|
|
| Author |
Message |
Riccardo Balistrerri
science forum beginner
Joined: 19 Apr 2006
Posts: 11
|
 Posted: Tue May 23, 2006 10:20 am Post subject:
poisson's ratio
|
|
|
Dear all,
As Poisson's ratio regards the material properties... is it valid for both
compression and extention? I've seen that in most of the tests to determine
it on a material the sample is pulled... how about compression?
regards,
R. |
|
| Back to top |
|
 |
Tom Sanderson
science forum addict
Joined: 22 Dec 2005
Posts: 55
|
| Posted: Tue May 23, 2006 4:03 pm Post subject:
Re: poisson's ratio
|
|
|
"ri" <riccardo.balistreri@poste.it> wrote:
| Quote: | As Poisson's ratio regards the material properties... is it valid for both
compression and extention? I've seen that in most of the tests to
determine it on a material the sample is pulled... how about compression?
|
For normal isotropic materials it's about the same. For composites and
non-linear stuff that's not always true.
Tom. |
|
| Back to top |
|
|
Riccardo Balistrerri
science forum beginner
Joined: 19 Apr 2006
Posts: 11
|
| Posted: Wed May 24, 2006 12:06 am Post subject:
Re: poisson's ratio
|
|
|
"Tom Sanderson" <tdscanuck@yahoo.com> wrote in message
news:Izq7A0.2IC@news.boeing.com...
| Quote: | "ri" <riccardo.balistreri@poste.it> wrote:
As Poisson's ratio regards the material properties... is it valid for
both compression and extention? I've seen that in most of the tests to
determine it on a material the sample is pulled... how about compression?
For normal isotropic materials it's about the same. For composites and
non-linear stuff that's not always true.
Tom.
Interesting, but then let's say I want to test for example thick paper, like |
for the carton box, let's say even thicker to .2 inches, shall I pull the
sample or compress it, and does it make sense this parameter on orthotropic
materials like paper... same thing about the elastic modulus, does it make
sense?
Thank you very much Tom,
Ri. |
|
| Back to top |
|
|
Tom Sanderson
science forum addict
Joined: 22 Dec 2005
Posts: 55
|
| Posted: Wed May 24, 2006 1:31 pm Post subject:
Re: poisson's ratio
|
|
|
"ri" <riccardo.balistreri@poste.it> wrote:
| Quote: | Interesting, but then let's say I want to test for example thick paper,
like for the carton box, let's say even thicker to .2 inches, shall I pull
the sample or compress it, and does it make sense this parameter on
orthotropic materials like paper... same thing about the elastic modulus,
does it make sense?
|
It does make sense but, since it's an anisotropic material, you need to
determine the Poisson's Ratio and Young's Modulus for each axis
independantly. For 0.2" paper, I'm guessing you're actually talking about
corrugated, as opposed to really thick cardboard. Corrugated has other
wierd properties due to it being, structurally, a skin-stringer panel. I
would expect the properties to be different in compression than in tension,
so to fully charachterize a material like that I think you'll have to do
compression and tension testing along each axis.
FYI, if you're working with corrugated, the packaging industry has probably
done all this testing already. Some phone calls and/or Googling might turn
up some data.
Good luck,
Tom. |
|
| Back to top |
|
|
Riccardo Balistrerri
science forum beginner
Joined: 19 Apr 2006
Posts: 11
|
| Posted: Thu May 25, 2006 12:18 am Post subject:
Re: poisson's ratio
|
|
|
"Tom Sanderson" <tdscanuck@yahoo.com> wrote in message
news:IzruwG.4L6@news.boeing.com...
| Quote: | "ri" <riccardo.balistreri@poste.it> wrote:
Interesting, but then let's say I want to test for example thick paper,
like for the carton box, let's say even thicker to .2 inches, shall I
pull the sample or compress it, and does it make sense this parameter on
orthotropic materials like paper... same thing about the elastic modulus,
does it make sense?
