poisson's ratio

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.

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

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

compression?

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

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

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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

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Thank you JV.