Save, read and download stiffness values

In this tutorial, we will see how we can write and read stiffness data to/from text files, and take advantage of the Materials Project to automatically fetch data from its online database.

Read & write files

Write stiffness to file

To save a given stiffness tensor to a plain text file, just use the save_to_txt() command. For instance:

>>> from Elasticipy.FourthOrderTensor import StiffnessTensor
>>> C = StiffnessTensor.cubic(C11=186, C12=134, C44=77, phase_name='Cu')
>>> C.save_to_txt('Stiffness_Cu.txt')

By default, the file will contain the stiffness matrix, and additional data as well (symmetry and phase name). To save the matrix only, just use the option matrix_only=True.

Load stiffness from file

To read entries from an existing text file, just run StiffnessTensor.from_txt_file(<file_path>). Using the example above:

>>> StiffnessTensor.from_txt_file('Stiffness_Cu.txt')
Stiffness tensor (in Voigt notation) for Cu:
[[186. 134. 134.   0.   0.   0.]
 [134. 186. 134.   0.   0.   0.]
 [134. 134. 186.   0.   0.   0.]
 [  0.   0.   0.  77.   0.   0.]
 [  0.   0.   0.   0.  77.   0.]
 [  0.   0.   0.   0.   0.  77.]]
Symmetry: cubic

Download data from the Materials Project

The Materials Project (MP) contains various data about plenty materials, and stiffness values for some of them. They can be directly reached in Python thanks to the MP API, which is already implemented in Elasticipy.

Requirements

To be able to fetch data from MP, you need to register first, then get an API key. This may be accessible on your dashboard, and may look like this:

Ag5Kljg5iGcZ45mJ7bC7T9q4L56KgBcZ

In Python, you will need to install mp_api, for instance with PIP:

pip install mp_api

Fetching data from materials names

On MP, each material is given a unique name, like mp-xxx (where xxx is a number). Given this name, one can import the stiffness tensor (if available). For instance, to fetch data for mp-1048 (monoclinic TiNi):

>>> api_key = '<Your API key>'
>>> StiffnessTensor.from_MP("mp-1048", api_key=api_key)
Stiffness tensor (in Voigt notation) for TiNi:
[[231. 127. 104.  -0. -18.   0.]
 [127. 240. 131.  -0.   1.   0.]
 [104. 131. 175.  -0.  -3.  -0.]
 [ -0.  -0.  -0.  81.  -0.   3.]
 [-18.   1.  -3.  -0.  11.   0.]
 [  0.   0.  -0.   3.   0.  85.]]
Symmetry: Monoclinic

Note

In order to avoid passing the api_key as an argument, you can also define an environment variable, named MP_API_KEY and containing the proper string value.

Instead of a single material name, a list of material IDs can be passed to from_MP(); in this case, the function will return a list of stiffness tensors. If a material is not found (or if no data about the elastic properties are available), the corresponding stiffness tensor will be None.