# stressMask meaning in class PeriTriaxController

Asked by Rong Zhao on 2019-08-27

I want to know how stressMask in in class PeriTriaxController control stress or strain along three axis.

I guess I should convert the value of stressMask to the value of binary system first, then I can decide which axis direction is controlled by stress via 1 or strain via 0.

Take doc/sphinx/tutorial/06-periodic-triaxial-test.py as a example, the stressMask = 7, the coresponding binary is 111, so both three axis directions is controled by stress.
I am not sure wherther I understand the stressMask's meaning right?
Could you give me a detail explanation and whether there is a possible range (0~7) for the choice of the value of stressMask in class PeriTriaxController.

Thank you very much!

## Question information

Language:
English Edit question
Status:
For:
Assignee:
No assignee Edit question
Last query:
2019-08-27
2019-08-27
 Jérôme Duriez (jduriez) said on 2019-08-27: #1

Hi,

Everything you said is correct, so I guess you almost understood stress masks, congratulations !
In order to nail it down once for all (hopefully) and understand more complex cases than the isotropic 111 = 7, let say that

stressMask = a*2^0 + b*2^1 + c*2^2 = a + 2b + 4c, with a,b,c = 0 or 1.

Then a corresponds to x direction (direction "0"),
b corresponds to y direction (direction "1"),
and c corresponds to z direction (direction "2")

and the 0/1 values tell you whether each direction is strain (0) or stress (1)-controlled.

And, as you said, the range of possible values for a + 2b + 4c, with a,b,c = 0 or 1, indeed goes from 0 to 7.