JP2007192645A - Crack shape identifying method and system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely detect a change of a crack shape even in a case that a crack shows a minute shape change. <P>SOLUTION: In this crack shape identifying method, voltage is applied to the voltage applying position in the vicinity of the cracks of a plurality of preparatory test targets, which have cracks different in shape from each other are formed, in order to identify the shape of the crack of a test target and the potential difference at the potential difference measuring position in the vicinity of the cracks when a current is allowed to flow is evaluated to calculate potential difference standard data (S1 and S2). Next, voltage is applied to the voltage applying position to allow a current to flow to the test target and the potential difference at the potential difference measuring position is measured to determine potential difference actually measured data (S5). The crack shape is determined so that both of the square of the difference between the potential difference actually measured data and the potential difference reference data at the potential difference measuring position and the response of the sum total of them become minimum to identify the crack shape of the test target (S6). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a crack shape identification method and a crack shape identification system formed on a specimen.

  In structures such as reactor pressure vessel reactor structures and reactor primary system piping that come into contact with nuclear reactor primary system cooling water in nuclear power plants, stress corrosion cracking (SCC) may occur due to exposure to high-temperature water. . When a crack due to SCC or the like occurs in such a structure, it is necessary to accurately evaluate the crack propagation life and perform life prediction in order to evaluate the structural integrity. For this purpose, a crack propagation characteristic evaluation test is performed using a fracture mechanics type test piece or a pipe-shaped specimen under environmental conditions simulating the use environment, and crack propagation characteristic data by SCC of the target material is collected.

  When a crack is generated and propagated in such a structure, the crack is formed in the state of a surface crack on the surface of the structure, so the shape changes when such a crack propagates. Must be measured with high accuracy.

  As a method for detecting a semi-elliptical crack shape existing on the surface of a flat or pipe-shaped specimen, a method using a potentiometric method is disclosed. This method is a method of measuring a crack shape from a distribution of measured potential differences by installing a plurality of potential difference measuring probes in the vicinity of the crack (for example, see Non-Patent Documents 1 to 3).

In addition, in Patent Document 1, regarding a simple evaluation method of a crack shape by a potential difference method for a surface crack of a flat specimen, a potential difference ratio is obtained from a measured potential difference by a potential difference method, and a separately prepared crack length and potential difference ratio are obtained. A method of determining the crack depth and the surface length of the crack from the relationship with the master curve indicating the relationship is disclosed. Patent Document 2 discloses a method for measuring the depth of a crack by a potential difference in a sample when the depth is uniform.
Japanese Patent Laid-Open No. 10-300698 JP 2000-11509 A Hayashi, et al., “Detection of surface crack shape by DC potential method”, Materials, 1984, Vol. 33, No. 368, p. 602 Hayashi et al., “Detection of Fatigue Crack Shape on Stainless Steel Pipe by DC Potential Method”, Materials, 1986, Vol. 35, No. 395, p. 936 Y. Hashimoto, 4 others, "Procedure of Crack Shape Determination by Reversing DC Potential Method", Nuclear Engineering Design, 1992, 138, p. 259

  Cracks due to SCC generated on the surface of the structure are generally semi-elliptical, and the progress due to SCC is often small, unlike fatigue. Although the prior art shows a crack shape detection method by a potential difference method for a state in which a semi-elliptical crack on the surface of a specimen changes greatly in a similar shape in the plate thickness direction, No means or method for accurately measuring a minute shape change is known.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to detect a crack shape change with high accuracy even when the crack shows a minute shape change.

  In order to solve the above-mentioned problems, the present invention provides a crack shape identification method for identifying the shape of a crack in a specimen, and voltage application in the vicinity of a crack in a plurality of preliminary specimens in which cracks having different shapes are formed. A potential difference evaluation preliminary step for evaluating potential differences at a plurality of potential difference measurement positions in the vicinity of the crack when a voltage is applied to the position and flowing a current to obtain potential difference reference data; and a voltage is applied to the voltage application position. A potential difference measurement step for obtaining a potential difference actual measurement data by passing a current through the test body and measuring a potential difference at the potential difference measurement position, and the potential difference actual measurement data and the potential difference reference data at each potential difference measurement position regarding a change in crack shape. To identify the crack shape of the specimen by determining the crack shape that minimizes both the square of the difference and the response of the sum of them. And having a degree, the.

