KR20210086111A - Method and System for Evaluating Tensile Stress of Structure Using Ultrasound - Google Patents

Abstract

Disclosed are a method for evaluating tensile stress of a structure using an ultrasonic wave, and a system therefor. The present invention measures ultrasonic signals propagating in a tensionless structure at various temperature. Under a constant temperature condition, the present invention measures the ultrasonic signal propagating in the structure while applying various tension. Under a condition that the tension and a temperature state of the structure are unknown, the present invention measures the ultrasonic signal propagating in the structure. By correcting a propagating speed change amount of the ultrasonic signal according to the temperature, the present invention measures propagating speed of the ultrasonic signal propagating in the structure to calculate the tension of the structure. For evaluating the tension of the structure, the present invention can correct the temperature of the ultrasonic wave without temperature information and can be applied to the cylindrical structure like a rod.

Description

{Method and System for Evaluating Tensile Stress of Structure Using Ultrasound}

The present invention relates to the field of tensile stress measurement technology, and more particularly, to a technology for measuring stress using the propagation speed of ultrasonic waves.

Suspension bridges are mainly composed of cables, pylons, and anchorages, and when a load is applied to the bridge, all the loads are supported by the tensile force of the cable. Therefore, the cable is the main load member that maintains the shape and performance of the suspension bridge, and if the tension loss occurs in the cable due to factors such as external impact, abrasion, corrosion, etc., it may lead to the collapse of the entire bridge. Therefore, monitoring of cable tension in suspension bridges is very important and essential.

As a cable tension evaluation method, techniques using sensors such as an electromagnetic sensor, a fiber optic sensor, an accelerometer, and a load cell are known.

The method using the electromagnetic sensor is a relatively high-quality technology that is being applied in the actual field. It is a method to evaluate the tension of a cable by winding a coil around the cable and analyzing the voltage induced by generating a strong electromagnetic pulse. This method has advantages of quantification and short diagnosis time, but has disadvantages in that it requires a high power of several tens to hundreds of W and is difficult to install due to the large size of the sensor.

The method of using the optical fiber sensor inserts the optical fiber and the FBG sensor into the steel wire constituting the cable, and measures and analyzes the wavelength change according to the change in tension to measure the tension. Although it has advantages of quantification of tension and high precision, it has a disadvantage that it is difficult to apply to the field due to the heavy economic burden of introducing the system, such as purchasing expensive optical equipment and changing the existing cable manufacturing process.

The method of using the accelerometer is a cable tension measurement technology by installing the accelerometer on the cable and measuring the resonance frequency. There is an advantage of using a cheap sensor, but there is a disadvantage that a large error occurs if the mass, length, and cross-sectional area of the cable are not accurately known.

The method of using a load cell is a technique of estimating the tension acting on the cable by monitoring the load of the anchorage. The rod serves to support the tension so that the cable is not pulled out, and the force varies according to the tension of the cable. The change in anchorage load stress according to the change in cable tension can be observed through three-dimensional numerical analysis using ABAQUS. It is possible to model the rod, nut, and strand shoe constituting the anchorage, respectively, and analyze the stress of the rod and nut while changing the displacement corresponding to the cable tension. As the displacement increases, many stress changes occur in the middle of the rod, and the stress change tends to increase in proportion to the displacement. Therefore, the cable tension can be estimated through load monitoring.

On the other hand, the propagation characteristics of ultrasonic waves are sensitive to stress. The fact that the propagation speed of ultrasonic waves can be slightly changed by stress ( ^{changes in approximately 10 -8} s units), and the change in the excitation frequency of ultrasonic waves (Frequency shift) and harmonization and modulation of the excitation frequency by stress (nonlinear) It is known that the size of the components can be varied. The stress can be measured using the propagation characteristics of the ultrasonic wave. However, the method using the excitation frequency change has a disadvantage in that it is difficult to apply the Lamb wave propagating to the structure. Since the method using the size change of the non-linear component changes not only by the stress change but also by the micro-damage generated in the material, the practicality of the application to real structures and complex structures in the future may be lowered. Since the ultrasonic propagation speed is free from these disadvantages, it can be effectively used for stress measurement.

