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3286 views
03:29 Jan-29-2004
Reymondin Jean-Pascal
NDT of sandwich structure

I have to test larges sandwich structures.
Skins about 1,5 mm ( carbon / epoxy )
Core ( aluminium honeycomb )
Total thickness about 30 mm
I have to detect flaws in the skins, in both adhesive layers and in the core. ( If possible, test only from one side )
Witch method will be the most efficient for my job ?
Thanks for any answer.
Best regards
JP



 
03:43 Jan-31-2004

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT,
United Kingdom,
Joined Oct 1999
512
Re: NDT of sandwich structure If an automated inspection is required, and access from both sides is possible, Then a C-scan ultrasonic system, either water or Air-coupled, will probably be the best approach.

If a manual, single sided approach is preferred, then a low-frequency pitch-catch ultrasonic ("Sondicator") type instrument is likely to be suitable.

Bothe methods are commonly used in composite inspection for aerospace and similar industries.

If you require more information please contact me directly.

----------- Start Original Message -----------
: I have to test larges sandwich structures.
: Skins about 1,5 mm ( carbon / epoxy )
: Core ( aluminium honeycomb )
: Total thickness about 30 mm
: I have to detect flaws in the skins, in both adhesive layers and in the core. ( If possible, test only from one side )
: Witch method will be the most efficient for my job ?
: Thanks for any answer.
: Best regards
: JP
------------ End Original Message ------------




 
07:55 Feb-02-2004
Jörg Collrep
Re: NDT of sandwich structure Dear Sir,
in addition to the US scanning mentioned by Joe Buckley you can also use Shearography as a quite fast and reliable inspection method. As an advantage to US you don't have to prepare the surface for the inspection ( no water, no coating ) and you inspect a 350 mm x 250 mm area within 10 seconds. As for US you have to do the inspection from both sides.
We have recently developed a system for Airbus for this particular ispection. If you would like to have further information please drop me a email. Best regards
Jörg Collrep

----------- Start Original Message -----------
: I have to test larges sandwich structures.
: Skins about 1,5 mm ( carbon / epoxy )
: Core ( aluminium honeycomb )
: Total thickness about 30 mm
: I have to detect flaws in the skins, in both adhesive layers and in the core. ( If possible, test only from one side )
: Witch method will be the most efficient for my job ?
: Thanks for any answer.
: Best regards
: JP
------------ End Original Message ------------




 
09:30 Feb-02-2004

Randy Plis

Sales, Consultant
AMDATA NDE Technology LLC,
USA,
Joined Oct 1999
23
Re: NDT of sandwich structure Hello JP,

It is not clear whether you are interested in buying a system to do the inspection, or to subcontract it out to an inspection company to be conducted as a service.

In either case, it will be necessary to further define your needs - for example, providing details of the part lay-up, and identifying the minimum defect size.

Ultimately, you will want to create a test sample that is representative of your part lay-up/geometry, and contains simulated defects. This sample can then be used to prove up the inspection technique, and also be later used as your inspection calibration standard. If you are planning to purchase equipment, the same sample could be used for system acceptance testing.

As mentioned by others, an Ultrasonic C-Scan system may meet your needs. An AMDATA IntraSpect UT Laptop is one such system - additional information can be found at www.amdatande.com or via our NDT.net exhibit stand.

Regarding an inspection service company, Metals Testing Company (MTC) has used an IntraSpectsystem to perform a similar skin-to-skin, and skin-to-honeycomb bond test on an aircraft control surface part. Additional details about MTC can be found at www.mtc62.com. Details about the bond test can be found under their website's literature section "Aircraft Skin to Honeycomb Assemblies". Please note that this was with aluminum skins. There will be a significant UT difference with composite layers. This difference will need to be quantified and tested via your sample.

Hope this helps.

Best regards,
Randy Plis
AMDATA NDE Technology


 
01:21 Feb-02-2004

Tadeusz Stepinski

R & D
Uppsala University,
Sweden,
Joined Nov 1998
14
Re: NDT of sandwich structure I am afraid that if you have to detect flaws in both skins you must have access from both sides.
There is an instrument designed for this purpose that hasn't been mentioned in the discussion: Staveley's Bond Master. In fact, you get three instruments in one box operating on three different principles: resonace spectroscopy, mechanical impedance analysis and plate waves. All the princiles are useful in your application for detecting different flaws.
A serious disadvantage may be that the instrument is designed for manual testing of aircraft structures.
Check Staveley's home page for details.

TS

----------- Start Original Message -----------
: I have to test larges sandwich structures.
: Skins about 1,5 mm ( carbon / epoxy )
: Core ( aluminium honeycomb )
: Total thickness about 30 mm
: I have to detect flaws in the skins, in both adhesive layers and in the core. ( If possible, test only from one side )
: Witch method will be the most efficient for my job ?
: Thanks for anyanswer.
: Best regards
: JP
------------ End Original Message ------------




 
04:12 Feb-03-2004
Richard Kazares
Re: NDT of sandwich structure We produce UT systems with both "conventional" characteristics (which have been used for many honeycomb inspection applications) and also Acousto-Ultrasonic systems (NOT CONVENTIONAL) - which are based on VERY low frequency acoustic emission sensor technology with fully controllable input waveform, energy and frequency control. This results in VERY high penetrating capability for MANY composite and similar multi-material, complex geometry structures. This could be most applicable for your "core" inspection, as well as looking for larger, near surface indications. Conventional UT is available for bond analysis.

