KR20190037912A - Method of Non-destructive Test - Google Patents

Abstract

According to the present invention, a non-destructive test method comprises: a step of measuring a response signal by sensors on a plurality of positions after transmitting an input signal on a plurality of positions, calculating a damage signal by removing a reference signal from the response signal, and then calculating a propagation speed in a 360^o propagation direction of an elastic wave from the response signal; a step of calculating time taken to allow the elastic wave to propagate from each actuator to damage from the damage signal; a step of using the calculated propagation speed in the 360^o propagation direction of the elastic wave and the time taken to allow the elastic wave to propagate from each actuator to the damage to calculate a distance from each actuator to the damage; and a step of applying an imaging technique to the previously calculated distance from each actuator to the damage to visualize the position of the damage to detect the damage. According to the present invention, a plurality of sets of actuators and sensors installed on a flat structure made of an anisotropic material by a PC-method are used to visualize the position of the damage to easily detect the damage by a calculation method of the propagation speed in the 360^o propagation direction of the elastic wave from measured elastic waves (Lamb waves), a method of calculating the distance from an arbitrary actuator to the damage, and an imaging technique.

Description

{Method of Non-destructive Test}

   The present invention relates to a nondestructive inspection method, and more particularly, to a method of non-destructive inspection, in which damage to an anisotropic plate structure such as a composite material plate is detected by a pitch-catch (PC) The present invention relates to a method for detecting a position of a damage through an imaging technique after calculating a distance from an actuator having an acoustic wave to a damaged area.

In general, non-destructive inspection, which detects damage to a structure by using elastic waves propagating in a structure, is a very important technique for maintenance of a more systematic structure. The history of these nondestructive tests is now quite old and the kinds of technologies are also diverse. Lamb wave is an elastic wave generated in a thin structure like a flat plate, and it is widely used for non-destructive inspection technique because it is advantageous to search a wider area of a structure quickly because the propagation distance is considerably large [1, 2 ]. The present invention is one of the methods using Lamb waves.

The pitch-catch (PC) method is widely used as a non-destructive inspection method using acoustic waves [4, 5]. In the PC-method, when an acoustic wave is generated by using an actuator placed at a position of a flat plate, an excited acoustic wave propagates and spreads inside the flat plate, and at this time, a seismic wave propagated through a sensor . An acoustic wave signal measured using several sets of actuators and sensors before damage occurs is commonly referred to as the baseline data or baseline signal.

After the damage, the seismic signals measured through the same set of actuators and sensors will be different from the reference signal due to the direct or indirect effect of the damage. This difference from this reference signal caused by damage is often referred to as a damage signal.

Most non-destructive testing is to detect damage caused by this damage signal and is generally referred to as non-destructive testing using reference data. The present invention is one of nondestructive inspection methods utilizing reference data.

As mentioned above, by analyzing the damage signal measured by using a plurality of sets of actuators and sensors, it is possible to calculate the time required for the elastic waves starting from any actuator to reach the arbitrary sensor through damage.

In the case of a flat plate structure made of an isotropic material such as most metal materials, the propagation velocity of the acoustic wave is almost the same regardless of the propagation direction. Therefore, applying a uniform elastic wave propagation velocity at the time of the damage signal measured by using a plurality of sets of actuators and sensors, it is possible to calculate the distance from each actuator to the damage, and if applied to a well known imaging technique, Can be graphically displayed and can be detected.

However, in the case of a plate structure made of an anisotropic material such as a composite material plate, the propagation velocity of the acoustic wave may be different depending on the propagation direction, so that damage detection is not as easy as in the case of the above-described isotropic material. Accordingly, the present invention relates to nondestructive inspection applicable to flat plate structures made of anisotropic materials such as composite plate.

SUMMARY OF THE INVENTION The present invention has been conceived in view of the above-described problems, and it is an object of the present invention to provide a method and apparatus for measuring elasticity of a seismic wave from an elastic wave (lamb wave) signals measured using a plurality of sets of actuators and sensors installed on a flat plate structure made of an anisotropic material according to the PC- ^{o A} method for calculating the propagation velocity along the propagation direction and a method for calculating the distance from an arbitrary actuator to the damage are proposed and a nondestructive inspection technique for detecting and detecting the position of the damage through the imaging technique is provided.

According to an aspect of the present invention, there is provided an apparatus for measuring an impulse response of an input signal, the method comprising: transmitting an input signal through an actuator at a plurality of positions, measuring a response signal through a sensor at a plurality of positions, Calculating a propagation velocity along the 360 ^o propagation direction of the elastic wave from the response signal;

Calculating a time required for the elastic wave to propagate from each actuator to the damage from the damage signal;

Calculating a distance from each actuator to a damage using the propagation velocity of the elastic wave in the 360 ^o propagation direction and the time taken to propagate from each actuator to the damage;

And detecting damage by visualizing the position of the damage by applying an imaging technique to the distance from each actuator to the damage calculated in the previous step.

