Reduce a solved FERS document to the plate numbers an engineer actually reads, and derive extreme-fibre stresses. READ-ONLY: it returns a summary, not a model.

You need this because plate results cannot be read back through the model. The mesh is generated on an internal working copy, so the returned document has model.plate_elements = [] and plate_surfaces[].generated_plate_element_ids = [], and the mesh node ids in displacement_nodes have no coordinates anywhere in model.nodes. The only georeferenced plate output is results.<case|combination>.plate_results, keyed by element id, carrying centroid {X,Y,Z}, centroid_displacement_global/local and the stress resultants.

UNITS AND CONVENTION, from the engine's own denormalisation: nx, ny, nxy, qx, qy are membrane forces and transverse shears per unit width, in force/length (N/m); mx, my, mxy are moments per unit width, in force (N.m/m, numerically N). mx is the moment PRODUCING sigma_x (conjugate to curvature about local y), not "the moment about x" — on a rectangular slab spanning the short way with local_x along the long side, the large resultant is my. The sign of mx/my/mxy follows the element normal, which follows the boundary/connectivity ordering, so reversing it flips all three; von Mises and |principal| are immune. qx and qy are identically ZERO for Kirchhoff/DKT plates by construction, so non-zero transverse shear is itself proof the Mindlin element was used. results..summary.total_plate_forces is a COUNT of plate results, not a force.

Give thickness and the tool derives the extreme-fibre stresses exactly as the engine's own plate unity check does: sigma_x = nx/t +/- 6mx/t^2, sigma_y = ny/t +/- 6my/t^2, tau_xy = nxy/t +/- 6mxy/t^2, evaluated at both fibres with the governing (larger von Mises) one reported, then vonMises = sqrt(sx^2 - sx.sy + sy^2 + 3txy^2) and the in-plane principals. Add yield_stress for a utilisation.