I will personally e-mail you some C-Scan images of honeycomb structures - made by customers using our UT scanning systems.


----------- Start Original Message -----------
: I have to test larges sandwich structures.
: Skins about 1,5 mm ( carbon / epoxy )
: Core ( aluminium honeycomb )
: Total thickness about 30 mm
: I have to detect flaws in the skins, in both adhesive layersand in the core. ( If possible, test only from one side )
: Witch method will be the most efficient for my job ?
: Thanks for any answer.
: Best regards
: JP
------------ End Original Message ------------





 
03:21 Feb-03-2004

David Forsyth

R & D
TRI/Austin,
USA,
Joined Nov 2001
41
Re: NDT of sandwich structure More information about the flaw types would be useful. Large delaminations within composite skin, or disbonds between skin and core, are detectable with ultrasonic methods in my experience. Also with thermography. Through thickness ultrasound with a squiter system will work. A Bondmaster will probably also work, but you will need access to each side.

A problem of interest to many air forces is water ingress in these structures. Ultrasonic methods are still somewhat useful here, thermography will probably do better.

These are methods I have used or seen used, with success. I can not comment about the other suggestions, links to publications would be interesting.

Regards, Dave.

----------- Start Original Message -----------
: I have to test larges sandwich structures.
: Skins about 1,5 mm ( carbon / epoxy )
: Core ( aluminium honeycomb )
: Total thickness about 30 mm
: I have to detect flaws in the skins, in both adhesive layers and in the core. ( If possible, test only from one side )
: Witch method will be the most efficient for my job ?
: Thanks for any answer.
: Best regards
: JP
------------ End Original Message ------------




 
00:52 Feb-04-2004
Wolfgang Bisle
Re: NDT of sandwich structure Yes, that's it.
Forget Ultrasonics. Can't deal with it completely.
... No, do not really forget it. But it is very restricted for single side application.

In aircraft maintenance - which is a typical situation for limited access, single side application is normally a must - resonance techniques are used, we prefer the Bondmaster. Which is a very universal tool. It offers much more then only simple ultrasound. It gives you the advantage of pitch&catch mode (guided waves), acoustical impedance measurement and others. These alternatives make the Bondmaster quiet universal to deal with sandwich inspection problems. But still it is a point-to-point technique. A technique from yesterday (????) or maybe from today. But latest tomorrow you should use imaging techniques.
And hat can you do?
Of coarse Shearography. As it measures stiffness and a flaw in a honeycomb sandwich is always acompanied with a significant loss in stiffness, it is more or less ideal. Indeed, the Steinbichler Portable head for Shearography was developed addressing especially also Sandwich structure inspection problems.
So take this method seriously in consideration, it could save lots of time. But needs a new training -of coarse different from UT.
Let me remind a fact:
Testspecimen / adjustment blocks with artificial flaws used to validate UT and resonance inspection techniques mostly don't work with other techniques!!!!
DON't make the mistake to use a test specimen for instance with flaws simulated by Foil inclusions. Or with special double layered teflon foils or similar tricky things. It does not work.
You might get the wrong image that something works with UT but does not work with shearography, Thermography etc. It is your mistake, not the method failing !!!!
Even you have cheated yourself in case of Ultrasonics, because also here it does not really simulate the real behaviour of a flaw (delamination etc.) Normally these foils bake together and with shearography as well as with thermography you can visualize this. A "crispy" pattern in the fringes or in the demodulated image on the display shows the truth. Looking accurately with ultrasound, you could identify this too - the echo behaviour is different from a real delamination or flaw.

Back to the original question:
other methods to detect flaws in sandwich singlesided with full field imaging is pulsed thermography or
lockin thermography.

One draw back:
With the optical and thermooptical methods you cannot do in parallel a determination of porosity content of your skin laminates! If you need this, you have to get back to ultrasonics. Thats for instance still the fact for some production lines.

Yes now the loop is closed. Don't forget UT.

Have fun with NDT
Wolfgang Bisle


refer also to:
http://www.ndt.net/wshop/forum/messages-1/1609.htm


 
02:57 Feb-05-2004
Rami Elazar
Re: NDT of sandwich structure ----------- Start Original Message -----------
: I have to test larges sandwich structures.
: Skins about 1,5 mm ( carbon / epoxy )
: Core ( aluminium honeycomb )
: Total thickness about 30 mm
: I have to detect flaws in the skins, in both adhesive layers and in the core. ( If possible, test only from one side )
: Witch method will be the most efficient for my job ?
: Thanks for any answer.
: Best regards
: JP
------------ End Original Message ------------

You can test with C-scan ultrasonic system, either water or Air-coupled, will probably be the best approach. You can visit our site http://www.scanmaster-irt.com/ and find the DS200 system.



 


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