KR20210006107A - Damage detection method using lamb wave signal energy - Google Patents

Abstract

The present invention relates to a damage detection method using the signal energy of an elastic wave which can accurately predict the position of a damaged portion of a composite material in comparison to a conventional technique. The damage detection method using the signal energy of an elastic wave comprises: (a) a step of generating an input signal which is an elastic wave by an excitation unit installed on a composite material to propagate the input signal along the composite material, and measuring a signal propagated along the composite material by a sensor installed on the composite material; (b) a step of estimating the size of a noise signal in a measurement signal measured by the sensor by using the input signal, and then calculating a correction signal obtained by removing the noise signal from the measurement signal; (c) a step of separating signals included in the correction signal, and determining a first signal arriving at the sensor first from the excitation unit among the signals included in the correction signal; (d) a step of using the distance between the excitation unit and the sensor and the time until the first signal arrives to calculate the speed of the input signal; and (e) a step of using a signal in a case where damage to the composite material is absent and the correction signal to calculate a difference signal before and after damage, and using the time when the difference signal before and after damage arrives and the speed of the input signal calculated in the step (d) to estimate a damage position of the composite material.

Description

Damage detection method using lamb wave signal energy

The present invention relates to a damage detection method using signal energy of an acoustic wave, and more particularly, to a damage detection method that can be used to detect damage to an aircraft.

The aircraft in operation operates under aerodynamic, drag, gravity and various loads, and these loads can cause damage to various structures constituting the aircraft. In order to prepare for such damage to aircraft, there are various detailed regulations for periodic inspection of aircraft. According to G. Anderson's paper "Providing best value IVHM solution for aging aircraft", inspection-related costs account for 49% of the costs used for maintenance/repair of aircraft, and the manpower required for maintenance/repair of aircraft also accounts for 35%. Because it occupies more simplification, it is possible to improve the damage detection efficiency of the aircraft, and there is a need for a method to reduce maintenance / repair costs.

One of the periodic inspection methods of aircraft may be non-destructive testing, and representative examples of non-destructive testing include radiographic testing (X-ray), ultrasonic testing, and eddy current testing. In recent years, research on an inspection method using guided ultrasonic waves (elastic waves) that can be applied to composite materials, which has relatively less cost and inspection time than the non-destructive inspection methods described above, and can increase inspection efficiency, is being conducted.

Guided ultrasound refers to an acoustic wave propagating along a structure medium surrounded by an interface such as a beam, pipe, or flat plate, and the guided ultrasound transmitted to the flat plate is an acoustic wave (lamb wave). The nondestructive testing method using seismic waves uses a sinusoidal signal composed of a combination of sine and cosine as an input signal as shown in Equation 1 below, and the elastic wave has a form of a burst wave.

[Equation 1]

(Where A is the acoustic wave, w is the center frequency, and n is the period of the burst wave)

1 is an elastic wave determined by Equation 1 when n is 5, that is, when the period of the burst wave is 5. The n value may be selected differently according to the object to be measured (eg, composite material) and the type of damage to be measured, and the shape of the elastic wave shown in FIG. 1 varies according to the n value. The acoustic wave as an input signal is generated through a piezo-electric actuator and propagated on the composite material, and is collected by a piezo-electric sensor located on the composite material.

FIG. 2 schematically shows the actuator 10 and the sensor 11 installed on the composite material, and the damaged part (hereinafter, the damage location 12) in the composite material, and FIG. 3A is when there is no damage location 12 in the composite material. , It shows the waveform of the signal measured by the sensor 11, Figure 3b shows the waveform of the signal measured by the sensor 11 when there is a damage position 12 in the composite material.

As shown in FIG. 3A, when there is no damage to the composite material, one signal is measured by the sensor 11, and the first signal S1, which is a corresponding signal, is transferred from the actuator 10 of FIG. 2 to the sensor 11. It is a signal transmitted directly. On the other hand, as shown in FIG. 3B, when there is damage to the composite material, the sensor 11 sequentially measures two signals. As described above, the first signal S1 is a signal directly transmitted from the actuator 10 of FIG. 2 to the sensor 11, and the second signal S2 measured later than the first signal S1 is the actuator 10 ) Is a signal transmitted to the sensor 11 through the damage location 12. The reason that the time at which the first signal S1 and the second signal S2 are measured is different is that the transmission speed of the elastic wave input from the actuator 10 is constant, but the actuator 10 and the sensor ( 11) This is because the distance between the actuator 10, the damage location 12, and the distance through the sensor 11 are different. Since the second signal S2 moves to the sensor 11 through the damage location 12, the amplitude changes compared to the first signal S1.

