Solid Carbon Fiber Rods vs. Hollow Carbon Fiber Tubes: Quick‑Reference on Weight, Stiffness & Applications
Author: Aohong Carbon Fiber Technology Center
1. Conclusion Up Front
- Need maximum stiffness, impact resistance, small size? Choose Solid Carbon Fiber Rods
- Need lightweight, high specific stiffness, medium-to-long spans? Choose Hollow Carbon Fiber Tubes
- Need cable routing, sleeve fittings, or vibration damping? Hollow tubes add a functional dimension
2. Mechanical Data Comparison (T300‑3K, Epoxy Matrix)
| Metric (Ø10 mm) | Solid Rod | Hollow Tube (t = 1 mm) | Notes |
|---|---|---|---|
| Cross‑Sectional Area (mm²) | 78.5 | 28.3 | Hollow saves 64 % weight |
| Linear Mass (g/m) | 122 | 44 | ρ = 1.55 g/cm³ |
| Bending Stiffness EI (N·m²) | 6.1 | 4.2 | Solid is 45 % stiffer |
| Specific Stiffness EI/(ρA) | 51 | 96 | Hollow is 88 % higher |
| Torsional Stiffness | High | Moderate | Solid resists thin‑wall buckling |
| Critical Buckling Length | 1.0× (simply supported) | 0.8× | Hollow needs local buckling check |
Interpretation: With the same outer diameter, a solid rod is “harder,” but a hollow tube is “lighter and more material‑efficient.” Specific stiffness is the engineering gold standard for selection.
3. Manufacturing & Cost
| Aspect | Solid Rod | Hollow Tube |
|---|---|---|
| Forming Processes | Pultrusion, molding | Pultrusion, winding, wrapping |
| Tooling Compatibility | High (no core tool) | Requires mandrel or bladder |
| Volume Cost Factor | 1.0× | 1.1–1.3× |
| Secondary Machining | Easy to cut/drill | Must prevent collapse; t ≥ 1 mm |
4. Perfect Match by Application
| Scenario | Recommended Shape | Rationale |
|---|---|---|
| Arrow shafts, model landing gear | Ø6–8 mm Solid Rod | Impact resistance, easy machining |
| Drone arms (500 mm cantilever) | Ø15×1.5 mm Hollow Tube | 55 % weight reduction, +90 % specific stiffness |
| 1 m Robot arm cross‑beam | 20×20×2 mm Hollow Square Tube | Bending + cable routing in one profile |
| Automotive anti‑roll bar | Ø20×3 mm Hollow Tube | Low torsional inertia, good vibration damping |
5. 30‑Second Selection Formula
- Compute required specific stiffness:Specific Stiffness=EIρA\text{Specific Stiffness} = \frac{EI}{\rho A}
- If space/weight is limited → Hollow Tube
- If short length & high impact → Solid Rod
- If cabling or inserts needed → Hollow Tube offers natural conduit
6. One‑Sentence Summary
Solid Carbon Fiber Rods are “stiff and robust,” while Hollow Tubes are “light and versatile.” Balance specific stiffness, functional needs, and cost to choose the optimal “skeleton” in the world of “black gold.”
