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/decks/tests/planar.rs

@@ -32,8 +32,11 @@ fn plate(kind: SectionKind, element: ElementKind, formulation: Formulation) -> M
     m.add_set("all", Set { elements: all, ..Set::default() }).unwrap();
     m.add_set("left", Set { nodes: vec![1, 4], ..Set::default() }).unwrap();
     m.add_set("right", Set { edges: vec![right], ..Set::default() }).unwrap();
-    m.add_material("Steel", Material { elastic: Some(Elastic::Isotropic { young: 210_000.0, poisson: 0.3 }), density: Some(7.85e-9), fluid: None })
-        .unwrap();
+    m.add_material(
+        "Steel",
+        Material { elastic: Some(Elastic::Isotropic { young: 210_000.0, poisson: 0.3 }), density: Some(7.85e-9), ..Material::default() },
+    )
+    .unwrap();
     m.add_section("plate", Section { set: "all".into(), material: "Steel".into(), kind, formulation }).unwrap();
     m.add_boundary_condition("hold", BoundaryCondition::Fixed { target: Target::Set("left".into()) }).unwrap();
     m.add_load("press", Load::Pressure { set: "right".into(), magnitude: 5.0 }).unwrap();