  The present invention also relates to a crack shape identification system for identifying the shape of a crack in a specimen, wherein the power source, a pair of current application probes connected to the power source, a potentiometer, and the potentiometer are connected. Plural pairs of potentiometric probes and a plurality of proximate cracks when a current is applied to a voltage application position near the cracks of a plurality of preliminary test specimens formed with cracks having different shapes. Potential difference reference data obtained by evaluating a potential difference at a potential difference measurement position, and potential difference actual measurement data obtained by applying a voltage to the voltage application position to cause a current to flow through the specimen and measuring the potential difference at the potential difference measurement position. The difference squared and the total sum response of the potential difference measurement data and the potential difference reference data at each potential difference measurement position with respect to the crack shape change By determining the so defunct 裂形 shape having a small, and having a data acquisition and control device for identifying the shape of the crack of the specimen.

  According to the present invention, it is possible to accurately detect a crack shape change even when the crack shows a minute shape change.

  An embodiment of a crack shape identification method 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.

[Embodiment 1]
FIG. 3 is a block diagram of the crack shape identification system according to the first embodiment of the present invention.

  The crack shape identification system 9 includes a potentiometer 10, a DC power supply 11, a current alternating switch 12, and a data collection / control device 13. The potentiometer 10, the DC power supply 11, and the current alternating switch 12 are each connected to a data collection / control device 13.

  A current application probe 16 is connected to the DC power source 11 via a current application line 17. The DC power supply 11 is connected to a current alternation switch 12 so that a DC current flowing through the current application probe 16 can be alternated.

  A potentiometer 11 is connected to the potentiometer 11 via a potential difference measuring line 15. The potential difference between the potential difference measuring probes 14 is transmitted to the data collection / control device 13 via the potentiometer 10.

  FIG. 4 is a diagram showing details of a method of attaching the current application probe and the potential difference measurement probe of the crack shape identification system according to the first embodiment of the present invention to a test specimen, wherein (a) shows the surface of the test specimen. FIG. 2B is a cross-sectional view of the specimen.

In the present embodiment, A ₃ , A ₂ , A ₁ , A ₀ , A _{1 ′} , A _{2 ′} , A _{3 ′ are} positioned at the potential difference measurement position in the vicinity of the crack 7 to be identified formed on the surface of the specimen 8. 7 pairs of potential difference measuring probes 14 are installed. The potential difference measurement position is represented as i (i = 3, 2, 1, 0, 1 ′, 2 ′, 3 ′). Each pair of potential difference measuring probes 14 is attached to the surface of the test body 8 as shown in FIG. 4A so as to sandwich the crack 7 indicated by the oblique lines in FIG. The potential difference measuring probe 14 is attached to the surface of the specimen 8 by spot welding, for example. A pair of current application probes 16 is provided at a voltage application position across the potential difference measurement probe 14. The current application probe 16 is attached to the surface of the specimen 8 by spot welding, for example.

  The number of pairs of potential difference measuring probes 14 is not limited to seven, and can be arbitrarily set according to the size of the crack, the target crack resolution, and the like.

  Next, a crack measurement method using this crack shape identification system 9 will be described.

  FIG. 1 is a flowchart showing a procedure of a crack shape identification method by a potential difference method according to the present invention.

  The measurement procedure is divided into two parts: a database creation part A at the front stage and a crack shape identification part B at the rear stage. The determination part A of the calibration formula is divided into steps S1 to S4, and the crack shape identification portion B is divided into steps S5 and S6.

  In the database creation part A, potential difference distributions corresponding to various crack shapes are obtained between a plurality of potential difference measuring probes 14 in the vicinity of the crack, and a potential difference distribution reference database relating to crack shapes and potential differences is created.

  A step of evaluating a change in potential difference when the shape of the crack 7 changes between a plurality of potential difference measurement probes 14 in the vicinity of the crack is referred to as a potential difference evaluation preliminary step. This process can be divided into process S1 and process S2.

  FIG. 2 is a cross-sectional view of a test body in which a crack is formed.

  In step S1, the shape of a surface crack having a plurality of combinations of different crack depths a and crack lengths 2c as shown in FIG. 2 is set.