It does make sense but, since it's an anisotropic material, you need to
determine the Poisson's Ratio and Young's Modulus for each axis
independantly. For 0.2" paper, I'm guessing you're actually talking about
corrugated, as opposed to really thick cardboard. Corrugated has other
wierd properties due to it being, structurally, a skin-stringer panel. I
would expect the properties to be different in compression than in
tension, so to fully charachterize a material like that I think you'll
have to do compression and tension testing along each axis.
FYI, if you're working with corrugated, the packaging industry has
probably done all this testing already. Some phone calls and/or Googling
might turn up some data.
Good luck,
Tom.
Actually is thick paper... used in loudspeakers... high power ones. Gets |
from .07 in (2mm) to .2 (6mm) in an average product. The problem is that if
fibers do have an orientation, then the difficulty is also to find it. I
think also that the thicker the product, less is a pattern of orientation.
Is not like some kind of paper products that you can tear them apart and
see a pattern (like tissue paper). Lets say I could measure them along the
correct axis, have the parameters, for compression and tension. Is there any
kind of simulation program that is able to work with similar materials? I
know many are able to work with non linear, but I don't know of any that
accepts the 3d proprieties of a material for simulation. I know
superficially Mark, Adina, Ansys, Opera... Does Abaqus does it?
Thank you |
|
| Back to top |
|
|
Riccardo Balistrerri
science forum beginner
Joined: 19 Apr 2006
Posts: 11
|
| Posted: Thu May 25, 2006 12:18 am Post subject:
Re: poisson's ratio
|
|
|
"Tom Sanderson" <tdscanuck@yahoo.com> wrote in message
news:IzruwG.4L6@news.boeing.com...
| Quote: | "ri" <riccardo.balistreri@poste.it> wrote:
Interesting, but then let's say I want to test for example thick paper,
like for the carton box, let's say even thicker to .2 inches, shall I
pull the sample or compress it, and does it make sense this parameter on
orthotropic materials like paper... same thing about the elastic modulus,
does it make sense?
It does make sense but, since it's an anisotropic material, you need to
determine the Poisson's Ratio and Young's Modulus for each axis
independantly. For 0.2" paper, I'm guessing you're actually talking about
corrugated, as opposed to really thick cardboard. Corrugated has other
wierd properties due to it being, structurally, a skin-stringer panel. I
would expect the properties to be different in compression than in
tension, so to fully charachterize a material like that I think you'll
have to do compression and tension testing along each axis.
FYI, if you're working with corrugated, the packaging industry has
probably done all this testing already. Some phone calls and/or Googling
might turn up some data.
Good luck,
Tom.
Actually is thick paper... used in loudspeakers... high power ones. Gets |
from .07 in (2mm) to .2 (6mm) in an average product. The problem is that if
fibers do have an orientation, then the difficulty is also to find it. I
think also that the thicker the product, less is a pattern of orientation.
Is not like some kind of paper products that you can tear them apart and
see a pattern (like tissue paper). Lets say I could measure them along the
correct axis, have the parameters, for compression and tension. Is there any
kind of simulation program that is able to work with similar materials? I
know many are able to work with non linear, but I don't know of any that
accepts the 3d proprieties of a material for simulation. I know
superficially Mark, Adina, Ansys, Opera... Does Abaqus does it?
Thank you |
|
| Back to top |
|
|
Tom Sanderson
science forum addict
Joined: 22 Dec 2005
Posts: 55
|
| Posted: Thu May 25, 2006 2:02 pm Post subject:
Re: poisson's ratio
|
|
|
"ri" <riccardo.balistreri@poste.it> wrote:
| Quote: | Actually is thick paper... used in loudspeakers... high power ones. Gets
from .07 in (2mm) to .2 (6mm) in an average product. The problem is that
if fibers do have an orientation, then the difficulty is also to find it.
|
You might be able to derive it from the manufacturing process...probably
need to talk to the paper supplier to get that.
| Quote: | I think also that the thicker the product, less is a pattern of
orientation.
|
That might be true, but they might also build the thickness up from lots of
thinner wet sheets, each of which would have an orientation. You could tune
the speaker response that way, I suspect, but then you'd have to anaylyze
the cone as a laminate of serveral fiber layers with different orientations.
| Quote: | Lets say I could measure them along the correct axis, have the parameters,
for compression and tension. Is there any kind of simulation program that
is able to work with similar materials?
|
I know Patran/Nastran can do it...not sure about others, since I don't do
FEA that much.