The damage location 12 in the actuator 10 and the sensor 11 may be calculated through the first signal S1 and the second signal S2 shown in FIG. 3B. More specifically, since the distance between the actuator 10 and the sensor 11 is known, the time until the sensor 11 measures the first signal S1 after inputting the acoustic wave from the actuator 10 The speed of the elastic wave can be obtained, and the time until the second signal S2 is measured by the sensor 11 after the speed of the elastic wave and the actuator 10 is input, and the actuator 10-the damage location (12)-The distance d1 between the sensors 11 can be obtained. Therefore, the candidate location where the damage location 12 may be may be represented by an ellipse, which is a point where the sum of the distances d1 to the actuator 10 and the sensor 11 as a vertex is different from that of the sensor 11 shown in FIG. Position By repeating the above-described process in at least two or more sensors, at least three or more ellipses may be obtained and the intersection of the ellipses may be calculated as the damage position 12.

Meanwhile, the acoustic wave used for damage detection has a multi-mode characteristic in which the propagation speed changes according to the center frequency, and a discrete characteristic in which the shape changes while propagating on the composite material. In addition, when an elastic wave propagates on a flat composite material, the elastic wave is composed of a Symmetric Mode (hereinafter referred to as S mode) in which the vertical movement is symmetrical with respect to the center of the plate, and an Anti-Symmetric Mode (hereinafter referred to as A mode) that is asymmetric. Depending on the center frequency to be excitation, the S-mode and A-mode may be overlapped in various forms. Due to the characteristics of these elastic waves, the signals obtained from the flat-type composite material are combined and reflected by the differentiated signals due to discrete characteristics. It is measured by the combination of the signal and the sum of the various signals in which the S mode and A mode are combined. In addition, the white-noise component can also be measured. FIG. 4A shows an elastic wave input from the actuator 10, and FIG. 4B shows an example of a signal measured by the sensor 11 by mixing various signals as described above. As shown in FIG. 4B, the sensor 11 ), since various signals are mixed and measured, a method of extracting the damage signal or damage information according to the damage location 12 among the measured signals is important.

In order to reduce the noise component of the signal measured by the conventional sensor 11, a Spectral Subtraction method was proposed in speech signal processing in 1979, and this method is the signal v of the noise component in the signal x(t) measured by the sensor 11 This is a method of estimating (t) and estimating the signal s(t) due to the input acoustic wave among the signals measured by the sensor 11 by removing the energy of the noise signal estimated in the frequency domain. This method is a method of reducing the energy of the noise and reducing the size of the noise, and this method may be illustrated as shown in FIG. 5.

In order to use the conventional method shown in Fig. 5, it is necessary to estimate the energy level of the noise signal v(t). However, the size of the noise signal among signals measured for damage detection may vary depending on the shape of the object and the attachment state of the sensor, and the method of estimating the energy level of the noise signal is practically limited.

Korean Laid-Open Patent Publication No. 10-2009-0012818 ("Non-destructive inspection device", published date 2009.02.04.)

The present invention was conceived to solve the above problems, and an object of the method for detecting damage using signal energy of an elastic wave according to the present invention is to predict the location of a damaged part on a composite material more accurately than the conventional method. It is to provide a damage detection method using signal energy.

In order to solve the above problems, the method for detecting damage using signal energy of an elastic wave according to the present invention is a) generating an input signal, which is an elastic wave, from an excitation part installed in a composite material to propagate along the composite material, and a sensor installed in the composite material. Measuring a signal propagating along the composite material at; b) estimating a magnitude of a noise signal using the input signal from the measurement signal measured by the sensor, and then calculating a correction signal from which the noise signal is removed from the measurement signal; c) separating signals included in the correction signal, and determining a first signal that arrives first from the excitation unit to the sensor from among signals included in the correction signal; d) calculating the speed of the input signal using the distance between the excitation unit and the sensor and the time until the first signal arrives; And e) calculating a difference signal before and after damage using the correction signal and a signal when there is no damage to the composite material, and using the time at which the difference signal before and after damage arrives and the speed of the input signal calculated in step d). It characterized in that it comprises; estimating the damage location of the composite material.

