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 <noreply@anthropic.com>
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 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* clippy

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

---------

Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/decks/src/abaqus.rs

@@ -294,6 +294,7 @@ fn check_expressible(model: &Model) -> Result<()> {
             ));
         }
     }
+    bad.extend(crate::thermal_items(model));
     for (name, c) in model.couplings() {
         if c.kind == CouplingKind::Distributing && !(1..=3).all(|d| c.dofs.contains(d)) {
             bad.insert(format!("coupling `{name}`: an Abaqus distributing coupling always couples translations 1-3"));
@@ -911,6 +912,8 @@ impl Deck {
                     };
                     self.line(&format!("{target}, {s}"));
                 }
+                // Refused up front (check_expressible).
+                BoundaryCondition::Temperature { .. } => {}
                 BoundaryCondition::Displacement { values, .. } => {
                     for (dof, v) in (1u8..).zip(values) {
                         if let Some(v) = v {
@@ -1068,8 +1071,8 @@ impl Deck {
                         self.comment("loads have no effect on natural frequencies and are not written");
                     }
                 }
-                Procedure::ExplicitDynamic(_) => {
-                    return Err(Error::Unsupported { format: FORMAT, what: format!("step `{}`: explicit dynamic steps", step.name) });
+                Procedure::ExplicitDynamic(_) | Procedure::HeatTransfer { .. } | Procedure::CoupledTemperatureDisplacement {} => {
+                    return Err(Error::Unsupported { format: FORMAT, what: format!("step `{}`: {} steps", step.name, step.procedure.name()) });
                 }
             }
             self.output(step);