Poisson's ratio of 0.5

[bethluxmoore]

Hi all

I want to model a part of my model with incompressible material properties. I had initially thought that a Poisson's ratio of 0.5 would return an error and so assumed Nu=0.4999. However when I later tried Nu=0.5 the model ran with no errors and the deformation patterns that were seen for the incompressible material were significantly different.

Does anyone know why there is such a significant change between Nu=0.4999 and Nu=0.5? I assume that for Nu=0.5 a different algorithm is used. Is this correct? Any ideas as to what is going on here?

Many thanks for any thoughts or ideas!

 

[simen999]

Hi, I would first check what element is used for your analysis. If you have an poisson`s ratio of (or closed to) 0.5 you need to take an element with mixed aproaches. An element that is just based on displacements will not give you convergence. A mixed Element (for example Hu-Washizu) is an element that is based on displacement and stress and/or stain. That element can handle poisson`s ratio of 0.5.

regards
Grischa

 

[biomechanist]

Hi, I guess it very much can depend on your problem and meshing, element disortion and other parameters. For Nu=0.5 you may need to use different elements (like hybrid elements). These differences may lead to a bit of difference in the outcomes. But as far as I had the experience with my models so far, the differences were not significant (something less than 5%).