An object of the present invention is to provide a method and a system for measuring the tensile stress of a structure such as a steel bar or a cable using the propagation speed of a temperature-corrected ultrasonic signal.

The problem to be solved by the present invention is not limited to the above problems, and may be variously expanded without departing from the spirit and scope of the present invention.

A method for evaluating tensile stress of a structure using ultrasound according to embodiments for realizing an object of the present invention includes: a first step of measuring an ultrasound signal propagating in a structure to which tension is not applied at various temperatures; a second step of measuring an ultrasonic signal propagating in the structure while applying various tensions under a constant temperature condition; a third step of measuring an ultrasonic signal propagating in the structure under a condition in which the tension and temperature state of the structure are unknown; and a fourth step of calculating the tension of the structure by measuring the propagation speed of the ultrasonic signal propagating within the structure while correcting the change in the propagation speed of the ultrasonic signal according to the temperature.

In an exemplary embodiment, in the first step, in a state in which no tension is introduced to the structure to be measured for tension, the ultrasonic signal propagated in the structure is measured while the ultrasonic signal is applied to the structure, and the ultrasonic wave is changed according to the temperature change. establishing a first relation between the time delay of the C11 propagation mode of the signal and the time delay of the C23 propagation mode, wherein the C11 propagation mode represents the ultrasonic signal mode propagating in the longitudinal direction of the structure, and the C23 propagation mode The mode represents an ultrasonic signal mode propagating in a direction perpendicular to the longitudinal direction of the structure.

In an exemplary embodiment, the second step is by measuring the ultrasonic signal propagating in the structure while applying the ultrasonic signal to the structure while applying tension while changing the size of the structure under a constant temperature condition, The method may include establishing a second relational expression between the change in tension and the time delay of the C11 propagation mode of the ultrasound signal.

In an exemplary embodiment, the third step is to extract the C11 propagation mode and the C23 propagation mode by measuring the ultrasonic signal propagating from the structure while applying the ultrasonic signal to the structure without knowing the temperature and tension conditions may include steps.

In an exemplary embodiment, the fourth step may include calculating time delays of the extracted C11 propagation mode and the C23 propagation mode, respectively, using a predetermined reference signal; And when the time delay of the C23 propagation mode is 0, the tension of the structure is calculated based on the extracted time delay value of the C11 propagation mode without temperature correction, and when the time delay of the C23 propagation mode is not 0, After performing temperature compensation on the extracted time delay value of the C11 propagation mode, calculating the tension of the structure based on the corrected time delay value of the C11 propagation mode.

A computer-executable program stored in a computer-readable recording medium may be provided to perform the method for evaluating the tensile stress of a structure using ultrasonic waves according to the above various embodiments.

A computer-readable recording medium in which a computer program for performing the method for evaluating tensile stress of a structure using ultrasonic waves according to the above embodiments is recorded may be provided.

On the other hand, a system for evaluating tensile stress of a structure using ultrasound according to embodiments for realizing an object of the present invention includes a waveform generator for generating an excitation signal necessary for generating an ultrasound; an excitation sensor attached to the surface of the structure, receiving the excitation signal and outputting an ultrasonic signal into the structure; a first ultrasonic sensor attached to the surface of the structure and spaced apart from the excitation sensor by a predetermined distance in the longitudinal direction of the structure and configured to detect ultrasonic waves propagating from the excitation sensor in the longitudinal direction; a second ultrasonic sensor attached to the surface of the structure and spaced apart from the excitation sensor by a predetermined distance in the shear direction orthogonal to the longitudinal direction of the structure and configured to detect ultrasonic waves propagating from the excitation sensor in the shear direction; a digitizer converting the analog ultrasonic signals detected by the first and second ultrasonic sensors into digital signals; Then, by executing a predetermined operation program, the temperature-compensated tension of the structure is calculated using the digital ultrasound signal provided from the digitizer, and the temperature-compensated tension of the structure is C11 propagation of the ultrasound signal propagated from the structure. A control unit configured to calculate using the mode and the C23 propagation mode may be provided.

