📐 Carbon Fiber Tube Deflection / Stiffness Calculator
Note: default E = 135 GPa (typical axial modulus of standard-modulus roll-wrapped tube). High-modulus exceeds 200 GPa, pultruded ≈ 120 GPa. Simply-supported beam, center point load model — for sizing reference only.
⚠️ Disclaimer: Dimensions, layup schedules, and manufacturing processes vary by specification and supplier — results are theoretical estimates for reference only. Actual values may differ and shall not be used as acceptance criteria.
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How to Use the Deflection Calculator
This carbon fiber tube deflection calculator uses the simply-supported beam, center point load model: enter OD, wall thickness, span (L), load (F), and pick the elastic modulus preset. It returns maximum deflection δ in mm and bending stiffness in N/mm, plus the section moment of inertia for your records. Three modulus presets cover pultruded (120 GPa), standard roll-wrapped (135 GPa), and high-modulus (200 GPa) constructions.
The Engineering Behind It
Deflection follows δ = F·L³ ÷ (48·E·I) with I = π·(OD⁴ − ID⁴) ÷ 64. Two practical takeaways: stiffness scales with the fourth power of diameter (a 40 mm tube is ~3× stiffer than a 30 mm tube at the same wall), but only cubically inverse with span — halving your support distance cuts deflection 8×. When a prototype sags too much, increasing diameter beats adding wall thickness almost every time for weight efficiency.
Carbon Fiber vs Aluminium Stiffness
Axial modulus of standard T300 tube (~135 GPa) already approaches aluminium (69 GPa) at less than half the density — specific stiffness is roughly 3–4× better. That means equal rigidity at 40–60% less weight, which is why carbon fiber tubes dominate robotic arms, gantry rails, and telescope masts. For extreme cases (long camera jibs, CMM frames), high-modulus layups push E past 200 GPa — ask about custom layup schedules.
Limitations & Next Steps
This tool covers static center loads on simply-supported spans. Cantilever arms, distributed loads, and torsional cases need FEA — send our engineers your loading sketch and we will run the numbers free with your quote. Ready to order? Match your required stiffness to a stock size in our product range, or request a custom diameter/wall combo with zero tooling fee for most sizes.
Frequently Asked Questions
Why is my real tube stiffer (or softer) than calculated?
Layup matters: 0°-dominant schedules raise axial E; hoop-heavy roll-wrapped tubes trade axial stiffness for crush strength. End fixity also matters — clamped ends cut deflection ~4× versus simply supported.
What deflection is acceptable?
Rule of thumb: L/360 for visual structures, L/500+ for optical/motion stages. Drone arms often tolerate L/100 under max thrust.
Do you test bending strength?
Yes — every production batch passes three-point bend testing in our QC lab with traceable reports. Request a sample test.