Shock Initiation Process Research Articles

Experiment and Numerical Prediction on Shock Sensitivity of HMX–Based Booster Explosive with Small Scale Gap Test at Low and Elevated Temperatures

In order to analyze the effect of temperature changes on the shock initiation performance of HMX–based booster explosive, which consists of 95% HMX and 5% FPM2602 by weight, a temperature calibration test of acceptor was designed. The temperature changes in the booster at low and elevated temperatures under the constraint of steel sleeve were obtained. Based on the temperature calibration results, polymethyl methacrylate (PMMA) was selected as gap material to conduct a small scale gap test (SSGT) of HMX–based booster under different temperature conditions. The corresponding critical gap thickness was tested. Based on SSGT results at different temperatures, the shock initiation processes were simulated by adjusting parameters of ignition and growth reactive rate model. The critical gap thickness and critical initiation pressure of HMX–based booster at different temperatures were numerically predicted. By combining SSGT experimental data and simulation results, the attenuation law and fitting prediction formula of the critical initiation pressure of HMX–based booster were proposed. The mechanism of temperature effect on the shock sensitivity of HMX–based booster explosive was analyzed. The research results indicate that the critical gap thickness of HMX–based booster gradually increases with the rise in temperature, and the critical initiation pressure gradually decreases during the shock initiation process under the heating temperature conditions. In addition, the simulation results show that the heated HMX–based booster under steel constraints becomes more sensitive at high temperatures (>120 °C), while the cooled booster is more insensitive, but its critical initial pressure does not change significantly between 88 °C and 120 °C. The experimental and numerical prediction results are important for the shock initiation safety and design of an insensitive booster explosive.

Effects of encapsulation of manganin gauges on the pressure profiles from shock initiation experiments

AbstractThe Lagrangian test can measure the shock initiation process of explosives for different incident shock pressures. The manganin gauges record pressure histories for several DNAN‐based melt‐cast explosives. The encapsulation of the gauges results in three types of characteristic signals: (1) a step signal on the low‐pressure shock front, (2) a flatten Von Neuman's (VN's) spike on the high‐pressure shock front, and (3) a V‐shape signal behind the shock front. To reveal the mechanism underlying these characteristic signals, a one‐dimensional Lagrangian hydrocode, was used to simulate the propagation of a sustained shock in both ideal and non‐ideal systems. The simulation results show that the impedance mismatch between encapsulation material and explosives is the main reason for the three characteristic signals. The calibration of shock initiation model should take the encapsulation material into account so as to determine shock initiation model parameters accurately.

Numerical Study on Asteroid Deflection by Penetrating Explosion Based on Single-Material ALE Method and FE-SPH Adaptive Method

An asteroid impact can potentially destroy life on this planet. Therefore, asteroids should be prevented from impacting the Earth to impede severe disasters. Nuclear explosions are currently the only option to prevent an incoming asteroid impact when the asteroid is large or the warning time is short. However, asteroids exist in an absolute vacuum, where the explosion energy propagation mechanism differs from that in an air environment. It is difficult to describe this process using standard numerical simulation methods. In this study, we used the single-material arbitrary Lagrangian–Eulerian (ALE) method and the finite element-smoothed particle hydrodynamics (FE-SPH) adaptive method to simulate the process of deflecting hazardous asteroids using penetrating explosions. The single-material ALE method can demonstrate the expansion process of explosion products and energy coupling in absolute vacuum. The FE-SPH adaptive method can transform failed elements into SPH particles during the simulation, avoiding system mass loss, energy loss, and element distortion. We analyzed the shock initiation and explosion damage process and obtained an effective simulation of the damage evolution, stress propagation, and fragment distribution of the asteroid. In addition, we decoupled the penetrating explosion into two processes: kinetic impact and static explosion at the impact crater. The corresponding asteroid damage modes, velocity changes, and fragmentation degrees were simulated and compared. Finally, the high efficiency of the nuclear explosion was confirmed by comparing the contribution rates of the kinetic impact and nuclear explosion in the penetrating explosion scheme.

