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Poisson NU=0.5 error (ERROR 3203)

Genius
Genius

Hi, I am analysing an elastomer sample in a static linear simulation (SOL101). The material model is a linear isotropic model with E=2.5 MPa and NU=0.5.

However when I try to run, I get the following error messages:

NASTRAN Msg: *** USER WARNING MESSAGE 2251 (IFS1P)
ONE OR MORE MAT1 ENTRIES HAVE UNREASONABLE OR INCONSISTENT VALUES OF 
E,G OR NU. ID OF FIRST ONE = 1
NASTRAN Msg: *** USER WARNING MESSAGE 2251 (IFS1P)
THE NUMBER OF MAT1 ENTRIES HAVING UNREASONABLE OR INCONSISTENT VALUES 
FOR E,G AND/OR NU IS 1
NASTRAN Msg: *** USER FATAL MESSAGE 3203 (EMG)
AN ILLEGAL VALUE OF -NU- HAS BEEN
NASTRAN Msg: *** USER FATAL MESSAGE 3203 (EMG)
AN ILLEGAL VALUE OF -NU- HAS BEEN
NASTRAN Msg: *** USER FATAL MESSAGE 3203 (EMG)
AN ILLEGAL VALUE OF -NU- HAS BEEN

[and so on...]

Obviously the problem is the poisson ratio = 0.5. Indeed if i put NU=0.499, the simulation work properly. How do I solve it? Regards, A.

3 REPLIES 3

Re: Poisson NU=0.5 error (ERROR 3203)

Gears Phenom Gears Phenom
Gears Phenom

FEA solvers don’t like fully incompressible materials with NU = 0,5. There is rule of thumb to use NU = 0,495...0,499 for elastomers.

With NU = 0,5 your bulk modulus K become infinite and solver cannot handle with infinite values. In addition, you can face with hourglassing effect.

https://www.quora.com/What-is-the-hourglass-effect-in-finite-element-analysis-How-does-the-reduced-i...

Re: Poisson NU=0.5 error (ERROR 3203)

Solution Partner Valued Contributor Solution Partner Valued Contributor
Solution Partner Valued Contributor

@AlbertoM,

If modeling elastomer, I'd suggest you use a proper material law - hyperelastic material available in a bunch of solutions (e.g. 106,601,701,402...)

In that case, you'd still not specify and infinite bulk modulus, but a bulk ~10-100 times your shear.

Hope that helps,

Jacques

FYI. Your poisson ratio bounds must be -1<v<0.5

Re: Poisson NU=0.5 error (ERROR 3203)

Genius
Genius

@JacquesL, can you suggest me some references/videos/tutorials to learn about the simulation of elastomers using NX Nastran?