In step S2, a plurality of test bodies 8 (preliminary test bodies) having the crack shape set in step S1 are used, and a potential difference measurement position in the vicinity of the crack 7 when a voltage is applied to the voltage application position and a current flows. The potential difference at is evaluated. First, a pair of current application probes 16 is attached to the test body 8 at a voltage application position that sandwiches the crack 7. Further, seven pairs of potential difference measurement probes 14 are attached to the test body 8 at potential difference measurement positions that sandwich the crack 7. Thereafter, a voltage is applied between the current application probes 16 to cause a current to flow through the specimen 8, and the potential difference measurement probe 14 measures the potential difference at the potential difference measurement position by the potential difference method. Here, the measured potential difference at the potential difference measurement position i (i = 3, 2, 1, 0, 1 ′, 2 ′, 3 ′) is V _i .

  As the potential difference method, generally two types of methods, a direct current method and an alternating current method, are known, and either method can be adopted. Here, a measurement system 9 using an alternating DC potential difference method is used.

  In step S3, a reference potential difference that is a fixed value for normalization is measured. This process is referred to as a reference potential difference evaluation preliminary process.

  FIG. 5 is a diagram showing details of a method of attaching the current application probe and the potential difference measurement probe of the crack shape identification system according to the first embodiment of the present invention to a test specimen in order to measure a reference potential difference. a) is a surface view of the specimen, and (b) is a cross-sectional view of the specimen.

Unlike the step S2, the current application probe 16 and the potential difference measurement probe 14 are respectively attached to the specimen 8 having no crack or the place where the influence of the crack of the specimen 8 can be ignored. At this time, the reference voltage application position and the reference potential difference measurement position to which the current application probe 16 and the potential difference measurement probe 14 are attached are the same as the voltage application position and the potential difference measurement position in step S2. The reference potential difference measurement position corresponding to i (i = 3, 2, 1, 0, 1 ′, 2 ′, 3 ′) is ir (i = 3, 2, 1, 0, 1 ′, 2 ′). , 3 ′) and attached to the reference potential difference measurement position corresponding to the potential difference measurement probe A ₃ , A ₂ , A ₁ , A ₀ , A _{1 ′} , A _{2 ′} , A _{3 ′} attached to the potential difference measurement position. The obtained potential difference measurement probes 14 are referred to as A _r3 , A _r2 , A _r1 , A _r0 , A _{r1 ′} , A _{r2 ′} , and A _{r3 ′} , respectively. The potential difference at the measured reference potential difference measurement position ir (i = 3, 2, 1, 0, 1 ′, 2 ′, 3 ′) is defined as V _ir .

FIG. 6 is a graph showing a characteristic example of the potential difference V _i near the crack and the reference potential difference V _ir .

  In step S2 and step S3, the potential difference at the potential difference measurement position may be obtained by performing a potential distribution analysis using a finite element method or the like instead of actually measuring the specimen 8 by the potential difference method. .

In step S4, the potential difference value at each potential difference measurement position obtained by measurement or analysis in step S2 is divided by the fixed value obtained in step S3. That is, the potential difference V _i at the potential difference measurement position i (i = 3, 2, 1, 0, 1 ′, 2 ′, 3 ′) is converted into the corresponding reference potential difference measurement position ir (i = 3, 2, 1). , 0, 1 ′, 2 ′, 3 ′) is divided by the reference potential difference V _ir of the crack-free portion. As a result, the normalized potential difference (potential difference distribution reference data) V _i / V _ir at the potential difference measurement position i is obtained, and a potential difference distribution reference database is created for crack shapes of various combinations of crack depth a and crack length c. To do. This process is called a database creation process.

  In the crack shape identification portion B, first, measurement by the potential difference method is performed on the target specimen. This step is referred to as a potential difference measurement step (step S5). Next, the crack shape is determined by the response surface method. This process is called an identification process (process S6).

In step S5, first, as in step S2, the potential difference at the potential difference measurement position in the vicinity of the crack 7 when a voltage is applied to the voltage application position and a current flows is evaluated. At this time, the voltage application position and the potential difference measurement position to which the current application probe 16 and the potential difference measurement probe 14 are attached are the same as the voltage application position and the potential difference measurement position in step S2. First, a pair of current application probes 16 is attached to the test body 8 at a voltage application position that sandwiches the crack 7. Further, seven pairs of potential difference measurement probes 14 are attached to the test body 8 at potential difference measurement positions that sandwich the crack 7. Then, a voltage is applied between the current application probe 16, a current flows to the specimen 8, the potential difference measuring probe 14 to measure the potential difference P _i in potentiometric measurement position i by potentiometry.

