JPS61237045A - Defect detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a crack detection technique for detecting cracks generated in metal structural members, and in particular, a method suitable for detecting the shape of surface cracks with high accuracy. METHODS AND APPARATUS.

[Background of the invention]

Conventional potential method (for example, Japanese Patent Application Laid-Open No. 58-41341)
) is known as the so-called four-terminal method. This method scans the surface of a structural member with a probe that has a pair of power supply terminals and a pair of measurement terminals arranged in a row on the inside of the probe, and detects cracks from changes in the potential difference distribution. Cracks are determined in areas where no cracks are expected. The potential difference is used as a reference potential difference, and a crack is determined to exist where the potential difference is larger than the reference potential difference. Therefore, although the four-probe method can determine the presence or absence of a crack and the shape of the crack to some extent, it has the disadvantage that it is not possible to accurately determine the shape of the crack.

[Purpose of the invention]

An object of the present invention is to provide a method and apparatus capable of accurately detecting the shape of defects or surface cracks occurring in structural members.

[Summary of the invention]

Using test pieces with surface defects of various aspect ratios, we applied a direct current in a direction perpendicular to the defects and measured the potential distribution or potential difference distribution around the defects. The potential difference at the tip of the defect changed significantly and reached its maximum value at the deepest point of the defect. There was a monovalent relationship between the defect depth and potential difference at each location of the surface defect, but the relationship between the two varied depending on the aspect ratio of the defect. However, it has been found that when the aspect ratio becomes smaller than 0.25, the relationship between the two tends to become independent of the aspect ratio. We also analyzed the electric field of a member with surface defects using the finite element method and compared it with the results measured using a test piece, and found that the two agreed well.

Therefore, create defect elements with several aspect ratios and depths, measure the potential difference distribution around the defect on the surface of the part, and extract elements with aspect ratios that closely correspond to the potential difference distribution. Compare the potential difference distribution, and if there is a difference in the potential difference distribution, partially modify the node position of the element, analyze the electric field, and use the defect shape when they match as the actual defect shape to accurately determine the defect shape. That's what I found out.

[Embodiments of the invention]

An embodiment of the present invention will be described below. FIG. 2 is an equipotential diagram showing the potential distribution near the surface crack. This is a 20m thick flat plate with a surface length of 30m.

These are the results obtained by analyzing a case where there is a semicircular crack with a depth of 15 cm using the finite element method. If we pay attention to the potential distribution on the crack surface, the equipotential lines sink into the crack surface. The number of equipotential lines that penetrate into the crack surface changes depending on the crack depth. It can also be seen that the potential distribution shows a symmetrical distribution with respect to the crack surface. That is, since the potential shows an opposite distribution across the crack, it is easy to determine the position of the crack. Of course, when measuring the potential difference across a crack, the potential difference becomes larger where there is a crack, so it can be detected.

Next, FIG. 3 shows the results of calculating the potential distribution around the crack. This was obtained for the crack shown in Figure 2.
These are the potential distributions at positions 1.2, 3, 4, and 5 degrees and 10 electrons away from the crack. As can be seen from Figure 3, from the crack 1
It is possible to determine the crack shape to some extent even at a distance of 0 m.

However, accurate detection of the crack shape is difficult.

In particular, it is difficult to identify the crack tip on the surface.

However, when the measurement position is brought closer to the crack, a singular point appears at the tip of the crack on the surface, making it easier to determine the tip of the crack on the surface. It can also be seen that the potential is proportional to the crack depth. Therefore, the crack shape can be determined by measuring the potential distribution along the crack in the very vicinity of the crack and from in front of the crack tip, or by measuring the potential difference across the crack. However, as a result of a detailed investigation of the relationship between crack depth and potential difference by varying the crack aspect ratio a/C (a: maximum crack depth, 2C crack length at two surfaces), we found that the relationship between crack depth and potential difference was It was found that the relationships were influenced by the aspect ratio and differed from each other. Therefore, we devised a method and device that accurately determines the shape of cracks or defects by analyzing electric fields using the finite element method and comparing measured values.

FIG. 1 is a diagram showing a defect detection device. In FIG. 1, a flaw detection head driving device 1 has a structure capable of detecting cracks or defects on the surface of a nearly flat structure. A flaw detection head 20 using the DC potential method is provided with a power supply terminal 5 for supplying a tidal current and a measurement terminal 10 for measuring a potential difference.

