Method and device for testing defect based on ultrasonic lamb wave tomography

Patent metadata

Field	Value
Publication number	US-10197534-B2
Application number	US-201514948398-A
Country	US
Kind code	B2
Filing date	Nov 23, 2015
Priority date	Nov 24, 2014
Publication date	Feb 5, 2019
Grant date	Feb 5, 2019

Abstract

Disclosed are a method and a device for testing a defect based on an ultrasonic Lamb wave tomography. The method includes: partitioning an imaging area of a material to be tested into grids; exciting electromagnetic acoustic transducers for emitting to emit Lamb waves with a A 0 mode in all directions, and electromagnetic acoustic transducers for receiving to receive the Lamb waves; obtaining a time-frequency analysis result and recording time-of-flights of testing waves; determining a first slowness of each grid to obtain a first defect area; establishing an extrapolation formula according to the first defect area, and iterating the extrapolation formula to trace and revise paths of the Lamb waves until a better imaging precision is obtained.

First claim

What is claimed is:

1. A method for testing a defect based on an ultrasonic Lamb wave tomography, comprising following acts performed by a computer:
S 1 , selecting an imaging area on a material to be tested, and partitioning the imaging area into N 1 ×N 2 grids, wherein M electromagnetic acoustic transducers for emitting are set on a first side of the imaging area, M electromagnetic acoustic transducers for receiving are set respectively opposite to the M electromagnetic acoustic transducers for emitting on a second side of the imaging area, and N 1 , N 2 , M are positive integers;
S 2 , exciting the M electromagnetic acoustic transducers for emitting to emit Lamb waves with a A 0 mode in all directions and the M electromagnetic acoustic transducers for receiving to receive the Lamb waves successively, such that M×M testing waves corresponding to M×M Lamb waves are obtained;
S 3 , performing a time-frequency analysis and a mode recognition on the M×M testing waves, so as to obtain time-of-flights of the M×M Lamb waves;
S 4 , recording the time-of-flights of the M×M Lamb waves;
S 5 , determining a first slowness of each grid according to the time-of-flights and a size of each grid to obtain a first defect area;
S 6 , establishing a three-dimensional Cartesian coordinate system in the imaging area, and defining an original emission angle;
S 7 , for a path of a Lamb wave through the defect, obtaining a phase velocity c p at a point P(x,y) on a forward direction of the Lamb wave through the defect and calculating ∂c p /∂x and ∂c p /∂y according to the phase velocity c p , where x is a coordinate value of the point P(x,y)in a x-direction, y is a coordinate value of the point P(x,y)in a y-direction;
S 8 , calculating an extrapolation point of the Lamb wave through the defect by introducing c p , ∂c p /∂x and ∂c p /∂y into an extrapolation formula;
S 9 , judging whether a coordinate value of the extrapolation point reaches or exceeds boundary coordinates of a corresponding grid, if no, using the extrapolation point of the Lamb wave through the defect as a new point on the forward direction of the Lamb wave through the defect and executing steps S 6 -S 9 , if yes, recording the coordinate value of the extrapolation point as a coordinate value of the end point of the Lamb wave through the defect;
S 10 , judging whether the coordinate value of the end point of the Lamb wave through the defect reaches or is close to the electromagnetic acoustic transducers for receiving, if yes, obtaining a path with a shortest time-of-flight of the Lamb wave through the defect, if no, changing the original emission angle and executing steps S 6 -S 10 until the path with the shortest time-of-flight of the Lamb wave through the first defect area is found;
S 11 , obtaining a second slowness of each grid according to the time-frequency analysis result and the shortest time-of-flight and a change of a slowness curve in the defect to obtain a second defect area and to determine a size and a distribution of the second defect area.

2. The method according to claim 1 , wherein a diameter of the electromagnetic acoustic transducer is within a range of 20 mm to 80 mm, a distance between centers of each two adjacent electromagnetic acoustic transducers at the same side is within a range of 20 mm to 100 mm.

3. The method according to claim 1 , wherein the M electromagnetic acoustic transducers for emitting are excited by a radio frequency power amplifier, in which an excitation frequency of the radio frequency power amplifier is within a range of 50 kHz to 500 kHz.

4. The method according to claim 1 , wherein the Lamb wave emitted by the electromagnetic acoustic transducer for emitting is a Lamb wave with a single A 0 mode.

5. The method according to claim 1 , wherein the first or the second slowness of each grid is determined according to formula (1):

T
i

=

∑

j
=
1

n

⁢

L
ij

*

S
j

,

⁢

(

i
=
1

,
2
,
…
⁢

,
m

)

,

(
1
)

where S j is a slowness of a j th grid, L ij is a length of a i th Lamb wave in the j th grid, T i is a time-of-flight of the i th Lamb wave, n =N 1 ×N 2 , and m =M×M .

6. The method according to claim 1 , wherein the original emission angle is within a range of 0˜180°.

7. The method according to claim 1 , wherein obtaining a phase velocity c p at a point P(x,y) on a forward direction of the Lamb wave through the defect and calculating ∂c p /∂x and ∂c p /∂y according to the phase velocity c p comprises:
obtaining 16 pixels with the extradition point used as a center;
obtaining 16 phase velocities corresponding to the 16 pixels;
introducing the 16 phase velocities respectively into a formula (2) to perform a two-dimensional surface fitting on a distribution of the phase velocities:

c
p

⁡

(

x
p

,

y
p

)

=

∑

k
=
0

3

⁢

∑

Assignees

• Univ Tsinghua

Inventors

• Huang Songling
• Wang Shen
• Zhao Wei
• Li Shisong
• Wei Zheng

Classifications

• G01N29/2412

  using the magnetostrictive properties of the material to be examined, e.g. electromagnetic acoustic transducers [EMAT]; (investigating the presence of flaws using eddy currents G01N27/90, magnetostrictive transducers B06B1/08, measuring magnetostrictive properties G01R33/18) · CPC title

• G01N2291/0427

  Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever · CPC title

• G01N29/069 Primary

  Defect imaging, localisation and sizing using, e.g. time of flight diffraction [TOFD], synthetic aperture focusing technique [SAFT], Amplituden-Laufzeit-Ortskurven [ALOK] technique · CPC title

• G01N29/0672

  by acoustic tomography (medical tomography A61B8/13) · CPC title

• G01N29/07

  by measuring propagation velocity or propagation time of acoustic waves · CPC title