The piezoelectric transducer (PZT) can be used as an actuator for transmitting an input signal to an ultrasonic wave and as a sensor for measuring an acoustic-wave response signal.

According to the invention, the propagation velocity in accordance with according to the method PC- from the actuator and the acoustic wave sensor (Lamb wave) signal measured using a plurality of set is installed on a flat structure made of an anisotropic material in the direction of propagation of the acoustic wave 360 ^o The location of the damage can be easily visualized by the calculation method and the method of calculating the distance from the arbitrary actuator to the damage and the imaging method.

1 is a diagram of a test apparatus for a nondestructive inspection according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a response signal measured in a j-th PZT after an input signal is applied to an i-th PZT using a PC-method according to an embodiment of the present invention.
3 is a distribution diagram of Lamb wave propagation speeds in all 360 ^o directions calculated using the propagation velocity of Lamb waves traveling between all the PZTs calculated by Equation (1) of the present invention.
FIG. 4 is a diagram illustrating an embodiment of the present invention. Referring to FIG. 4, an input signal is applied to an i-th PZT using a PC method and then an identical input signal is applied to an i-th PZT before a damage occurs in a response signal measured at a j- And the damage signal caused by the purely remnant remaining when the response signal measured at the j-th PZT is removed.
FIG. 5 is a distribution diagram of 360 ^° directions of d _1D , d _2D , d _3D , and d _4D , which are linear distances up to the damage calculated based on each PZT in FIG. 1, which is handled as one embodiment of the present invention.
FIG. 6 is a diagram illustrating a position where damage occurs when all of the distribution curve curves coincide when the PZTs are superimposed on each other in the present invention.
7
8
FIG. 9 is an image derived by applying Equation (7) to PZT1, PZT2, PZT3, and PZT4 of FIG. 1, which is an embodiment of the present invention, in which damage is located at positions where four closed curves overlap in common .
10 and 11 are views showing another embodiment to which the nondestructive inspection method according to the present invention is applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a bar fracture inspection method according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram of a test apparatus for a nondestructive inspection according to an embodiment of the present invention. That is, it is a test apparatus for detecting damages occurring in a flat plate structure by attaching four PZTs on a flat plate structure made of a composite material and using the same as an actuator and a sensor.

Although only four PZTs are shown on Fig. 1, there are no particular restrictions on the number and location of PZTs used as actuators and sensors. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely examples for illustrating the working principle of the present invention, and not all of the technical ideas of the present invention are described. Therefore, It should be understood that there are many variations that can be substituted.

In Figure 1, the mounting position of each PZT (x _i, y _i) (where, i = 1, 2, 3 , 4); Let d _{ij be} the linear distance between each PZT, where i = 1, 2, 3, 4; The linear distance from each PZT to the damage is d _iD (where i = 1, 2, 3, 4); Let τ _ij (where i, j = 1, 2, 3, 4) is the time it took for the acoustic wave (lamb wave) to propagate the linear distance between each PZT; The time required for the elastic wave (lamb wave) to propagate the linear distance from each PZT to the damage is described as t _ij (where i, j = 1, 2, 3, 4).

FIG. 2 shows a response signal measured in the j-th PZT after applying the input signal to the i-th PZT using the PC-method as an embodiment. The input signal is generally available if it is a narrow band signal including a tone-burst signal.

Two or more lamb wave components are applied to the response signal according to the center frequency of the input signal and the frequency band of the spectrum. The center frequency of the input signal is set so that the response signal component is limited to two components of the Lamb wave, The center frequency is tuned so that the size of the A component becomes much larger than the size of the S component so that the S component can be ignored.

2 shows the time required to propagate the linear distance from the i-th PZT to the j-th PZT and the first time measured by the j-th PZT based on the time point when the input signal is applied to the i-th PZT τ _ij .

The straight line distance d _ij from the i-th PZT to the j-th PZT is already known. Therefore, the propagation velocity (v _ij ) propagating in the direction of the linear path connecting the i-th PZT and the j-th PZT is calculated by Equation (1).

[Equation 1]

3 is a distribution diagram of Lamb wave propagation speeds in all 360 ^o directions calculated using the Lamb wave propagation velocity of the PZT calculated by Equation (1). In order to calculate the propagation velocity for all 360 ^o directions using the Lamb wave propagation velocity calculated from Equation 1 with respect to the direction of a limited number of linear paths connecting PZT and PZT attached to the plate structure, Can be applied.

FIG. 4 illustrates an example of a method of applying an input signal to an i-th PZT using a PC-method and then applying the same input signal to an i-th PZT before a damage occurs in a response signal measured at a j- PZT is the damage signal caused purely by the damage that is left when the response signal is removed.

