Micro-scale damage sensing in self-sensing nanocomposite material based CNTs

Abstract

Self-sensing nanocomposites based on multi-walled carbon nanotubes (MWCNTs) offer a remarkable range of properties and can be used successfully for many important industrial and engineering applications. Here, we demonstrate the performance of these nanocomposites material when subjected to structural damage at the micro-scale level. Nanocomposite specimens containing different weight % of MWCNTs were prepared using a hot pressing technique. The homogenous distribution of the MWCNTs inside the nanocomposite matrix was investigated using both scanning electron microscopy (SEM) and Raman spectroscopic techniques. The self-sensing nanocomposite specimens were indented to produce sub-surface damage using a Vickers nano-indentation test. The change in the electrical resistance was measured experimentally after each indentation event in order to establish and understand, the structural behaviour of the specimen following the micro-damage incurred. The experimental results show that adding MWCNTs can effectively enhance the electrical and mechanical properties of the nanocomposite materials. Hardness and electrical conductivity increased with increasing MWCNTs concentrations, reaching the highest values at 4.0 wt% MWCNTs. Accompanying these changes both the indentation depth and the defined plasticity index was observed to decrease. Moreover, changes in the electrical resistance of the specimens and the permanent electric damage parameter (β) values also increased with increases in the applied indentation load. A simple micro-scale model is suggested to predict the change in resistance caused by the micro-indentation damage. The results obtained from this model correlate well with the results obtained from the experimental tests. Therefore, it is speculated that the suggested model can be used to predict the damage in a structure in a self-sensing manner, for damage occurring at the micro-scale level.