where expertise comes together - since 1996 -

The Largest Open Access Portal of Nondestructive Testing (NDT)

Conference Proceedings, Articles, News, Exhibition, Forum, Network and more

where expertise comes together
- since 1996 -

1567 views
Technical Discussions
Chirag
India, Joined Aug 2015, 17

Chirag

India,
Joined Aug 2015
17
13:53 Oct-19-2015
Back wall echo higher than front wall echo

Hi,

I was just trying out a few things with the olympus phased array scan. I was testing CFRP laminates and noticed that in most of the laminates the back wall echo is higher than the front wall echo. is this possible? And the distance between the front wall and back wall echo should give me the thickness (i think) but i have noticed an offset of around 1.5 mm. can anyone let me know why?

Thanks and Regards
Chirag

2
 
 Reply 
 
Tom Nelligan
Engineering,
retired, USA, Joined Nov 1998, 390

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
15:44 Oct-19-2015
Re: Back wall echo higher than front wall echo
In Reply to Chirag at 13:53 Oct-19-2015 (Opening).

You didn't indicate what probe you are using, but if it includes a straight plastic "wedge" as is usually the case, then what you see with respect to amplitude ratios is normal. Plastic wedges or delay lines represent a fairly close impedance match to typical carbon fiber composites, so there is relatively little reflection from the front surface when well coupled, and if the composite isn't too thick then there is relatively little signal loss across the sound path in the test material. Thus, the backwall echo from an air boundary (with essentially 100% reflection of energy) can easily be larger than the front surface echo from a plastic/composite boundary where there is a close impedance match.

Regarding the apparent thickness measurement error, you haven't provided any information about how you calibrated your instrument, and incorrect velocity/zero calibration is the most common cause of an offset. Other possibilities include significant phase distortion or localized velocity variations in the test material, but those are less likely.

3
 
 Reply 
 
chirag
India, Joined Aug 2015, 17

chirag

India,
Joined Aug 2015
17
15:53 Oct-20-2015
Re: Back wall echo higher than front wall echo
In Reply to Tom Nelligan at 15:44 Oct-19-2015 .

Hi Tom, thanks for your reply.. the probe i used was straight plastic wedge. so in case i didnt use a plastic wedge i would get a higher front wall reflection right?
I dont think the calibration is done for the instrument. I will calibrate and then check if the error comes again.. Thanks again!!

1
 
 Reply 
 
Tom Nelligan
Engineering,
retired, USA, Joined Nov 1998, 390

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
16:04 Oct-20-2015
Re: Back wall echo higher than front wall echo
In Reply to chirag at 15:53 Oct-20-2015 .

If you do not use a straight wedge or delay line, you will not see a distinct front surface reflection since it will occur within the excitation pulse ringdown envelope.

2
 
 Reply 
 

Product Spotlight

Conformable wedge transducer

The conformability is obtained with a flexible membrane filled with water between the transducer and
...
the inspected component. The coupling between the membrane and the component requires a small quantity of water or couplant. The conformable wedge combines the acoustic performance of immersion technique with good coupling and low attenuation.
>

CIVA 2020 UT Module

CIVA NDE Simulation Software is the world leader of NDT Simulation. The UT simulation Module incl
...
udes: - "Beam computation": Beam propagation simulation - "Inspection Simulation": Beam interaction with flaws or specimens The user can simulate a whole inspection process (pulse echo, tandem or TOFD) with a wide range of probes (conventional, Phased- arrays or EMAT), components, and flaws.
>

Research Center IDEKO develops an ultrasonic train wheel inspection system for CAF

The Basque Research centre IK4-IDEKO has developed a state-of-the-art ultrasonic inspection system f
...
or the train wheel. This system secures a sound condition of train wheels and is thus a significant contribution to rail transport safety. The device was delivered to CAF recently and its use allows the manufacturer to become an approved supplier of rolling stock in Italy, as it meets the demanding homologation standards of this country. \\\\r\\\\n
>

NDTkit RT

NDTkit RT, TESTIA's Digital Radiography software The NDTkit product line software for X-ray analysi
...
s. NDTkit RT is a software benefiting from the Ultis kernel which is dedicated to radiographic image analysis. It offers a set of tools and filtering processes to assist RT operators in finding relevant flaws.
>

Share...
We use technical and analytics cookies to ensure that we will give you the best experience of our website - More Info
Accept
top
this is debug window