Low-pressure Shock Research Articles

A case of sepsis complicated by multiple organ dysfunction syndrome with CT appearance of subarachnoid hemorrhage.

A 39-year-old male patient was admitted to hospital with abdominal distension, unconsciousness, and anuria. Head computed tomography (CT) scan showed subarachnoid hemorrhage and diffuse cerebral edema. The high-density area of contrast accumulation region in the high-density CT plaque was 38 HU, and the preliminary diagnosis was SAH, incomplete intestinal obstruction, and sepsis caused by acute cerebrovascular disease. After admission, the patient had sudden upturned eyes, limb convulsions, serum procalcitonin level exceeding 100ng/mL, low blood pressure and septic shock. Imipenem was given for intensive anti-infection therapy. After treatment, the procalcitonin levels showed a slow decline, renal function returned to normal, intra-abdominal pressure dropped to normal, urine volume gradually increased, but platelets still showed a downward trend. The lumbar puncture showed colorless and clear cerebrospinal fluid, and the biochemical and routine results of cerebrospinal fluid were normal. SAH and intracranial infection were excluded, and it was considered that the head CT scan showed pseudo subarachnoid hemorrhage. On the 4th day of admission, laparoscopic exploratory laparotomy+appendectomy+abdominal drainage under general anesthesia were performed. During the operation, purulent gangrene was observed in the appendix, abscess and moss were observed on the surface of the intestine, and a large amount of pus was found in the abdominal cavity. Rhabdomyolysis syndrome appeared after surgery. After continuous renal replacement therapy, the indicators gradually returned to normal level. The patient was conscious, and the head CT examination was normal. The patient was discharged from the hospital on the 10th day after surgery, and no special discomfort and abdominal pain and distension occurred during the 3-month follow-up.

Shock features in carbonates from CM carbonaceous chondrites

We have investigated different carbonate minerals (calcite, aragonite, and ankerite) from two meteorites with different shock metamorphic stages (Boriskino, CM2 − ∼ S3-S4 and Murchison CM2.5–2.2 − S1-S2) using various electron microscope techniques. Our detailed transmission electron microscopy study shows that carbonates are valuable recorders of the shock metamorphic environment and help interpret shock metamorphic conditions on the chondrite parent asteroids. We show the occurrence of fine-scale complex microstructures (dislocations, modulations, mosaic blocks, and microfractures) in all carbonates analyzed, indicating that they were modified during deformation processes at a variable degree. The presence of shock features in all generations of carbonates (Type 0, 1, and 2) indicates that shock deformation event/(s) occurred after the precipitation of all types of carbonates. In Boriskino, the most shocked meteorite analyzed, carbonates record very distinct microstructures compared to Murchison, an unshocked or very weakly shocked sample. We divided these microstructures into two different categories as a function of the degrees of deformation, and several features could be used as diagnostic tools for low and high shock pressures in meteorites. Deformation features are pervasive in calcites, aragonites (Type 1 and 2 Ca carbonates), and ankerites from Boriskino. However, the abundance and distribution of these deformation features are minimal in all calcite crystals analyzed from Murchison and one Type 0 Ca carbonate from Boriskino. This suggests the presence of a correlation between these microstructural features and the degree of shock metamorphic stages of the samples analyzed. The low amount of deformation features in the Type 0 calcite from Boriskino could indicate that the least altered lithologies from Boriskino were not subject to high-intensity impacts.

Probing the effect of fuel components on the auto-ignition behavior of ammonia/natural gas blends: A case study of ethane addition

Ammonia (NH3) is carbon-free and is known as a promising renewable fuel to achieve carbon reduction and carbon neutrality. However, ammonia presents much lower fuel reactivity compared to hydrocarbon fuels. Thus, ammonia is often blended with high reactivity fuels in practical combustion facilities, and natural gas is a good candidate due to its low carbon emissions and massive reserves. Methane is often used to represent natural gas in previous experimental and simulation studies, while the larger alkanes in natural gas can affect the fuel reactivity of ammonia/natural gas blends. This study aims to explore the effects of fuel components on the auto-ignition behaviors of ammonia/natural gas blends. As methane and ethane are the most important species in natural gas, a blend of 90 % methane and 10 % ethane by volume is used to represent natural gas in this study. A low-pressure shock tube was used to measure the ignition delay times (IDTs) of ammonia/methane, ammonia/ethane, and ammonia/natural gas blends in ‘air’ mixtures, with different ammonia blending ratios, at stoichiometric condition, at 1 atm and over the temperature range 1200 – 1800 K. The experimental results show that the IDTs of fuel blends increase with ammonia blending ratios. Meanwhile, 10 % ethane in natural gas can influence the fuel reactivity of ammonia/natural gas blends. A detailed kinetic model proposed in our previous study is used to simulate these new IDTs in addition to experimental data available in the literature. Overall, the kinetic model can predict well the auto-ignition behavior of ammonia/methane, ammonia/ethane, and ammonia/natural gas blends over a wide range of experimental conditions. The simulation and sensitivity analyses results show that the interaction reaction between ammonia and ethane, C2H6 + ṄH2 〈=〉 Ċ2H5 + NH3, is important for predicting the fuel reactivity of ammonia/ethane blends below 1600 K at the studied conditions.

