JP5865964B2 - Fracture toughness test method - Google Patents

Description

The present invention relates to a fracture toughness test method and a fracture toughness test method.

A reactor pressure vessel of a boiling water reactor (hereinafter referred to as BWR) is a vessel containing a fuel, a control rod, a shroud, a steam separator, a steam dryer, and the like. Conventionally, boiler steel sheets have been used for the reactor pressure vessel, but research and development have progressed, and ferritic steels have been studied. ASTM A533 steel and the like are now in wide use.

Ferritic steel used in nuclear reactor pressure vessels has a body-centered cubic structure, and it is known that the brittle-ductile transition temperature rises due to neutron irradiation due to embrittlement at low temperatures and the energy on the upper shelf decreases. . Therefore, in the reactor pressure vessel, material embrittlement is concerned due to the influence of the operating environment such as temperature during operation, neutron irradiation, etc. In order to confirm the degree of material embrittlement,
A surveillance test is being conducted. The specimen used for analysis in this surveillance test is
It is stored in the same material and usage environment as the device under test, and the state of the device in service is estimated from the change in the material properties of this test piece.

In BWR, Charpy impact test pieces and tensile test pieces are loaded in the pressure vessel as monitoring test pieces used in the steel surveillance test in pressure vessels, and Charpy absorbed energy obtained from Charpy impact tests is evaluated in fracture toughness. From the master curve method.

The fracture toughness value evaluated from this Charpy absorbed energy is effective as a deterioration evaluation, but is not an absolute value of the fracture toughness value that can be directly reflected in design and evaluation. The Charpy impact test is a dynamic test, and a fracture toughness test using a double cantilever test piece in a form defined by general ASTM or JSME, that is, a CT (Compact Tension) test piece is a test speed. Are different and may not necessarily match in the brittle and ductile transition regions.

In BWR, the method of regenerating the monitoring specimen was standardized by JECA4201 of the Japan Electric Association, but this is not an evaluation method that directly acquires the fracture toughness value.

JP 2003-294880 A

From the monitoring specimen of the pressure vessel steel in the conventional BWR described above, there is a problem that there is no evaluation method for directly obtaining the fracture toughness value.

The present invention has been made in order to solve the above-described problems. Focusing on the tensile test piece among the monitoring test pieces of the reactor pressure vessel steel, the parallel portion of the remaining material after the tensile test or the parallel of the tensile test piece is provided. An object is to provide a method of obtaining a fracture toughness value from a maximum load during a test by introducing a notch into a part and then performing a fracture test by bending or tension.

In the fracture toughness test method according to the present invention, a mechanical notch is introduced into a parallel part of a monitoring tensile test piece having a parallel part formed in the center, and then a test piece into which a fatigue precrack is introduced is produced, and a bending test is performed. Alternatively, a tensile test is performed, and the fracture toughness value is obtained from the maximum load leading to fracture.

  In the present invention, a fracture toughness test result can be obtained from one monitored tensile test piece.

Explanatory drawing which shows the tension | pulling and fracture toughness testing method based on this invention. The side view which shows the test piece used for the other Example of this invention. (A)-(c) is sectional drawing which shows the state of a perimeter, both sides, and one side notch, respectively. The side view which shows the test piece which processed the one side used for the other Example of this invention to the parallel part diameter. The side view which shows the round bar test piece which removed the tensile test piece screw part used for the other Example of this invention. The block diagram which shows the fracture toughness evaluation flow using the monitoring tensile test piece.

Hereinafter, for the fracture toughness test method using a tensile test piece of the monitoring test piece according to the present invention,
This will be described with reference to the drawings.

Example 1
A method of performing a fracture toughness test from the remaining specimen of the monitored tensile test piece 1 cut by using the monitored tensile test using a tensile test piece having a parallel portion formed in the center, which is one of the surveillance tests, will be described. .

After producing the round bar 2 thinned to the diameter of the parallel part 1c of the original monitored tensile test piece 1 for the longer remaining material 1a of the monitored tensile test piece 1 cut after the test, By forming a mechanical notch in the center in the axial direction, introducing a fatigue crack 6 on one side, and performing a fracture test by bending, the maximum load leading to fracture can be obtained, and the fracture toughness value can be obtained .

