JPS58127159A - Reference sample body for magnetic powder flaw detection - Google Patents

Abstract

PURPOSE:To enable to perform a reliable and theoretically consistent accuracy test of a detecting force of a magnetic powder probing, by a method wherein a sample, in which a flaw, being of a similar type to that of a natural flaw to be probed, is processed, and which is of the same material as that of a sample product, is welded to a sample body. CONSTITUTION:A notch 12 is formed in a sample material 10, being of the magnetically same material as that of a sample product, the material is positioned between the nip formed by jigs 13 of a fatigue tester, and a crack 14 is produced to form a sample 16 in which a flaw 15 is produced to the same extent to that of a natural flaw. A JIS A type reference sample 6 is adhered thereto, and a grinding is made by the strength of a magnetic field which is strong enough for a magnetic powder pattern to appear on the sample 6 and so that a magnetic powder pattern appears on the flaw 15 also. The sample 6 is fitted in a sample body 11 for welding to form a reference sample body. Thus, the sample body is of the same material as that of a sample product, whereby there is neither any problem on a material, nor any problem on the adhesion gap of the reference sample 6. This enables to perform a reliable and theoretically consistent test of a detecting output of a magnetic powder probing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a standard test piece for magnetic particle flaw detection.

Conventionally, the accuracy of detection power in magnetic particle flaw detection has been determined using the method shown in FIG. 1 in the case of the residual method. That is, the test article I is magnetized while the JIS doll standard test piece 6 is adhered to the surface of the test article 1 so that the side with the artificial flaw is in close contact with the surface of the test article 1 using a test article IVC adhesive tape f7 or the like. This example shows an example of the axial energization method in which the test item 1 is passed through the cable 3 and electrode 2 in the direction of the arrow to generate magnetic flux 5, but the magnetization method allows magnetization in a direction close to perpendicular to the flaw to be detected. If it is a method, JIS G plot method, penetrating magnetic flux method etc.
A variation of the method shown in 0565 may also be used. Then, when a magnetic powder liquid 8 made at an appropriate concentration is poured onto the test piece 1 after magnetization, if a magnetic particle pattern in the form of an artificial flaw pattern is observed on the standard test piece 6, it is determined that there is detection power. . Although wet magnetic powder is used in this example, dry magnetic powder may also be used.

However, this method has the following essential drawbacks.

1) The doll standard test piece is originally used to check the performance of the device, magnetic powder, and test liquid, as well as the strength and direction of the effective magnetic field on the surface of the test piece in the continuous method, and the suitability of test operations. Therefore, even if a magnetic particle pattern is detected on the doll standard test piece, it is due to the strength of the magnetic field.

It only determines the suitability of the direction, magnetic powder liquid, etc., and does not directly indicate the detectability of flaws in the test product.

2) In the residual method, the magnetic particle pattern of the doll standard test piece is
Although it is related to the residual magnetic flux density of the test item, it is greatly influenced by the material of the test item, the contact condition between the standard test piece and the test surface, and the magnetic poles generated in the test item. Therefore, it is difficult to determine a stable residual magnetic flux density.

Therefore, it is best to use an item with natural flaws as a test specimen instead of a standard doll test piece, but this method also has the following drawbacks.

1) In order to be used as a test specimen, the lowest limit of the flaw detection specifications, that is, the smallest natural flaw is required, but such microscopic natural flaws do not always occur and are extremely difficult to obtain. be.

2) Even if you can obtain a small natural flaw that can be used as a test specimen, the size of the flaw cannot be determined from its appearance, so it is necessary to cut the flaw and examine its cross-sectional dimensions, but once cut, it can be used as a test specimen. It disappears.

It is also possible to use items with artificial flaws created by electrical discharge machining or laser machining as test specimens, but these artificial flaws are too large to be used for detecting accuracy of magnetic particle testing, and also have large surface defects. Since the opening is wide, there is a drawback that magnetic powder liquid can accumulate even if there is no residual magnetism.

The object of the present invention is to provide a standard test piece for magnetic particle flaw detection that can eliminate the above-mentioned drawbacks.

