fem: finite-strain material point, total Lagrangian elements and follower pressure

The material point interface returns the Kirchhoff stress and the spatial
tangent of its Lie derivative from the deformation gradient, with per-point
history committed by the solver: St Venant–Kirchhoff (pushed forward from
S = D E) and the decoupled compressible neo-Hookean with its isochoric and
volumetric parts. Total Lagrangian solids (tet4, tet10, wedge6, hex8, hex20
full and reduced) and plane strain and axisymmetric elements give internal
forces and the consistent tangent with its geometric stiffness; hybrid
solids use the Simo–Taylor–Pister three-field formulation on the existing
pressure fields. Incompatible modes and plane stress are refused by name.
Follower pressure on faces and 2D edges with its load stiffness. Every
tangent is checked against central differences of its forces.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

crates/fem/src/lib.rs

@@ -13,8 +13,13 @@
 //! - [`shape`]: the hand-written first-order functions of tet4, tet10, wedge6, hex8, hex20 that
 //!   the solid kernels evaluate;
 //! - [`material`]: isotropic and orthotropic elasticity matrices, von Mises stress;
+//! - [`constitutive`]: the material point of finite-strain analysis (Kirchhoff stress and
+//!   spatial tangent from the deformation gradient, with history): St Venant–Kirchhoff and
+//!   neo-Hookean;
 //! - [`element`]: the element table, stiffness (full, reduced, incompatible modes), consistent
 //!   and lumped mass, body forces, integration-point stresses and their extrapolation to nodes;
+//! - [`finite`]: total Lagrangian solid and 2D elements (internal forces, the consistent tangent
+//!   with its geometric part, mixed u–p at finite strain, Cauchy stress and logarithmic strain);
 //! - [`plane`]: 2D elements (plane stress, plane strain, axisymmetric) on tri3, tri6, quad4 and
 //!   quad8, with two displacement components per node;
 //! - [`shell`]: flat MITC4 quadrilateral and MITC3 triangle shells with a drilling rotation, six
@@ -44,10 +49,12 @@
 
 pub mod basis;
 pub mod beam;
+pub mod constitutive;
 pub mod dense;
 pub mod dof;
 pub mod element;
 pub mod face;
+pub mod finite;
 pub mod frame;
 pub mod heat;
 pub mod hybrid;