Sant'Ambrogio di Torino, Italy
Sant'Ambrogio di Torino, Italy

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Pugno N.M.,Polytechnic University of Turin | Pugno N.M.,National Institute of Nuclear Physics, Italy | Pugno N.M.,National Institute of Metrological Research
Journal of the Mechanics and Physics of Solids | Year: 2010

The study reported in this paper suggests that the influence of the surrounding nanotubes in a bundle is nearly identical to that of a liquid having surface tension equal to the surface energy of the nanotubes. This surprising behaviour is supported by the calculation of the polygonization and especially of the self-collapse diameters, and related dog-bone configurations, of nanotubes in a bundle, in agreement with atomistic simulations and nanoscale experiments. Accordingly, we have evaluated the strength of the nanotube bundle, with or without collapsed nanotubes, assuming a sliding failure: the self-collapse can increase the strength up to a value of about ∼30%, suggesting the design of self-collapsed super-strong nanotube bundles. Other systems, such as peapods and fullerites, can be similarly treated, including the effect of the presence of a liquid, as reported in the appendices. © 2010 Elsevier Ltd. All rights reserved.

Ferrero C.,National Institute of Metrological Research
3rd IEEE International Workshop on Metrology for Aerospace, MetroAeroSpace 2016 - Proceedings | Year: 2016

In recent years the exceptional development of cryogenic technology in connection with applications in the fields of superconductivity in the spatial sector, of particle acceleration and of research concerning thermonuclear fusion, has clearly shown the necessity of characterizing materials and transducers suitable to operate in the range from room temperature to that of liquid helium (4,2 K) At the Istituto di Metrologia «G. Colonnetti» (IMGC), Torino, of the National Research Council of Italy (C.N.R), a laboratory was established with the purpose of carrying out such characterization work. The present paper describes the IMGC (now INRIM) facilities for strain gauge characterization from room temperature down to 1,53 K. Thermal outputs and Gauge Factors are given from 293 K to 1,55 K for two different kinds of strain gauges to be used at cryogenic temperatures. © 2016 IEEE.

Chen Q.,Nanjing Southeast University | Pugno N.M.,Polytechnic University of Turin | Pugno N.M.,National Institute of Nuclear Physics, Italy | Pugno N.M.,National Institute of Metrological Research
European Journal of Mechanics, A/Solids | Year: 2013

In this paper, we analytically calculate the in-plane elastic properties (linear-elasticity and elastic buckling) of a new class of bio-inspired nano-honeycomb materials possessing a hierarchical architecture. Incorporating the surface effect, modifications to the classical results for macroscopic and nonhierarchical honeycombs are proposed, and the results are compared with those in the literature. A parametrical analysis reveals the influences of two key geometrical parameters on the overall elastic properties. We discuss the relevant mechanical properties, e.g. stiffness efficiency (stiffness-to-density ratio) and strength efficiency (strength-to-density ratio), which are indices reflecting the mechanical efficiency of materials, and discover that the structural strength can be optimized. The developed theory allows us to design a new class of nano materials with tailored mechanical properties at each hierarchical level and could be useful for many applications. © 2012 Elsevier Masson SAS. All rights reserved.

Chen Q.,Polytechnic University of Turin | Chen Q.,National Institute of Metrological Research | Pugno N.M.,Polytechnic University of Turin | Pugno N.M.,National Institute of Nuclear Physics, Italy
European Journal of Mechanics, A/Solids | Year: 2012

In this paper, we study the elastic buckling of a new class of honeycomb materials with hierarchical architecture, which is often observed in nature. Employing the topedown approach, the virtual buckling stresses and corresponding strains for each cell wall at level n - 1 are calculated from those at level n; then, comparing these virtual buckling stresses of all cell walls, the real local buckling stress is deduced; also, the progressive failure of the hierarchical structure is studied. Finally, parametric analyses reveal influences of some key parameters on the local buckling stress and strength-to-density ratio; meanwhile the constitutive behaviors and energy-absorption properties, with increasing hierarchy n, are calculated. The results show the possibility to tailor the elastic buckling properties at each hierarchical level, and could thus have interesting applications, e.g., in the design of multiscale energy-absorption honeycomb light materials. © 2011 Elsevier Masson SAS.

Pugno N.M.,Laboratory of Bio Inspired Nanomechanics Giuseppe Maria Pugno | Pugno N.M.,National Institute of Nuclear Physics, Italy | Pugno N.M.,National Institute of Metrological Research
Materials Today | Year: 2010

Cross-links are nowadays recognized to play a key role in the overall mechanical strength of buckypapers, nanotube or graphene based materials; material scientists or chemists are thus developing new nanomaterials with denser and stronger cross-links in order to maximize their mechanical strength. However, in spite of some fascinating achievements of material science and chemistry today, we are evidently far from an optimal result; the reported mechanical strength of a buckypaper, for example, is comparable to that of a classical sheet of paper. In this concept article we try to solve the paradox showing that the cross-link stiffness, a parameter still ignored in the literature, governs (more than its strength) the overall mechanical strength. New strategies for the experimentalists, e.g. the use of graded cross-links, are consequently suggested. © 2010 Elsevier Ltd. All rights reserved.