In addition, step b) may include: b-1) estimating the magnitude of the noise signal using Equation 5 below; It characterized in that it comprises a.

[Equation 5]

는 추정된 상기 잡음신호의 크기,

는 상기 측정신호의 에너지 크기,

는 상기 입력신호의 에너지 크기)(

Is the estimated size of the noise signal,

Is the energy level of the measurement signal,

Is the energy level of the input signal)

In addition, step b) is performed after step b-2) and step b-1), and calculating the correction signal in the time domain using Equation 6 below; It characterized in that it further comprises.

[Equation 6]

는 상기 측정신호를 STFT(Short Time Fourier Transform)한 신호, 상기

는 주파수 영역에서의 상기 보정신호,

는 상기

을 inverse STFT한 시간영역에서의 보정신호)(remind

Is a signal obtained by short-time fourier transform (STFT) of the measurement signal,

Is the correction signal in the frequency domain,

Is reminded

Correction signal in time domain inverse STFT)

을 상기 수식 6을 통해 구해진

로 대체하여 상기 보정신호에 포함된 잡음신호의 크기를 추정하고, 상기 보정신호의 크기 대비 상기 보정신호에 포함된 잡음신호의 크기가 기준치 이상일 경우, 상기 수식 6의

을 상기

로 대체하여 잡음신호의 크기가 줄어든 보정신호를 생성하는 단계; 를 더 포함하는 것을 특징으로 한다.In addition, step b) is performed after step b-3) b-2), and

Obtained through Equation 6 above

In the case where the size of the noise signal included in the correction signal is estimated and the size of the noise signal included in the correction signal is greater than or equal to the reference value,

Remind

Generating a correction signal having a reduced noise signal by replacing it with It characterized in that it further comprises.

In addition, the step b-3) is characterized in that it is repeatedly performed until the size of the noise signal included in the generated correction signal becomes less than or equal to a reference value.

In addition, step c) may include: c-1) separating a signal having the highest energy among signals included in the correction signal using Equation 7 below, and determining the separated signal as the first signal; It characterized in that it comprises a.

[Equation 7]

는 시간영역에서의 보정신호를 STFT한 신호,

는 입력신호)(r(t) is the signal with the largest energy among the signals included in the correction signal,

Is the signal obtained by STFT of the correction signal in the time domain,

Is the input signal)

In addition, in step e), one of the signals included in the difference signal before and after damage is separated using Equation 7 below, and the time when the separated signal arrives and the speed of the input signal calculated in step d) are used. It characterized in that the damage location of the composite material is estimated.

[Equation 7]

는 시간영역에서의 상기 손상 전후 차이 신호를 STFT한 신호,

는 입력신호)(r(t) is the signal with the largest energy among the signals included in the difference signal before and after damage,

Is a signal obtained by STFT of the difference signal before and after damage in the time domain,

Is the input signal)

신호는 이전에 수행된 e) 단계의

신호에서 이전에 수행된 e) 단계에서 분리된 신호를 뺀 신호인 것을 특징으로 한다.In addition, when step e) is repeatedly performed to separate a predetermined number of signals included in the difference signal before and after damage, and when step e) is repeatedly performed, in Equation 7

The signal was previously performed in step e).

It is characterized in that it is a signal obtained by subtracting the signal separated in step e) previously performed from the signal.

In addition, the step e) is repeatedly performed to separate a predetermined number of signals included in the difference signal before and after damage to estimate an area of the damage location.

In addition, it is characterized in that a plurality of sensors installed in the composite material.