Tom. |
|
| Back to top |
|
|
Juan Vazquez
science forum beginner
Joined: 18 Apr 2005
Posts: 12
|
| Posted: Thu May 25, 2006 2:11 pm Post subject:
Re: poisson's ratio
|
|
|
"Tom Sanderson" <tdscanuck@yahoo.com> escribió en el mensaje
news:Izq7A0.2IC@news.boeing.com...
| Quote: | "ri" <riccardo.balistreri@poste.it> wrote:
As Poisson's ratio regards the material properties... is it valid for
both
compression and extention? I've seen that in most of the tests to
determine it on a material the sample is pulled... how about
compression?
For normal isotropic materials it's about the same. For composites and
non-linear stuff that's not always true.
|
I would like to add which seems to be a technicality, because since I read
this thread a few days ago, I was left with some uneasiness.
IMO an isotropic material is just a model, defining a material that has the
same properties along any axis.
That's a characteristic of "homogeneous" materials, which actually do not
exist.
Materials are not "continuous". They are composites of crystals, grains,
molecules, etc.
I can't remember if the definition of isotropy includes the extension and
compression behaviour, but it should.
Having included that in the definition, for isotropic materials the
Poisson's ratio in extension and in compression is exactly the same.
It happens that there are some materials which behave that way or closely
and for those materials the Poisson's ratio in extension and in compression
it's about the same. This is characteristic of materials which do not have
appreciable oriented "constituents", grains, crystals, etc.
My two cents,
JV
--
To e-mail me substitute "_"s by "e" and "c". |
|
| Back to top |
|
|
Riccardo Balistrerri
science forum beginner
Joined: 19 Apr 2006
Posts: 11
|
| Posted: Fri May 26, 2006 12:27 am Post subject:
Re: poisson's ratio
|
|
|
"Juan Vazquez" <jdepetar_@_antv.net> wrote in message
news:e54dv3$qm7$1@newsreader.mailgate.org...
| Quote: | "Tom Sanderson" <tdscanuck@yahoo.com> escribió en el mensaje
news:Izq7A0.2IC@news.boeing.com...
"ri" <riccardo.balistreri@poste.it> wrote:
As Poisson's ratio regards the material properties... is it valid for
both
compression and extention? I've seen that in most of the tests to
determine it on a material the sample is pulled... how about
compression?
For normal isotropic materials it's about the same. For composites and
non-linear stuff that's not always true.
I would like to add which seems to be a technicality, because since I read
this thread a few days ago, I was left with some uneasiness.
IMO an isotropic material is just a model, defining a material that has
the
same properties along any axis.
That's a characteristic of "homogeneous" materials, which actually do not
exist.
Materials are not "continuous". They are composites of crystals, grains,
molecules, etc.
I can't remember if the definition of isotropy includes the extension and
compression behaviour, but it should.
Having included that in the definition, for isotropic materials the
Poisson's ratio in extension and in compression is exactly the same.
It happens that there are some materials which behave that way or closely
and for those materials the Poisson's ratio in extension and in
compression
it's about the same. This is characteristic of materials which do not have
appreciable oriented "constituents", grains, crystals, etc.
My two cents,
JV
--
To e-mail me substitute "_"s by "e" and "c".
I agree that materials have this non continuities, but that's in the |
microscopic... in the macroscopic these factors statistically compensate
themselves giving the material it's proprieties. Anomalies like big size
grains fractures etc. make the material "defective" and is hopefully not
utilized.
