Element library
ModelCraft's finite element library (crates/fem), family by family, with status. The scope is
modelled on what a full CAE code offers (Abaqus's element library is the reference for breadth);
names, formulations and tests are our own, written from the published literature. Deck writers map
each of our elements to each solver's name (see crates/decks). Simple elements first: 1D and 2D,
then shells, special-purpose and multiphysics elements.
Status: done (on main, verified against analytic solutions), in progress (an agent task is
open), planned.
Every element builds on the shared foundation of docs/fem.md: it declares its nodal degrees of
freedom (DofKind: translations, rotations, temperature, pressure) and condensed internal ones
(ElementDofs), the solvers number them with DofLayout, and its interpolation comes from the
shape-function library (Basis: line2/3, tri3/6, quad4/8/9, tet4/10, wedge6/15, pyramid5,
hex8/20/27 with first and second derivatives).
Point and discrete elements
| Element |
Use |
Status |
| Point mass |
Lumped mass at a node or reference point (isotropic or per direction) |
done (implicit, explicit; Abaqus MASS, Nastran CONM1, LS-DYNA ELEMENT_MASS; per direction: Nastran only) |
| Rotary inertia |
Inertia tensor at a 6-DOF node |
done (implicit; Abaqus ROTARYI, Nastran CONM1, LS-DYNA ELEMENT_INERTIA; explicit when it has rotations) |
| Spring to ground / two-point spring |
Linear spring in a fixed direction or along the line of nodes |
done (implicit, explicit translational; Abaqus SPRING1/2/A, Nastran CELAS2, LS-DYNA ELEMENT_DISCRETE; skew fixed directions: LS-DYNA only) |
| Dashpot to ground / two-point |
Linear viscous damper (dynamic steps; ignored in static) |
done (explicit; ignored with a warning in static and frequency steps; Abaqus DASHPOT1/2/A, Nastran CDAMP2, LS-DYNA ELEMENT_DISCRETE) |
| Nonstructural mass |
Mass spread over a region without stiffness |
planned |
| Connectors |
Kinematic joints (hinge, slot, universal…) with elasticity, damping, stops |
planned (M7) |
1D elements
| Element |
Use |
Status |
| Truss, 2-node (2D and 3D) |
Axial members, cables (compression allowed) |
done (rod2: implicit, in plane models with their two unknowns per node; explicit, corotational under nonlinear geometry; Abaqus T3D2 / T2D2, Nastran CROD, LS-DYNA truss beam (3D models)) |
| Truss, 3-node (2D and 3D) |
Curved axial members |
done (rod3: implicit, plane models too; explicit with small displacements; Abaqus T3D3 / T2D3; no Nastran or LS-DYNA counterpart) |
| Beam, 2-node Timoshenko, 3D |
Frames, stiffeners; shear deformable |
done (exact interdependent interpolation, profile properties, orientation vector; modelcraft_fem::beam) |
| Beam, 2-node Euler–Bernoulli (cubic), 2D and 3D |
Slender frames; exact for end-loaded prismatic members |
planned (1D elements II) |
| Beam, 3-node Timoshenko (quadratic), 2D and 3D |
Curved and stocky beams |
planned (1D elements II) |
| Beam, 2D (planar frames) |
In-plane frames with 3 DOFs per node |
planned (1D elements II) |
| Pipe / elbow |
Pipes with internal pressure, ovalisation |
planned (1D elements II) |
| Open-section beams with warping |
Thin-walled sections in torsion |
planned |
| Rebar / stringers |
Reinforcement along edges or embedded |
planned |
2D elements
| Element |
Use |
Status |
| Plane stress tri3, tri6, quad4, quad8 |
Thin plates loaded in their plane |
in progress (2D elements) |
| Plane strain tri3, tri6, quad4, quad8 |
Long sections (dams, tunnels, extrusions) |
in progress (2D elements) |
| Axisymmetric tri3, tri6, quad4, quad8 |
Revolved solids (shafts, vessels, discs) |
in progress (2D elements) |
| Incompatible-mode and reduced-integration quads |
Bending-accurate and cheap variants |
in progress (2D elements) |
| Generalized plane strain |
Plane strain with a free out-of-plane strain |
planned |
| Axisymmetric with twist |
Revolved parts under torsion |
planned |
| Axisymmetric shells (2-node, 3-node) |
Thin revolved shells (tanks, domes) |
planned |
| Hybrid (mixed u–p) variants |
Nearly incompressible materials |
planned |
Shells and membranes
| Element |
Use |
Status |
| Shell quad4 (MITC4), triangle (locking-free) |
Thin and thick shells |
done (flat MITC4 and MITC3 with a Hughes–Brezzi drilling rotation; modelcraft_fem::shell) |
| Shell quad8 / tri6 |
Curved thick shells |
planned |
| Continuum shells (8-node, on swept hex) |
Thick-to-thin shells, composites through thickness |
planned (M8) |
| Membranes (tri3, quad4, quad8) |
Fabrics, inflatables, skins without bending |
planned |
| Surface elements |
Massless surfaces for loads and contact |
planned |
| Composite layups on shells |
Ply tables, orientations |
planned (M8) |
3D solids
| Element |
Use |
Status |
| tet4, tet10 |
Free meshes of any part |
done |
| hex8 (full, incompatible modes), hex20 (full, reduced) |
Structured and swept meshes |
done |
| wedge6 |
Swept meshes from triangles, transitions |
done |
| hex8 one-point with hourglass control, nodal-pressure tet4 (explicit) |
Explicit dynamics |
done |
| wedge15, pyramid5/13 |
Quadratic transitions, tet–hex transition |
planned (M5); wedge15 and pyramid5 shape functions done |
| Hybrid (mixed u–p) solids |
Nearly incompressible materials (rubber) |
done for hex8 (constant pressure), hex20 (linear pressure) and tet10 (constant pressure), discontinuous pressure condensed, isotropic materials; tet4/wedge6 refused (they lock); continuous-pressure (Taylor–Hood) elements planned with an indefinite factorization |
| Modified quadratic tet (tet10 for contact/plasticity) |
Robust quadratic tets |
planned |
Special-purpose and multiphysics
| Element |
Use |
Status |
| Cohesive (2D, 3D) |
Adhesive layers, delamination |
planned |
| Gasket |
Through-thickness gasket behaviour |
planned |
| Infinite elements |
Unbounded domains |
planned |
| Heat transfer (all shapes), coupled temperature–displacement |
Thermal and thermal-stress analyses |
done for solids (tet4/10, wedge6, hex8/20: steady and transient conduction, flux, convection, sources; coupled temperature–displacement); thermal strain in solids, trusses, 2D elements (plane stress, plane strain, axisymmetric) and explicit dynamics (one-point hex8, nodal-pressure tet4, with plasticity); 2D/shell/beam conduction and shell/beam thermal strain planned |
| Acoustic |
Fluid acoustics, structural–acoustic coupling |
planned |
| Rigid elements |
Rigid bodies from meshes |
planned (M7) |