According to the damage detection method using the signal energy of the acoustic wave according to the present invention as described above, the correction signal is removed from the measurement signal by estimating the magnitude of the noise signal using the energy magnitude of the input signal known in advance in step b). Therefore, it is possible to obtain a more accurate signal than the conventional method of removing the noise signal from the measurement signal by estimating the size of the incorrect measurement signal, there is an effect of more accurately predicting the location of the damaged portion of the composite.

In addition, according to the present invention, since the first signal is separated from the measurement signal by using Equation 7, it is possible to more accurately separate the first signal, so that the location of the damaged part of the composite material can be more accurately predicted.

1 is a waveform of an acoustic wave composed of a combination of sine and cosine.
Figure 2 is a schematic diagram of an actuator, a sensor, and a damage location installed on a composite material.
3 is a waveform of a change in an elastic wave signal according to the presence or absence of a damage location in the composite material.
4 is an example of a measurement signal that is measured by combining a plurality of signals according to characteristics of an input signal and an acoustic wave.
5 is a schematic diagram of a method of removing noise by estimating the energy level of a noise signal from a conventional measurement signal.
6 is a schematic diagram of the excitation unit and sensors installed in the composite material.
7 is a schematic diagram of a method of estimating the magnitude of a noise signal in step b) of a method for detecting damage using signal energy of an acoustic wave according to an embodiment of the present invention.
8 is a schematic diagram of separating a first signal in step c) of a method for detecting damage using signal energy of an acoustic wave according to an embodiment of the present invention.
9 is a waveform of a difference signal before and after damage used in a damage detection method using signal energy of an acoustic wave according to an embodiment of the present invention.
10 is an enlarged waveform of a difference signal before and after damage and a waveform of a split signal.

Hereinafter, a preferred embodiment of a damage detection method using signal energy of an acoustic wave according to the present invention will be described in detail with reference to the accompanying drawings.

A method of detecting damage using signal energy of an elastic wave according to an embodiment of the present invention may include steps a), b), c), d) and e) sequentially performed.

First, as described in the background art, the damage detection method using the signal energy of an elastic wave according to an embodiment of the present invention was devised to determine the location of the damaged part when a part of the composite material is damaged. And sensors are available. The excitation unit installed in the composite material can generate an elastic wave having a specific center frequency to propagate along the composite material, and the elastic wave generated by the excitation unit is in the form of a burst wave having a period of n as described in the background art.

6 schematically shows the excitation part 200 and sensors installed in the composite material 100.

As shown in FIG. 6, in order to apply a damage detection method using signal energy of an elastic wave according to an embodiment of the present invention, an excitation unit 200 and a plurality of sensors are installed in one composite material 100. In more detail, as shown in FIG. 6, a first sensor 310, a second sensor 320, and a third sensor 330 are installed on the surface of the composite material 100, which are signals from at least three sensors. This is because it is possible to grasp the exact position of the damaged part only by measuring the value, which will be described later.

Step a) generates an input signal that is an elastic wave in the excitation unit 200 installed in the composite material 100, so that the input signal propagates along the composite material 100. The input signal propagated from the composite material 100 may be integratedly transmitted to each of the sensors as shown in FIG. 6 or may be transmitted to each of the sensors through the damaged portion 110 of the composite material 100, and the sensor is You can measure the signal transmitted through the composite.

Step b) calculates a correction signal from which the noise signal is removed from the measurement signal measured by each of the sensors. More specifically, the input signal generated by the excitation unit 200 may change in amplitude or frequency while traveling along the composite material 100, and a white-noise signal due to disturbance may be included. When a noise signal is included in the input signal, the variance of the measurement signal due to the exact original input signal is increased, which may be a factor in which the location of the damaged part 110 cannot be accurately identified. It is important to eliminate.

In step b) of this embodiment, in order to solve the technical problem as described above, after estimating the magnitude of the noise signal using the input signal, the noise signal is removed from the measurement signal, and step b-1), b-2) It may include steps and b-3).

은 잡음이 없는 탄성파의 성분

와 잡음성분

의 구성으로 표현할 수 있으며, 이는 아래와 수식 2와 같다.The measurement signal measured by the sensor

Is the component of the acoustic wave without noise

And noise component

It can be expressed as the composition of, which is shown in Equation 2 below.

[Equation 2]

Equation 2 can be expressed as a Short Time Fourier Transform (STFT) as shown in Equation 3 below.

