You are correct that specific names need to be used for the different types of strain (invariants). This is a good reminder we need to write a manual section about this, but below are some brief answers.
I tried with total_strain, but I am not sure how to output the value in the postprocess.
The strain invariants are tracked on fields or particles (user selects), and to access these values in the solution file one simply has to look at the corresponding compositional field or particle values.
I used particles and in the particle properties, I used intergrated strain invariant. However, it give me an error said no total_strain field.
Yes, depending on what strain weakening mechanisms you select, you need to use specific names for the corresponding fields.
Details of this are in the following file from lines 185-256.
What may be even more useful is to look at existing examples, such as the continental extension cookbook or the tests listed below (found using
ls *weakening*.prm in the tests folder). These tests should illustrate the proper variables to set for any combination of strain weakening.
I am using visco-plastic material model. I try to run a model without weakening mechanism, but still want to track the finite strain invariant.
You can do this by setting the weakening factors for the friction, cohesion, and/or prefactor viscosity to 1.
the start and end plasticity strain weakening intervals are the accumulated plastic strain, not the plastic strain within dt?
Yes, exactly. They represent the values of the plastic (or other strain) where weakening (linear) begins and ends.
For the output variables, I used named additional outputs, is the plastic strain in the output the accumulated strain?
If you are using field to advect properties, the accumulated plastic strain values will be located in a field value (i.e., in the vtk file) named
The additional plastic outputs option will give the cohesion and friction angle at every point. If you set the weakening factors to 1, these latter values should be the same as the values you set in the .prm file.
I hope this helps!