Orthotropic material and its stiffness matrix

[VincentDG]

I'm implementing an elastic orthotropic material. When checking the compliance matrix, it is not positive definite (but it is symmetric). Is this to be expected in some cases? If so, when?

Thanks.

 

[MartinShane]

I don't believe so.
Positive Definite compliance matrix is a necessary condition for maintaining positive strain energy.

 

[IceBreakerSours]

Or, at least, positive semi-definite.

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[VincentDG]

@MartinShane: thanks for confirming my initial thoughts. I'll check everything again (and again) ...