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- since 1996 -
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Technical Discussions
mhrn sphri
mhrn sphri
09:08 Nov-06-2012
adhesive bonding

Dears,
I am working on ''Ultrasonic testing of multilayer adhesive bonding". The thickness of Al plates which are used in my initial samples are 4mm, bonded with a 1mm epoxy adhesive. Now, I am in trouble with testing 2nd interface of bonded surface. I'd used 10 & 15 MHz probes with pulse-echo method, but I couldn't distinguish echos.
Please suggest me solution for suitable methods, signal processing solutions etc.

 
 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
11:19 Nov-06-2012
Re: adhesive bonding
In Reply to mhrn sphri at 09:08 Nov-06-2012 (Opening).

Mention clearly all the echoes that you are getting with their times (distances). Have you tried lower frequencies?

Swamy

 
 Reply 
 
Richard Freemantle
NDT Inspector, Consultant, R&D
Wavelength NDT Limited, United Kingdom, Joined Nov 1998, 16

Richard Freemantle

NDT Inspector, Consultant, R&D
Wavelength NDT Limited,
United Kingdom,
Joined Nov 1998
16
11:57 Nov-06-2012
Re: adhesive bonding
In Reply to mhrn sphri at 09:08 Nov-06-2012 (Opening).

Hi,

I worked on this problem some years ago. As Swamy says it would be good to state the echo times you see or preferably post a time trace from your sample. You should be looking for a small echo reflected from the far side of the adhesive layer which will arrive some time after the first backwall echo from the aluminium sheet nearest to the probe. The phase of this echo will be sensitive to the bonding condition between the adhesive layer and the second alumunium sheet. However it may be possible that the echo from the adhesive layer arrives at the same time as the second backwall echo in the first sheet and therefore will be hidden. If you are not using a delay line with the probe you should also try this as this may improve your resolution.

I worked on a filtering method to remove the masking echoes from the first sheet which produced good results allowing you to more easily see the adhesive echo and its phase even when it is normally masked by the aluminium sheet echoes. More here:

http://www.ndt.net/article/wsho0597/freem/frame_b.htm

The following figures from this article show the phase change due to disbonds between the adhesive layer in the second sheet of aluminium for the raw and filtered datasets:

http://www.ndt.net/article/wsho0597/freem/fig5a.gif
http://www.ndt.net/article/wsho0597/freem/fig5b.gif

You will see in the raw datasets that easily finding the adhesive echo and determining its phase is very difficult. I suspect you may have the same problem here.



Good luck !

Richard

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

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
14:54 Nov-06-2012
Re: adhesive bonding
In Reply to mhrn sphri at 09:08 Nov-06-2012 (Opening).

The problem of interfering echoes in a multi-layer metal assembly is a familiar one. Because the adhesive is typically a poor acoustic impedance match to the metal, you get strong echoes from each boundary even if they are well bonded. You will probably have better luck with resonance or mechanical impedance techniques. The application note at this link focuses on carbon fiber composites, but the same approaches can be used for bonded metal plates.

http://www.olympus-ims.com/en/applications/multi-mode-adhesive-bond-testing/347-pos.30.html

Alternately, a simple through transmission ultrasonic test with a transducer on each side of the stack will identify disbonds through signal dropout. If you get a T-T signal all layers are bonded, and if you don't there is a disbond, although you won't be able to tell at which layer the disbond occurs.

 
 Reply 
 
mhrn sphri
Student,
Turkey, Joined Nov 2012, 3

mhrn sphri

Student,
Turkey,
Joined Nov 2012
3
01:04 Dec-29-2012
Re: adhesive bonding
In Reply to Richard Freemantle at 11:57 Nov-06-2012 .

zoom image



zoom image



Dear Swamy and Richard,

I am really sorry for the delay in my reply. Here is two images of my samples, first image shows a fully bonded joint and the second one presents disbonding in 2nd interface. As you see, there is no obvious evidence for determining the phase of echo. Maybe I must use an appropriate signal processing method. furthermore, I would prefer to find quantitive solutions, if available.
I also should notice that in this research, I'd used immersion probes so that I could adjust delay line to control masking echos' problem.
I really thank you for your attention and assistance. I will look forward for your reply.

sincerely,
Mehran
 
 Reply 
 
Mike Lee from Doppler company
Director,
Guangzhou Doppler Electronic Technologies Co.,Ltd, China, Joined Dec 2012, 14

Mike Lee from Doppler company

Director,
Guangzhou Doppler Electronic Technologies Co.,Ltd,
China,
Joined Dec 2012
14
03:13 Jan-05-2013
Re: adhesive bonding
In Reply to mhrn sphri at 01:04 Dec-29-2012 .

My dear friend:
for near surface detection and thin materials detection, high frequency probes needed in this application,but first of all, we need to short down the near filed distance to keep echo from start wave, in the other side, dampling is also very important in chose the probes

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

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
15:03 Jan-07-2013
Re: adhesive bonding
In Reply to mhrn sphri at 01:04 Dec-29-2012 .

Mehran -- As I wrote back in November in my message above, this is exactly what we would expect to see in a pulse/echo test because of the impedance mismatch between the aluminum and the adhesive. You will see strong multiple echoes even from a good bond. For that reason, simple pulse/echo testing is not a recommended approach. You should work in through transmission mode, which is straightforward, or alternately explore the advanced acoustic techniques discussed in the application note that I linked in my earlier message.

 
 Reply 
 
mhrn sphri
Student,
Turkey, Joined Nov 2012, 3

mhrn sphri

Student,
Turkey,
Joined Nov 2012
3
23:38 Jan-09-2013
Re: adhesive bonding
In Reply to Mike Lee from Doppler company at 03:13 Jan-05-2013 .

Dear Mike,
Please mention exactly what frequencies you mean.
As I wrote in my last message I've used immersion probes, so I can eliminate near field echos from main echos, but damping is an important problem, as you said.

 
 Reply 
 
mhrn sphri
Student,
Turkey, Joined Nov 2012, 3

mhrn sphri

Student,
Turkey,
Joined Nov 2012
3
23:56 Jan-09-2013
Re: adhesive bonding
In Reply to Tom Nelligan at 15:03 Jan-07-2013 .

Dear Tom

I am aware of the restrictions, but I am looking for clues so that I can interpret such echos without using substitutional techniques.

Regards.

 
 Reply 
 

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