JP3225286B2 - Method for measuring residual stress of metallic materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring residual stress of a metal material, which is one of means for evaluating the soundness or life of a metal material which is a component of various plants.

[0002]

2. Description of the Related Art As a conventional residual stress measurement technique, a resistance wire strain gauge (hereinafter, abbreviated as a strain gauge) is attached to the surface of an object to be measured with an adhesive, and the periphery of the strain gauge is perforated or cut. A method of measuring by releasing the residual stress of the strain gauge part, or using X-rays, irradiating X-rays from an X-ray source to a measurement target location, diffracting the X-rays at the measurement target location,
A method of measuring lattice distortion by analyzing diffracted X-rays detected by a line detector is the most widely used method.

However, these conventional methods have the following disadvantages. In other words, in the method using a strain gauge, it is necessary to clean the surface of the object in order to attach the strain gauge or to attach the strain gauge. There is a problem that the measurement of the part is difficult. In addition, since the stress is removed after the strain gauge is attached, there is a risk that the strain gauge or the lead wire may be damaged before the stress measurement is performed, and the measurement may not be performed.

On the other hand, in the method using X-rays, an X-ray source and an X-ray detector must be arranged in the immediate vicinity of an object, so that a larger work space is required than the method using strain gauges, and There is a drawback in that it is inconvenient to carry because the measuring equipment becomes large.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a simple method for measuring residual stress, which overcomes the above-mentioned disadvantages of the prior art and can easily carry measuring equipment even in a narrow portion. I do.

[0006]

SUMMARY OF THE INVENTION The present inventors have proposed a method for imprinting a predetermined distance on the surface of an object to be measured and measuring the distance accurately as a method for measuring residual stress without particularly cleaning the surface. The inventors have found that the above-mentioned drawbacks of the prior art can be overcome by measurement, and have led to the present invention.

That is, in the method for measuring residual stress of a metal material according to the present invention, a plurality of indenters formed in a polygonal pyramid shape are fixed to a head portion of a marker at a predetermined interval with the top of a pyramid as a tip, and The head part is pressed against the surface of the metal to make a mark with the indenter, then the metal with the mark is separated from the surroundings to release the stress, and the distance between the marks measured in a state where the stress is released and the indenter of the indenter The method is characterized in that the residual stress of the metal is measured by comparing the distance between the tips.

In the measuring method of the present invention, the indenter is made of any one of diamond, sapphire and cemented carbide, and the shape of the polygon formed by the indenter is such that the top is above the center of the bottom surface. Is also preferable. Furthermore, the line connecting the tips of the indenter is
It is also preferable to arrange these indenters so as to form a straight line or a polygon.

[0009]

The marker used in the measurement method of the present invention is as follows:
Since a polygonal pyramid-shaped indenter is employed, even if the apex is worn, for example, the position of the apex can be determined by following the ridge line (generating line) of the pyramid.

That is, in the present invention, the distance between two points can always be imprinted accurately on the surface of the metal to be measured for residual stress, and the distance between the imprints is determined using a measuring microscope or the like after releasing the stress. In addition to measuring accurately and comparing the measured value with the distance between the indenter tips of the above markers, no special treatment such as cleaning or polishing is required, It is possible to easily measure the residual stress of the material.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described.

FIGS. 1 to 5 are a front view and a side view showing a head portion of a marker according to an embodiment of the present invention, and FIGS. 6 and 7 are a front view and a side view showing an indenter of the marker.

The marker used in the measuring method of the present invention is
For example, as shown in FIGS. 6 and 7, a plurality of indenters 1 having a regular triangular pyramid or a quadrangular pyramid having a top c right above a center b of a bottom surface a is provided. These indenters 1 are made of a material having a high hardness such as diamond, sapphire, or a super hard metal. It is fixed to.

