Search results for "scienza"
showing 10 items of 1408 documents
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.
On the numerical implementation of a 3D fractional viscoelastic constitutive model
2015
The aim of this paper is the implementation of a 3D fraction al viscoelastic constitutive law in a user material subroutine (UMAT) in the finite element software Abaqus. Essential to the implementation of the model is access to the strain history at each Gauss point of each element in a constructive manner. Details of the UMAT and comparison with some analytical results are presented in order to show that the fractional viscoelastic constitutive law has been successfully implemented.
Mechanical properties of basalt fiber reinforced composites manufactured with different vacuum assisted impregnation techniques
2016
Abstract This work describes an experimental mechanical characterisation campaign on composites made out of a quasi-unidirectional basalt fabric. In order to evaluate the ability of commercial basalt fabrics and their composites to meet the potentials of basalt fibers, the work has used raw materials from commercial catalogs with no further modification. Two common manufacturing techniques for medium performance composites have been adopted: vacuum assisted resin infusion, and hand-impregnated vacuum bagging. Two panels, one for each technique, have been fabricated, able to provide a sufficient number of samples for a comprehensive stiffness and strength characterization through Tensile, Fl…
Inter-Element Crack Propagation with High-Order Stress Equilibrium Element
2021
The present contribution proposes a formulation based on the use of hybrid equilibrium elements (HEEs), for the analysis of inter-element delamination and fracture propagation problems. HEEs are defined in terms of quadratic stress fields, which strongly verify both the homogeneous and inter-element equilibrium equations and they are employed with interfaces, initially exhibiting rigid behavior, embedded at the elements’ sides. The interface model is formulated in terms of the same degrees of freedom of the HEE, without any additional burden. The cohesive zone model (CZM) of the extrinsic interface is rigorously developed in the damage mechanics framework, with perfect adhesion at the pre-…