SAMPE Journal - March/April 2021 - 18
FEATURE / RECYCLED CARBON FIBRE
repurposed and have a layer of sizing over the fibre
surface. Besides the higher strength of the intermediate modulus fibres itself, the improved adhesion
of the pyrolysed fibres with the epoxy resin due to
roughening of their fibre surface, caused by the oxygen rich pyrolytic treatment, may have improved
its fatigue resistance26.
The efficiency of fibre packing has the most influence on the fatigue resistance as depicted by the
cross-ply laminates in Figure 6. SM45D laminate of
0.34 Vf has an improved resistance to fatigue than
that of IM56R of 0.25Vf, despite the differences in
the strength between the fibres and improved adhesion of pyrolysed fibres as discussed in the previous section.
The predominant mode of failure in the laminates was matrix damage, as shown by the micrographs of the cross-sections in Figure 7. The failure
at coupon level resembles that of tensile failure
modes but, in this case, rupture occurs due to the
accumulation of the matrix damages through the
thickness of the material, which develops over the
course of its fatigue life. This is more apparent in
laminates with lower reinforcement content, as in
the case of 0.22 Vf SM45D. Instances of fibre pullout, fibre meta-delaminations and debonding were
observed at higher stress levels. The matrix breakdown is spread through the length of the specimen
at higher loads but at lower stress levels, where the
matrix damage is not widely spread out, the damage may be restricted to the initial point of failure
and could possibly arise due to the presence of a
void or defect.
The dynamic moduli of the material, measured
at stress levels of 70%, 65%, 60%, 50% and 10% of
the material UTS, did not drop through its fatigue
life as shown in Figure 8. In certain cases, the modulus showed an indication of increased stiffness after fatigue. This could possibly be the influence of
the nature of the random, discontinuous, non-woven reinforcement that was similar to observations
18
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SAMPE JOURNAL
Mar Apr Journal 2021.indd 18
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Figure 4. Fatigue resistance in the warp and weft directions of a 0.22 Vf,
SM45D laminate.
Figure 5. Fatigue resistance of IM56L in comparison with SM45D.
Figure 6. Influence of Vf on fatigue resistance of rCF.
M A R C H /A P R I L 2 0 2 1
w w w. s a m p e . o r g
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SAMPE Journal - March/April 2021
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SAMPE Journal - March/April 2021 - Table of Contents
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