Journal
PHILOSOPHICAL MAGAZINE
Volume 91, Issue 7-9, Pages 1179-1189Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1080/14786435.2010.487474
Keywords
in situ nanoindentation; fracture toughness; brittle-ductile transition; silicon; fracture mechanics; nanoparticle
Categories
Funding
- National Science Foundation [CTS-0506748]
- Air Force Office of Scientific Research [AOARD-08-4134]
- Abu Dhabi-Minnesota Institute for Research Excellence (ADMIRE)
- Petroleum Institute (PI) of Abu Dhabi and the Department of Chemical Engineering and Materials Science of the University of Minnesota
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Smaller is stronger is now a tenet generally consistent with the predominance of evidence. An equally accepted tenet is that fracture toughness almost always decreases with increasing yield strength. Can smaller is tougher then be consistent with these two tenets? It is taught in undergraduate engineering courses that one design parameter that allows for both increased strength and fracture toughness is reduced grain size. The present study on the very brittle semiconductor silicon proves this exception to the rule and demonstrates that smaller can be both stronger and tougher. Three nanostructures are considered theoretically and experimentally: thin films, nanospheres, and nanopillars. Using a simple work per unit fracture area approach, it is shown at small scale that toughness is inversely proportional to the square root of size. This is supported by experimental evidence from in situ electron microscopy nanoindentation at length scales of less than a micron. It is further suggested that dislocation shielding can explain both strength and toughness increases at the small scales.
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