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Hi-Spec Systems
we are specialised in the design, development and manufacture of Phased Array and Time-of-Flight Diffraction (ToFD) ultrasonic inspection systems.
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Technical Discussions
Lirin Philip
,
VALDEL , India, Joined Sep 2019, 10

Lirin Philip

,
VALDEL ,
India,
Joined Sep 2019
10
06:01 Sep-10-2019
UT TESTING -VELOCITY OF MATERIAL

As know material velocity is property of material its depend on density and Poisson ratio,so its should be same for all the probes,e,g we using CFRP composite material velocity is 2800 m/sec,
we doing thickness calibration of laminate e.g 3 mm plate ,with 5MHz ,getting velocity 2800 m/sec,when we try with 2.25MHz for same thickness velocity found 2400 m/sec,its varring with probes frequency as we know velocity of material ,should be constant for all probes.

 
 Reply 
 
Edward Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1300

Edward Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1300
14:02 Sep-10-2019
Re: UT TESTING -VELOCITY OF MATERIAL
In Reply to Lirin Philip at 06:01 Sep-10-2019 (Opening).

Lirin, although 400m/s seems to be a rather high difference if the samples were tested in the same orientations, indeed some materials can be dispersive. By this we mean that the phase velocity is dependent on frequency. (See https://en.wikipedia.org/wiki/Acoustic_dispersion
and the reference #2 in that URL to the paper by Ping for how it is measured).
Your CFRP materials add to the complexities by their anisotropic characteristics.

Was there a question in your posting?

 
 Reply 
 
Wieslaw Bicz
Engineering,
PBP Optel sp. z o.o., Poland, Joined Feb 2009, 276

Wieslaw Bicz

Engineering,
PBP Optel sp. z o.o.,
Poland,
Joined Feb 2009
276
15:44 Sep-10-2019
Re: UT TESTING -VELOCITY OF MATERIAL
In Reply to Lirin Philip at 06:01 Sep-10-2019 (Opening).

Ed can be correct with the assumption, but there could be another reason: The method, how the signal is evaluated to get the information about the time of flight and - as result - about the thickness. We are delivering since many years systems, that measures - among other parameters - material thickness and sound speed in different materials. Based on huge experience with very different applications and conditions I would assume, that the method of measuring time of flight can be the reason. If you calibrate with one frequency and measure with other this can be the main reason. I do not know, what device you are using, and how it is working, but I would assume, that this is a very realistic reason.

 
 Reply 
 
Lirin Philip
,
VALDEL , India, Joined Sep 2019, 10

Lirin Philip

,
VALDEL ,
India,
Joined Sep 2019
10
06:01 Sep-11-2019
Re: UT TESTING -VELOCITY OF MATERIAL
In Reply to Wieslaw Bicz at 15:44 Sep-10-2019 .

Sir, we are using Omni scan SX 16:64 by olympus. We are using Pulse echo method.

 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 805

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
805
19:20 Sep-11-2019
Re: UT TESTING -VELOCITY OF MATERIAL
In Reply to Lirin Philip at 06:01 Sep-11-2019 .


You need to use external UT pulser with oscilloscope to take velocity measurement.

 
 Reply 
 
Wieslaw Bicz
Engineering,
PBP Optel sp. z o.o., Poland, Joined Feb 2009, 276

Wieslaw Bicz

Engineering,
PBP Optel sp. z o.o.,
Poland,
Joined Feb 2009
276
15:18 Sep-12-2019
Re: UT TESTING -VELOCITY OF MATERIAL
In Reply to Lirin Philip at 06:01 Sep-11-2019 .

I have not enough experience with it to be able to tell, how you device is processing data. Measuring sound speed (time of flight)or thickness requires in all cases where accuracy is important some signal analysis. Ultrasonic signal is namely never a Dirac delta, but always much more complicated. To determine, when the signal arrived (what was the time of flight) requires some assumptions, especially in the case, if the signal is changing its form due to attenuation (higher frequencies are attenuated stronger than lower). It is naturally possible to solve the problems connected with such measurements, but it requires sometimes some relatively sophisticated procedures. I assume, that in your case the material is relatively strongly attenuating, but without experience with your case and equipment I am not able to tell more.

 
 Reply 
 
Joe Buckley
Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT, United Kingdom, Joined Oct 1999, 528

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT,
United Kingdom,
Joined Oct 1999
528
16:21 Sep-12-2019
Re: UT TESTING -VELOCITY OF MATERIAL
In Reply to Lirin Philip at 06:01 Sep-10-2019 (Opening).

What procedure are you using to measure the velocity?

3mm CFRP is only 2-3 wavelengths thick at 2.2MHz, It can be very difficult to get an accurate measurement on materials this thin in relation to the wavelength unless you are very careful about measurement points. most calibration routines are set up assuming a much longer path.

A good check would be to measure the velocity for a piece of steel - around 6-8mm thick (so about the same transit time.) and confirm you get consistent velocity at the two frequencies.

 
 Reply 
 
Wieslaw Bicz
Engineering,
PBP Optel sp. z o.o., Poland, Joined Feb 2009, 276

Wieslaw Bicz

Engineering,
PBP Optel sp. z o.o.,
Poland,
Joined Feb 2009
276
13:42 Sep-13-2019
Re: UT TESTING -VELOCITY OF MATERIAL
In Reply to Joe Buckley at 16:21 Sep-12-2019 .

If the thickness will be 3 mm, frequency 2.25 MHz and sound speed 2800 m/s the distance must be counted double and in wave lengths it will be around 5 (the thickness must be counted double). Using transducer with short signal such thickness can be quite easily calculated with relatively simple procedures.

 
 Reply 
 
J.B.
J.B.
17:14 Sep-18-2019
Re: UT TESTING -VELOCITY OF MATERIAL
In Reply to Edward Ginzel at 14:02 Sep-10-2019 .

By no way the speed of sound in CFRP is constant 2800m/sec.
The material is anisotropic, and behaves in each direction different.
The fibers have their own speed - We measured it together with a lot of other material parameters years ago in specific CFRP sample having completely unidirectional laminate (lot of unidirectional tape layers to get something like a big black brick). In that case the speed of sound in fiber direction was 9000m/sec, perpendicular to fibers it was 3000m/sec. and perpendicular to those both directions it was 2900m/sec. In fiber direction we got a second pulse around 2500m/sec resulting from the resin/epoxy. So the sound speed is a function of Fiber/Resin ratio, which can be different in each dimension. Be aware this depends also from the frequency used as you have to deal with dispersion! (Ed explained it)
Forget everything you may have learned from inspecting isotropic material. Take into account small fiber waviness, microcracking in the interfaces of Resin and Fiber, which comes after first time loading of a FRP-Structure (If you do Acoustic Emission you can hear this if you cycle a fresh CFRP structure the first time, it's a settling of the fibers to reduce inner strain). So this affects also sound transmission. other effects are adding too…
A fabric laminate is different from one made of unidirectional tape, even if tape layers are varying in directions.

 
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