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# positive definite stiffness matrix

## Positive definite stress-strain matrix in Ansys

Fri, 2011-04-22 08:36 - muhendismrt

Dear friends,

I'm an MSc. student at Bogazici University, Turkiye and I'm working on a thesis project about the failure behaviour of fiber reinforced laminated composite plates under different loading types. The material which we use are AS4 fiber reinforced prepregs and their mechanical properties are the following:

E11 =134,000 MPa

E22 = E33= 9480 MPa

G12 = G13= 5490 MPa

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## Positive definite stress-strain matrix

Fri, 2011-04-22 08:06 - muhendismrtDear friends,

I'm an MSc. student at Bogazici University, Turkiye and I'm working on a thesis project about the failure behaviour of fiber reinforced laminated composite plates under different loading types. The material which we use are AS4 fiber reinforced prepregs and their mechanical properties are the following:

E11 =134,000 MPa

E22 = E33= 9480 MPa

G12 = G13= 5490 MPa

G23 MPa =3272

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## Elastic Material Constants Question

Sun, 2010-06-06 16:55 - ahmed.husseinI have a very basic question regarding anisotropic materials elastic constants.

The elastic constants must satisfy the condition of the positive definiteness of the stiffness matrix so that the strain energy is guaranteed to be positive for any strain state. However, are there any extra conditions on these constants ?

In particular, can we have a material with shear stiffness higher than the normal stiffness even if the stiffness matrix is still positive definite ?

If so, is there any physical explanation, on the microlevel or something, for this phenomenon ?

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