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Technical Discussions
elgazery
Consultant
National Institute for Standards, Egypt, Joined May 2003, 10

elgazery

Consultant
National Institute for Standards,
Egypt,
Joined May 2003
10
02:43 Apr-08-2004
proper couplant

Please!
What is the proper couplant can be used in velocity measurement of ceramic porous material.
I used water, motor oil and gel, it was found that they soak the samples and affect measurements



    
 
 Reply 
 
Uli Mletzko
R & D, Retired
Germany, Joined Nov 1998, 89

Uli Mletzko

R & D, Retired
Germany,
Joined Nov 1998
89
03:37 Apr-11-2004
Re: proper couplant
----------- Start Original Message -----------
: Please!
: What is the proper couplant can be used in velocity measurement of ceramic porous material.
: I used water, motor oil and gel, it was found that they soak the samples and affect measurements
------------ End Original Message ------------

This seems to be a really difficult task. You could try to use dry coupling, i.e. to press the probe with some force against the surface of the specimen, using no liquid couplant.

For longitudinal (compression) waves any standard straight beam probe might be applicable, in general.

For transversal (shear waves) it's more difficult. Years ago the probe manufacturers were selling shear wave straight beam probes (i.e. quartz probes with a special crystal cut, where the oscillation is parallel to the probe surface). There you definitely had to use dry pressure coupling (or 'special' couplants like honey).

Another solution might be to use contactless laser techniques (ultrasound generated by an power laser impulse; surface movement of the reflected backwall echo detected by laser interferometry). This technique is available and used to on-line monitoring the wall thickness of hot steel pipes during the milling process. Possibly too expensive for your application.

Regards
Uli Mletzko
(MPA, University of Stuttgart, Germany)


    
 
 Reply 
 
Dave Davies
Dave Davies
03:32 Apr-12-2004
Re: proper couplant
----------- Start Original Message -----------
: : Please!
: : What is the proper couplant can be used in velocity measurement of ceramic porous material.
: : I used water, motor oil and gel, it was found that they soak the samples and affect measurements
: This seems to be a really difficult task. You could try to use dry coupling, i.e. to press the probe with some force against the surface of the specimen, using no liquid couplant.
: For longitudinal (compression) waves any standard straight beam probe might be applicable, in general.
: For transversal (shear waves) it's more difficult. Years ago the probe manufacturers were selling shear wave straight beam probes (i.e. quartz probes with a special crystal cut, where the oscillation is parallel to the probe surface). There you definitely had to use dry pressure coupling (or 'special' couplants like honey).
: Another solution might be to use contactless laser techniques (ultrasound generated by an power laser impulse; surface movement of the reflected backwall echo detected by laser interferometry). This technique is available and used to on-line monitoring the wall thickness of hot steel pipes during the milling process. Possibly too expensive for your application.
: Regards
: Uli Mletzko
: (MPA, University of Stuttgart, Germany)
------------ End Original Message ------------
***
I don't like the idea of pressure on the probe, have you tried a thin plastic sheet between the probe and job? this can sometimes be used to take up surface irregularities. A very small amount of couplant on the probe side and none on the item side may be enough. I guess as you are measuring velocity you are using compression waves. The thickness of the sheet would affect measurements but it depends on the items you are testing and the accuracy you require, may be acceptable.
***


    
 
 Reply 
 
S.V.Swamy
Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex , India, Joined Feb 2001, 787

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
787
04:35 Apr-12-2004
Re: proper couplant
Dear friends,

Yes, it is a difficult job. But Dry coupling transducers are available for this special application. An extremely thin plastic film will also solve the problem with little effect on the accuracy of the result, if you must use a normal probe.

Swamy

----------- Start Original Message -----------
: : : Please!
: : : What is the proper couplant can be used in velocity measurement of ceramic porous material.
: : : I used water, motor oil and gel, it was found that they soak the samples and affect measurements
: : This seems to be a really difficult task. You could try to use dry coupling, i.e. to press the probe with some force against the surface of the specimen, using no liquid couplant.
: : For longitudinal (compression) waves any standard straight beam probe might be applicable, in general.
: : For transversal (shear waves) it's more difficult. Years ago the probe manufacturers were selling shear wave straight beam probes (i.e. quartz probes with a special crystal cut, where the oscillation is parallel to the probe surface). There you definitely had to use dry pressure coupling (or 'special' couplants like honey).
: : Another solution might be to use contactless laser techniques (ultrasound generated by an power laser impulse; surface movement of the reflected backwall echo detected by laser interferometry). This technique is available and used to on-line monitoring the wall thickness of hot steel pipes during the milling process. Possibly too expensive for your application.
: : Regards
: : Uli Mletzko
: : (MPA, University of Stuttgart, Germany)
: ***
: I don't like the idea of pressure on the probe, have you tried a thin plastic sheet between the probe and job? this can sometimes be used to take up surface irregularities. A very small amount of couplant on the probe side and none on the item side may be enough. I guess as you are measuring velocity you are using compression waves. The thickness of the sheet would affect measurements but it depends on the items you are testing and the accuracy you require, may be acceptable.
: ***
------------ End Original Message ------------




    
 
 Reply 
 
elgazery
Consultant
National Institute for Standards, Egypt, Joined May 2003, 10

elgazery

Consultant
National Institute for Standards,
Egypt,
Joined May 2003
10
00:41 Apr-12-2004
Re: proper couplant
Dear all
Thanks for your helpful forum.
I think i solved the problem and i want to discuss the solution together.
i spried one face of the samples by thin PMMA film. i found that it is very helpful and the measurements are stable.
please, tell me your comments


    
 
 Reply 
 

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