[Equation 3]

In addition, the above equation can be expressed by the following equation 4 in a discrete form.

[Equation 4]

In this embodiment, the Hann window function was used as the window function when STFT the signal.

Step b-1) uses Equation 5 below to estimate the size of the noise signal included in the measured signal measured by the sensor.

[Equation 5]

는 추정된 상기 잡음신호의 크기,

는 상기 측정신호의 에너지 크기,

는 상기 입력신호의 에너지 크기)(

Is the estimated size of the noise signal,

Is the energy level of the measurement signal,

Is the energy level of the input signal)

을 수식 4를 이용해 STFT해서 주파수 영역에서의 신호인

을 구하고, 가진부(100)에서 버스트 웨이브 형태의 탄성파로 생성되는 입력신호인

을 마찬가지로 STFT하여

을 구한다. 수식 5에서 사용되는 p값과

값은 복합재의 재질에 따라 달리 결정되는 값이다.Including the above formula, in other formulas hereinafter, uppercase letters refer to signals in the frequency domain, and lowercase letters refer to signals in the time domain. That is, this embodiment is a measurement signal in the time domain measured by the sensor to use Equation 5

STFT using Equation 4 to get the signal in the frequency domain

Is obtained, and the input signal generated as a burst wave type elastic wave in the excitation unit 100

Likewise by STFT

Find The p-value used in Equation 5 and

The value is determined differently depending on the material of the composite material.

의 길이와 측정신호인

의 길이는 서로 다르므로, 수식 4의 STFT와 수식 5를 이용하여 입력신호와 측정신호 각각의 에너지를 계산하였으며, STFT의 창함수의 크기는 입력신호의 크기와 동일하게 설정하였다. 여기서 STFT의 창함수의 크기를 입력신호의 크기와 동일하게 설정한다는 뜻은, 시간영역에서의 신호의 길이를 동일하게 한다는 의미이다. 상기한 수식 4 및 수식 5를 이용하여 잡음신호의 에너지 크기를 추정하는 과정은 도 7에 개략적으로 도시되어 있다.In this process, the input signal

Length and measurement signal

Since the lengths of are different, energy of each input signal and measurement signal was calculated using the STFT of Equation 4 and Equation 5, and the size of the window function of the STFT was set equal to the size of the input signal. Here, setting the size of the window function of the STFT equal to the size of the input signal means that the length of the signal in the time domain is the same. A process of estimating the energy level of a noise signal using Equations 4 and 5 is schematically illustrated in FIG. 7.

Step b-2) is performed after step b-1), and the correction signal in the time domain is calculated using Equation 6 below.

[Equation 6]

는 주파수 영역에서의 상기 보정신호,

는 상기

을 inverse STFT한 시간영역에서의 보정신호)(

Is the correction signal in the frequency domain,

Is reminded

Correction signal in time domain inverse STFT)

에 포함된 보정신호의 비율이 기준치 이상일 경우, b-1) 단계와 b-2) 단계를 반복 수행하는 단계이다. 즉, b-1) 단계와 b-2) 단계가 한 번 수행되었을 때 계산되는

로 수식 5의

을 대체한 후,

에 포함되는 잡음신호의 크기가 기준치 이상일 경우, b-1) 단계 및 b-2) 단계를 반복 수행할 수 있으며, b-2) 단계가 반복 수행될 때, 수식 6에서

는

로 대체될 수 있다.Step b-3) is obtained through the above steps b-1) and b-2).

If the ratio of the correction signal included in is greater than or equal to the reference value, steps b-1) and b-2) are repeatedly performed. That is, when steps b-1) and b-2) are performed once,

As of Formula 5

After replacing

If the size of the noise signal included in is greater than or equal to the reference value, steps b-1) and b-2) may be repeatedly performed, and when step b-2) is repeatedly performed, in Equation 6

Is

Can be replaced with

Step c) separates the signals included in the correction signal, and among the signals included in the correction signal, the first signal that arrives first from the excitation unit to the sensor is determined, and in step d), the excitation unit 100 ) And the distance between the sensors, and the time until the first signal of the correction signal arrives after the input signal is generated by the excitation unit 100, and calculates the speed of the input signal, step e) is the correction signal The difference signal before and after damage is calculated using the signal when there is no damage to the composite material, and the damage location of the composite material is determined using the time the difference signal before and after damage arrives and the speed of the input signal calculated in step d). Estimate. The schematic operations of steps c) and e) described above are the same as those described in the background art, and a detailed description will be given of the process of separating signals in steps c) and d).