In an exemplary embodiment, the excitation sensor and the first and second ultrasonic sensors may be micro fiber composite (MFC) sensors that can be stably attached to and used even on the structure having a curved surface.

In an exemplary embodiment, the waveform generator and the digitizer may establish time synchronization with each other in order to trigger measurement start by the control unit, and to simultaneously perform ultrasound generation and measurement, respectively.

According to exemplary embodiments of the present invention, temperature correction of ultrasonic waves is possible without temperature information in the tension evaluation of a structure, and it is applicable to a cylindrical structure such as a rod. In addition, there are advantages in that the installation of the sensor is easy and inexpensive, and the time for measuring the tension is short.

1 shows the propagation of ultrasonic waves generated when an ultrasonic wave is applied to a structure on which a uniaxial force acts.
FIG. 2 illustrates a propagation shape of ultrasonic waves measured by the first sensor and the second sensor of FIG. 1 .
3 and 4 show the change characteristics of the arrival time of the longitudinal ultrasonic waves according to the C11 mode and the change characteristics of the arrival time of the shear-direction ultrasonic waves according to the C23 mode, respectively, while changing the magnitude of the tensile stress applied to the structure.
5 is a block diagram illustrating a configuration of a structure tensile stress evaluation system and a tension evaluation method according to an exemplary embodiment of the present invention.
6 shows an overall process of a method of measuring the tensile stress of a structure using ultrasonic waves in a state of varying temperature, according to an exemplary embodiment of the present invention.
7 schematically shows the measurement (first stage) of the ultrasonic signal at various temperatures.
8 shows the relationship between the C11 mode and the C23 mode time delay among the propagation modes of the ultrasonic signal.
9 schematically shows a second step of measuring ultrasonic signals for various tensions applied to the structure 150 under a constant temperature condition.
10 shows the relationship between the tension obtained through the second step and the C11 mode time delay.
11 schematically shows a third step of measuring ultrasonic waves under conditions in which tension and temperature states are unknown and a fourth step of calculating accurate tension through ultrasonic temperature correction.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. The same reference numerals are used for the same components in the drawings, and repeated descriptions of the same components are omitted.

With respect to the embodiments of the present invention disclosed in the text, specific structural and functional descriptions are merely exemplified for the purpose of describing the embodiments of the present invention. Embodiments of the present invention may be embodied in various forms, and should not be construed as being limited to the embodiments described herein. That is, since the present invention can have various changes and can have various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

The terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof. Also, terms such as first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another.

1 shows the propagation of ultrasonic waves generated when an ultrasonic wave is applied to a structure on which a uniaxial force acts. FIG. 2 illustrates a propagation shape of ultrasonic waves measured by the first sensor and the second sensor of FIG. 1 .

1 and 2, a uni-axial force (uni-axial force), that is, a normal stress (σ ₁₁ ) in the longitudinal direction (first direction) of the structure is applied to the isotropic structure 20 in which the ultrasonic sensor 32 is applied. When the ultrasonic wave is excitation through, the excited ultrasonic wave may be propagated in two directions: a longitudinal direction (first direction) of the structure 20 and a shear direction (second direction) orthogonal to the longitudinal direction. Ultrasound propagating in the first direction and the second direction, respectively, may be divided into three waves according to the vibration direction.

The velocity (C11, C12, C13) and (C21, C22, C23) of the propagating ultrasound can be derived using the following five equations. Here, the number in front of the subscript indicates the direction in which the ultrasonic wave propagates, and the number after the subscript indicates the direction in which the ultrasonic waves vibrate.

