Search results for "Viscoelasticity"
showing 10 items of 224 documents
On the influence of the initial ramp for a correct definition of the parameters of fractional viscoelastic materials
2014
Creep and/or Relaxation tests on viscoelastic materials show a power-law trend. Based upon Boltzmann superposition principle the constitutive law with a power-law kernel is ruled by the Caputo's fractional derivative. Fractional constitutive law posses a long memory and then the parameters obtained by best fitting procedures on experimental data are strongly influenced by the prestress on the specimen. As in fact during the relaxation test the imposed history of deformation is not instantaneously applied, since a unit step function may not be realized by the test machine. Usually an initial ramp is present in the deformation history and the time at which the deformation attains the maximum …
Health monitoring of high performance composite pressure vessels,
2018
International audience; The most important form of damage in carbon fiber reinforced composite pressure vessels is the failure of the fibers however the rate of fiber failure is controlled by the viscoelastic nature of the matrix, which determines overall in-service lifetimes. This type of damage is very different from that encountered with metal pressure vessels and requires a detailed understanding in order to ensure reliability. Innovative proof testing methods based on these processes are necessary. The damage processes and the means of quantifying them are discussed. Their reliability under pressure over periods of decades is analyzed. Intrinsic safety factors linked directly to the pr…
Impact of hydrothermal ageing on the thermal stability, morphology and viscoelastic performance of PLA/sisal biocomposites
2016
The influence of the combined exposure to water and temperature on the behaviour of polylactide/sisal biocomposites coupled with maleic acid anhydride was assessed through accelerated hydrothermal ageing. The biocomposites were immersed in water at temperatures from 65 to 85 °C, between the glass transition and cold crystallisation of the PLA matrix. The results showed that the most influent factor for water absorption was the percentage of fibres, followed by the presence of coupling agent, whereas the effect of the temperature was not significant. Deep assessment was devoted to biocomposites subjected to hydrothermal ageing at 85 °C, since it represents the extreme degrading condition. Th…
Magnetic wire-based sensors for the micro-rheology of complex fluids
2013
We propose a simple micro-rheology technique to evaluate the viscoelastic properties of complex fluids. The method is based on the use of magnetic wires of a few microns in length submitted to a rotational magnetic field. In this work, the method is implemented on a surfactant wormlike micellar solution that behaves as an ideal Maxwell fluid. With increasing frequency, the wires undergo a transition between a steady and a hindered rotation regime. The study shows that the average rotational velocity and the amplitudes of the oscillations obey scaling laws with well-defined exponents. From a comparison between model predictions and experiments, the rheological parameters of the fluid are det…
Cell motility probed by noise analysis of thickness shear mode resonators.
2006
The quartz crystal microbalance (QCM) technique is an emerging bioanalytical tool to study the behavior of animal cells in vitro. Due to the high interfacial sensitivity of thickness shear mode (TSM) resonators it is possible to monitor the formation and breakage of cell-matrix interactions and changes in viscoelasticity of the cell bodies, as well as minute cell volume alterations by the time course of their resonance frequency even with millisecond time resolution. We found that mammalian MDCK-II cells grown on TSM resonators impose characteristic fluctuations on the resonance frequency, which are a quantitative indicator for dynamic activities of the cells on the surface and report on th…
Effect of moisture on elastic and viscoelastic properties of fiber reinforced plastics: Retrospective and current trends
2019
Abstract This chapter is a brief review of journal papers and books about moisture and composites with polymer matrix (mostly fiber reinforced composites but not exclusively). Most polymer materials and composites absorb moisture. It is well known from many papers (some of them mentioned in this chapter) over several decades that absorbed moisture essentially affects mechanical and many other important properties of polymers and polymer-based composites. The key question is: How does absorbed moisture affect mechanical properties of composites? Furthermore, the process of moisture absorption in composite structures may occur over many months and even years. More questions then arise: What i…
Effect of various moisture content on the mechanical and viscoelastic properties of giant reed Arundo donax L.
2015
The giant reed Arundo donax L. is an aggressive grass widely diffused throughout warm temperate regions. Thanks to its remarkable features as fast-growing, eco friendly and high specific properties (i.e. high strength/weight and modulus/weight ratios), it is widely used in ancient and traditional buildings, especially in the realization of supports for roof cladding and paneling of walls. A better understanding and a consequent standardization of its properties could make it more suitable for general application in the sustainable building industry. Mechanical and viscoelastic properties of the giant reed were studied as a function of the moisture content. To this scope, various sets of ree…
Modeling of creep for multiwall carbon nanotube/epoxy nanocomposite
2013
The effect of multiwall carbon nanotubes (MWCNTs) on creep of epoxy matrix was evaluated on the basis of short-term creep-recovery tests performed at different stresses and temperatures. Six different compositions of MWCNT and bisphenol A epoxy resin (0-3.8 wt % of MWCNTs) were investigated. Slight reduction of creep compliance, strain rate, and residual strain were revealed experimentally for nanocomposite comparing to the neat resin. The development of viscoelastic strain for creep stage was described by the use of time-temperature-strain superposition principle with the parameters obtained from the approximation of recovery stage using modified Schapery model. The model accounted for the…
Stochastic analysis of a non-local fractional viscoelastic beam forced by Gaussian white noise
2017
Recently, a displacement-based non-local beam model has been developed and the relative finite element (FE) formulation with closed-form expressions of the elastic and fractional viscoelastic matrices has also been obtained. The static and quasi-static response has been already investigated. This work investigates the stochastic response of the non-local fractional viscoelastic beam, forced by a Gaussian white noise. In this context, by taking into account the mass of the beam, the system of coupled fractional differential equations ruling the beam motion can be decoupled with the method of the fractional order state variable expansion and statistics of the motion of the beam can be readily…
Stochastic dynamic analysis of fractional viscoelastic systems
2011
A method is presented to compute the non-stationary response of single-degree-of-freedom structural systems with fractional damping. Based on an appropriate change of variable and a discretization of the fractional derivative operator, the equation of motion is reverted to a set of coupled linear equations involving additional half oscillators, the number of which depends on the discretization of the fractional derivative operator. In this context, it is shown that such a set of oscillators can be given a proper fractal representation, with a Mandelbrot dimension depending on the fractional derivative order a. It is then seen that the response second-order statistics of the derived set of c…