625 research outputs found
Corrigendum
No full textPutignano S, Gareri P, Castagna A, Cerqua G, Cervera P, Cotroneo AM, Fiorillo F, Grella R, Lacava R, Maddonni A, Marino S, Pluderi A, Putignano D, Rocca F. Retrospective and observational study to assess the efficacy of citicoline in elderly patients suffering from stupor related to complex geriatric syndrome. Clin Interv Aging. 2012;7:113–118.One of the author’s names was listed incorrectly as Roberto Grella, it should have been Rodolfo Grella.Read the original articl
Indenting viscoelastic thin layers: A numerical assessment
No full textNormal indentation of viscoelastic bodies is a technique widely employed to characterize the viscoelastic material properties. Here, a numerical Boundary Element methodology is developed to model the indentation process also when the solids in contact are thin layers. Specifically, two boundary conditions for the thin slabs are considered: the case of a confined layer, perfectly bonded to a rigid substrate, and that one of a free layer, supported by a constant pressure. Numerical analyses focus, firstly, on creep and relaxation indentation tests and show that finite values of the contacting layers thickness produce dramatic quantitative changes in comparison with what obtained under the half-plane (HP) assumption. Similar effects are found also in the case of loading and deformation indentation cycles: this results crucial for vibrational phenomena and confirms the opportunity of introducing the numerical technique here presented
On the Role of Roughness in the Indentation of Viscoelastic Solids
No full textA numerical boundary element methodology is employed to understand how fractality intervenes when a 1D rigid rough profile indents a linear viscoelastic half-plane. The focus is, in particular, on the viscoelastic dissipation and how this is influenced by the profile statistical parameters, namely, the mean square roughness h(rms) of the profile, the mean square slope m(2) and the Hurst exponent H. Our numerical investigation, properly supported by a dimensional analysis, reveals that, in the one-dimensional case under investigation, the leading role is played by h(rms) and, thus, mainly by the large scales of the rough spectrum. Clearly, on an experimental level, this implies that a simple measure of the roughness parameter h(rms) is sufficient to determine the viscoelastic dissipation
Mechanics of rough contacts in elastic and viscoelastic thin layers
No full textContact mechanics between rough solids usually relies on the half-space approximation, which assumes that the contact area dimension is much smaller than the thickness of the layers of materials that characterize the surfaces of the contacting bodies. However, such simplifying assumption is often inadequate when industrially relevant applications are considered, in particular those of biomechanical interest. Indeed, a large variety of systems, including not only classical engineering applications such as gear boxes, shafts, tyres, etc., but also biological tissues such as human skin, is characterized by superficial coatings; very often the mechanical properties of these coatings are very different from those of the bulk region of the bodies in contact. The aim of this paper is to shed light on the role played by the thickness of the layer of material used as a coating, with specific focus on the contact between a rigid rough surface and a thin deformable layer bonded to a rigid substrate. Starting from a recently developed boundary element formulation (Carbone and Putignano, 2013), we derive a methodology which accounts for finite thickness by a corrective coefficient modulating the classical Greens function, and extends our analyses to periodic domains. This enables to avoid border effects and provides an innovative tool to tackle viscoelastic contacts with realistic roughness. This is exploited to perform a thorough investigation of the mechanisms responsible for frictional losses in layered systems characterized by different materials, thickness and loading conditions. Results show that decreasing the layer thickness corresponds to an increase in the contact stiffness. Furthermore, in the case of viscoelastic layer, particular attention has to be paid to the changes in the viscoelastic dissipation due to the finite thickness of the surface layer
Peptidi HLA e tolleranza immunitaria nel trapianto d'organo.Vito Radio Editore, Putignano(Bari)
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Ruthenium and osmium complexes for the transfer hydrogenation, hydrogenation and dehydrogenation network
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Thermoelastic effects in the contact mechanics of 1D+1D rough profiles
No full textRough contact mechanics is a challenging topic that has attracted the interest of many scientists in the past and recent years. Notwithstanding a large amount of literature on the topic, there is a lack of studies investigating the contact behaviour of rough elastic bodies exchanging heat at the interface. For this reason, we propose a deterministic model to investigate the thermoelastic contact of a linear elastic half-plane indented by a rigid rough punch. Surprisingly, an increase in the temperature difference between the contacting solids does not change the relationship between contact area and load as well as that between interfacial mean separation and load. However, the thermal expansion causes an increase in the force required to sustain the contact at a given penetration. In addition, thermal contact resistance (TCR) is predicted to be a decreasing function of the contact pressure in agreement with the trend suggested by experimental data available in the literature. On the contrary, the dependence on the temperature difference ΔT seems to be strictly related to the characteristics of the materials and, for the elastic case investigated in this work, TCR is found to be almost independent of ΔT
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