Formation of diamond and lonsdaleite in ureilites by impact shock processing of graphite

AbstractThe origin of diamond in ureilites has been frequently debated. We investigated carbon phase assemblages (CPAs) in five ureilitic samples of the brecciated asteroid 2008 TC3, found within the Almahata Sitta (AHS) strewn field, by transmission electron microscopy, Raman spectroscopy, synchrotron X‐ray diffraction, and cathodoluminescence. Samples MS‐MU 006, MS‐187, and MS‐170, are of low to moderate shock degree (U‐S2 and U‐S3), and samples MS‐MU 027 (U‐S4) and MS‐MU 045 (U‐S5) have a higher shock degree. In MS‐MU 006 and MS‐187, we did not find any diamond grains. MS‐170 contains disordered and distorted graphite with diamond grains up to 12 μm in size and containing inclusions of Fe,Ni‐metal, FeS, Fe‐phosphide, and Cr,Fe‐oxide. These diamond grains formed under relatively low (5–15 GPa) shock pressures through a catalytic process in the presence of a Fe,Ni,Cr,S,P‐rich melt. The highly shocked and fine‐grained ureilites MS‐MU 027 and MS‐MU 045 have three different types of CPAs, namely a nanopolycrystalline assemblage of diamond and defect‐rich diamond/lonsdaleite, disordered and distorted graphite, and polycrystalline diamond with abundant Fe‐rich mineral inclusions. The CPAs that have only diamond and planar defect‐rich diamond (e.g., MS‐MU 027) most likely formed through martensitic transformation of graphite to diamond and lonsdaleite at >15 GPa and >2000 K. The assemblage of diamond, defect‐rich diamond, and disordered and distorted graphite (e.g., MS‐MU 045) formed by martensitic transformation of graphite to diamond and lonsdaleite, followed by back‐transformation to disordered graphite. We did not find any conclusive evidence to support the formation of diamond grains under high static pressure.

Twinned calcite as an indicator of high differential stresses and low shock pressure conditions during impact cratering

AbstractShock‐related calcite twins are characterized in calcite‐bearing metagranite cataclasites within crystalline megablocks of the Ries impact structure, Germany, as well as in cores from the FBN1973 research drilling. The calcite likely originates from pre‐impact veins within the Variscan metagranites and gneisses, while the cataclasis is due to the Miocene impact. Quartz in the metagranite components does not contain planar deformation features, indicating low shock pressures (<7 GPa). Calcite, however, shows a high density (>1/μm) of twins with widths <100 nm. Different types of twins (e‐, f‐, and r‐twins) crosscutting each other can occur in one grain. Interaction of r‐ and f‐twins results in a‐type domains characterized by a misorientation relative to the host with a misorientation angle of 35°–40° and a misorientation axis parallel to an a‐axis. Such a‐type domains have not been recorded from deformed rocks in nature before. The high twin density and activation of different twin systems in one grain require high differential stresses (on the order of 1 GPa). Twinning of calcite at high differential stresses is consistent with deformation during impact cratering at relatively low shock pressure conditions. The twinned calcite microstructure can serve as a valuable low shock barometer.

A strategy to introduce multi-gradient structures into iron by explosive shock wave processing

A strategy combining shock-induced phase transition, twins, and dislocations to produce a multi-gradient structure in Fe is designed and proposed by the explosive processing method. A specific emulsion explosive is designed to introduce gradient pressure into iron ranging from 8.3 to 13.4 GPa by smooth particle hydrodynamics method. The pressure range generated by explosive processing covered shock loading phase transition point, shock unloading phase transition point, twin activating point and elastoplastic dislocation point of iron, creating gradient phase transition, gradient twins, gradient dislocations and gradient grain size structures in iron. The mechanism of gradient grain size formation is illustrated based on the twins and dislocation boundaries. Due to the multi-gradient microstructure, a demonstrating gradient hardness range from 1231.3 Hv to 89.8 Hv is distributed from the surface to the internal of the iron. This method lays an experimental foundation for Fe, Ti, Mg based gradient materials that undergo phase transition under low shock pressure.

