The Fatigue behavior of composite materials is compared to an aluminum alloy in the diagram. These S-N tests are performed with the samples in tension, compression testing shows a stress level decrease of about a factor of two for the same fatigue life.

Kevlar-epoxy and Graphite - epoxy both perform better than the 2024-T3 aluminum alloy and are interesting bicycle materials. Glass fiber- epoxy matrix composites are of lower cost but have a poor performance compared to either the metal or the other composites.

From: Smith, "Principles of Materials Science and Engineering," McGraw Hill (1986)