But what interests me is that poisson ratio is for isotropic materials same
for compression and extension. Do you think it could be assumed that an
orthotropic material that presents itself in randomly orienteded fibers
could be reputed for big size (were the size of the piece makes it's fiber's
size irrelevant, let's say at least 0.01% of any dimention of the sample) as
an isotropic material for simulation?
Thank you |
|
| Back to top |
|
|
Juan Vazquez
science forum beginner
Joined: 18 Apr 2005
Posts: 12
|
| Posted: Wed May 31, 2006 3:11 am Post subject:
Re: poisson's ratio
|
|
|
"ri" <riccardo.balistreri@poste.it> escribió en el mensaje
news:447a544e$1_2@news.tm.net.my...
| Quote: |
But what interests me is that poisson ratio is for isotropic materials
same
for compression and extension. Do you think it could be assumed that an
orthotropic material that presents itself in randomly orienteded fibers
could be reputed for big size (were the size of the piece makes it's
fiber's
size irrelevant, let's say at least 0.01% of any dimention of the sample)
as
an isotropic material for simulation?
|
I think the Poisson ratio should be the same in extension and compression
for isotropic materials, particularly if they are ductile, which tend to
behave the same in both ways until plastic failure.
OTH, I think that an "orthotropic" material, with small random oriented
fibres, would not behave "orthotropically". I believe that isotropy is a
behaviour related to homogeneity, orientation and size of constituents
("fibres").
To be sure, the best thing to do is conduct laboratory tests according to
ASTM standards (for example). I remember having seen a Standard on
evaluation of Poisson ratio on the ASTM manuals, but I can't recall if there
was anything regarding extension-compression behaviour.
JV
To e-mail me substitute "_"s by "e" and "c". |
|
| Back to top |
|
|
Riccardo Balistrerri
science forum beginner
Joined: 19 Apr 2006
Posts: 11
|
| Posted: Thu Jun 01, 2006 12:11 am Post subject:
Re: poisson's ratio
|
|
|
"Juan Vazquez" <jdepetar_@_antv.net> wrote in message
news:e5j1hn$5a9$1@newsreader.mailgate.org...
| Quote: |
"ri" <riccardo.balistreri@poste.it> escribió en el mensaje
news:447a544e$1_2@news.tm.net.my...
But what interests me is that poisson ratio is for isotropic materials
same
for compression and extension. Do you think it could be assumed that an
orthotropic material that presents itself in randomly orienteded fibers
could be reputed for big size (were the size of the piece makes it's
fiber's
size irrelevant, let's say at least 0.01% of any dimention of the sample)
as
an isotropic material for simulation?
I think the Poisson ratio should be the same in extension and compression
for isotropic materials, particularly if they are ductile, which tend to
behave the same in both ways until plastic failure.
OTH, I think that an "orthotropic" material, with small random oriented
fibres, would not behave "orthotropically". I believe that isotropy is a
behaviour related to homogeneity, orientation and size of constituents
("fibres").
To be sure, the best thing to do is conduct laboratory tests according to
ASTM standards (for example). I remember having seen a Standard on
evaluation of Poisson ratio on the ASTM manuals, but I can't recall if
there
was anything regarding extension-compression behaviour.
JV
Thank you JV. |
|
|
| Back to top |
|
|
Google
|
|
| Back to top |
|
|
|
|
The time now is Thu Jan 08, 2009 11:24 pm | All times are GMT
|
|
MPAA | Cell Phones | The Best Myspace Layouts | Credit Card Consolidation | Mobile Phones
|
|
Copyright © 2004-2005 DeniX Solutions SRL
|
|
Other DeniX Solutions sites:
Electronics forum |
Medicine forum |
Unix/Linux blog |
Unix/Linux documentation |
Unix/Linux forums
|
Powered by phpBB © 2001, 2005 phpBB Group
|
|
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
Forum index
»
Science and Technology
»
Engineering
»
Mechanics
