Element library#

femorph-solver ships a library of structural finite elements. Each element is built from published FEM theory (textbook / journal citations on its theory page). Element names are topology-first and vendor-neutral — HEX8, HEX20, TET10, BEAM2, QUAD4_SHELL, etc. Foreign-deck spellings (e.g. MAPDL SOLID185, NASTRAN CHEXA, Abaqus C3D8) are translated to these neutral names at each interop boundary; every internal call- site sees only the neutral form.

Correctness is verified against two independent evidence sources: analytical / textbook closed-form solutions (tests/analytical/) and migration-safety agreement with established commercial solvers on shared benchmarks. Commercial solvers are yardsticks for migration safety, not a source of implementation detail.

Pick an element by dimension and kinematics:

Element

Kind

Notes

TRUSS2

3D 2-node truss

Axial only; 3 DOF/node.

SPRING

3D 2-node spring

Longitudinal mode; 3 DOF/node.

POINT_MASS

1-node point mass

Translational-only (3 DOF/node).

BEAM2

3D 2-node Euler–Bernoulli beam

6 DOF/node; axial + torsion + two bending planes.

QUAD4_PLANE

2D 4-node quad

2 DOF/node; plane stress / plane strain.

QUAD4_SHELL

4-node Mindlin shell

Selective reduced integration; drilling stabilisation.

HEX8

3D 8-node hex

2×2×2 Gauss; B-bar / enhanced-strain options.

HEX20

3D 20-node serendipity hex

Reduced 2×2×2 stiffness with Irons 14-point mass; degenerate WEDGE15 and PYR13 auto-dispatched.

TET10

3D 10-node tet

4-point Keast Gauss (both K and M).

Registry and dispatch#

Element classes register into femorph_solver.elements and are discovered by their neutral kernel name:

from femorph_solver.elements import get, registered

registered()
# ['BEAM2', 'HEX20', 'HEX8', 'POINT_MASS', 'PYR13', 'QUAD4_PLANE',
#  'QUAD4_SHELL', 'SPRING', 'TET10', 'TRUSS2', 'WEDGE15']

hex_kernel = get("HEX8")

The native API (femorph_solver.Model.assign()) takes a typed ELEMENTS spec rather than a string:

import femorph_solver as fs
model = fs.Model.from_grid(grid)
model.assign(fs.ELEMENTS.HEX8, {"EX": 2.1e11, "PRXY": 0.30, "DENS": 7850.0})
model.assign(
    fs.ELEMENTS.HEX8(integration="enhanced_strain"),
    {"EX": 2.1e11, "PRXY": 0.30, "DENS": 7850.0},
)

Foreign-deck readers (femorph_solver.interop.mapdl.from_cdb(), femorph_solver.interop.nastran.from_bdf(), femorph_solver.interop.abaqus.from_inp()) translate their respective catalogue names into the neutral kernel names above before the model is constructed.

Every element class implements the ElementBase interface — ke() for stiffness, me() for mass, optional ke_batch() / me_batch() for vectorised assembly.