Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session J6: Particulate/Porous Materials II: Mesoscale Effects |
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Chair: Ananda Barua, Georgia Institute of Technology Room: Grand Ballroom VI |
Tuesday, June 28, 2011 11:00AM - 11:15AM |
J6.00001: The Shock Compaction of Brittle Granular Materials: Particle Size Effects William Neal, David Chapman, William Proud Several continuum models can represent the shock compaction of brittle granular materials. Their success is limited by their insensitivity to mesoscopic features. There is therefore a need to quantify the effects of these mesoscopic features on the material's bulk shock response. impact experiments have been conducted on mono and bi-disperse glass microspheres with differing particle size distributions. Hugoniot relationships and shock-wave profile features are discussed with regard to the differences in particle size. [Preview Abstract] |
Tuesday, June 28, 2011 11:15AM - 11:30AM |
J6.00002: Nonlinear Resonance Phenomena Leading to Strong Pulse Attenuation in Granular Diatomic Chains with no Pre-Compression Jayaprakash KR, Yuli Starosvetsky, Alexander F. Vakakis We consider diatomic (dimer) chains with `heavy' and `light' beads interacting with elastic Hertzian law and with no pre compression. A new family of solitary waves analogous to the one in homogeneous chain studied by Nesterenko was discovered in these systems. We observe that these waves lead to no separation between beads; rather satisfy special symmetries or, equivalently anti-resonances. Further, we discuss a contrasting phenomena of resonance that leads to efficient pulse attenuation. We attribute anti-resonance to symmetric waveforms whereas resonance to the break of symmetry and thus leading to attenuation of traveling pulses, maximum amplitude amplification of radiated waves emanating from the propagating pulse and distortion of waveforms due to radiation of energy in the form of travelling waves to the far field. We show that the capacity of the dimer to attenuate propagating pulses is reduced when system is precompressed. These results have interesting implications on applications where granular media is employed as shock transmitters/attenuators. [Preview Abstract] |
Tuesday, June 28, 2011 11:30AM - 11:45AM |
J6.00003: Propagation of rarefaction pulses in particulate materials with strain-softening behavior Eric Herbold, Vitali Nesterenko We investigate rarefaction waves in nonlinear periodic systems with a `softening' power-law relationship between force and displacement to understand the dynamic behavior of this class of materials. A closed form expression describing the shape of the strongly nonlinear rarefaction wave is exact for exponent in force interaction law equal to 0.5 and agrees well with the shape and width of the pulses resulting from discrete simulations. A chain of particles under impact was shown to propagate a rarefaction pulse as the leading pulse in initially compressive impulsive loading in the absence of dissipation. Compression pulses generated by impact quickly disintegrated into a leading rarefaction solitary wave followed by an oscillatory train. Such behavior is favorable for metamaterials design of shock absorption layers as well as tunable information transmission lines for scrambling of acoustic information. [Preview Abstract] |
Tuesday, June 28, 2011 11:45AM - 12:00PM |
J6.00004: Effect of Uncertainties on Pulse Attenuation in Dimer Chains with and without Precompression M.A. Hasan, L. Pichler, D.M. McFarland, A.F. Vakakis Unlike homogeneous granular chains which lead to the formation of a solitary wave, polydisperse systems usually exhibit waves with dispersion. For the case of 1d granular chains obeying a strongly nonlinear Hertzian law interaction, much emphasis has been given to diatomic (dimer) granular chains, made of alternating heavy and light beads. When an initial impulse is applied to the free left boundary, this leads to localized oscillations of the light bead and reduces the amplitude of the applied pulse. For certain mass disorder value, considerable attenuation of the applied impulse by up to about 75{\%} can be achieved. However, the response of the dimer chain varies when the effect of uncertainties is included in the system. Here, we model the radii of the light beads as random variables, while keeping the radius of the heavy bead fixed. The effect of uncertainty is investigated using Monte Carlo Simulation and the corresponding transmitted force and time delay are observed. In addition, the same investigation is carried out for a dimer chain with precompression. [Preview Abstract] |
Tuesday, June 28, 2011 12:00PM - 12:15PM |
J6.00005: Shear Stress Behavior in Mesoscale Simulations of Granular Materials Don Fujino, Ilya Lomov, Efrem Vitali, Tarabay Antoun 3D mesoscale simulations of shock propagation in porous solids and powder have been performed with the hydrocode GEODYN. The results indicate that voids can have a profound effect on the stress state in the material behind the shock front. The simulations can explain experimentally observed quasielastic precursors in reshock profiles that are difficult to interpret in the context of the classical elastic-plastic theory. This effect persists even at extremely low porosity values, down to 0.01\% by volume. Stress relaxation is pronounced in simulations involving wave propagation, but is not observed in uniform ramp loading. Thus this relaxation mechanism is non-local in nature and continuum models may not be inadequate for its description. Simulations show that response of highly porous powders are dominated by deviatoric stress relaxation in the shock regime. We propose an enhancement which can be easily integrated into most existing porous material continuum models for modeling the shock-induced relaxation phenomena observed in the mesoscale simulation. The model calculates microkinetic energy generated by dynamic loading and store it as an internal state variable. The rate of production and dissipation of microkinetic energy is calibrated based on the mesoscale results. The augmented continuum model represent deviatoric stress behavior observed under different loading regimes. [Preview Abstract] |
Tuesday, June 28, 2011 12:15PM - 12:30PM |
J6.00006: Shear Stress Measurements During High-Speed Impacts with Sand and Glass Beads William Cooper, Keiko Watanabe, Hiroaki Yamamoto, Koichi Tanaka, Kazuyoshi Takayama Right-circular (15 mm OD x 26 mm) and spherical (10mm) projectiles were fired vertically-downward (300-1,000 m/s) into acrylic containers (100-190 mm ID) containing quartz Eglin sand and solid, amorphous glass beads. A variety of shearing conditions were observed; allowing estimation of stresses along the various shearing surfaces. Under certain conditions a false nose was formed of partially-crushed particles on the front of the projectile and the particulate media sheared along the false nose surface. The included angle of the false nose varies with impact velocity (up to a velocity of 375 m/s) and appears to be a residual artifact of initial impact conditions. An analytical model is presented to explain the false nose formation and stability during the projectile deceleration. Other impact conditions resulted in shearing along the surface or surface abrasion. Experimental and theoretical results will be presented. [Preview Abstract] |
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