Experimental and numerical study of shock-to-detonation transition in tri-amino-tri-nitro-benzene explosive with temperature effects

ABSTRACT The present work completed a series of one-dimensional plate impact experiments combined with an temperature control system, which could study the temperature effects on shock initiation characteristics of the tri-amino-tri-nitro-benzene (TATB)-based explosives. Buildup to detonation was measured with aluminum-based electromagnetic particle velocity (EMV) gauge technique, and the shock tracker gauges recorded the change in position of shock wave in the explosive sample over time. As temperature cooling to −20°C, the fitting line of Hugoniot had an obvious inflection point, and the run distance to detonation became longer than ambient temperature under the same initiation pressure, indicating that the explosives became less sensitive. Finally, the numerical simulation of the shock initiation process for explosives was performed by the Arrhenius, Wescott, Stewart, and Davis (AWSD) reaction rate model . The results indicated that the AWSD reaction rate model based on the impact temperature and pressure can better simulate the shock-to-detonation transition at different temperatures by only one set of model parameters.

A chemical reaction insight of shock initiation criterion

Shock initiation criteria are essential to the shock initiation process and applications in modern pyrotechnics. The most commonly used shock initiation criteria are Walker and James criterion, which can very well describe the threshold data of the impactor with sufficient size. However, the criteria were also found not to provide a good fit to the data of thin, curve, or small flyers. By comparing the wave structure of the shock process with the stable detonation wave structure, a shock initiation criterion is developed based on the concept of the chemical reactions during the impact, focusing more on the properties of the explosives. Furthermore, a desktop micro-flyer initiating system was designed for the initiation of the thin metal flyer. The obtained data and classical historical data were analyzed with the proposed criterion, producing an excellent fit, with R2 values greater than 0.96. Compared to the existing criteria, the proposed criterion can weaken the influence of the interfacial properties of the impact and collapse the threshold velocity data with different impactor types to a single curve. The shock sensitivities of various explosives are also discussed based on the criterion. A denser impactor or the incorporation of impurities may contribute to the generation of the hot spot during the impact, leading to an increase in the sensitivity. The proposed criterion provides insight into the development of the shock initiation criteria and may help to understand the mechanism of shock initiations.

A new Ignition-Growth reaction rate model for shock initiation

Accurately predicting reactive flow is a challenge when characterizing an explosive under external shock stimuli as the shock initiation time is on the order of a microsecond. The present study constructs a new Ignition-Growth reaction rate model, which can describe the shock initiation processes of explosives with different initial densities, particle sizes and loading pressures by only one set of model parameters. Compared with the Lee-Tarver reaction rate model, the new Ignition-Growth reaction rate model describes better the shock initiation process of explosives and requires fewer model parameters. Moreover, the shock initiation of a 2, 4-Dinitroanisole (DNAN)-based melt-cast explosive RDA-2 (DNAN/HMX (octahydro- 1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazoncine)/aluminum) are investigated both experimentally and numerically. A series of shock initiation experiments is performed with manganin piezoresistive pressure gauges and corresponding numerical simulations are carried out with the new Ignition-Growth reaction rate model. The RDA-2 explosive is found to have higher critical initiation pressure and lower shock sensitivity than traditional explosives (such as the Comp. B explosive). The calibrated reaction rate model parameters of RDA-2 could provide numerical basis for its further application.

Shock Initiation Investigation of a Pressed Trinitrotoluene Explosive

AbstractThe shock initiation process of a pressed trinitrotoluene (TNT) at density of 1.563 g cm−3 was studied by manganese‐copper gauge measurement experiments as well as numerical simulation for assessing the performance and detonation growth characteristics in such pressed samples. Through gap test, the shock pressure histories at different inner positions of the target TNT charges were measured. The parameterization on shock initiation model proposed by Lee & Tarver for numerical simulation were accomplished. The equation of state for unreacted explosive in the model was obtained by fitting Hugoniot data calculated from molecular dynamic simulation and shock temperature based on Walsh's solution. The equation of state for the detonation products was theoretically predicted by EXPLO5. Combining those procedures, the ignition and growth model for a pressed TNT was accurately parameterized together with experimental pressure history data. Experiment and simulation indicate that when the input pressures are 6.13 GPa and 8.67 GPa, respectively, the corresponding run distances to detonation are >9 mm and 6 mm. The calculated pressure growth histories at different inner positions of the pressed TNT sample can well reproduce the correspondingly measured values. The determined ignition and growth model will be expected to put in use in subsequent simulation analysis with complex geometrical scenarios.