Similarly to the step S3, the current application probe 16 and the potential difference measurement probe 14 are respectively attached to the test body 8 having no crack or the place where the influence of the crack of the test body 8 can be ignored. At this time, the reference voltage application position and the reference potential difference measurement position to which the current application probe 16 and the potential difference measurement probe 14 are attached are the same as the voltage application position and the potential difference measurement position in step S5. Thereafter, a voltage is applied between the current application probes 16 to pass a current through the test body 8, and the potential difference P _ir at the reference potential difference measurement position ir is measured by the potential difference measurement probe 14.

Further, the potential difference P _i at each potential difference measurement position is divided by the potential difference P _ir at each reference potential difference measurement position to create normalized potential difference distribution measurement data P _i / P _ir .

In step S6, for each potential difference measurement position (i), the response surface of the square (P _i / P _ir −V _i / V _ir ) ² of the difference between the potential difference actual measurement data and the potential difference distribution reference data, and the total potential difference measurement position A response surface of the sum of squares Σ (P _i / P _ir −V _i / V _ir ) ² of the difference between the potential difference distribution actual measurement data and the potential difference distribution reference data is obtained. These response surfaces are used to minimize the response at any potential difference measurement position, or to minimize the response of these differences and the sum of squares of the differences at each potential difference measurement position. Identify crack depth a and crack length 2c, or a / c).

  In addition, process S6 is called an identification process.

  When this method is applied to a crack growth evaluation test of a flat or pipe-shaped specimen 8 having a crack, crack identification is performed periodically or at any time as the test progresses. The process S5 and the process S6 of the part B are repeatedly executed. In this way, by determining the crack shape from the measurement result by the potential difference method, it is possible to measure the temporal change of the crack shape.

  In the present embodiment, the potential difference is normalized by dividing by the reference potential difference, but the measured or evaluated potential difference itself may be used.

[Embodiment 2]
In this embodiment, the crack existing on the inner surface of the pipe-shaped specimen is measured from the outer surface side, or the crack present in the flat specimen is measured from the opposite surface of the surface where the crack opens. Is.

  FIG. 7 is a view showing a position where the current application probe and the potential difference measurement probe of the crack shape identification system according to the second embodiment of the present invention are attached to a test body, (a) is a surface view of the test body, (B) is sectional drawing of a test body.

Seven pairs of potential difference measurement probes 14 and a pair of current application probes 16 of A ₃ , A ₂ , A ₁ , A ₀ , A _{1 ′} , A _{2 ′} , A _{3 ′} are shown by diagonal lines in FIG. On the opposite surface of the crack 7, as shown in FIG. 7 (a), the crack projection position 7B is interposed. In such a situation, the crack shape can be identified by performing measurement by the potential difference method as in the first embodiment.

  As in the first embodiment, the current application probe 16 may be attached to the surface where the crack 7 opens. The potential difference measurement probe 14 may be attached to the surface where the crack 7 opens.

[Embodiment 3]
In this embodiment, eight pairs of the potential difference measuring probes 14 of the first embodiment are used, and one of them is a reference potential difference measuring probe 20.

  FIG. 8 is a diagram showing a position where the current application probe and the potential difference measurement probe of the crack shape identification system according to the third embodiment of the present invention are attached to a test body, (a) is a surface view of the test body, (B) is sectional drawing of a test body.

  The reference potential difference measurement probe 20 is attached to a reference potential measurement position away from the crack 7 where a potential difference does not occur due to a change in the shape of the crack 7 indicated by hatching in FIG. The potential difference measured at the position of the reference potential difference measuring probe 20 does not respond to a change in the shape of the crack 7, but responds to external factors such as temperature fluctuations. Therefore, when the measurement potential difference in the potential difference measurement probe 14 is affected by external factors other than the crack shape change, more accurate measurement, that is, by compensating for the change in the measurement potential difference by the reference potential difference measurement probe, that is, It is possible to determine the crack shape with higher accuracy.

  The above description is merely an example, and the present invention can be implemented by combining each of the above-described embodiments in order to improve accuracy.

