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Sonotron NDT
Original developer and manufacturer of advanced ultrasonic instruments
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Technical Discussions
Navdeep singh
Navdeep singh
02:21 Sep-20-2001
UT testing of composite patches

I am a gradute reserach assistant at University of Missouri-Rolla. I have been trying to detect delaminations in a composite patch bonded to aluminum skin,however the delamination does not show in the C-scan image. I was wondering what type a UT transducer would be needed to see the Delamination clearly. Presently i am using a 5 mHz transducer, should I go to a higher frequency one


    
 
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Trevor Liddell
Trevor Liddell
03:01 Sep-20-2001
Re: UT testing of composite patches
Assuming the patch is a Carbon Fiber Composite of some description and that you are inspecting from the Composite side I have in the past had good results with 3.5Mhz transducers. As you also tend to get a frequency down shift within the composite depending upon the flaw detector used it may be better to have it set to a broadband frequency


    
 
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Tom Nelligan
Engineering,
retired, USA, Joined Nov 1998, 390

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
03:14 Sep-20-2001
Re: UT testing of composite patches
You didn't indicate the thickness or the composition of the of the composite, which are important factors in transducer selection. Do you have a detached piece of the material? Does your transducer provide a clean backwall echo from a detached reference standard? If so, your current transducer is probably fine. If not, please tell us more about your material and I'd be happy to comment further on transducer selection.

Also, you should be aware that because of the significant acoustic impedance mismatch between aluminum and nonmetallic composites, you will get a large echo from the boundary even if the materials are well bonded. You should test from the composite side and look for a phase reversal in the unrectified RF waveform. At a disbond, the RF signal will invert as well as getting slightly larger. In cases of severe impedance mismatch that's often a more reliable test than amplitude, particularly if the composite is rough and coupling is variable.

--Tom Nelligan
Panametrics, Inc.


    
 
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Navdeep Singh
Navdeep Singh
06:33 Sep-21-2001
Re: UT testing of composite patches
: You didn't indicate the thickness or the composition of the of the composite, which are important factors in transducer selection. Do you have a detached piece of the material? Does your transducer provide a clean backwall echo from a detached reference standard? If so, your current transducer is probably fine. If not, please tell us more about your material and I'd be happy to comment further on transducer selection.
.
: Also, you should be aware that because of the significant acoustic impedance mismatch between aluminum and nonmetallic composites, you will get a large echo from the boundary even if the materials are well bonded. You should test from the composite side and look for a phase reversal in the unrectified RF waveform. At a disbond, the RF signal will invert as well as getting slightly larger. In cases of severe impedance mismatch that's often a more reliable test than amplitude, particularly if the composite is rough and coupling is variable.
.
: --Tom Nelligan
: Panametrics, Inc.
.

The aluminum skin is a piece about 15'X 6'.The thickness of the aluminum skin is 0.125' and the unidirectional boron epoxy patch is about 27 mills thick bonded with an adhesive about 7 mills thick. The through transmission mode is being used. I am using the immersion technique. The immersion tank is from the Digital Wave corporation and the Pulser/receiver is the 5072PR from Panametrics. The transducer being used as Pulser and receiver are both Valpey Fisher standard case style ISO504HR 5.0MHz.


    
 
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Navdeep Singh
Navdeep Singh
06:37 Sep-21-2001
Re: UT testing of composite patches
: Assuming the patch is a Carbon Fiber Composite of some description and that you are inspecting from the Composite side I have in the past had good results with 3.5Mhz transducers. As you also tend to get a frequency down shift within the composite depending upon the flaw detector used it may be better to have it set to a broadband frequency
.

The dimensions of the aluminum piece are 15’ X 6’.The thickness of the aluminum skin is 0.125' and the unidirectional boron epoxy patch is about 27 mills thick bonded with an adhesive about 7 mills thick. The through transmission mode is being used. I am using the immersion technique. The immersion tank is from the Digital wave corporation and the Pulser/receiver unit is the 5072PR from Panametrics. The transducersbeing used as Pulser and receiver are both Valpey Fisher standard case style ISO504HR 5.0MHz.


    
 
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Joakim Andersson
Joakim Andersson
03:40 Sep-21-2001
Re: UT testing of composite patches
: The size of the delamination to detect may be the problem. Using a focused transducer to improve the resolution is one way to detect smaller defects. Of course also higher frequency will help up the detectability.

If the delamination is large compared to the soundfield of the transducers. I do not believe the problem is due to the inspection parameters (size of transducer, frequency and so on). Then I suspect that the defect you are searching for is not a pure delamination. If the delamination is open to the surroundingy you may have got water into the bondline filling up the delamination. This will more or less make detection impossible with through transmission ultrasonic. This problem and other defects like kissing bond are difficult to detect. If you have water in the delamination try to dry it out and the seal the bondline before inspection. Please feel free to contact us for further advice and visit us on our website www.csm.se.

Regards
Joakim Andersson
CSM Materialteknik



    
 
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Mike Naranjo
NDT Inspector
USA, Joined Aug 2001, 1

Mike Naranjo

NDT Inspector
USA,
Joined Aug 2001
1
05:34 Sep-24-2001
Re: UT testing of composite patches
: I am a gradute reserach assistant at University of Missouri-Rolla. I have been trying to detect delaminations in a composite patch bonded to aluminum skin,however the delamination does not show in the C-scan image. I was wondering what type a UT transducer would be needed to see the Delamination clearly. Presently i am using a 5 mHz transducer, should I go to a higher frequency one
.
What are the dimensions of the item being examined? What kind of material classification does ASME section II Non-ferritic material states? What is the thickness or dimensions? Have you tried an "A" Scan presentation? Give us a little more information and we can answer your question my friend.



    
 
 Reply 
 
Kelly Phelps
Consultant, IT Manager/Marketing Manager
NDT Engineering Corporation, USA, Joined Oct 2001, 6

Kelly Phelps

Consultant, IT Manager/Marketing Manager
NDT Engineering Corporation,
USA,
Joined Oct 2001
6
08:29 Nov-02-2001
Re: UT testing of composite patches
: I am a gradute reserach assistant at University of Missouri-Rolla. I have been trying to detect delaminations in a composite patch bonded to aluminum skin,however the delamination does not show in the C-scan image. I was wondering what type a UT transducer would be needed to see the Delamination clearly. Presently i am using a 5 mHz transducer, should I go to a higher frequency one.

You are using TTU and that is good.
Is the known disbond area a manufactured disbond? If you know the area of the disbond then it is very likely that the patch is in intimate contact with the aluminum skin. If so, sound will pass thru it. Try vibrating the area of disbond to break the contact, and if that doesn't work then hit it with a hammer. I know it sounds crude, but sometimes it is the only thing that works.




    
 
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Steven Young
Steven Young
01:39 Apr-24-2002
Re: UT testing of composite patches
: I am a gradute reserach assistant at University of Missouri-Rolla. I have been trying to detect delaminations in a composite patch bonded to aluminum skin,however the delamination does not show in the C-scan image. I was wondering what type a UT transducer would be needed to see the Delamination clearly. Presently i am using a 5 mHz transducer, should I go to a higher frequency one
.I think you ought to try a dual element transducer!! I am at Cowley College and they are the best!! woo hoo.
Halla Back Youngun



    
 
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