Shock Wave Behaviour of Polymeric Materials for Detonation Waveshapers

This paper discusses the experimental determination of explosive shock attenuation parameters of four different polymers viz., Teflon, Phenol formaldehyde, Polyethylene foam and Polypropylene foam. These polymers are candidate materials for waveshapers in shaped charge warheads. Cylindrical specimens of the polymer materials were subjected to explosive shock loading by the detonation of RDX:Wax (95:5). Shock arrival time was measured using piezo-wafers positioned at known spatial intervals in the specimens. Initial shock velocity, stabilised shock velocity and attenuation constant were determined. These parameters are essential for the design of waveshapers. Foams have better shock attenuating properties compared to solids due to their cellular structure. Polypropylene foam has the highest shock attenuating characteristic among the four materials studied.

Initial Decomposition Mechanism of 3-Nitro-1,2,4-triazol-5-one (NTO) under Shock Loading: ReaxFF Parameterization and Molecular Dynamic Study

We report a reactive molecular dynamic (ReaxFF-MD) study using the newly parameterized ReaxFF-lg reactive force field to explore the initial decomposition mechanism of 3-Nitro-1,2,4-triazol-5-one (NTO) under shock loading (shock velocity >6 km/s). The new ReaxFF-lg parameters were trained from massive quantum mechanics data and experimental values, especially including the bond dissociation curves, valence angle bending curves, dihedral angle torsion curves, and unimolecular decomposition paths of 3-Nitro-1,2,4-triazol-5-one (NTO), 1,3,5-Trinitro-1,3,5-triazine (RDX), and 1,1-Diamino-2,2-dinitroethylene (FOX-7). The simulation results were obtained by analyzing the ReaxFF dynamic trajectories, which predicted the most frequent chain reactions that occurred before NTO decomposition was the unimolecular NTO merged into clusters ((C2H2O3N4)n). Then, the NTO dissociated from (C2H2O3N4)n and started to decompose. In addition, the paths of NO2 elimination and skeleton heterocycle cleavage were considered as the dominant initial decomposition mechanisms of NTO. A small amount of NTO dissociation was triggered by the intermolecular hydrogen transfer, instead of the intramolecular one. For α-NTO, the calculated equation of state was in excellent agreement with the experimental data. Moreover, the discontinuity slope of the shock-particle velocity equation was presented at a shock velocity of 4 km/s. However, the slope of the shock-particle velocity equation for β-NTO showed no discontinuity in the shock wave velocity range of 3–11 km/s. These studies showed that MD by using a suitable ReaxFF-lg parameter set, could provided detailed atomistic information to explain the shock-induced complex reaction mechanisms of energetic materials. With the ReaxFF-MD coupling MSST method and a cheap computational cost, one could also obtain the deformation behaviors and equation of states for energetic materials under conditions of extreme pressure.

Reflecting laser-driven shocks in diamond in the megabar pressure range

In this work we present experimental results on the behavior of diamond at megabar pressure. The experiment was performed using the PHELIX facility at GSI in Germany to launch a planar shock into solid multi-layered diamond samples. The target design allows shock velocity in diamond and in two metal layers to be measured as well as the free surface velocity after shock breakout. As diagnostics, we used two velocity interferometry systems for any reflector (VISARs). Our measurements show that for the pressures obtained in diamond (between 3 and 9 Mbar), the propagation of the shock induces a reflecting state of the material. Finally, the experimental results are compared with hydrodynamical simulations in which we used different equations of state, showing compatibility with dedicated SESAME tables for diamond.

Shock Wave Physics as Related to Primary Non-Impact Blast-Induced Traumatic Brain Injury

ABSTRACT Introduction Blast overpressure exposure, an important cause of traumatic brain injury (TBI), may occur during combat or military training. TBI, most commonly mild TBI, is considered a signature injury of recent combat in Iraq and Afghanistan. Low intensity primary blast-induced TBI (bTBI), caused by exposure to an explosive shock wave, commonly leaves no obvious physical external signs. Numerous studies have been conducted to understand its biological effects; however, the role of shock wave energy as related to bTBI remains poorly understood. This report combines shock wave analysis with established biological effects on the mouse brain to provide insights into the effects of shock wave physics as related to low intensity bTBI outcomes from both open-air and shock tube environments. Methods Shock wave peak pressure, rise time, positive phase duration, impulse, shock velocity, and particle velocity were measured using the Missouri open-air blast model from 16 blast experiments totaling 122 mice to quantify physical shock wave properties. Open-air shock waves were generated by detonating 350-g 1-m suspended Composition C-4 charges with targets on 1-m elevated stands at 2.15, 3, 4, and 7 m from the source. Results All mice sustained brain injury with no observable head movement, because of mice experiencing lower dynamic pressures than calculated in shock tubes. Impulse, pressure loading over time, was found to be directly related to bTBI severity and is a primary shock physics variable that relates to bTBI. Discussion The physical blast properties including shock wave peak pressure, rise time, positive phase duration, impulse, shock velocity, and particle velocity were examined using the Missouri open-air blast model in mice with associated neurobehavioral deficits. The blast-exposed mice sustained ultrastructural abnormalities in mitochondria, myelinated axons, and synapses, implicating that primary low intensity blast leads to nanoscale brain damage by providing the link to its pathogenesis. The velocity of the shock wave reflected back from the target stand was calculated from high-speed video and compared with that of the incident shock wave velocity. Peak incident pressure measured from high sample rate sensors was found to be within 1% of the velocity recorded by the high-speed camera, concluding that using sensors in or close to an animal brain can provide useful information regarding shock velocity within the brain, leading to more advanced knowledge between shock wave physics and tissue damage that leads to bTBIs.

