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3711 views
01:11 Jul-08-2008

john howard

Engineering
United Kingdom,
Joined Jun 2008
2
creeping wave?

Can anyone help? Is there or is there not a 'creeping wave'? Can it be proven either way?


 
03:33 Jul-08-2008

J. Mark Davis

Teacher, And Consultant
University of Ultrasonics, Birmingham, Alabama,
USA,
Joined Mar 2000
83
Re: creeping wave? John,

Yes, there is a Creeping Wave.

The term Creeping Wave is not a new sound source. It is a L-wave energy that skims or creeps along the opposite surface from the scanning surface. The Creeping wave travels a short distance ( about 2 mm to 12 mm) to detect a planar defect at the ID surface. It is

The Creeping Wave is the result of a shearwave which mode converts to an L-wave from the ID surface.

See Dr. Wustenbergs Doctorate 1977 Thesis. There are numerous papers on the wave physics and the resulting effects of these critically refracted L-waves and shear waves.

The main point is that Creeping Waves are very effective for detection, charcaterization and sizing of Cracks.

Sincerely,

J. Mark Davis


----------- Start Original Message -----------
: Can anyone help? Is there or is there not a 'creeping wave'? Can it be proven either way?
------------ End Original Message ------------




 
04:55 Jul-08-2008
Slawomir Mackiewicz
Re: creeping wave? ----------- Start Original Message -----------
: Can anyone help? Is there or is there not a 'creeping wave'? Can it be proven either way?
------------ End Original Message ------------

Creeping wave is not a wave in the same meaning as the “standard” L, T or Rayleigh waves, which are strictly speaking the mathematical solutions of the Wave Equation. It is just a practical term used by UT specialists for description of diffracted part of longitudinal wave beam which travels along the object surface (doesn’t matter external or internal).

The creeping wave is heavily attenuated because it looses its energy by transformation into transversal waves as it travels along the object surface.

The widely known application of creeping wave is TOFD where it is normally the first wave registered by the system.



 
05:39 Jul-08-2008

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1185
Re: creeping wave? Nice try Mark… but giving a “signal” a name does not make it a wave.
Slawomir’s description is most appropriate and very practical.
The so-called creeping wave was mathematically refuted by Langenberg et al.
Your description in http://www.ndt.net/article/1198/davis/davis2.htm uses the term CE-2 to describe what you have just stated to John stresses the events on the far side of a component after the pulse has reached the far side. But your description does not match the echo-dynamics of the signal. The signal you identified as originating from a “creeping wave” is in fact a long-lasting signal (with respect to probe motion) and is accounted for by the shear head-wave and bulk shear wave.

The “practical term” (as described by Slawomir) creeping wave is also called the “lateral wave” in TOFD but there it is the direct compression mode under the near surface. A mode conversion can occur on the far side. The reflecting head-wave and the head-wave formed by the mode converted compression wavereflecting off a notch on the far side of a plate will be difficult to separate.

A more graphic video illustration of the details is available at Bill Blanshan’s website http://www.autsolutions.net/Creeping-waves.html

----------- Start Original Message -----------
: John,
: Yes, there is a Creeping Wave.
: The term Creeping Wave is not a new sound source. It is a L-wave energy that skims or creeps along the opposite surface from the scanning surface. The Creeping wave travels a short distance ( about 2 mm to 12 mm) to detect a planar defect at the ID surface. It is
: The Creeping Wave is the result of a shearwave which mode converts to an L-wave from the ID surface.
: See Dr. Wustenbergs Doctorate 1977 Thesis. There are numerous papers on the wave physics and the resulting effects of these critically refracted L-waves and shear waves.
: The main point is that Creeping Waves are very effective for detection, charcaterization and sizing of Cracks.
: Sincerely,
: J. Mark Davis
:
: : Can anyone help? Is there or is there not a 'creeping wave'? Can it be proven either way?
------------ End Original Message ------------




 
00:13 Jul-08-2008
Bill Blanshan
Re: creeping wave? The technique still works either way you look at it, but with the technology if Ed's Photoelestic Imaging system, we can now see the true origins of the wave modes in high detail, and when I say "high detail”, you can even see and measure the actual pulse "wavelength" which could not be done in the older schlieren films; see http://www.ndt.net/article/v11n05/ginzel1/ginzel1.htm

From my knowledge you could not see the "Head Waves" in the older schlieren films either, which is the key component to how you actually see the CE2 signal.

Please go to my website and see for yourself; the proof is in the pudding. http://www.autsolutions.net/Creeping-waves.html

Mark, would you be able to post on your website some of your Schlieren films which shows a “creeping wave” propagating on the I.D. surface? It would be nice to show the differences between both imaging techniques, pros and cons.