[Equation 1]

......(1-1)

......(1-1)

......(1-2)

......(1-2)

......(1-3)

......(1-3)

......(1-4)

......(1-4)

......(1-5)

......(1-5)

where ρ is the mass density, c _ij is the velocity of a wave propagating in direction i (x, y, z) and polarized in direction j, σ ₁₁ is the normal stress in direction 1, and (λ, μ) is the lamé ( Lame), and (m, n, l) is Murnaghan's coefficient.

)가 응력 변화와 온도에 가장 민감하게 변하고, 응력이 작용하는 방향과 수직으로 발생하는 shear wave의 전파속도(

)는 응력의 변화에도 거의 변화가 없음을 알게 되었다. The present inventors tried to apply the above five equations to ultrasound transmission in the structure. According to him, the propagation speed (

) is the most sensitive to changes in stress and temperature, and the propagation speed (

) was found to have almost no change even with the change in stress.

From this, it can be seen that the tensile stress of the structure can be measured by calculating the velocity change of the C11 mode, which is most sensitive to stress change and temperature.

In addition, the speed of the ultrasonic wave is affected not only by the acoustic elastic effect but also by the elastic modulus and density change of the structure 20 . In general, the modulus of elasticity decreases when the temperature increases, and the speed of ultrasonic waves decreases due to the decreased modulus of elasticity. Therefore, temperature correction is required for tension monitoring using the ultrasonic velocity change.

For temperature compensation, C23, which is not affected by tensile stress but is affected by temperature, can be used. That is, it is possible to check whether the temperature effect of the ultrasonic wave is affected by using the C23 mode, and if there is a temperature effect, the tension can be evaluated after correcting the speed change due to the temperature of C11 using the C23 mode.

))의 변화 특성과, C23모드에 따른 shear wave의 도달시간(전파속도(

))의 변화 특성을 각각 나타낸다.3 and 4 show the arrival time (propagation velocity (propagation speed) of a longitudinal wave according to the C11 mode while changing the magnitude of the tensile stress applied to the structure.

)) and the arrival time of shear wave (propagation speed (

))), respectively.

The graphs of FIGS. 3 and 4 show the ultrasonic signal waveforms measured during stress measurement while increasing the load applied to the structure based on the measured ultrasonic signal when there is no load applied to the structure (0 Mpa) for estimating the arrival time of the ultrasonic signal. The result of calculating the delay degree (ie, propagation speed) of the arrival time of the ultrasound signal by analyzing the cross correlation of Referring to FIG. 3 , as the load applied to the structure increases, the arrival time of the longitudinal wave according to the C11 mode of the ultrasonic signal is gradually increased compared to the arrival time of the ultrasonic signal measured when no load is applied to the structure (0 MPa). You can see the delay. The arrival time is delayed almost proportionally according to the magnitude of the applied load. In contrast, referring to FIG. 4 , even if the load applied to the structure increases, the arrival time of the shear wave according to the C23 mode of the ultrasonic signal is the arrival time of the ultrasonic signal measured when no load is applied to the structure (0 MPa). It can be seen that there is almost no change compared to

That is, in the case of the C11 mode, the degree of delay of the arrival time of the ultrasound signal increases as the tension applied to the structure increases, but in the case of the C23 mode, it can be seen that there is no change. The tensile stress applied to the structure can be calculated by using the characteristic of the arrival time of the ultrasound signal in the C11 mode and the C23 mode of the ultrasound signal, that is, the characteristic of the propagation speed.

Fig. 5 shows the configuration of a structure tensile stress evaluation system and a tensile stress evaluation method according to an exemplary embodiment.

5, the structure tensile stress evaluation system 100 is a waveform generator (Arbitrary Waveform Generator: AWG) 110 for excitation of ultrasonic waves to the measurement target structure (eg, a rod-shaped sample of a cable anchorage) 150, It may include a digitizer 120 for measuring an ultrasonic signal, a waveform generator 110 , and a control unit 130 for controlling the digitizer 120 .

