occurs outside the gauge distance of the extensometer set in the center of the pipe. When the fracture position becomes B fracture, there is a method of estimating the elongation at break at break A from the elongation at break at that time, but this conversion cannot be performed accurately and the elongation cannot be measured accurately. was there.

[0009]Also, when a fracture occurs outside the gauge length of the extensometer, a method of converting the elongation at that time to that when the fracture occurs within the gauge length of the extensometer has been studied, but this is insufficient.
There was a disadvantage that the elongation at break could not be automatically detected and the butt elongation had to be measured manually.

[0010] Furthermore, when the material of the test piece 1 becomes hard, it becomes easy to break within the chuck, and in this case, there are disadvantages in that not only the elongation cannot be measured but also the test piece cannot be recovered after being broken.

The present invention has been made in order to solve these shortcomings, and provides a tensile testing device and testing method for metallic materials that can cause a bar or tubular test piece to break at the center of the gauge length. The purpose is to

0012

[Means for Solving the Problems] A tensile testing device for metallic materials according to the present invention includes a cooling means for cooling the surfaces of gripping portions at both ends of a rod-shaped or tubular test piece to a predetermined temperature below room temperature, and and temperature control means for controlling the surface temperature of the parallel portion between the grip portions at both ends to a predetermined temperature.

[0013] Furthermore, in the tensile testing method for metal materials according to the present invention, while controlling the surface temperature of the parallel portion between the gripping portions at both ends of the rod-shaped or tubular test piece to a predetermined temperature, After cooling the test piece to a constant temperature below a predetermined room temperature and creating a temperature gradient between the surface temperature of the parallel part of the tubular test piece and the surface temperature of the gripping parts at both ends, the above test piece was subjected to a tensile test. Features.

[0014]

[Operation] In this invention, while controlling the surface temperature of the parallel part of a rod-shaped or tubular metal material test piece to a predetermined temperature, the temperature of the gripping parts at both ends of the test piece is kept at a predetermined constant temperature. After cooling and creating a temperature gradient so that the temperature of the test piece gradually decreases from the parallel part to the gripping part, the tensile strength of the gripping parts at both ends is higher than that of the parallel part of the tubular specimen. Perform a tensile test on the test piece and focus the fracture location on the center of the test piece.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a tubular test piece cut from a tube material to be tested, and the tubular test piece 1 is formed from gripping parts 3 and parallel parts 2 at both ends. Gauge points 5 and 6, which serve as a reference for elongation measurement, are marked on the parallel portion 2 with a punch or a scribing needle, separated by a predetermined gauge distance L. A testing machine that performs a tensile test on the tubular test piece 1 includes a cooling coil 8 connected to a cooling device 7, a temperature sensor 9, and a temperature control device 10.
It has one set of heating coil 11 and one temperature sensor 12 connected to each other. The cooling coils 8 are attached to the surfaces of the gripping portions 3 at both ends of the tubular test piece 1, respectively, to cool the gripping portions 3. The temperature sensor 9 is attached to the end of the grip 3 and detects the temperature of the grip 3 during cooling. The heating coil 11 is attached near the boundary between the grip part 3 and the parallel part 2. The temperature sensor 12 detects the temperature near the boundary between the grip part 3 and the parallel part 2 and sends it to the temperature control device 10. The temperature control device 10 controls the current flowing through the heating coil 11 based on the temperature detected by the temperature sensor 11.

[0016] The test temperature for performing the tensile test is generally 5 to
It is within the range of 35°C, and 20±2°C is standard for materials sensitive to temperature changes. Therefore, while cooling the gripping portions 3 at both ends of the tubular test piece 1, the temperature sensor 12
By detecting the surface temperature of the central part of the tubular test piece 1 and varying the current flowing through the heating coil 11 with the temperature control device 10 according to the detected temperature, the temperature distribution as shown in FIG. 2, that is, the parallel part The surface temperature of the tubular test piece 1 is controlled such that the temperature of the test piece 2 is maintained within the specified test temperature range, and the temperature of the gripping part 3 gradually decreases toward the end.

Next, the operation when performing a tensile test on the tubular test piece 1 using the testing machine configured as described above will be explained. First, the cooling coil 8 and the temperature sensor 9 are attached to the surfaces of the gripping parts 3 at both ends of the tubular test piece 1.
A heating coil 11 and a temperature sensor 12 are attached near the boundary. Thereafter, the cooling device 7 is driven to cool the grip portion 3 by the cooling coil 8. While the grip portion 3 is being cooled, the temperature sensor 12 successively detects the temperature near the boundary between the grip portion 3 and the parallel portion 2 and sends it to the temperature control device 10. The temperature control device 10 adjusts the temperature detected by the temperature sensor 12 to a preset specified test temperature, for example, 20
℃, and the current applied to the heating coil 11 is controlled so that the temperature of the parallel portion 2 does not fall below the specified test temperature. When the temperature at the end of the grip part 3 detected by the temperature sensor 9 drops to a predetermined temperature depending on the size of the test piece, for example, -5°C, the cooling device 7 is stopped and driven repeatedly for a certain period of time, and the tubular test is carried out. Stabilize the temperature distribution of piece 1.

