This records activates calculation of invariants of strains and stresses. Here unknown can be one of the matrices -materi_stress, -materi_strain_elasti, -materi_strain_plasti, -materi_strain_total or unknown can be one of the vectors -materi_velocity, -materi_displacement.
The results of these calculations are stored for each node_dof record in a node_dof_calcul record, and are stored for each post_point_dof record in a post_point_dof_calcul record, and are stored for each post_line_dof record in a post_line_dof_calcul record, and are stored for each post_quadrilateral_dof record in a post_quadrilateral_dof_calcul record.
We denote a matrix unknown with Aij and denote a vector unknown with Ai.
If operat is -prival then three principal values of a matrix Aij are calculated. Each principal value contains the size of the principal vector. The principal values are ordered (the first value is the largest one, and the last value is the smallest one).
If operat is -privec then three principal vectors of a matrix Aij are calculated. Each principal vector contains the x, y and z component of the principal vector. The same ordering as used for -prival is used here also.
If operat is -average then
is calculated for a matrix
or
is calculated for a vector.
If operat is -positive then the average of the positive principal values for a matrix is calculated. If materi_strain_plasti is taken for the matrix Aij, then this operator typically can be used as a measure for the amount of tensile failure (cracking).
If operat is -negative then the average of the negative principal values for a matrix is calculated. If materi_strain_plasti is taken for the matrix Aij, then this operator typically can be used as a measure for the amount of compression failure (crunching).
If operat is -size then
is calculated for a matrix or
is calculated for a vector.
This measures the size of a matrix or the size of a vector.
If operat is -sizedev then
is calculated
where Bij is the deviatoric part of a matrix Aij:
where
is 1 if i=j and is 0 otherwise.
This measures the size of the deviatoric part of the matrix.
Specially for geotechnics you can set operat to -phimob in case unknown is -materi_stress. Then the 'mobilised friction angle' is calculated in degrees.
The next piece of input file
...
materi_stress
materi_strain_plasti
end_initia
...
post_calcul -materi_stress -sizedev -materi_strain_plasti -size
...
control_timestep 1 ...
control_print 1 -node_dof_calcul
will print records like
node_dof_calcul index 0.2 1.1e-4
Here the 0.2 is the equivalent Von Mises stress and 1.1e-4 measures the plastic strain matrix.