JP2008164515A - Crack length detection method and crack length detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a crack length on a fatigue sensor or the like highly accurately at a distance. <P>SOLUTION: In order to estimate the degree of a fatigue damage of a structure, a metal foil 2 with a slit 2b on the fatigue sensor 1 is fixed on the structure on both side positions sandwiching the slit 2b. A plurality of strain gages S are stuck beforehand on the side of an elongation of the slit 2b on the metal foil 2. The crack 2c length from the slit 2b on the fatigue sensor 1 is detected at a distance based on an output signal from each strain gage S. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The claimed invention relates to a crack length detection method for knowing the length of a crack generated from a fatigue sensor or various crack generating members that measure the degree of fatigue damage of a structure by the amount of crack propagation. And a crack length detection apparatus.

  What is shown in FIG. 22 is known as a fatigue sensor used for the measurement of the fatigue damage degree about the member in a structure. That is, the fatigue sensor 1 is configured by fixing the metal foil 2 in which the slit 2b is formed in advance on the surface of the base foil 3 at the joint portions 4 on both sides of the slit 2b. Such a fatigue sensor 1 is affixed on the member of a structure by providing an adhesive layer on the bottom surface of the base foil 3 (the surface on the side without the metal foil 2). When the fatigue sensor 1 is attached in this way, the strain amplitude generated in the member is transmitted to the metal foil 2 through the base foil 3, and the crack progresses from the tip of the slit 2b as the strain repeats. The degree of fatigue damage of the member can be estimated. In the portion including the slit 2b, the thin portion 2a is formed on the metal foil, and the strain generated in the member is intensively generated in the vicinity of the slit 2b, so that the fatigue damage degree of the member can be measured with high sensitivity and high accuracy. I am doing so. In addition, it is also possible to comprise a fatigue sensor not directly using the base foil 3 but directly sticking to the member by the fixing portions on both sides in the metal foil 2 that sandwich the slit 2b.

  The fatigue sensor is applied to many steel structures such as large structures such as ships and bridges, or railroad equipment of railway vehicles, and enables estimation of fatigue damage state and repair time. As a result, planned and rational maintenance and repair can be performed.

  However, in order to know the change in the crack length of the fatigue sensor, it is necessary to go directly to the installation site of the sensor and visually observe or replicate (mold transfer) the sensor crack. For large structures such as ships and bridges, the fatigue sensor may be attached to places that are not normally accessible such as high places. Sometimes you have to do it.

There are the following patent documents as technologies that can reduce such a burden. Both show methods for enabling remote monitoring by converting the crack length into an electrical signal and transmitting it. In order to convert the crack length into an electrical signal, as shown in FIG. 23, a plurality of electric resistance lines R (or strain gauges) are formed at the right end of the crack 2c in the progress destination of the crack 2c from the slit 2b. Paste in parallel. When a part or all of the electric resistance line R or the like is cut by the progress of the crack 2c, the measured electric resistance value changes, so that an electric signal corresponding to the length of the crack 2c is obtained.
Japanese Patent No. 2952576 Japanese Patent No. 2952594 JP 2001-272319 A

In the case of the technique described in the above patent document, there are the following problems.
That is, when a large number of resistance wires R and the like are connected in parallel as shown in FIG. 23, it is not easy to measure the initial crack length because the change in the overall electrical resistance due to one disconnection is small. For example, when 8 or 16 resistance wires R are used, the relationship between the number of broken resistance wires R and the overall electrical resistance is as shown in FIG. 24, and the change in the electrical resistance value accompanying the first disconnection of the resistance wires. Is very small.

If the number of resistance lines R, etc. is reduced, the change in the electric resistance value also increases when the first line is cut. In this case, the distance between the resistance lines R, etc. increases, so that the length of the crack 2c is gradually increased. You can only know. That is, it becomes impossible to detect a minute change in the crack length.
Although it is conceivable to connect the resistance wires R in series, in that case, if one resistance wire R is cut, then the resistance becomes infinite and the crack length cannot be measured.

  The invention of the claims is for solving the above-described problems, and makes it possible to remotely detect a crack length in a fatigue sensor or the like with high accuracy.

The crack length detection method according to the present invention provides a method for detecting the crack length in a crack generating member that receives a load and generates a crack (eg, left or right or both sides of the crack growth destination). A plurality of strain gauges are attached to the portion), and the length of the crack is measured based on the output signals thereof. Examples of the crack generating member include various members including steel structures such as ships and bridges.
When the crack generating member is repeatedly loaded, the crack develops in the member, and the strain distribution near the crack changes accordingly. According to the inventors' investigation (described later), this strain distribution is determined by the length of the crack and is similar regardless of the magnitude of the load. Therefore, if a plurality of strain gauges are attached to the side of the crack propagation portion as described above and their output signals are analyzed, the length of the crack in the crack generating member can be known. Since the change in strain distribution in the vicinity of the crack is not small at the initial stage and other stages where the amount of crack growth is small, this method includes the initial stage and accurately detects the crack length. It is possible. If the output signal is received remotely, remote detection can be performed.

In the above method, the relationship between the strain distribution and the crack length indicated by the plurality of strain gauges and the load-independent relationship (for example, as shown in FIG. 8) is grasped in advance, and the output of each strain gauge. The crack length should be measured from the strain distribution indicated by the signal. The above-mentioned relationship that does not depend on the load, for example, normalizes the value of each strain gauge so that the strain values indicated by two of the plurality of strain gauges attached at the two ends that are the most separated are 0 and 1. It is good to ask by doing.
If you know in advance the relationship between the strain distribution and the crack length indicated by the multiple strain gauges attached and not depending on the load, when an output signal is received from each strain gauge, the strain The crack length can be easily known by applying the distribution to the relationship. At this time, the strain distribution may be obtained by normalizing the output signal of each strain gauge in the same manner as described above.

Alternatively, in the above method, the relationship between the output and the crack length of a specific strain gauge out of a plurality of strain gauges is not grasped in advance (for example, as shown in FIG. 9), It is also preferable to measure the crack length from the magnitude of the strain indicated by the output signal of one strain gauge. In this case as well, the above-mentioned relationship that does not depend on the load is that the values of the strain gauges are set so that the strain values indicated by the two ends of the plurality of strain gauges that are affixed to each other are 0 and 1. It may be obtained by normalization.
When the relationship between strain distribution and crack length (for example, as shown in FIG. 8 above) can be grasped, a specific strain gauge (for example, the one provided at the center cage position in FIG. 8) The relationship between the output and the crack length that is not dependent on the load (for example, the relationship as shown in FIG. 9) can be grasped. If only the output of the specific strain gauge is received and applied to such a relationship, it becomes possible to know the crack length more easily. The output of the specific strain gauge received should be normalized in the same manner as described above and applied to the above relationship.

In particular, in order to estimate the fatigue damage degree of a structure (for example, various structures including steel structures such as ships and bridges), a metal foil with a slit is fixed to the structure at both sides of the slit, and the metal It is preferable to attach a plurality of strain gauges to the side of the extension line of the slit in the foil (for example, the part away from the crack growth destination on either side of the left or right). That is, the metal foil used as a so-called fatigue sensor is used as a crack generating member, and a plurality of strain gauges are attached thereto.
By doing so, the crack length in the metal foil can be detected with high accuracy, and the fatigue damage degree of the structure can be estimated. Rather than affixing a plurality of strain gauges directly as a crack generating member to the above structure, it is better to affix a plurality of strain gauges to the metal foil in advance and fix the metal foil to the structure. There is also the advantage that the work required to start crack length detection is much easier.

As another crack length detection method, in order to estimate the fatigue damage degree of a structure, a metal foil with a slit is fixed to the structure at both positions sandwiching the slit, and in the vicinity of the extension line of the slit in the metal foil (that is, In the vicinity of the crack growth destination), it is also possible to apply a voltage, measure and output the current value, and know the crack length from the output signal.
In the vicinity of the crack growth destination, for example, when a current is generated and the current value is measured as shown in FIGS. 11, 12, and 13, if a crack occurs and its length changes, the resistance of the metal foil The value changes continuously with the crack length, and the current value changes continuously as well. And the output signal about the current value can be easily transmitted to the remote. Therefore, according to this method, the crack length can be easily and continuously known from the current value as the output signal continuously and remotely.

As another crack length detection method, in order to estimate the fatigue damage degree of a structure, a metal foil with a slit is fixed to the structure at both sides of the slit, and near the extension line of the slit in the metal foil. Then, light is transmitted along the surface of the light-transmitting body provided on the surface of the metal foil (for example, as shown in FIGS. 14 and 15), or light is applied to the surface of the metal foil in the thickness direction (for example, FIG. 16).・ Measure the transmission of light through the transparent body, the passage of light from the surface of the metal foil to the opposite surface, or the reflection of light on the surface of the metal foil. It is also possible to know the length of the crack from the output signal.
If a crack occurs near the crack growth destination and its length changes, the amount of light transmitted through the translucent material, or the amount of light passing from the surface of the metal foil to the opposite surface, or of the metal foil The amount of light reflected from the surface changes. The amount of transmitted light, amount of passage, and amount of reflection all change linearly and continuously according to the length of the crack, and it is easy to transmit the signal to a remote location. Therefore, according to this method, the crack length in the fatigue sensor can be remotely detected with high accuracy.

As another crack length detection method, in order to estimate the degree of fatigue damage of a structure, a metal foil with a slit is fixed to the structure at both sides of the slit, and near the extension line of the slit in the metal foil. It is also possible to install an imaging means and output a photographed image (an image near the extension line of the slit) and know the length of the crack from the output signal.
According to this method, for example, by the method shown in FIG. 19 or the like, an easily transmitted output signal indicating a continuous change in crack length can be obtained. Therefore, it becomes possible to detect the crack length in the fatigue sensor remotely with high accuracy.

In the above crack length detection method, an output signal is transmitted from a plurality of locations (a plurality of locations where the occurrence of cracks is to be detected) to one monitoring location, and the transmitted signal is used to transmit the output signal to the monitoring location. It is preferred to know the length of each crack at multiple locations.
By doing so, it is possible to receive and recognize information on the crack propagation length at a plurality of locations (a crack generating member or a metal foil) at one monitoring location. FIG. 2 schematically illustrates this method.

  The above transmission is particularly preferably carried out by a Bluetooth daisy chain system, through an optical fiber, by a PHS standard system, or via the Internet. This is because all such transmission systems are suitable for transmitting signals to a remote location.

The crack length detection device according to the present invention includes a plurality of strain gauges attached to a side of a crack propagation location in a crack generating member, strain detection means for detecting strain from the strain gauge, and Pre-processing means for normalizing the strain value detected by the strain detecting means, storage means for storing the relationship between strain and crack length, and crack length corresponding to the strain value normalized by the pre-processing means. It is characterized by comprising an arithmetic means for reading from the storage means.
For example, a) a plurality of strain gauges affixed to the side of the crack propagation point in the crack generating member, b) a transmission means for wirelessly transmitting an output signal of each strain gauge, and c) receiving the output signal Receiving means, d) storage means for storing a load-independent relationship between the output and the crack length of a specific one of the plurality of strain gauges, and e) the output of the one strain gauge. May be applied to the above relationship stored in the storage means to have a calculation means for obtaining the crack length.
This device has the following effects. That is,
Based on the output signals from the plurality of strain gauges, the crack length in the crack generating member can be known as described above.
-The above crack length can be known remotely by the action of the above transmission means and reception means.
-Only the output of one specific strain gauge can be obtained by using the relation stored in the storage means (the relation between the output of the specific single strain gauge and the load between the crack length and not depending on the load). Therefore, the crack length can be known very easily.

The above-mentioned multiple strain gauges are metal foils used as fatigue sensors--that is, slits are formed to estimate the degree of fatigue damage of the structure, and the fixing parts on both sides sandwiching the slits are on the surface of the structure. It is more preferable that the metal foil to be fixed is attached in advance to the side of the extension line of the slit.
In that case, the fatigue damage degree of the structure can be estimated by detecting the crack length in the metal foil. Since a plurality of strain gauges are attached to the metal foil in advance and the metal foil is fixed to the structure, there is an advantage that the construction work, that is, the work until the detection of the crack length is facilitated.

The fatigue sensor according to the present invention has a metal foil with a slit fixed to a base foil at both sides of the slit, and a plurality of strain gauges attached to the side of the extension line of the slit in the metal foil (for example, As shown in FIG.
When such a fatigue sensor is fixed to the surface of the structure and used together with the necessary transmission means, reception means, storage means, calculation means, etc., based on the output signals from the plurality of strain gauges described above, You can know the length of the crack. It is also possible to know the crack length remotely.
Since a plurality of strain gauges are already attached to the metal foil, it is sufficient to attach one fatigue sensor to the structure, and the difficult task of attaching each strain gauge directly to the structure is difficult. It becomes unnecessary. In addition, since the above metal foil is fixed to the base foil at both sides of the slit, it is sufficient to attach the entire bottom surface of the base foil to the structure, and a predetermined interval is provided between the fixing positions on both sides of the slit. It is not necessary to perform work that requires high accuracy at the site of the structure.

According to the crack length detection method of the present invention, the crack length in the crack generating member can be detected with high accuracy at a location away from the crack generating member.
A plurality of strain gauges are attached to the side of the extension line of the slit in the metal foil with the slit of the metal foil with the slit of the metal foil with the slit (fatigue sensor) sandwiched between the slit and the metal foil. It becomes easy to fix to the structure at both sides of the sandwiched area and to estimate the degree of fatigue damage of the structure by detecting the crack length in the metal foil. The same detection and estimation can be performed by generating current near the slit extension line in the metal foil, applying light, or using imaging means instead of attaching multiple strain gauges. is there.
It is also possible to grasp information related to the growth of cracks at a plurality of locations at a single monitoring station away from each location.

  According to the crack length detection device of the present invention, the crack length in the crack generating member can be detected with high accuracy at a remote location based on the detection method.

The form about implementation of invention is shown in FIGS.
First, FIGS. 1-10 is a figure shown about the 1st form of invention. FIGS. 1A and 1B are a plan view and a side view showing an outline of the fatigue sensor 1, and FIGS. 2A and 2B are conceptual views showing a usage state of the fatigue sensor 1. FIG. 3 to 9 are diagrams in which output signals of the respective strain gauges S (FIG. 1) attached to the fatigue sensor 1 are analyzed. FIG. 10 is a flowchart showing a crack length detection method implemented according to this embodiment.

  A fatigue sensor 1 shown in FIG. 1 is obtained by fixing a metal foil 2 having a slit 2b formed in a middle thin portion 2a on the surface of a base foil 3 at joints 4 on both sides of the slit 2b. . By affixing the entire bottom surface of the base foil 3 to the surface of the structure with an adhesive or the like, the crack 2c is propagated from the tip of the slit 2b along with the repeated strain generated in the structure. The degree of fatigue damage of the structure can be estimated from the degree of progress of the crack 2c.

  In this fatigue sensor 1, a plurality of (in the example shown in the figure) along the crack propagation direction on the side of the crack propagation point 2d (in the example shown, on the right side of the crack extension part that has deviated from the thin portion 2a). Five strain gauges S (S1 to S5) are attached in a line. The direction of each strain gauge S is determined to be perpendicular to the direction in which the crack 2c propagates (the left-right direction in FIG. 1). In the example of FIGS. 1 to 10, the output of the strain gauge S is received remotely, and the length of the crack 2 c is detected from the change in the distribution of the output (strain).

  As shown in FIG. 2A, the fatigue sensor 1 is attached to the surface of the structure 5, and each strain gauge S is connected to the control box 11. For example, the control box 11 uses a solar cell 12 as a power source, and converts the output signal of each strain gauge S into a digital signal. The control box 11 is installed for each fatigue sensor 1 as a slave unit, and each control box 11 is given an ID number as shown in FIG. The signal of each strain gauge S in the fatigue sensor 1 is transmitted by the control box 11 via the antenna 13 by radio waves of a single frequency, and the receiver 14 provided as a master unit at a remote monitoring station recognizes each sensor by ID recognition. 1 crack propagation information is received. The received signal is analyzed and displayed by the storage calculation display 15.

  The apparatus including the equipment shown in FIGS. 1 and 2 detects the length of the crack 2c of the fatigue sensor 1 according to the principle described below.

1. Strain distribution around the crack Generally, the strain concentrates near the crack tip, and a large strain exceeding the yield strain occurs. Average value according to the size. On the other hand, as the crack progresses, no load flows around the crack, no strain occurs, and the strain distribution changes. However, this change in strain distribution is an elastic phenomenon in the range of the normal load size to which the fatigue sensor is applied, and is similar to the crack growth regardless of the load size. It is considered to be distributed.

2. Measurement of Strain As shown in FIG. 1, a test piece (structure 5 or the like) was repeatedly loaded with five strain gauges S applied thereto, and the length of the crack 2c and the output of each gauge S were recorded. According to this, the crack propagates as shown in FIG.

3. Relationship between crack growth and strain Initially, the output of each strain gauge S is about 400μ for all gauges S (S1, S3, S5), but as crack 2c progresses, First, the strain value of the gauge S1 that is behind the crack is lowered, and then the values of the strain gauges S3 and S5 are successively lowered.
If this is shown as the strain distribution at each crack length stage, the strain that was a horizontal straight line as shown in FIG. 4 (Δ in FIG. 4; strain with respect to the peak load of the load that changes in a sine wave shape) As the crack length increases, the strain value decreases from the smaller gauge position (closer to the side where the slits 2b are provided), and changes in a S-shaped curve (FIG. 4). ◆ mark, △ mark, * mark).
Since the initial tensile internal force is applied to the metal foil 2 and the zero point of the strain is adjusted in a state where this internal force is present, when this internal force is released due to the progress of the crack, the strain gauge Outputs the compression strain value corresponding to the internal force.

4). Normalization of strain distribution On the other hand, the strain value at the peak load (3200 kgf) at the time of applying a repeated load has been shown so far, but the strain value varies depending on the magnitude of the load as shown in FIG. However, it can be seen that the maximum value in the strain distribution (the right end in FIG. 5) is almost proportional to the magnitude of the load and is a linear elastic phenomenon.
When this strain distribution is normalized so that it becomes 0, 1 at both ends with reference to the values of the gauges S1 and S5 at both ends, the load value is obtained as shown in FIGS. Regardless, it can be seen that the normalized strain distribution shape is almost constant. This also shows that this is a linear elastic phenomenon regardless of the magnitude of the load.
In the measurement using the actual fatigue sensor 1, since the magnitude of the load is unknown, it is important that the crack growth length can be estimated regardless of the magnitude of the load.

5. Relationship between strain distribution and crack length By normalizing the output of each strain gauge S in this way, a strain distribution shape determined by the crack length is obtained. When this is obtained for each crack length, it becomes FIG. 8, and it can be seen that the distribution form of the normalized strain greatly changes with the progress of the crack.
Therefore, if the relationship between crack length and normalized strain distribution is determined in advance for each type of fatigue sensor 1 by repeated load tests, the crack length can be known from the normalized strain distribution. It becomes.

6). Relationship between the strain value at the center and the crack length In this example of the fatigue sensor 1, when the strain values at the center gauge S3 among the normalized strain gauge S values are plotted by the crack length, FIG. It can be seen that it decreases almost linearly as the crack length increases.
Therefore, the crack length can be obtained from the normalized strain value of the gauge S3.
Although five strain gauges S are attached to the fatigue sensor 1, as can be seen from FIGS. 8 and 9, only three strain gauges S including the gauges S1 and S5 at both ends and the center gauge S3 are provided. By pasting, the crack length can be obtained as described above by normalizing the strain value. For the fatigue sensor 1, if the crack length can be detected, the magnitude of the load can be estimated from the normalized maximum strain using the strain distribution for each load with respect to each crack length (for example, FIG. 5). Is possible.

The procedure for detecting the length of the crack 2c of the fatigue sensor 1 using the apparatus of FIGS. 1 and 2 is shown in the flowchart of FIG.
First, at the stage of manufacturing the fatigue sensor 1, a plurality of strain gauges S are attached to the fatigue sensor 1 as shown in FIG. 1, and the relationship between the normalized strain distribution and the crack length is obtained for each same type of fatigue sensor 1. (Step s1).

  At the stage of attachment, the fatigue sensor 1 is attached to the point to be monitored on the structure 5 (step s2), and the transmission means (control box 11 etc.) and the reception means (receiver 14 etc.) are arranged and turned ON. (Step s3).

  In the measurement stage, as the load is repeatedly applied to the structure 5 (step s4), the transmission means / reception means transmit and receive signals output from the respective strain gauges S (step s5).

  In the analysis stage, the memory calculation display 15 normalizes the output of each strain gauge S based on the received signal (step s6), and obtains the strain (normalized) by the center strain gauge S3 ( Step s7). Further, the normalized strain value is calculated by applying it to the relationship obtained and stored in step s1, and the length of the crack 2c is estimated (step s8).

  The memory calculation display 15 displays the crack length thus determined (step s9), and if it exceeds the specified value, it is shown to the worker as a warning (step s10). When there is a warning or the like, the worker approaches the structure 5 and confirms the actual crack length visually or by shaping.

Each of FIGS. 11 to 22 shows an embodiment different from the above for outputting a crack length detection signal in the fatigue sensor 1.
FIG. 11 shows a change in the current value measured by applying a voltage to the fatigue sensor 1 including the metal foil 2 in the vicinity of the extension line of the slit 2b (that is, the portion including the propagation portion 2d of the crack 2c). The method for detecting the crack length (for example, remotely, the same applies hereinafter) is shown. Reference sign A1 in the figure is an AC power supply, and reference sign A2 is a voltage measuring device.
FIG. 12 shows an example in which the electrical resistance in the vicinity of the crack propagation point 2d in the fatigue sensor 1 is measured by the ohmmeter B, and the crack length is detected from the output signal.
FIG. 13 shows an example in which the eddy current is measured by the magnetic sensor C at the crack propagation point 2d in the fatigue sensor 1 and the crack length is detected from the output signal.

FIG. 14 shows an example in which a large number of optical fibers are attached to the thin-walled portion 2a (that is, the crack propagation portion 2d) in the fatigue sensor 1 and connected in parallel. When the optical fiber is disconnected along with the progress of the crack from the slit 2b, the amount of light passing through the optical fiber decreases, so that the crack length can be known.
FIG. 15 shows the crack length by forming a glass thin film E on one plane of the fatigue sensor 1 and sending light along the surface, and measuring the amount of transmitted light of the thin film E that changes as the crack progresses. It shows how to know.

It is also possible to know the crack length by applying light to one surface of the metal foil 2 of the fatigue sensor 1 and measuring the amount of light reaching the opposite surface or the amount of light reflected. FIG. 16 shows an example in which the light emitting diode F1 is provided on the lower side of the metal foil 2 (thin wall portion) in the figure and the phototransistor F2 is arranged on the upper side. When the crack progresses, the output of the phototransistor F2 changes. .
FIG. 17 is an example in which the crack length is detected by irradiating infrared rays to the progressed portion of the crack 2c of the fatigue sensor 1 and measuring the change in the reflected wavelength distribution. Reference numeral G1 in the figure is an infrared light source, and reference numeral G2 is an infrared camera.
In FIG. 18, glass is applied in a thin film shape at the crack 2 c of the fatigue sensor 1, and the crack length is detected by using the change in reflection of light irradiated on the surface. Symbol H1 is a light emitting diode, and negative symbol H2 is a line sensor.

The crack length can also be known from the image. FIG. 19 shows an example in which the crack 2c of the fatigue sensor 1 is observed with an artificial retina LSI (symbol I) and the crack length is detected from the output signal. A digital microscope (not shown) or the like may be used.
As shown in FIG. 20, if a scale J is added in the vicinity of a crack 2c, it is useful when the crack length is known by an image (or by direct visual observation) as described above.

  Output signals from strain gauges, resistance meters or various sensors provided in the fatigue sensor 1 may be transmitted by radio waves as shown in FIG. 2, but may be transmitted by other transmission means. For example, as shown in FIG. 21, it can be transmitted by a daisy chain method using Bluetooth. Reference numeral 21 in the figure is an A / D converter, 22 is Bluetooth, and 23 is an information collecting device on the receiving side.

