This comes from the composites store website:

These high performance carbon shapes are produced by packing a high volume of carbon fiber into epoxy resin under tension resulting in an unmatched tensile and compression stength.

These shapes are twice the stiffness of Aluminum.

Compared to a wet lay-up of Carbon Tow the shapes are:

350% Stronger in Tension

550% Stronger in Compression

Quote source

It doesn't explain why. Carbon Tow are long continuous strands of carbon fiber. So somehow putting it under tension first, then fixing it in position with the epoxy makes it stronger? How?


1 Answer 1


Its not about the tension in the final product. [They are claiming] tension during fabrication buys them a much higher fiber loading. See 67 vol%.. a typical "wet layup" is maybe half that. Having the fibers very very straight probably contributes somewhat as well.

Note also the 3+GPa claimed strength is for some "micro" composite. If you look elsewhere on that site you will see practical size rods of "graphlite" are more like 2GPa.

  • $\begingroup$ Also think of gun barrels that have an inner core compressed by an outer sleeve under tension... $\endgroup$
    – Solar Mike
    Commented Nov 16, 2017 at 15:21
  • $\begingroup$ "Having the fibers very very straight probably contributes somewhat as well." -This should be negligible, by the small angle approximation.. "tension during fabrication buys them a much higher fiber loading" -why? and why is this not about tension in the final product? ...could it be that because the fibers are already under tension, the force they are able to resist -without- stretching is greater? (since the epoxy is essentially holding them in their stretched position) ..in this case their ultimate strength hasn't actually changed at all. $\endgroup$
    – juggler
    Commented Nov 16, 2017 at 17:26
  • $\begingroup$ The fibers are approx 100x stiffer than the matrix. They simply can't be under very much residual tension, and whatever there is would tend to very slightly lower the ultimate strength by reducing the matrix contribution to the strength. You should contact the manufacturer if you need clarification of what their ad says. diversified-composites.com/rdtbshp.php?mid=6&aid=14 $\endgroup$
    – agentp
    Commented Nov 16, 2017 at 18:06
  • $\begingroup$ @juggler No, this is not negligible. Orientation uniformity is extremely important because of carbon's high modulus. It will begin to form tiny cracks if these high fiber density composites aren't very carefully produced. In lower fiber densities, the matrix epoxy can accommodate more fiber inconsistencies because of the matrix's lower modulus. $\endgroup$
    – Phil Sweet
    Commented Nov 18, 2017 at 23:55
  • $\begingroup$ @agentp I did ;-) you folks have beaten them to the punch so far :-) $\endgroup$
    – juggler
    Commented Nov 19, 2017 at 4:40

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