JP4764249B2 - Crack growth test method and crack growth test apparatus - Google Patents

Description

  The present invention relates to a crack propagation test method and a crack propagation test apparatus for propagating a crack formed on a test piece in order to test the soundness of a structural material.

  There is a possibility that stress corrosion cracking (SCC) occurs in the in-core equipment of a boiling water reactor and the structural integrity is impaired. For this reason, there is a need for a test method for measuring the crack growth rate by SCC with high accuracy.

For example, Patent Document 1 discloses a small and inexpensive crack growth characteristic evaluation apparatus.
JP-A-8-278241

  In general, it is considered that the crack growth rate is governed by the stress intensity factor. For this reason, the crack growth life evaluation of the actual machine is performed using the relationship between the crack growth rate and the stress intensity factor by SCC obtained by the test.

  The crack growth rate data from tests in a simulated reactor water environment vary widely, and obtaining reliable test data is desired to determine the crack growth rate at a certain stress intensity factor. However, in the conventional test method using a compact tension type test piece, the stress intensity factor changes as the crack length increases, so that there is a problem that the crack growth rate at a specific stress intensity factor cannot be accurately determined.

  In order to solve the above-described problems, an object of the present invention is to make it possible to perform a crack growth test in which a crack is propagated with a constant stress intensity factor.

In order to achieve the above-mentioned object, the present invention provides a flat test piece having a pair of short sides and a pair of long sides, and the crack of the test piece having a crack on one of the pair of long sides. In the crack growth test method for propagating cracks, a crack is formed in the test piece to form a crack with a value obtained by dividing the crack length by the length of the short side of the test piece from 0.4 to 0.7. A step of applying a uniform forced displacement to one of the pair of short sides of the test piece perpendicular to the direction in which the crack extends and the entire short side, and maintaining the forced displacement constant; and It is characterized by having.

Further, the present invention provides a flat plate-shaped test piece having a pair of short sides and a pair of long sides, and a crack propagation for propagating a crack of the test piece having a crack on one of the pair of long sides. In the test apparatus, one of the pair of short sides of the test piece in which a crack having a value obtained by dividing the crack length by the length of the short side of the test piece is 0.4 to 0.7 is formed. It has a holding means which applies a uniform forced displacement to the whole of the short side perpendicular to the direction in which the crack extends, and keeps the forced displacement constant.

  According to the present invention, it is possible to perform a crack growth test in which a crack is propagated with a constant stress intensity factor.

  Embodiments of a crack growth test method and a test apparatus therefor according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or similar structure, and the overlapping description is abbreviate | omitted.

[First Embodiment]
FIG. 1 is a front view of a test piece used in the crack growth test method according to the first embodiment of the present invention. FIG. 2 is a side view of the test piece of FIG.

  The test piece 1 is a rectangular plate having a uniform plate thickness and surrounded by a pair of long sides 21 and a pair of short sides 22.

  The crack growth test has a crack forming process for forming a crack 2 on the test piece 1 and a holding process for applying displacement to the test piece 1 and holding it. In the crack forming step, the crack 2 is formed so that the tip 20 is positioned substantially in the center of the test piece 1 so as to be substantially parallel to one long side 21 to the short side 22 of the test piece 1.

  One short side 22 is fixed to the rigid wall 3 so that the crack 2 is substantially parallel to the rigid wall 3. In the holding step, a uniform forced displacement is applied to the entire side of the side facing the rigid wall 3 across the crack 2 of the test piece 1, and the forced displacement is held constant. In FIG. 1, the direction of forced displacement applied to the test piece 1 is indicated by a dashed arrow 4.

  Next, the fact that the stress intensity factor is almost constant in such a crack growth test is shown using the results of numerical analysis simulating this test.

  FIG. 3 is a diagram showing a numerical analysis model simulating a crack growth test.

  Here, the length of the test piece 1 is 200 mm, the width is 100 mm, and a crack 2 having a length a is formed vertically from one long side 21. In the analysis, a half portion is modeled in consideration of symmetry. A state in which a uniform forced displacement of 0.025 mm is applied to the entire short side 22 of the test piece 1 in the direction of the long side 21 so as to pull the test piece 1 is simulated.

  FIG. 4 is a graph showing the stress intensity factor K obtained by numerical analysis while changing the crack length a. The horizontal axis of the graph represents the non-dimensional crack length a / W obtained by dividing the crack length a by the length W of the short side 22 of the test piece 1 to make it dimensionless.

  From FIG. 4, the stress intensity factor K increases with increasing crack length when a / W is between 0.1 and 0.4, while a / W is between 0.4 and 0.7, It can be seen that the crack length is almost constant when the crack length is between 40% and 70% of the plate width. Therefore, this range is set as a test range.

  Thus, when the crack length a is within a predetermined ratio range of the width of the test piece 1, the stress intensity factor K is substantially constant. Therefore, by forming a crack 2 having a crack length in this range on the test piece 1, the stress intensity factor is constant by a very simple method of giving a uniform displacement to one end of the test piece 1. A crack growth test can be performed.

  In the crack growth test, after the holding process, a release process for unloading the force applied to apply the forced displacement to the test piece 1 is added, and after the release process, the crack 2 of the test piece 1 is again performed. The forced displacement may be repeatedly applied to the test piece 1 by applying a uniform forced displacement to the entire side facing the rigid wall 3 across the surface and keeping the forced displacement constant.

  In addition, the shape of the test piece 1 is not limited to a rectangle.