Lacquaniti V.,National Institute of Metrological Research | Belogolovskii M.,Ukrainian Academy of Sciences | Cassiago C.,National Institute of Metrological Research | De Leo N.,National Institute of Metrological Research | And 2 more authors.
New Journal of Physics | Year: 2012

We report low-temperature measurements of current-voltage characteristics for highly conductive Nb/Al-AlO x-Nb junctions with thicknesses of the Al interlayer ranging from 40 to 150 nm and ultrathin barriers formed by diffusive oxidation of the Al surface. In a superconducting state these devices have revealed a strong subgap current leakage. Analyzing Cooper-pair and quasiparticle currents across the devices, we conclude that the strong suppression of the subgap resistance compared with conventional tunnel junctions is not related to technologically derived pinholes in the barrier but rather has more fundamental grounds. We argue that it originates from a universal bimodal distribution of transparencies across the aluminum oxide barrier proposed earlier by Schep and Bauer (1997 Phys. Rev. Lett. 78 3015). We suggest a simple physical explanation of its source in the nanometer-thick oxide films relating it to strong local barrier-height fluctuations in the nearest to conducting electrode layers of the insulator which are generated by oxygen vacancies in thin aluminum oxide tunnel barriers formed by thermal oxidation. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Biasetti J.,KTH Royal Institute of Technology | Spazzini P.G.,National Institute of Metrological Research | Swedenborg J.,Karolinska Institutet | Christian Gasser T.,KTH Royal Institute of Technology
Frontiers in Physiology | Year: 2012

Abdominal Aortic Aneurysms (AAAs) are frequently characterized by the presence of an Intra-LuminalThrombus (ILT) known to influence their evolution biochemically and biome-chanically. The ILT progression mechanism is still unclear and little is known regarding the impact of the chemical species transported by blood flow on this mechanism. Chemical agonists and antagonists of platelets activation, aggregation, and adhesion and the proteins involved in the coagulation cascade (CC) may play an important role in ILT development. Starting from this assumption, the evolution of chemical species involved in the CC, their relation to coherent vortical structures (VSs) and their possible effect on ILT evolution have been studied. To this end a fluid-chemical model that simulates the CC through a series of convection-diffusion-reaction (CDR) equations has been developed. The model involves plasma-phase and surface-bound enzymes and zymogens, and includes both plasma-phase and membrane-phase reactions. Blood is modeled as a non-Newtonian incompressible fluid. VSs convect thrombin in the domain and lead to the high concentration observed in the distal portion of the AAA. This finding is in line with the clinical observations showing that the thickest ILT is usually seen in the distal AAA region. The proposed model, due to its ability to couple the fluid and chemical domains, provides an integrated mechanochemical picture that potentially could help unveil mechanisms of ILT formation and development. © 2012 Biasetti, Spazzini, Swedenborg and Gasser.

Chen Q.,Polytechnic University of Turin | Pugno N.M.,Polytechnic University of Turin | Pugno N.M.,National Institute of Nuclear Physics, Italy | Pugno N.M.,National Institute of Metrological Research
Composites Part B: Engineering | Year: 2011

In this paper, the elastic properties of a 2-D woven hierarchical tissue are modeled, assuming the warp and fill yarns at level 0 as an orthotropic material. Tissues at level (n - 1) are considered as warp and fill yarns at level n; correspondingly, considering matrix transformation and stiffness averaging, stiffness matrices of the tissues at level (n - 1) are employed to calculate those of the tissues at level n. We compare the theory with experiments on tendons from the literature and on leaves performed by ourselves. The results show the possibility of designing a new class of hierarchical 2-D scaffolds with desired elastic anisotropy, better matching that of biological tissues and thus maximizing the tissue regeneration at each hierarchical level. © 2011 Elsevier Ltd. All rights reserved.

Pugno N.M.,Polytechnic University of Turin | Pugno N.M.,National Institute of Nuclear Physics, Italy | Pugno N.M.,National Institute of Metrological Research
International Journal of Fracture | Year: 2011

In this paper we derive the theory of multiple peeling, extending the pioneering energy-based single peeling theory of Kendall, including large deformations and pre-stretching. We can thus treat a complex system of films, adhering over a substrate and having a common hinge where the pulling force is applied. Two case studies are investigated: the asymmetric V-shape double peeling and the symmetric cone-shape configuration with N peeling tapes, both requiring the solution of six nonlinear coupled equations (instead of the one needed in the simpler single peeling problem). Remarkable implications emerge: (1) for moderate deformations, the critical strain of a tape is identical to that of the single peeling; (2) an optimal peeling angle, at which adhesion is maximal, is discovered; (3) an additional optimization, even for hierarchical structures, is introduced by imposing the delamination force equal to the intrinsic fracture of the tape. Also, the length of the peeling process zone is calculated, suggesting different optimal values for flaw-tolerant peeling at different angles. Applications to gecko adhesion, for which the flaw-tolerant peeling is demonstrated, and spider silk anchors, that we are going to discuss in details in subsequent papers, are envisioned (including a new pre-stretching mechanism for adhesion control) and suggested by the evidence of a smart mechanism capable of maximizing adhesion simply by increasing the applied tension. © 2011 Springer Science+Business Media B.V.

Bosia F.,University of Turin | Abdalrahman T.,Polytechnic University of Turin | Pugno N.M.,Polytechnic University of Turin | Pugno N.M.,National Institute of Nuclear Physics, Italy | Pugno N.M.,National Institute of Metrological Research
Nanoscale | Year: 2012

Natural materials are often organized in complex hierarchical architectures to optimize mechanical properties. Artificial bio-inspired materials, however, have thus far failed to successfully mimic how these architectures improve material characteristics, for example strength. Here, a method is proposed for evaluating the role of hierarchy on structural strength. To do this, we consider different hierarchical architectures of fiber bundles through analytical multiscale calculations based on a fiber bundle model at each hierarchical level. In general, we find that an increase in the number of hierarchy levels leads to a decrease in the strength of material. However, when a composite bundle with two different types of fibers is considered, an improvement in the mean strength is obtained for some specific hierarchical architectures, indicating that both hierarchy and material "mixing" are necessary ingredients to obtain improved mechanical properties. Results are promising for the improvement and "tuning" of the strength of bio-inspired materials. © 2012 The Royal Society of Chemistry.

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