JPH04370740A - Device and method for testing tensile strength of tubular metal material - Google Patents

Abstract

PURPOSE:To enable a tensile test to be performed by controlling a tensile speed of a test piece without any parallel portion highly accurately. CONSTITUTION:When performing a tensile test with a specified distortion increase rate, a test piece is pulled with an initial value Vc of a cross head traveling speed which is preset and the distortion increase rate is calculated from an amount of elongation between gauges which are measured at that time. A compensation value Vco of the cross head traveling speed corresponding to a target value of the distortion increase rate is calculated from the calculated distortion increase rate, an initial value Vco of the cross head traveling speed which is preset, and a target value V of the distortion increase rate. The cross head is moved according to the compensation value of the cross head traveling speed which is calculated and the tensile test is performed with a specified distortion increase rate.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a tensile testing method for tubular metal materials, and more particularly to a method for uniformizing the rate at which a load is applied to 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. In this tensile test, it is desirable that the speed of applying the load to the test piece be as uniform as possible. Therefore, the upper yield point,
When measuring the lower yield point or proof stress, apply a load to the test piece at a stress increase rate determined depending on the material and measure the upper yield point, lower yield point, or proof stress. In addition, if the upper yield point, lower yield point, or proof stress is not measured, or if the tensile strength is determined after measuring the upper yield point, lower yield point, or proof stress, the value corresponds to the specified value of tensile strength. 1/ of load
The strain increase rate of the parallel part of the specimen after exceeding 2 loads is within the range determined depending on the material, for example 20 to 80% in the case of steel.
Pull at a speed that maintains a constant value within the range of /min.

Gauge length control (hereinafter referred to as GL control) and crosshead control are used as methods for controlling this strain increase rate to a constant value. GL control is a method in which the gage length of an extensometer is sampled at regular intervals, and the moving speed of the crosshead is controlled so that the elongation speed becomes a constant value. Crosshead control is a method of controlling the moving speed of the crosshead to a constant value.

0004

[Problems to be Solved by the Invention] By using the GL control and the crosshead control, it is possible to control the strain increase rate to a constant value when there is a parallel portion in the center, such as in a test piece such as a plate. However, in the case of a tube or a strip test piece without processed parallel parts, the length of the parallel part is the distance between the chucks attached to the crosshead. In this way, test pieces without parallel parts do not necessarily break between the gauge marks, but often break outside of the gauge marks. When local elongation occurs outside the gauge point,
The rate of elongation between the gauges where elongation is being measured decreases. If this elongation speed is controlled to a constant value by GL control, the moving speed of the crosshead increases, and the moving speed of the crosshead at the time of breakage becomes extremely large.

Furthermore, in crosshead control, in order to correctly set the crosshead movement speed, it is necessary to accurately grasp the distance between the chucks, which are parallel parts. However, the crosshead positioning is generally less accurate than an extensometer, and when a V-chuck is used, it changes depending on the dimensions of the test piece. Therefore, it is difficult to accurately determine the distance between chucks.

For this reason, when applying GL control or crosshead control to a test piece without parallel parts, such as a tubular test piece,
There were disadvantages in that the strain increase rate could not be controlled to a constant level and the tensile rate could not be controlled accurately.

[0007] The present invention has been made in order to solve these disadvantages, and the object thereof is to obtain a tensile test method that can control the tensile speed of a test piece without parallel parts with high precision. .

[0008]

[Means for Solving the Problems] A tensile test device for tubular metal materials according to the present invention is capable of increasing strain from the amount of elongation between gauges measured when a test piece is pulled at a preset crosshead movement speed. and a correction value calculating means that calculates a correction value for the crosshead movement speed from the calculated strain increase rate and a preset target value for the crosshead movement speed and strain increase rate. It is characterized by having

[0009] Furthermore, in the tensile test method for tubular metal materials according to the present invention, a test piece is pulled at a preset crosshead movement speed, and the amount of elongation between the gauges at that time is measured to determine the strain increase rate. Calculate a correction value for the crosshead moving speed from the calculated strain increase rate and a preset target value for the crosshead moving speed and strain increase rate,
The method is characterized in that the test piece is pulled using the calculated crosshead movement speed correction value.

