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Technical Discussions
Smit
Engineering,
Tata Lockheed Martin Aerostructure Limited, India, Joined Nov 2011, 8

Smit

Engineering,
Tata Lockheed Martin Aerostructure Limited,
India,
Joined Nov 2011
8
16:01 Apr-15-2019
Single porosity detection

Hello Everyone,

Request to share your views on detection of single porosity.

What will be the minimum size of single porosity detection specially in composite material with any kind of instrument.
You can also share your views for different type of material for single porosity detection.

    
 
 Reply 
 
Krishna bharathi
NDT Inspector,
India, Joined Jun 2015, 15

Krishna bharathi

NDT Inspector,
India,
Joined Jun 2015
15
16:55 Apr-15-2019
Re: Single porosity detection
In Reply to Smit at 16:01 Apr-15-2019 (Opening).

Single pore,Amplitude appears constant when orbital motion and it will disappear in rotational motion of the probe.



Thanks,

    
 
 Reply 
 
Smit
Engineering,
Tata Lockheed Martin Aerostructure Limited, India, Joined Nov 2011, 8

Smit

Engineering,
Tata Lockheed Martin Aerostructure Limited,
India,
Joined Nov 2011
8
08:41 Apr-16-2019
Re: Single porosity detection
In Reply to Krishna bharathi at 16:55 Apr-15-2019 .

That is OK but my query is regarding what is the minimum size we can detect for Single por.?

    
 
 Reply 
 
Krishna bharathi
NDT Inspector,
India, Joined Jun 2015, 15

Krishna bharathi

NDT Inspector,
India,
Joined Jun 2015
15
15:28 Apr-16-2019
Re: Single porosity detection
In Reply to Smit at 08:41 Apr-16-2019 .

I understand your question,it can be whatever,but is a volumetric defect we can accept or reject based on our standards,as per ASME thickness divided by 3 we can accept or reject,

    
 
 Reply 
 
Edward Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1261

Edward Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1261
16:11 Apr-16-2019
Re: Single porosity detection
In Reply to Smit at 16:01 Apr-15-2019 (Opening).

This does not seem like a practical question. Can you be specific as to the material, the component, access, shape of pore, etc. You state "with any kind of instrument". So can you put your component in a nanofocus CT cabinet?

1    
 
 Reply 
 
Smit
Engineering,
Tata Lockheed Martin Aerostructure Limited, India, Joined Nov 2011, 8

Smit

Engineering,
Tata Lockheed Martin Aerostructure Limited,
India,
Joined Nov 2011
8
15:35 Apr-17-2019
Re: Single porosity detection
In Reply to Edward Ginzel at 16:11 Apr-16-2019 .

Hi Edward,

We are measuring porosity/void for composite material which is having adhesive bondline.
i.e. two monolithic compoite are bonded with adhesive.

We are looking for a round pore indication which can be detected by Ultrasonic C-scan method Or if any other NDT technique is there to have more sensitivity than UT then also we can go with that.What will be sensitivity of por detection in composite bonded with adhesive.

We have not any specific instrument for C-scan and even not decided which method will be best suitable to detect smallest por/void.

Please suggest me and provide the details regarding the same.If you need any specific information then let me know.

    
 
 Reply 
 
Edward Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1261

Edward Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1261
17:42 Apr-17-2019
Re: Single porosity detection
In Reply to Smit at 15:35 Apr-17-2019 .

There is still no information about the material and your present approach. How thick is it? Are you already using a particular ultrasound option with a C-scan? Or are you using resonance testing.
It sounds like these are not spherical pores, but instead regions of non-bonded layers. Would it be like a kissing bond? What is the critical size of disbond in accordance with the code you are working to or the critical size as determined by fracture mechanics?

1    
 
 Reply 
 
Ger Carolan
Engineering,
Terma Aerostructures Manufacturing, Denmark, Joined Mar 2016, 2

Ger Carolan

Engineering,
Terma Aerostructures Manufacturing,
Denmark,
Joined Mar 2016
2
00:07 Apr-18-2019
Re: Single porosity detection
In Reply to Smit at 15:35 Apr-17-2019 .

Smit
So, it looks like your specimen consists of 2 monolithic composite details bonded with adhesive. The composite material - are we talking prepreg laminates? What type of fiber, what type of resin system?
Were the detail parts cured and NDT inspected prior to the bonding operation? Are you examining only the adhesive bondline between 2 pre-accepted details?

If this is the case, and you want to visualize voids and porosity in the bondline, is radiography an option for you?
I think film RT is a good approach, using slow speed film (for sensitivity to fine detail) and low kV (for contrast).
Examine the area of interest on the radiograph using a measuring magnifier comparator with reticle, typically featuring a 20mm scale in 0,1mm increments.