Experimental Evidence for Shear‐Induced Melting and Generation of Stishovite in Granite at Low (<18 GPa) Shock Pressure

AbstractKnowledge of the shock behavior of planetary materials is essential to interpret shock metamorphism documented in rocks at hypervelocity impact structures on Earth, in meteorites, and in samples retrieved in space missions. Although our understanding of shock metamorphism has improved considerably within the last decades, the effects of friction and plastic deformation on shock metamorphism of complex, polycrystalline, non‐porous rocks are poorly constrained. Here, we report on shock‐recovery experiments in which natural granite was dynamically compressed to 0.5–18 GPa by singular, hemispherically decaying shock fronts. We then combine petrographic observations of shocked samples that retained their pre‐impact stratigraphy with distributions of peak pressures, temperatures, and volumetric strain rates obtained from numerical modeling to systematically investigate progressive shock metamorphism of granite. We find that the progressive shock metamorphism of granite observed here is mainly consistent with current classification schemes. However, we also find that intense shear deformation during shock compression and release causes the formation of highly localized melt veins at peak pressures as low as 6 GPa, which is an order of magnitude lower than currently thought. We also find that melt veins formed in quartz grains compressed to >10–12 GPa contain the high‐pressure silica polymorph stishovite. Our results illustrate the significance of shear and plastic deformation during hypervelocity impact and bear on our understanding of how melt veins containing high‐pressure polymorphs form in moderately shocked terrestrial impactites or meteorites.

2022 Joint Barringer Medal for Kai Wünnemann and Gareth S. Collins

2022 Joint Barringer Medal for Kai Wünnemann and Gareth S. Collins

Equation of state remeasurements for aluminum and copper under low-impact loading

In this work, the Hugoniot equation of state for aluminum and copper under low-impact loading was measured by using the plane impact technique and laser Doppler velocimetry. The linear relationship between shock wave velocity and particle velocity was fitted by a least squares method, with D=5.28114+1.306(17)us for an Al pressure range from 2.5 to 13.9 GPa and D=3.9386+1.484(14)us for Cu at 5.7–47.5 GPa. The linear fitting correlation coefficient was greater than 0.99, which was better than the previous experimental data. The results demonstrate that the Doppler pin system has great advantages for measuring the Hugoniot EoS at low shock pressure compared with the electric pin technique The experimental data obtained in this work extend to a lower pressure range. This can provide more accurate Mie–Grüneisen EoS of Al and Cu under low shock pressure.

Microstructures in shocked quartz: linking nuclear airbursts and meteorite impacts

Many studies of hypervelocity impact craters have described the characteristics of quartz grains shock-metamorphosed at high pressures of >10 GPa. In contrast, few studies have investigated shock metamorphism at lower shock pressures. In this study, we test the hypothesis that low-pressure shock metamorphism occurs in near-surface nuclear airbursts and that this process shares essential characteristics with crater-forming impact events. To investigate low-grade shock microstructures, we compared quartz grains from Meteor Crater, a 1.2-km-wide impact crater, to those from near-surface nuclear airbursts at the Alamogordo Bombing Range, New Mexico in 1945 and Kazakhstan in 1949/1953. This investigation utilized a comprehensive analytical suite of high-resolution techniques, including transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). Meteor Crater and the nuclear test sites all exhibit quartz grains with closely spaced, sub-micron-wide fractures that appear to have formed at low shock pressures. Significantly, these micro-fractures are closely associated with Dauphiné twins and are filled with amorphous silica (glass), widely considered a classic indicator of shock metamorphism. Thus, this study confirms that glass-filled shock fractures in quartz form during near-surface nuclear airbursts, as well as crater-forming impact events, and by extension, it suggests that they may form in any near-surface cosmic airbursts in which the shockwave is coupled to Earth’s surface, as has been proposed. The robust characterization of such events is crucial because of their potential catastrophic effects on the Earth’s environmental and biotic systems.