The control unit 130 may include a processor capable of executing a program, a memory providing a data processing space for arithmetic processing of the processor, and a data storage for storing various software programs and data necessary for carrying out the present invention. can Hardware for implementing the control unit 130 includes a processor, a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable array (FPA), a programmable logic unit (PLU), a microprocessor, Or it may be implemented using one or more general purpose computers or special purpose computers, such as any other device capable of executing and responding to instructions.

In the measurement target structure 150 , an ultrasonic excitation sensor 142 for excitation of ultrasonic waves, and an ultrasonic signal excited by the ultrasonic excitation sensor 142 pass through the measurement target structure 150 in a longitudinal direction and a direction perpendicular to the longitudinal direction. First and second ultrasonic sensors 144 and 146 for respectively detecting ultrasonic signals propagating in the shear direction may be attached. The surface of the structure 150 , such as a cable or a steel rod, may be curved. It is very difficult to attach a general ultrasonic sensor installed on a flat surface to a curved surface, and it is impossible to maintain the attached state even if it is temporarily attached. A piezoelectric fiber composite (MFC) sensor that can be stably attached to the measurement target structure 150 having a curved surface as well as the ultrasonic sensor 142 and the first and second ultrasonic sensors 144 and 146 are used. It can be used to generate and measure ultrasonic waves. The MFC sensor has the advantage of being easily applied to a flexible and curved structure based on a piezoelectric ceramic fiber. In addition, it has the advantage of using the d33 piezoelectric constant to achieve great operating efficiency and anisotropic driving.

In an exemplary embodiment, the hardware of the structure tensile stress evaluation system 100 may be constructed using, for example, a National Instrument (NI) PXI system. In the control unit 130, for example, Lab View software may be installed. For ultrasonic excitation and measurement for stress measurement, a Lab View-based ultrasonic measurement interface (software) may be developed and installed in the control unit 130 . The user may execute the Lab View program through the ultrasonic measurement interface, and may control the hardware of the structure tensile stress evaluation system 100 as desired through the execution of the program.

In the structure tensile stress evaluation system 100 of FIG. 5 , the waveform generator 110 generates an excitation signal necessary for ultrasonic generation under the control of the controller 130 and applies it to the excitation sensor 142 . . The excitation sensor 142 to which the excitation signal is input may generate an ultrasound signal into the measurement target structure 150 . The ultrasonic signal generated by the excitation sensor 142 may propagate in the longitudinal direction and the shear direction perpendicular to the longitudinal direction in the structure 150 . The ultrasonic wave propagated in the longitudinal direction may be detected by the first ultrasonic sensor 144 , and the ultrasonic wave propagated in the shear direction orthogonal to the longitudinal direction may be detected by the second ultrasonic sensor 146 . The ultrasound signals detected by the first and second ultrasound sensors 146 are analog signals, and may be transmitted to the digitizer 120 and converted into digital data. The digital data may be transmitted to and stored in the controller 130 .

The digital data transmitted to the controller 130, that is, the measured ultrasonic waves, can be used as an input of a tensile stress calculation program executed by the controller 130, and act on the structure 150 as a result of the calculation processing of the tensile stress calculation program. Tensile stress can be calculated.

The structure tensile stress evaluation system 100 may operate as follows. A specimen of the structure 150 is installed in the MTS equipment, and a static tensile load is applied in units of 100 kN (105.20 Mpa), for example, from 0 to 1500 kN. In addition, by applying an ultrasonic signal to the structure 150, a change in the propagation speed of the ultrasonic wave can be measured. At this time, the load applied to the specimen of the structure 150 may be controlled and measured in real time through the load cell of the MTS equipment.

