# Step 1: research

## Read First

- `/AGENTS.md`
- `/docs/ABAQUS_SUBROUTINE_AGENT_DESIGN.md`
- `/docs/ARCHITECTURE.md`
- `/docs/ADR.md`
- `/.codex/skills/abaqus-subroutine-research/SKILL.md`
- `/.codex/skills/fem-theory-query/SKILL.md`
- `/docs/requirements/uel-3d-euler-beam.md`
- `/docs/research/README.md`

## Task

Create `/docs/research/uel-3d-euler-beam-research.md`.

Research only the evidence needed to support a two-node 3D Euler-Bernoulli beam `UEL` implementation and validation plan. Separate:

- Source-backed facts.
- Inferences made from those facts.
- Applicability limits for this implementation.

Cover at minimum:

- Abaqus/Standard `UEL` responsibilities for `RHS`, `AMATRX`, `SVARS`, `ENERGY`, `NDOFEL`, `NNODE`, `MCRD`, `LFLAGS`, `PROPS`, `COORDS`, `U`, `DU`, and `JPROPS`.
- Euler-Bernoulli 3D beam stiffness matrix in local coordinates for axial, torsion, bending about local 2 and local 3 axes.
- Local-to-global transformation for two-node beam elements, including orientation-vector edge cases.
- Residual sign convention needed by Abaqus `UEL`.
- Verification benchmarks appropriate for no-Abaqus tests and external Abaqus CSV comparison.

Prefer official Abaqus documentation and reliable FEM references. Public example repositories may be used only as learning references, not acceptance evidence, unless license/version/provenance are documented.

Do not create or modify Fortran source, tests, reference artifacts, or implementation plans in this step.

## Tests To Write First

- None. This is a research artifact step.

## Acceptance Criteria

```bash
python -m unittest discover -s scripts -p "test_*.py"
python scripts/validate_reference_artifacts.py
python scripts/validate_workspace.py
```

The step is complete only when the research document cites sources and clearly marks facts, inferences, and applicability limits.

## Validation Notes

- Abaqus execution remains external to this repository.
- Update `/phases/uel-3d-euler-beam/index.json` step 1 with `completed`, `error`, or `blocked` and a concrete summary or reason.

## Forbidden

- Do not add JavaScript/TypeScript/npm fallback.
- Do not run Abaqus analyses from this project.
- Do not generate reference CSVs.
- Do not create Fortran production source.
- Do not break existing tests.