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- since 1996 -
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Technical Discussions
herb cumbaa
herb cumbaa
03:32 Aug-23-2006
sizing

I'm tasked with detecting a flat bottom drilled hole 3/16" dia. In a 1.125" thk. sample of solid carbon composite material with a 1.125" dia. Transducer 1 Mhz. Can you tell me the minimum size that 's detectable for this dia. Thanks any input would be greatly appreciated.

Old UT guy
Old UT guy
04:23 Aug-23-2006
Re: sizing
----------- Start Original Message -----------
: I'm tasked with detecting a flat bottom drilled hole 3/16" dia. In a 1.125" thk. sample of solid carbon composite material with a 1.125" dia. Transducer 1 Mhz. Can you tell me the minimum size that 's detectable for this dia. Thanks any input would be greatly appreciated.
------------ End Original Message ------------

Do you want to know the minimum size of a discontinuity detectable with that particular transducer, or the minimum size of transducer needed to detect the 3/16" FBH?
In either case, the acoustic properties of the material will be the determining factor, as they effect the wavelength of a given UT pulse. Given a reasonable amount of transmisivity, you should be able to detect the 3/16" dia hole in the carbon composite, as long as it is not too close to the entry surface.

Philippe Rubbers
Engineering
SCM, South Africa, Joined Nov 1998, 22

Philippe Rubbers

Engineering
SCM,
South Africa,
Joined Nov 1998
22
04:55 Aug-23-2006
Re: sizing
Dear Sir

The probe is 1.125":, the FBH is 3/16"
What is the depth of the FBH?, what is the material sound velocity? what is the probe bandwidth?
1) With these figures you could work out the focal spot size and see if sufficent energy will be reflected.
2) You can also work out the wavelength for the 1MHz, and find the expected minimum FBH size.
3) If the FBH is < 2 wavelengths from the back wall, you can check if the resolving power will be sufficient to see the signal. For this you require the probe bandwidth.

Since the material is a composite, these figures may be only a rough guide...
Good luck

----------- Start Original Message -----------
: I'm tasked with detecting a flat bottom drilled hole 3/16" dia. In a 1.125" thk. sample of solid carbon composite material with a 1.125" dia. Transducer 1 Mhz. Can you tell me the minimum size that 's detectable for this dia. Thanks any input would be greatly appreciated.
------------ End Original Message ------------

herb cumbaa
herb cumbaa
05:58 Aug-23-2006
Re: sizing
to detect the 3/16" FBH?
: In either case, the acoustic properties of the material will be the determining factor, as they effect the wavelength of a given UT pulse. Given a reasonable amount of transmisivity, you should be able to detect the 3/16" dia hole in the carbon composite, as long as it is not too close to the entry surface.

I want the minimum detectable size for a 1.125" dia transducer the depth is 25,50,&75% of the material thk.
I can get a backwall signal of the base material but the FBH'S aren't showing up

MW Moyer
MW Moyer
02:58 Aug-23-2006
Re: sizing
If it is assumed that you are doing a contact inspection and the part is not excessively thick, the amplitude of the FBH compared to the back surface signal should be the ratio of the areas. The ratio is 1/36 so you should expect a signal that is 2.8% of the backwall echo. To improve the sensitivity, try an immersion inspection with a focused trandsucer.

----------- Start Original Message -----------
: to detect the 3/16" FBH?
: : In either case, the acoustic properties of the material will be the determining factor, as they effect the wavelength of a given UT pulse. Given a reasonable amount of transmisivity, you should be able to detect the 3/16" dia hole in the carbon composite, as long as it is not too close to the entry surface.
:
: I want the minimum detectable size for a 1.125" dia transducer the depth is 25,50,&75% of the material thk.
: I can get a backwall signal of the base material but the FBH'S aren't showing up
------------ End Original Message ------------

Neil Burleigh
Sales
Krautkramer Australia Pty Ltd, Australia, Joined Dec 2002, 158

Neil Burleigh

Sales
Krautkramer Australia Pty Ltd,
Australia,
Joined Dec 2002
158
01:44 Aug-24-2006
Re: sizing
Dear Herb,
The 1st thing I must ask is what sort of 1 MHz probe are you using? Is it a single crystal or twin crystal probe? If it is a single crystal probe are you using it with a delay line?
Now if you apply this information to a known material, say steel, we will know from experience that you can detect a reflector (as a rule of thumb)of 1/2 the wavelength. The wavelength of a 1 MHz in steel is 6 mm (using L waves) so we can detect a 3mm FBH which meets your criteria.
Now the following:
1. The dead zone of a typical 1 MHz probe 28 mm dia will be around 25 -30 mm or 1.0 inch in steel. Therefore if you use the probe without a delay line you would not be able to detect any of the FBHs at the depths that you mentioned.
2. If you use a delay line you may be able to detect the 50% depth FBH and you would be able to detect the 75% depth FBH.
3. If you use a twin crystal probe you should be able to detect all 3 FBHs.

You have said that you can 'get a backwall signal' What is the gain reserve or signal to noise ratio between the maximised backwall signal and base line noise, dB difference?

Finaly what is the longitudinal sound velocity of this carbon composite that you are testing?

Regards
Neil

----------- Start Original Message -----------
: to detect the 3/16" FBH?
: : In either case, the acoustic properties of the material will be the determining factor, as they effect the wavelength of a given UT pulse. Given a reasonable amount of transmisivity, you should be able to detect the 3/16" dia hole in the carbon composite, as long as it is not too close to the entry surface.
:
: I want the minimum detectable size for a 1.125" dia transducer the depth is 25,50,&75% of the material thk.
: I can get a backwall signal of the base material but the FBH'S aren't showing up
------------ End Original Message ------------

herb cumbaa
NDT Inspector,
USA, Joined Aug 2007, 10

herb cumbaa

NDT Inspector,
USA,
Joined Aug 2007
10
07:47 Aug-24-2006
Re: sizing
thanks for the responses I got what I needed and then some

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