The flaw detection head 20 is rotatable around axes (two axes) perpendicular to the surface by a stepping motor 25, and has an air cylinder 30 for pressing measurement and power supply terminals against the surface of the member.
Equipped with: Furthermore, in order to enable the flaw detection head 20 to move on a two-dimensional surface, it has drive mechanisms for an X-axis 51 and a Y-axis 56, and each coordinate axis is driven by a stepping motor 52.
．． 57 and speed reducers 53 and 58. The Y-axis 56 is fixed to a side plate 60, and a suction cup 62 operated by compressed air supplied from a compressor 61 is attached to the side plate 60, and has the function of fixing the drive device 1 to the surface of the member. Therefore, it is possible to detect not only wall-like defects but also ceiling-like defects. The coordinate axis drive motors 52 and 57 are connected to a drive control device 65, and the drive control device 65 is controlled by the computer 100.

FIG. 4 shows the structure of a flaw detection head 20 for potential difference measurement.

The substrate 21 of the flaw detection head 20 is made of a nonconductor such as Bakelite or acrylic.

A large number of power supply terminals 5 for supplying direct current are arranged at equal intervals in two rows in parallel, with the terminals facing each other. The measurement terminals 10 are provided in one row at equal intervals so that they are located in the center of the two rows of power supply terminals 5 and in the center of the adjacent power supply terminals. Further, a DC power supply 66 is provided independently for each pair of power supply terminals, and a switching device 6
7 will be provided. The switching device 67 is for canceling the thermoelectromotive force generated between the measurement terminal 10 and the structure by switching the polarity of the direct current applied to the structure at regular intervals. In this case, the potential difference must be measured after the DC current has stabilized, and the best time is just before switching the polarity.

Next, FIG. 5 shows the structure for attaching the power supply terminal 5 and the measurement terminal 10 to the substrate 21. FIG. 5 shows only one row of terminals when the number of terminals is six. It is necessary to press the measurement terminal 10 and the power supply terminal 5 to the structure to the extent that contact resistance does not occur between them, and even if the structure has some unevenness or curvature, it is necessary to press the measurement terminal 10 and the power supply terminal 5 to the structure in the same way. must be maintained. Furthermore, in order to accurately determine the shape of a defect, it is necessary to measure the potential distribution within 1 to 2 meters from the defect, as shown in FIG. For this reason, the tip of the measurement terminal 10 is made into a conical shape, 7 langes are provided behind it, and a coil spring is inserted between the 7 langes and the board 21. When the flaw detection head 2o is pressed against the structure, the terminal is evenly distributed by the 6 flange. Since it is important that the measurement terminal distance be accurate so that it can be pressed against the structure, the substrate 21
The hole in the hole must be long and finished to serve as a guide surface. Furthermore, when measuring the potential difference distribution across a crack, two rows of potential difference measuring terminals 10 may be arranged so that their centers coincide with the centers of the power supply terminals 5 as shown in FIG.

Below, a method for measuring potential distribution and a method for determining defect shape will be described. 1st v! At J, a DC current is applied from the plurality of DC power supplies 66 to the power supply terminal 5 provided on the flaw detection head 20 via the switching device 67t to form an electric field in the structural member. The potential difference generated between a large number of measurement terminals 1° is inputted to a minute potentiometer 71 via a scanner 70 and measured.
00 and stored in the storage device 103 connected to the computer 100 as a potential distribution together with the position information from the drive device control device 65. The computer 100 determines the crack position from the stored potential distribution, measures the detailed potential distribution around the crack, and determines the crack shape from a comparison operation with the potential distribution obtained by analyzing the electric field.

FIG. 6 shows a flowchart for determining the forged shape using the DC potential method. First, using the drive device 1 shown in FIG. 1, the flaw detection head 20f roughly scans the entire area inside the drive device to examine the potential distribution. At this time, since the direction in which cracks occur is roughly determined by the structural member, the direction of the flaw detection head 20 is set by the stepping motor 25 so that a direct current flows orthogonally to the surface to be cracked.

