Carbon Fiber Tubes Material Properties: Modulus, Strength and Density Reference

Introduction

Carbon fiber tubes material properties decide whether a design survives its first load cycle or fails at a fraction of the predicted force. The same outer diameter can mean a 40 GPa modulus tube or a 150 GPa tube depending on fiber grade, fiber orientation and how the tube was made, and the wrong assumption costs a program weeks of redesign. This reference collects the numbers engineers actually quote, explains how to read them off a carbon fiber data sheet, and shows why pultruded vs wrapped carbon fiber are not interchangeable despite looking identical from the outside.

Use it as a working table during early design, then confirm every critical value against the laminate schedule and test certificate from your actual supplier, because layup sequence, fiber volume fraction and cure cycle all shift the published figures.

Carbon Fiber Tubes Material Properties: The Numbers That Matter

Four properties cover most structural screening decisions for a carbon fiber tube. Tensile modulus tells you stiffness per unit strain, tensile strength sets the failure envelope, density sets the mass budget, and coefficient of thermal expansion tells you how much the part grows or shrinks with temperature. The table below uses typical ranges for unidirectional carbon fiber tubes cured in autoclave, based on standard-modulus T300-class fiber at 55 to 60 percent fiber volume.

Property	Typical range	Unit	What shifts it
Tensile modulus, axial	70 to 150	GPa	Fiber grade, winding angle, fiber volume
Tensile strength, axial	1200 to 2200	MPa	Fiber grade, void content, surface finish
Compressive strength	600 to 1200	MPa	Matrix system, fiber-matrix adhesion
Density	1.50 to 1.65	g/cm3	Fiber volume, resin type
Thermal expansion, axial	-0.5 to +1.0	10-6/K	Layup symmetry, fiber orientation
Thermal expansion, hoop	+15 to +30	10-6/K	Hoop layer content

Axial modulus near 150 GPa belongs to high-modulus or intermediate-modulus fibers laid up close to zero degrees; standard-modulus tubes usually land between 70 and 100 GPa. Hoop-direction thermal expansion is an order of magnitude larger than axial because the fibers restrain expansion along their length but not across it, which is why thin-walled tubes under thermal cycling often show delamination at the ends.

Carbon Fiber Data Sheet: How to Read It Without Getting Lost

A credible carbon fiber data sheet separates measured laminate values from fiber-only values, and states the test method next to each number. Look for the following lines before accepting any quote.

• Fiber grade and tow size: Named grade such as T300, T700 or T800, with tow size in K. Unnamed high-strength claims cannot be compared.
• Fiber volume fraction: Aerial weight and resin content together give fiber volume, usually stated as a percentage with tolerance.
• Test standard: Tensile and compressive values should reference ASTM D3039 or ISO 527 for tension and ASTM D6641 or ISO 14126 for compression.
• Void content: Below 1 percent is good autoclave practice; above 2 percent cuts compressive strength measurably.
• Conditioning: Dry-as-cured, hot-wet, or both. Hot-wet values can be 10 to 20 percent lower than dry ones for epoxy systems.

Numbers without a test standard are marketing figures, and mixing laminate values with fiber-only values in the same table is the most common way a data sheet overstates performance.

Pultruded vs Wrapped Carbon Fiber: Same Material, Different Behavior

Pultruded and wrapped carbon fiber tubes look similar from the outside, but the fiber architecture is fundamentally different and so are the mechanical results.

Aspect	Pultruded tube	Filament-wound tube
Fiber orientation	Almost all axial (0 degrees)	Helical, mixed angles
Axial tensile modulus	100 to 150 GPa	70 to 110 GPa
Hoop strength	Low, limited by matrix	High, tailored by wind angle
Best use	Beams, masts, arms in pure bending	Pressure vessels, bicycle frames, shafts
Wall thickness control	Uniform, thin possible	Builds up with each layer

Choosing between pultruded vs wrapped carbon fiber is a load-path question, not a price question. If the dominant load is axial tension or bending, pultruded wins on stiffness per gram. If the tube sees internal pressure, torsion or point loads from a clamp, wrapped construction distributes those loads into the fibers instead of into the matrix.

Carbon Fiber Tube Custom Specs: What to Specify Before You Order

When a project calls for a carbon fiber tube custom profile, write the requirements in laminate terms, not just dimensions. Outer diameter, inner diameter and length define the envelope, but the following lines define performance and should appear in the purchase specification.

• Layup schedule: Number of plies, angle of each ply, and total thickness. A 0/90 balanced layup behaves very different from a 0/90 with extra hoop plies.
• Fiber grade: T300 class for general structural work, T700 for higher strength, high-modulus grades when stiffness governs.
• End finish: Machined square, bonded end caps, or co-cured fittings. Specify tolerance on squareness and concentricity.
• Surface: Peel ply finish for secondary bonding, or painted and polished for appearance parts.

Share the load case with your supplier and ask for the laminate schedule used in their calculation, then compare it against the property table above. A tube that meets diameter tolerance but misses the modulus target will still fail the structure.

Frequently Asked Questions

Are carbon fiber tubes stronger than aluminum tubes of the same size?

In tension and bending, yes by a wide margin: a typical pultruded carbon tube shows axial tensile strength of 1200 MPa or more against roughly 310 MPa for 6061-T6 aluminum, at about one sixth the density. In compression and under point crush loads the gap narrows, because carbon fiber compressive strength is limited by matrix support rather than by fiber strength.

How do I choose between pultruded and filament-wound carbon fiber tube?

Match the fiber architecture to the load path. Pure axial tension or bending favors pultruded construction for higher axial modulus. Internal pressure, torsion or clamp loads favor filament-wound construction because the helical fibers carry those loads directly instead of relying on the matrix.

What is a realistic density range for a structural carbon fiber tube?

Expect 1.50 to 1.65 g/cm3 for standard epoxy carbon tubes, compared with 2.70 g/cm3 for aluminum and 7.85 g/cm3 for steel. The variation comes from fiber volume fraction and resin type, not from the fiber itself.

Conclusion

Carbon fiber tubes material properties are set by fiber grade, layup and manufacturing method, not by the outer diameter stamped on the drawing. Read every data sheet against test standards, decide between pultruded vs wrapped carbon fiber from the load path, and write custom tube specifications in laminate terms before you request a quote.

YongXian supplies pultruded and filament-wound carbon fiber tubes to custom specifications, with laminate schedules and test data available on request. Browse our carbon fiber tube range or send us your tube specification for a quotation.