Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session B5: BIEP: Fragmentation I |
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Chair: Frederick Ouellet, University of Florida Room: Broadway I/II |
Monday, June 17, 2019 9:15AM - 9:30AM |
B5.00001: Modeling the Fragmentation of a Brittle Zinc Compact Cameron Stewart, Thomas McGrath, James Warner The fragmentation behavior of a cold-isostatically pressed zinc powder is numerically simulated using a couple Eulerian/Lagrangian framework. The material of interest is a compacted zinc powder that is ductile in compression but brittle in tension. The fragmentation behavior has been studied experimentally by Tang and Hooper. The computational model mimics the experimental scenario in which a 10 mm (L/D$=$1) right cylinder of the zinc compact is fired at a thin aluminum plate to induce fragmentation. The experimental investigation caught the fragments in artificial snow and reported the resulting particle size distribution. The zinc cylinder and plate are modeled as finite elements while the snow is represented in the Eulerian field. Initial fragment velocities up to 800 m/s were considered. A Grady-Kipp type method is applied to determine the particle sizes in major failure zones and an automated fragment counting mechanism is applied to quantify the particles that remain discretized on the computational mesh. The results are compared to experimental findings and used to suggest future work to improve fragmentation simulation. [Preview Abstract] |
Monday, June 17, 2019 9:30AM - 9:45AM |
B5.00002: Characterization of Fracture, Dispersion and Energy Dissipation due to High Velocity Fragment Impacts on Warhead Cases and Armor Materials Daniel Pudlak, Kevin Miers Many munitions react violently when subject to Fragment Impact (FI) threats. Previous efforts have identified materials that mitigate / partially mitigate munition FI response at 6000fps, but have had shortfalls at 8300fps. While existing materials are known to improve / mitigate FI response at 8300fps, the materials / configurations are costly, both logistically and financially. One facet of successful mitigation that has proven to result in less violent reactions is the break-up and dispersion of the steel fragment, resulting in reduced velocity, spreading the imparted kinetic energy into the explosive, thereby reducing the power density. It is conceived that high density and layered protection materials provide the ballistic properties needed to fracture and disperse the fragment projectile. There is a shortfall in empirical data demonstrating this fragment break up as a result of different protection schemes. This paper will discuss the methodology for the parametric study and the data analysis and results of the break-up and dispersion of an 8300fps standard NATO mild steel fragment (IAW STANAG 4496), after impacting baseline and armor targets at specified thickness, based on experimental testing and comparative modeling. [Preview Abstract] |
Monday, June 17, 2019 9:45AM - 10:00AM |
B5.00003: High Pressure Oblique Shock Interactions in NATO Fragment Impacts Kevin Miers, Nausheen Al-Shehab, Daniel Pudlak Efforts are ongoing to design munitions to pass the NATO Insensitive Munitions Fragment Impact (FI) test. The NATO FI projectile is a 14.3mm diameter, L/D 1, 160 degree conical nosed mild steel fragment which impacts the munition under test at 2530 m/s. Yawed impacts of this projectile are commonly observed. Hydrocode calculations for these scenarios consistently predict regions of high pressure behind the oblique shock emanating from the contact point in the initial impact, in excess of that which would be expected for 1D planar impacts at the same velocity. We believe these predictions are physical. The theory of Walsh [1], describing steady oblique impacts and the onset of jetting, is reviewed and applied to typical impact conditions. It is calculated that pressures up to approximately twice the 1D shock pressure can be generated by an oblique shock for the same impact velocity. This is verified with hydrocode calculations. Such pressures are relatively localized and transient, but do arise and may contribute to the input shock for thin cased munitions. References: [1] Walsh, J. M., Shreffler, R. G., Willig, F. J. ``Limiting Conditions for Jet Formation in High Velocity Collisions''. Journal of Applied Physics 24, 349 (1953) [Preview Abstract] |
Monday, June 17, 2019 10:00AM - 10:15AM |
B5.00004: Mach stem: large scale experiment to validate analytical model. Nicolas Lecysyn, Didier Capdeville, Jean-Yves Vincont, Pierre Slangen, Alexandre Lefrancois, Yves Grillon, Antoine Osmont Blast overpressure due to detonation is a major concern in terms of homeland security. Immediately after an explosion, an induced shockwave, which is initially spherical, can be reflected to form a bridge wave which is called Mach Stem. This paper deals with a large scale experimental approach to validate Mach stem (Pressure and Triple Point Height) predictions. Two different spherical explosive charges, were set off at different heights and mass above the ground with respect to Sachs' scaling law between both experiments. The choice of Height Of Burst, according with our prediction Model tool, was such as a mach stem reflexion occurs. Overpressure measurements on the ground were carried out. Mach stem, and triple point height were precisely visualized and measured thanks to Edgerton in line shadowgraphy. Among lot of visualization techniques, shadowgraphy gives the best resolved images with less difficulty of implementation at large scale. An analytical model for pressure and triple point height dedicated to nuclear explosions has been modified in order to be used for chemical explosive. There is a good agreement between analytical model and experimental measurement for height of triple point and also for pressure measurement. [Preview Abstract] |
Monday, June 17, 2019 10:15AM - 10:30AM |
B5.00005: Failure model for boron carbide ceramics improved with using explosive experiments data Sergey Dyachkov, Anatoly Parshikov, Vasily Zhakhovsky, Sergey Kuratov Boron carbide is known for its outstanding mechanical properties. Being lightweight, it has the considerable failure strength of about 15-19 GPa under impact loading. However, heavy loads result in material failure which is observed both in wave profiles in plate impact tests and shock hugoniot data. Johnson and Holmquist incorporated the observations to the well-known failure model for fluid dynamics simulations. However, being validated on one dimensional tests the model applications to complex three dimensional systems containing boron carbide parts are limited. Here we suggest an improved explicit failure model and apply it for modeling of explosively compressed boron carbide spherical shell. Using x-ray images of the shell dynamics captured after the main load of tens of GPa, it is found that the further evolution of boron carbide shell is guided by the failure strength curve at low pressures of several GPa. The adjustement of failure model made at low pressures is shown to have almost no effect on usual plate impact tests, but it is essential for the predictive modeling of boron carbide samples during unloading. [Preview Abstract] |
Monday, June 17, 2019 10:30AM - 10:45AM |
B5.00006: Fragmentation of a liquid tin droplet by a short laser pulse Sergey Grigoryev, Vasily Zhakhovsky, Sergey Dyachkov, Bogdan Lakatosh, Mikhail Krivokorytov, Vyacheslav Medvedev Fragmentation mechanisms of a micrometer-sized liquid tin droplet irradiated by a short laser pulse are studied. Our experiments show either symmetric or asymmetric expansion of the droplet depending on laser pulse intensity. To reveal the underline processes we perform simulations complying with the experiments using the smoothed particle hydrodynamics. It is demonstrated that, as a result of fast laser energy deposition, a strong shock wave followed by a tensile wave is formed and propagates from the frontal side to the rear side of droplet. Convergence of such waves inside the droplet induces cavitation nearby the center, which causes the droplet to expand symmetrically. Reflection of a shock wave from the rear side of droplet may lead to spallation producing a thin layer moving in the laser pulse direction, which results in the asymmetrical expansion. The calculated laser intensity threshold for the rear-side spallation is higher than a threshold required for the central cavitation. The corresponding expansion velocities and thresholds agree well with the experimental results in both regimes of droplet expansion. [Preview Abstract] |
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