1,635 research outputs found
Hierarchical Fibers with a Negative Poisson’s Ratio for Tougher Composites
No full textIn this paper, a new kind of hierarchical tube with a negative Poisson’s ratio (NPR) is proposed. The first level tube is constructed by rolling up an auxetic hexagonal honeycomb. Then, the second level tube is produced by substituting the arm of the auxetic sheet with the first level tube and rolling it up. The Nth ( ) level tube can be built recursively. Based on the Euler beam theory, the equivalent elastic parameters of the NPR hierarchical tubes under small deformations are derived. Under longitudinal axial tension, instead of shrinking, all levels of the NPR hierarchical tubes expand in the transverse direction. Using these kinds of auxetic tubes as reinforced fibers in composite materials would result in a higher resistance to fiber pullout. Thus, this paper provides a new strategy for the design of fiber reinforced hierarchical bio-inspired composites with a superior pull-out mechanism, strength and toughness. An application with super carbon nanotubes concludes the paper
Laura Pugno (Roma, 1970)
No full textLaura Pugno ha publicado cinco novelas: La chica salvaje (Marsilio, 2016), La caza (Ponte alle Grazie, 2012), Antártida (Minimum fax, 2009), Cuando vengas (Minimum fax, 2011) y Sirenas (Einaudi, 2007); y el volumen de relatos Sleepwalking (Sironi, 2002). Como poeta destacamos Nácar (Huerga y Fierro, 2016, edición bilingüe), blanco (Nottetempo, 2016), La mente paisaje (Perrone, 2010) y El color oro (Le Lettere, 2007). Ha sido incluida en numerosas antologías, como Nuevos poetas italianos 6 (Einaudi, 2012). Codirige la colección I domani de la editorial Aragno. Ha recibido el Premio Dedalus, el Frignano y el Libro del Mare. www.laurapugno.i
Elastic and Transport Properties of the Tailorable Multifunctional Hierarchical Honeycombs
No full textIn this paper, we analytically studied the in-plane elastic and transport properties of a peculiar hexagonal honeycomb, i.e., the multifunctional hierarchical honeycomb (MHH). The MHH structure was developed by replacing the solid cell walls of the original regular hexagonal honeycomb (ORHH) with three kinds of equal-mass isotropic honeycomb sub-structures possessing hexagonal, triangular and Kagome lattices. Formulas to calculate the effective in-plane elastic properties and conductivities of the MHH structure at all densities were developed. Results show that the elastic properties of the MHH structure with the hexagonal sub-structure were weakly improved in contrast to those of the ORHH. However, the triangular and Kagome sub-structures result in substantial improvements by one or even three orders of magnitude on Young’s and shear moduli of the MHH structure, depending on the cell-wall thickness-to-length ratio of the ORHH. The present theory could be used in designing new tailorable hierarchical honeycomb structures for multifunctional applications
Velcro® nonlinear mechanics
No full textIn this letter a Velcro® nonlinear mechanics is presented. In particular, a calculation of the “elastic strength” of hooks with friction is derived. The author quantifies, as the intuition and Velcro® material suggest, that hooks (and loops) allow reversible strong attachment, finding elastic plastic or hyperelastic nonlinear behaviors, as a function of the competition between friction and finite displacements. Thus, the author presents here a Velcro® nonlinear mechanics to design and optimize hooked systems
Systematic numerical investigation of the role of hierarchy in heterogeneous bio-inspired materials
No full textIt is well known that hierarchical structure is an important feature in biological materials to optimise various properties, including mechanical ones. It is however still unclear how these hierarchical architectures can improve material characteristics, for example strength. Also, the transposition of these structures from natural to artificial bioinspired materials remains to be perfected. In this paper, we introduce a numerical method to evaluate the strength of fibre-based heterogeneous biological materials and systematically investigate the role of hierarchy. Results show that hierarchy indeed plays an important role and that it is possible to “tune” the strength of bio-inspired materials in a wide range of values, in some cases improving the strength of non-hierarchical structures considerably
A model for hierarchical anisotropic friction, adhesion and wear
No full textDue to a widespread number of examples, biological hierarchical structures have been studied for years, founding that surface properties are strictly correlated to the surface roughness. Since friction appears to be a multiscale phenomenon and hierarchy optimizes the macroscopic mechanical properties of bodies, it may be of great interest to develop a model to predict friction of structures with hierarchical surfaces. Thus, we propose an analytical model to describe anisotropic friction, adhesion and wear of hierarchical surfaces. The model describes friction between two generic rough surfaces in contact, sliding one against the other. Then, it has been extended to adhesion, wear and finally to multiple hierarchical levels to obtain the global frictional response
Nanotribology of Spiderman
No full textInvited lecture, Int. Conf. Nanoscience & Nanotechnology, Frascati (ITA), Nov. 6-9, 2006. --- Spiders can produce cobwebs with high strength to density ratio and surprisingly display self-cleaning, strong and releasable adhesion (as geckos). Nanointerlocking, capillary and van der Waals forces, all potential adhesive mechanisms, were thus discussed, demonstrating the key role played by hierarchy to the design of super-hydrophobic, i.e. self-cleaning (by activating fakir drops as in lotus' leaves) and super-adhesive materials. The reversibility of the strong attachment was quantified thanks to an improved nonlinear peeling model, for which the solution in closed form was provided. Thus, mimicking Nature, thanks to carbon nanotube-based technology, we have suggested [N. Pugno, J. Phys. Condens. Matter 19, 395001 (2007)] the feasibility of large invisible cables, as well as of self-cleaning, super-adhesive and releasable hierarchical smart materials. We have found that a man can be supported by a transparent cable with cross-section of 1 cm2 and feasibly, with spider material gloves and boots, could remain attached even to a ceiling: a preliminary step towards a Spiderman sui
Mimicking water striders’ legs superhydrophobicity and buoyancy with cabbage leaves and nanotube carpets
No full textIn this work, we have studied the superhydrophobicity and buoyancy of two types of nanostructured surfaces: the cabbage leaf and a vertically aligned carbon nanotubes (VACNTs) carpet. The wettability of these surfaces were characterized by contact angle, tilting angle, sliding volume and sliding speed measurements. The results were correlated to the related surface topologies, which were investigated by scanning electron microscopy. Buoyancy of different surfaces has been investigated through measurements of the forces acting on the surface. Finally, we demonstrate that cabbage leaves and VACNT carpets have some common features with the water strider’s leg, better understanding the mechanisms of buoyancy related to the structural shape and size of natural or artificial nanostructures
Mechanical properties of a hollow-cylindrical-joint honeycomb
No full textIn this paper, we constructed a new honeycomb by replacing the three-edge joint of the conventional regular hexagonal honeycomb with a hollow-cylindrical joint, and developed a corresponding theory to study its mechanical properties, i.e., Young's modulus, Poisson's ratio, fracture strength and stress intensity factor. Interestingly, with respect to the conventional regular hexagonal honeycomb, its Young's modulus and fracture strength are improved by 76% and 303%, respectively; whereas, for its stress intensity factor, two possibilities exist for the maximal improvements which are dependent of its relative density, and the two improvements are 366% for low-density case and 195% for high-density case, respectively. Moreover, a minimal Poisson's ratio exists. The present structure and theory could be used to design new honeycomb materials
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