The standard test body of the present invention is obtained by welding a test piece made of the same material as a test piece processed with flaws of the same type as natural flaws to be detected, to a test body main body.

An embodiment of the present invention will be described below with reference to FIGS. 2 to 6. As mentioned above, it is necessary to create extremely fine scratches on the test piece, but the inventors focused on the fact that the width of the cracks that occur during material fatigue tests are extremely small, and developed a method to grind these cracks from the surface. The idea was to process the scratches by leaving a minute part. According to the theory of fracture mechanics, the growth rate of fatigue cracks is expressed by the following equation.

a −=cΔK”, °, a=F−′(N)
・---------(1)N where a is the crack growth depth, N is the number of stress repetitions, C・n is a constant depending on the material, and Δ is the stress intensity factor at the crack length at. This means that once the fatigue test method, sample material, and two dimensions are determined, the depth of the crack can be controlled by the number of repetitions N. Figure 2 (,) shows how fatigue cracks are generated on one side by three-point bending of a strip. When the crack length is a, the opening width δ of the crack is given by the following formula: expressed.

δ=±1 soil ・V(ξ) ・・・・・・・・・
......(2) Here, σo = 3 S P /
2W2. ξ=a/WV 0.76-2.28ξ+3.
87ξ2-2.04ξ'+ 0.66 /(1-ξ)2
E is Young's modulus (kP/tone) This crack is polished from the surface, and when only a' remains, as shown in Figure 2 (b), the opening width at that point δ'
However, when considering a model in which δ' is proportional to the depth a' of the residual crack, δ' can be made smaller as follows.

a′ δl−−×δ・・・・・・・・・・・・・・・
(3) Specifically, test pieces were prepared by the method shown in FIGS. 3 and 4. In the figure, 10 is a 4012 grade test piece material that is magnetically the same as the test piece (or a part of the test piece), and its size is 60 cuts 70 x 25 rrs.

The surface of this test material 10 has a θ flaw (for example, a width of 0.2 mm).
, a depth of about 3I11++1) or a notch 12, such as a notch, to create a state where stress concentration is likely to occur. Then, the test piece material 10 with the notch 12 processed was placed between the jigs 13, 13 of the fatigue tester, and a load of P=2000 kg was applied to
By repeating bending 400,000 times, a fatigue clutch 14 having a depth of 3 fins was generated from the end of the notch 12.

Next, the surface of the test piece material 10 where the fatigue clutch 14 was generated was ground by 3 m to remove the notch 12, expose the fatigue crack fleas 14 on the surface, and process the same type of flaw 15 as the natural flaw. A test piece 16 is obtained. In this case, as shown in Figure 4 (,
A JISA type standard test piece 6 (A 1-15150) is attached to the surface, and for simplicity, a continuous method (e.g., hand magnet) is applied to apply a magnetic field strength to the extent that a magnetic particle pattern appears on the standard test piece 6. Then, polishing is further performed so that the magnetic particle pattern of the flaw 15 appears, leaving a small opening flaw 15. This flaw 15 is almost invisible, and its size was determined from a cross-sectional photograph: width 0.5μ, depth 0.2+mm.
Met. This size is based on the theory of fracture mechanics (1) above.

It is in good agreement with equations (2) and (3). That is, if we insert the above-mentioned size and load P conditions of the test piece material 10 into equation (2) and set a = 3 runs, then = 7.2 x 10''''3 (m + n), and the remaining length of the crack is 0. Substituting .22mm into equation (3) gives δ' = 0.22/3. OX7.2 = 0.53
(μ).

In the same manner as above, various standard test pieces (A1-7750
, Al-15150, A2-7150, A2-
15150 etc.) Test piece 16 processed with flaws 15
Create. If necessary, the strength of the magnetic field at which the magnetic particle pattern appears on the standard test piece 6 is twice, three times, or half,
A standard piece 16 in which a magnetic particle pattern appears on the flaw 15 can be made with 1/3 the strength of the magnetic field.

