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 Airstar Inc.Application of the newest technologies, such as air-coupled ultrasound, digital instrumentation, signal processing, and transducer technology.
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Technical Discussions
Tony Martland
, Joined ,
03:09 Sep-24-2002

Hello

Can anybody help me ? I am trying to find out how to calculate the particle velocity of a longitudinal wave in a solid. I am applying the wave by means of a transducer, into mild steel, and I know the wavespeed in the mild steel (5900 m/s) but how do I calculate the actual particle velocity.

ANY help would be much appreciated.

Thanks

Tony

Paul A. Meyer
R & D,
GE Inspection Technologies, USA, Joined Nov 1998, 47

Paul A. Meyer

R & D,
GE Inspection Technologies,
USA,
Joined Nov 1998
47
06:15 Sep-24-2002
Hi Tony,
The particle velocity is proportional to the ratio of the sound pressure to the acoustic impedance. You know the acoustic impedance but the sound pressure is a function of the transducer design, the driving pulse, and the coupling conditions, making it very difficult to determine. If you have access to a KLM transducer model, you can perhaps estimate the sound pressure in the steel.
Paul
: Hello
.
: Can anybody help me ? I am trying to find out how to calculate the particle velocity of a longitudinal wave in a solid. I am applying the wave by means of a transducer, into mild steel, and I know the wavespeed in the mild steel (5900 m/s) but how do I calculate the actual particle velocity.
.
: ANY help would be much appreciated.
.
: Thanks
.
: Tony
.

luis marques
refinery inspector
petrogal, Portugal, Joined Jul 2002, 5

luis marques

refinery inspector
petrogal,
Portugal,
Joined Jul 2002
5
06:50 Sep-24-2002
It depends on what kind of apparatus you are using. Simple digital ultrasonic equipment such as a Krautkramer DM4 will do what you want. With this equipment if you do not know the sound velocity in the medium you are scanning, you just need a calibration block of a known thickness and same material, you want to scan. In these calibration conditions the equipment will display automatically the sound velocity.

Regards

Luis

Joe Buckley, Sonatest Plc
Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT, United Kingdom, Joined Oct 1999, 526

Joe Buckley, Sonatest Plc

Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT,
United Kingdom,
Joined Oct 1999
526
07:21 Sep-24-2002
This is one that could 'get extremely silly'
remember that:

1. The net value of the particle velocity is zero - They dont move, just oscillate about a fixed point (thats why its solid)

2. The bulk properties of the material (Youngs modulus etc) are not necessarily appropriate things to use when you get to the atomic level.

3. You cant necessarily assume a sine wave or anything like that, so building up a theoretical model will be quite complex -

May be worth asking exactly what is it you 'really' want to know?

Joe

: Hi Tony,
: The particle velocity is proportional to the ratio of the sound pressure to the acoustic impedance. You know the acoustic impedance but the sound pressure is a function of the transducer design, the driving pulse, and the coupling conditions, making it very difficult to determine. If you have access to a KLM transducer model, you can perhaps estimate the sound pressure in the steel.
: Paul
: : Hello
: .
: : Can anybody help me ? I am trying to find out how to calculate the particle velocity of a longitudinal wave in a solid. I am applying the wave by means of a transducer, into mild steel, and I know the wavespeed in the mild steel (5900 m/s) but how do I calculate the actual particle velocity.
: .
: : ANY help would be much appreciated.
: .
: : Thanks
: .
: : Tony
: .
.

Pierre Marty
R & D
Saab Aeronautic, Sweden, Joined Jul 2002, 5

Pierre Marty

R & D
Saab Aeronautic,
Sweden,
Joined Jul 2002
5
04:02 Sep-26-2002
HI Tony

A possible way is to use a dynamic Finite Element Model. It is not so difficult to estimate the profile of the sound pressure at the interface betrween the transducer and the sample, so that you can model the system with a good accuracy.
If you have any mean (laser probe ?9 to measure the displacement at the outer surface of the transducer and if you assume a good coupling between the transducer and the sample than the FE method will give you a fair estimation of the particle displacement in the bulk of the steel sample. The limits of such aproach are those of the FE method and of your own assumptions in term of displacement profile and magnitude at the surface of the transducer.

I beleive commercial FE programs such as ANSYS, PZFLEX can do that. IF you need contact me for more info on that subject. I did some similar models myself with another FE code.

Pierre

: Hello
.
: Can anybody help me ? I am trying to find out how to calculate the particle velocity of a longitudinal wave in a solid. I am applying the wave by means of a transducer, into mild steel, and I know the wavespeed in the mild steel (5900 m/s) but how do I calculate the actual particle velocity.
.
: ANY help would be much appreciated.
.
: Thanks
.
: Tony
.

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