Determination of transverse and shear moduli of single carbon fibres

Journal article, 2020

Carbon fibres are extensively used for their high specific mechanical properties. Exploiting their high
axial stiffness and strength, they are employed to reinforce polymer matrix materials in advanced
composites. However, carbon fibres are not isotropic. Data of the elastic properties in the other directions
of the fibres are still largely unknown. Furthermore, standardised methods to characterise these properties
are lacking. In the present work, we propose a methodology to determine the transverse and shear
moduli of single carbon fibres. An experimental procedure is developed to fabricate high-quality, flat
fibre cross-sections in both longitudinal and transverse directions using Focused Ion Beam, which gives
full control of the specimen geometry. Indentation modulus on those surfaces are obtained using both
Atomic Force Microscopy (AFM) and nanoindentation tests. Hysteresis was found to occur in the
nanoindentation tests. The hysteresis response was due to nano-buckling and reversible shear deformation
of the carbon crystals. For this reason, indentation tests using AFM is recommended. From the
AFM indentation tests the transverse and shear moduli of three different carbon fibres (IMS65, T800 and
M60J) are successfully determined.