Shock-induced Reactions Research Articles

Mesoscale study on explosion-induced formation and thermochemical response of PTFE/Al granular jet

The dynamic formation, shock-induced inhomogeneous temperature rise and corresponding chemical reaction behaviors of PTFE/Al reactive liner shaped charge jet (RLSCJ) are investigated by the combination of mesoscale simulation, reaction kinetics and chemical energy release test. A two-dimensional granular model is developed with the randomly normal distribution of aluminum particle sizes and the particle delivery program. Then, the granular model is employed to study the shock-induced thermal behavior during the formation and extension processes of RLSCJ, as well as the temperature history curves of aluminum particles. The simulation results visualize the motion and temperature responses of the RLSCJ at the grain level, and further indicate that the aluminum particles are more likely to gather in the last two-thirds of the jet along its axis. Further analysis shows that the shock, collision, friction and deformation behaviors are all responsible for the steep temperature rise of the reactive jet. In addition, a shock-induced chemical reaction extent model of RLSCJ is built based on the combination of the Arrhenius model and the Avrami-Erofeev kinetic model, by which the chemical reaction growth behavior during the formation and extension stages is described quantitatively. The model indicates the reaction extent highly corresponds to the aluminum particle temperature history at the formation and extension stages. At last, a manometry chamber and the corresponding energy release model are used together to study the macroscopic chemical energy release characteristics of RLSCJ, by which the reaction extent model is verified.

Quantitative prediction and ranking of the shock sensitivity of explosives via reactive molecular dynamics simulations

A deep understanding of explosive sensitivities and their factors is important for safe and reliable applications. However, quantitative prediction of the sensitivities is difficult. Here, reactive molecular dynamics simulation models for high-speed piston impacts on explosive supercells were established. Simulations were also performed to investigate shock-induced reactions of various high-energy explosives. The fraction of reacted explosive molecules in an initial supercell changed linearly with the propagation distance of the shock-wave front. The corresponding slope could be used as a reaction rate for a specific shock-loading velocity. Reaction rates that varied with the shock-loading pressure exhibited two-stage linearities with different slopes. The two inflection points corresponded to the initial and accelerated reactions, which respectively correlated to the thresholds of shock-induced ignition and detonation. Therefore, the ignition and detonation critical pressures could be determined. The sensitivity could then be a quantitative prediction of the critical pressure. The accuracies of the quantitative shock sensitivity predictions were verified by comparing the impact and shock sensitivities of common explosives and the characteristics of anisotropic shock-induced reactions. Molecular dynamics simulations quantitatively predict and rank shock sensitivities by using only crystal structures of the explosives. Overall, this method will enable the design and safe use of explosives.

Molecular-Dynamics Study on the Impact Energy Release Characteristics of Fe-Al Energetic Jets.

Fe–Al energetic material releases a large amount of energy under impact loading; therefore, it can replace traditional materials and be used in new weapons. This paper introduces the macroscopic experiment and microscopic molecular-dynamics simulation research on the energy release characteristics of Fe–Al energetic jets under impact loading. A macroscopic dynamic energy acquisition test system was established to quantitatively obtain the composition of Fe–Al energetic jet reaction products. A momentum mirror impacting the Fe–Al particle molecular model was established and the microstructure evolution and impact thermodynamic response of Fe–Al particles under impact loading were analyzed. The mechanism of multi-scale shock-induced chemical reaction of Fe–Al energetic jets is discussed. The results show that the difference in velocity between Fe and Al atoms at the shock wave fronts is the cause of the shock-induced reaction; when the impact strength is low, the Al particles are disordered and amorphous, while the Fe particles remain in their original state and only the oxidation reaction of Al and a small amount intermetallic compound reaction occur. With the increase of impact strength, Al particles and Fe particles are completely disordered and amorphized in a high-temperature and high-pressure environment, fully mixed and penetrated. The temperature of the system rises rapidly, due to a violent thermite reaction, and the energy released by the jet shows an increasing trend; there is an impact intensity threshold, so that the jet release energy reaches the upper limit.

