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 U4: Inelastic Deformation VIII: Recovery |
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Chair: Ruqiang Feng, University of Nebraska, Lincoln Room: Hyatt Regency Constellation E |
Thursday, August 4, 2005 3:00PM - 3:15PM |
U4.00001: Microstructural Characterization of Shock Recovered AD995 Alumina James McCauley, Mingwei Chen, Neil Bourne, Dattatraya Dandekar The present work was initiated to characterize the crystallographic and microstructural changes in shock recovered specimens of AD995 alumina subjected to shock induced stress between 4 and 8 GPa, below and above its HEL, i.e., 6.7 GPa. The AD995 was recovered intact, but containing macroscopic cracks, when shocked to 4 GPa, a stress well below the HEL. The AD995 specimen recovered from the plate impact test at a stress (7.8 GPa) above the HEL showed visual evidence of extensive macroscopic damage and fragmentation. The AD995 specimen recovered from the 6 GPa impact test showed evidence of localized plastic deformation and the presence of dislocations primarily in the vicinity of grain boundaries. However, the AD995 specimen recovered from the 8 GPa test exhibited deformation twins. The aforementioned change in the shock induced plastic behavior/deformation and failure in AD995 below and above the HEL was simultaneously associated with a change in the fracture behavior of AD995, from intergranular fracture below the HEL to intragranular cleavage fracture above the HEL. [Preview Abstract] |
Thursday, August 4, 2005 3:15PM - 3:30PM |
U4.00002: Diffuse X-ray Scattering from Shock Recovered Metals* R.I. Barabash, G.E. Ice, W. Liu, J. Belak, G.H. Campbell, M. Kumar, H.E. Lorenzana, J.S. Wark A detailed understanding of plasticity during shock loading has been inhibited by the need to examine soft recovered samples. Diffuse X-ray scattering offers the prospect of quantifying the plastic state in situ during shock loading. The disorder created at the shock front leads to significant diffuse scattering surrounding the Bragg peaks. Analysis of this diffuse scattering results in a measure of dislocation density and local lattice rotation. Prior to fielding the in situ experiment at synchrotron light sources, we have measured polychromatic X-ray microdiffraction from shock recovered samples of Al and Cu at the Advanced Photon Source. The density and organization of dislocations will be presented as well as comparison to TEM. $* $Use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. W-31-109-Eng-38 and work sponsored by the Metals {\&} Ceramics Division through the ORNL operated by UT-Battelle LLC for the U.S. Department of Energy under contract DE-AC05-00OR22725 and performed under the auspices of the U.S. Department of Energy by University of California, LLNL under Contract W-7405-Eng-48. [Preview Abstract] |
Thursday, August 4, 2005 3:30PM - 3:45PM |
U4.00003: Heterogeneous Deformation of Copper in Shock Waves at Subgrain Scale Level Viktor Raevsky It is known that waves of sufficient intensity cause formation of periodic bands with increased strain intensity in metals. These bands are localized in separate grains, and they are located, as a rule, in parallel with each other. They have period of $\approx $10 $\mu $m, i.e. they differ from ``classical'' Luder's bands, which have mesolevel and are oriented in planes with the highest shear stress. Transition to heterogeneous regime of deformation in shock waves is accompanied with significant temporal reduction of shear strength of substance (approximately 2-3 times). It should be taken into account when developing models of high-rate strain. At the same time, conditions of formation of heterogeneous structures and the dependences of the loading process have been poorly studied. Also there are no data on substance structure inside bands of localized deformation. The paper presents results of new experimental and numerical-theoretical studies of heterogeneous regime of deformation in copper, which were performed in 2003 -- 2004 in RFNC-VNIIEF. The paper includes results of studies of formation of heterogeneous structures at mesolevel under shock-wave and shockless high-rate loading for monocrystals of copper and polycrystal copper with various grain sizes. [Preview Abstract] |
Thursday, August 4, 2005 3:45PM - 4:00PM |
U4.00004: Crystal Structure Effects on Surface Fractures of Impacted Cubes William H. Holt, Willis Mock, Jr. Cubes (9.53 mm on edge) of polycrystalline and single-crystal forms of a nickel-based superalloy (62.5 percent Ni) were impacted in vacuum at 747 m/sec by gas-gun-accelerated 3.18-mm-thick disks of 7075-T6 aluminum. Each cube was supported in a frangible holder on the gun muzzle. Impacts occurred between a disk flat surface and a cube flat surface, followed by soft recovery of these items. Visible fractures on the cubes were primarily associated with the impact surfaces. The polycrystalline cube showed an irregular pattern of many open cracks, forming columnar regions with axes normal to the impact plane; some of these regions at the edges were broken away. The single crystal cube (impacted on a face perpendicular to the [100] direction) showed only minor cracks at the center of the cube face and near the centers of the face edges. The observed differences suggest higher impact toughness for the single crystal material; the absence of grain boundaries may increase the threshold for fracture initiation. [Preview Abstract] |
Thursday, August 4, 2005 4:00PM - 4:15PM |
U4.00005: High-speed Photographic Study of Wave Propagation and Impact Damage in Fused Silica and AlON Using the Edge-on Impact (EOI) Method Parimal Patel, James McCauley, Elmar Strassburger, Douglas Templeton An Edge-on Impact (EOI) test method coupled with a high speed Cranz-Schardin camera has been developed at the Fraunhofer-Institute for High-Speed Dynamics, Ernst-Mach-Institut (EMI), Efringen-Kirchen, Germany to visualize damage propagation and dynamic fracture in structural ceramics. Most work in the past has been carried out in a reflection mode from the surface of impacted ceramics. In the current study, the test was reconfigured to photograph the propagation of damage in the transmission mode using shadowgraphs. In addition to plain light observations, the stress wave was also visualized in crossed polarizers using the photoelastic effect. Plates of fused silica measuring 100X100X13mm were impacted at velocities from 151 to 350 m/s. Plates of AlON measuring 100X100X10mm were impacted using solid cylinder steel projectiles with velocities ranging from 270 to 925 m/s. Detailed analysis of the macroscopic fracture patterns, stress wave characteristics and velocity, various damage zones structures, single crack and crack front velocities will be presented. [Preview Abstract] |
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