Author Topic: Output elastic deformation gradient for fcc crystal of different orientation  (Read 216 times)

Haomin

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Dear all,

I want to get the elastic deformation gradient for fcc crystal with different orientations along z direction via OVITO.

I use elastic strain calculation modifier and select input crystal as face-centered cubic. Two different crystal orientations of (001) and (110) in z-axis are used for the calculation before applying external load.

When I check the elastic deformation gradient, it returns the value:[1 0 0, 0 0.7 0.7, 0 -0.7 0.7] for (110) orientation, [1 0 0, 0 1 0, 0 0 1] for (001) orientation.

It seems that when mapping the current configuration with the fcc structure catalog(stress-free configration), crystal with different orientation is considered to have rotation from (100) direction and it is counted into the elastic deformation gradient.

I want to get rid of the orientation effect on the calculation of elastic deformation gradient. Is there any ways that I can edit the fcc structure catalog? Any suggestion is appreciated.

Thanks,
Haomin


Alexander Stukowski

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Hi Haomin,

I can confirm that the elastic deformation gradient computed by this function of OVITO contains the rigid-body rotations of the crystal and the reference orientation for the cubic lattices is hard-coded to be [100] pointing along x and [001] pointing along z.

OVITO currently does not provide an option for the user to change the reference orientation. But it shouldn't be a big problem to work around that limitation. You simply need to multiply the elastic deformation gradient tensor computed by OVITO with a rotation matrix of your choice (from the right).

Performing this matrix multiplication can be accomplished using OVITO's Python modifier facility (if you want to do it within OVITO). Just a few lines of Python code should be sufficient. Are you familiar with Python/Numpy programming?

Regards,
Alex

Haomin

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Hi Dr. Stukowski,

Thanks for your reply.

Since you confirm that the reference orientation for the cubic lattices is hard-coded to be [100] pointing along x and [001] pointing along z, I am wondering for the hcp lattice, what would be the orientation?

And you're right. The limitation could be solved by multiplying a rotation matrix. I am not quite familiar with  Python/Numpy programming, but I think I can perform that multiplication in MATLAB.

Many thanks for you suggestions!

Haomin

Alexander Stukowski

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The reference orientation for hexagonal crystal lattices (HCP, hex diamond) is the following:

The z-axis of the Cartesian reference frame is oriented along the crystal's c-axis. The x-axis points along one of the six neighbor vectors in the basal plane.

I will try to add this information to the user manual when I find some time.