It is a flowchart which shows the procedure of the crack shape identification method by the potential difference method of Embodiment 1 which concerns on this invention. It is sectional drawing of the test body in which the crack was formed. It is a block diagram of the crack shape identification system of Embodiment 1 which concerns on this invention. It is a figure which shows the voltage application position and potential difference measurement position of the crack shape identification system of Embodiment 1 which concerns on this invention, Comprising: (a) is a surface view of a test body, (b) is sectional drawing of a test body. It is a figure which shows the reference voltage application position and reference potential difference measurement position of the crack shape identification system of Embodiment 1 which concerns on this invention, Comprising: (a) is a surface figure of a test body, (b) is sectional drawing of a test body. is there. It is a graph which shows the example of the potential difference near a crack, and a reference potential difference. It is a figure which shows the voltage application position and potential difference measurement position of the crack shape identification system of Embodiment 2 which concerns on this invention, Comprising: (a) is a surface figure of a test body, (b) is sectional drawing of a test body. It is a figure which shows the voltage application position and potential difference measurement position of the crack shape identification system of Embodiment 3 which concerns on this invention, Comprising: (a) is a surface figure of a test body, (b) is sectional drawing of a test body.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 7 ... Crack, 7B ... Projection position of crack, 8 ... Specimen, 9 ... Crack shape identification system, 10 ... Potentiometer, 11 ... DC power supply, 12 ... Switch for alternating current, 13 ... Data collection Control device, 14 ... potential difference measurement probe, 15 ... potential difference measurement line, 16 ... current application probe, 17 ... current application line, 20 ... reference potential difference measurement probe

Claims (10)

In the crack shape identification method for identifying the shape of the crack in the test specimen,
Evaluate the potential difference at multiple potential difference measurement positions in the vicinity of the crack when a voltage is applied to the voltage application position in the vicinity of the crack of multiple preliminary test specimens with cracks of different shapes. Potential difference evaluation preliminary process for obtaining potential difference reference data,
A potential difference measuring step of applying a voltage to the voltage application position to cause a current to flow through the specimen, measuring a potential difference at the potential difference measurement position, and obtaining potential difference actual measurement data;
By obtaining a crack shape that minimizes the square of the difference between the potential difference actual measurement data and the potential difference reference data at each potential difference measurement position and the sum of their responses regarding the change in the crack shape, An identification step for identifying the shape of the crack of the specimen;
A crack shape identification method characterized by comprising: In the potential difference evaluation preliminary step, a current is applied by applying a voltage to the voltage application position and the potential difference measurement position arranged in the same manner as the potential difference evaluation step in a place where the influence of the crack of the specimen can be ignored. The potential difference measurement data is obtained by dividing the potential difference at the potential difference measurement position by the reference potential difference.
The crack shape identification method according to claim 1.   The crack shape identification method according to claim 1, wherein the potential difference evaluation preliminary step evaluates a potential difference at the potential difference measurement position by potential distribution analysis.   2. The crack shape identification method according to claim 1, wherein in the potential difference evaluation preliminary step, a current is passed through a preliminary test body in which a simulated crack is formed, and the potential difference at the potential difference measurement position is measured.   5. The crack shape according to claim 1, wherein the voltage application position is located on at least one of the same surface as the surface where the crack opens of the specimen and the opposite surface thereof. 6. Identification method.   The crack shape according to any one of claims 1 to 5, wherein the potential difference measurement position is located on at least one of the same surface as the surface where the crack opens of the test body and the opposite surface thereof. Identification method.   The crack shape identification method according to any one of claims 1 to 6, wherein the voltage application position is located so as to sandwich the crack.   The crack shape identification method according to claim 1, wherein the potential difference measurement position is located so as to sandwich the crack. A reference potential measurement step of applying a voltage to the voltage application position to cause a current to flow through the specimen and measuring a potential difference at a reference potential measurement position where a change in potential difference due to a difference in crack shape can be ignored;
A correction step of correcting the shape of the crack identified in the identification step based on a potential difference at the reference potential measurement position;
The crack shape identification method according to claim 1, comprising: In the crack shape identification system that identifies the shape of the crack in the specimen,
Power supply,
A pair of current application probes connected to the power source;
A potentiometer;
A plurality of pairs of potentiometric probes connected to the potentiometer;
Evaluate the potential difference at multiple potential difference measurement positions in the vicinity of the crack when a voltage is applied to the voltage application position in the vicinity of the crack of multiple preliminary test specimens with cracks of different shapes. The potential difference reference data obtained in this way and the potential difference actual measurement data obtained by applying a voltage to the voltage application position and passing a current through the test body and measuring the potential difference at the potential difference measurement position are received, and the crack shape changes. By obtaining a crack shape that minimizes the square of the difference between the measured potential difference data and the potential difference reference data at each potential difference measurement position and the sum of their responses, the A data collection and control device that identifies the shape of the crack;
The crack shape identification system characterized by having.

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