Specifically, when the control unit 130 sends a trigger signal informing the start of measurement to the waveform generator 110 and the digitizer 120, the waveform generator 110 and the digitizer 120 each perform ultrasonic generation and measurement at the same time. Time synchronization can be established between Thereafter, the signal generated by the waveform generator 110 generates an ultrasonic wave through the excitation sensor 142 , and the information of the propagated ultrasonic signal is collected through the two ultrasonic sensing sensors 144 and 146 and the digitizer 120 . can Data of the collected ultrasound signal may be transmitted to and stored in the controller 130 . The controller 130 may analyze the data of the collected ultrasound signal to evaluate the current tension state of the structure 150 . In the exemplary embodiment, since it is necessary to measure a minute change in propagation speed of an ultrasonic signal due to tensile stress, high temporal resolution is required. In an exemplary embodiment, data measurement is performed with a sampling frequency of 10 MHz, that is, with ^{a time resolution of 10 -7} sec, and then interpolated to obtain a higher time resolution, for example, 10 ^{-9 sec.} .

6 shows an overall process of a method of measuring the tensile stress of the structure 150 using ultrasonic waves in a state where the temperature is variable.

Referring to FIG. 6 , the tensile stress acting on the structure 150 may be obtained through four steps as follows: (1) measuring ultrasonic signals at various temperatures (first step); (2) measuring ultrasonic signals at various tensions under constant temperature conditions (second step); (3) ultrasonic measurement under conditions of unknown tension and temperature (third step); And (4) last is ultrasonic temperature correction and tension estimation (fourth step). Hereinafter, each step will be described in more detail.

7 schematically shows the first step of measuring the ultrasonic signal at various temperatures.

Referring to FIG. 7 , the first step is an ultrasonic measurement step according to a temperature change at a time point before tension is introduced into the structure 150 . In a state in which the excitation sensor 142 for generating ultrasonic waves and the first and second ultrasonic sensors 144 and 146 for measuring ultrasonic waves propagating through the structure 150 are installed, the excitation sensor 142 by changing the temperature. ), the ultrasonic waves may be excited to the structure 150 . In this case, as the ultrasonic excitation frequency, a frequency (eg, 170 kHz) that is easy to distinguish a waveform may be selected for propagation speed analysis.

The first and second ultrasonic sensors 144 and 146 detect a propagated ultrasonic signal, and digital data of the detected ultrasonic signal is transmitted to the controller 130 . The controller 130 may extract the C11 mode and the C23 mode from the measured signal, respectively, select a reference signal, and calculate a time delay between the measured signals and the reference signal. Comparing the C11 propagation mode and the C23 propagation mode of the ultrasonic signal measured using the first and second ultrasonic sensors under different temperature conditions, it shows that the propagation speed of the ultrasonic signal decreases as the temperature increases. A signal measured at a temperature of 0°C can be selected as a reference signal, and a time delay can be calculated with the signals measured at each temperature. With the time delay data thus calculated, a relational expression between the C11 mode and C23 mode time delays calculated using linear regression analysis can be established. 8 illustrates the relational expression between the time delay of the C11 mode and the C23 mode as follows.

......(6)

......(6)

where t ₁₁ with t ₂₃ denotes the time delay of the C11 propagation mode and the C23 propagation mode, respectively, and A and B are model parameters.

9 schematically shows a second step of measuring ultrasonic signals for various tensions applied to the structure 150 under a constant temperature condition.

