Toughening effect of nanocomposite-wall microcapsules on the fracture behavior of epoxy

Abstract In this research the reinforcing effect of nanocomposite-wall microcapsules on the fracture toughness and fracture energy of epoxy under mode I was studied. The fracture specimens with the geometry of localized tapered double cantilever beam (TDCB) were used to take the advantage of crack length independent-measurement in determining the fracture properties. The crack length investigations were performed experimentally and numerically to extract the calibration parameters and also evaluate the optimal crack length of TDCB specimens. Three types of microcapsules including hollow microcapsule (CH), ethyl phenylacetate core microcapsule (CEPA) and NH2-CNT reinforced-wall microcapsule (CCNT) were synthesized and used as reinforcements. The scanning electron microscopy study of synthesized microcapsules proved the successful presence of CNTs in the shell and on the wall of CCNT microcapsules. The hollow capsule-loaded epoxy composite exhibited enhanced fracture properties as compared to the neat epoxy. Moreover, the SEM study of fracture surface of CH reinforced specimen revealed a characteristic crack tail toughening mechanism. The CEPA microcapsule decreased fracture properties of neat epoxy. The maximum improvement of fracture properties belonged to the specimen containing the CCNT microcapsules. It was observed that the composite-wall microcapsule was able to increase the fracture toughness and fracture energy of neat epoxy by 59% and 165%, respectively, due to the developments of considerable out-of-plane fracture and large plastic deformation.