I don't have experience in porosity measurement with nonfilm RT techniques like CR and DR. I'd say for sensitivity, CR would be the better nonfilm technique.

Kind regards,
Ger.

    
 
 Reply 
 
Smit
Engineering,
Tata Lockheed Martin Aerostructure Limited, India, Joined Nov 2011, 8

Smit

Engineering,
Tata Lockheed Martin Aerostructure Limited,
India,
Joined Nov 2011
8
13:10 Apr-18-2019
Re: Single porosity detection
In Reply to Ger Carolan at 00:07 Apr-18-2019 .

Thanks carolen for your suggestion.

We are having DRT facility but because of the size of the component we can not accomodate in enclosure room.So we need to escape this option.

Apart from that we are having prepeg material which will be adhesively bond two laminates.
In this only we need to get the minimum size of porosity.

That is the reason we are worried UT method will be more sensitive upto what

    
 
 Reply 
 
J.B.
J.B.
12:40 Apr-23-2019
Re: Single porosity detection
In Reply to Smit at 13:10 Apr-18-2019 .

I wonder a little about your approach.
With Lockheed-Martin in your company name you should be familiar with the way of working about porosity effects and checks in CFRP aero structures.

With the inhomogenious material CFRP usually it is not worth to care about the question how small pores you are able to detect. Usually in production you look for delamination of about 0.6mm or 1/4" diameter. So this is key for the selection of your transducers.
Next question is effect of porosity. as porosity is a stochastic effect, regarding distribution of pore size and distribution, you have to work with statistics. in the time of UT Through Transmission technique the effect of porosity was just handled by evaluation of the attenuation of the material. e.g. 3dB signal loss compared to a porosity free reference was a criterium etc, So the designers of a CFRP structure define a porosity content (Linear or Volume) which is acceptable. So experimentally the allowable attenuation is determined.
Now with PAUT replacing UT-TT things have moved to determining the backscattered Noise. Long time it was discussed how to determine the Porosity reference standards.
Long years cross section cuts had been used and had been mandatory for qualification.
This is - if you look carefully - total Bullshit. As you only by chance hit a pore in its larges extend - you can never reliably image with a 2D cross section a 3D-distribution. So from the mid 1990ties people thought about other possibilities, especially as the Computer Tomography seemed to offer new options. But at that time buying a CT machine was very expensive. So the idea was just to directly make porosity reference samples with different porosity and to determine the effect on Ultrasound in Transmission as well as in Reflection (e.g. PAUT) - but not using any intermediate step by cutting cross sections or doing CT to determine any pore content. The reference samples were finally put into a stress machine and the resulting material parameters were compared with UT signals. So you get direct a quality parameter array for the UT signals like attenuation, frequency content etc. (by the way usually the backwall echo is used, but for non parallel surfaces also other methods are used)
Long time the Dispersion (frequency dependent attenuation) was a big task for researchers but this is difficult to determine industrially.
Today mostly frequencies like 5MHz, 3.5MHz and 2.5MHz are used for CFRP inspection or aerostructures (except very thick attachment fittings). According to these frequencies simple rules depending on the thickness of the part to be inspected are given… Refer e.g. to manufacturing test procedures of LockheedMartin, Boeing or Airbus.

here some interesting patents: https://patentimages.storage.googleapis.com/89/da/f5/f4063cce552e1a/US6684701.pdf (good old stuff from Lockheed Martin)
From Boeing you may look for papers & patents from Gary Georgeson like these patents
https://patents.google.com/patent/US7617715B2/en
United States Patent US7823451 - http://www.freepatentsonline.com/7823451.pdf

1    
 
 Reply 
 
Smit
Engineering,
Tata Lockheed Martin Aerostructure Limited, India, Joined Nov 2011, 8

Smit

Engineering,
Tata Lockheed Martin Aerostructure Limited,
India,
Joined Nov 2011
8
05:11 Apr-24-2019
Re: Single porosity detection
In Reply to J.B. at 12:40 Apr-23-2019 .

Hello J.B.,

Thanks a lot for sharing these valuable feedback.

We are already detecting 1/4" of delamination in existing products but our design team has given some requirement in thou to detect a pore that is impossible with any technique available in NDT.

That is reason i was looking a expert confirmation like you.

I already wrote back them for 1/4" of detectibility but still they are asking for minimum detectability that is the reason i wtote back again if any one is having expert opinion on the same.
Thanks a lot for the articles once again.

    
 
 Reply 
 
J.B.
J.B.
17:00 Apr-24-2019
Re: Single porosity detection
In Reply to Smit at 05:11 Apr-24-2019 .

