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Sant'Ambrogio di Torino, Italy

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

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. Source

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

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. Source

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

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. Source

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

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. Source

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

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. Source

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