Search results for " meccanica"
showing 10 items of 819 documents
Analysis of the leaf deposit in chemical distribution on vineyard in different wind conditions
2008
Numerical model for composite material with polymer matrix reinforced by carbon nanotubes
2008
Due to the high stiffness and strength, as well as their ability to act as conductors, carbon nanotubes are under intense investigation as fillers in polymeric materials. The nature of the carbon nanotube/polymer bonding and the curvature of the carbon nanotubes within the polymer have arisen as particular factors in the efficacy of the carbon nanotubes to actually provide any enhanced stiffness or strength to the nanocomposite. Here the effects of carbon nanotube curvature and interface interaction with the matrix on the nanocomposite stiffness are investigated using nanomechanical analysis. In particular, the effects of poor bonding and thus poor shear lag load transfer to the carbon nano…
A numerical-analytical model for the characterization of composites reinforced by carbon nanotubes
2010
A mixed model, numerical-analytical, is presented that allows one to predict the elastic properties of carbon nanotube (CNT)/polymer composites containing a random distribution of CNTs, while taking account of the curvature that they show when immersed in the polymer. This hybrid approach is a significant advance over micromechanical modeling and can be applied to all nanostructured composites.
Investigation on the indentation behavior of sandwich beams using crushable and hyperelastic foam cores
2010
In this work the indentation behaviour of sandwich beams is studied adopting the classical approach representing the core material as a Winkler-type foundation. It is shown how most of the proposed theories can be derived from a general fourth order linear differential equation expressing the equilibrium of the indented beam skin. Different assumptions on the supporting boundary constraints and materials constitutive behaviour, lead to simplifications of the general equation and to the prediction of different indentation features. An extension of the Segment-Wise approach recently proposed in the literature is in particular presented with potential to better simulate foam cores with markedl…
Valutazione delle lesioni nell’impatto ciclista adolescente -veicolo con simulazione multibody
2016
Le situazioni di impatto e la dinamica di ciclista e pedone sono le informazioni fondamentali per lo sviluppo di soluzioni efficaci per migliorare la protezione del pedone e del ciclista in caso di urto con autovetture. La casistica degli incidenti a Palermo, negli ultimi anni, avvenuti su strade urbane (84%) che coinvolgono adolescenti (6,4%), mostra che i ciclisti hanno in genere una posizione di impatto superiore rispetto al pedone, con una quota maggiore di lesioni per urti nella zona del parabrezza. In questo lavoro è eseguita la simulazione dinamica per lo studio delle lesioni alla testa e al torace dell’adolescente, tra una bicicletta generica e un modello di auto che presenta caratt…
CONSIDERAZIONI TEORICHE E PRATICHE SUL METODO DEL MASSIMO RETTANGOLO CIRCOSCRITTO PER LA VALUTAZIONE DELL’AMPIEZZA DELLA TENSIONE TANGENZIALE NEI CRI…
2012
The multiaxial fatigue criteria based on the approach of the critical plane require the determination of the amplitude of the alternating shear stress τ aacting on different planes passing through the point of the material analyzed. In the case of non-proportional stresses the shear stress vector varies both in modulus and direction and its tip describes a curvedefined loading path. In these cases τ ais identified and evaluated by means of special procedures the most recent, and apparently more effective, of which is that of the Maximum Circumscribed Rectangle (MCR) to the loading path itself. In particular τ ais equal to the length of the diagonal of the MCR. In this paper, the MCR method …
Improvements in the algorithms for the determination of the shear stress components in critical plane class fatigue criteria
2010
This paper presents two improvements in the procedure for the evaluation of the amplitude and mean values of the shear stress in critical plane class fatigue criteria, when the method of the Minimum Circumscribed Circle (MCC) to the path of the tip of the vector is used. In particular, the paper shows how it is possible to reduce the number of material planes passing through the point of interest in which the MCC has to be determined and the number of points of each curve that has to be considered for the determination of the MCC, noticeably reducing the computational time.
APPLICAZIONE DI UN PROTOTIPO DI MOTOVANGATRICE PER PRESERVARE LA FERTILITÀ DEL SUOLO
Negli ambienti caratterizzati da forti pendenze o sistemati a terrazze, nell’ambito delle lavorazioni superficiali, viene impiegato diffusamente il motocoltivatore provvisto di zappatrice rotativa. Tuttavia, l’effetto dell’uso ripetuto della zappatrice per lavorazione del terreno ha una notevole influenza sulle caratteristiche del terreno, che si presenta finemente polverizzato, soffice e astrutturato. Al fine di limitare tali inconvenienti, è stata progettata dalla sezione Meccanica del Dipartimento Scienze Agrarie e Forestali dell’Università di Palermo, in collaborazione con la ditta costruttrice Agrotec di Padova, una macchina innovativa semovente provvista di organi di lavoro del tipo a…
Mechanical properties of carbon nanotube reinforced nanocomposites
2013
One way to take advantage of the marvelous properties of the carbon nanotubes consists in incorporating them into a matrix to build composite materials. The best candidates for this task are undoubtedly polymers thanks to their strength, toughness, low weight, and easy processing. A mixed model, numerical-analytical, is presented that allows one to predict the elastic properties of carbon nanotube (CNT)/polymer composites containing a random distribution of CNTs, while taking account of the curvature that they show when immersed in the polymer. A three-dimensional model, using a single CNT immersed in an infinite matrix, allows us to numerically evaluate the concentration tensor by evaluati…
An Efficient Damping Technique for the Unstable Hysteretic Rotor Whirl by Proper Suspension Systems
2009
This paper shows as the destabilising influence of the shaft hysteresis on the supercritical rotor whirl can be efficiently counterbalanced by external dissipative sources. After calculating the steady whirling paths of the rotor and the bearing due to unbalance, the stability is checked by the Routh-Hurwitz procedure, investigating the influence of the stiffness anisotropy of the supports. A fairly interesting result is that the instability phenomena can be conveniently prevented by different suspension stiffness in the horizontal and vertical planes.