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3283 views
09:52 Jul-29-2000

Mahmoud elgazery

Consultant
National Institute for Standards,
Egypt,
Joined May 2003
10
plotting Ultrasonic beam profile

i'd like to get help about plotting the beam profile of ultrasonic
contact (normal and angle) probes.

i want a method to imagine the bem shape (Near and far fields) in
solids


 
08:58 Jul-31-2000
Dipl.-Ing. Martin Heinz
Re: plotting Ultrasonic beam profile : i'd like to get help about plotting the beam profile of ultrasonic
: contact (normal and angle) probes.

: i want a method to imagine the bem shape (Near and far fields) in
: solids

Normaly such beam shape plots are done in an immersion tank with a stepper motor controled XYZ-scanning system, where an hydrophone is moved in several planes in front of the transducer to be tested. We provide this as a service.
I have never heard until now that it is possible to do same in solids. In this case you should have several slices of different thickness of the solid, and you had to move a second probe to the other side of the test block. But because of multiple sound reflections the results of the measurement would probably not be applicable.

Best regards,

Martin Heinz.


 
04:27 Jul-31-2000

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1208
Re: plotting Ultrasonic beam profile : : i'd like to get help about plotting the beam profile of ultrasonic
: : contact (normal and angle) probes.

: : i want a method to imagine the bem shape (Near and far fields) in
: : solids

: Normaly such beam shape plots are done in an immersion tank with a stepper motor controled XYZ-scanning system, where an hydrophone is moved in several planes in front of the transducer to be tested. We provide this as a service.
: I have never heard until now that it is possible to do same in solids. In this case you should have several slices of different thickness of the solid, and you had to move a second probe to the other side of the test block. But because of multiple sound reflections the results of the measurement would probably not be applicable.

: Best regards,

: Martin Heinz.

Assessing beam plots in solids has been a much debated subject.
Modelling algorithms such as those used in several of the papers submitted to www.NDT.net provide reasonable approximations usually based on huygens or finitie element methods. But manufactured probes and actual metal conditions are not always the same as the model, so some method of assessing the real beam is desireable.
Codes and standards such as BS, ASTM, ISO and ESI typically rely on measurements of pulse-echo signal amplitudes with respect to probe displacement.
Targets may vary and include flat or round bottom holes and side or through drilled holes.

But there are problems associated with beam assessment for contact probes that do not exist for immersion probes.
1. Since contact probes usually use SV shear waves, immersion techniques are not suitable as they assess only compression mode.
2. Maintaining constant coupling on a metal test surface is always difficult, even in mechanised systems, but this is essential as we must eliminate coupling variation as a variable when we assess amplitude drops.
3. Orientation of the target in a solid when assessing the vertical plane is limited. Since we must move the probe on a flate surface the best we can do is traverse the tqarget in the plane of the test surface. This is not a problem for compression mode using normal incidence as the beam axis can be made to traverse the target at right angles. However, for angled beams the beam axis will always be at an angle to the target when assessing the vertical plane. We are then left with making discrete measurements from targets at several different distances. These are then assembled on plots such as described in British Standards or ASME or simlar standards.
This method requires that we accept the error introduced by the change in sound path distance that results because we cannot maintain a constant distance to the target as we move the probe.

The only option to this is described in DIN 25-450 (1990). In Section 5.3.3 it describes a through transmission technique using EMAT receivers and a semicylindrical block.
This technique is accurate but requires you have access to EMAT devices and a series of semicylindricalblocks with several different radii.
There are several other beam assessment parameters described in the DIN document that seem to be more effective or more comprehensive that other standards, I suggest you take a look at this document.

One other item about beam assessment:
Most beam modelling assumes a point reflector but this is not a practical item and the effects of target shape and size cause different results in pulse-echo measurements.
An option that I adapted from a conversation with people in Southwest Research is to observe the signal drop from an infinite reflector. This is described in the paper on amplitude assessments by E.Ginzel in the June 2000 issue of www.NDT.net. The beam sizes determined by this technique were actually VERY close to the theoretical dimensions predicted by modelling.

Ed



 
05:02 Jul-31-2000

Tim MacInnis

Senior NDT Engineer
SAIC/Ultra Iamge International,
USA,
Joined Dec 1999
10
Re: plotting Ultrasonic beam profile : i'd like to get help about plotting the beam profile of ultrasonic
: contact (normal and angle) probes.

: i want a method to imagine the bem shape (Near and far fields) in
: solids

The ISO 12715:1999(E) standard "Ultrasonic non-destructive testing -
Reference blocks and test procedures for the characterization of
contact search unit beam profiles". An earlier standard
ISO 10375: 1997(E) "Non-destructive testing - Ultrasonic inspection -
Characterization of search unit and sound field" Both of these
standards do an excellent job of defining the task. The reference
blocks of 12715 are a must for determining the index points and angles
with respect to aluminum.


 
03:34 Jul-31-2000

Robert (Rocky) A. Day

Engineering
Milky Way Jewels,
USA,
Joined Nov 1998
40
Re: plotting Ultrasonic beam profile I have a beam profile article at . Although it and most other articles are immersion oriented it may be of some help.

: i'd like to get help about plotting the beam profile of ultrasonic
: contact (normal and angle) probes.

: i want a method to imagine the bem shape (Near and far fields) in
: solids




 
03:24 Aug-01-2000
Wieslaw Bicz
Re: plotting Ultrasonic beam profile : i'd like to get help about plotting the beam profile of ultrasonic
: contact (normal and angle) probes.

: i want a method to imagine the bem shape (Near and far fields) in
: solids

We have made such measurements (in glass) using small point reflector or small receiver.
With enough care and some experience it is possible to get a good picture of the ultrasonic field.
Problems can arose, if you want to make measurements, that should not only give comparison between two transducers, but also
exact amplitude. But - I think, it is mostly not a large problem.

If you are interested, we can offer you our experience with such measurements. We have made some devices for such purpose.

Regards

Wieslaw Bicz

optel@optel.com.pl
http://www.optel.com.pl



 


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