摘要：Multiscale nano-composites have been reported tohave enhanced toughness especially with the use of nanotubes. Nano-materials tend to arrest the growth of crackwhen loaded. An increase of 8.5% in stiffness was reportedwith the addition of nano-fillers in the matrix [1]. Similarresults were obtained by Ashish Warrier et.al when CNTswhere used in both the matrix and the sizing [2]. Thus itcould be said with fair amount of confidence that, a genuine increase in mechanical properties-fracture toughness,inter-laminar shear strength-is observed when CNTs areeither deposited on the fibre or dispersed in the matrix. Thedegree to which these properties are improved depends ona variety of factors like the way in which CNTs are integrated in the composites-like growing on fibres, mixed inthe resin, added to fibre sizing, type of CNTs, surface functionalization, toughness of base matrix etc. [3]. The enhancement of fracture toughness in polymer compositesdepends on the length of the CNTs. The bridging processcould either be due to the CNT pull-out or CNT rupture. Ineither of the cases the nanotubes bridge the crack surface,thereby shielding the crack front from carrying the entiretensile load [4]. Thus, from these positive developmentsreported, nanotubes formed an essential part of this study.Crack propagation can be considered as an ultimate formof failure mechanism, which takes place in the interlaminar zone during de-lamination. Since it can be evaluated visually it could be considered as a macroscopic failureactivity. Microscopic phenomena leading to de-laminationsuch as fibre rupture, matrix cracking etc. could be monitored by acoustics emissions [5–9]. AE is an efficientmethod to monitor in real time the damage growth in structural components and laboratory specimens. In loadedmaterials, strain-energy release due to micro-structuralchanges results in stress wave propagation. In compositematerials many mechanisms have been confirmed to produce AE signals which includes matrix-cracking, fibrematrix interface de-bonding, fibre breakage and delamination. AE deals with the detection of such waves atthe surface of the material. Thus, this technique allows notonly to determine the location of the source of the emissionbut also helps in determination of its nature [9].