Abu Hureyra, Syria, Part 1: Shock-fractured quartz grains support 12,800-year-old cosmic airburst at the Younger Dryas onset

A previous investigation revealed that shock-fracturing, a form of low-pressure shock metamorphism in quartz grains, can be produced during near-surface atomic airbursts and in cosmic impact structures, most likely at pressures lower than 8 GPa. This discovery implies that similar shock-fracturing may also form in quartz grains exposed to near-surface airbursts by comets and asteroids. Here, we investigate this hypothesis by examining quartz grains in a sedimentary profile from Abu Hureyra, a prehistoric archaeological site in northern Syria. This site was previously proposed to have experienced a nearby, low-altitude cosmic airburst at the onset of the Younger Dryas (~12,800 years ago). The Younger Dryas boundary layer (YDB) at Abu Hureyra has previously been shown to contain a rich assemblage of materials consistent in indicating a cosmic impact. These include anomalously high concentrations of melted micro-spherules displaying increased remanent magnetism; meltglass with low water content indicative of high-temperature melting; nanodiamonds, potentially including lonsdaleite; carbon spherules produced by biomass burning; black carbon or soot; total organic carbon; and abnormally high-temperature melted refractory minerals and elements, including platinum, iridium, chromite, and zircon. To further test this impact hypothesis, we searched for evidence of shocked quartz, a robust, widely accepted indicator of cosmic impacts. We used a comprehensive analytical suite of high-resolution techniques, including transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD), to examine and characterize quartz grains from the YDB layer at Abu Hureyra. Our analyses revealed the presence of quartz grains with sub-planar, sub-parallel, and sub-micron-wide intragranular fractures, most likely produced by mechanical and thermal shock or the combination of both. Furthermore, these fractures are typically filled with amorphous silica (glass), a classic indicator of shock metamorphism. Elemental analyses of the weight percentages of oxygen in the amorphous silica indicate that this could not have formed from the deposition of hydrated silica (e.g., opal and hyalite), which is enhanced in oxygen. Instead, the silica we observed is typically depleted in oxygen, consistent with melting under highly reducing conditions. The shock fractures in quartz grains also display Dauphiné twinning, which sometimes develops during the stress of high temperatures or pressures. This evidence is consistent with the hypothesis that the glass-filled fractures in quartz grains were produced by thermal and mechanical shock during a near-surface cosmic airburst at Abu Hureyra. These glass-filled fractures closely resemble those formed in near-surface atomic airbursts and crater-forming impact events.

Reaction kinetics for high pressure hydrogen oxy-combustion in the presence of high levels of H2O and CO2

Novel shock tube experimental ignition delay time (IDT) data are provided to delineate the impact of high concentrations (45% by mole) of H2O and CO2 on IDTs of stoichiometric 4% H2. Ignition delay experiments were conducted using a high- and a low-pressure shock tube facility. High-pressure experiments were performed at pressures of 37-43.8 bar and temperatures of 1084-1242 K in four different bath gases, namely: Ar, 45%H2O/Ar, 30%H2O/15%CO2/Ar, and 45%CO2/Ar. Low-pressure experiments were conducted at 2.1-2.7 bar and 926-1198 K in Ar and 45%CO2/Ar bath gases. Impacts of non-ideal ignition phenomena that may occur in the presence of large amounts of H2O and CO2 were also analyzed. A minimally-tuned H2/CO reaction mechanism, CanMECH 1.0, targeting high-pressure combustion in the presence of large concentrations of H2O and CO2 is presented. The mechanism is constructed from unadjusted kinetic rate parameters from theoretical / experimental elementary reaction rate determinations. The only adjusted rate in CanMECH 1.0 is the much disputed Ar-specific low-pressure-limit pre-exponential factor of H + O2 (+Ar) = HO2 (+Ar) within the uncertainty bounds of the source rate. Validity of CanMECH 1.0 is confirmed against shock tube IDT data of this work, as well as selected H2 and H2/CO shock tube IDT datasets from literature. The performance of the model is compared to Keromnes et al. model (Combust. Flame 160 (2013) 995-1011). CanMECH 1.0 outperformed Keromnes et al. for 16 datasets out of 26 and exhibited a similar performance for another two. In particular, CanMECH 1.0 outperformed Keromnes et al. in predicting shock tube IDTs for H2O- and CO2-laden reactive mixtures, as well as all IDT data at pressures of 17-43.8 bar, which are of distinct value to pressurized oxy-fuel combustion applications relevant to this work.

