Replace I2-Invariant in isotropic hyperelastic materials

adtzlr / matadi

Material Definition with Automatic Differentiation

GNU General Public License v3.0

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Replace I2-Invariant in isotropic hyperelastic materials #15

Closed adtzlr closed 3 years ago

adtzlr commented 3 years ago

I2 is not trace(C @ C), it's (trace(C)**2 - trace(C @ C)) / 2 (the second invariant from the characteristic polynomial) for invariant based material formulations.

[x] Mooney-Rivlin
[x] Third-Order-Deformation