Ultrasonic non-destructive testing

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.

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 C 5  and a shear wavelength λ B , where λ B =C 5 /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.