Phase transitions in Zr at sub-nanosecond time scales

Solid-solid phase transitions are investigated in Zr thin films using shock compression induced by a short laser pulse (<1 ns). Shock wave profiles are measured at free surfaces for films of different thicknesses (a few micrometers) using chirped-pulse line velocimetry with 10 ps time resolution. Experiments are performed at pressures up to ∼50 GPa, which is sufficient to reach the ω and β phases under equilibrium conditions. The shock wave structures are analyzed using a general Lagrangian analysis method, which allows for the calculation of stress–strain paths and assessments of phase transition behavior. In agreement with recent short laser pulse experiments using ultra-fast x-ray diffraction, we do not find any clear evidence of the α–ω transition, though this would be expected from the phase diagram. Instead, we infer a direct transformation to a metastable β-phase at lower shock pressures (<20 GPa) and equilibrium β at higher pressures. Through the velocimetry analysis, we find α–β transformation onset times of less than ∼100 ps and completion times of less than ∼200 ps.

Apollo 15 regolith breccia provides first natural evidence for olivine incongruent melting

Abstract The Apollo 15 mission returned various samples of regolith breccias, typical lunar rocks lithified by impact events on the Moon’s surface. Here we report our observations on shock features recorded in a section of the Apollo Sample 15299. We observe the presence of ferropericlase crystals confined in a shock-melt pocket and conclude that their formation is related to a shock-induced incongruent melting of olivine. While predicted by experiments, this phenomenon has never been observed in a natural sample. The incongruent melting of olivine provides an important signature of melting under high-pressure conditions and allows for estimating the pressure-temperature (P-T) experienced by the studied sample during the impact event. We infer that the fracture porosity that likely characterized the studied sample prior to the shock event critically affected the P-T path during the shock compression and allowed the studied sample to be subjected to elevated temperature during relatively low shock pressures.

Compression and spallation properties of polyethylene terephthalate under plate impact loading

We conduct plate impact experiments to investigate shock compression and spallation properties of polyethylene terephthalate. The Hugoniot equation of state, the apparent velocity–particle velocity relation, and the indices of refraction are obtained from Hugoniot experiments. Spall strength, as well as tensile strain rate is deduced at shock pressures up to ∼2.4 GPa in spallation shots. At low shock pressures (<0.6 GPa), the spall strength increases slightly with increasing shock pressure, as a result of increasing tensile strain rate. Release melting is observed at high impact velocities (>816 m s−1). Via X-ray computed tomography, three-dimensional void and crack structures are revealed for shock-recovered specimens. Small voids appear thin and curved for low-speed impacts but become ellipsoidal for high-speed impacts. Such different void shapes may be attributed to the diverse damage mechanisms at different impact velocities.

Stishovite nucleation at low shock pressures in soda-lime glass

Highly dense and ultra-hard Stishovite phase is the most stable form of SiO2. It is formed when fused silica is subjected to extreme pressures (>34 GPa). In this communication, we report nucleation of the Stishovite phase in shock-loaded soda-lime glass (SLG) samples at a remarkably low compressive stress of 7 GPa. Although it falls within the reported Hugoniot Elastic Limit of SLG between 2.5 and 7 GPa, it is significantly below the crystallization threshold of 34 GPa observed for fused silica. SLG plates were shock loaded by impacting them at 1–2.5 km/s using a table-top experimental setup in which 1 mm-dia Al micro flyer plates of 25–50 μm thickness were generated and propelled using a top-hat Nd:YAG laser pulse of 8 ns duration. The shocked samples were imaged using High Resolution Transmission Electron Microscopy (HRTEM) and further analyzed using Selected Area Electron Diffraction and FFT analyses. All samples showed nucleation of 4 nm Stishovite crystals distributed within the amorphous SLG matrix. The stress state was determined by directly measuring the flyer speed, particle velocity, and shockwave speed by using a state-of-the-art Photonic Doppler Velocimeter (PDV).

The Dynamic Calibration Uncertainty of Fast Response Pressure Probes

Abstract In this article, error sources affecting the dynamic calibration of fast-response pressure probes in shock tubes are examined. In particular, the sensors uncertainty, the uncertainty in the rising point of the pressure step, and the nonideality of the step are treated. The latter refers to the presence of pressure oscillations past the shock front, which are particularly important in the case of low-pressure shock tubes, typically used for the calibration of pressure probes for turbomachinery applications. The nonideality effect is investigated using a linear time invariant (LTI) second-order model for the transfer function of the probe’s line-cavity system and an existing analytical model for the post-shock oscillations. The effects of these uncertainty sources to the experimentally determined transfer function of a fast-response probe calibrated in the von Karman Institute (VKI) shock tube are finally presented.