Thereafter, the cooling coil 8, temperature sensors 9, 12, and heating coil 11 were removed from the tubular test piece 1, and as shown in FIG.
As shown in the figure, the mandrel 4 is inserted into the grip part 3, and the tubular test piece 1 is placed in the upper crosshead 1 of the testing machine by manual or automatic operation.
3 and the chuck 15 of the lower crosshead 14. Then, the upper crosshead 13 is raised at a predetermined speed, and a load is applied to the tubular test piece 1 until it locally stretches and breaks. While measuring the load applied to the tubular test piece 1, the amount of elongation is measured using an extensometer using an electric micrometer, strain gauge, or the like. Then, the total elongation at break of the tubular test piece 1 is measured using an extensometer, or the fractured surfaces of the two broken pieces are brought together and the length between the gauge points 5 and 6 is measured to obtain the elongation at break.

When testing the tensile strength of the tubular test piece 1 as described above, the tensile strength of the tubular test piece 1 is gradually decreased from the parallel part 2 to the grip part 3 while maintaining the parallel part 2 at a specified temperature. Since there is a temperature gradient, the tensile strength of the grip portion 3 can be gradually increased compared to the tensile strength of the parallel portion 2. Therefore, the position where local elongation occurs and breakage occurs in the tensile test can be concentrated in the center of the parallel portion 2.

FIG. 4 shows the fracture positions when a tensile test was conducted with different materials and dimensions of the test material. In the figure, the vertical axis represents the ratio of the distance from the gauge to the shorter fracture position to the gauge distance after fracture, that is, the center fracture rate, and the horizontal axis represents the material and dimensions of the tubular specimen 1. , A shows the fracture rate at the center when the gripping part 3 of the tubular test piece 1 is cooled, and B shows the breakage rate at the center when the test is carried out at room temperature without cooling. As shown in the figure, when the grip portion 3 was cooled, the center portion breakage rate was 46 to 50%, and the A breakage rate was able to be improved compared to the case where the test was performed at room temperature. In addition, almost the same characteristic values were obtained when the grip portion 3 was tested while being cooled and when it was tested at room temperature.

In the above embodiment, the temperature of the grip portion 3 is detected by the temperature sensor 9 to control the cooling temperature, but the cooling time may be detected in advance depending on the material and size of the test piece. The cooling temperature of the grip portion 3 may be controlled by the cooling time.

Furthermore, in the above embodiment, the case where the gripping portions 3 at both ends of the tubular test piece 1 are cooled by the cooling coil 8 has been described. Even if the gripping portions 3 at both ends of the tubular test piece 1 are cooled, the same effect as in the above embodiment can be achieved.

[0023] Furthermore, in the above embodiment, the tubular test piece 1
Although the case where the tensile test was performed has been described, it can be similarly applied to No. 2 test pieces and No. 3 test pieces for testing rod-shaped metal materials.

[0024]

Effects of the Invention As explained above, the present invention is capable of controlling the surface temperature of the parallel part of a test piece of a rod-like or tubular metal material to a predetermined temperature, and at the same time controlling the temperature of the gripping parts at both ends of the test piece in advance. The specimen is cooled to a predetermined constant temperature, and a temperature gradient is created so that the temperature of the specimen gradually decreases from the parallel part to the gripping part, so that the tensile strength of the gripping part at both ends is higher than that of the parallel part of the tubular specimen. After setting the
Since the tensile test is performed on the test piece, the fracture position due to the tensile test can be concentrated in the center of the test piece. Therefore, the amount of elongation can be measured with high accuracy even in an automatic testing machine with an extensometer set in the center of the tubular test piece, and the work efficiency of the tensile test of the tubular test piece can be improved.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a temperature distribution diagram of a tubular test piece.

FIG. 3 is an explanatory diagram showing how the tubular test piece is attached.

FIG. 4 is a characteristic diagram showing the center portion fracture rate.

FIG. 5 is a stress-strain diagram.

FIG. 6 is a front view showing a test piece of steel plate, flat steel, etc.

FIG. 7 is a front view showing a tubular test piece.

FIG. 8(a) is a front view showing a broken state, and FIG. 8(b) is an elongation distribution diagram showing elongation at break.

FIG. 9 is an explanatory diagram showing classification of test pieces according to their fracture positions.

FIG. 10 is a front view showing gauge points of a tubular test piece.

[Explanation of symbols]

1 Tubular test piece 2 Parallel part 3 Grip part 5, 6 Gauge point 7 Cooling device 8 Cooling coil 9,12 Temperature sensor 10 Temperature control device 11 Heating coil 15 Chuck

Claims (2)

[Claims] [Claim 1] Cooling means for cooling the surface of the gripping portions at both ends of a rod-shaped or tubular test piece to a predetermined temperature below room temperature; 1. A tensile testing device for metal materials, comprising: temperature control means for controlling the temperature to a specified temperature. 2. While controlling the surface temperature of the parallel portion between the gripping portions at both ends of the rod-like or tubular test piece to a predetermined temperature, the gripping portions at both ends of the test piece are held at a constant temperature below a predetermined room temperature. 1. A method for tensile testing a metal material, comprising: cooling the test piece to a temperature of 100 mL to give a temperature gradient between the surface temperature of the parallel portion of the tubular test piece and the surface temperature of the gripping portions at both ends, and then subjecting the test piece to a tensile test.