Shock initiation performance of NTO-based polymer bonded explosive

3-nitro-1,2,4-tri-azol-5-one (NTO) is a high energy insensitive explosive. To study the shock initiation process of NTO-based polymer bonded explosive JEOL-1 (32%octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 32% NTO, 28% Al and 8% binder system), the cylinder test, the gap experiments and numerical simulation were carried out. Firstly, we got the detonation velocity (7746 m/s) and the parameters of Jones-Wilkins-Lee (JWL) equation of state (EOS) for detonation product by cylinder test and numerical simulation. Secondly, the Hugoniot curve of unreacted explosive for JEOL-1 was obtained calculating the data of pressure and time at different Lagrangian positions. Then the JWL EOS of unreacted explosive was obtained by utilizing the Hugoniot curve as the reference curve. Finally, we got the pressure growth history of JEOL-1 under shock wave stimulation and the parameters of the ignition and growth reaction rate equation were obtained by the pressure-time curves measured by the shock-initiation gap experiment and numerical simulation. The determined trinomial ignition and growth model (IG model) parameters can be applied to subsequently simulation analysis and design of insensitive ammunition with NTO-based polymer bonded explosive.

Shock initiation characteristics of four-component HTPB solid propellant containing RDX

In order to investigate the characters of the four-component HTPB solid propellant containing RDX initiated by shock waves and evaluate its adaptability to low temperature, Lagrange analytical experiments were carried out in normal and low temperature conditions. In the Lagrange analytical experiments, sensors were embedded in different locations of the material, and the dynamic mechanical behavior of the material was obtained by analyzing the variation of some mechanical parameters (such as stress or pressure, particle velocity, strain or specific volume and temperature) measured by the sensors. Since the thickness of gap affected the initiation pressure, the manganese-copper sensors were used to measure the pressure changes in different positions of the propellant with the gap thicknesses of 40, 45 and 50 mm, respectively. When the gap thickness was 40 mm, the propellant detonated. In contrast, the propellant burned for the gap thicknesses of 45 and 50 mm. The ionization probes were used to collect the detonation velocity of the propellant. In normal temperature conditions, the detonation velocities with the gap thicknesses of 10 and 40 mm were measured. In low temperature conditions, the detonation velocities with the gap thicknesses of 10, 30 and 40 mm were measured. The growth laws of the detonation were analyzed, and the parameters such as detonation pressure, detonation velocity and detonation distance of the solid propellant were obtained. Numerical simulation was carried out to calculate the shock initiation process of the propellant, and the parameters of the ignition and growth model and the JWL state equation of the nonreactive propellant were determined by fitting the experimental data. The results show that the detonation pressure of the solid propellant is about 12.5 GPa, the critical initiation pressure is 5.16−5.61 GPa, the detonation distance is about 13.3 mm, and the detonation velocity is 5.719−6.013 km/s. The research results indicate that the low temperature has little effect on the shock initiation characteristics of the solid propellant.

Study on the reaction rate model for shock initiation of aluminized hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) explosive under shock waves

To investigate the influence of the aluminum (Al) powder sizes on shock initiation of aluminized hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), shock initiation experiments were carried out. The experimental results show that as the Al constituent size decreases, a rapid increase in the propagation velocity of the precursory shock waves enhances the peak pressures, shortens the time intervals between the peak pressures and the arrival times of precursory shock waves, and improves the shock sensitivity of the aluminized RDX. Consequently, to predict and evaluate the stability of aluminized RDX with small-size Al powder, a microscopic reaction rate model for shock initiation was established. This model includes the pore collapse model of a double-layered spherical shell structure composed of an RDX spherical shell and a mixture (of Al powder and binders) spherical shell and the reaction model of Al powder in RDX decomposition products under the effect of shock waves and thermal energy released by RDX. The simulation results show that when the diameter of the Al powder is about 1/5 or less of the size of the base explosive (RDX) particles, the microscopic reaction rate model can accurately simulate the shock initiation process of aluminized RDX. As the Al powder size decreases, the reaction rate and the proportion of the Al involved in the initiation reaction for aluminized RDX increase.

