Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session Y2: ID-8: Spallation of Metals |
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Chair: James Asay, Sandia National Laboratories Room: Hermitage AB |
Friday, July 3, 2009 8:00AM - 8:15AM |
Y2.00001: Geometry of Damage Cavities in Shock Loaded Tantalum Davis Tonks, John Bingert, Veronica Livescu Cavities of coalesced voids have been found in recovered samples of Tantalum in gas gun and high-explosive-driven experiments. The boundaries of these cavities are imprinted with details of the coalescence and void growth processes. One way of quantifying these details is to measure the roughness of the surfaces. In this work, we calculate the roughness of 2D cross sections of such cavity surfaces from micrographs by analyzing the images with the box counting technique. Both gas gun samples and explosively driven samples are treated. The cavities in the explosively driven samples appear rougher than those in the gas gun samples so we expect a larger roughness exponent for them. Possible reasons for the roughness differences will be discussed. [Preview Abstract] |
Friday, July 3, 2009 8:15AM - 8:30AM |
Y2.00002: Influence of dynamic properties on growth of perturbations in tantalum Sergey Nadezhin, Olga Ignatova, Vlad Igonin, Aleksandr Lebedev, Margarita Lebedeva, Aleksey Podurets, Viktor Raevsky, Marvin Zocher, Ann Kaul The work is devoted to experimental and numerical-theoretical study of peculiarities of plastic deformation of Ta at pressures 10-80 GPa and strain rates 10E3$\div$10E9 sE-1. Tantalum has a body- centered cubic lattice, and, in the mentioned ranges of pressures and strain rates, tantalum behavior differs from those of aluminum and copper, which have a face-centered cubic lattice. The studies were conducted by the perturbation method and the metallographic method with use of samples recovered after loading. Basic results are the following: 1. In contrast to copper and aluminum, shock-wave softening was not revealed in tantalum. 2. Model of Ta strength was developed. [Preview Abstract] |
Friday, July 3, 2009 8:30AM - 8:45AM |
Y2.00003: Comparison of Line-Imaging VISAR Inferences of Spalled Sample Distension with Metallographic Analysis of Recovered Samples M.D. Furnish, G.T. Gray III, J.F. Bingert Using a line-imaging VISAR to infer the position (x) and time (t) dependent distension of a spalling sample requires two assumptions: (1) a calculated velocity surface v[no spall] (x,t) for the no-spall case to compare with the observed v [observed](x,t) surface, and (2) a lack of significant wave processing by the near-surface microstructure. We have designed and are conducting a matrix of experiments to evaluate these assumptions. In each experiment, we use a line-imaging VISAR to measure the velocity history of carefully characterized tantalum or copper samples taken to an incipient spall condition. The pre-shot characterization included spatially resolved mapping of grain locations and orientations by electron backscatter diffraction (EBSD). These samples are then soft-recovered and sectioned along the same line as monitored by the line-imaging VISAR. [Preview Abstract] |
Friday, July 3, 2009 8:45AM - 9:00AM |
Y2.00004: Numerical simulation of spall failure in metals under shock compression Yuriy Bayandin, Oleg Naimark, Sergey Uvarov Nonlinear aspects of damage localization and damage-failure transition are the subject of long-term research and arise both fundamental and applied interest related to multiscale nature of failure mechanism. The developed statistical model of solid with mesoscopic defects allowed the formulation of phenomenological model in terms of two independent variables - the defect density tensor and structural scaling parameter and the simulation of shock wave propagation in the linkage with structural relaxation phenomena. Presented investigation is related to the study of damage-failure scenario in the plate impact test (spall failure) taking into account long-range correlation properties induced by the collective modes of defects. Numerical simulation of plane shock wave propagation was carried out to establish spall conditions and to propose the mechanism of damage-failure transitions as a specific form of self-organized criticality in the ensemble of mesoscopic defects - structural-scaling transition. Characteristic features of this transition are the generation of collective modes in mesodefect ensemble that are responsible for damage localization and transition to failure. [Preview Abstract] |
Friday, July 3, 2009 9:00AM - 9:30AM |
Y2.00005: The effects of shockwave profile shape and shock obliquity on spallation: studies of kinetic and stress-state effects on damage evolution and spallation Invited Speaker: While much has been learned over the past five decades concerning the kinetics of the damage evolution and spallation in shock-loaded materials these studies have focused principally on 1-D shocked samples where the shocks produced possessed ``square-topped'' profiles as a function of peak stress. However, considerably less is known concerning spallation resulting from direct in-contact HE-driven, where a ``Taylor-wave'' shockwave profile is applied let alone a sweeping detonation Taylor-wave loading stress path where the applied stress tensor evolves as a function of obliquity. In this talk the influence of HE-driven shock loading, both 1-D and as a function of shock obliquity on the damage evolution and spallation response of Cu, 1018 steel, and Ta is compared and contrasted to that seen in each material subjected to flyer-plate driven ``square-topped wave'' shock profile prestraining. [Preview Abstract] |
Friday, July 3, 2009 9:30AM - 9:45AM |
Y2.00006: Explosively Driven Damage in Beryllium Lawrence Hull Four explosive shots were fired in a simple plane wave-driven shock arrangement to begin characterization of damage in Be. Two explosives, PBX-9501 and TNT were used as the driver and two thicknesses of Be were tested. The thinner Be was intended to not spall while the thicker samples were intended to spall. The primary diagnostic was PDV (three probes on each sample). The shot with the thick Be sample driven by PBX-9501 also included an x-ray taken 4 us after shock breakout. The velocity records reveal various features of interest for comparison to computational models. There is a precursor wave, appearing as a toe, on the initial shock. The shock amplitude and ultimate sample velocity is a function of the explosive type and, to a lesser degree, sample thickness. The classic ringing of the velocity in the spall scab is readily apparent in the thicker samples, and the details of the subsequent re-compressions are seen to be a function of the shot parameters. The x-ray was taken after the re-compression and analysis shows no evidence of an opening in the material at that particular time. Radiography alone indicates an intact sample after re-compression, but velocimetry indicates spall. This is an enigma encountered often, the usual explanation is that the damaged region is too slight to detect radiographically after re-compression. [Preview Abstract] |
Friday, July 3, 2009 9:45AM - 10:00AM |
Y2.00007: Crack-resistance and spall strength of cerium under dynamic loading Victor Pushkov, Vladimir Ogorodnikov, Sergey Erunov For cerium, a series of characteristics under static compression and tension and some other characteristics are known. At the same time, there is poor knowledge on cerium characteristics under dynamic loading, such as dynamic crack-resistance and spall strength, which are important for some applications. For example, material crack-resistance is one of parameters of the model, which is used for numerical description of the dispersion process. In this work the crack-resistance evaluation was performed by study of material spall strength $\sigma _{ }$, determination of specific work for material break $\lambda $, and using the Irvine-Griffiths criterion. Loading of the samples by planar impactor was performed at ballistic impact tube BUT-76 and impactor velocity in the tests varied within 100-400 m/s. Profiles of samples free surface velocity W(t) recorded by laser interferometer in the tests. Cerium of the type TsE-0 was researched. It is observed that damage nucleation occurs in cerium through formation of voids. [Preview Abstract] |
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