Bulletin of the American Physical Society
15th APS Topical Conference on Shock Compression of Condensed Matter
Volume 52, Number 8
Sunday–Friday, June 24–29, 2007; Kohala Coast, Hawaii
Session G3: Inelastic Deformation II |
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Chair: Davis Tonks, Los Alamos National Laboratory Room: Fairmont Orchid Hotel Plaza I |
Tuesday, June 26, 2007 10:30AM - 10:45AM |
G3.00001: Effects of Processing Techniques on the Shock Response of Be Eric Loomis, Shengnian Luo, Damian Swift, Scott Greenfield, Dennis Paisley, Randall Johnson Microstructural effects including material anisotropy, impurities, grain size, and texture alter a materials response to dynamic loading through wave front dispersion and inelastic processes. The spatial variations created by these effects may ultimately prevent significant energy gain from being attained with inertial confinement fusion (ICF) due to instability seeding if they are not minimized through material processing. To this end, laser-driven confined shock experiments have been conducted on Be to characterize its dynamic strength properties and usefulness as a possible ICF ablator. Disks of Be 3 mm in diameter and 100 to 250 microns thick in the form of single crystal, rolled foil, equal channel angular extruded, and sputtered Be-Cu were dynamically loaded to 100's kbar while the material behavior was measured with \textit{in-situ} diagnostics. Clear two-wave structures were observed in free surface velocity records providing a comparison of flow stress and other dynamic properties between Be types. 2-D continuum mechanics simulations were used to elucidate the underlying physics involved in the dynamic material response of the shocked Be. [Preview Abstract] |
Tuesday, June 26, 2007 10:45AM - 11:00AM |
G3.00002: Dynamic Compression of a Zr-Based Bulk Metallic Glass Confined by a 304 Stainless Steel Sleeve Morgana Martin, Laszlo Kecskes, Naresh Thadhani We will report on our current work on dynamic high-strain-rate mechanical properties of a zirconium-based bulk metallic glass (LM106m) with and without a stainless steel confinement sleeve. The dynamic compression experiments were conducted using reverse Taylor anvil-on-rod impact tests to generate strain rates of $\sim $10$^{3}$ s$^{-1}$. High-speed digital photography was used to obtain transient images of the deformation history. Velocity interferometry was also used to determine the back surface velocity of the impacted rod-shaped sample. These tests provide qualitative and quantitative information about the transient deformation and failure response of the specimens, which is used to better correlate the deformation path with the final recovered geometry. The recovered impacted specimens were analyzed using microscopy and AUTODYN modeling to elucidate the deformation and failure mechanisms of the bulk metallic glass and the effects of the altered stress state caused by the confinement sleeve. In this paper, the dynamic compression results and corresponding analysis of the failure mechanisms will be presented. [Preview Abstract] |
Tuesday, June 26, 2007 11:00AM - 11:15AM |
G3.00003: Dislocation Patterning and Dynamic Fracture in Shock-Loaded Tantalum and Uranium Alloys Luke Hsiung Deformation substructures in fragments of bcc metals and alloys: Ta, Ta-2.5{\%}W, Ta-10{\%}W, and U-6wt{\%}Nb recovered from HE-driven shock experiments; all were conducted under a peak pressure of $\sim $30GPa, were characterized and analyzed using transmission electron microscopy (TEM) techniques. The relationships between dislocation patterning and dynamic fracture mode of the fragments are correlated. The results reveal that dynamic damage and fracture in bcc metals are intimately related to the reactions for dislocation patterning, such as deformation twinning and the formation of cell walls or sub-boundaries, which in turn are governed by the mobility of dislocations under dynamic-pressure conditions.\textbf{ }Deformation twinning phenomenon becomes significantly enhanced in U-6Nb containing high-density and low-mobility dislocation structure. The embrittlement of U-6Nb under dynamic-pressure conditions is found to mainly be caused by the structural instability and the mutual collision of twin bands, which lead to the enhancement of spall-like damage. This work was performed under the auspices of the U. S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. [Preview Abstract] |
Tuesday, June 26, 2007 11:15AM - 11:30AM |
G3.00004: Shock Wave Profile and Bauschinger Effect in Depleted Uranium Darcie D. Koller, George T. Gray III Bauschinger effect is observed in many metals and is characterized by a microstructural stress distribution that results in an increase in compressive yield strength at the expense of tensile yield strength. Experiments to explore this phenomena are accomplished by applying a stress to the specimen in one direction to the yield point and then reversing the direction of the applied stress to the same magnitude. When the loading is applied in the negative direction, materials displaying the Bauschinger effect will yield before reaching the same load that yielding occurred at in the positive direction. This series of experiments applies uniaxial compressive loading followed by uniaxial tensile loading (negative direction of compressive load) by means of plate impact experiments on depleted uranium samples. Wave profiles are observed with VISAR to compare the HEL during the compressive loading with the HEL seen during release while the sample undergoes tensile loading. The expected 2 wave structure (elastic-plastic behavior) is observed during the compressive loading (shock up), but this structure is diminished on the release portion of the wave profile indicating a diminished yield strength during the tensile loading. [Preview Abstract] |
Tuesday, June 26, 2007 11:30AM - 11:45AM |
G3.00005: Influence of Microstructure on the Bauschinger Effect and the Shock Hardening in 1080 High-Carbon Steel. George Gray III, Ellen Cerreta, Lisa Dougherty, Carl Trujillo, Mike Lopez The importance of a microstructurally-controlled Bauschinger component to defect storage during the shock loading process has been shown to be correlated to both quasi-elastic release effects and reduced shock hardening in materials. In the current study shock recovery experiments have been conducted on a high-carbon 1080 steel as a function of two microstructural states; fully pearlitic and where the cementite has been spheriodized. The 1080 steel in the fully-pearlitic condition is shown to exhibit a significant Bauschinger effect while the spheriodized microstructure is observed to display significantly higher shock hardening when shock prestrained to an equivalent shock peak stress. The shock hardening response of 1080 steel is discussed in terms of the micromechanisms controlling defect generation and storage during shock loading in materials. [Preview Abstract] |
Tuesday, June 26, 2007 11:45AM - 12:00PM |
G3.00006: Failure above and below the elastic limit in AD995 Neil Bourne, Jeremy Millett, M.W. Chen, Datta Dandekar, James MacCauley There is an ongoing interest in identifying inexpensive armour materials for use in protection of personnel and vehicles. The response of AD995 under shock loading is one of the materials most extensively investigated. Over recent years, workers have reported failure occurring in various polycrystalline ceramics behind the shock front. This phenomenon has been investigated using embedded stress sensors and a recovery technique that has allowed observation of the microstructure above and below the HEL and these results are brought together here to explain the observed behaviour. The failure front velocity is found to change with the applied stress, in particular it slows markedly as the HEL is exceeded. The evidence in the microstructure shows the response below HEL is dominated by intergranular failure whilst above HEL the response dominated by plasticity in grains (including twinning), which alters failure characteristics. [Preview Abstract] |
Tuesday, June 26, 2007 12:00PM - 12:15PM |
G3.00007: ABSTRACT WITHDRAWN |
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