284 research outputs found
Strongly nonlinear wave dynamics in a chain of polymer coated beads
Strongly nonlinear phononic crystals were assembled from a chain of Parylene-C coated steel spheres in a polytetrafluoroethylene holder. This system exhibits strongly nonlinear properties and extends the range of materials supporting sonic-vacuum-type behavior. The combination of a high density core and a soft (low elastic modulus) coating ensures a relatively low velocity of wave propagation. The bead contact interaction caused by the deformation of the Parylene coating can be described by classical nonlinear elastic Hertz theory with an effective value of the elastic modulus equal to 15 GPa for the contact interaction. Strongly nonlinear solitary waves excited by impacts were investigated experimentally and compared to chains composed of uniform steel beads. Fracture of the polymer coating was detected under relatively large pulse amplitude
Highly nonlinear contact interaction and dynamic energy dissipation by forest of carbon nanotubes
Mechanical response and energy dissipation of an array of carbon nanotubes under high-strain rate deformation was studied using a simple drop-ball test with the measurement of the dynamic force between the ball and forest of nanotubes. This convenient process allows extracting forceâdisplacement curves and evaluating dissipated energy by the nanotubes. The contact force exhibits a strongly nonlinear dependence on displacement being fundamentally different than the Hertz law. The forest of vertically aligned nanotubes may be used as a strongly nonlinear spring in discrete systems for monitoring signal propagation speed, and as a microstructure for localized energy absorption
Highly nonlinear pulse splitting and recombination in a two-dimensional granular network
The propagation of highly nonlinear signals in a branched two-dimensional granular system was investigated experimentally and numerically for a system composed of chains of spherical beads of different materials. The system studied consists of a double Y-shaped guide in which high- and low-modulus/mass chains of spheres are arranged in various geometries. We observed the transformation of a single or a train of solitary pulses crossing the interface between branches. We report fast splitting of the initial pulse, rapid chaotization of the signal and impulse redirection and bending. Pulse and energy trapping was also observed in the branches. Numerical analysis based on Hertzian interaction between the particles and the side walls of the guide was found in agreement with the experimental data, except for nonsymmetric arrangements of particles excited by a large mass striker
Influence of Controlled Viscous Dissipation on the Propagation of Strongly Nonlinear Waves in Stainless Steel Based Phononic Crystals
Strongly nonlinear phononic crystals were assembled from stainless steel
spheres. Single solitary waves and splitting of an initial pulse into a train
of solitary waves were investigated in different viscous media using motor oil
and non-aqueous glycerol to introduce a controlled viscous dissipation.
Experimental results indicate that the presence of a viscous fluid dramatically
altered the splitting of the initial pulse into a train of solitary waves.
Numerical simulations qualitatively describe the observed phenomena only when a
dissipative term based on the relative velocity between particles is
introduced.Comment: 4 pages, 3 figures, conference pape
Multiscale mass-spring models of carbon nanotube foams
This article is concerned with the mechanical properties of dense, vertically aligned CNT foams subject to one-dimensional compressive loading. We develop a discrete model directly inspired by the micromechanical response reported experimentally for CNT foams, where infinitesimal portions of the tubes are represented by collections of uniform bi-stable springs. Under cyclic loading, the given model predicts an initial elastic deformation, a non-homogeneous buckling regime, and a densification response, accompanied by a hysteretic unloading path. We compute the dynamic dissipation of such a model through an analytic approach. The continuum limit of the microscopic spring chain defines a mesoscopic dissipative element (micro-meso transition) which represents a finite portion of the foam thickness. An upper-scale model formed by a chain of non-uniform mesoscopic springs is employed to describe the entire CNT foam. A numerical approximation illustrates the main features of the proposed multiscale approach. Available experimental results on the compressive response of CNT foams are fitted with excellent agreement
Strongly nonlinear waves in a chain of Teflon beads
One dimensional "sonic vacuum" type phononic crystals were assembled from a
chain of Teflon spheres with different diameters in a Teflon holder. It was
demonstrated for the first time that this polymer-based "sonic vacuum", with
exceptionally low elastic modulus of particles, supports propagation of
strongly nonlinear solitary waves with a very low speed.Comment: 33 pages, 6 figure
Strongly Nonlinear Waves in Polymer Based Phononic Crystals
One dimensional "sonic vacuum"-type phononic crystals were assembled from chains of polytetrafluoroethylene (PTFE) beads and Parylene coated spheres with different diameters. It was demonstrated for the first time that these polymer-based granular system, with exceptionally low elastic modulus of particles, support the propagation of strongly nonlinear solitary waves with a very low speed. They can be described using classical nonlinear Hertz law despite the viscoelastic nature of the polymers and the high strain rate deformation of the contact area. Trains of strongly nonlinear solitary waves excited by an impact were investigated experimentally and were found to be in reasonable agreement with numerical calculations. Tunability of the signal shape and velocity was achieved through a non-contact magnetically induced precompression of the chains. This applied prestress allowed an increase of up to two times the solitary waves speed and significant delayed the signal splitting. Anomalous reflection at the interface of two "sonic vacua"-type systems was reported
Delayed Scattering of Solitary Waves from Interfaces in a Granular Container
In granular media, the characterization of the behavior of solitary waves
around interfaces is of importance in order to look for more applications of
these systems. We study the behavior of solitary waves at both interfaces of a
symmetric granular container, a class of systems that has received recent
attention because it posses the feature of energy trapping. Hertzian contact is
assumed. We have found that the scattering process is elastic at one interface,
while at the other interface it is observed that the transmitted solitary wave
has stopped its movement during a time that gets longer when the ratio between
masses at the interfaces increases. The origin of this effect can be traced
back to the phenomenon of gaps opening, recently observed experimentally.Comment: To appear in Physical Review E, vol 7
Angular Dependence of Highly Nonlinear Pulse Splitting in a Two Dimensional Granular Network
We investigate experimentally and numerically the
propagation of highly nonlinear signals in a branched two-dimensional
granular system composed by chains of uniform
spherical beads. The system consists of a Y-shaped guide with
various branch angles in which stainless steel spheres are
arranged. We study the dynamic behavior of a solitary pulse
crossing the bifurcated interface, and splitting between the two
branches. We report for the first time the dependence of the
split pulses' speed on the branch angles. Numerical simulations
based on Hertzian interaction between the particles are found in
agreement with the experimental data
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