Spalling fracture of Ni/Al nanolaminates influenced by chemical reaction

We investigate spalling behaviors of Ni/Al nanolaminates by molecular dynamics simulations. First, we discuss spalling damage distributions in shocked Ni/Al nanolaminates. Voids nucleate in Al layers, while no voids are located in Ni layers or along the Ni/Al interfaces. This is because the spall strength of single-crystalline Ni is higher than that of single-crystalline Al. We reveal influences of a shock-induced chemical reaction on dynamic spalling damage and fracture processes. An abnormal “decrease → increase → decrease” zigzag variation tendency of the spall strength of Ni/Al nanolaminates as the impact velocity increase is observed in our simulations, which resulted from combining effects of micro-structures, chemical reactions, and temperature softening. When the impacting intensity is relatively low, the spall strength of Ni/Al nanolaminates decreases as the impact velocity increases due to micro-structure effects. However, when the loading velocity increases to a certain magnitude (2.5 km/s), the intimate contact of liquid Al with amorphous Ni near the interface makes the chemical reaction rate increase rapidly to form a large amount of Ni/Al alloys and enhances the spall strength.

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.

Bondi-Hoyle-Lyttleton Accretion in a Reactive Medium: Detonation Ignition and a Mechanism for Type Ia Supernovae.

Detonation initiation in a reactive medium can be achieved by an externally created shock wave. Supersonic flow onto a gravitating center, known as Bondi-Hoyle-Lyttleton (BHL) accretion, is a natural shock wave creating process, but, to our knowledge, a reactive medium has never been considered in the literature. Here, we conduct an order of magnitude analysis to investigate under which conditions the shock-induced reaction zone recouples to the shock front. We derive three semianalytical criteria for self-sustained detonation ignition. We apply these criteria to the special situation where a primordial black hole (PBH) of asteroid mass traverses a carbon-oxygen white dwarf (WD). Since detonations in carbon-oxygen WDs are supposed to produce normal thermonuclear supernovae (SNe Ia), the observed SN Ia rate constrains the fraction of dark matter (DM) in the form of PBHs as log_{10}(f_{PBH})<0.8log_{10}(M_{BH}/3×10^{22}g) in the range 10^{21}-10^{22} g (10^{20}-10^{22} g) from a conservative (optimistic) analysis. Most importantly, these encounters can account for both the rate and the median explosion mass of normal sub-Chandrasekhar SNe Ia if a significant fraction of DM is in the form of PBHs with mass 10^{23} g.

Effects of Al Particle Size on the Impact Energy Release of Al-Rich PTFE/Al Composites under Different Strain Rates.

Polytetrafluoroethylene (PTFE)/Al reactive material with different aluminum particle sizes were prepared by molding and sintering, and the effect of aluminum particle size on the impact behavior of PTFE/Al reactive material with a mass ratio of 50:50 was investigated. The results show that aluminum particle size has significant effects on the shock-reduced reaction diffusion, reaction speed, and degree of reaction of the PTFE/Al reactive material. At a moderate strain rate, the reaction delay of PTFE/Al increased, and the reaction duration and degree decreased, with the increase of aluminum particle size. Under the strong impact of explosive loading, aluminum particle size has little effect on the reaction delay, which maintains at about 1.5 μs–2.5 μs, but the reaction durability and degree of reaction of PTFE/Al decrease with increasing aluminum particle size. There is also a strain rate threshold for the shock-induced reaction of PTFE/Al reactive material, which is closely related to aluminum particle size. The shock-induced reaction occurs when the strain rate threshold is exceeded.

Detonation response mechanism of shocked LLM-105 using ReaxFF-lg and MSST

ABSTRACT Based on the ReaxFF-lg reaction force field, the thermodynamic and kinetic quantities of LLM-105 decomposition at different shock waves were analysed. The equation of state, bulk modulus and pressure derivative of the shock decomposition process of LLM-105 were obtained. In addition, using Rankine-Hugoniot relationship, the detonation pressure was estimated to be 29.3 Gpa. The bond breaking of the molecular structure during the reaction was determined by the bond sequence, and the number of reactants, clusters and small molecules formed during the shock process was counted. Based on the obtained results, the decomposition of LLM-105 occurs when the shock wave velocity is greater than 8 km/s. The pyrazine ring in LLM-105 is connected by C–N–N or C–N–O–C to form the multimeric structure of LLM-105, accompanied by a small amount of hydrogen transfer, which is the main initial pathway for the shock-induced reaction of LLM-105. Subsequently, the multimer of LML-105 starts to decompose and finally forms small stable molecules such as N2 and H2O.