As shown in FIG.
A hole 17 into which the test piece 16 is inserted is made in the test piece 1, and the test piece 16 prepared above is welded as shown in FIG. 6, and the weld bead is ground to obtain a standard test piece. In this case, it goes without saying that the flaw 15 should be aligned with the direction of the flaw in the detection specification of the test article.

The standard specimen thus obtained is one in which the standard specimen 16 made of the same material as the test specimen is welded to the main body 11, so there is no problem with the material as in the conventional method, and the adhesive gap between the standard specimen 6 is There is no problem, and the accuracy test of the detection power by the residual method can be performed theoretically correctly. In addition, test piece 16
Since it is small, it is easy to process, and it can be installed at the position of the test item as soon as the detection power is confirmed.

Furthermore, a test piece 16 having the necessary detection sensitivity can be created. Note that this standard test specimen can also be applied to the continuous method.

Next, another embodiment will be described with reference to FIGS. 7 to 9. This differs from the previous example only in the flaws provided on the test piece 16, and the material of the test piece 16 and the welding to the test piece main body 1 are the same as in the previous example. That is, for the test piece material,
As shown in FIG. 7, a test piece 16 was prepared by drilling a drill hole 18 as a flaw 15 with a diameter d and a length l parallel to the surface at a distance from the surface.

In this case, by changing the diameter d of the drill hole 18 and the distance from the surface, it is possible to substitute flaws for surface flaws and internal flaws of various sizes. For example, the diameter d1. om
, length l 20 mm, distance h1 from surface to center
．． The test piece 16 in which the drill hole 18 of OM was drilled and the flaw 15 was processed passed JIS A 1-151 in the continuous method.
The magnetic particle pattern appeared in a magnetic field of approximately the same strength as the magnetic field that produced the magnetic particle pattern on the 50 standard test pieces. Note that creating the flaws 15 using the drill holes 18 as in this embodiment is compared to forming the flaws 15 by generating fatigue cracks 14 in the test piece material 10 and then grinding them as in the previous embodiments. Processing is relatively easy.

Next, we will introduce the above two types of test pieces 16 and A I-15, which is the most commonly used of the JIS A type standard test pieces.
The following table shows the results of comparing the detection power with No. 150 in terms of how the magnetic particle pattern appears for the same magnetizing force.

Note ○ Magnetic particle pattern is clear △ 〃 is unclear × 〃 is unknown From this result, the commonly used JISA 1-
Even if a magnetic particle pattern appears on the 15150 standard test piece,
Width 0.5μ and depth 0.2 as an example of extremely fine defects
It has become clear that there is a limit to the detection of defects, as it may not be possible to detect surface flaws of the order of 211III+ and defects located at a depth of 0.5 or more. Therefore, by using the standard test specimen of the present invention, more severe detection power can be determined.

The standard test specimen of this invention is as described above, and it has a structure in which a test piece made of the same material as the test product processed with the same type of natural flaw as the natural flaw to be detected is welded to the test specimen body, which is theoretically contradictory. It is possible to reliably test the detection power of magnetic particle flaw detection without any problems.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are explanatory diagrams showing the procedure of a conventional detection power accuracy test, Figure 2 (,) is an explanatory diagram of the fatigue crack generation mechanism, and Figure 2 (b) is an explanatory diagram showing the procedure of a conventional detection power accuracy test. The enlarged explanatory views of the cracked portion in Figures (,) and Figures 3 to 6 show an example of the standard test specimen of this invention, and Figure 3 shows the situation in which fatigue cracks occur in the test piece material. Fig. 4 is a perspective view showing the adjustment status of fatigue cracks in the test piece;
The figure is a perspective view of the test specimen body, FIG. 6 is a longitudinal section of a standard test specimen, and FIGS. 7 to 9 show other embodiments. FIG. 9 shows the fifth example of the above embodiment.
FIG. 6 is a diagram corresponding to FIG. Throat...Test body, 15...Flaws, 16...Test piece applicant's representative Patent attorney Takehiko Suzue Figure 4 Figure 5 Figure 6 Figure 1 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] A standard test piece for magnetic particle flaw detection, made by welding a test piece made of the same material as the test piece with the same type of natural flaw to be detected to the test piece body.