FEM foundation B: heat transfer and thermal stress (solids, 2D, explicit), coupled temperature–displacement, solve.heat (#45)

* Heat transfer and thermal stress: thermal materials, temperature BCs, heat loads, heat transfer and coupled temperature–displacement steps, solve.heat

Model: Material.thermal (conductivity, specific heat, expansion, isotropic or
per axis; reference temperature), BoundaryCondition::Temperature (dof 11),
loads SurfaceFlux, Convection, HeatSource and Temperature (a field in static
steps), procedures HeatTransfer { transient (θ-method) } and
CoupledTemperatureDisplacement; checks for missing conductivity/specific
heat/expansion. fem: heat conduction kernels (conductivity, capacity,
source, face flux/film, heat flux) on the DofLayout (one T per node), thermal
strain load and stress D(ε − ε_th) for every solid formulation incl.
incompatible modes. Solver: steady and transient heat transfer, thermal loads
in static steps, coupled steps (exact one-way coupling). Engine: solve.heat,
temperature/heat-flux result fields, probes. Decks refuse heat transfer by
name. Analytic verification: slab, source+convection/flux, thick cylinder,
erfc semi-infinite solid, free/constrained expansion, bimetal strip, coupled
step.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* thermal: strains in 2D elements and explicit dynamics

Plane::thermal_load and stresses_with for plane stress (εzz free), plane
strain (σzz = −D₃·ε_th) and axisymmetric elements, incompatible modes
included; the solver's 2D kernels take them. Explicit dynamics turns a
step's temperature loads into a per-element thermal strain rate (reached
linearly over the step) subtracted from each strain increment, so it feeds
J2 and Johnson–Cook updates. Verified: free expansion in every 2D theory
and element, a biaxially held plate, an explicit free bar (ΔL = αΔT L,
stress-free) and a clamped bar at −EαΔT, capped at the yield stress with
perfect plasticity.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* clippy

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* thermal: trusses take the axial thermal strain; keep the roadmap's M7 line

Truss::thermal_load and stresses_with project the thermal strain on the
member's tangent (Σ αₖ tₖ² ΔT); the static solver applies them to rod2/rod3
(#38). Explicit trusses take none yet and a warning says so.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

---------

Co-authored-by: jyviko <[email protected]>
Co-authored-by: Claude Opus 5.5 <[email protected]>

crates/decks/src/nastran/mod.rs

@@ -327,6 +327,7 @@ impl<'m> Deck<'m> {
         self.plan_discrete()?;
         self.plan_constraints()?;
         self.plan_loads()?;
+        self.problems.extend(crate::thermal_items(self.model));
         for sub in &mut self.subcases {
             if matches!(sub.step.procedure, Procedure::Frequency { .. }) {
                 sub.method = Some(next_id(&mut self.next_sid)?);
@@ -705,6 +706,8 @@ impl<'m> Deck<'m> {
                     OutputVariable::ReactionForce => "SPCFORCES",
                     OutputVariable::Stress => "STRESS",
                     OutputVariable::Strain => "STRAIN",
+                    // Heat transfer steps are refused (thermal_items).
+                    OutputVariable::Temperature | OutputVariable::HeatFlux => continue,
                 };
                 let _ = writeln!(out, "  {request} = ALL");
             }
@@ -928,7 +931,7 @@ impl<'m> Deck<'m> {
                     let a = angular_velocity / (2.0 * std::f64::consts::PI);
                     entry(Card::new("RFORCE").int(*sid).blank().blank().real(a).reals(*axis), out, &mut first)?
                 }
-                Load::BodyForce { .. } => {}
+                Load::BodyForce { .. } | Load::SurfaceFlux { .. } | Load::Convection { .. } | Load::HeatSource { .. } | Load::Temperature { .. } => {}
             }
         }
         for (sid, loads) in &self.combinations {