Damage sensing and fracture detection of CNT paste using electrical resistance measurements

The damage sensing properties of carbon nanotube (CNT) paste were investigated as an easy means of detecting cracking. 1wt% CNT paste was fabricated with different epoxy formulations and hardeners (amino and polyamide types) for use in stress sensing tests. The inherent properties of epoxy resins with the different hardeners were compared for different CNT paste applications. An electrical resistance test method was used to evaluate the state of dispersion of the CNT in the epoxy matrices. In the damage sensing tests, 30wt% CF/PP composites were used as the base materials because the polypropylene (PP) has a low crack resistance. In the damage sensing tests an artificial crack was introduce first in the 30wt% CF/PP composites. Then this crack was filled with CNT paste for the evaluation of crack extension and fracture. It was observed that when fracture occurred at the interface between CF/PP composite and the CNT paste the electrical resistance of the test specimen underwent a sudden jump. The changes in electrical resistance facilitated the detection of fracture and crack extension in the CF/PP composites. Additionally, layers of CNT paste was spread on CF/PP composite specimen at three different locations. As these specimens were tested in tension the location of damage in the in the CF/PP composites could also be identified by following the changes in electrical resistance. CNT paste was feasible to repair crack region by blunting due to the stress transfer through crack interface. The tests revealed that CNT pastes based on amino type epoxy was better for this damage detection than the polyamide type, at least in part due to its enhanced dispersion.