Calculating engineering strain from Green-Lagrange strain

[Arulmurugan Senthilnathan]

Hello, 

The output file "stressstrain.txt" reports the Green-Lagrange strain tensor, but I need engineering strain values, and I am doing uniaxial tension simulations.

In the tutorial video, Dr. Yaghoobi mentions that "To generate the engineering strain from Green-Lagrange strain, in case of uniaxial load, we know that we are applying the increment strain of 1x10-5. So, we add that value to all Green-Lagrange strain values."

Can you please explain where are we applying the increment strain of 1x10^-5 and why that value?

In the following website, under the uniaxial tension tab, the value of 1x10^-5 is not applied to calculate engineering strain: https://www.continuummechanics.org/greenstrain.html. However, I am not sure if this website is right. Can you please let me know how to calculate the engineering strain from the Green-Lagrange strain tensor? Thank you very much!

Regards,

Arul.

 

[Chaitali Patil]

Hi, Arulmurugan

1. Can you please explain where are we applying the increment strain of 1x10^-5 and why that value?
The value comes according to the simulation set up in the input files. Assuming you are referring to  PRISMS-Plasticity: Session04 (Output Files) video tutorial, the final displacement was setup to 0.01 in total time of 5 with time increment of 0.005.  Thus, strain increment in each time step is (0.01/5)*0.005=1e-5.  Reza might be in better position to explain the addition of the strain increment, but I hope the  above answer help your initial query. 
2. The website you mentioned correctly explains the green tensor . The most simple approach to get different strain measures would be to output the deformation gradient along with Fe values and postprocess according to required definitions of strain tensor.

-Regards,

Chaitali