چكيده به لاتين
The main purpose of this thesis is to investigate the effect of the presence of carbon nanotubes (CNTs) on critical strain energy release rate (CSERR) at delamination initiation of laminated composites under mixed mode I/II loading state using an analytical method. To achieve this aim, the analytical models were developed based on this assumption that the occurrence of energy dissipation mechanisms due to the presence of CNTs at a rich resin region located between the long fibers layers of the laminated composites. The energy dissipation can be categorized into zone and contact shielding mechanisms based on location of the CNTs regarded to the pre-crack. Influence of CNTs debonding from the surrounding resin and subsequent plastic void growth at the zone around the crack tip were introduced as the zone shielding toughening mechanisms. Using correlation between nano, micro and macro-scales, the strain energy release rate enhancement due to these mechanisms was presented. In this research, some contact shielding toughening mechanisms such as CNTs pull-out, interfacial debonding, breakage under tension and shear were also considered. Finally, according to the developed models and considering some assumptions, a correlation for predicting the mixed mode I/II CSERR of hybrid-laminated composites was presented.
To validate the proposed model, the results calculated through the analytical relations must be compared with experimental results of other researchers and the present research. Therefore, first, the experimental data available in the literature were used in order to verify the analytical model. Then, an experimental study was also carried out in the current research. The effect of 0.5 wt.% of multi-walled CNTs on the CSERR of epoxy-based laminated composites reinforced with glass long fiber was investigated. Mode I, mode II and mixed mode I/II delamination in glass/epoxy and glass/CNTs/epoxy laminated composites were studied. The results showed that the present model has an acceptable ability to predict the CSERR of laminated composites reinforced with CNTs.