# Sandwich Beam

**Type:** Primary structural component
**Material:** Steel (AISI) — see [steel-aisi.md](../materials/steel-aisi.md)
**Status:** Baseline documented, optimization pending

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## Description

Sandwich I-beam serving as primary load-bearing member in a test fixture assembly. Cross-section features a core layer flanked by face sheets on top and bottom flanges. Web contains a pattern of lightening holes (circular cutouts) to reduce mass.

## Specifications

| Parameter | Value | Units | Source |
|-----------|-------|-------|--------|
| Mass (baseline) | ~974 | kg | NX expression `p173` |
| Tip displacement (baseline) | ~22 | mm | SOL 101 result |
| Half-core thickness | 20 (baseline) | mm | DV range: 10–40 |
| Face thickness | 20 (baseline) | mm | DV range: 10–40 |
| Hole diameter | 300 (baseline) | mm | DV range: 150–450 |
| Hole count | 10 (baseline) | — | DV range: 5–15 (integer) |
| Beam length | ❓ TBD | mm | Gap G1 |
| Support conditions | ❓ TBD | — | Gap G1 |

## Structural Behavior

*From Technical Breakdown (Gen 001):*

The beam is **bending-dominated**:

| Behavior | Governing Parameters | Notes |
|----------|---------------------|-------|
| Bending stiffness (EI) | Face thickness, core thickness | Faces carry bending stress, core carries shear. Stiffness scales ~quadratically with distance from neutral axis |
| Mass | All four variables | Core and face add material; holes remove material from web |
| Stress concentrations | Hole diameter, hole spacing | Larger holes → higher SCF at edges. Closely spaced holes can interact |
| Shear capacity | Core thickness, hole count, diameter | Holes reduce shear-carrying area |

## Design Variable Interactions

1. **Core × Face** — classic sandwich interaction. Optimal stiffness balances core depth (lever arm) vs face material (bending resistance)
2. **Hole diameter × Hole count** — both remove web material. Large + many could leave insufficient ligament width
3. **Face × Hole diameter** — thicker faces reduce nominal stress, allowing larger holes
4. **Core × Hole diameter** — core thickness determines web height, constrains max feasible hole diameter

## Key Risk

> ⚠️ Baseline FAILS displacement constraint (22 mm vs 10 mm target). Optimizer must increase stiffness by >50% while reducing mass. Feasible region may be tight.

## History

- **Gen 001** (2026-02-09): Initial documentation from intake + technical breakdown