If there is a crack, a potential distribution as shown in FIG. 3 will occur, so it can be easily detected. Although it is sufficiently detectable even at a distance of 10 mm from the crack, there is a risk that it may be overlooked if it is a shallow crack. Since it is safe to measure at a position 5 minutes apart, it is sufficient to set the measurement interval to 10 IllI. By measuring the potential distribution at coarse measurement intervals in this manner, the approximate location of the crack, in other words, the region where it exists is determined. As shown in FIG. 2, the potential distribution is reversed before and after the crack, so it can be determined that the crack is in a reversed position. Alternatively, when measuring the potential difference distribution across a crack, it is determined that the potential difference is in the vicinity of the measured potential difference that is larger than the reference potential difference when there is no crack. In order to accurately determine the crack shape, it is necessary to set the distance of the measurement position from the crack accurately, so the potential distribution is measured at intervals of, for example, 11111 within the reversed measurement position, and the accuracy of the cracked surface is determined. Set the position. For further accuracy, the flaw detection head 20 may be scanned finely to find a position where the reversed potential distributions are equal. In the case of potential difference distribution measurement, the crack is located at the position where the potential difference is maximum. Next, the potential distribution parallel to the armored surface or the potential difference distribution across the crack is measured in detail at INR or two positions before and after the crack. In the case of potential distribution, it is necessary to find the reference potential difference in a place where there is no crack and standardize it for evaluation.In the end, the crack shape is determined using the same method as in the case of potential difference distribution, so below we will explain the potential difference. We will describe the method for distribution.

The crack length 2C at the surface is determined from the detailed potential difference distribution around the crack, and the approximate shape of the crack, in other words, the aspect ratio a/c of the crack is determined from the maximum potential difference ratio V/ve.
f is determined by comparison calculation with various master curves stored in the potential difference distribution storage device 102 shown in FIG. Next, from among the nodal element data of various aspect ratios stored in the mesh shape memory device 101, the nodal element data with the aspect ratio closest to the aspect ratio estimated from the measurement result is selected, and the nodal element data is estimated from the master curve. The nodal element at the crack tip is moved and modified according to the determined crack depth, and the potential distribution is analyzed.

The potential difference distribution around the crack is calculated from the analyzed potential distribution, and compared with the measurement results, the crack shape is corrected for areas that do not match. In other words, the nodal elements at the crack tip are corrected by the amount of the mismatch. The crack shape used in the analysis is determined to be the actual crack shape when it is repeated repeatedly and finally matches the measurement result.

The details of the forging shape determination shown in FIG. 6 will be described below.

Cracks that occur in structural members generally have a semi-elliptical or semicircular arc shape. For example, create a semicircle as shown in Figure 7 as a nodal element for analyzing the potential distribution of a structural member, and move the nodes according to the measured potential difference distribution to create an arbitrary aspect ratio. All you need to do is create node element data.

However, since it is time-consuming in practice, for example, an element division diagram with an aspect ratio a/c of 0°5 is shown in FIG. It is more efficient to extract the nodal element data with the aspect ratio closest to the aspect ratio estimated from the potential distribution measurement results, and then slightly modify it.

The aspect ratio a/c of the node element data stored in advance in the storage device 101 is 1°0, 0.75, 0.
．． 5°0.2 and 0.1, it is sufficient to divide the crack depth into 5% increments between 5% and 100% of the plate thickness of the member.

The specific method will be described below. FIG. 9 shows the potential difference distribution obtained by setting the distance between the measurement terminals to 5B across the surface crack. The horizontal axis is the measurement position xw1 in the surface direction with the crack center as the origin, and the vertical axis is the potential difference ratio V/Vo. Here, Vo is the potential difference where there is no crack, and as seen in FIG. 9, Vo is approximately constant where there is no crack. Where there is a crack, the potential difference increases as in FIG. 3. Similar to Figure 3, a singular point appears in the potential difference distribution at the tip of the crack on the surface, so the crack length on the surface is 2C.
is easily determined. In FIG. 9, 2c=17■. Next is the estimation of the crack aspect ratio a/C.

The point where the potential difference ratio is maximum corresponds to the deepest point of the crack. Let the potential difference ratio at the deepest point be V/VOmax. In the potential difference distribution storage device 102 of FIG. 1, as shown in FIG. 10, the potential difference ratio V/Vo and the crack depth at the central part of the crack having various aspect ratios, in other words, at the deepest point are stored. The relationship with a is stored in advance. Here, the crack is generally standardized by the plate thickness t of the structure to be measured.

