Biography
La Ragione is Assistant Professor at the Department of Civil and Environmental Engineering at Politecnico di Bari since 2002 after spending two years as a research associate at Cornell University (U.S.A.), Schlumberger-Doll Research (U.S.A.) and Kingston University (U.K.) where he contributed to the development of continuum theories for granular materials. He has held visiting positions at Max-Planke Institute in Dresda- Germany, Isaac Newton Institute in Cambridge -U.K., Cornell University, Henry Poincarè Institute de Paris - France, Kavli Institute for Theoretical Physics in Santa Barbara- U.S.A.
Research Plan
My research interest concern the mechanical behavior of aggregate of particles focusing, in particular, on constitutive relations for granular materials, contact mechanics, wave propagations, localization, microstructure and particle phase in suspensions. More emphasis has been given to granular materials because of the varieties of unsolved basic problems and for a possible connection between them and other materials. For example, idealized as an aggregate of particles, the mechanical behavior of a granular material can also offer understanding of the behavior of emulsions, concentrated suspensions, glasses, and biological material. The relation between stress and strain for such materials is developed by focusing, at the micro-level, on the contact interaction between the particles. By means of suitable averages, it is then possible to obtain an overall response of the aggregate. Two possible regimes of deformations can be studied: quasi- static deformations, in which the particles are in contact during the loading, and rapid deformations, in which collisions between the particles is the relevant interaction of the problem. In the quasi-static regime, the constitutive relation describes deformations that occur prior to the onset of localization. There, it is possible to predict both the elastic and inelastic response of the aggregate. My research plan will be devoted to applying the micro-mechanical approach, as briefly described above, to develop an understanding of the behavior of a granular material - in particular, to the possibility of predicting shear bands. The study will be conducted using numerical simulations with the D.E.M code (Distinct Element Method) and theoretical modeling to extend the theory so far developed. Moreover, my curiosity will be directed towards the behavior of an aggregate of particles in a Newtonian fluid and the capacity of such a suspension to behave as non-Newtonian fluid at low Reynolds numbers. The presence of particle pressure and the development of anisotropy is very fascinating topic that has stimulated a number of researchers. A recent development of my work has been related to the relationship between the behavior of an aggregate of particles and the trusses of structural mechanics. The concepts of statically determined and overdetermined seem to offer several explanations of the response of an idealized granular material. Another natural extension of the micro-mechanical approach would be to study capillary phenomena in dense granular materials, where, for example, a goal would be the understanding of the role of the water menisci between neighboring particles and their influence on the macroscopic response of the aggregate. Possible extensions of my research to new recent bio- mechanics application are in itinere; they regard the study of suspensions as a dense, random identical, neutrally buoyant spheres subject to a steady, homogeneous, deviatoric shearing. In this situation suspension exhibit a migration phenomena that has been also observed in the blood flow, known as the Fahreus-Lindqvist effect, where it is evident a decrease in apparent viscosity close to the boundary of the vessel.
Current Research Projects
2005-2007 - Theoretical, Numerical and Experimental Models on granular materials, Ministero degli Affari Esteri (MAE), Collaborazione Scientifica e Tecnologica Bilaterale, Protocollo Italia- Stati Uniti (Annex IV)
2008-2010 - PRIN - M.I.U.R. - Modellazione e tecniche di approssimazione numerica avanzati della meccanica dei continui e delle strutture.
2006-2009 - P.S.T. Regione Puglia - Landslide risk assessment for the planning of small urban settlements within chain areas: the case of Daunia.
Workshop: Deformation and Failure of Geomaterials.
Teaching Interests
Courses I have taught include Theory of Elasticity, Plasticity, Continuum Mechanics, Structural Dynamics, Strength of Materials, Solid Mechanics, Microstructural Material Behavior (with specialization in granular or particulate media). I have also been a Visiting Professor and Lecturer at Cornell Univeristy, USA (2004), where I taught Calculus for Engineering.
Pubblications