Quantized Failure Criteria and Indirect Observation for Predicting the Nanoscale Strength of Materials: The Example of the Ultra Nano Crystalline Diamond

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.