By this method, both a tensile test result and a fracture toughness test result can be obtained from a single monitored tensile test piece.

However, only the round bar 2 processed from the longer remaining material 1a is short, and there is a possibility that a sufficient bending test cannot be performed. Therefore, as shown in FIG. 1, the longer remaining material 1a after the tensile test
For both of the remaining material 1b and the shorter remaining material 1b, after manufacturing the round bars 2 and 3 processed to the diameter of the parallel portion 1c of the initially monitored tensile test piece 1, the round bar 3 manufactured with the shorter remaining material 1b is prepared. A round bar test piece 4 in which a round bar 3 made of the shorter remaining material 1b divided into two at both ends of the round bar 2 made of the longer remaining material 1a is cut and joined 5 by welding or the like. Is produced.

By introducing a mechanical notch + fatigue precrack 6 on one side at the center of the round bar test piece 4 and conducting a fracture test by bending, the maximum load leading to fracture can be obtained, and the fracture toughness value can be obtained. .

In general, welding can be considered as a method 6 for joining the round bar 2 processed from the longer remaining material 1a of the monitored tensile test piece 1 and the round bar 3 manufactured from the shorter remaining material 1b. However, considering that the test piece is small, a joining method with low heat input is desirable.

As a low heat input joining method, non-melting joining is performed such as friction welding (friction stir welding) in which two members to be joined are brought into contact with each other while rotating at high speed, and these are joined by frictional heat at the contact portion, Diffusion bonding that includes heating and pressurization without melting the material, diffusing atoms at the bonding interface across the bonding surface, and obtaining a metallurgically complete bonding portion is used, but other bonding methods are used as appropriate Of course you can.

(Example 2)
Next, a method of performing a direct fracture toughness test without performing a tensile test from the monitored tensile test piece 1 will be described.

As a test material, ASTM A533 Gr. B Cl. 1 low alloy steel (C: 0.2
1%, Si: 0.26%, Mn: 1.46%, P: 0.018%, S: 0.023%, N
i: 0.56%, Mo: 0.48%), and a small test piece 7 (parallel part: φ6.35 mm) described in ASTM A370 shown in FIG. 2 was used as the test piece.

As the notch introduction position on the surface, there are three possible positions, ie, the notch 11 on the entire circumference, the notch on both sides 12 and the notch 13 on one side shown in FIGS. In addition, as a method of destroying the test piece, there are two methods of tensioning in the axial force direction and the bending test shown in Example 1. In the case of tensioning in the axial force direction, both the axial force moment and the bending moment are considered. Considering that there is a need to consider and that the monitoring specimen is in an irradiation environment and is not easy to handle, the bending test is considered easier.

In conducting the bending test, the notch portions 11, 12, 1 introduced into the bending support portion and the parallel portion.
3 must be on the same surface, as shown in FIG. 4, a test piece 21 with one side processed to a parallel part diameter, or a round bar test piece 31 with the entire parallel part diameter shown in FIG. It is necessary to manufacture a test piece from which the tensile test piece screw part is removed.

Here, a round bar test piece 31 was used, and the notch size obtained by machining before introducing the fatigue precrack was set to about 1.5 mm, and then the fatigue precrack was introduced on one side of the surface. Moreover, the bending test in a present Example repeatedly implemented two tests in the environment of -150 degreeC as a brittle material simulation. When the fracture surface after this bending test was observed, all of them except the mechanical notches 11, 12, 13 and the fatigue precrack 14 were brittle fracture surfaces. As a result, brittle fracture occurred and the maximum load value could be obtained by the proposed bending test.

The K value of round bars with surface cracks subjected to bending is shown in Reference 1 (Kiuchi et al., Brittle Fracture Strength Evaluation of Round Bars with Surface Notches, Iron and Steel, Vol68, No13 (1982), p1830-1838). For reference (1
) Formula.

K = M _b · σ _b · √ (πa) (1)
M _b = 1.12- (2.37 / D + 0.36 / R) a + (4.44 / D ² + 0.663 / (R ・) a ² + (1.35 / D ³ -2.81 / (R ・ D ² ) a ³
D: Specimen diameter
M _b : Bending moment
a: Crack length σ _b : K value can be obtained using a round bar test piece 31 using an equation greater than bending stress, and it can be confirmed that a fracture toughness value is obtained directly from a monitoring tensile test. It was.

