Explicit X2: large deformation, J2 and Johnson-Cook plasticity, damage and erosion (M10)

- model: materials gain solver-neutral plastic (bilinear isotropic/kinematic,
  hardening table, Johnson-Cook with adiabatic heating), damage (Johnson-Cook
  D1-D5) and erosion (plastic strain); explicit steps gain nonlinear_geometry
  (default on) and stress_rate (jaumann | green_naghdi).
- fem: rotation (Hughes-Winget, Flanagan-Taylor), plasticity (radial return,
  capped bracketed Newton for Johnson-Cook, damage; the update takes the
  mechanical strain increment so thermal strains can be subtracted), closed-form
  hex8 gradients for deformed configurations.
- explicit: updated Lagrangian hex8/tet4, per-element material state, erosion
  with reported energy, plastic work in the energy account.
- solver: warns that the linear solver uses the elastic constants of plastic
  materials (results hash-identical).
- decks: Abaqus *PLASTIC (+ Johnson-Cook keywords), Nastran MATS1/TABLES1,
  LS-DYNA *MAT_PLASTIC_KINEMATIC / *MAT_PIECEWISE_LINEAR_PLASTICITY; what a
  format cannot express is reported as Unsupported.
- engine: model.material.plasticity, model.material.damage (catalogue ready),
  explicit element probe, eroded elements in the solve summary.

Step commits before the rebase onto the DOF framework: branch explicit-x2-steps.

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

crates/explicit/src/lib.rs

@@ -17,10 +17,12 @@
 //! - **Integration** ([`integrate`]): the time loop, kinematic constraints, energy accounting
 //!   with a balance check, history samples and field frames ([`result`]).
 //!
-//! This first version is geometrically linear (small displacements and strains; the elements'
-//! gradients are those of the undeformed mesh) with linear elastic materials, which is what the
-//! analytic verification problems need. Large deformation kinematics with objective stress rates
-//! and inelastic materials come next (docs/solvers/literature.md, Part F, X2).
+//! With nonlinear geometry (the default) the elements are updated Lagrangian and the material
+//! state is integrated in rate form with an objective stress rate (Jaumann by Hughes–Winget,
+//! Green–Naghdi by Flanagan–Taylor); materials are hypoelastic or J2 plastic (bilinear,
+//! tabulated, Johnson–Cook) with Johnson–Cook damage and element erosion ([`elements`];
+//! docs/solvers/literature.md, Parts F and J). Without it the gradients stay those of the
+//! undeformed mesh (small displacements).
 //!
 //! Everything is sequential, with elements in label order and no parallel reductions, so the
 //! same model gives the same numbers bit for bit; sizes, increments and output are capped by
@@ -35,8 +37,9 @@ pub mod integrate;
 pub mod result;
 pub mod system;
 
+pub use elements::Failure;
 pub use integrate::solve_explicit;
-pub use result::{ControllingElement, Energies, ExplicitResult, Frame, History};
+pub use result::{ControllingElement, Energies, ErodedElement, ExplicitResult, Frame, History};
 
 #[derive(Debug, Clone, PartialEq, thiserror::Error)]
 pub enum Error {