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 L7: Inelastic Deformation-Aluminum |
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Chair: Jim Asay, Sandia National Laboratories Room: Fairmont Orchid Hotel Promenade III |
Wednesday, June 27, 2007 8:00AM - 8:15AM |
L7.00001: 1D Continuum and 2D Mesoscale Simulations of Plate Impact Spall Experiments in 6061-T6 Aluminum S.K. Dwivedi, J.N. Johnson, Y.M. Gupta A comprehensive study has been initiated to understand the spallation of 6061-T6 aluminum in plate impact experiments, and to relate the features in pull-back velocity profile to material damage. Plate impact spall experiments at three stress levels 4.1 GPa, 13.7 GPa, and 21 GPa with two sample thicknesses at 4.1 GPa were simulated using Johnson's void growth and coalescence model in a 1D wave code COPS. The results show that the model allows determination of a common set of parameters (with some tolerance) that simulates pull-back velocity profile for all the four experiments. More importantly, the maximum tensile stress at the spall plane is higher than the spall threshold stress calculated from the pull-back velocity and does not increase with thickness reduction. These phenomena are under further study through 2D mesoscale simulations which are known to predict quasi-elastic unloading without shear modulus degradation as needed in 1D COPS. Results from 1D COPS and 2D mesoscale simulations will be compared to highlight the material phenomena. Work supported by DOE. [Preview Abstract] |
Wednesday, June 27, 2007 8:15AM - 8:30AM |
L7.00002: Dynamic Response of 5083-H131 Aluminum Alloy John Boteler, Dattatraya Dandekar The material response of 5083-H131 aluminum alloy subjected to dynamic loading has been investigated. In the work reported here we examine the spall strength, Hugoniot EOS, and Hugoniot Elastic Limit (HEL) over the stress range 1.5-8.0 GPa. Measurement of these dynamic properties provide hydrocode modelers with critical information required for accurate modeling of material response to intense loading. Experiments were performed on the Army Research Laboratory 102 mm bore single-stage light gas gun. Impact conditions were uniaxial and planar to within 1 mrad of tilt. VISAR was used to record particle velocity histories with 0.5 ns temporal resolution. The shock Hugoniot for 5083-H131 is extrapolated to 50 GPa and compared to the previous high pressure results of Hauver (1973). The dynamic response including HEL and spall strength of 5083-H131 is compared to other commonly used aluminum alloys. [Preview Abstract] |
Wednesday, June 27, 2007 8:30AM - 9:00AM |
L7.00003: 2D Mesoscale Simulations of Quasielastic Reloading and Unloading in Shock Compressed Aluminum Invited Speaker: 2D mesoscale simulations of planar shock compression, followed by either reloading or unloading, are presented that predict quasi-elastic (QE) response observed experimentally in shocked polycrystalline aluminum. The representative volume element (RVE) of the plate impact experiments included a realistic representation of a grain ensemble with apparent heterogeneities in the polycrystalline sample. Simulations were carried out using a 2D updated Lagrangian finite element code ISP-TROTP incorporating elastic-plastic deformation in grain interior and contact/cohesive methodology to analyze finite strength grain boundaries. Local heterogeneous response was quantified by calculating appropriate material variables along in-situ Lagrangian tracer lines and comparing the temporal variation of their mean values with results from 2D continuum simulations. Simulations were carried out by varying a large number of individual heterogeneities to predict QE response on reloading and unloading from shock state. The heterogeneities important for simulating the QE response identified from these simulations were: hardened grain boundaries, hard inclusions, and micro-porosity. It is shown that the shock-deformed state of polycrystalline aluminum in the presence of these effects is strongly heterogeneous with considerable variations in lateral stresses. This distributed stress state unloads the shear stress from flow stress causing QE response on reloading as well as unloading. The simulated velocity profiles and calculated shear strength and shear stresses for a representative reloading and unloading experimental configuration were found to agree well with the reported experimental data. Work supported by DOE. [Preview Abstract] |
Wednesday, June 27, 2007 9:00AM - 9:15AM |
L7.00004: Laser-Induced Spall of Aluminum and Aluminum Alloys at High Strain Rates Douglas Dalton, Jonathan Brewer, Aaron Bernstein, Will Grigsby, Despina Milathianaki, Evan Jackson, Richard Adams, Patrick Rambo, Jens Schwarz, Aaron Edens, Matthias Geissel, Ian Smith, Eric Taleff, Todd Ditmire We report on laser-induced spall experiments aimed at studying how a material's microstructure affects the tensile fracture characteristics at high strain rates ($>$10$^{6}$ s$^{-1})$. We used the Z-Beamlet Laser at Sandia National Laboratory to drive shocks and to measure the spall strength of aluminum targets with various microstructures. The targets were recrystallized, high-purity aluminum (Al-HP RX), recrystallized aluminum + 3 wt.{\%} magnesium (Al-3Mg RX), and cold-worked aluminum + 3 wt.{\%} magnesium (Al-3Mg CW). The Al-3Mg RX and Al-3Mg CW are used to explore the roles that solid-solution alloying and cold-work strengthening play in the spall process. Using a VISAR and sample recovery techniques, we are able to measure spall strength and failure morphology in these targets simultaneously. We find that the spall strength is highest for Al-HP RX. Analysis reveals that material grain size plays a vital role in the fracture morphology and spall strength results. [Preview Abstract] |
Wednesday, June 27, 2007 9:15AM - 9:30AM |
L7.00005: Behavior of Ultrasonic Consolidated Aluminum under Shock Loading Daniel Casem, George Gazonas The shock response of Ultrasonic Consolidated (UC) aluminum is investigated by plane shock wave experiments. The UC material is manufactured by the Solidica company using a process during which thin layers (50 micron) of 1100 aluminum are bonded together by ultrasound to create what is effectively a solid state weld. The primary interest of this research is in determining the spall strength of these bonds and how it compares to that of solid 1100 aluminum. Of secondary interest is how shock waves propagate through the layered material, i.e., the effect on the development of the plastic wave and dispersion through the heterogeneous media. [Preview Abstract] |
Wednesday, June 27, 2007 9:30AM - 9:45AM |
L7.00006: Shock Consolidation of Nanocrystalline Aluminum Powders for Bulk Component Formation David A. Fredenburg, Tracy Vogler, Christopher Saldana, Naresh Thadhani Shock compression is used to consolidate micron-size nanocrystalline metal particles formed from Al-6061 T6 stock through frequency modulated severe plastic deformation (SPD) machining methods. Compaction characteristics are developed in the quasi-static and dynamic regime. Shock recovery experiments are performed to determine the degree of densification, and the microstructure and mechanical properties of compacts following shock compression. At lower impact velocities compacts show slight increase in crystallite size and reduction in residual strain for bulk compacts reaching 85-92{\%} theoretical density, with microstructures revealing a lack of mechanical bonding between neighboring particles. At higher impact velocity of 650 m/s compacts reach 95-96{\%} theoretical density. Mesoscale simulations using real microstructures obtained from powder compacts are performed to examine the shock propagation characteristics through the simulated compacts and determine the effect of particle morphology on compaction characteristics. Simulations will also aid in design of the compaction experiments to ensure fabrication of bulk compacts with retention of nanocrystalline grain structure. [Preview Abstract] |
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