Step c) may include step c-1) for the above-described operation.

In step c-1), among the signals included in the correction signal, a signal whose energy is most similar to an input signal is separated using Equation 7 below, and the separated signal is determined as a first signal.

[Equation 7]

는 시간영역에서의 보정신호를 STFT한 신호)(r(t) is the signal that has the most similar energy to the input signal among the signals included in the correction signal,

Is the signal obtained by STFT of the correction signal in the time domain)

값은 복합재의 재질에 따라 달리 결정되는 값이다.The reason for determining the first signal having the most similar energy level with the input signal in Equation 7 above is that in the case of the first signal that first reaches the sensor from the excitation unit 100, a different path (excitation unit-sensor-sensor or This is because the attenuation of the amplitude occurs less than the signals reached by the excitation part-damaged part-sensor). r(t) is a signal in the time domain in which R is inverse STFT, and it is described as Inverse FFT in Equation 7, but it has the same meaning as the inverse STFT, and the p value used in Equation 7 and

The value is determined differently depending on the material of the composite material.

FIG. 8 schematically shows the input signal generated by the excitation unit 100 and the measurement signal measured by the sensor, and shows the separation of the first signal from the measurement signal.

로 하여 수식 7을 적용할 수 있다.As shown in FIG. 8, the measurement signal measured by the sensor includes a signal having the same waveform as the input signal at the time when the excitation unit 100 generates the input signal. This is a noise component generated by an electromagnetic interference (EMI, Electro Magnetic Interference). In step c-1), before applying Equation 7 above, the signal minus the input signal from the correction signal is

Equation 7 can be applied by

As shown in FIG. 8, after the excitation unit 100 excites the input signal, the first signal S1 is first measured by the sensor after a predetermined time has passed, and the step d) is the first signal S1. The speed at which the input signal is transmitted is calculated through the time until is measured and the distance between the excitation unit 100 and a specific sensor known in advance.

9 shows the difference between each signal and the signal measured by the sensor having different conditions different from only the presence or absence of a damaged part. More specifically, FIG. 9A is a measurement signal measured by the sensor when there is no damaged part in the composite material, FIG. 9B is a signal measured by the same sensor when there is a damaged part in the composite material, and FIG. 9C is shown in FIGS. 9A and 9B. It shows the difference of the illustrated signal, that is, the difference signal before and after damage.

Since the signal shown in FIG. 9c is a signal that has been transformed by the presence of a damaged part in the composite material, it can be seen that the input signal is a signal that has moved to the sensor through the excitation part 100 and the damaged part, so that the signal shown in FIG. Using one hour, the distance between the excitation unit 100-the damaged part-the sensor can be known.

10 is an enlarged view of the difference signal before and after damage shown in FIG. 9C, and then the difference signal before and after damage is divided into a plurality of signals.

As shown in FIG. 10, the difference signal before and after damage is a signal in the form of a combination of a plurality of signals, because the damaged part 110 is formed over a certain area, not a point. Therefore, using the time when each of the plurality of signals separated in FIG. 10 arrives and the speed of the input signal obtained in step d), as shown in FIG. 10, the area around the excitation unit 100-damaged part 110 It is possible to obtain the distance between the partial position-sensor, and to estimate the area of the damaged part 110 by drawing an ellipse centered on the excitation part 100 and the sensor.

The method of estimating the location of the damaged part using the excitation part and multiple sensors in step e) is the excitation part-damage estimated by each of the excitation part-first sensor, the excitation part-second sensor, and the excitation part-third sensor. By using the distance of the part-sensor, an ellipse centered on the excitation part and the sensor is drawn, and a part where the three ellipses overlap is estimated as a damaged part, which is the same as the conventional method described in the background art.

