Multi-walled carbon nanotube reinforced polymer as a bonded repair for Al 2024-T3 fatigue crack growth

Abstract

The influence on multi walled carbon nanotubes (MWCNT, or simply CNT) as a reinforcement material in
an epoxy resin in order to decrease the fatigue crack propagation rate in the 2024 T3 aeronautical Al alloy
was studied. CT samples were pre-cracked in a resonant fatigue machine until a 4 mm pre-crack length. Four
groups of samples were considered: a non-repaired reference group, two groups repaired with epoxy resin
reinforced with two CNT proportions (0.5 and 1 vol %) and a group repaired by the conventional “stop drill”
technique. The crack was propagated until a length of 16 mm, measuring the number of cycles to this crack
propagation. Resin Hysol EA9320 NA was used, mixing it with the CNT and the hardener, by ultrasonic stirring.
S-N curves (stress vs number of cycles) were plotted obtaining an increment of 104% for a 0.5 vol% of
CNT, 128% for 1 vol% of CNT and 400% for “stop drill” repairing. These results were referred to the nonrepaired
samples at the lower load level. These results showed that in repaired samples with CNT reinforced
resin, the initiation and propagation of cracks would be delayed, constituting this method a reasonable and
convenient repairing procedure useful for aeronautical cracked structures.
Keywords: Multi-walled carbon nanotubes (MWCNT), Al 2024, Fatigue.