problem with saint_venant_kirchhoff model

[Sad-Abd]

Hi @adtzlr,
I was working with saint_venant_kirchhoff model and figured out it does not yield expected answers. Then I tried the Lab module to illustrate material performance, but I encountered errors, only for saint_venant_kirchhoff model, while other models was working smoothly.

Here is my code:

from matadi import Lab, MaterialHyperelastic
from matadi.models import saint_venant_kirchhoff


mat = MaterialHyperelastic(
    saint_venant_kirchhoff, 
    mu = 5.1,
    lmbda = 171.5
)

lab = Lab(mat)
data = lab.run(
    ux=True, 
    stretch_min=1.0, 
    stretch_max=2.0, 
)
fig, ax = lab.plot(data, stability=True)

and the error mention that there is a singular matrix that can not get inverted.

[adtzlr]

Hi,

and thanks for reporting. I'll have a look in a few hours.

[adtzlr]

Sounds great!

Sorry not to assist more but I have some other paper in the pipeline with figures which would definitely help but I can't share them yet.

About the stretch range: Yes, you're right. And that value is different for the load cases. So it would be better to analyze only one load case in the Lab.

For the non-zero value at the undeformed state: That is definitely a bug - could be related to the conversions from the invariants (Green-Lagrange strain invariants to right Cauchy-Green deformation tensor invariants).

[Sad-Abd]

#137 will solve the problem entirely, and the Lab also works fine 👍

[adtzlr]

Thanks for figuring that out. Before merging #137 I'll check whats wrong with dot().

[adtzlr]

New release 0.1.21 is on PyPI, thanks for your contribution!

[Sad-Abd]

I just added my two cents, and it was more like pocket change! 😄