Question about the source codes of LAM-submodel

[Weisserlinks]

Dear Pybamm team,

may I ask one question about the codes of the stress-driven LAM model:
stress_h_surf = (stress_r_surf + 2 * stress_t_surf) / 3
stress_h_surf *= stress_h_surf > 0
stress_h_surf_min = stress_h_surf * 0
j_stress_LAM = ( -beta_LAM * ((stress_h_surf - stress_h_surf_min) / stress_critical) ** m_LAM )
According to the literature stress_h_surf should be the maximal hydrostatic stress. How could it be calculated in this way? Why stress_h_surf multiplied itself?

Thanks a lot!

[brosaplanella]

In the docs for the loss of active material model you can find the references where the models are defined, which should provide more details about why the stress is defined this way.

[valentinsulzer]

It is not multiplied by itself, it is multiplied by (stress_h_surf > 0) i.e. no stress if it's negative.
The maximum hydrostatic stress is hard to define numerically (leads to issues in the jacobian), which is why we assume it's the surface value