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 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

crates/model/tests/definition.rs

@@ -56,8 +56,11 @@ fn defined() -> Model {
     m.add_set("all", Set::of_geometry(vec![GeometryRef::body("Bar").unwrap()])).unwrap();
     m.add_set("root", Set::of_geometry(vec![GeometryRef::face("Bar", "left").unwrap()])).unwrap();
     m.add_set("end", Set::of_geometry(vec![GeometryRef::face("Bar", "right").unwrap()])).unwrap();
-    m.add_material("Steel", Material { elastic: Some(Elastic::Isotropic { young: 2.1e5, poisson: 0.3 }), density: Some(7.85e-9), fluid: None })
-        .unwrap();
+    m.add_material(
+        "Steel",
+        Material { elastic: Some(Elastic::Isotropic { young: 2.1e5, poisson: 0.3 }), density: Some(7.85e-9), ..Material::default() },
+    )
+    .unwrap();
     m.add_section("bar", Section { set: "all".into(), material: "Steel".into(), kind: SectionKind::Solid {}, formulation: Formulation::default() })
         .unwrap();
     m.add_reference_point("RP", ReferencePoint { xyz: [3.0, 0.5, 0.5], label: 0 }).unwrap();
@@ -121,7 +124,8 @@ fn the_check_names_what_is_missing() {
     m.add_set("side", Set { faces: vec![ElementFace { element: 1, face: 3 }], ..Set::default() }).unwrap();
     m.add_load("ghost-load", Load::Pressure { set: "ghost".into(), magnitude: 1.0 }).unwrap();
     m.add_load("twist", Load::Moment { target: Target::Set("end".into()), vector: [1.0, 0.0, 0.0], distribution: Distribution::Total }).unwrap();
-    m.add_material("Soft", Material { elastic: Some(Elastic::Isotropic { young: 2.1e11, poisson: 0.3 }), density: None, fluid: None }).unwrap();
+    m.add_material("Soft", Material { elastic: Some(Elastic::Isotropic { young: 2.1e11, poisson: 0.3 }), density: None, ..Material::default() })
+        .unwrap();
     m.add_section("again", Section { set: "side".into(), material: "Soft".into(), kind: SectionKind::Solid {}, formulation: Formulation::default() })
         .unwrap();
     m.add_section(
@@ -327,8 +331,11 @@ fn a_total_force_on_a_face_is_the_same_on_every_mesh() {
     m.set_units(UnitSystem::MmTonneS);
     m.add_set("all", Set::of_geometry(vec![GeometryRef::body("Block").unwrap()])).unwrap();
     m.add_set("end", Set::of_geometry(vec![GeometryRef::face("Block", "end").unwrap()])).unwrap();
-    m.add_material("Steel", Material { elastic: Some(Elastic::Isotropic { young: 2.1e5, poisson: 0.3 }), density: Some(7.85e-9), fluid: None })
-        .unwrap();
+    m.add_material(
+        "Steel",
+        Material { elastic: Some(Elastic::Isotropic { young: 2.1e5, poisson: 0.3 }), density: Some(7.85e-9), ..Material::default() },
+    )
+    .unwrap();
     m.add_section("block", Section { set: "all".into(), material: "Steel".into(), kind: SectionKind::Solid {}, formulation: Formulation::default() })
         .unwrap();
     let force = |distribution| Load::Force { target: Target::Set("end".into()), vector: [100.0, 0.0, -50.0], distribution };
@@ -417,8 +424,11 @@ fn plate(kind: SectionKind, x0: f64) -> Model {
     m.add_set("all", Set::of_geometry(vec![GeometryRef::face("Plate", "area").unwrap()])).unwrap();
     m.add_set("left", Set::of_geometry(vec![GeometryRef::new("Plate", Entity::Edge("left".into())).unwrap()])).unwrap();
     m.add_set("right", Set::of_geometry(vec![GeometryRef::new("Plate", Entity::Edge("right".into())).unwrap()])).unwrap();
-    m.add_material("Steel", Material { elastic: Some(Elastic::Isotropic { young: 2.1e5, poisson: 0.3 }), density: Some(7.85e-9), fluid: None })
-        .unwrap();
+    m.add_material(
+        "Steel",
+        Material { elastic: Some(Elastic::Isotropic { young: 2.1e5, poisson: 0.3 }), density: Some(7.85e-9), ..Material::default() },
+    )
+    .unwrap();
     m.add_section("plate", Section { set: "all".into(), material: "Steel".into(), kind, formulation: Formulation::default() }).unwrap();
     m.add_boundary_condition("clamp", BoundaryCondition::Fixed { target: Target::Set("left".into()) }).unwrap();
     m.add_load("pull", Load::Traction { set: "right".into(), vector: [10.0, 0.0, 0.0] }).unwrap();