Creating materials with poissons ratio higher than 0.5

[seraphi]

Hi there,
As the subject describes, i need help with creating a material that has a Poisson's ratio that is higher than 0.5. In this case 0.77, carbon fiber. I'm sure its easy but i'm quite new to abaqus and would appreciate any help. Thanks.

 

[seraphi]

Does no one know how to do it at all? i'd really appreciate some help.

 

[Jessika]

hi
can you lear for me what is your problem to model and whether you work with explicit or standar abaqus then would know how to answer

 

[DBen]

Hi,
There is a problem with your question.
Thermodynamicaly speaking, it is impossible to have a Poisson's ratio higher than 0.5 (included) or lower than -1 (excluded). If so, your material would have a non convex energy function.

The 0.5 maximum value is reached for incompressible material (such as rubber).

A Poisson's ratio higher would imply a negative lambda coefficient (First Lame coefficient) and a negative dilatation coefficient. It means that your material has a decreasing volume when heated and an increasing volume under pure compressive pression. Both are highly improbable.

If you insist with your 0.77 value, you will have to deal with an non convex energy, it means that your mechanical solution is not unique (for a single value of stress, several values of strain are solution or sideways). ABAQUS deals with that kind of problem with the explicit algorithm or a buckling analysis but I don't think there is a material that allow a 0.77 Poisson's ratio.

 

[MechIrl]

@DBen - This is true for isotropic materials. With anisotropy, such as in carbon fibre composites, there can be effectively >0.5 poissons ratios in certain directions.

@seraphi - You should model your material as a composite layup in Abaqus and not simply an isotropic material.

 

[Jessika]

@MechTrl -thats right he might work with anisotropy