Bill

----------- Start Original Message -----------
: Nice try Mark… but giving a “signal” a name does not make it a wave.
: Slawomir’s description is most appropriate and very practical.
: The so-called creeping wave was mathematically refuted by Langenberg et al.
: Your description in http://www.ndt.net/article/1198/davis/davis2.htm uses the term CE-2 to describe what you have just stated to John stresses the events on the far side of a component after the pulse has reached the far side. But your description does not match the echo-dynamics of the signal. The signal you identified as originating from a “creeping wave” is in fact a long-lasting signal (with respect to probe motion) and is accounted for by the shear head-wave and bulk shear wave.
: The “practical term” (as described by Slawomir) creeping wave is also called the “lateral wave” in TOFD but there it is the direct compression mode under the near surface. A mode conversion can occur on the far side. The reflecting head-wave and the head-wave formed by the mode converted compression wave reflecting off a notch on the far side of a plate will be difficult to separate.
: A more graphic video illustration of the details is available at Bill Blanshan’s website http://www.autsolutions.net/Creeping-waves.html
: : John,
: : Yes, there is a Creeping Wave.
: : The term Creeping Wave is not a new sound source. It is a L-wave energy that skims or creeps along the opposite surface from the scanning surface. The Creeping wave travels a short distance ( about 2 mm to 12 mm) to detect a planar defect at the ID surface. It is
: : The Creeping Wave is the result of a shearwave which mode converts to an L-wave from the ID surface.
: : See Dr. Wustenbergs Doctorate 1977 Thesis. There are numerous papers on the wave physics and the resulting effects of these critically refracted L-waves and shear waves.
: : The main point is that Creeping Waves are very effective for detection, charcaterization and sizing of Cracks.
: : Sincerely,
: : J. Mark Davis
: :
: : : Can anyone help? Is there or is there not a 'creeping wave'? Can it be proven either way?
------------ End Original Message ------------




 
02:27 Jul-09-2008

Andrew Cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
Re: creeping wave? ----------- Start Original Message -----------
: Can anyone help? Is there or is there not a 'creeping wave'? Can it be proven either way?
------------ End Original Message ------------

John

On this subject, I have to agree in part with Ed Ginzel. Not wanting to sound too controversial, I have to say there is no such thing as a ‘creeping wave’. When a shear wave hits the underside interface it will generate a small L wave, but this is not what generates a high amplitude signal (which is so commonly, but wrongly referred to as a ‘creep wave’ signal).
This signal is just acoustics. Quite simply, it is the same phenomenon that occurs when you position stereo speakers at 45 degrees in the corner of a room to amplify the sound that is reflected from the 90 degree angle of the corner.
The reflection will always return as a high amplitude reinforced signal at half the angle of the corner.
For those of you interested, this topic and many others are explained in my book (see www.practical-ndt.com), a practical guide for manual ultrasonics written in a clear, concise way that will help you understand the propagation of sound.

Andrew Cunningham



 
07:33 Jul-09-2008

Hermann Wüstenberg

R & D
BAM Berlin,
Germany,
Joined Nov 1998
26
Re: creeping wave? ----------- Start Original Message -----------
: : Can anyone help? Is there or is there not a 'creeping wave'? Can it be proven either way?
: John
:
: On this subject, I have to agree in part with Ed Ginzel. Not wanting to sound too controversial, I have to say there is no such thing as a �creeping wave�. When a shear wave hits the underside interface it will generate a small L wave, but this is not what generates a high amplitude signal (which is so commonly, but wrongly referred to as a �creep wave� signal).
: This signal is just acoustics. Quite simply, it is the same phenomenon that occurs when you position stereo speakers at 45 degrees in the corner of a room to amplify the sound that is reflected from the 90 degree angle of the corner.
: The reflection will always return as a high amplitude reinforced signal at half the angle of the corner.
: For those of you interested, this topic and many others are explained in my book (see www.practical-ndt.com), a practical guide for manual ultrasonics written in a clear, concise way that will help you understand the propagation of sound.
: Andrew Cunningham
------------ End Original Message ------------