Also, since the relationship between the potential difference ratio V/VJ) and the crack depth is simple, V/Vo=1+Aa+Ba"+Ca"+Da'+Ea'
It may also be approximated by an n-dimensional equation as shown in FIG. When the crack depth is determined using the relationship between v/vomaxt obtained at the deepest point of the crack and the potential difference ratio V/Vo stored in the storage device 102 and the crack depth a as shown in FIG. Aspect ratio a/c; O-1e O-2+ 0.5 eO, 7
5, and 1.0, respectively, aI.

It is found as al + al * a4 + al. Determined crack depth al t al + al e
When finding the aspect ratio a/c using a4 + aS, we get al/c, al/c.

al /c, a4 /c, al /c are obtained. Therefore, find the ratio between a 1 / c - a 5 / c and the aspect ratio a / C of the master curve used, and find that the aspect ratio of the master curve that is closest to 1 is close to the aspect ratio of the actual crack. , let this be the aspect ratio of the crack. Here, it is assumed that the aspect ratio a/c is 0.5. Next is the calculation of potential distribution. First, nodal element data with a tentatively determined aspect ratio a/C=0.5 is read from the mesh shape storage device 101 to the computer 100. First, as shown in Figure 11, select the node closest to the surface crack length 2c=17. In the depth direction, nodes are set every 5%, and here the plate thickness is 2.
Since this is an example of 0 cabinets, 20 = 1 on the surface
The closest nodes in order of 7 are within ±10 range from the crack center and 5 in depth.
It becomes the thing of ■. The nodes connecting the crack tips of 2C=20M shown by solid lines are moved as shown by broken lines in both the surface direction (X direction) and the depth direction (y direction) so that 2C=17rm. Next, as shown in FIG. 12, the first
Move the nodes corrected in Figure 1. Here, the shape of the crack tip moves to become a semi-ellipse. The electric field is analyzed by the computer 100 using the corrected nodal element data indicated by the broken line in FIG. The electric field analysis method is described in, for example, Publication Example 1, Materials Society of Japan, 18th Symposium on X-ray Material Strength, Preprint, pp.

125-131''.

Based on the analyzed potential distribution, the potential difference distribution around the crack corresponding to the actual measurement position is shown in FIG. If there is a difference from the measured value shown by the solid line, the nodal coordinates at the crack tip are moved in the depth direction by the difference between the measured potential difference ratio and the analyzed potential difference ratio. This is shown in FIG. 1st
In Figure 4, the second solid line from the surface shows the crack tip when analyzed, and the broken line is the crack tip corrected by the difference between the measured value and the analytical value. Next, the computer 100 analyzes the electric field again using the nodal element data indicated by the broken line in FIG. 14, and compares it with the actual measured value. The movement of the node at the crack tip is corrected until the two match. When the two finally match, the crack shape used in the analysis is determined to be the actual crack shape. According to this method, it is possible to determine the crack shape with an accuracy of approximately ±0.1 m. Of course, for this purpose, it is necessary to accurately measure the potential difference distribution around the crack, but it is usually sufficient to measure it several times using a microvoltmeter with a resolution of about 1 μV and average it. In addition, in FIGS. 11 to 14, the nodal elements stored in the mesh shape memory device 101 are moved and modified, but the electric field may be analyzed by adding new nodal elements as shown by the broken lines in FIG. .

Other embodiments are shown in FIG. 15 and below. FIG. 15 shows a case where the element shape is rectangular. A method using this rectangular element will be described. Assuming that a potential difference distribution as shown in FIG. 9 is obtained in the structure, the nodes read from the mesh shape memory device 101 are moved as shown in FIG. That is, the same method as shown in FIGS. 10 and 11,
First, select the node closest to the surface crack length 2C=17■. In Fig. 16, the node spacing in the X direction is set to 2. ．． Since 5■ is closed, the node 7.5■ from the center of the crack is closest to it, so the coordinate of that node in the X direction is moved together with the node in the depth direction so that C=&5■.

Next, as shown in Fig. 10, the potential difference ratio V / V (81~aI and crack length C = &
The crack depth, for example a3, obtained by using the master curve that is closest to the aspect ratio a/C of the master curve used most among the ratios of 5 and 5 is determined. x closest to a3
= Owm The node (on the Y-axis) is the tentative deepest point of the crack. The node is moved so that it matches the crack depth a3, and the crack is moved so that the shape of the crack becomes a semi-ellipse from the tip of the surface crack to the deepest point.

