Calculating the Poisson's for a material ratio using percentages of strain at break.

[Sarah800]

Hello

I have been provided a data sheet for laser-sintered polyamide. It had the values for percentages of axial and transverse strain at break.
I have tested the mechanical properties of the actual material, but i want to calculate the Poisson's ratio using the provided values in the data sheet for computational FEA.
I want to make sure that by dividing the proivided transverse strain at break by the axial strain at break, i will get the Poisson's ratio for the laser-sintered polyamide.

Thank you

 

[CoryPad]

Poisson's ratio is for elastic strain, so if there is any plastic strain in the material at break, then the calculated ratio will be wrong.

 

[btrueblood]

Poisson's ratio can be described for any material, plastic or elastic deformation, it's just a ratio of strains. The value for most materials in their elastic range (metals, polymers like PA) is typically about 0.3, and increases to around 0.5 in post-yield or plastic deformation regimes; so as Cory says, the value estimated from a heavily yielded fracture sample will likely not have the same ratio as it would in elastic deformation.

 

[Compositepro]

I don't think the strain ratios in the data sheet have anything to do with Poissons's ratio. It is simply an artifact of the manufacturing process that the strengths are different in the two directions.

 

[chicopee]

Is that laser sintered polyamide a brittle material?