2026-02-15 08:00:21 +00:00
# Sandwich Beam
**Type:** Primary structural component
**Material:** Steel (AISI 1005) — see [steel-aisi.md ](../materials/steel-aisi.md )
**Status:** Confirmed from KBS session (Gen 002)
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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. Beam is extruded from an I-beam sketch profile.
## Geometry — NX Expressions
| Parameter | NX Expression | Baseline Value | Units | DV? | Range | Notes |
|-----------|--------------|----------------|-------|-----|-------|-------|
| Beam half-height | `beam_half_height` | ❓ TBD (Gap G12) | mm | No (currently) | — | Half total I-beam height |
| Beam half-width | `beam_half_width` | ❓ TBD (Gap G13) | mm | No (currently) | — | Half flange width |
| Face thickness | `beam_face_thickness` | 20 | mm | **Yes (DV2) ** | 10–
| Core half-thickness | `beam_half_core_thickness` | 20 | mm | **Yes (DV1) ** | 10–
| Beam length | `beam_length` | 5,000 | mm | No | Fixed | ✅ Confirmed (KBS) |
| Hole count | `hole_count` | 10 | — | **Yes (DV4) ** | 5–
| Hole diameter | ❓ (Gap G14) | 300 | mm | **Yes (DV3) ** | 150–
| Hole span | `p6` | 4,000 | mm | Potential (G15) | TBD | ✅ Confirmed (KBS) — total span for hole distribution |
| Hole start offset | (fixed) | 500 | mm | No | Fixed | Requirement — not parametric |
| Hole end offset | (fixed) | 500 | mm | No | Fixed | Requirement — not parametric |
## Mass
| Parameter | NX Expression | Value | Units | Source |
|-----------|--------------|-------|-------|--------|
| Mass (baseline) | * * `p1` ** | **11.33 ** | kg | ✅ KBS session 20260210-163801 |
| Density | (material card) | 7.3 | g/cm³ | ✅ KBS session — Antoine stated directly |
> ⚠️ **Previous value of ~974 kg (expression `p173`) is superseded.** See Gen 002 mass discrepancy resolution.
## Construction Method
1. **Sketch: ** I-beam cross-section profile with 4 key expressions (`beam_half_height` , `beam_half_width` , `beam_face_thickness` , `beam_half_core_thickness` )
2. **Extrusion: ** Sketch extruded to `beam_length` (5,000 mm) → solid body
3. **Holes: ** `hole_count` circular holes of specified diameter, distributed over `p6` span (4,000 mm), centered in web, starting 500 mm from each end
4. **Idealization: ** Promote body → mid-surface extraction (pair mid-surface function) → thin shell sheet bodies
## Hole Geometry Constraints
- **Span:** Holes are distributed over 4,000 mm (expression `p6` )
- **Fixed offsets:** First hole center at ≥500 mm from beam start, last hole center at ≤4,500 mm from beam start
- **Spacing:** At baseline: 10 holes in 4,000 mm → ~444 mm center-to-center, 300 mm diameter → ~144 mm ligament
- **Collision risk:** At extremes (15 holes × − **HOLES OVERLAP ** → infeasible
- **Feasibility formula:** `ligament = (hole_span / (hole_count - 1)) - hole_diameter > 0`
- Must also check: `hole_diameter < web_height` (hole fits in web vertically)
## Structural Behavior
*From Technical Breakdown (Gen 001), confirmed by KBS session:*
The beam is a **cantilever ** (left side fixed, right side free with 10,000 kgf downward load). It 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 × ** — classic sandwich interaction. Optimal stiffness balances core depth (lever arm) vs face material (bending resistance)
2. **Hole diameter × ** — both remove web material. Large + many could leave insufficient ligament width
3. **Face × ** — thicker faces reduce nominal stress, allowing larger holes
4. **Core × ** — core thickness determines web height, constrains max feasible hole diameter
## History
- **Gen 001** (2026-02-09): Initial documentation from intake + technical breakdown
- **Gen 002** (2026-02-10): Updated with confirmed values from KBS sessions. Mass corrected from 974 kg → 11.33 kg. Beam length confirmed 5,000 mm. Hole parameters detailed. Expression names confirmed.
