Carbon fibres (CF) represent a significant volume fraction of modern
structural airframes. Embedded into polymer matrices, they provide significant
strength and stiffness gains over unit weight as compared to other competing
structural materials. Nevertheless, no conclusive structural model yet exists
to account for their extraordinary properties. In particular, polyacrynonitrile
(PAN) derived CF are known to be fully turbostratic: the graphene layers are
slipped sideways relative to each other, which leads to an inter-graphene
distance much greater than graphite. Here, we demonstrate that CF derive their
mechanical properties from those of graphene itself. By monitoring the Raman G
peak shift with strain for both CF and graphene, we develop a universal master
plot relating the G peak strain sensitivity of all types of CF to graphene over
a wide range of tensile moduli. A universal value of - average- shift rate with
axial stress of ~ -5{\omega}0^-1 (cm^-1 MPa^-1)is calculated for both graphene
and all CF exhibiting annular ("onion-skin") morphology