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ULTRASOUND INSTITUTE
The Ultrasound Institute can develop new advanced ultrasonic measurement, imaging and NDT techniques for non-conventional applications.
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Technical Discussions
prasoon
Other, QUALITY CONTROL ENGINEER
U.P.STEELS, India, Joined Mar 2012, 7

prasoon

Other, QUALITY CONTROL ENGINEER
U.P.STEELS,
India,
Joined Mar 2012
7
19:42 Aug-23-2013
Significance of appearing an echo between first and second back walls.


Dear all

sometimes i found while performing ultrasonic testing on castings that an echo appears between first and second back wall but it dosnt appear before first backwall. what the reason behind?

    
 
 Reply 
 
andrew cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

andrew cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
19:57 Aug-23-2013
Re: Significance of appearing an echo between first and second back walls.
In Reply to prasoon at 19:42 Aug-23-2013 (Opening).

They are shear wave reflections

    
 
 Reply 
 
Gerald R. Reams
Engineering,
Industry, USA, Joined Aug 2012, 180

Gerald R. Reams

Engineering,
Industry,
USA,
Joined Aug 2012
180
20:11 Aug-23-2013
Re: Significance of appearing an echo between first and second back walls.
In Reply to andrew cunningham at 19:57 Aug-23-2013 .

Mode conversion. Shear wave velocity ~1/2 the longitudinal wave velocity.

    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1266

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1266
20:14 Aug-23-2013
Re: Significance of appearing an echo between first and second back walls.
In Reply to prasoon at 19:42 Aug-23-2013 (Opening).

Prasoon, Andrew's reply is more than likely the explanation. The formation of the shear mode results due to the diffraction effect at the ends of the transducer where the beam is no longer a plane wavefront. You can see how they form in the article and associated video at http://www.ndt.net/article/ndtnet/2013/9_Ginzel.pdf

    
 
 Reply 
 

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