FESADev/phases/1-linear-static-mitc4-rebaseline/step10.md

Sprint Contract: MITC4 Stiffness Drilling

Objective

Assemble the MITC4 element stiffness and internal force kernel using the documented strain, material, integration, six-DOF transform, and drilling stabilization.

Required Reading

• /AGENTS.md
• /docs/MITC4_FORMULATION.md
• /docs/NUMERICAL_CONVENTIONS.md
• /docs/ADR.md

Scope

• Accumulate K_e = integral B^T D B dV.
• Add local drilling stabilization with drilling_stiffness_scale = 1.0e-3.
• Transform local element stiffness/internal force to global 24-DOF order.
• Preserve parameterization and diagnostics for drilling scale.

Allowed Files

• include/
• src/
• tests/
• PLAN.md
• PROGRESS.md

Explicit Non-Goals

• Do not add assembly/global solve.
• Do not tune drilling scale to match one reference case.
• Do not output stresses/resultants as mandatory fields.

Tests To Write First

• Stiffness dimension and symmetry tests.
• Drilling diagonal reference tests using minimum positive physical local stiffness diagonal.
• Zero/invalid reference diagonal diagnostic tests.
• Rigid body physical strain-energy tests with documented drilling effects.
• Internal force consistency test f_int_e = K_e u_e for linear elastic Phase 1.

Reference Artifacts

• None.

Acceptance Commands

python scripts/validate_workspace.py

Evaluator Checklist

• Old 1.0e-6 * E * thickness drilling rule is gone.
• Global 24-DOF ordering matches UX,UY,UZ,RX,RY,RZ per node.
• Stiffness remains linear elastic and symmetric.

Handoff Requirements

• Record element kernel readiness in PROGRESS.md.

Do Not

• Do not optimize or parallelize before element tests pass.