0010

[Operation] In this invention, when performing a tensile test at a predetermined strain increase rate, the test piece is pulled at a preset initial value of the crosshead movement speed, and the elongation between gauge points measured at that time is The strain increase rate is calculated from the calculated strain increase rate, the initial value of the crosshead movement speed set in advance, and the target value of the strain increase rate, and a correction value of the crosshead movement speed according to the target value of the strain increase rate is calculated. Calculate. The crosshead is moved based on the calculated correction value of the crosshead movement speed, and the test piece is pulled.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a crosshead movement control section according to an embodiment of the present invention. As shown in the figure, the crosshead movement control section includes a condition setting means 1, an extensometer 2, a strain increase rate calculating means 3, a correction value calculating means 4, and a crosshead moving means 5. In the condition setting means 1, a target value V of the stress increase rate and strain increase rate of the tensile rate, an initial value VCO of the crosshead moving speed when the test piece is stretched at a predetermined strain increase rate, etc. are set. As shown in FIG. 2, the extensometer 2 has a mandrel 23 inserted into the grip part 22 and the chuck 2 of the upper crosshead 24 and lower crosshead 25 of the testing machine.
The elongation between the gauge points 27 and 28 of the tubular test piece 21 set at 6 is measured. The strain increase rate calculation means 3 calculates the strain increase rate VGL between the gauge points 27 and 28 based on the elongation amount ΔL measured by the extensometer 2, the original gauge length, and the unit time T sent from the time signal generation means 6. The correction value calculation means 4 inputs the strain increase rate VGL calculated by the strain increase rate calculation means 3, the target value V of the strain increase rate set in the condition setting means 1, and the initial value VCO of the crosshead moving speed, and operates the crosshead. A correction value VC of the moving speed is calculated and sent to the crosshead moving means 5.

In explaining the operation of the embodiment configured as described above, the principle of operation of this embodiment will first be explained. When the test piece 21 is stretched at the initial value VCO of the crosshead movement speed, the strain increase rate VGL is given by the amount of elongation ε between the gauge points 27 and 28 per unit time T. This elongation ε is the length L between the gauge points 27 and 28 when a tensile load is gradually increased and applied to the test piece 21, and the original gauge length L0.
The difference ΔL is expressed as the ratio ΔL/L0 to the gauge length L0. Therefore, the strain increase rate VGL is VGL=ΔL/L0
・Become T. At this time, if the total elongation between the chucks of the tubular test piece 21 whose distance LCK between the chucks is all parallel is ΔLCK, then the crosshead moving speed VC
O can be expressed as VCO=ΔLCK/T. Furthermore, when no local contraction occurs, ΔLCK/LCK=ΔL/L0, so VCO=VGL·LCK, and the inter-chuck distance LCK at this time is obtained by LCK=VCO/VGL. Using this inter-chuck distance LCK=VCO/VGL and the preset strain increase rate V, the correction value VC for the crosshead movement speed is VC=(VCO・V)/V
Obtained from GL. By correcting the initial value VCO of the crosshead movement speed with this correction value VC, the test piece 21 can be pulled at a predetermined strain increase rate V.

Next, the operation of the embodiment of the present invention based on the above principle will be explained. First, the tubular test piece 21 is set in the chucks 26 of the upper crosshead 24 and lower crosshead 25. Next, after setting the stress increase rate and strain increase rate V of the tensile speed and the initial value VCO of the crosshead movement speed in the condition setting means 1, the test piece 21 is Measure the upper yield point, lower yield point, or yield strength. After performing this measurement, the initial value VCO of the crosshead moving speed is sent to the crosshead moving means 5, which is a hydraulic device, for example, and the upper crosshead 24 is raised at this moving speed VCO to pull the test piece 21. While the test piece 21 is being stretched, the extensometer 2 measures the distance between the gauge points 27 and 28 of the test piece 21 at the start of the tension and the amount of elongation, and sends the measured values to the strain increase rate calculating means 3.