In the second step, ultrasonic waves according to a change in tension applied to the structure 150 under a constant temperature condition may be measured. The structure 150 specimen used for the temperature experiment and the ultrasonic measurement system may be used as they are. While maintaining the temperature constant, ultrasonic generation/measurement may be performed at each tension while increasing, for example, from 0 to 1500 kN at 100 kN intervals on the specimen of the structure 150 . Similarly, the controller 130 may extract the C11 mode from the measured ultrasound and select a reference signal to calculate a time delay between the measured signals and the reference signal. That is, comparing the C11 propagation mode and the C23 propagation mode of the ultrasonic signal measured under different tension conditions, it can be seen that the speed of the C11 propagation mode decreases as the tension increases, but the speed of the C23 propagation mode is constant. Here, a signal measured at 0 kN may be selected as a reference signal, and a time delay may be calculated with the signals measured at each tension. Then, as shown in FIG. 10 , a relational expression can be established by performing a linear regression analysis between the tension and the C11 mode time delay. The relationship between the tension applied to the structure 150 and the C11 mode time delay may be expressed as a function as follows. The relational expression between the C11 propagation mode and tension established using linear regression also has high linearity, and since the C23 propagation mode does not change its speed even when the tension increases, the time delay can also be calculated as 0.

[Equation 2]

Here, F is the tension applied to the structure 150, and C and D are model parameters.

11 schematically shows a third step of measuring ultrasonic waves under conditions in which tension and temperature states are unknown and a fourth step of calculating accurate tension through ultrasonic temperature correction.

Referring to FIG. 11 , when two relational expressions are established in the third step, the ultrasonic signal is excited in the same manner as above without knowing the temperature and tension conditions applied to the structure 150 , and the first and second ultrasonic sensors The ultrasonic signal propagated through 144 and 146 is detected, and the controller 130 calculates digital data of the detected ultrasonic signal to calculate the ultrasonic arrival time in the C11 mode and the C23 mode.

In the fourth step, each time delay may be calculated using the reference signal used in the second step. If no temperature change has occurred compared to the temperature in the second step, the time delay ( t ₂₃ ^U ) of the C23 mode will be zero, and the tension without temperature correction for the C11 mode time delay ( t ₁₁ ^U ) is calculated using the equation below. can be calculated using

[Equation 3]

However, if the time delay ( t ₂₃ ^U ) of the C23 mode is not 0, since a temperature change has occurred , after temperature compensation of the C11 mode time delay ( t ₁₁ ^U ) is performed, the tension is increased using the corrected time delay. can be calculated. In this case, the tension calculation formula is as follows. In Equation (4-1), the second term on the right is for temperature compensation.

[Equation 4]

......(4-1)

......(4-1)

......(4-2)

......(4-2)

According to the present invention, it is recognized that a change in temperature can significantly affect the tension evaluation of the structure 150, and in order to solve this problem, the tension evaluation is performed after performing temperature correction. By doing so, the maximum error of the measured tension can be greatly reduced. Through various experiments, it can be confirmed that when temperature correction is performed, the error is reduced by almost 90% or more compared to the case where temperature correction is not performed.

The method according to the above-described embodiment may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the medium may be specially designed and configured for the embodiment, or may be known and available to those skilled in the art of computer software. Examples of the computer-readable recording medium include magnetic media such as hard disks, floppy disks and magnetic tapes, optical media such as CD-ROMs and DVDs, and magnetic such as floppy disks. - includes magneto-optical media, and hardware devices specially configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine language codes such as those generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

The present invention can be used to monitor the tension applied to a cable or rigid body that carries a load of a bridge or structure.

Although the embodiments have been described with reference to the limited drawings as described above, those skilled in the art can variously modify and change the present invention within the scope without departing from the spirit and scope of the present invention described in the claims below. You will understand that you can. For example, the described techniques are performed in a different order than the described method, and/or the described components of the system, structure, apparatus, circuit, etc. are combined or combined in a different form than the described method, or other components Or substituted or substituted by equivalents may achieve an appropriate result. Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (10)

