  In this paper theoretical and statistical/experimental criteria for
determining the nanoscale strength of materials are proposed. In particular,
quantized criteria in fracture mechanics, dynamic fracture mechanics and
fatigue, as well as an experimental indirect observation of the nanoscale
strength, are proposed. The increasing of the dynamic resistance and the role
of a fractal crack surface formation are also rationalized. The analysis shows
that materials can be sensitive to flaws also at nanoscale (as demonstrated for
carbon nanotubes), in contrast to the conclusion of a recently published paper,
and that the surfaces are weaker than the inner parts of a solid by a factor of
about 10%. In addition, the proposed statistical/experimental procedure is
applied for predicting the nanoscale strength of the ultrananocrystalline
diamond (UNCD), an innovative material only recently developed.