11, 12, and 14, 16, and 17 are shown in two dimensions for convenience, but in reality, nodal elements also exist in the direction perpendicular to the wearing surface. It is a certain three-dimensional element. Further, since the crack shape is curved in terms of the number of nodes forming the element, a middle node is provided as a 21-node element to make it curved. However, when using a rectangular element as shown in FIG. 16, it is necessary to match nodes, nodes, and intermediate nodes different from those of the elliptical element.

By using the nodal element data in FIG. 16 and assuming that the potential on the armored surface is zero, the electric field is analyzed on the computer 1oo, and the electric potential distribution around the crack, and thus the electric potential difference distribution, can be determined. If it becomes as shown in Fig. 13, the node at the crack tip shown by the solid line in Fig. 17 will be the same as Fig. 14, by the amount of the potential difference ratio measured in the structure relative to the analyzed potential difference ratio. The coordinates are moved in the depth direction to form the shape shown by the broken line. We will analyze the electric field for this new crack shape element and compare it again with the measured values. Repeat fine corrections to the nodes at the crack tip until the analytical value and the measured value match, and when they match, the crack shape used in the analysis is defined as the actual crack shape. Although this method can determine the crack shape with almost the same accuracy as the case of using the nodal element data of crack shapes with various aspect ratios described above, only one set of nodal element data is stored in the mesh storage device 101. Moreover, since the nodes are arranged in a regular manner, the data is easy to create, and since the data is actually created by automatic increment, there is an advantage that the amount of data is very small.

FIG. 18 shows another embodiment. It is time-consuming to create elliptical nodal element data and rectangular nodal element data with various aspect ratios and then change the nodal element data to match the crack shape. The method described below is a simple method for determining the approximate crack shape without changing the node data.

First, the structure, especially the area around the crack, is divided into relatively small elements as shown in FIG. Here, the length of one side is II
The elements of III were adopted. When the measurement results shown in FIG. 9 are obtained, the surface crack length is 2C=17 m.

Next, the crack is assumed to be symmetrical and C=8 m. If #) a3 is determined by the method shown in Figure 10, the depth of the deepest point, in other words, the length of the short axis of the semielliptic crack is the length of the ant surface, that is, the long axis of the semielliptic crack. - Calculate the electric field using an element that fits inside a semi-ellipse with length C as a crack surface. For example, in Figure 18, the element hatched on the left is used as the crack plane, in other words, the potential distribution is calculated with the potential as zero, and if there is a difference in twist in Figure 13, the element shaded in black is used as the crack surface. The electric field added to the surface is analyzed, the potential difference distribution is compared with the measured value, and the element with the best match is determined to be the crack shape. Although the final crack shape shown in FIGS. 14 and 17 is shown by a broken line in FIG. 18, it can be seen that even the crack shape obtained by this method has good accuracy.

〔Effect of the invention〕

According to the present invention, by measuring the potential distribution or potential difference distribution on the surface of a structural member, it is possible to analyze the electric field by modifying the shapes of various elements that have been input into a computer in advance according to the measured values. By repeating this process, the shape of the crack can be detected with high accuracy.

[Brief explanation of drawings]

FIG. 1 shows a defect detection device, and FIG. 2 shows a potential distribution around a surface crack determined by analysis, where the solid line in the center is the crack and the broken line is the equipotential line. Figure 3 shows the potential distribution parallel to the crack near the crack shown in Figure 2, Figure 4 shows the structure of the flaw detection head for measuring potential distribution, and Figure 5 shows the shape of the terminal. Figure 6 is a flowchart for determining the shape of the plate, Figure 7 is an element division diagram with an aspect ratio of 1.0, Figure 8 is an element division diagram with an aspect ratio of 0.5, Figure 9 shows the actual measured potential difference distribution around the crack, Figure 10 shows the relationship between potential difference ratio and crack depth, Figures 11, 12, and 14 show how to correct the nodal element data, and Figure 13. 15 is a diagram showing a comparison between measured values and analytical values of potential difference distribution, FIG. 15 is a rectangular element division diagram, and FIG. 16 is. Figure 17 is a diagram showing how to modify node element data, Figure 18
The figure shows a method for determining the shape of a crack without moving nodes using rectangular elements. DESCRIPTION OF SYMBOLS 1... Drive device, 5... Power supply terminal, 10... Measurement terminal, 20... Flaw detection head, 21... Board, 25...
...Stepping motor, 30...Air cylinder, 5
1...X axis, 52...Stepping motor, 53...
...Reducer, 56...Y axis, 57...Stepping motor, 58...Reducer, 60...Side plate, 61...
・Compressor, 62... Suction cup, 65... Drive control device, 6.6... DC power supply, 67... Switching device, 70... Scanner, 71... Micro voltmeter,
72... Interface, 100... Computer, 101... Mesh shape memory device, 102...
Potential distribution storage device, 103... storage device. % + Fig. J Z Country ￥ J3 Fig. 4 Fig. 5 Fig. FJ 6 Fig. Fig. Fig. 7 "IQ Fig. 5″ Figure 16