Experimental observations of shock-wave-induced bubble collapse and hot-spot formation in nitromethane liquid explosive

We studied the collapse of individual helium gas bubbles in the homogeneous explosive nitromethane (NM) to investigate effects of hot-spot formation on the detonation process. A bubble was injected into a NM sample, and a shock wave from an explosive detonator compressed the bubble, creating a localized hot spot. We measured shock and detonation wave speeds with optical velocimetry, and we used a high-speed camera to image the shock propagation and the pre- and post-bubble collapse processes. An infrared camera image showed the residual radiance temperature distribution after the bubble collapse, and an optical fiber pyrometer measured the time-resolved thermal radiance. We measured the optical spectra of light emitted from detonating NM without a bubble and from a collapsing bubble in shocked, undetonated NM. We estimated temperatures of the detonation fronts and of the hot spots formed by bubble collapse. To study the incipient detonation process, we performed all bubble collapse experiments at pressures below the threshold for creating a sustained detonation. Where the bubble collapsed, we observed an opaque, thermally emissive region believed to be chemical reaction products. Chemical reactions in NM can be produced with lower shock pressures (∼1 GPa) when a helium bubble is present than without a bubble (∼10 GPa). We used hydrodynamic modeling to predict shock wave propagation, extent of chemical reaction, and subsequent temperature rise from the collapsing bubble. Simulations using a temperature-dependent Arrhenius burn model gave much better results than reactive burn models that depend only on pressure and density.

Insight into the Chemistry of PETN Under Shock Compression Through Ultrafast Broadband Mid-Infrared Absorption Spectroscopy.

Thin films of pentaerythritol tetranitrate (PETN) were shock compressed using the laser driven shock apparatus at Los Alamos National Laboratory (LANL). Two spectroscopic probes were available to this apparatus: visible white light transient absorption spectroscopy (VIS) from 400 to 700 nm and mid-infrared transient absorption spectroscopy (MIR) from 1150 to 3800 cm-1. Important PETN vibrational modes are the symmetric and antisymmetric NO2 stretches at 1280 and 1650 cm-1, respectively, as well as CH stretches at ∼2900 cm-1. Shock strength was varied from approximately 3 to 55 GPa to span from the chemically unreactive regime to the regime in which fast chemical reaction took place on the 250 ps time scale of the measurements. VIS and MIR results suggest irreversible chemistry was induced in PETN at pressures above 30 GPa. At lower shock pressures, the spectroscopy showed minimal changes attributable to pressure induced effects. Under the higher-pressure reactive conditions, the frequency region at the antisymmetric NO2 stretch mode had a significantly increased absorption while the region around the symmetric NO2 stretch did not. No observable increased absorption occurred in the higher frequency regions where CH-, NH-, and OH- bond absorptions would be observed. A broad absorption appeared on the shoulder at the red-edge of the CO2 vibrational band around 2200 cm-1. In addition to the experiments, reactive molecular dynamics were carried out under equivalent shock conditions to correlate the evolution of the infrared spectrum to molecular processes. The simulations show results consistent to experiments up to 30 GPa but suggest that NO and NO2 related features provided the strongest contributions to the shocked infrared changes. Proposed mechanisms for shocked PETN chemistry are analyzed as consistent or inconsistent with the data presented here. Our experimental data suggests C≡O or N2O bond formation, nitrite formation, and absence of significant hydroxyl or amine concentrations in the initial chemistry steps in PETN shocked above 30 GPa.

Influence of cellophane diaphragm rupture processes on the shock wave formation in a shock tube

Diaphragm opening processes with a finite time affect the generated shock waves and shock tube flows. This effect is dominant in short and low-pressure shock tubes. In this research, a high-speed visualization of the opening process of a cellophane diaphragm, which is a suitable material for operation in a low-pressure shock tube, is conducted. The self-shaping opening morphology of cellophane diaphragms is observed at the initial stage with an approximate crack propagation speed of 807 m/s, which is greater than the speed of sound of the test gas. The initial opening motion of the petals, which are formed by cracks, is successfully modeled by the rotational equation of motion. Through analysis of the generation and coalescence of compression waves, whose characteristic velocities are calculated from the measured pressure histories, the shock formation distance is reasonably estimated. From the visualized diaphragm opening processes and analysis of coalescence of compression waves, we revealed that the initial stage of the diaphragm opening process plays a dominant role in shock wave formation rather than the entire process.