A first step of measuring an ultrasonic signal propagating in a structure to which tension is not applied at various temperatures;
a second step of measuring an ultrasonic signal propagating in the structure while applying various tensions under a constant temperature condition;
a third step of measuring an ultrasonic signal propagating in the structure under a condition in which the tension and temperature state of the structure are unknown; And
and a fourth step of calculating the tension of the structure by measuring the propagation speed of the ultrasonic signal propagating within the structure while correcting the change in the propagation speed of the ultrasonic signal according to the temperature. Stress evaluation method. According to claim 1, wherein, in the first step, in a state in which no tension is introduced to the structure to be measured for tension, while applying the ultrasonic signal to the structure, the ultrasonic signal propagated from the structure is measured, and the ultrasonic signal is changed according to the temperature change. establishing a first relation between the time delay of the C11 propagation mode and the time delay of the C23 propagation mode, wherein the C11 propagation mode represents an ultrasonic signal mode propagating in the longitudinal direction of the structure, and the C23 propagation mode is the A method for evaluating tensile stress of a structure using ultrasound, characterized in that it indicates a mode of an ultrasound signal propagating in a direction perpendicular to the longitudinal direction of the structure. According to claim 1, wherein in the second step, by measuring the ultrasonic signal propagating in the structure while applying the ultrasonic signal to the structure while applying tension while changing the size of the structure under a constant temperature condition, the tension A method for evaluating tensile stress of a structure using ultrasound, comprising the step of establishing a second relational expression between the change and the time delay of the C11 propagation mode of the ultrasound signal. The method of claim 1 , wherein the third step comprises: extracting a C11 propagation mode and a C23 propagation mode by measuring an ultrasonic signal propagating from the structure while applying an ultrasonic signal to the structure without knowing the temperature and tension conditions A method for evaluating tensile stress of a structure using ultrasound, characterized in that it comprises a. The method of claim 1, wherein the fourth step comprises: calculating time delays of the extracted C11 propagation mode and the C23 propagation mode, respectively, using a predetermined reference signal; And when the time delay of the C23 propagation mode is 0, the tension of the structure is calculated based on the extracted time delay value of the C11 propagation mode without temperature correction, and when the time delay of the C23 propagation mode is not 0, Tensile of the structure using ultrasound, comprising the step of calculating the tension of the structure based on the corrected time delay value of the C11 propagation mode after performing temperature compensation on the extracted time delay value of the C11 propagation mode Stress evaluation method. A computer-executable program stored in a computer-readable recording medium to perform the method for evaluating tensile stress of a structure using ultrasonic waves according to any one of claims 1 to 5. A computer-readable recording medium in which a computer program for performing the method for evaluating tensile stress of a structure using ultrasonic waves according to any one of claims 1 to 5 is recorded. a waveform generator for generating an excitation signal required for ultrasonic generation;
an excitation sensor attached to the surface of the structure, receiving the excitation signal and outputting an ultrasonic signal into the structure;
a first ultrasonic sensor attached to the surface of the structure and spaced apart from the excitation sensor by a predetermined distance in the longitudinal direction of the structure and configured to detect ultrasonic waves propagating from the excitation sensor in the longitudinal direction;
a second ultrasonic sensor attached to the surface of the structure and spaced apart from the excitation sensor by a predetermined distance in a shear direction orthogonal to the longitudinal direction of the structure and configured to detect ultrasonic waves propagating from the excitation sensor in the shear direction;
a digitizer converting the analog ultrasonic signals detected by the first and second ultrasonic sensors into digital signals; And
Execute a predetermined operation program and calculate the temperature-compensated tension of the structure using the digital ultrasound signal provided from the digitizer, wherein the temperature-compensated tension of the structure is the C11 propagation mode of the ultrasound signal propagated in the structure. and a control unit configured to calculate using the C23 propagation mode. The ultrasonic wave according to claim 8, wherein the excitation sensor and the first and second ultrasonic sensors are piezoelectric fiber composite (MFC) sensors that can be stably attached and used even on the structure having a curved surface. The tensile stress evaluation system of the used structure. The tension of the structure using ultrasound according to claim 8, wherein the waveform generator and the digitizer are triggered to start measurement by the control unit, and time synchronization is established with each other in order to simultaneously perform ultrasound generation and measurement, respectively. Stress rating system.

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