Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session H4: Inelastic Deformations, Fracture and Spall VI |
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Chair: Neil Bourne, University of Manchester Room: Regency Ballroom A |
Tuesday, July 11, 2017 9:15AM - 9:30AM |
H4.00001: The Effects of Stress and Release Rate on the Spall Behavior of Single Crystal [100] Copper Gerald Stevens, William Turley, Brandon La Lone, Lynn Veeser, Robert Hixson A systematic study was performed of the spall behavior of single crystal [100] copper as a function of impact stress and release-rate at the spall plane. The release rate is governed by material thicknesses, peak stress, and the intrinsic wave-speeds of copper. Release rates were varied from 4.3 to 24.5 GPa/$\mu $s, and peak stress was varied from 5.3 to 14.0 GPa. PDV measurements of the target free surface velocity were used to measure spall-strengths which varied from 1.7 to 2.7 GPa. Our data are well described by a simple, semiempirical two-parameter model. By focusing on single crystal behavior, we have removed the influence of grain-size and also limited the slip systems available to the shocked metal. Measured velocity profiles show pronounced acceleration at spall, which suggests that [100] copper exhibits brittle tensile fracture. This is in contrast to the other crystal orientations [111] and [110] which have spall-velocity profiles similar to polycrystalline copper. [Preview Abstract] |
Tuesday, July 11, 2017 9:30AM - 9:45AM |
H4.00002: Microstructure Effects on Spall Strength of Titanium-based Bulk Metallic Glass Composites. Rene Diaz, Douglas Hofmann, Naresh Thadhani The spall strength of Ti-based metallic glass composites is investigated as a function of varying volume fractions (0-80{\%}) of in-situ formed crystalline dendrites. With increasing dendrite content, the topology changes such that neither the harder glass nor the softer dendrites dominate the microstructure. Plate-impact experiments were performed using the 80-mm single-stage gas gun over impact stresses up to 18 GPa. VISAR interferometry was used to obtain rear free-surface velocity profiles revealing the velocity pullback spall failure signals. The spall strengths were higher than for Ti-6Al-4V alloy, and remained high up to impact stress. The influence of microstructure on the spall strength is indicated by the constants of the power law fit with the decompression strain rate. Differences in fracture behavior reveal void nucleation as a dominant mechanism affecting the spall strength. The microstructure with neither 100{\%} glass nor with very high crystalline content, provides the most tortuous path for fracture and therefore highest spall strength. The results allow projection of spall strength predictions for design of in-situ formed metallic glass composites. [Preview Abstract] |
Tuesday, July 11, 2017 9:45AM - 10:00AM |
H4.00003: Spall of a High Strength, High Toughness Fe-Mn-Cr-Ni-Mo-Si-0.28C Steel Christopher Neel, Sean Gibbons, Rachel Abrahams We investigate the spall behavior of a high strength, low-alloy Fe-Mn-Cr-Ni-Mo-Si alloy steel using gun-driven, planar-shock impact studies. The study utilized laser velocimetry to obtain the spall strength using the form of the ``pullback'' in the velocity profile, and also soft-recovery and post-experiment metallurgical examination using both optical and electron microscopy to investigate the underlying mechanisms of spall failure. We also report a spall failure sequence in which voids nucleate and grow beginning at the incipient spall threshold and initially become more prevalent as the impact velocity increases. Then, as the impact velocity increases further, traditional void nucleation becomes almost completely absent and is replaced by adiabatic shear bands occurring along the spall plane. Finally, as impact velocity continues to increases, voids re-form and eventually result in complete spall failure. Throughout the range of velocities between incipient and complete spall, the calculated spall strength remains approximately constant at 6.7 GPa, which compares favorably with other low alloy steels. We compare these observations with similar spall studies of other steels and speculate on the underlying cause of the unusual spall failure sequence. [Preview Abstract] |
Tuesday, July 11, 2017 10:00AM - 10:15AM |
H4.00004: Unraveling the Evolution of Microstructure during Shock Loading and Spall Failure at the Atomic Scales and the Mesoscales Avinash Dongare, Garvit Agarwal, Sergey Galitskiy The modeling of the spall failure of metals requires a fundamental understanding of the evolution of defects and the nucleation, growth and coalescence of voids under shock loading. Classical molecular dynamics (MD) simulations are used to investigate the links between the microstructure and the evolution of dislocation densities and damage (voids) during shock compression and spall failure of single crystal and nanocrystalline Al microstructures. However, this understanding of the onset of spallation at scales beyond the capability of MD simulations is still in an infancy. The ``quasi-coarse-grained dynamics'' (QCGD) method is able to scale up MD simulations to the mesoscales using scaling relationships for interatomic potentials and degrees of freedom for a reduced number of atoms. The spall failure behavior is investigated for polycrystalline Al systems with dimensions ranging from 0.1 microns to 10 microns for strain rates ranging from 10$^{\mathrm{7}}$ s$^{\mathrm{-1}}$ to 10$^{\mathrm{10}}$ s$^{\mathrm{-1}}$. The strain rate and grain size dependence on the evolution of dislocation densities and damage will be presented. The predicted atomic scale evolution of dislocation densities and void fraction at the mesoscales will be presented. [Preview Abstract] |
Tuesday, July 11, 2017 10:15AM - 10:30AM |
H4.00005: ZrCuAl Bulk Metallic Glass spall induced by laser shock. Benjamin Jodar, Didier Loison, Yoshihiko Yokoyama, Emilien Lescoute, Laurent Berthe, Jean-Christophe Sangleboeuf To face High Velocity Impacts, the aerospace industry is always seeking for innovative materials usable as debris shielding components. Bulk Metallic Glasses (BMG) revealed interesting mechanical properties in case of static and quasi-static loading conditions: high elasticity, high tenacity, low density and high fracture threshold... The department of Mechanics and Glass of the Institut of Physics Rennes conducted on the ELFIE facility, laser shock experiments to study the behavior of a ternary ZrCuAl BMG under high strain rate, up-to fragmentation process. On the one hand, in-situ diagnostics were used to measure ejection velocities with PDV and debris morphologies were observed by Shadowgraphy. On the other hand, spalled areas (dimensions and features) were characterized through post-mortem analysis (optical observations, profilometry and SEM). These results are compared to experimental and numerical data on the crystalline forms of the ZrCuAl basic compounds. [Preview Abstract] |
Tuesday, July 11, 2017 10:30AM - 10:45AM |
H4.00006: Spall failure of ultra-high purity single crystals Sara Adibi, Justin Wilkerson Spall failure of metals is governed by void nucleation, growth, and coalescence. Recent experimental observations suggest that under extreme conditions nano-void nucleation may be mediated by vacancy clustering in addition to the more traditional view of void nucleation at second phase particles. Here, we use molecular dynamics simulations as a tool to investigate the time-dependence associated with vacancy clustering in ultra-high purity single crystals. The time evolution of the vacancy cluster size statistics are investigated as a function of temperature, pressure, and vacancy concentration. It is shown that increasing the temperature and/or initial vacancy concentration can accelerate the incubation time for generating a cluster of a critical size. Since the critical stress to grow these nano-voids is strongly size-dependent, an interesting time-temperature-vacancy concentration coupling may arise in spall failure. We propose a continuum theory for this diffusion-fracture coupled process, which is shown to provide favorable agreement with our molecular dynamics simulations. This atomistically-informed theory of void nucleation may be integrated into multiscale frameworks of ductile fracture of metals to predict the macroscopic implications of these atomistic processes. [Preview Abstract] |
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