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Orthotropic Material Properties error


Orthotropic Material Properties error

I have a user who is running structural analysis using Orthotropic
materials properties to represent different carbon fiber composites.
When he runs an analysis using the latest data from the manufacturer, he
gets the following error: "The material properties are not physically
possible because deformation of the material would result in negative
strain energy. This error is usually caused by entering incorrect
Poisson's ratio data. See the online help for more details". In the
online help, it tells me that the 6x6 stiffness matrix needs to have a
positive definite determinant. As an admin, it's been a very long time
since I did any engineering calculations never mind figured out a
stiffness matrix. Could anyone help translate this into an explanation
of what might be wrong with these properties?

I've attached images of 2 orthotropic material definitions. The first
one works, the second one doesn't.

Any help is highly appreciated!

Abby Dawkins
MCAD Support
KLA-Tencor Corp

Material below works...

Material below does not work...

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5-Regular Member


in your "does not work" material, you have a poisson's ratio of 0.68 ! crazy ! is that a typo or really what the manufacturer claims ? fea has problems with values greater than 0.5 because values for the moduli need to be positive.

hope that helps.

ray miya

you can set possion's ratio less than 0.5

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