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 B4: Inelastic Deformation I - Spall I |
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Chair: Kaliat Ramesh, John Hopkins University Room: Hyatt Regency Constellation E |
Monday, August 1, 2005 9:00AM - 9:15AM |
B4.00001: Abnormal Spall Behavior Observed in Pure Iron and FeMnNi Alloy Undergoing \textbf{$\alpha -\varepsilon$} Phase Transition Zhiping Tang, Xinhua Zhang, Weiwei Xu, Xiaojun Tang, Haibo Hu The spall behaviors of pure iron DT2 and FeMnNi alloy were investigated experimentally by using a light gas gun and a double-sensitivity VISAR. The impacts for DT2 were symmetric and with same thickness of 6.28mm for both flyer and target plates. It was found that for the peak pressure lower than the $\alpha -\varepsilon $ transition threshold (13GPa), there was no spall occured. When the pressure was higher than the transition threshold, the spall happened based on the VISAR record. The recovered sample showed the multiple spalls at about 2 mm from the impact surface and the free surface, respectively. In the experiments for FeMnNi alloy, the flyer plate was A3 steel of 4.8mm thick and the target plate was FeMnNi alloy of 8-10mm thick. When impact pressure was higher than the $\alpha -\varepsilon $ transition pressure of A3 (13GPa), a shallow spall happened in the target plate at the distance of 1.26mm from the free surface. Such abnormal spall phenomena (the multi-spall occurred in homo-thickness target impact in DT2 and the shallow spall in FeMnNi alloy) are believed to relate to the $\alpha -\varepsilon $ phase transition of iron. [Preview Abstract] |
Monday, August 1, 2005 9:15AM - 9:30AM |
B4.00002: Iron damage and spalling behavior below and above shock induced alpha $\alpha \Leftrightarrow \varepsilon $ phase transition Christophe Voltz, Fran\c{c}ois Buy, Gilles Roy The study of dynamic damage and fracture of iron has been undertaken below and above phase transition by series of time resolved experiments using both light gas launcher and powder gun. Shock wave tests were conducted by symmetrical impacts of high purity iron. To reveal the material behavior we have done shock experiments where the target is covered with a window in order to limit release amplitude and to avoid specimen fragmentation. Metallurgical analysis of soft recovered samples yields informations about damage and fracture processes related to thermo-mechanical loading paths. Tests conducted without window allow studying effects of both phase change and release transition. Optical and SEM characterizations lead us to observe several modes of damage: brittle, ductile diffuse with void growth and heavily localized smooth one. These figures are related with: material where $\alpha \Leftrightarrow \varepsilon $ occurs or interfaces between transformed and not transformed iron. Simulations are performed with the 1D CEA hydrocode Hesione to compare experimental data with numerical results. We explain post-mortem observations by the complex shock wave structure: P1 and P2 shock fronts associated with some corresponding shock release during unloading stages. [Preview Abstract] |
Monday, August 1, 2005 9:30AM - 9:45AM |
B4.00003: Large tensions and strength of iron in different structure states Sergey Razorenov, Gennady Kanel, Andrey Savinykh, Vladimir Fortov With the object of verifying the presence of a region of anomalous iron compressibility at negative pressures, as predicted by the \textit{ab initio }calculations, the reflection of compression pulses from the surfaces of iron single crystals was studied. No evidence of the expected formation of rarefaction shock waves was observed in the range of attained tensile stresses up to 7.6 GPa at 293 K and at 175 K. The breaking stresses achieved 25--50{\%} of the theoretical iron ultimate strength for a load duration of $\sim $10$^{-8}$ s. The dependence of spall strength on the extension rate did not reveal any singularities in the region of assumed anomaly in iron compressibility. The spall strength of a coarse-grain Armco-iron is much less than that of single crystals. Armco-iron with a sub-micron grain size demonstrates nearly the same spall strength as the crystals do. The resistance to fracture for the different inner structure images the kinetics of void nucleation and growth on different structure levels in the material. [Preview Abstract] |
Monday, August 1, 2005 9:45AM - 10:00AM |
B4.00004: Peculiarities of Damage Nucleation Stage at Intensive Loading of Copper Olga Ignatova The models of shear and spall strength, which are currently used, are semi-empirical, and they take no account for some factors occurred at microlevel. Though these factors can significantly influence on the processes of deformation, destruction and compaction of materials. One of these factors is state of material after passing of shock and quasi-isentropic waves of compression in this material. Loading of copper by compression waves (shock and quasi-isentropic waves) causes significant growth of shear and spall strength. In some cases, during damage growth in extension wave, which occurs after shock or quasi-isentropic wave of compression ($P$=30~GPa), it is possible to observe localization of damage zones alternating with zones, which have no visible damages. This new phenomenon, which is observed at comparatively small damages (\textit{$\omega $}$\sim $0.1$\div $0.2), has no a single physical explanation yet. The experimental setup for loading materials by shock or quasi-isentropic waves of compression, which is followed by release to gap, allows to observe both the damage nucleation and the process of compaction of damaged material by compression wave. [Preview Abstract] |
Monday, August 1, 2005 10:00AM - 10:15AM |
B4.00005: Damage Characterization in Copper Deformed Under Hydrostatic Stress - Experimental Analysis Philip Flater, Robert De Angelis, Joel House This paper presents an experimental investigation to characterize the effect of damage created by hydrostatic tensile loading on the properties of copper. Three metallurgical conditions were investigated: half-hard OFHC copper in the as worked, annealed 2hr at 400$^{\circ}$C ($\sim$40 micron grain diameter), and annealed 2hr at 800$^ {\circ}$C ($\sim$80 micron grain diameter). Quasi-static testing of each condition included uniaxial tension and compression, round notched bar tension, and flat tapered bar tension. Dynamic properties under uniaxial tension and compression were tested using a split-Hopkinson pressure bar. Damaged structures were created employing Taylor impact tests and rod-on-rod impact experiments. The resulting damage was characterized employing optical and scanning electron microscopy. Quasi-static compression samples machined from recovered samples were tested to determine the influence of damage on deformation behavior and elastic modulus. The compression experimental results will be discussed in relationship to the starting microstructure and subsequent damaged material. [Preview Abstract] |
Monday, August 1, 2005 10:15AM - 10:30AM |
B4.00006: Scaling Relationships and Dynamic Failure Roger Minich, Mukul Kumar Dynamic failure is modeled as a driven nonlinear dissipative system, which manifests pattern formation and scaling reminiscent of critical phenomena. Statistical fluctuations play a key role in bridging length and time scales from the atomic level to the macroscopic scales observed in laser and gas-gun experiments. The statistical fluctuations are manifested in observed experimental scaling laws. The theoretical approach is briefly reviewed and tested computationally against gas gun experiments that suggest a scaling law for the relationship between dynamic strength and void nucleation and growth rate for Cu single crystals, silica doped Cu single crystals and Cu polycrystals of different grain sizes. Additionally, we observe a sharp contrast in the rebound signal in the velocity-time trace from single crystals and polycrystalline samples. This will be examined in detail and discussed in the context of an apparent rate dependence of the void growth process. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. [Preview Abstract] |
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