Mathematical modeling of transfer intensive of edges of spatial cracks on the fronts of longitudinal and shear waves by a ray method

В ближайшей окрестности вершины плоской трещины, а в общем случае, вблизи передней кромки пространственной трещины, деформирование материала носит неупругий характер. В работе предложено лучевое моделирование высокоскоростного деформирования материала в δ-окрестности подвижной передней кромки трещины, используя динамическую упруговязкопластическую модель тела Бингама с условием пластичности Мизеса. Показано, что распространяющаяся передняя кромка трещины продольного сдвига лежит на поверхности сильного разрыва продольной скорости, бегущей со скоростью упругих продольных волн, а передняя кромка трещины отрыва и трещины поперечного сдвига лежит на поверхности сдвиговой волны, бегущей со скоростью волн сдвига. Введены интенсивности передних кромок трещин: скачок скорости сдвига поперек передней кромки трещины продольного сдвига, скачок поперечной скорости на передней кромке трещины отрыва, скачок касательной скорости к передней кромке трещины поперечного сдвига. Построены обыкновенные дифференциальные уравнения переноса интенсивностей передних кромок трещин вдоль лучей как ортогональных траекторий точек переднего фронта. Получены приближенные решения уравнений переноса интенсивностей передних кромок пространственных трещин в напряженный материал и приведены выражения для глубины проникания пространственных трещин. Показано изменение направления сдвига и отрыва в передних кромках соответствующих трещин в зависимости от напряженного состояния перед трещинами. Приведены графики численных расчетов переноса интенсивностей передних кромок трещин и глубины их проникания. In the near neighborhood of the top of the plane crack, and in General, in the space case, near the edge of the spatial crack, the deformations of the material have the inelastic character. In this article proposes the elasticviscoplastic model of the Bingham body with the condition of plasticity of Mises for modeling high velocity deformation material near of the top of crack. Shown that an edge of crack belong a surface of elastic wave: cracks of longitudinal shear belong of longitudinal wave and a crack of untiplane shear and avulsion belong a surface of shear wave. For intensity of the crack suggest a shock velocity on the curve of the edge of crack and made ordinary differential equation for transfer intensity of crack on the front of the wave. Shown that a distant of propagation edge of the crack depend from plastic deformation material on the front of the wave. In the process of propagation crack this direction of shear can change from a stresses in front of the wave. Three-D graphics show change intensity of the crack in a process of propagation from parameters.

The ultraluminous X-ray source bubble in NGC 5585

ABSTRACT Some ultraluminous X-ray sources (ULXs) are surrounded by collisionally ionized bubbles, larger and more energetic than supernova remnants: they are evidence of the powerful outflows associated with super-Eddington X-ray sources. We illustrate the most recent addition to this class: a huge (350 pc × 220 pc in diameter) bubble around a ULX in NGC 5585. We modelled the X-ray properties of the ULX (a broadened-disc source with LX ≈ 2–4 × 1039 erg s−1) from Chandra and XMM–Newton, and identified its likely optical counterpart in Hubble Space Telescope images. We used the Large Binocular Telescope to study the optical emission from the ionized bubble. We show that the line emission spectrum is indicative of collisional ionization. We refine the method for inferring the shock velocity from the width of the optical lines. We derive an average shock velocity ≈125 km s−1, which corresponds to a dynamical age of ∼600 000 yr for the bubble, and an average mechanical power Pw ∼ 1040 erg s−1; thus, the mechanical power is a few times higher than the current photon luminosity. With Very Large Array observations, we discovered and resolved a powerful radio bubble with the same size as the optical bubble, and a 1.4-GHz luminosity ∼1035 erg s−1, at the upper end of the luminosity range for this type of source. We explain why ULX bubbles tend to become more radio luminous as they expand while radio supernova remnants tend to fade.

Monte Carlo simulations of fast Newtonian and mildly relativistic shock breakout from a stellar wind

ABSTRACT Strong explosion of a compact star surrounded by a thick stellar wind drives a fast (>0.1c) radiation mediated shock (RMS) that propagates in the wind, and ultimately breaks out gradually once photons start escaping from the shock transition layer. In exceptionally strong or aspherical explosions, the shock velocity may even be relativistic. The properties of the breakout signal depend on the dynamics and structure of the shock during the breakout phase. Here we present, for the first time, spectra and light curves of the breakout emission of fast Newtonian and mildly relativistic shocks, that were calculated using self-consistent Monte Carlo simulations of finite RMS with radiative losses. We find a strong dependence of the νFν peak on shock velocity, ranging from ∼1 keV for vs/c = 0.1 to ∼100 keV for vs/c = 0.5, with a shift to lower energies as losses increase. For all cases studied the spectrum below the peak exhibits a nearly flat component (Fν ∼ ν0) that extends down to the break frequency below which absorption becomes important. This implies much bright optical/ultraviolet emission than hitherto expected. The computed light curves show a gradual rise over tens to hundreds of seconds for representative conditions. The application to SN 2008D/XRT 080109 and the detectability limits are also discussed. We predict a detection rate of about one per year with eROSITA.