arXiv subjects

Nicola M. Pugno

Publications and source records attributed to Nicola M. Pugno.

60 records · Page 4Linked to original sources

arXiv2007

Atomistic Simulations of the Mechanical Properties of 'Super' Carbon Nanotubes

The mechanical properties of the so-called `super' carbon nanotubes (STs) are investigated using classical molecular dynamics simulations. The STs are built from single walled carbon nanotubes (SWCNTs) connected by Y-like junctions forming an ordered carbon nanotube network that is then rolled into a seamless cylinder. We observed that the ST behavior under tensile tests is similar to the one presented by fishing nets. This interesting behavior provides a way to vary the accessible channels to the inner parts of STs by applying external mechanical load. The Young's modulus is dependent on the ST chirality and it inversely varies with the ST radius. Smaller reduction of breaking strain values due to temperature increase is predicted for zigzag STs compared to SWCNTs. The results show that, for STs with radius ~ 5 nm, the junctions between the constituent SWCNTs play an important role on the fracture process. The Young's modulus and tensile strength were estimated for hierarchical higher-order STs using scaling laws related to the ST fractal dimension. The obtained mechanical properties suggest that STs may be used in the development of new porous, flexible, and high-strength materials.

cond-mat.mtrl-sci↗

arXiv2006

On the Strength of the Carbon Nanotube-Based Space Elevator Cable: From Nano- to Mega-Mechanics

In this paper different deterministic and statistical models, based on new quantized theories proposed by the author, are presented to estimate the strength of a real, thus defective, space elevator cable. The cable, of ~100 megameters in length, is composed by carbon nanotubes, ~100 nanometers long: thus, its design involves from the nano- to the mega-mechanics. The predicted strengths are extensively compared with the experiments and the atomistic simulations on carbon nanotubes available in the literature. All these approaches unequivocally suggest that the megacable strength will be reduced by a factor at least of ~70% with respect to the theoretical nanotube strength, today (erroneously) assumed in the cable design. The reason is the unavoidable presence of defects in a so huge cable. Preliminary in silicon tensile experiments confirm the same finding. The deduced strength reduction is sufficient to pose in doubt the effective realization of the space elevator, that if built as today designed will surely break (according to the s opinion). The mechanics of the cable is also revised and possibly damage sources discussed.

cond-mat.mtrl-sci↗

arXiv2006

A Universal Scaling Law for Nanoindentation, But Not only

In this letter we derive a universal law for nanoindentation, considering different sizes and shapes of the indenter. The law matches as limit cases all the well-known hardness scaling laws proposed in the literature. But our finding can also explain their deviations experimentally observed at the nanoscale. An even more general scaling law is then formulated, also in the fast and slow dynamics; it is based only on the surface over volume ratio of the domain in which the energy flux occurs: thus, its application in different fields, also for chaotic and complex (e.g., biological) systems, is demonstrated.

cond-mat.mtrl-sci↗

arXiv2006

High Strength Over Density Ratio Invisible Cables

Spiders suggest us that producing high strength over density ratio invisible cables could be of great importance. In this letter we show that such invisible cables could in principle be built, thanks to carbon nanotube bundles. Theoretical strength of about 10MPa, Young modulus of about 0.1GPa and density of 0.1Kg per cubic meter are estimated.

cond-mat.mtrl-sci↗

arXiv2005

Design and Optimization of Nano-Bio-Inspired Hierarchical or Nano-Grained Materials

In this letter a mathematical model to design nano-bio-inspired hierarchical materials is proposed. An optimization procedure is also presented. Simple formulas describing the dependence of strength, fracture toughness and stiffness on the considered size-scale are derived, taking into account the toughening biomechanisms. Furthermore, regarding nano-grained materials the optimal grain size is deduced: incidentally, it explains and quantitatively predicts the deviation from the well-known Hall-Petch regime. In contrast with the common credence, this deviation does not arise at a universal value of grain size but it is strongly dependent on the mechanical properties of the mixture.

cond-mat.mtrl-sci↗

arXiv2004

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.

cond-mat.mtrl-sci↗