calculix-fem

CalculiX FEM

CalculiX (ccx) is an open-source FEM solver (GPLv2, no license). It reads Abaqus-style .inp decks and writes text .dat results plus .frd field output. ccx returns exit code 0 even on *ERROR, so never judge success by the exit code — the solver layer checks stdout for *ERROR and requires a data row in the .sta.

When to Use

Use this skill when an agent must run an open-source linear-static FEA analysis on CalculiX: parse/inspect a .inp deck, tune section/material/load parameters, solve with ccx, read .dat results, or export a viewer-renderable result. For commercial solvers (Abaqus/Ansys), use those solvers' own skills instead.

Workflow

1. fea_health — confirm meshio is available and ccx is detected.
2. parse_inp — inspect the .inp (nodes, elements, sections, materials, loads).
3. list_design_vars_tool — list tunable variables; each carries a var_id.
4. modify_card_tool — change a variable by var_id (pure-text, in place).
5. run_solver_tool — submit the deck to ccx.
6. read_results_tool — read max von Mises (self-computed), max |U|, volume, mass.
7. export_results_tool — write result_mesh.json for the viewer.

Rules

• Units follow the .inp working system (commonly mm-t-s-MPa). Report them.
• .dat has no von Mises column and no total volume/mass — these are derived.
• Never rewrite a deck with meshio.write (it drops cards and corrupts element types). Use modify_card_tool.
• For the deck to produce both text results and the field output the viewer needs, include *NODE PRINT/*EL PRINT (for .dat) and *NODE FILE/*EL FILE (for .frd).

Example

MCP/CalculiX/examples/cantilever.inp is a public cantilever benchmark (steel C3D8 solid bar, clamped end, transverse tip load). Hand-calc targets at P = 100 N: tip deflection ≈ 0.8 mm, root stress ≈ 140 MPa.