FESADev/phases/1-linear-static-mitc4-rebaseline/step9.md

Sprint Contract: MITC4 Material Integration

Objective

Implement or rebuild local plane-stress material behavior, shear correction, material transformation, and 2 x 2 x 2 Gauss integration scaffolding.

Required Reading

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

Scope

• Implement isotropic linear elastic shell material matrix with sigma_33 = 0 and kappa = 5/6.
• Define material/strain ordering tests.
• Implement or verify convected-to-local material transformation for Phase 1 cases.
• Add 2 x 2 x 2 integration point and weight infrastructure.

Allowed Files

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

Explicit Non-Goals

• Do not add composite sections.
• Do not add stress/strain output recovery as mandatory output.
• Do not switch to analytic thickness integration without equivalence tests and doc update.

Tests To Write First

• Isotropic matrix value tests for known E, nu, and kappa.
• Shear row ordering tests.
• Integration point count and weights tests.
• Flat element material transform identity/equivalence tests.
• Invalid material/thickness diagnostic tests if not covered earlier.

Reference Artifacts

• None.

Acceptance Commands

python scripts/validate_workspace.py

Evaluator Checklist

• 2 x 2 x 2 integration is the active baseline.
• Material transform behavior is tested.
• No reduced integration or hourglass logic is introduced.

Handoff Requirements

• Record material and integration readiness in PROGRESS.md.

Do Not

• Do not make S4R assumptions in material or integration code.