The technical idea should not be interpreted as limited to the above-described embodiments of the present invention. As well as a variety of application ranges, various modifications may be made at the level of those skilled in the art without departing from the gist of the present invention claimed in the claims. Therefore, these improvements and changes will fall within the scope of protection of the present invention as long as it is apparent to those skilled in the art.

S1: first signal
S2: second signal
10: actuator
11: sensor
12: Damage location
100: composite
110: damaged part
200: excitation part
310: first sensor
320: second sensor
330: third sensor

Claims (10)

a) generating an input signal that is an elastic wave from an excitation part installed in the composite material to propagate along the composite material, and measuring a signal propagating along the composite material by a sensor installed in the composite material;
b) estimating a magnitude of a noise signal using the input signal from the measurement signal measured by the sensor, and then calculating a correction signal from which the noise signal is removed from the measurement signal;
c) separating signals included in the correction signal, and determining a first signal that arrives first from the excitation unit to the sensor from among signals included in the correction signal;
d) calculating the speed of the input signal using the distance between the excitation unit and the sensor and the time until the first signal arrives; And
e) The difference signal before and after damage is calculated using the correction signal and the signal when the composite material is not damaged, and the difference signal before and after damage arrives and the speed of the input signal calculated in step d) Estimating the damage location of the composite material;
Damage detection method using the signal energy of the acoustic wave comprising a.
The method of claim 1,
Step b),
b-1) estimating the magnitude of the noise signal using Equation 5 below;
Damage detection method using the signal energy of the acoustic wave comprising a.
[Equation 5]

(

Is the estimated size of the noise signal,

Is the energy level of the measurement signal,

Is the energy level of the input signal)
The method of claim 2,
Step b),
b-2) performing the step b-1) and calculating the correction signal in the time domain using Equation 6 below;
Damage detection method using the signal energy of the acoustic wave, characterized in that it further comprises.
[Equation 6]

(remind

Is a signal obtained by short-time fourier transform (STFT) of the measurement signal,

Is the correction signal in the frequency domain,

Is reminded

Correction signal in time domain inverse STFT)
The method of claim 3,
Step b),
b-3) is performed after step b-2), and in Equation 5

Obtained through Equation 6 above

In the case where the size of the noise signal included in the correction signal is estimated and the size of the noise signal included in the correction signal is greater than or equal to the reference value,

Remind

Generating a correction signal having a reduced noise signal by replacing it with
Damage detection method using the signal energy of the acoustic wave, characterized in that it further comprises.
The method of claim 4,
Step b-3) is a damage detection method using signal energy of an acoustic wave, characterized in that it is repeatedly performed until the magnitude of the noise signal included in the generated correction signal becomes less than a reference value.
The method of claim 1,
Step c)
c-1) separating a signal having the largest energy among signals included in the correction signal using Equation 7 below, and determining the separated signal as the first signal;
Damage detection method using the signal energy of the acoustic wave comprising a.
[Equation 7]

(r(t) is the signal with the largest energy among the signals included in the correction signal,

Is the signal obtained by STFT of the correction signal in the time domain,

Is the input signal)
The method of claim 1,
In the step e), one of the signals included in the difference signal before and after the damage is separated using Equation 7 below, and the composite material is performed using the time the separated signal arrives and the speed of the input signal calculated in step d). Damage detection method using the signal energy of the acoustic wave, characterized in that estimating the damage location of.
[Equation 7]

(r(t) is the signal with the largest energy among the signals included in the difference signal before and after damage,

Is a signal obtained by STFT of the difference signal before and after damage in the time domain,

Is the input signal)
The method of claim 7,
Step e) is repeatedly performed to separate a predetermined number of signals included in the difference signal before and after damage,
When step e) is repeatedly performed, in Equation 7

The signal was previously performed in step e).

A damage detection method using signal energy of an acoustic wave, characterized in that the signal is a signal obtained by subtracting the signal separated in step e) previously performed from the signal.
The method of claim 8,
The step e) is repeatedly performed to separate a predetermined number of signals included in the difference signal before and after the damage, and estimate the area of the damage location.
The method of claim 1,
Damage detection method using signal energy of an acoustic wave, characterized in that a plurality of sensors installed in the composite material.

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