(Example 3)
Next, the tensile toughness test will be examined. In order to obtain a fracture toughness value from a round bar type tensile test piece, it is necessary to introduce a notch into the test piece. In particular, since the notch shape is important, it is important to introduce the target notch shape to the round bar test piece. In the round bar type tensile test piece, as shown in Fig. 3 (a), if a uniform notch 11 can be given to the entire circumference, a published literature (STRESS INTENSITY FACTORS HANDBOOK, Vol.2, 643 -64
5 `` A CIRCUMFERENTAL CRACK OR AN INFINITE ROW OF CIRCUMFERENTIAL CRACKS IN A CYLI
Fracture toughness evaluation described in “NDICAL BAR UNDER TENSION”) is possible.

However, the object this time is a brittle material, and it is difficult to give a uniform notch to the entire circumference. In addition, when a test is performed with a load applied in the axial force direction with a one-side surface notch, there is a possibility that bending is generated only on one side and bending stress is generated. Therefore, in order to perform a tensile type fracture toughness test, it is desirable to have notches on both sides as shown in FIG. 3 (b), where fracture is assumed to progress evenly in the direction of the tensile axis.

Example 4
When a fracture toughness test is performed using an actual monitored tensile specimen, it is assumed that the test material is not brittle but is ductile. In the case of a ductile material, the K value cannot be obtained, and the J value is obtained. A plurality of crack specimens can be considered as a method for obtaining the J value, but it is difficult to apply to a monitoring tensile specimen having a limited number.

Since it is desirable to acquire the fracture toughness value from one monitored tensile test piece, the fracture toughness value acquisition using the round bar type tensile test piece can be performed with one test piece by proceeding with the evaluation according to the flow of FIG. Evaluation is possible. After the fatigue precrack is introduced, the crack is propagated by bending and a load-opening displacement diagram is obtained. If it is brittle, the K value is obtained from the maximum load value and the fracture surface observation result. If yes, evaluate as a ductile material.

Therefore, according to Examples 1 to 4, both the tensile test result and the fracture toughness test result can be obtained from one monitored tensile test piece.

DESCRIPTION OF SYMBOLS 1 ... Monitoring tensile test piece, 1a, 1b ... Remaining material, 1c ... Parallel part, 2 ... Round bar processed from longer remaining material, 3 ... Round bar processed from shorter remaining material, 4 ... Remaining material Round bar specimen manufactured by joining, 5
... Junction, 6 ... Notch + fatigue pre-crack, 7 ... Small tensile specimen, 11, 12, 13 ... Machined notch, 14 ... Fatigue pre-crack, 21 ... Partially flat bending specimen, 31 ... Round bar bending test piece.

Claims (5)

After introducing a mechanical notch into the parallel part of a monitored tensile test piece with a parallel part in the center, manufacture a test piece with a fatigue precrack, and perform a bending test or a tensile test. A fracture toughness test method characterized by obtaining a fracture toughness value from a load. Said mechanical notch, said is a notch on one side of a mechanical cut formed from the outer surface in one direction perpendicular to the axis of the monitoring tensile bar, with respect to the test piece, carried out destructive test by bending The fracture toughness test method according to claim 1, wherein a fracture toughness value is obtained from a maximum load leading to fracture. The test piece is removed by machining the threaded portion of the monitoring tensile specimen, introducing the mechanical notch fracture toughness testing according to claim 2, characterized in that the introduction of Fatigue pre Crack Method. The test piece, after said monitor tensile specimen machined by a round bar which is removed to the diameter of all the parallel portion, and introducing the mechanical notch, characterized in that the introduction of Fatigue pre Crack The fracture toughness test method according to claim 2. The mechanical notch is formed by introducing a uniform mechanical notch on the entire circumference or a mechanical notch on both sides formed in one direction from the outer surface perpendicular to the axis and in a direction opposite to this one direction. The fracture toughness test method according to claim 1, wherein a fatigue precrack is introduced.

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