ULTRASONIC NON-DESTRUCTIVE TESTING

• US 20110016976A1
• Filed: 09/27/2010
• Published: 01/27/2011
• Est. Priority Date: 11/04/2005
• Status: Abandoned Application

• Current Assignee: Imperial Innovations Limited (Imperial College London)
• Original Assignee: Imperial Innovations Limited (Imperial College London)
• Inventors: Cawley, Peter, Cegla, Frederick Bert
• Application Number:
  US12/891,231
• Publication Number:
  US 20110016976A1
• Time in Patent Office: Days
• US Class Current: 73/596
• CPC Class Codes: G01N 2291/0234 Metals, e.g. steel
• CPC Class Codes: G01N 2291/02854 Length, thickness
• CPC Class Codes: G01N 2291/0421 Longitudinal waves
• CPC Class Codes: G01N 2291/0422 Shear waves, transverse waves, horizontally polarised waves
• CPC Class Codes: G01N 2291/044 Internal reflections (echoes), e.g. on walls or defects
• CPC Class Codes: G01N 29/069 Defect imaging, localisation and sizing using, e.g. time of flight diffraction [TOFD], synthetic aperture focusing technique [SAFT], Amplituden-Laufzeit-Ortskurven [ALOK] technique
• CPC Class Codes: G01N 29/2412 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 Class Codes: G01N 29/28 providing acoustic coupling , e.g. water impedance matching G10K11/02
• CPC Class Codes: G01N 29/34 Generating the ultrasonic, sonic or infrasonic waves , e.g. electronic circuits specially adapted therefor
• CPC Class Codes: G10K 11/24 for conducting sound through solid bodies, e.g. wires

Abstract

An apparatus and method for ultrasonic non-destructive testing provides an elongate strip of ultrasound transmissive material coupled at a proximal end to an object under test. The elongate strip has a transverse cross-section with a width and thickness giving an aspect ratio greater than unity and matched to the ultrasonic transducer such that excitation induces a substantially non-dispersive ultrasonic signal to propagate along the elongate strip to the proximal end and to enter the object under test. These non-dispersive pulses are particularly suited for time-of-flight measurements, thickness measurements, crack measurements and the like. The elongate strip helps to separate the transducer from a potentially hostile environment associated with the object under test. The elongate strip also has a large area of contact with the object under test allowing efficient transmission of energy into the object under test.

Claims

1. A method of ultrasonic testing of an object under test, said method comprising:

coupling a proximal end of an elongate strip to an object under test;

exciting substantially non-dispersive ultrasonic signals within said elongate strip to propagate along said elongate strip and to enter said object under test.

2. The method of claim 1, wherein said elongate strip is formed of a material having a shear velocity of C₅ and a shear wavelength λ

_B, where λ

_B=C₅/F and F is the frequency corresponding to λ

_B, and said substantially non-dispersive ultrasonic pulses are formed of components of different frequencies and having shear wavelengths extend from λ

_short to λ

_long.

3. The method of claim 2 wherein said elongate strip has a transverse cross-section with a thickness less than 2.5 λ

_short.

4. The method of claim 2, wherein said elongate strip has a transverse cross-section with a thickness less than λ

_short.

5. The method of claim 2, wherein said elongate strip has a transverse cross-section with a width great than 3.5 λ

_long.

6. The method of claim 2, wherein said elongate strip has a transverse cross-section with a width great than 5 λ

_long.

7. The method of claim 2, wherein said elongate strip has a transverse cross-section with a thickness less than λ

_long.

8. The method of claim 1, where said substantially non-dispersive ultrasonic signals comprises lowest order shear mode vibrations with a polarisation perpendicular to propagation direction and parallel to a width of said elongate strip.

9. The method of claim 1, wherein said elongate strip is formed of a material having a bar velocity C_bar and a wavelength λ

_bar, where λ

_bar=C_bar/F and F is the frequency corresponding to λ

_bar, and said substantially non-dispersive ultrasonic signals are formed of components of different frequencies and having bar wavelengths extending from λ

_short=to λ

_long.

10. The method of claim 9, wherein said thickness is less than 2.5 λ

_short.

11. The method of claim 9, wherein said thickness is less than λ

_short.

12. The method of claim 9, wherein said width is great than 5 λ

_long.

13. The method of claim 9, wherein said width is greater than 5 λ

_long.

14. The method of claim 9, wherein said thickness is less than λ

_long.

15. The method of claim 9, wherein said substantially non-dispersive ultrasonic signals comprise lowest order compression mode vibrations with polarisation parallel to the propagation direction.

16. The method of claim 1, wherein substantially only a single mode of propagated guided wave is excited in said elongate waveguide.

17. The method of claim 1, wherein said ultrasonic non-destructive testing is thickness measurement.

18. The method of claim 1, wherein said ultrasonic non-destructive testing is crack monitoring.

19. The method of claim 1, wherein said object under test is:

(i) at a temperature great than 200°

C.; and

(ii) subject to the above background levels ionising radiation.