Indentation Fracture Resistance Vs Conventional Fracture Toughness of Carbon Nanotube/Alumina Nanocomposites

Multiwalled carbon nanotube (MWCNT)/alumina (Al2O3) nanocomposites were fabricated using two varieties of CNT to access the effect of morphological variation of the filler on fracture resistance (K (R))/toughness (K (IC)) of studied specimens. Special attention was also given to compare K (R) and K (IC) values for tracing out the primary selection criterion of appropriate indentation fracture (IF) equation used in relatively faster and simpler 'direct crack measurement' (DCM) technique to evaluate K (R) values close to stringent 'single edge notched beam' (SENB) derived K (IC) data. While K (IC) was calculated using the unique expression suitable for specimens tested under four-point flexure, K (R) values were evaluated using a series of IF equations suitable for Palmqvist and/or median crack systems. As far as change in K (R) and/or K (IC) of nanocomposites was concerned, it was noticed that for longer/thicker CNTs having relatively higher internal bamboo structures, much lower amount (0.15 vol pct) was adequate to achieve the highest improvement in K (R) (similar to 87 pct) or K (IC) (similar to 50 pct) over pure Al2O3 ((Laugier) K (R) a parts per thousand 3.83 MPa-m(0.5); K (IC) a parts per thousand 3.48 MPa-m(0.5)) than that required for smaller/thinner CNTs (a parts per thousand yen0.3 vol pct). On contrary, resistance to fracture up to 1.2 vol pct CNT loading was much enhanced in specimens fabricated with smaller/thinner CNTs over those fabricated using longer/thicker CNTs. Comparatively better morphology, adequate CNT dispersion, and higher population of bridging elements in specimens containing smaller/thinner CNTs were the key factors behind such toughness retention. (C) The Minerals, Metals & Materials Society and ASM International 2015