Claims (1)

[Claims] 1. Direct current is applied to the surface of the member through one or more power supply terminal pairs spaced apart from each other, and a potential difference measuring terminal pair is scanned between the power supply terminal pairs to measure the potential distribution. death,
In the device for detecting the shape of a defect from the potential distribution, an electric field analysis device capable of analyzing the electric field by a finite element method is provided, along with a device for scanning the measurement terminal for measuring the potential difference distribution and a control device for driving the device. The potential difference distribution is determined by analyzing the electric field using the finite element method based on a temporary defect shape determined by comparing the measured potential difference distribution with the potential difference distribution of defects of various shapes stored in advance in the electric field analysis device. The analyzed potential difference distribution is compared with the measured potential difference distribution, and the defect shape to be analyzed is corrected and calculated again. This process is repeated until the measured value and calculated value of the potential difference distribution match. A defect detection method and device characterized in that the defect shape when the defect is detected is determined to be the defect shape of the member. 2. In the device described in claim 1, semi-elliptical elements with various aspect ratios are stored in the storage circuit of the electric field analyzer, and potential distributions when the defect depths are different are calculated. Then, select the aspect ratio of the potential difference distribution closest to the measured potential difference distribution and the defect shape of the defect depth, and move the depth of the element node by the ratio of the measured potential difference and the analyzed potential difference at each position. By repeatedly analyzing the electric field and determining the potential difference distribution using the arithmetic circuit of the electric field analyzer, the defect shape when the analyzed potential difference distribution and the measured potential difference distribution match is determined to be the defect shape of the member. Characteristic defect detection method and device. 3. In the item described in claim 2, the aspect ratio of the defect to be stored in the storage circuit of the electric field analyzer is 1.0, 0.75, 0.5, 0.2, 0.1, and the defect Depth: 5%, 10%, 15%, 20% of the thickness of the member
, 25%, 30%, 35%, 40%, 45%, 50%,
55%, 60%, 65%, 70%, 75%, 80%, 8
5%, 90%, 95%, and 100% defect detection method and device. 4. Select the defect shape of the defect depth and the aspect ratio of the potential difference distribution closest to the measured potential difference distribution in the item described in claim 2, and calculate the ratio of the measured potential difference to the analyzed potential difference at each position. A defect detection method and device characterized in that a defect shape obtained when the depth of an element node is moved by a depth is determined to be a defect shape of a member. 5. In the device described in claim 1, a small rectangular element is stored in the memory circuit of the electric field analyzer, and the element portion to be defected is made to match the shape of the measured potential difference distribution. the potential difference distribution is analyzed by the arithmetic circuit, and if there is a difference between the analyzed potential difference distribution and the measured potential difference distribution, the element portion to be determined as a defect is increased or decreased, and the potential difference distribution is analyzed by the arithmetic circuit. A defect detection method and device characterized in that the shape of a defective element portion when it matches a repeatedly measured potential difference distribution is determined to be a defect shape of a member. 6. In the device described in claim 1, a device for scanning the power supply terminal and the measurement terminal for measuring the potential distribution and a control device for driving the device are provided, and the shape of the member is input to the electric field analysis device. By this, the member is divided into elements by an automatic element division program built into the electric field analysis device,
Analyzes the potential distribution by inputting the defect shape and current input position, calculates the potential distribution by changing the defect shape until it matches the measured potential distribution, and determines the defect shape when it matches as the defect shape of the member. A defect detection method and device characterized by: