JPH0584862B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is directed to non-destructively detecting disconnection of wires constituting parallel wire strands used as tension members in long bridges such as cable-stayed bridges. Regarding the method that makes it possible.

(Prior Art and its Problems) As a tension member used in long bridges and the like, there is, for example, a parallel wire strand 1 as shown in FIG. Parallel wire strand 1
In this method, wire ropes 2 made of relatively large steel wires with a diameter of about 5 to 7 mm are bundled together, and a fastening portion 3 is assembled.
This is a tension member in which a zinc alloy or the like is cast between two wires. Such a parallel wire strand type tension member has been used favorably in recent years, and the breakage portions (illustratively shown as 2a and 2b in FIG. 6) that occur in the strand 2 during its use can be avoided. Detecting the presence non-destructively is important for safety confirmation, and the reliability of this technology is strongly desired.

Conventionally, the mainstream method for detecting wire breaks has been magnetic flaw detection, which magnetizes the wire and detects leakage magnetic flux due to defects. However, in cables with large wire diameters and bundle diameters used for long bridges, etc., it becomes difficult to detect defects by magnetic flaw detection as these dimensions increase, and the sensor part becomes large and the sensor part is moved in the longitudinal direction of the cable. It becomes extremely difficult to scan the image.

On the other hand, the ultrasonic flaw detection method can be applied not only to steel materials but also to non-magnetic materials, and various application techniques have been proposed depending on the form of defects to be detected. Its presence is detected using ultrasound as follows. A detection method (reflection method), which is an example of an ultrasonic flaw detection method, will be explained below with reference to FIG. As shown in the figure, ultrasonic waves of a constant frequency are incident from an ultrasonic probe 4. Thereafter, the incident ultrasonic wave is reflected at the disconnection part 2a, and as a result, a reflected echo is detected again via the ultrasonic probe 4 in a waveform as shown in FIG. 7, for example. By examining this reflected echo,
It detects the presence and position of a disconnection.

Such an ultrasonic flaw detection method exhibits considerable effectiveness. However, it was found that there are certain restrictions on its application.

In other words, since a zinc alloy or the like is cast between the strands of the parallel wire strand at the fastening section, the amount of attenuation when the ultrasonic wave propagates through the fastening section (casting section) is larger as the frequency of the ultrasonic wave becomes lower. On the other hand, the restriction is that the higher the frequency of the ultrasonic wave, the greater the amount of attenuation when the ultrasonic wave propagates in a portion that is not a fastened portion (no casting) (non-fastened portion). If ultrasonic waves with a low flaw detection frequency of, for example, 4 MHz or less are incident on the fastening part, the ultrasonic waves will be dissipated into the zinc alloy etc. while propagating through the wire, and can be efficiently propagated in the length direction of the wire. As a result, even if there is a disconnection, the reflected echo from the disconnection part is not received, and there is a possibility that it may be mistaken as a non-disconnection. On the other hand, in parts that are not fastened parts (no casting), if ultrasonic flaw detection is performed at a high frequency,
Because the amount of attenuation of the ultrasonic wave is large, reflected echoes may not be detected. As mentioned above, in the conventional method, ultrasonic flaw detection is carried out by keeping the ultrasonic frequency constant, so there is a problem that some breaks may not be detected even though they exist. It was hot.

(Objective of the Invention) The object of the present invention is to solve the problems of the prior art described above and to provide a method for accurately detecting a broken part of a parallel wire strand, regardless of the broken part, with a simple configuration. It is to be.

(Means for Achieving the Object) In order to achieve the above object, the method for detecting a wire break in a parallel wire strand according to the present invention provides an optimal flaw detection method that provides the minimum amount of attenuation, depending on the position of the estimated break. The frequency is calculated based on the attenuation constant of the ultrasonic waves propagating through the wire, and flaws are detected using the ultrasonic waves at that frequency.

(Embodiment) FIG. 1 is a schematic configuration diagram showing an embodiment in which the method for detecting breakage of a wire in a parallel wire strand 1 according to the present invention is applied to flaw detection using a single detection method (reflection method). As shown in FIG. 1, this embodiment is provided with a function generator 5 that generates an ultrasonic waveform to be excited. The function generator 5 generates a waveform of a frequency that minimizes the amount of attenuation, as will be described later, based on the estimated length l ₀ to the disconnection part and the length l ₁ of the fastening part 3. The amplifier 6 amplifies the waveform generated by the function generator 5 and outputs it to the ultrasound probe 4. The ultrasonic probe 4 excites ultrasonic waves according to the output waveform of the amplifier 6, and makes the ultrasonic waves incident on the end face of the wire 2 constituting the parallel wire strand 1. Thereafter, the waveform of the ultrasonic wave reflected from the strand 2 obtained from the end face of the strand 2 is outputted to the receiver 7 again. The receiver 7 observes the waveform obtained through the ultrasonic probe 4 and detects a disconnection.

Now, the method for determining the frequency of the waveform generated by the function generator 5 (that is, the frequency of the ultrasonic waves excited by the ultrasonic probe 4) is as follows. In this case, when it is estimated that there is a disconnection at a position l ₀ (m) from the end face of the wire 2, which is the ultrasonic input end, the attenuation amount α (dB)
can be approximated by the following equation.

α=C ₀ l ₀ + C ₁ l ₁ / ...(1) In formula (1), l ₁ (m) is the length of the fastening part 3 (cast part) as described above, (MHz) is the flaw detection frequency,
C ₀ and C ₁ are constants determined by the configuration of the parallel wire strand 1 (attenuation constants).

When the equation (1) changes, = ₀ = √ _{1 1 0 0} = C√ _{1 0} ... (2) (C = √ _{1 0} ), the attenuation amount α becomes minimum, and the minimum attenuation amount at this time is α If it is set to ₀ , α ₀ =2√ _{0 1 0 1} ...(3).

Therefore, by adopting a flaw detection frequency of ₀ , the attenuation amount is suppressed by α−α ₀ = (√ _{0 0} −√ _{1 1} ) ² ...(4), and as a result, the S/N improves and there is no disconnection. Detection accuracy and flaw detection range will be expanded.

In accordance with the above-mentioned principle, in this embodiment, for example, 1 m from the end face of the connected strands 2 of the ultrasonic probe 4.
Detection is performed while changing the estimated position of the disconnection. In other words, as shown in FIG. 4, for example, the flaw detection section is divided into 1m sections from the end face of the wire 2 in the fastening section 3, and the estimated position of the broken wire is changed in the order of section 1, section 2, section 3, etc. Perform flaw detection while doing so.

While changing the estimated position of the disconnection as described above, the function generator 5 calculates the amount of attenuation according to the relationship of equation (2) above according to the change in the estimated position of the disconnection. Generate a waveform with the lowest frequency. This waveform is then amplified by the amplifier 6, and the ultrasonic probe 4
An ultrasonic wave corresponding to the output waveform of is excited and is incident on the strand 2 of the parallel wire strand 1 from the end face. Thereafter, the reflected wave from the strand 2 is transmitted to the receiver 7 through the ultrasonic probe 4, and the existence and exact position of the broken part of the strand 2 are detected from the presence of the reflected echo and the arrival time. The existence and position of the disconnection detected in this way is 1 m
Based on the assumption that there is a disconnection in a predetermined interval and a predetermined section, flaw detection is performed while changing the frequency so that the amount of attenuation is minimized using equation (2), so it is reliable and accurate. High detection results can be obtained.

In Figures 2 and 3, C ₀ = 1.24 (dB/m・M
Hz), C ₁ = 300 (dB・MHz/m), and l ₁ = 0.4 (m) when a parallel wire strand is tested for flaws, and it is a diagram showing the waveform of the reflected wave at the disconnected part. That is, both figures show the received waveform of the reflected wave when it is estimated that a disconnection exists in the non-fastened part near the fastened part 3 in the strand. Among these, in Figure 2, l ₀ =
This is the case of 2.7 m, and in this case, the optimal flaw detection frequency ₀ calculated from the above equation (2) is approximately 6 MHz. Second
Figure a shows the flaw detection results at a flaw detection frequency of 4 MHz, which is deviated from the optimum flaw detection frequency _{of 0} , and at this time, the attenuation amount α is approximately 43 dB. On the other hand, FIG. 2b shows the case according to the present invention, showing the flaw detection results at the optimum flaw detection frequency ₀ = 6 MHz, and at this time, as can be seen from the above equation (3), the attenuation amount α ₀ = approximately 40 dB. In the case of Fig. 2b according to this invention, the attenuation is improved by about 3 dB compared to the case of Fig. 2a, and as a result, the S/N
The difference between the reflected echo from the disconnected part and the noise has become clearer.

Also, Figure 3 shows the case where l ₀ = 6.0m, and in this case, the optimum flaw detection frequency ₀ calculated from the above equation (2) is approximately
It becomes 4MHz. Figure 3 a shows this optimal flaw detection frequency ₀
The flaw detection results are shown at a flaw detection frequency of 6 MHz, which deviates from the above, and at this time, the attenuation amount α is approximately 65 dB. On the other hand, Fig. 3b shows the case according to the present invention, showing the flaw detection results at the optimum flaw detection frequency ₀ = 6 MHz, and at this time, as can be seen from the above equation (3), the attenuation amount α ₀ = approximately 60 dB.
It is. In the case of FIG. 3b according to this invention, the attenuation is improved by about 5 dB compared to the case of FIG. The difference is becoming very clear.

FIG. 5 is a schematic configuration diagram showing another embodiment of the present invention, in which two ultrasonic probes are provided. One ultrasonic probe 4a is provided on the incident end side and is used for transmission, and the other ultrasonic probe 4b is provided on the strand end opposite to the incident end and is used for reception. In this case, the ultrasonic probe 4a
The broken wire is detected by detecting whether or not the ultrasonic wave reaches the ultrasonic probe 4b, and the ultrasonic detection is performed by changing the flaw detection frequency according to the total length of the strand 2 to be flawed. The amount of attenuation of the ultrasonic waves reaching the child 4b is minimized. As a result, the presence of a disconnection can be detected with a good S/N ratio, similarly to the above embodiment. According to the above configuration, compared to the embodiment shown in FIG. It has the advantage of being able to perform detection.

(Effects of the Invention) According to the present invention, the existence and position of a wire breakage can be detected accurately and with high precision, whether the wire breakage point is in a fastened part or in a non-fastened part. can be detected. In particular, in the past, the frequency of the ultrasonic waves was not optimized in the fastened part and the unfastened part in the vicinity, so there were cases where the wire was mistakenly recognized as non-broken. This makes it possible to reliably detect the presence of a disconnection with a high S/N ratio. In addition, since the position of the estimated dashed line part is changed at predetermined intervals or for each section, ultrasonic waves at the optimal flaw detection frequency are applied and detected sequentially, resulting in a good S/N ratio and the shortest time possible. It also has the effect of being able to detect wire breaks. With this effect, efficient disconnection detection can be realized.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams showing a comparison of reflected waves between a conventional method and a method according to an embodiment of the present invention, and FIG. 4 FIG. 5 is a schematic configuration diagram showing another embodiment of the invention, and FIG. 6 shows the vicinity of the fastening portion of the parallel wire strand. The configuration diagram and FIG. 7 are reflection waveform diagrams of a wire having a disconnection portion. DESCRIPTION OF SYMBOLS 1... Parallel wire strand, 2... Element wire, 2a, 2b... Disconnection part, 3... Fastening part, 4...
...Ultrasonic probe, 5...Function generator, 7...Receiver.

Claims (1)

[Scope of Claims] 1. In order to detect a break in the strands of a parallel wire strand having a fastened part and a non-fastened part in which a plurality of strands are cast, ultrasonic waves are applied from the end faces of the strands. A method for detecting a break in the wire by propagating the ultrasonic wave within the wire from the fastening portion to the non-fastening portion and receiving a reflected wave of the ultrasonic wave caused by the presence of the break, the method comprising: Based on the attenuation constant of the ultrasonic wave propagating in the wire, depending on the position of the broken wire, calculate the optimum flaw detection frequency that provides the minimum attenuation at that position, and use the ultrasonic wave at the optimum flaw detection frequency. A method for detecting a break in a wire of a parallel wire strand, comprising: detecting a break in the wire by observing a received waveform of a reflected wave that enters the wire from an end surface of the wire. 2. The optimum flaw detection frequency is given by the square root of the product of the reciprocal of the length of the estimated broken line from the end face, the length of the fastening part from the end face, and the attenuation constant. A method for detecting wire breakage in a parallel wire strand according to claim 1. 3. Calculating the optimum flaw detection frequency for each position of each estimated disconnection while changing the position of the estimated disconnection at a predetermined interval from the end face of the wire toward the fastened portion and the non-fastened portion. 3. The method for detecting a break in a parallel wire strand according to claim 2, wherein ultrasonic waves having an optimum flaw detection frequency are applied. 4 Divide the flaw detection range of the wire including the fastened portion and the non-fastened portion into a plurality of sections at predetermined intervals from the end face side of the wire, and divide each section based on the assumption that the broken wire exists in the section. 4. The method for detecting a break in a wire of a parallel wire strand according to claim 3, wherein the optimum flaw detection frequency is calculated for each time, and the ultrasonic wave having the optimum flaw detection frequency is applied.