Look at the NodalValueSamplervectorpostprocessor and see if you can use its "block" parameter to output the pillars_normal_lm variable on the pillars_secondary_subdomain subdomain.

Add the following block to the step02.i input

[VectorPostprocessors]
  [normal0]
    type = NodalValueSampler
    variable = pillars_normal_lm
    block = pillars_secondary_subdomain
    sort_by = id
    execute_on = 'INITIAL TIMESTEP_END'
  []
[]

In the [Outputs] block add the csv = true parameter. Run the input and you should end up with the new output file step02_out_normal0_0000.csv through step02_out_normal0_0010.csv (one output for each time step plus one for the initial condition).

In the CSV files you will find multiple columns. The rows are ordered according to node ID, which should result in a continuous path along the mortar subdomain. You can also order the rows by any coordinate component.

In the same directory as the tutorial inputs you will find a small python script to plot the contact pressure (using matplotlib and pandas). It should serve as a starting point for custom plot generation.

Note that since we did not explicitly request the NodalValueSampler to use the displaced mesh with use_displaced_mesh = true the coordinates in the CSV file refer to the undeformed positions along the contact surface.

Try increasing the "end_time" to 10 and replot the contact pressures with the supplied script.