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2675 views
10:57 Jun-01-2009
Jaeseok Park
Distance Law for Notch Reflection of Ultrasound

What law fits for notches as artificial reflectors (in the far field) when doubling the
notch depth?

 
09:38 Jun-02-2009

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
784
Re: Distance Law for Notch Reflection of Ultrasound In Reply to Jaeseok Park at 10:57 Jun-01-2009 (Opening).

The inverse square law would apply. The effective surface area has to be 4 times if the distance is double. Test it and confirm.

Swamy

 
13:37 Jun-02-2009

Roger Duwe

NDT Inspector, API-510, 570, 653
MISTRAS,
USA,
Joined Jan 2009
148
Re: Distance Law for Notch Reflection of Ultrasound In Reply to S.V.Swamy at 09:38 Jun-02-2009 .

Should actually be worse than inverse square. In addition to the beam spreading loss [inverse square] there will be a linear loss due to sound attenuation by the grain structure of the material [linear per increase in unit length of soundpath, thus depth]

 
18:16 Jun-02-2009

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
174
Re: Distance Law for Notch Reflection of Ultrasound In Reply to Roger Duwe at 13:37 Jun-02-2009 .

There is a discrepancy between the head lines and the original question which is:
What law fits for notches as artificial defects when doubling the notch depth? This means 'area law' not 'distance law'.

The reaction of a notch depends on its size compared to wavelength, on its angle to the surface and on the relative angle between the notch flanks and the incident sound beam and additionally on the length of the notch, whether it is larger than the sound beam or smaller.
The result is very complex; there is no simple rule.

With notches smaller than the wave length the main effect is scattering and the measured echo amplitude increases with a power higher than 3 with increasing depth. At larger notch depth reflection starts and there may be an intervall where there is an increase of amplitude with the power of 2. But with further growing notch depth the signal goes into saturation, i.e. when the notch depth gets larger than the beam and therefore the echo amplitude will not grow further.

But this monotonous growing of amplitude with depth holds only for a beam angle of 45° degrees (perfect retro-reflector).

For higher beam angles there is a zone of interference, i.e. the echo amplitude decreases with increasing notch depth in this area, especially for 60°.

With distance a notch smaller than the sound beam behaves like a limited reflector: then there is an inverse square law. But if the notch length is larger than the sound beam, the notch behaves like a infinite cylinder: the power is (-3/2) not 2 as for finite reflectors.

Hope this clears the question and the previous answers.

 
18:56 Jun-02-2009
Jaseok Park
Re: Distance Law for Notch Reflection of Ultrasound In Reply to Udo Schlengermann at 18:16 Jun-02-2009 .

Thank you very much for your valuable information. I guess you gave me sufficient description about notch reflection, but I'm still hungry. If possible, would you recommend a reference book or paper which describe this problem in detail? Krautkramer's book haven't got any explanation about this.

 
20:29 Jun-02-2009

Roger Duwe

NDT Inspector, API-510, 570, 653
MISTRAS,
USA,
Joined Jan 2009
148
Re: Distance Law for Notch Reflection of Ultrasound In Reply to Jaseok Park at 18:56 Jun-02-2009 .

Excellent reply Herr Schlengermann! I learned something today, making it a GOOD day. Thank you.

 
01:09 Jun-04-2009

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
784
Re: Distance Law for Notch Reflection of Ultrasound In Reply to Roger Duwe at 20:29 Jun-02-2009 .

I fully second you. We always learn good things from him.

 
16:32 Jun-08-2009
Slawomir Mackiewicz
Re: Distance Law for Notch Reflection of Ultrasound In Reply to Udo Schlengermann at 18:16 Jun-02-2009 .

The explanation of “area low” for notches given by Mr. Udo Schlengermann is comprehensive and generally correct but seems to include a false statement concerning the amplitude-notch depth dependence for long wave regime (i.e. for the cases when the notch depth is much smaller than ultrasonic wave length).

For ultrasonic scattering at reflectors longer than the beam width which cross section sizes are much smaller than the wave length the scattered wave amplitude is directly proportional to the cross section area of the scatterer. For cylindrical reflectors it means, for example, that scattered wave amplitude is proportional to the square root of the cylinder diameter.

In the case of surface notches the general shape of this relationship depends not only on the notch height but also on the notch width. If we consider “narrow notches”, similar to the surface fatigue cracks, we can say that scattered wave amplitude is directly proportional to the notch depth (not to the 3 or 2 power of the depth). This linear relationship can be sometimes used for depth measurements of tiny surface cracks.

The problems of ultrasonic waves scattering are rather complicated and are not well treated at standard NDT UT courses. For interested NDT specialists I would recommend a paper by I.N. Jermolov, The Reflection of Ultrasonic Waves from Targets of Simple Geometry., Non-Destr. Test. 5 (1972), 2, p 87-91 which describes the problem in more details.

 
03:49 Jun-09-2009

Jaeseok Park

R & D,
DOOSAN,
South Korea,
Joined Jun 2009
7
Re: Distance Law for Notch Reflection of Ultrasound In Reply to Slawomir Mackiewicz at 16:32 Jun-08-2009 .

Thank you very much for all.

 
06:11 Jun-09-2009

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
784
Re: Distance Law for Notch Reflection of Ultrasound In Reply to Jaeseok Park at 03:49 Jun-09-2009 .

I would suggest that in addition to theoretical modelling, practical experiments should also be carried out and attempts should be made to make the theoretical model come close to the reality.

Best wishes.

Swamy

 
15:26 Aug-18-2009
lobgeois luce
Re: Distance Law for Notch Reflection of Ultrasound In Reply to Slawomir Mackiewicz at 16:32 Jun-08-2009 .

Good Afternoon,
I'm working for EDF (Electricité de France) for Non Destructive Testing Qualification and especially for technical justifications. Nowadays, several models are used to justify the conception of industrial applications.
I try to collect the scattering theory / basic principles (GTD and Kirchhoff) for the following configurations: direct pulse echo, corner effect and TOFD.
Do you know if I could find something about it in the article you mention in your message (reflection of ultrasonic waves from targets of simple geometry)?
If yes, could you send me a copy? If no, do you know where it is possible to find anything understandable, because as you wrotte it isn't well treated in NDT curses.
Regards.

 


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