Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session O6: Inelastic Deformations, Fracture and Spall VI |
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Chair: Naresh Thadhani, Georgia Institute of Technology, K.T. Ramesh, Johns Hopkins University Room: 8/9/10 |
Wednesday, June 17, 2015 9:15AM - 9:30AM |
O6.00001: Experimental observation of dynamic ductile damage development under various triaxiality conditions Laurianne Pillon, Lise-Marie Adolf Fracture in ductile materials finds its origin in microscopic mechanisms: the nucleation of voids that grow and coalesce in order to form a crack. The most popular of these models, proposed by Gurson, aims at describing the damage development with respect to the plastic behavior of porous material. The Gurson model has been extended by Perrin to describe damage evolution in ductile viscoplastic porous materials. The Gurson-Perrin model (GPm) allows representing damage development with respect to the stress triaxiality and strain-rate conditions. We propose a new experimental design able to test and validate the GPm under various dynamic conditions and for different triaxiality levels. The experimental project will be detailed. A notch is drawn in the Cu cylindrical target where damage develops and the local failure occurs. A variation of the notch radius enables a variation in the triaxiality level. Three notch radii have been tested. Observations with numerical cameras allow following the shape of the notch, a characteristic of damage development. Several PDV measurements have been performed around the target. A first analysis of this experimental process will be shown and comparisons with numerical simulations will be presented. [Preview Abstract] |
Wednesday, June 17, 2015 9:30AM - 9:45AM |
O6.00002: Dynamic Yielding and Spall Behavior of Commercially Pure Grade 4 Titanium Naresh Thadhani, R.L. Whelchel, Tom Sanders, D.S. Mehkote, K.A. Iyer The dynamic yielding and fracture (spalling) of commercially pure (grade 4) titanium are investigated using symmetric plate impact experiments over a peak stress range of 5.6 GPa to 12.5 GPa, using the 80-mm single-stage gas-gun. VISAR rear free surface velocity profiles display both a Hugoniot elastic limit (HEL) and a velocity pullback, which are indicative of dynamic compressive yielding and tensile fracture (spalling), respectively. The HEL values appear to show a slight decrease with peak stress from 2.2 GPa to 2.0 GPa along with a corresponding increase in twinning observed in recovered impacted samples. The spall strength on the other hand increases with peak stress from a value of 3.3 GPa to 3.8 GPa and shows a good power law fit with the decompression strain rate. The differing responses in dynamic yield and fracture behavior suggest that void nucleation may be the dominant mechanism affecting the spall strength of grade 4 titanium. [Preview Abstract] |
Wednesday, June 17, 2015 9:45AM - 10:00AM |
O6.00003: Effects of temperature and strain-rate on the dynamic mechanical behaviour of a fine grained Al-Sc alloy Z.A. Major, D. East, A.D. Brown, M.Z. Quadir, P.J. Hazell, J.P. Escobedo The influence of temperature and strain-rate on the dynamic mechanical behavior of a fine grained Al-Sc alloy has been investigated. The effect of strain-rate (10$^{-2}$-10$^{4})$ and temperature (25-500C) on the mechanical behavior of this alloy was assessed by conducting compression and tensile experiments utilizing a Hopkinson pressure bar equipped with a high temperature furnace. The deformed specimens were characterized via optical and electron microscopy (electron backscatter diffraction). The examination of the microstructural evolution allowed the assessment of the active deformation mechanisms at more extreme loading conditions: dislocation-based vs. grain boundary sliding. The most important results of this study will be presented. [Preview Abstract] |
Wednesday, June 17, 2015 10:00AM - 10:15AM |
O6.00004: Microstructural examination of the $\alpha$-$\omega$ Two-Phase Shock-Induced Microstructure in Zirconium Benjamin M. Morrow, J. Pablo Escobedo, Robert D. Field, Robert M. Dickerson, Patricia O. Dickerson, Carl P. Trujillo, Ellen K. Cerreta Omega phase can be formed in alpha-phase Zr during shock loading. Interestingly, the high pressure phase can be retained upon release allowing for post-mortem study of the omega phase. Currently, the transformation pathway is not well understood. To provide more insight into this pathway during dynamic loading, shocked-induced microstructures of Zr have been studied. Soft recovered, plate impact specimens have been examined via electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) to characterize the orientation relationships (OR) and habit planes (HP) between phases. This enables a better understanding of transformation path that is then compared to Molecular Dynamics (MD) simulations. Based on key microstructural features observed in the post-mortem microstructures, a significant amount of the observed alpha phase appears to have originated from the reverse transformation upon release. Results of microstructural analysis will be discussed, along with implications toward phase transformation pathways. [Preview Abstract] |
Wednesday, June 17, 2015 10:15AM - 10:30AM |
O6.00005: Temperature effects and strain rate effects on the piezoelectric charge production of PZT 95/5 Amnah Khan, William Proud The effects of varying strain rates and temperatures on the charge output and fracture of the piezoceramic PZT 95/5 have been investigated. The samples are studied in the temperature range of $-20\,^{\circ}\mathrm{C}$ to $+80\,^{\circ}\mathrm{C}$; a range of strain rates (10$^{-4}$ s$^{-1}$ to 10$^{+3}$ s$^{-1}$) is achieved using quasi-static loading equipment, drop weights and Split Hopkinson Pressure Bars. Stress-strain data is obtained, along with high-speed images, allowing the physical processes e.g. fracture, to be quantified. [Preview Abstract] |
Wednesday, June 17, 2015 10:30AM - 10:45AM |
O6.00006: Evolutions of elastic-plastic shock compression waves in different materials G.I. Kanel, E.B. Zaretsky, S.V. Razorenov, A.S. Savinykh, G.V. Garkushin Measurements of decay of the elastic precursor wave are used to determine the initial plastic strain rate as a function of the stress. Last years we performed large series of such kind experiments with metals and alloys at various temperatures, ceramics and glasses. In course of these measurements we observed several unexpected effects which have not got exhaustive explanations yet. In the presentation, we'll discuss a departure from self-similar development of the wave process which is accompanied with apparent sub-sonic wave propagation, changes of shape of elastic precursor wave as a result of variations in the material structure and the temperature, unexpected peculiarities of reflection of elastic-plastic waves from free surface, effects of internal friction at shock compression of glasses and some other effects. It seems the experimental data contain more information about kinetics of the time-dependent phenomena than we are able to get from their analysis now. [Preview Abstract] |
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