Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session Z3: Other Topics |
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Chair: Frank Zerilli, Naval Surface Warfare Center, Indian Head Room: Hyatt Regency Constellation D |
Friday, August 5, 2005 10:30AM - 10:45AM |
Z3.00001: Strongly Nonlinear Waves in Polymer-Based Phononic Crystals Chiara Daraio, Vitali Nesterenko, Eric Herbold, Sungho Jin ``Sonic vacuum'' type phononic crystals were assembled from chains of polytetrafluoroethylene (PTFE) beads and Parylene coated steel spheres. It was demonstrated for the first time that these polymer-based ``sonic vacui,'' with exceptionally low elastic modulus of particles, support propagation of strongly nonlinear solitary waves (and their trains) with a speed below 100 m/s for small amplitudes in reasonable agreement with numerical calculations. These solitary waves 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. Elastic modulus for PTFE taken from extrapolated Hugoniot data results in a good agreement with experimentally measured parameters of solitary waves. Tunability of signal shape and velocity was achieved through a non-contact magnetically induced precompression of the chains. This prestress allowed an increase up to two times of the solitary waves speed and a significant delay in signal splitting. This work was supported by NSF (Grant No. DCMS03013220). [Preview Abstract] |
Friday, August 5, 2005 10:45AM - 11:00AM |
Z3.00002: Influence of Controlled Viscous Dissipation on Propagation of Strongly Nonlinear Waves in Steel-Based Phononic Crystals Eric Herbold, Vitali Nesterenko, Chiara Daraio Strongly nonlinear phononic crystals were assembled from chains of stainless steel spheres with diameter 4.78 mm. Propagation of solitary waves and splitting of initial pulse into train of solitary waves excited by the impact of piston was investigated in different viscous media in experiments and in numerical calculations. Oil of various grades was used to introduce controlled dissipation into the system. Preliminary results indicate that splitting of the initial pulse into the train of solitary waves was dramatically influenced by viscosity. This work was supported by NSF (Grant No. DCMS03013220). [Preview Abstract] |
Friday, August 5, 2005 11:00AM - 11:15AM |
Z3.00003: Impulse Absorption by Tapered Alignments of Elastic Spheres Robert Doney, Surajit Sen A numerical parametric study of 1D granular systems with Hertzian spheres is investigated. The relevant and always-repulsive interaction potential is nonlinearly dependent upon the overlap of adjacent grains. Specifically, we report our extensive investigation of two distinct systems and provide hard- sphere approximations as well as results from the numerical solution to the equations of motion. Chains can be characterized by the number of grains, $N$, the successive decrease in particle size or tapering, $q$, and restitutive losses, $\omega$. By increasing the tapering, these chains act as shock absorbers by converting well-defined pulses into noise and spreading the energy among all members in the chain. [Preview Abstract] |
Friday, August 5, 2005 11:15AM - 11:30AM |
Z3.00004: New Phenomena Observed in Plate Impacts onto Alumina Bars Tim Beno, Stephan Bless Steel flyer plates were used to impact alumina bars at about 300 m/s. A manganin gauge was used to monitor the stress waves in the bar. The geometery of the impact was varied in an attempt to extend the gauge record. High-speed photos were also obtained. In Mod-1, the target alignment and mounting was improved. In Mod-2, ``Pillows'' were placed on the projectile impact surface, and Mod-3 consisted of the impact face being confined. Mod-1 had the biggest improvement in gauge records. It was established that after reaching a peak stress of 3.5 GPa, the stress relaxed to a plateau of 2 GPa. This apparently is the strength of material after failure in 1-D stress. The 1-D stress failure was largely by axial splitting. Later failures were by transverse faulting. Mod-2 resulted in less informative stress gauge signals. Mod-3 resulted in much higher peak stresses---some exceeded 5GPa. Explaining how such a high stress can occur in a 1-D stress environment is a severe challenge for the present conceptual framework of ceramic strength. [Preview Abstract] |
Friday, August 5, 2005 11:30AM - 11:45AM |
Z3.00005: Frictional Force Behavior in the Elastic Regime P.J. Crawford, P.M. Rightley, J.E. Hammerberg The friction force between materials in explosively driven events is an important constitutive relationship, even though defining the friction coefficient in the presence of large bulk deformations is difficult. Measuring the force at an interface near deformations, without significantly modifying the interface in the process, proves difficult as well. Few studies (the pressure-shear plate experiments originally performed by Clifton et al. being one) have investigated the nature of the friction force at the small time-scales and the very high sliding speeds and pressures involved in explosive events. In order to approach the study of such combinations, we have developed a novel experimental apparatus (the rotating barrel gas gun, or RBGG) that gives us independent control of sliding speed and pressure at the interface while keeping the impact elastic, allowing us to make measurements away from the interface and to interpret the results without resorting to a simulation. We measure the axial and torsional strain in an annular target rod produced by the impact of a spinning, translating annular projectile. Experiments performed using Cu/Cu, Cu/Stainless and Cu/Al tribopairs provide some insight into the kinetic coefficient of friction behavior at various sliding speeds and loads. [Preview Abstract] |
Friday, August 5, 2005 11:45AM - 11:59AM |
Z3.00006: Johnson-Cook Strength Model Constants for VascoMax 300 and 1080 Steels John D. Cinnamon, A.N. Palazotto, Z. Kennan, N.S. Brar, D. Bajaj High strength steels, VascoMax 300 and 1080 steel, are characterized under tension at strain rates of $\sim $1/s, $\sim $500/s, $\sim $1000/s, and $\sim $1500/s and at high temperatures (1000$^{\circ}$F for Vascomax 300 and 1080 steel to 750$^{\circ}$F) using the quai-static and split Hopkinson bar techniques. The data on 1080 steel exhibit a strain hardening response, whereas VascoMax 300 steel showed diminishing flow stress beyond yielding because of localized necking in gauge section of the tested specimens. The tension data are analyzed to determine the Johnson-Cook (J-C) strength model constants for the two steels. The J-C model constants A, B, n, C, and m for 1080 steel are 0.514 GPa, 2.83 GPa, 0.612, 0.031, and 0.890, respectively. For Vascomax 300 steel A=2.07 GPa; B=1.98 GPa; n=0.416; C=0.006; m=1.425. The temperature softening constant ``m'' for Vascomax 300 steel show variation with strain rate and need to be reevaluated in view of its unusual behavior in declining flow stress above yielding. In addition, an analysis of the necking observed in the tested specimens of both the steels is presented. [Preview Abstract] |
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