[Second Embodiment]
FIG. 5 is a front view of a test piece used in the crack growth test method according to the second embodiment of the present invention. FIG. 6 is a side view showing the test piece of FIG. 5 together with the main part of the crack growth test apparatus.

  On both short sides 22 of the test piece 1, grip portions 5 having a plate thickness greater than the plate thickness where the crack 2 is formed are formed. The rigidity of the grip portion 5 is larger than that of the portion where the crack 2 is formed because the plate thickness is thick.

  The crack growth test apparatus has a load mechanism including two chucks 6 and a ball screw 7 facing each other. Each of the two chucks 6 can hold the grip portion 5 of the test piece 1. A ball screw 7 is attached to one chuck 6. The other chuck 6 is fixed to the rigid wall 3. The ball screw 7 is guided by a guide 8.

  The grip 5 is held by two chucks 6. The ball screw 7 gives a constant forced displacement to the end surface of the test piece 1 by controlling the rotation angle.

  In addition, a seal member can be used as the guide 8 and a crack growth test can be performed in a simulated reactor water environment.

[Third Embodiment]
FIG. 7: is a side view which shows the test piece used for the crack growth test method of 3rd Embodiment based on this invention with the principal part of a crack growth test apparatus.

  The crack growth test apparatus according to the present embodiment includes a hydraulic cylinder 9 directly attached to the chuck 6, a displacement meter 10 that measures the displacement between the chuck 6, and a servo controller 11 that controls the displacement of the hydraulic cylinder. Have.

  The servo controller 11 receives the displacement between the chucks 6 measured by the displacement meter 10, and controls the displacement of the hydraulic cylinder 9 so that the amount of displacement is maintained constant. The hydraulic cylinder 9 applies a forced displacement to the chuck 6. Thereby, a highly accurate stress intensity factor constant crack growth test is possible.

  In this embodiment as well, a crack propagation test in a simulated reactor water environment is possible by using a seal member for the guide 8.

  The above description is merely an example, and the present invention is not limited to the above-described embodiments, and can be implemented in various forms. Moreover, it can also implement combining the characteristic of each embodiment.

It is a front view of the test piece used for the crack growth test method of a 1st embodiment concerning the present invention. It is a side view of the test piece of FIG. It is a figure which shows the numerical analysis model which simulated the crack growth test. It is a graph which shows the stress intensity factor K calculated | required by changing the crack length a by numerical analysis. It is a front view of the test piece used for the crack growth test method of 2nd Embodiment which concerns on this invention. It is a side view which shows the test piece of FIG. 5 with the principal part of a crack growth test apparatus. It is a side view which shows the test piece used for the crack growth test method of 3rd Embodiment which concerns on this invention with the principal part of a crack growth test apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Test piece, 2 ... Crack, 3 ... Rigid body wall, 5 ... Grab part, 6 ... Chuck, 7 ... Ball screw, 8 ... Guide, 9 ... Hydraulic cylinder, 10 ... Displacement meter, 11 ... Servo controller

Claims (10)

In the crack growth test method for propagating a crack of the test piece having a pair of short sides and a pair of long sides and having a crack on one of the pair of long sides ,
A crack forming step for forming a crack in which the value obtained by dividing the crack length by the length of the short side of the test piece is 0.4 to 0.7 on the test piece ;
One of the pair of short sides of the test piece is subjected to a uniform forcible displacement perpendicular to the direction in which the crack extends and the entire short side , and the forced displacement is kept constant.
A crack growth test method characterized by comprising:
After the holding step, a releasing step of unloading the force applied to apply the forced displacement to the test piece;
After the releasing step, applying the forced displacement to the test piece, a re-holding step of keeping the forced displacement constant,
The crack growth test method according to claim 1, wherein: The holding step includes
A measuring step for measuring a displacement applied to the test piece;
Feeding back the displacement measured in the measuring step to servo-control the displacement applied to the test piece;
The crack growth test method according to claim 1 or 2, characterized by comprising:   The crack growth test method according to any one of claims 1 to 3, wherein in the holding step, the test piece is disposed in water.   2. The method according to claim 1, further comprising an analysis step of determining, by numerical analysis, a shape of the test piece and a range of a crack length to be advanced in the holding step before the crack formation step. 5. The crack growth test method according to any one of 4 above. In a crack growth test apparatus for propagating a crack of the test piece having a pair of short sides and a pair of long sides and having a crack on one of the pair of long sides ,
The crack is formed on one of the pair of short sides of the test piece on which a crack having a value obtained by dividing the crack length by the length of the short side of the test piece is 0.4 to 0.7 is formed. Holding means for applying a uniform forced displacement to the whole of the short side perpendicular to the extending direction, and keeping the forced displacement constant;
A crack growth test apparatus characterized by comprising:
The test piece includes a grip portion having a predetermined rigidity at both ends in a direction in which displacement is applied across the crack,
The holding means grips the grip part, applies the forced displacement that is uniform over the entire direction parallel to the crack of the grip part, and keeps the forced displacement constant.
The crack growth test apparatus according to claim 6.   The crack propagation test apparatus according to claim 6 or 7, wherein the holding means has a ball screw mechanism extending in the direction of the forced displacement. The holding means is
A cylinder extending in the direction of the forced displacement;
A hydraulic mechanism capable of controlling the displacement of the cylinder;
The crack growth test apparatus according to claim 6 or 7, characterized by comprising: The holding means is
Measuring means for measuring the displacement applied to the test piece;
Control means for feeding back the displacement measured by the measuring means to servo-control the displacement of the cylinder via the hydraulic mechanism;
The crack growth test apparatus according to claim 9, wherein:

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