Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session J1: Inelastic Deformation, Fracture, and Spall IV |
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Chair: John Clayton, Army Research Laboratory Room: Grand Ballroom II-III |
Tuesday, June 28, 2011 11:00AM - 11:15AM |
J1.00001: Dynamic Characterization of Eglin Steel by Symmetric Impact Experimentation Philip Flater, Rachel Abrahams, Christopher Neel, Lalit Chhabildas, William Reinhart Well-controlled impact studies have been conducted on heat treated ES-1, Eglin steel to determine their dynamic material properties. In particular gas-gun and time-resolved laser interferometry has been used to measure the fine structure in the particle velocity profile resulting from symmetric impact. Nominal impact pressures range from 8 -- 20 GPa. These experiments have allowed us to estimate the dynamic yield and spall strength and the phase transition kinetics of the material. Results of these experiments will be discussed in detail and compared to the results of other steels in the literature. [Preview Abstract] |
Tuesday, June 28, 2011 11:15AM - 11:30AM |
J1.00002: On the shock response of the magnesium alloy Elektron 675 Paul Hazell, Gareth Appleby-Thomas, Clive Siviour, Euan Wielewski Alloying elements such as aluminium, zinc or rare-earths allow precipitation hardening of magnesium (Mg). The low densities of such strengthened Mg alloys have led to their adoption as aerospace materials and (more recently) they are being considered as armour materials. Consequently, understanding their response to high-strain rate loading is becoming increasingly important. Here, the plate-impact technique was employed to measure longitudinal stress evolution in armour-grade wrought Mg-alloy Elektron 675 under 1D shock loading. The strength and spall behaviour was interrogated, with an estimate made of the material's Hugoniot elastic limit. Finally, electron backscatter diffraction (EBSD) techniques were employed to investigate post-shock microstructural changes. [Preview Abstract] |
Tuesday, June 28, 2011 11:30AM - 12:00PM |
J1.00003: Post-mortem Microstructural Observations of Spall Processes Invited Speaker: Spall in ductile metals is a mode of dynamic tensile failure caused by the nucleation, growth, and coalescence of voids. In general, laser interferometric measurements of the free surface velocity are recorded and the spall strength is inferred from the pull back velocity. Recent results have shown the strong role of the microstructure on the resistance of a material to spallation. The spall pullback signals clearly indicate the influence of the spatial density of intercrystalline defects such as grain boundaries and triple junctions in comparison with the work-hardening characteristics that are more dominant in the single crystal samples. However, complementary microstructural analyses of recovered samples to further elucidate the role of grain boundary crystallography and elastic anisotropy on the nucleation and growth process are only now starting to attain a more prominent place as recovery techniques become more robust and commonplace. Of particular note is the emergence of SEM-based electron backscatter diffraction microscopy to complement transmission electron and optical microscopy observations. The technique affords a wide and statistically significant spectrum of spatial and angular information that would enable the development of more physics-based failure models. Observations of spall behavior, particularly crystallography around the voids will be presented. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, June 28, 2011 12:00PM - 12:15PM |
J1.00004: Study of dislocation walls evolution during spall in pure aluminum Benny Glam, Shalom Eliezer, Daniel Moreno, Dan Eliezer The micro-structure of the spall plane of pure aluminum (99.9999{\%}) was investigated in symmetric plate impact experiments. The aluminum targets were first heated at 450$^{o}$C for 22 h for grain growth. The impacted targets were softly caught and collected for metallurgical analysis. It was found that at weak impacts with partial spall, voids with average size of 50$\pm $10 $\mu $m were developed along the grain boundaries. The grain size in the vicinity of the voids is 50-250 $\mu $m, smaller than their size in the rest of the specimen: 400-1000 $\mu $m, revealing that the grains split into smaller grains when dynamic tension is applied. Transmission Electron Microscopy (TEM) and electron diffraction revealed evaluation of parallel dislocation walls, that create a sub-grain micro-structure inside grains with (011) orientation. In grains with other orientations no dislocation walls or sub-grain structure was found. These findings reveal a dislocation glide mechanism along {\{}111{\}} planes during the spall process in an fcc aluminum. [Preview Abstract] |
Tuesday, June 28, 2011 12:15PM - 12:30PM |
J1.00005: The Spall Strength and Hugoniot Elastic Limit of Tantalum with Various Grain Size Sergey Razorenov, Gennady Garkushin, Gennady Kanel, Ol'ga Ignatova The VISAR free surface velocity histories have been measured for commercial grade coarse grain (50 -- 60 $\mu $m) and ultra fine grained ($\sim $1 $\mu $m grain size after severe plastic deformation) tantalum and, for comparison, tantalum single crystals, at peak stresses around 12-14 GPa and strain rates of 10$^{5}$--10$^{6}$ c$^{-1}$. The decrease in the grain size, which resulted in $\sim $25 {\%} increase of the hardness, did not cause any essential influence on the HEL, the value of which is $\sim $2 GPa, but increases slightly the spall strength of the ultra fine grained tantalum (7.4 GPa) in comparison with the coarse grain samples ($\sim $7 GPa). In both cases the spall strength does not appreciably vary with increase of the peak shock stress up to 70 GPa. Insignificant influence of preceding shock compression on the spall strength value has been confirmed by experiments with samples recovered after shock-wave treatment at 40 GPa and 100 GPa peak stresses. The spall strength of tantalum single crystals has been found equal to $\sim $10 GPa that points to non-monotonous dependence of this value on the grain surface area. Different influence of the grain size on static and dynamic yield stresses are discussed in terms of general strain rate effects. [Preview Abstract] |
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