NLRC4 gene silencing-dependent blockade of NOD-like receptor pathway inhibits inflammation, reduces proliferation and increases apoptosis of dendritic cells in mice with septic shock.

Septic shock is one of the most significant health concerns across the world, involving hypo-perfusion and defects in tissue energy. The current study investigates the role of NLR family CARD domain containing protein 4 (NLRC4) in septic shock-induced inflammatory reactions, lung tissue injuries, and dendritic cell (DC) apoptosis. Septic shock mice models were established by modified cecal ligation and puncture and injected with retroviral vector expressing siRNA-NLRC4. DCs were then isolated and transfected with siRNA-NLRC4. The degree of lung tissue injury, cell cycle distribution, cell apoptosis and cell viability of DCs were assessed. NLRC4 was found to be expressed at high levels in mice with septic shock. NLRC4 silencing inhibited the activation of the NOD-like receptor (NLR) pathway as evidenced by the decreased levels of NOD1, NOD2, RIP2, and NF-κB. In addition, NLRC4 silencing reduced the inflammatory reaction as attributed by reduced levels of IL-1β, TNF-α and IL-6. Suppressed NLRC4 levels inhibited cell viability and promoted cell apoptosis evidenced by inhibited induction of DC surface markers (CD80, CD86, and MHC II), along with alleviated lung tissue injury. In conclusion, NLRC4 silencing ameliorates lung injury and inflammation induced by septic shock by negatively regulating the NLR pathway.

Shock Induced Chemical Reactions of Intermetallic Mixture of Nickel and Aluminum and Associated Transition States

In this paper, numerical simulation of shock-induced chemical reactions of intermetallic mixtures is discussed. Specifically, the paper focuses on intermetallic mixture of nickel and aluminum. To initiate the chemical reactions, the thermal input or the shockwave should supply the energy to take the reactants, mixture of nickel and aluminum, to the transition state. Thus, for any numerical simulation or analysis of the shock or thermally induced chemical reaction in a continuum scale or a meso scale, it is necessary to identify the transition state. The transition state for the intermetallic mixture of nickel and the aluminum is identified in this paper and a result of the numerical simulation of the shock-induced chemical reaction, in a continuum scale is presented. The numerical solutions clearly show the chemical reactions, release of heat energy, increase of the temperature and the formation of products, following the transition state and the resulting shock-induced chemical reaction of a binary intermetallic energetic mixture of nickel and aluminum. The studies also show that the collapse of porosity is a mechanism that takes the reactants to the transition state, in shock-induced chemical reactions of binary intermetallic mixtures.

Study on energy release characteristics of reactive material casings under explosive loading

Reactive Materials (RMs), a new material with structural and energy release characteristics under shock-induced chemical reactions, are promising in extensive applications in national defense and military fields. They can increase the lethality of warheads due to their dual functionality. This paper focuses on the energy release characteristics of RM casings prepared by alloy melting and casting process under explosive loading. Explosion experiments of RM and conventional 2A12 aluminum alloy casings were conducted in free field to capture the explosive fireballs, temperature distribution, peak overpressure of the air shock wave and the fracture morphology of fragments of reactive material (RM) warhead casings by using high-speed camera, infrared thermal imager temperature and peak overpressure testing and scanning electron microscope. Results showed that an increase of both the fireball temperature and air shock wave were observed in all RM casings compared to conventional 2A12 aluminum ally casings. The RM casings can improve the peak overpressure of the air shock wave under explosion loading, though the results are different with different charge ratios. According to the energy release characteristics of the RM, increasing the thickness of RM casings will increase the peak overpressure of the near-field air shock wave, while reducing the thickness will increase the peak overpressure of the far-field air shock wave.

