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Technical Discussions
augereau
augereau
07:39 Jan-03-2005
comparison of young's modulus measured by tensile tests and ultrasounds

Dear All,
I am looking for references on the comparison of the values of the young's modulus obtained by tensile test, flexural methods and so on, versus ultrasonic echography.
For the moment, I got a 5 and 10% disperancy between my ultrasonic measurements and classic mechanical data on 6061t6 and ag3 aluminium alloys?????


 
 Reply 
 
Godfrey Hands
Consultant,
PRI Nadcap, United Kingdom, Joined Nov 1998, 304

Godfrey Hands

Consultant,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
304
04:20 Jan-04-2005
Re: comparison of young's modulus measured by tensile tests and ultrasounds
----------- Start Original Message -----------
: Dear All,
: I am looking for references on the comparison of the values of the young's modulus obtained by tensile test, flexural methods and so on, versus ultrasonic echography.
: For the moment, I got a 5 and 10% disperancy between my ultrasonic measurements and classic mechanical data on 6061t6 and ag3 aluminium alloys?????
------------ End Original Message ------------

Hi,
Tensile tests will let you determine the Youngs Modulus of a sample in a condition of plastic deformation.
Sound Velocity based techniques (Flexural and Ultrasonic) will determine the elastic constants under elastic deformation, which is closer to the real life situation.

Quasar International in the USA (+1 505 247 9660, contact Kim Johnson) manufactures and markets an instrument (called the RU-Spec) which determines the elastic constants of solids with a claimed accuracy of better than 0.1%.

NDT Consultants markets this same instrument for Quasar in the United Kingdom and large parts of Europe.
Contact us for more information. (+44 2476 511 151 or email to Godfrey@ndt-consultants.co.uk).

Regards,

Godfrey Hands




 
 Reply 
 
Robert Paynter
Robert Paynter
09:23 Jan-04-2005
Re: comparison of young's modulus measured by tensile tests and ultrasounds
: Godfrey Hands wrote:
> Tensile tests will let you determine the Youngs Modulus of a sample in a condition of plastic deformation.

That's not really the case, is it? If you don't load
the material past its yeild stress then - it's elastic.
The real challenge is to measure the (very small)
elastic deformation as you load it. To get over that
you might try flexure tests to get large deflections
for small strains.

Robert Paynter

Oxford UK


 
 Reply 
 
M. Kim Johnson
M. Kim Johnson
00:09 Jan-04-2005
Re: comparison of young's modulus measured by tensile tests and ultrasounds
Actually, most tensile tests for Young's modulus measure the *static* modulus. I believe the desire here is to measure the *dynamic* modulus which is what Robert and Godfrey are speaking of. I believe this is a simple matter of semantics, as they say. And, that is what the Quasar instrument does - it determines the static modulus by resonating a known shape/mass sample at very low amplitudes (on the order of 10 nm - not anywhere near enough to cause plastic deformation). Multiple resonant frequencies are measured and compared with analytic calculations for what the resonances should be. The elastic constants are then varied in the software to find the best fit between measured and calculated resonances. The elastic constants are then used to calculate Young's Modulus along with other constants of interest (Shear Modulus, Poisson's Ratio, etc.)

For a well made sample lacking any physical defects, extraordinarily accurate results are obtained - sometimes to better than 0.1% if one is inclined to make the near perfect test sample. Half a percent is usually adequate and is easily obtained for most all common crystaline structures. (Metals are generally treated as isotropic for samples greater than a few mm on a side.)

It is usually the dynamic modulus that people wish to use in making calculations. If you need to measure this, and wish more details, please see http://www.quasarintl.com/ruspec/ruspec.html.

M. Kim Johnson
Quasar International, Inc.
5550 Midway Park NE
Albuquerque, NM 87109

505 247-9660
kim@quasarintl.com

----------- Start Original Message -----------
: : Godfrey Hands wrote:
: > Tensile tests will let you determine the Youngs Modulus of a sample in a condition of plastic deformation.
: That's not really the case, is it? If you don't load
: the material past its yeild stress then - it's elastic.
: The real challenge is to measure the (very small)
: elastic deformation as you load it. To get over that
: you might try flexure tests to get large deflections
: for small strains.
: Robert Paynter
: Oxford UK
------------ End Original Message ------------




 
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