1,721,042 research outputs found
Asymptotic models for buckling and dynamics of thin films resting on soft, prestretched substrates
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Scaling laws and ultra-wide band gaps in generalized Fibonacci structures: a new paradigm for the design of quasicrystalline waveguides
No full textWave propagation in one-dimensional quasicrystalline structures: dynamical trace mapping and self-similar stop/pass band distribution
No full textOne-dimensional quasiperiodic and quasicrystalline structures: dynamic spectra and self-similar pattern identification
No full textWaves in one-dimensional quasicrystalline structures: dynamical trace mapping, scaling and self-similarity of the spectrum
No full textHarmonic axial waves in quasiperiodic-generated structured rods are investigated. The focus is on infinite bars composed of repeated elementary cells designed by adopting generalised Fibonacci substitution rules, some of which represent examples of one-dimensional quasicrystals. Their dispersive features and stop/pass band spectra are computed and analysed by imposing Floquet–Bloch conditions and exploiting the invariance properties of the trace of the relevant transfer matrices. We show that for a family of generalised Fibonacci substitution rules, corresponding to the so-called precious means, an invariant function of the circular frequency, the Kohmoto's invariant, governs self-similarity and scaling of the stop/pass band layout within defined ranges of frequencies at increasing generation index. Other parts of the spectrum are instead occupied by almost constant ultrawide band gaps. The Kohmoto's invariant also explains the existence of particular frequencies, named canonical frequencies, associated with closed orbits on the geometrical three-dimensional representation of the invariant. The developed theory represents an important advancement towards the realisation of elastic quasicrystalline metamaterials
New actuation modes of dielectric elastomer composite devices
No full textFor a usual Dielectric Elastomer (DE) actuator, the attraction between the electrodes owing to Maxwell forces entails a reduction of thickness with an expansion of in-plane area. However, the overall response also depends on the local effects induced by polarization, which can be macroscopically accounted for assuming the dielectric constant as a function of the strain. In this case, actuators can exhibit the remarkable theoretical property of CONTRACTING and THICKENING under an electric stimulation. In this work, we show that such counterintuitive behaviours can be achieved by tuning the electric input on tailored hierarchical dielectric composites whose phases obey an ideal dielectric behaviour. Our study concerns laminates for which we highlight the main design parameters, i.e. the shear modulus-- and dielectric constant-ratios as well as the lamination angle, to achieve the new modes. The effect of the layout in limiting, suppressing or promoting electromechanical instability under voltage control is also presented; in some cases, where the instability is suppressed, the maximum in-plane stretch orthogonal to the laminae can increase considerably with respect to a homogeneous actuator. On the basis of our results, hierarchical DE composite materials can be conceived, whose counterintuitive properties can be taken advantage of in the design of innovative actuators, sensors and energy harvesters
Elastic waves in two-phase composite quasicrystalline-generated metamaterials: scaling of frequency spectra and negative refraction
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