Skip to content

Conversation

@mvanzulli
Copy link
Member

@mvanzulli mvanzulli commented Feb 3, 2023

Closes #599
Deploy: docs

Just a detail: PR number = 600 💯 🚀 🤓

@mvanzulli mvanzulli requested a review from jorgepz February 3, 2023 23:36
@mvanzulli mvanzulli marked this pull request as ready for review February 3, 2023 23:36
@mvanzulli
Copy link
Member Author

mvanzulli commented Feb 3, 2023

I have solved the problem considering different neo-Hookean models but I couldn't find the one who gives me the cosserat stress tensor implemented in ONSAS. I have tried with:

$$\Psi(\mathbf{C}) = \frac{\mu}{2} (I_1 - 3) - \mu \ln(J) + \frac{\lambda}{2} \ln(J)^2,$$

and

$$\Psi(\mathbf{C}) = \frac{\mu}{2} (I_1 - 3 - 2\ln(J))$$

Here are some useful identities that I have used:

$$\mathbf{S} = 2 \frac{\partial \Psi }{ \partial \mathbf{C} }$$ $$\frac{\partial tr(\mathbf{C})}{\partial \mathbf{C}} = \mathbf{I}\\$$$$ $$\frac{\partial det(\mathbf{C})}{\partial \mathbf{C}} = det( \mathbf{C} ) \mathbf{C}^{-T}$$

Ohh I think I found it:

$$\Psi(\mathbf{C}) = \frac{\mu}{2}(I_1 -3) + 1/D (J -1)^2$$

then Cosserat is:

$$\mathbf{S} = 2 \frac{\partial \Psi }{\partial \mathbf{C}} = \mu (I_{3,3}) + \frac{2}{D}(J-1) J C^{-T}$$

but in ONSAS we have:

S       = shear * ( eye(3) - invC ) + bulk * ( J * (J-1)* invC) ;

with $K(bulk) = D/2$
@jorgepz ?

@jorgepz
Copy link
Member

jorgepz commented Feb 4, 2023

Excellent! You found the strain energy function, it is the isotropic term in Equation 2 in this paper.

To obtain the cosserat derivative it could be useful to see that

$$det(C) = J^2$$

mvanzulli and others added 10 commits February 4, 2023 11:36
Co-authored-by: Jorge Pérez Zerpa <42485529+jorgepz@users.noreply.github.com>
Co-authored-by: Jorge Pérez Zerpa <42485529+jorgepz@users.noreply.github.com>
Co-authored-by: Jorge Pérez Zerpa <42485529+jorgepz@users.noreply.github.com>
Co-authored-by: Jorge Pérez Zerpa <42485529+jorgepz@users.noreply.github.com>
Co-authored-by: Jorge Pérez Zerpa <42485529+jorgepz@users.noreply.github.com>
@mvanzulli mvanzulli merged commit eb98e6f into master Feb 4, 2023
@mvanzulli mvanzulli deleted the mvanzulli/UniaxialCompression branch February 4, 2023 15:53
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Labels

None yet

Projects

None yet

Development

Successfully merging this pull request may close these issues.

Add uniaxial compression into docs

3 participants