It is a figure shown about the 1st form of invention, Comprising: It is the top view (FIG. 1 (a)) and side view (the same (b)) which show the outline | summary of the fatigue sensor 1. FIG. FIGS. 2A and 2B are conceptual diagrams showing the usage state of the fatigue sensor 1. FIG. 2 is a diagram in which an output signal of each strain gauge S attached to the fatigue sensor 1 of FIG. 1 is analyzed, and shows a history of maximum strain and crack length indicated by each strain gauge S. In the diagram which analyzed the output signal of each strain gauge S stuck on the fatigue sensor 1 of FIG. 1, the strain distribution is shown. It is the diagram which analyzed the output signal of each strain gauge S affixed on the fatigue sensor 1 of FIG. 1, and has shown strain distribution by each load. It is the diagram which analyzed the output signal of each strain gauge S affixed on the fatigue sensor 1 of FIG. 1, The strain distribution normalized by each load is shown. It is the diagram which analyzed the output signal of each strain gauge S affixed on the fatigue sensor 1 of FIG. 1, The strain distribution normalized by each load is shown. FIG. 2 is a diagram obtained by analyzing the output signal of each strain gauge S attached to the fatigue sensor 1 of FIG. 1 and shows a normalized maximum strain distribution. FIG. 2 is a diagram in which an output signal of each strain gauge S attached to the fatigue sensor 1 of FIG. 1 is analyzed, and shows the relationship between the normalized maximum strain of the gauge S3 and the crack length. It is a flowchart which shows the crack length detection method implemented with the apparatus shown in FIG. It is a conceptual diagram which shows the form different from FIG. 1 for outputting the crack length detection signal in the fatigue sensor. It is a conceptual diagram which shows another form for outputting the crack length detection signal in the fatigue sensor. It is a conceptual diagram which shows another form for outputting the crack length detection signal in the fatigue sensor. It is a conceptual diagram which shows another form for outputting the crack length detection signal in the fatigue sensor. It is a conceptual diagram which shows another form for outputting the crack length detection signal in the fatigue sensor. It is a conceptual diagram which shows another form for outputting the crack length detection signal in the fatigue sensor. It is a conceptual diagram which shows another form for outputting the crack length detection signal in the fatigue sensor. It is a conceptual diagram which shows another form for outputting the crack length detection signal in the fatigue sensor. It is a conceptual diagram which shows another form for outputting the crack length detection signal in the fatigue sensor. It is a conceptual diagram which shows another form for obtaining the signal for crack length detection in the fatigue sensor 1. FIG. FIG. 3 is a conceptual diagram showing a form different from FIG. 2 for transmitting a crack length detection signal in the fatigue sensor 1. They are a top view (Drawing 22 (a)) and a side view (Drawing (b)) showing general fatigue sensor 1. It is a conceptual diagram which shows the conventional crack length detection method. It is a diagram which shows the change of the resistance value accompanying the progress of a crack in the case of being based on the method of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fatigue sensor 2 Metal foil 3 Base foil 5 Structure S (S1, S2, ..., S5) Strain gauge

Claims (7)

  A crack length detection method in which a plurality of strain gauges are attached to the side of a crack propagation point in a crack generating member that receives a load and generates a crack, and the length of the crack is measured based on an output signal thereof.   The relationship between the strain distribution and the crack length indicated by the strain gauges described above is determined in advance, and the crack length is determined from the strain distribution indicated by the output signal of each strain gauge. The crack length detection method according to claim 1, wherein the crack length is measured.   The relationship between the output and crack length of a specific strain gauge among the above-mentioned multiple strain gauges is determined in advance, and the magnitude of strain indicated by the output signal of the single strain gauge is determined. The crack length detection method according to claim 1, wherein the crack length is measured.   To estimate the degree of fatigue damage of a structure, a metal foil with a slit is fixed to the structure at both sides of the slit, and a plurality of strain gauges are attached to the side of the extension line of the slit in the metal foil. The crack length detection method according to any one of claims 1 to 3. A plurality of strain gauges affixed to the side of the crack propagation point in the crack generating member;
Strain detecting means for detecting strain from the strain gauge;
Pre-processing means for normalizing the strain value detected by the strain detection means;
Storage means for storing the relationship between strain and crack length;
A crack length detection apparatus comprising: a calculation unit that reads out from the storage unit a crack length according to a strain value normalized by the preprocessing unit.   The plurality of strain gauges are formed with slits to estimate the degree of fatigue damage of the structure, and the extension lines of the slits are attached to the metal foil fixed on the surface of the structure at the fixing portions on both sides of the slit. The crack length detection apparatus according to claim 5, wherein the crack length detection apparatus is attached in advance to the side.   A fatigue sensor for estimating the degree of fatigue damage of a structure, wherein a metal foil with a slit is fixed to a base foil at both sides of the slit, and a plurality of metal foils are provided on the side of the extension line of the slit in the metal foil. Crack length detector with a single strain gauge attached.

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