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# afallah's blog

## end of file error during read text file

Sat, 2015-09-19 03:27 - afallahDear friends,

I'm working on multiscale modeling of connective soft tissues. To this end, I employed abaqus to do computational homogenization. I faced with surprising problem during my research.

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## Plane stress formulation of hyperelastic material

Sat, 2015-03-07 02:38 - afallahHi

I'm looking for good refrences for plane stress formluation of transvesrly isotropic hyperelastic materials (imcompressible). I'm wondering if someone help me and introduce some usefull material about it.

Kind Regards

Ali

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## Using different types of stress rates in ABAQUS UMAT

Tue, 2015-01-27 03:23 - afallahDear friends,

As you maybe know, ABAQUS uses the Jaumann or Green-Naghdi stress rate for large deformation analysis. Recently i found some refrences that show these stress rates leads to major errors for some special cases. Now my question is, how can I change the stress rate used in analysis process using ABAQUS UMAT?

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## Periodic boundary condition on non-rectangular RVE

Sun, 2014-10-05 10:03 - afallahDear friends,

Hi. I'm working on multiscale modeling of soft tissues. For micromechanical modeling of the tissue i consider an RVE with sinusoidal edges as figure 1.

I imposed periodic boundary conditions on the RVE using corner nodes as master nodes and define the displacement of the other nodes on the boundary related to these master nodes displacements using constraint equations as figure 2.

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## jacobian matrix caculation

Sun, 2014-09-07 07:38 - afallahDear friends

Hi. I'm working on multiscale modeling of soft tissues. In my research I faced with a problem about computing the jacobian matrix in ABAQUS UMAT. In my model the material properties are function of external parameter like ef (ef is kind of strain and obtained from loading conditions) and relation between the "ef" and the strin in the model in unkown. Now, i want to calculate the jacubian matrix for this material, as you konw, the jacobian is defined as delta_sigma/delta_epsilon.

I have two question;** **

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## element coordinate system orientation after nonlinear static structural solution

Wed, 2014-05-28 08:18 - afallahHi. I'm working on multiscale modeling of soft tissues. I'm working

on modeling an orthotropic wavy fiber in WB. I write an APDL routine to

change the element coordinate system of each element with accordance to

the fiber curvature. Ansys documentation said that in the case of large

deflection analysis, the element coordinate system will be rotated with

accordance to element rigid body rotation. My problem is that, after the

solution, the elements coordinate system of some elements rotate

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