The request of your stress & design department sounds familiar with me - typical beginner request. Seems that they are new in the business, fresh from academy. Experienced CFRP designers would not come up with those requests. I remember such discussion 40 years ago, as the first flying CFRP parts had been designed in European aerospace industry, We got it later on if young engineers showed up with "brilliant" new ideas. Usually they have never heard about the challenge of inspecting fiber reinforced plastics. We did therefore always familarization NDT training for design engineers with some hands on to teach them, what are the physics of NDT on FRPs. Such personal experience helps a lot to understand the challenge and how to find a viable approach.

I think the most promizing approach to check for real tiny pores is CT - here are some papers from recent and older research - which was done with industrial support:
• https://www.ndt.net/article/wcndt2016/papers/we2a2.pdf - Porosity determination of carbon fiber reinforced plastics (CFRP) in aviation applications using ultrasound without a back wall echo
• https://www.ndt.net/events/aeroNDT2014/app/content/Paper/31_RuizRequena.pdf
• https://2015.ndt-aerospace.com/Portals/aerospace2015/BB/mo5a3.pdf - EVALUATION OF CFRP-REFERENCE SAMPLES FOR POROSITY MADE BY DRILLING AND COMPARISON WITH INDUSTRIAL POROSITY SAMPLES BY MEANS OF QUANTITATIVE XCT.
• https://www.dlr.de/fa/Portaldata/17/Resources/dokumente/institut/2002/u2002_2.pdf - DETERMINATION OF POROSITY IN AEROSPACE.DLR-Airbus
• https://www.researchgate.net/publication/302233319_Determination_of_Porosity_in_Fiber_Reinforced_Plastics_by_Computer_Aided_Ultrasonic_Signal_Analysis_CAMPUS - Determination of Porosity in Fiber Reinforced Plastics by Computer Aided Ultrasonic Signal Analysis
• https://www.researchgate.net/publication/273454859_CFRP_porosity_characterisation_using_-Computed_Tomography_with_optimized_test_parameters_supported_by_XCT-simulation/download see also
• https://mediatum.ub.tum.de/doc/1360649/1360649.pdf Sorry, in German, a PhD-thesis with support from several Airbus business units – finally you may check the reference list of publications which contains a lot of (English) publications valuable to read to understand the thesis without being able to read the German text. You may also check the English abstract.
Be careful with academic papers: you will find a lot of HighTech-statements, but usually you cant use the methods industrially - evaluation of the methods often only with a limited set of samples not imaging industrial conditions and usually the scientist knows well where the simulated defect is located - so he can easily optimize his set-up. I personally do not trust - by experience - papers from Universities or Research Institutes if I don't know any industrial (big) partner. Even SMEs tell a lot....

You may check with companies like OLYMPUS, GE, Tecnatom, AREVA, PAR etc. as they build the inspection machines for Lockheed Martin, Boeing, Airbus.
There are some papers from FACC about this topic too - FACC in Austria put a lot of money into R&D in Austria to optimize their NDT - interestingly FACC works as well for Boeing as for Airbus, so they have access to both worlds, as you may see in their papers: they cite the inspection procedures from both worlds (Airbus AITM6-0011 / Boeing BAC5980)- refer to e.g. http://projects.npl.co.uk/vitcea/docs/20150217-bam-workshop-facc.pdf

Finally I can recommend this Boeing paper - https://www.boeing.com/resources/boeingdotcom/features/innovation-quarterly/nov2017/btj_nde_full.pdf. Why? The "ACKNOWLEDGMENT"-Paragraph list all important NDT-Researchers from Boeing, so if you check those names for papers and patents you get a nice overview about Boeings NDT - as in the us patents are easier to get compared to Europe, the tendency is bigger in the US to protect their IP with patents. Not all are really worth and solid enough, but it clearly gives a good insight what is their range of developments. I found in the past a lot of interesting topics. By the was Google patent search is a powerful tool to access the original patent documents.

By the way - in may last post it should be 6mm or 1/4" min defect diameter to detect in production.

    
 
 Reply 
 
Smit
Engineering,
Tata Lockheed Martin Aerostructure Limited, India, Joined Nov 2011, 8

Smit

Engineering,
Tata Lockheed Martin Aerostructure Limited,
India,
Joined Nov 2011
8
05:04 Apr-25-2019
Re: Single porosity detection
In Reply to J.B. at 17:00 Apr-24-2019 .

yes you are absolutely right about situation here as you faced 40 years back.They are fresh team and not ready to understand that 1/4" will be minimum criteria for detectability.

Anyhow it has been a great learning from your last articles you shared.As i can see that it will take time to go through the articles again but i am sure will be a great learning .

Thanks a lot for the conclusion & shared data. I am going to remember you for this much help & surely get back to you for other expert opinion.

    
 
 Reply 
 

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