Effect of Amino Multi-Walled Carbon Nanotubes Reinforcement on the Plane Strain Fracture Toughness of Neat Epoxy

Carbon Nanotubes (CNTs) are considered to be one of the ideal reinforcements for developing advanced nanocomposites due to their excellent electrical, mechanical, and magnetic properties as well as unique atomic structure with unusually very high aspect ratio. In an advanced structural development programme, Defence Research and Development Organisation’s (DRDO) Advanced System Laboratory (ASL), Hyderabad has undertaken to obtain appropriately dispersed CNTs (namely amino multi-walled carbon nanotubes) in a polymer matrix (namely neat epoxy), in order to minimize entanglements and to reduce the size of agglomerates. As an extended part of this programme an academic investigation is conducted to determine the effects of amino Multi-Walled Carbon Nanotube (MWCNT) reinforcements on the mechanical properties of neat epoxy/ amino MWCNT nanocomposites were studied. The present paper places a special emphasis on plane strain fracture toughness under mode-I or tensile loading condition in these nanocomposites. The fracture toughness values were measured by using single edge notch beam specimens, subjected to three point bend loading as per ASTM standards. From the experimental results obtained, the reinforcements of amino MWCNTs to the neat epoxy were found to improve the ambient temperature fracture toughness by around 20% and such enhancement is essentially due to LEFM controlled toughening. This conclusion was derived due to the fact that the ratio of fracture toughness to the strength (flexural strength) is found to remain same for both matrix neat epoxy resin and amino MWCNTs reinforced nanocomposites. Field emission scanning electron microscopy studies were conducted to study the effects of morphology of reinforcing CNTs and their dispersion quality in the epoxy matrix and the same are correlated to rationalize the observed toughening to the fractographic features. All these observations have been presented and discussed in the present paper.