I came across a concept in the paper "Progress in the theory of ultrasonic flaw detection. Problems and prospects" by I.N. Ermolov, Russian Journal of Nondestructive Testing, Vol 40, No 10, 2004 pp 655-678. He discusses the well-known concept of "nonmirror reflection". However, I have never heard of this term until reading this paper!
It states that there are 2 different cases where the ray's reflection point shifts along the surface, causing it to reflect at different location than the incidence point. This is termed nonmirror reflection or ray-bundle shift.
The first scenario is for incidence angles close to the critical angle (i.e. - for steel 33 degrees). I assume this refers to the head-wave phenomena as explained in
http://www.autsolutions.net/Creeping-waves.html Does anyone agree with this assumption?
The second case states that nonmirror reflection occurs for all transverse wave incidence angles different from 45 degrees. It states that this is due to the phase shift. This one I don't understand. I have seen in my own experiments that modelled ray reflections do not necessarily matching with my measurements, but I assumed that this was because of the slight deviations in ultrasonic velocity for varying incidence angles.
Has anyone else come across this nonmirror reflection term? Do you understand the phenomena behind this?
I have personally seen that the modelled ray paths do not match up with measurements. I assumed that this was mainly because of velocity variations. Are there other factors that I should be aware of?
Also, for the first scenario, at what angles is a head wave produced? Is it at any angle where the longitudinal wave skims the surface? At what angles would a shear wave need to hit a surface to create a head wave?
Thanks for clarification! I apologize for my ignorance, but I am new to the ultrasonics field.
I. N. Ermolov is one big name in NDT with ultrasound. In the years 70' he creates "Ermolov's Equations", that are also today very used. You can take for granted all the allegation of N Ermolov.
I am sorry but the "slip" on a reflexion surface of one angled ultrasound fascicle is produced by the physical phenomenon of reflexion with gain or loose of a quarter wave length. I do not insist, you can find it in every elementary course on ultrasound. For more information I need some time. But the phenomenon exists.
I cannot give you exact explanation for the other fascicle deviations, but in different concret cases.
I will be delighted to read the article you mentioned. Do you have a copy in English?
Natasha: It would seem that the tem "non-mirror" might be a literal translation for the word we might normally use in English, "non-specular" (Latin speculum = mirror). This would seem to imply diffraction. There have been several good papers on NDT.net that describe this process. An earlier paper by Gendru and Berriet (http://www.ndt.net/article/0498/berriet2/berriet2.htm) touches on the process. This also covers the formation of the headwave.
The "discovery" of the headwave is generally attributed to Ludger Mintrop (see a good description of the origins at www.dgg-online.de/geschichte/johannes/Ch79-24CDpartA.pdf) and it is sometimes referred to as the Mintrop wave in seismology.
As for shear modes forming headwaves, I would welcome others to comment. I and others have observed a shear wavefront incident on a cylinder forming spiral wavefronts that appear to be linked to the Rayleigh wave that forms on the cylindrical surface. As to whether or not these are "headwaves" would be an interesting debate (when constructing DACs in manual UT we can see multiples forming after the main signal peaks and I have for my own convenience called them spiral headwaves).
"Does anyone have a suggestion for a good textbook that discuss the details of ultrasound theory?"
If you can find a copy, the definitive work is probably the comprehensive "Ultrasonic Testing of Materials" by J. Krautkramer and H. Krautkramer, which unfortunately has been out of print for some time. I have a 1990 English language edition published by Springer-Verlag, which I think is the most recent version in English.
On a more introductory level, there is the very good on-line tutorial posted by Iowa State University at
Concerning the non specular reflection discussed within the previous contributions I would like to mention a basic publication from L. Niklas, a former researcher at Krautkrämer Cologne of the year 1965
L. Niklas Gruppenlaufzeit und Bündelversetzung bei Schrägreflexion; Auswirkungen auf die praktische Werkstoffprüfung mit Ultraschall (Time of flight and beam shift at inclined reflection and its influence for the practical material testing with ultrasound)
Materialprüfung 7 (1965) p. 281 - 288
He demonstrates that this phenomenon is linked to an angular dependent phase shift between incoming and reflected wave for planar waves. This occurs in practical NDT with ultrasound mainly at the reflection of shear waves at free surfaces. E.g. in the case of steel there is a typical angular phase shift dependency for shear waves between 33,2 degree angle and 90 degree angle declining from 33,2 angle (90 degree phase shift) towards 45 degree angle (0 degree phase shift), where a negative angular dependency produces a positive beam shift reaching a zero value at 45 degree, and then again increasing towards a 90 degree phase shift at the 90 degree angle with a negative beam shift. That means that we have to do at the frequently used incidence angles of 60 or 70 degrees with a negative beam shift. The physical interpretation of this formally calculated behaviour uses the assumption of strongly decaying surface guided waves excited at the edges of limited beams like e.g the creeping waves linked to a headwave. Those surface waves are taking over the energy transfer for the beam shift.
Thankyou very much for the information about the original paper of Ludwig Niklas.
The complete description of the physical phenomenon, and the pertinent mathematical relationships, I found in the excellent book "H. D. Tietz, Ultraschall Messtechnik, Verlag Technik, Berlin, 1969". Professor Tietz mentioned in the book above the name of Ludwig Niklas, but not the paper that published first the article.
Thank you again,
With respect to an English-language book that is still in print, I would recommend the American Society of Nondestructive Testing's "Nondestructive Testing Handbook", Volume 7, Ultrasonics. It is available through >www.asnt.org> . It is nowhere near as comprehensive as the Krautkramer text I referenced earlier (and in my opinion, seeking a used copy of that book would be worth the effort), and the current Third Edition is not even as complete as the more detailed Second Edition from 1991, but at least it is still readily available.
And as long as I'm on the subject, another very good reference book that is probably also out of print is "Ultrasonic Methods of Nondestructive Testing" by Jack Blitz and Geoff Simpson (Chapman & Hall, 1996). Again, it's worth looking for a secondhand copy if you want to seriously study the theory.