Search results for " scienza"
showing 10 items of 1301 documents
BEAM ELEMENT UNDER FINITE ROTATIONS
2021
The present work focuses on the 2-D formulation of a nonlinear beam model for slender structures that can exhibit large rotations of the cross sections while remaining in the small-strain regime. Bernoulli-Euler hypothesis that plane sections remain plane and perpendicular to the deformed beam centerline is combined with a linear elastic stress-strain law. The formulation is based on the integrated form of equilibrium equations and leads to a set of three first-order differential equations for the displacements and rotation, which are numerically integrated using a special version of the shooting method. The element has been implemented into an open-source finite element code to ease comput…
In situ monitoring of moisture uptake of flax fiber reinforced composites under humid/dry conditions
2021
The use of green materials such as natural fiber-reinforced composites represents an increasingly stringent prerogative in the future planning of industrial and non-industrial production. The optimization of these materials is the main aim of the current research, focused on the evaluation of the behavior of flax fiber reinforced composites exposed to isothermal adsorption and desorption cycles, at varying the partial pressure of water vapor (P/P0). For this purpose, the moisture uptake and the morphology changes of the composite material and their constituents were in situ monitored through a measurement protocol, by using a dynamic vapor sorption (DVS) analysis, coupled with an environmen…
Effectiveness of sodium acetate treatment on the mechanical properties and morphology of natural fiber-reinforced composites
2021
This paper aims to investigate the ability of an eco-friendly and cheap treatment based on sodium acetate solutions to improve the mechanical properties of flax fiber-reinforced composites. Flax fibers were treated for 5 days (i.e., 120 h) at 25 °C with mildly alkaline solutions at 5%, 10% and 20% weight content of the sodium salt. Quasi-static tensile and flexural tests, Charpy impact tests and dynamical mechanical thermal (DMTA) tests were carried out to evaluate the mechanical properties of the resulting composites. Fourier transform infrared analysis (FTIR) was used to evaluate the chemical modification on the fibers surface due to the proposed treatment, whereas scanning electron micro…
Improving the mechanical properties of unidirectional flax fabrics reinforced epoxy composites by sodium bicarbonate treatment
2017
Despite their beneficial effects on the adhesion between natural fibers and polymeric matrices, chemical pretreatments have become less attractive since they are expensive and harmful to environment. The present paper deals with the effect of an eco-friendly and cost effective treatment, based on the use of a sodium bicarbonate solution, on the mechanical performances of flax reinforced epoxy composites. Materials and methods: A commercial epoxy resin and unidirectional flax fabrics (190 g/m2 areal density) were used as matrix and reinforcement, respectively. The fabrics were soaked in 5 and 10 wt% solutions of sodium bicarbonate for 5 days at 25°C, then dried at 105°C for 1 day. By using u…
A non-local model of thermal energy transport: The fractional temperature equation
2013
Abstract Non-local models of thermal energy transport have been used in recent physics and engineering applications to describe several “small-scale” and/or high frequency thermodynamic processes as shown in several engineering and physics applications. The aim of this study is to extend a recently proposed fractional-order thermodynamics ( [5] ), where the thermal energy transfer is due to two phenomena: A short-range heat flux ruled by a local transport equation; a long-range thermal energy transfer that represents a ballistic effects among thermal energy propagators. Long-range thermal energy transfer accounts for small-scale effects that are assumed proportional to the product of the in…
The fractal model of non-local elasticity with long-range interactions
2010
The mechanically-based model of non-local elasticity with long-range interactions is framed, in this study, in a fractal mechanics context. Non-local interactions are modelled introducing long-range central body forces between non-adjacent volume elements of the elastic continuum. Such long-range interactions are modelled as proportional to the product of interacting volumes, to the relative displacements of the centroids and to a distance-decaying function that is monotonically-decreasing with the distance. The choice of the decaying function is a key aspect of the model and it has been proved that any continuous function, strictly positive, is thermodynamically consistent and it leads to …
Fractional calculus for the solution of non-linear stochastic oscillators with viscous dampers devices
2009
Fluid viscoelastic dampers are of great interest in different fields of engineering. Examples of their applications can be found in seismic mitigation design of structures or in vibration absorption in airplane suspension. Such devices introduce a non-linear dissipative term in the equation of motion and therefore, the solution of even a single degree of freedom system excited by a white noise process, becomes prohibitive. The solution is usually obtained by approximated methods, like the stochastic linearization technique. In this paper it is shown that, by means of fractional operators, it is possible to find the solution of oscillators provided with fluid viscoelastic devices, approachin…
THE MECHANICAL MODEL OF FRACTIONAL VISCOELASTICITY
2010
Viscoelastic materials have been more and more used nowadays for their low-cost productions as well as for their dissipative capabilities that may be coupled with others, more performing materials, to form complex-type engineering elements. The main feature of viscoelastic behavior is the relaxation of the stress state and the creep of the strain field that may be experienced, respectively, in hard or soft test devices. Such phenomenological consideration has been extensively analyzed yet at the beginning of the twentieth century and simple rheological models representing linear, constitutive, stress-velocity relations of the studied material have been proposed. Moreover the rheological rel…
Visco-elastic behavior through fractional calculus: an easier method for best fitting experimental results
2011
In capturing visco-elastic behavior, experimental tests play a fundamental rule, since they allow to build up theoretical constitutive laws very useful for simulating their own behavior. The main challenge is representing the visco-elastic materials through simple models, in order to spread their use. However, the wide used models for capturing both relaxation and creep tests are combinations of simple models as Maxwell and/or Kelvin, that depend on several parameters for fitting both creep and relaxation tests. This paper, following Nutting and Gemant idea of fitting experimental data through a power law function, aims at stressing the validity of fractional model. In fact, as soon as rela…
Filter equation by fractional calculus
2014
Aim of this paper is to represent a causal filter equation for any kind of linear system in the general form L=f(t), where f(t) is the forcing function, x(t) is the output and L is a summation of fractional operators. The exact form of the operator L is obtained by using Mellin transform in complex plane.