Shock-induced reaction behaviors of functionally graded reactive material

In this paper, the ballistic impact experiments, including impact test chamber and impact double-spaced plates, were conducted to study the reaction behaviors of a novel functionally graded reactive material (FGRM), which was composed of polytetrafluoroethylene/aluminum (PTFE/Al) and PTFE/Al/bismuth trioxide (Bi2O3). The experiments showed that the impact direction of the FGRM had a significant effect on the reaction. With the same impact velocity, when the first impact material was PTFE/Al/Bi2O3, compared with first impact material PTFE/Al, the FGRM induced higher overpressure in the test chamber and larger damaged area of double-spaced plates. The theoretical model, which considered the shock wave generation and propagation, the effect of the shock wave on reaction efficiency, and penetration behaviors, was developed to analyze the reaction behaviors of the FGRM. The model predicted first impact material of the FGRM with a higher shock impedance was conducive to the reaction of reactive materials. The conclusion of this study provides significant information about the design and application of reactive materials.

The effect of temperature-induced phase transition of PTFE on the dynamic mechanical behavior and impact-induced initiation characteristics of Al/PTFE

PTFE is a semi-crystalline polymer which can undergo two phase transitions at 19°Ϲ and 30°Ϲ. To investigate influence of temperature-induced phase transition of PTFE on the mechanical behavior and impact-induced initiation characteristics of Al/PTFE, the dynamic mechanical analysis, split Hopkinson pressure bar test and drop-weight test were conducted at different temperatures. The correlation between fracture modes and ignition mechanism were analyzed associated with microstructures and reaction phenomena. The results show that with the temperature elevated, the mechanical behavior and reactive characteristics of Al/PTFE manifested a bilinear temperature dependence. Al/PTFE went through a gradual transition from brittleness to ductility. The ignition energy declined, explosion flare enhanced and reaction time prolonged consistent with the change of mechanical properties. The shock pressure and ignition time under drop-weight tests were far from the requirement of shock-induced reaction, indicating that it is fracture-induced reaction dominates the ignition of Al/PTFE at low strain rate.

Shock-induced reactions in metal nitride – Boron nanostructured composites

Shock-induced reactions were investigated in boron (B) – metal nitride (MeN: Me=Ga, Zr, Cr) exothermic systems. All considered powder mixtures were initially mechanically treated in a high-energy ball-mill to fabricate B-MeN nanostructured composite particles, which were subsequently shock loaded using an explosive charge. The structures of these materials were analyzed by conventional and synchrotron X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy. It was discovered that shock-induced reactions in the GaN+B system resulted in the formation of the metastable wurtzitic form of boron nitride (w-BN). This directly implies that ultra-fast (0.5–5 μs) reactions took place under the high-pressure conditions of the shock wave.

Mechanical shock-induced self-propagating exothermic reaction in Ti/Si multilayer nanofilms for low-power reactive bonding

In this study, we describe the development of a new solder bonding technique using a Ti/Si multilayer film, which can be conducted by mechanical shock only. A Ti/Si multilayer film is a self-propagating exothermic reactive material that can be ignited by applying both mechanical and electrical shocks (e.g. a spark in the latter case). The influence of bilayer thickness on film ignition was investigated by means of mechanical impact testing. The threshold energy for the exothermic reaction gradually decreased with decreasing bilayer thickness. We demonstrate the effectiveness of reactive solder bonding for a Si wafer by applying mechanical shock to a 25 nm bilayer thick Ti/Si film using an anisotropic wet-etched Si pyramid.

Transition States for Shock Induced Chemical Reactions in Binary Energetic Materials

In this paper, numerical simulation of shock induced chemical reactions of a thermite mixture of binary energetic material, aluminum and iron oxide, are discussed. To initiate the chemical reactions, the impact or the shockwave should supply the energy to take the reactants, aluminum and iron oxide, to the transition state. Thus, for any numerical simulation of the shock or impact induced chemical reaction in a continuum or mesoscale, it is necessary to identify the transition state. The transition state for the thermite mixture, of aluminum and iron oxide, is identified in this paper and a result from a numerical simulation of the shock induced chemical reaction, in a continuum scale is presented.

