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This investigation experimentally examines the effect of incorporating alumina nanoparticles on the off-axis stiffness and stress-relaxation of carbon fiber-reinforced polymer composites. Four epoxy–alumina nanoparticle nanocomposites incorporating 0.0, 1.0, 2.0, and 3.0 wt% alumina nanoparticles of the total weight of epoxy are examined. Off-axis tension stiffness and stress-relaxation tests were performed on carbon fiber-reinforced polymer coupons fabricated with alumina nanoparticles–epoxy nanocomposites. Dynamic mechanical analysis testing of neat epoxy and epoxy nanocomposites incorporating alumina nanoparticles was used to identify the stiffness and relaxation behavior of the alumina nanoparticles–epoxy nanocomposite matrix. Fourier transform infrared spectroscopy was used to observe chemical changes when alumina nanoparticles are mixed with epoxy. It is shown that using alumina nanoparticles at a concentration close to 2.0 wt%, can reduce the off-axis stiffness by ∼30% and increase the off-axis stress-relaxation of carbon fiber-reinforced polymer by ∼10%. [ABSTRACT FROM AUTHOR]

This investigation experimentally examines the role of multi-walled carbon nanotubes (MWCNTs) on the tension (on-axis tension test) and in-plane shear (off-axis tension test) behaviors of carbon fiber reinforced polymer composites. Both pristine and chemically functionalized MWCNTs were utilized with four different loadings: 0.1, 0.5, 1.0, and 1.5 wt% of epoxy. Our investigation showed that with 1.5 wt% functionalized MWCNTs, failure strain, ultimate strength, and toughness of the off-axis tension test are improved by 39%, 51%, and 121%, respectively. On the contrary, limited improvements were observed for the on-axis tested samples with functionalized or pristine MWCNTs. [ABSTRACT FROM PUBLISHER]