The time T _{ij shown} in FIG. 4 indicates that the ramp A component propagated in the direction of damage among the elastic waves generated by the input signal applied to the i-th PZT reaches damage and then is immediately reflected by the damage and arrives at the j-th PZT It represents the total time spent. The time required for the ramp A component to start from the i-th PZT to reach the damage is t _iD , and the time required for the _ramp A component to reach the j-th PZT after reflection from the damage is t _jD , do.

&Quot; (2) "

Considering FIG. 1 as an embodiment, three sets of all PZTs attached to a flat plate structure are alternately selected as one set, and the results of the measurement as shown in FIG. 4 are obtained according to the PC-method, Is applied to Equation (2), the following equation is derived.

For the [PZT1, PZT2, PZT3] sets,

(3a)

[PZT2, PZT3, PZT4] For the set

(3b)

[PZT3, PZT4, PZT1] For the set

&Quot; (3c) "

For [PZT4, PZT1, PZT2] sets

[Mathematical expression 3d]

In the above Equations 3a to 3d, the determinant [A] is defined by Equation (4).

&Quot; (4) "

를 구하고, Solve Equation 3a

Is obtained,

를 구하고, Solve Equation 3b

Is obtained,

를 구하고, Solve Equation 3c

Is obtained,

를 구한다.Solve Equation 3d

.

, 수학식 3c를 풀어 구한

, 수학식 3d를 풀어 구한

가 서로 일치하지 않을 수 있기 때문에 이들의 평균값을 t_1D로 사용하고, t_{2D ,} t_{3D ,} t_4D도 동일한 방식으로 수학식 5로부터 산출한다.Calculated by solving equation (3a)

, And the equation (3c)

, And the equation (3) is solved.

end The average values of these are used as t _1D , and t _{2D ,} t _{3D , and} t _4D are calculated from the equation (5) in the same manner.

&Quot; (5) "

Equation (5) represents the non-time required to propagate the linear distance from the PZT to the damage in the Lamb wave in FIG. 1, which is taken as an embodiment.

Figure 3 when Lamb waves A component in the anisotropic plate structures 360 ^o multiplied by the ratio of time given by the equation (5) on it represents the propagation speed for all the propagation direction, even in 3-propagation-velocity lies is damaged around the respective PZT It is possible to calculate a possible distance (position).

The closed curve of FIG. 5 is a distribution diagram of 360 ^° directions of the straight line distances d _1D , d _2D , d _3D , and d _4D to the damage calculated based on each PZT in FIG. 1 handled as an embodiment.

As shown in FIG. 6, the distribution curve for d _1D , d _2D , d _3D , and d _4D shown in FIG. 5 is centered on each PZT.

Figure 360 with a focus on the respective PZT shown in one embodiment in the 5 ^o can be implemented through the method image the position detection of the damage seen in the PZT in all directions in Fig. 6 by using the straight line distance distribution to the damaged.

For the implementation of the imaging method, the anisotropic plate structure is subdivided into fine pixels. When the position of the i-th PZT is (x _i , y _i ) and the position of an arbitrary pixel is (x, y), a position angle q can be obtained from the equation (6).

&Quot; (6) "

As an embodiment, the process of imaging the closed curve of the distribution of d _1D around the i-th PZT will be described. the position angle q of any pixel located at the coordinate (x, y) around the i-th PZT is calculated from Equation (6).

에 해당하는 d _1D의 좌표 값 (x _1D(q), y _{1 D} (q)) 값을 산출한다.5,

The coordinate values of the d _1D to _{(x 1D (q), y} 1 D (q)) values to be calculated.

From this, the image value I (x, y) is determined by equation (7). Imaging a pixel (x, y) satisfying the image value I (x, y) = 0 provides a distribution closed curve as shown in FIG. 5, and FIG. The image value of Equation (7) can be replaced by another form of equation.

&Quot; (7) "

FIG. 9 is an image derived by applying Equation (7) to PZT1, PZT2, PZT3, and PZT4 of FIG. 1, which is one embodiment of the present invention, and shows that damage is located at positions where four closed curves overlap in common.

   10 and 11 show another embodiment to which the nondestructive inspection method provided by the present invention is applied.

Claims (1)

Through actuator an input signal in a plurality of position measurement of the response signal through the sensor at a plurality of locations after transmission, and then by removing the reference signal from the response signal calculating a damage signal, 360 ^o of the acoustic wave from the response signal propagation direction, Calculating a propagation velocity according to the propagation velocity;
Calculating a time required for the elastic wave to propagate from each actuator to the damage from the damage signal;
Calculating a distance from each actuator to a damage using the propagation velocity of the elastic wave in the 360 ^o propagation direction and the time taken to propagate from each actuator to the damage;
Detecting damage by visualizing the position of the damage by applying an imaging technique to the distance from each actuator to the damage;
And a non-destructive inspection method.

Images