The indenter 1 is fixed to the head portion 2 by connecting a line connecting the tips c of the indenter 1 to a straight line as shown in FIG. 1, a right-angled isosceles triangle as shown in FIG. An equilateral triangular shape, a square shape as shown in FIG. 4, or a rectangular shape as shown in FIG. Each of the indenters 1 is fixed to the head portion by a strong adhesive.

In the method for measuring residual stress according to the present invention, the indenter 1 is pressed by pressing the head portion 2 of the marker against a metal surface.
Then, the metal with the mark is separated from the surroundings to release the stress, and the distance between the marks measured in the state where the stress is released and the distance between the tips of the indenter 1 are compared.

(Experimental Example 1) In order to verify the accuracy of the residual stress measurement method of the present invention, the following verification was performed using a two-point marker (see FIG. 1) having indenters of various shapes and materials shown in Table 1 below. went. To calculate the stress from the strain amount,
The following formula 1 was used, considering the test as uniaxial tension. The Young's modulus was calculated as 21,000 kg / mm ² .

[0017]

Σ = E · ε σ: stress E: Young's modulus ε: amount of distortion or less

[0018]

[Table 1] Below margin

That is, a high-tensile steel (Y
S: A strain gauge (gauge length 5 mm, 120 Ω, uniaxial) was attached to one surface of a tensile test piece S made of 78.3 kg / mm ² ), and the test piece S was set on a tensile tester, and tensile stress was applied. When a certain value was reached, marking was performed with a two-point marker, and at the same time, the value of the strain gauge was measured and then unloaded. The distance between the marks was measured with a measuring microscope, and the distance between the indenters of the marker was compared with the distance between the indenters. The amount of strain was measured and compared with the value of a strain gauge and the value of a testing machine. The results are shown in Table 1 above, and the measurement with any indenter gave an accuracy equal to or higher than that of the strain gauge. In addition,
Here, the actual load is a true value in the value of the tester, and the closer to this value, the higher the accuracy of the measured value.

(Experimental Example 2) Next, a three-point or four-point marker head 2 as shown in FIGS. 2 to 5 is used, and this head 2 is assembled into a marking jig as shown in FIG. 9 by way of example. It is also possible to inscribe the inside of the narrow pipe P. In the drawing, reference numeral 2 denotes a marker head portion that moves left and right in the figure, 3 denotes a reaction force receiver that receives the reaction force of the marker head portion 2, 4 denotes a drive transmission shaft, 5 denotes a clamp, and 6 denotes a motor.

If such a jig is used, it is possible to engrave if there is a gap into which the head part 2 of the marker can enter.
The stainless steel pipe having an inner diameter of 50 mm, an outer diameter of 70 mm, and a length of 2 m could be stamped on the inner surface of one end from the other end.

A strain gauge (gauge length: 1 mm, 120Ω, biaxial) is provided at one end of the same pipe P as shown in FIG.
After fixing to the position shown in (B), the end 50 mm was compressed with a compression tester, and when a certain load was reached, the engraved part was cut out from the opposite side of the pipe P, and between the two points in the pipe axial direction and the circumferential direction. Each distance was measured and compared with a strain gauge. Table 2 shows the results. In Table 2,-indicates a compressive force. However, four types of markers, a three-point marker and a four-point marker, were used, but the indenter was only a square pyramid diamond. As is clear from the above, it is understood that the measurement according to the present invention has obtained an accuracy equal to or higher than that of the method using a strain gauge.

The following equation 1 was used to calculate the stress from the amount of strain. The Young's modulus is 18000k
g / mm ² .

