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 H4: Inelastic Deformation III - Spall III |
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Chair: William Reinhart, Sandia National Laboratories Room: Hyatt Regency Constellation E |
Tuesday, August 2, 2005 9:00AM - 9:15AM |
H4.00001: Variability in Dynamic Properties of Tantalum: Spall, Attenuation and Load/Unload Michael D. Furnish, William D. Reinhart, Wayne M. Trott, Lalit C. Chhabildas, Tracy J. Vogler A suite of impact experiments was conducted to assess spatial and shot-to-shot variability in dynamic properties of tantalum. Samples had a uniform refined $\sim $ 20 micron grain structure with a strong axisymmetric [111] crystallographic texture. Two experiments performed with sapphire windows (stresses of approximately 7 and 12 GPa) clearly showed elastic-plastic loading and slightly hysteretic unloading behavior. An HEL amplitude of 2.8 GPa (corresponding to Y $\approx $ 1.5 GPa) was observed. Free-surface spall experiments showed clear wave attenuation and spallation phenomena. Here, loading stresses were $\sim $ 12.5 GPa and various ratios of impactor to target thicknesses were used. Spatial and shot-to-shot variability of the spall strength was $\pm $20{\%}, and of the HEL, $\pm $10{\%}. Experiments conducted with smaller diameter flyer plates clearly showed edge effects in the line and point VISAR records, indicating lateral release speeds of roughly 5 km/s. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE--AC04--94AL85000. [Preview Abstract] |
Tuesday, August 2, 2005 9:15AM - 9:30AM |
H4.00002: Affine Fractal Characterization of Damage Path in Incipiently Spalled Tantalum Davis Tonks, Ben Henrie, Carl Trujillo, William Thissell The damage in the ``spall plane'' of tantalum incipiently spalled in a gas gun consists of voids and regions of localized shear between the voids. A continuous path can be traced through these features from one side of the spall plane to the other. The geometry of this path has been analyzed using wavelets to show that it constitutes, to a good approximation, an affine fractal, i. e it is statistically invariant with power law dependence with different exponents normal to and along the spall plane. The details of this analysis will be presented together with insight as to the physical meaning of the results. [Preview Abstract] |
Tuesday, August 2, 2005 9:30AM - 9:45AM |
H4.00003: Effects of Annealing and Preheating on the Impact Response of Selected Braze Materials$^{1}$ J.L. Wise, S.C. Jones, C.A. Hall, W.D. Reinhart, R.J. Hickman, J.W. Gluth A series of gas-gun experiments has probed the impact response of six different braze alloys: Nicusil 3, Nicoro + titanium (98/2 wt{\%}), copper + gold (65/35 wt{\%}), copper + gold (50/50 wt{\%}), silver zirconate, and Cusil. Velocity interferometer data acquired during this investigation has been analyzed to reveal details of the time-resolved shock/release and spall behavior of these materials. As-received and annealed samples of each alloy were tested under both ambient (room temperature) and preheated (100$^{\circ}$C) initial conditions. The present data have been evaluated to determine the influences of annealing and preheating on the dynamic yield strength (i.e., Hugoniot Elastic Limit) and spall strength. [Preview Abstract] |
Tuesday, August 2, 2005 9:45AM - 10:00AM |
H4.00004: Spall Threshold Stress for Al Alloys with Varying Microstructures X.L. Chen, S.K. Dwivedi, J.R. Asay, D.F. Field A series of plate impact spall experiments was conducted on 6061 Al with three different grain sizes, ultra pure Al, and commercially pure (1060) Al samples for various thicknesses and impact stresses. The spall threshold stress, calculated from the pull back velocity, was determined for different initial microstructures, impact stresses, pulse durations, and loading rates. It is found that the spall threshold stress increases over the stress range of 4-13 GPa and then decreases for impact stress approaching 22 GPa. Results indicate that the threshold stress depends more on tensile loading rate than on the impact stress duration. Initial microstructure and impurities have a diminishing effect on the spall threshold stress as impact stress increases from 4-22 GPa. However, these properties have a pronounced effect on the structure of the pull back velocity profile at all stress levels. The change occurring in the profile slope is believed to signify either the transition from brittle to ductile fracture, or heterogeneous spallation resulting in secondary spall planes that are predicted by mesoscale simulations. Work supported by DOE. [Preview Abstract] |
Tuesday, August 2, 2005 10:00AM - 10:15AM |
H4.00005: Spallation Damage Experiments in Cylindrical Geometry Ann Kaul Spallation damage is the process of damage in a ductile material caused by void nucleation, growth and coalescence due to states of high tensile stress. Spallation damage of a ductile material is a concern in any situation where a high enough tensile wave can be produced. Typical spallation experiments are conducted using a gas gun in a planar, one-dimensional configuration. The assumption is made that the planar results translate directly to a cylindrical configuration. However, a cylindrical configuration is inherently two-dimensional due to the hoop stresses present in the target material. A series of 4 spall experiments on aluminum was successfully performed on the Atlas pulsed power facility at Los Alamos National Laboratory (LANL) in 2002. These experiments were conducted well above the velocity and/or pressure thresholds for nucleation and growth of voids. Planning for a series of 10 joint experiments by LANL and the All-Russia Research Institute of Experimental Physics (VNIIEF) are currently underway, with the first 3 planned for June and July. VNIIEF flux compression generators will be used to drive the experiments. These experiments are designed to explore the spallation damage threshold to determine if the window of incipient damage has moved in either velocity space or pressure space from the planar case. In addition, the effect of plastic work on the pressure wave profile as it moves through the material will be studied. Preliminary results for this initial series will be presented. [Preview Abstract] |
Tuesday, August 2, 2005 10:15AM - 10:30AM |
H4.00006: Tensile Failure of Tungsten-Nickel-Cobalt Stephan Bless, Ricky Chau Spall experiments were conducted on a 91W-Ni-Co alloy. The spall strength was 2.6~GPa. At 410 m/s, which is well above the spall strength, the damage consists of isolated voids. The failure starts mainly as grain cleavage. This result is very consistent with earlier measurements in which very rapid tensile failure was induced by transverse impact. [Preview Abstract] |
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