Modeling the shock-induced multiple reactions in a random bed of metallic granules in an energetic material

An investigation of shock–particle interactions in reactive flows is performed using an Eulerian hydrodynamic method with a hybrid particle level-set algorithm to handle the material interface dynamics. The analysis is focused on the meso- to macro-scale numerical modeling of a granular metalized explosive containing randomly distributed metal particles intended to enhance its blast effect. The reactive flow model is used for the cyclotrimethylene-trinitramine (RDX) component, while thermally induced deflagration kinetics describes the aerobic reaction of the metal particles. The complex interfacial algorithm, which uses aligned level sets to track deforming surface between multi materials and to generate the random shape of granule elements, is described for aluminized and copperized RDX. Then, the shock-induced collapse of metal particles embedded in the condensed phase domain of a high explosive is simulated. Both aluminized and copperized RDX are shown to detonate with a shock wave followed by the burning of the metal particles. The energy release and the afterburning behavior behind the detonating shock wave successfully identified the precursor that gave rise to the development of deflagration of the metal particles.

Compressive Mechanical Properties and Shock-Induced Reaction Behavior of a Ti–29Nb–13Ta–4.6Zr Alloy

The compressive mechanical properties of a Ti–29Nb–13Ta–4.6Zr alloy were investigated at room temperature under various strain rates. The parameters of a modified Johnson–Cook constitutive equation were determined to describe the strain softening behavior under dynamic conditions. The testing results under compression show yield strength evidently increases with the increase of the strain rate. Moreover, it was found that the strain-rate effect of the yield strength upon dynamic deformation is more significant than that upon quasi-static deformation. In order to characterize the impact-initiated reaction behavior of Ti–29Nb–13Ta–4.6Zr alloy, the quasi-sealed test chamber was used to measure the pressure caused by energy released of fragments. It was obviously shown that the exothermic chemical reaction was more intense with the increase of impact velocity.

Observations of shock-induced chemistry with subnanosecond resolution

We report observations of the effects of shock-induced chemical reactions that build to a steady detonation in an energetic material. The chemical reactions in certain materials initiate and build quickly, such that traditional characterization techniques for energetics cannot provide the spatial fidelity necessary to resolve the onset and build-up of reactions. In this work, physical vapor deposition was used to create films of an energetic material with precisely controlled thicknesses to investigate the growth to detonation resulting from shock-induced chemical reactions with microscale spatial resolution. Finite duration shocks were supplied from a well-defined electrically-driven flyer. The velocity of the transmitted shock was measured by photonic Doppler velocimetry with subnanosecond resolution. Initiation experiments were performed on deposited hexanitrostilbene samples ranging from 30 to 150 μm thickness to observe the emergent effects of chemical energy release. The resulting output interface velocity was observed to increase from that predicted for an unreacted shock to that of a chemically supported detonation within 100 μm. A build-up to detonation has not previously been quantified in such a short distance.

Mechanical properties and shock-induced chemical reaction behaviors of cold-rolled Al/Ni multi-layered composites

Al/Ni multi-layered composites were manufactured by cold rolling with different passes. The influence of cold rolling passes on the mechanical properties and shock-induced chemical reaction (SICR) behaviors of Al/Ni multi-layered composites was investigated by quasi-static compression tests and impact initiation experiments. A scanning electron microscopy (SEM) was used to obtain the microstructures of the Al/Ni multi-layered composites, and the microstructures from the scanning electron microscopy images were used to explain the experimental results. The results show that the cold-rolled Al/Ni multi-layered composites behave more plastically than the powder-compacted Al/Ni composites do. The compression strength of the Al/Ni multi-layered composites increases with the growth of rolling passes. On the other hand, more rolling passes result in decaying energy release capacity of the Al/Ni multi-layered composites under impact velocity from 800 m/s to 1 500 m/s.