The strain increase rate calculating means 3 uses the sent gauge points 27,
28, the amount of elongation, and the time T from the start of pulling to the time when elongation is measured, which is sent from the time signal generating means 6.
The strain increase rate VGL when the upper crosshead 24 is moved at the moving speed VCO is calculated and sent to the correction value calculation means 4. The correction value calculating means 4 calculates a correction value VC of the crosshead moving speed from the sent distortion increase rate VGL, the initial value VCO of the crosshead moving speed set in the condition setting means 1, and the target value V of the strain increase rate. The formula VC=(VCO・V)/VGL
is calculated and sent to the crosshead moving means 5. The crosshead moving means 5 raises the upper crosshead 24 according to the sent crosshead moving speed correction value VC, and moves the test piece 2.
Pull 1.

For example, the initial value VC of the crosshead moving speed
If O is 50 mm/min and the test piece 21 is pulled for 1 minute at this initial value, the distance 50 mm between the gauges 27 and 28 increases by 17.2 mm, then the strain increase rate VG
L becomes 34.4%/min. Here, if the target value V of the strain increase rate is 50%/min, this target value V=50%
The correction value V of the crosshead moving speed corresponding to /min becomes 72.7 mm/min. By raising the upper crosshead 24 using this correction value V and pulling the test piece 21, a load can be applied to the test piece 21 at a predetermined strain increase rate.

[0016] Although the above embodiment describes the case of performing a tensile test on the tubular test piece 21, it can also be applied to a tensile test on a strip-shaped No. 2 test piece without a parallel part in the center in the same manner as in the above embodiment. can do.

[0017]

Effects of the Invention As explained above, when carrying out a tensile test at a predetermined strain increase rate, the test piece is pulled at the initial value of the crosshead movement speed set in advance, and the gauge point measured at that time is The strain increase rate at that time is calculated from the amount of elongation between, and the strain increase rate is calculated from the calculated strain increase rate, the initial value of the crosshead moving speed set in advance, and the target value of the strain increase rate. Since the crosshead movement speed is corrected by calculating the correction value for the crosshead movement speed, a tensile test can be performed at a predetermined strain increase rate.

[0018] Furthermore, the crosshead can be moved in accordance with a predetermined strain increase rate without having to previously measure the distance between the chucks of a test piece that does not have a parallel part in the center, such as a tubular test piece.
Tensile tests can be performed with high accuracy.

Furthermore, since the tensile speed can be kept constant according to a predetermined strain increase rate, the tensile test can be carried out stably without falling into unstable control unlike GL control.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a crosshead movement control section according to an embodiment of the invention.

FIG. 2 is an explanatory diagram showing how a tubular test piece is attached. 1 Condition setting means 2 Extensometer 3. Distortion increase rate calculation means 4 Correction value calculation means 21 Tubular test piece 24 Upper cross head 25 Lower cross head 26 Chuck

Claims (2)

[Claims] Claim 1: Strain increase rate calculation means for calculating a strain increase rate from the amount of elongation between gauges measured when a test piece is pulled at a preset crosshead moving speed; 1. A tensile testing device for tubular metal materials, comprising correction value calculation means for calculating a correction value for crosshead movement speed from preset target values for crosshead movement speed and strain increase rate. [Claim 2] The test piece is pulled at a preset crosshead movement speed, the amount of elongation between the gauge points at that time is measured, and the strain increase rate is calculated, and the strain increase rate and the strain increase rate set in advance are calculated. A correction value of the crosshead movement speed is calculated from the target value of the crosshead movement speed and the strain increase rate, and the test piece is stretched using the calculated correction value of the crosshead movement speed. Tensile test method.