Concerning the debate about the imaging of ultrasonic wave propagation I would like to draw the attention to some works carried out at the BAM in Berlin during the years 2002 to 2006 by Hardy Ernst (H. Ernst, V. K. Munikoti, H. Wüstenberg “Experimentelle Verifizierung von Modellvorstellungen zur Schallausbreitung in anisotropen Materialien” ZfP-Zeitung 92, 2004, p 36 – 40) going back to publications of B. Köhler, F. Schubert und Schurig (Dresden 1996), where the lateral surface of a specimen is used to scan the soundfield and to produce video records of the wave propagation. The same approach has also been applied to produce video films demonstrating the ultrasonic wave propagation in concrete structures. (Frank Mielentz et alt. Ultrasonics 44 2006 p. 1561 – 1566). Of course the special character of the creeping wave as being a part of a head wave can be documented by this technique. The creeping wave approach has at the beginning been considered as a tool to detect defects close to the coupling surface not being influenced by disturbing surface conditions as it must be expected during the use of Rayleigh waves due to the fact, that the longitudinal part of the creeping wave has indeed only a particle movement parallel to the surface thus making it rather immune against acoustic charges at the surface. The drawback of a fast decay has been compensated by a suitably focussed transmitter-receiver probe concept. The further development of the creeping wave approach has seen applications for weld inspection especially also for stainless steel weldments including the opposite surface and the second creeping wave at that surface leading to very special echo patterns enabling a differentiating evaluation of complex weld structures. The typical echo patterns are now well known and are offered by commercial partners under different names ( e.g. “Chime” etc.)


 
00:06 Jul-10-2008

John Howard

Engineering
United Kingdom,
Joined Jun 2008
2
Re: creeping wave?

Thank you for your quick response.
As you appear knowledgeable on the subject can you answer this question?
I understand that the shear wave sound 30° will travel to the bottom surface and generate a small L wave that will propagate forward. If this L wave strikes an ID connected crack it will be reflected. Can you explain in simple English how does this reflected weak L wave gain the intelligence to know when it is aligned to the 30° to mode convert and head back to the probe?

----------- Start Original Message -----------
: John,
: Yes, there is a Creeping Wave.
: The term Creeping Wave is not a new sound source. It is a L-wave energy that skims or creeps along the opposite surface from the scanning surface. The Creeping wave travels a short distance ( about 2 mm to 12 mm) to detect a planar defect at the ID surface. It is
: The Creeping Wave is the result of a shearwave which mode converts to an L-wave from the ID surface.
: See Dr. Wustenbergs Doctorate 1977 Thesis. There are numerous papers on the wave physics and the resulting effects of these critically refracted L-waves and shear waves.
: The main point is that Creeping Waves are very effective for detection, charcaterization and sizing of Cracks.
: Sincerely,
: J. Mark Davis
:
: : Can anyone help? Is there or is there not a 'creeping wave'? Can it be proven either way?
------------ End Original Message ------------




 
04:37 Jul-10-2008
Slawomir Mackiewicz
Re: creeping wave? John
I think I understand your problem in spite of my poor English. It is all because you probably try to interpret the physical situation within the framework of the ray model of ultrasonic propagation.

My explanation of the “wave intelligence” is as follows.
The L-wave reflected from the ID connected crack creates a spread beam. To see that look at the excellent photoelastic images given by Ed Ginzel at website (http://www.autsolutions.net/Creeping-waves.html), especially at Figure 5 a,b,c.
Part of reflected L-beam travels along the ID surface. But, L-wave can not travel alone along the free surface because of physical restrictions. To meet the so called “free stress boundary conditions” there must exist also additional T-wave (this time called Head Wave). This Head Wave takes the energy from the propagating L-wave and reradiate it at an angle about 33 (in steel).

This process takes place all the time as L-wave is propagating along the free surface (see again Figure 5). So, at the certainpoint the reradiated T-wave will be inevitably directed straight to the receiving transducer, giving echo CE-2. The L-wave doesn’t have “to know” that specific point because it is reradiating energy all the time.


----------- Start Original Message -----------
: Thank you for your quick response.
: As you appear knowledgeable on the subject can you answer this question?
: I understand that the shear wave sound 30° will travel to the bottom surface and generate a small L wave that will propagate forward. If this L wave strikes an ID connected crack it will be reflected. Can you explain in simple English how does this reflected weak L wave gain the intelligence to know when it is aligned to the 30° to mode convert and head back to the probe?
: : John,
: : Yes, there is a Creeping Wave.
: : The term Creeping Wave is not a new sound source. It is a L-wave energy that skims or creeps along the opposite surface from the scanning surface. The Creeping wave travels a short distance ( about 2 mm to 12 mm) to detect a planar defect at the ID surface. It is
: : The Creeping Wave is the result of a shearwave which mode converts to an L-wave from the ID surface.
: : See Dr. Wustenbergs Doctorate 1977 Thesis. There are numerous papers on the wave physics and the resulting effects of these critically refracted L-waves and shear waves.
: : The main point is that Creeping Waves are very effective for detection, charcaterization and sizing of Cracks.
: : Sincerely,
: : J. Mark Davis
: :
: : : Can anyone help? Is there or is there not a 'creeping wave'? Can it be proven either way?
------------ End Original Message ------------




 


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