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We studied effects of material anisotropy on impact mitigation in single column woodpile structures. Local vibrations and nonlinear contacts of cylindrical members are key mechanisms of wave modulation in woodpile structures. We numerically obtained wave propagations in single column woodpile structures by changing longitudinal and/or transverse stiffness different from stiffness along the stacking direction. We found that changes in longitudinal and/or transverse stiffness altered wave propagation tendency as well as impact mitigation rate. We observed compact and wide waves propagated through single column woodpile structures with small stiffness ratio, while disintegrated but narrow waves with large stiffness ratio. According to dynamic behavior under impact loadings and frequency responses of woodpiles, bending vibration changed from 3rd to 1st mode and low energy band moved to relatively low frequency region when the single column woodpile structures had small stiffness ratio. This leads to increase impact mitigation characteristics of single column woodpile structures. [ABSTRACT FROM AUTHOR]

In the present work, we numerically and experimentally investigate the propagation of nonlinear waves in a hexagonally packed granular channel. Specifically, we assemble a simple 1-2-1 granular chain, which triggers not only normal but also tangential interactions of particles up on a striker impact. We experimentally measure the transmission of nonlinear waves propagating along the channel direction using an embedded piezoelectric sensor particle. For numerical simulations, we introduce a discrete element model that accounts for both elastic and damping effects in axial and rotational directions. As a result, we find that the wave propagation in this 1-2-1 hexagonal architecture is governed strongly by the rotational dynamics of particles. We also verify that the effect of rotational damping is crucial for the accurate description of the particle’s dynamics. The findings in this study hints the significance of particles’ rotational dynamics when stress waves propagate along hexagonally packed particle channels even in highly ordered 2D/3D granular architectures. [ABSTRACT FROM AUTHOR]

We assemble granular chains composed of spheres of uniform diameter in different curved configurations. We study the properties of highly nonlinear solitary waves traveling in the curved channels as a function of the curve angle and of the radius of curvature, using experiments and numerical simulations. We observe that solitary waves propagate robustly even under drastic deflection, such as $$90^{\circ }$$ and $$180^{\circ }$$ turns. When the solitary waves encounter a sharp turn with a radius of curvature as small as one spherical particle's diameter, we report the formation of secondary solitary waves resulting from the interaction with the guiding rail. We compare experimental results with numerical simulations based on a discrete element model that accounts for nonlinear and dissipative interactions between particles. This study demonstrates that granular chains are efficient wave-guides, even in complex geometrical configurations. Moreover, the findings in this study suggest that solitary waves could be used as novel information and/or energy carriers. [ABSTRACT FROM AUTHOR]

We study the formation and propagation of nonlinear stress waves in 3D woodpile elastic metamaterials consisting of vertically stacked slender cylindrical rods. We find the nonlinear waveforms transmitted through the woodpile architectures under impact are highly sensitive to their design parameters, particularly stacking distances and angles in 3D assemblies. We numerically and experimentally demonstrate that the woodpile system can localize, modulate, and ultimately attenuate propagating nonlinear waves in an efficient manner without relying on material damping. We also show the feasibility of constructing metamaterials with a simultaneous characteristic of high damping and high stiffness by using the controllable wave dispersion in the woodpile structures. These woodpile metamaterials offer enhanced degrees of freedom in manipulating stress waves, thereby offering a new way to design efficient impact protectors with high stiffness. [ABSTRACT FROM AUTHOR]

We investigate the tunable characteristics of mechanical waves propagating in quasi-1D phononic crystals composed of horizontally stacked short cylinders at various contact angles and offsets. According to the Hertzian contact theory, elastic compression of laterally-touching cylindrical bodies exhibits a various range of contact stiffness depending on their alignment angles. In this study, we first assemble cylindrical particles in various combinations of inclination angles and systematically examine their forming mechanisms of frequency bandgaps. We also investigate the effect of the rattling motions of cylindrical particles by introducing asymmetric center-of-mass offsets with respect to their contact points. We find that the frequency responses of these quasi-1D phononic crystals evolve into multiple band structures as we employ higher deviations of contact angles and offsets. We calculate the dispersive behavior of propagating waves using a discrete particle model for simple zero-offset cases, while we use a finite element method for simulating the rattling motions of particles under non-zero offsets. We report branching behavior of frequency band structures and the evolution of their vibration modes as we manipulate the contact angles and offsets of the phononic crystals. This study implies that we can leverage the versatile wave filtering characteristics of quasi-1D phononic crystals to construct tunable wave filtering devices for engineering applications. [ABSTRACT FROM AUTHOR]