[0024]

## EQU1 ## Stress in the x direction σ _X = E · (1−γ ² ) · (ε _x + ε _y · γ) Stress in the y direction σ _y = E · (1−γ ² ) · (ε _y + ε _x · γ) σ _x : stress in x direction E: Young's modulus ε _x : amount of strain in x direction σ _y : stress in y direction γ: Poisson's ratio ε _y : amount of strain in y direction

[0025]

[Table 2]

[0026]

As described above, in the method for measuring residual stress of a metal material according to the present invention, a plurality of indenters formed in the shape of a polygonal pyramid are formed by placing a plurality of indenters at a predetermined interval with the top of a pyramid as a tip. , The head of the marker is pressed against the surface of the metal, and the indenter is used to perform engraving. Thereafter, the engraved metal is cut off from the surroundings to release the stress, and the interval between the inscriptions measured in a state where the stress is released is obtained. The residual stress of the metal is measured by comparing the distance between the tip and the tip of the indenter, and the distance between two points is always accurately measured by the pyramidal indenter on the surface of the metal to be measured for residual stress. The distance between the marks can be precisely measured after the stress release, and the measured value can be compared with the distance between the indenter tips of the markers, especially before washing or polishing. Without the need for physical, yet those conventionally that a marked effect of the measurement can be conveniently measuring the residual stress in the narrow portion of the pipe inside such difficult.

[Brief description of the drawings]

FIG. 1A is a front view showing a two-point marker head used in the measurement method of the present invention. (B) The same is a side view.

FIG. 2A is a front view showing the same three-point marker head. (B) The same is a side view.

FIG. 3A is a front view showing another example of the three-point marker head. (B) The same is a side view.

FIG. 4A is a front view showing the same four-point marker head. (B) The same is a side view.

FIG. 5A is a front view showing another example of the same four-point marker head. (B) The same is a side view.

FIG. 6A is a front view showing a triangular pyramid-shaped indenter. (B) It is a side view.

FIG. 7A is a front view showing a quadrangular pyramid-shaped indenter. (B) It is a side view.

FIG. 8A is a front view showing a tensile test piece. (B) It is a side view.

FIG. 9 is a front view showing an example of a marker jig used in the measurement method of the present invention.

FIG. 10A is a schematic diagram showing a state of a stress measurement test using a pipe. (B) It is a schematic diagram which shows the state of the stress measurement test performed by changing 90 degree angle from FIG.

[Explanation of symbols]

 Reference Signs List 1 indenter 2 head (marker) 3 reaction force receiver 4 drive transmission shaft 5 clamp 6 motor c top of pyramid (tip of indenter)

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Norio Nakajima 123, Osamu, Minami-Ina, Yasuma-cho, Seika-cho, Soraku-gun, Kyoto Nuclear Safety Systems Research Institute, Inc. (72) Hiromichi Mitsuda Hiromichi Mitsuda 123, Otani Minami-Ina, Yasuma-Small, Otani, Japan Nuclear Safety Systems Research Institute, Inc. (56) References JP-A-62-44637 (JP, A) JP-A-61-269032 (JP, A) (58) (Int.Cl. ⁷ , DB name) G01L 1/00

Claims (4)

(57) [Claims] 1. A plurality of indenters formed in the shape of a polygonal pyramid are fixed to a head portion of a marker at predetermined intervals with a top of a pyramid as a tip, and the head portion of the marker is pressed against a surface of a metal to form The metal is imprinted with an indenter, and then the metal with the imprint is separated from the surroundings to release the stress.The distance between the indentations measured in a state where the stress is released and the distance between the tips of the indenter are compared with each other. A method for measuring the residual stress of a metallic material, comprising measuring the residual stress of a metal material. 2. The method according to claim 1, wherein the indenter is diamond, sapphire,
The method for measuring residual stress of a metal material according to claim 1, wherein the polygonal pyramid is formed of any one of a cemented carbide metal, and the shape of the polygonal pyramid formed by the indenter is a polygonal pyramid whose top is located at the center of the bottom surface. 3. The method according to claim 1, wherein the plurality of indenters are arranged such that a line connecting the tips of the indenters forms a straight line. 4. The method according to claim 1, wherein the plurality of indenters are arranged so that a line connecting the tips of the indenters forms a polygon.