Study on shock initiation of the charge covered by metal plate with penetrated notch

To analyze the coupling damage effect of high-speed fragments and near-field strong shock wave on the covered charge, a theoretical model of the shock initiation of the charge covered by metal plate with defects was established. The defect of the covered plate was simplified as a penetration notch, and the evolution characteristics of the shock wave in the notch were analyzed theoretically. The critical condition of the explosive detonation was determined by combining the explosive initiation criterion and the shock wave evolution characteristics. Take TNT covered by steel plate with a penetrated notch as an example, the nonlinear finite element program was used to simulate the shock initiation process of pressed charge, and the validity of the numerical simulation was verified by experimental results. The influence of the intensity of the shock wave, the thickness of the covered metal plate as well as the geometrical characteristics of the penetrated notch on the shock initiation of the pressed charge were analyzed by combining the theoretical model and numerical simulation results. The relationship of the notch size of the covered plate and the detonation distance was obtained by fitting, and the parameters n and K of the critical initiation criterion were obtained by least squares method. The theoretical calculation results and the numerical simulation results are agree with each other well and show that, the covered metal plate is beneficial for the protection of the charge. The existence of notch will weaken the protective performance of the covered plate, and the shape and size of the notch are also important factors that will affect the critical detonation distance of the charge. For the pressed TNT with and without 45# steel covered plate with the thickness 3 millimeters, the critical detonation distance of non-contact explosion was 13 millimeters and 81 millimeters, respectively. For the covered plate with a cylindrical notch, the critical detonation distance of the pressed TNT increases with increase of the diameter of the covered plate. For the covered plate has a frustum notch, the critical detonation distance of the pressed TNT decreases with increase of the slope in normal reflection.

Shock initiation of multi-component insensitive PBX explosives: Experiments and MC-DZK mesoscopic reaction rate model.

To facilitate the pre-estimation and optimization of the prescription design of a multi-component polymer bonded explosive (PBX), a multicomponent mesoscopic reaction rate model (MC-DZK model) is developed to predicate preferably the influence of both the explosive components and the particle size of on the shock initiation. All the parameters in the model are determined directly by the parameters in the DZK model for each explosive component. Furthermore, for the multicomponent insensitive explosive PBXC10 (70% TATB, 25% HMX, and 5% Kel-F800 by weight) with different explosive particle sizes, both shock initiation experiments and corresponding numerical simulations are performed, and there is satisfactory agreement between the numerical results and the available experimental data. It is found that the pressure histories present as a shape of step increase during the whole shock initiation process, which is resulted mainly from the rapid chemical reaction rate just behind the precursory shock wave front. It is also found that the smaller the size of the explosive particulates, the faster the pressure grows on the precursory shock wave front, the shorter the run distance to detonation, and the higher the chemical reaction rate just behind the precursory shock wave front.

Relating microstructure, temperature, and chemistry to explosive ignition and shock sensitivity

An analysis is put forth that relates explosive properties including microstructure, temperature, and chemistry to explosive ignition and sensitivity. Unlike approaches that focus only on elucidating mesoscopic mechanisms important to ignition, the present analysis seeks a methodology directly applicable to continuum explosive burn models. Because the Scaled Uniform Reactive Front (SURF) burn model has a microstructural basis, it is chosen as the starting point of the present analysis. To build upon the SURF framework, a literal translation is performed of the high-level conceptual notions for which SURF is based, to concrete ignition–combustion parameters, a statistical description of the microstructure, and other thermo-chemical data acquired by non-shock experiments. The analysis requires a void volume fraction distribution acquired from ultra-small angle neutron scattering (USANS). The shock response of PBX 9502 is used to illustrate the theory. While the analysis requires calibration to a shock experiment (the pop plot, for example), the results are a self-consistent set of realistic physical quantities that contribute to the shock initiation process including, initial temperature, chemical kinetics, a statistical description of the microstructure, and the hot spot size, spacing, and temperature. The utility of having a mesoscale based theory is that once the critical hot spot temperature, as a function of shock pressure, is known for a given explosive and initial porosity distribution, the entire set of meso- and macro-scale results, including the pop plot can be calculated for any other porosity. Thus, one can understand changes in sensitivity at different densities (void size distributions), relying only on the assumption that the hot spot temperature curve would not differ significantly if the morphology of the hots spots were similar. Another important utility of the present analysis is to address the question of the role of initial temperature on the observed shock sensitivity of PBX 9502 and other explosives.

A mesoscopic reaction rate model for shock initiation of multi-component PBX explosives

The primary goal of this research is to develop a three-term mesoscopic reaction rate model that consists of a hot-spot ignition, a low-pressure slow burning and a high-pressure fast reaction terms for shock initiation of multi-component Plastic Bonded Explosives (PBX). Thereinto, based on the DZK hot-spot model for a single-component PBX explosive, the hot-spot ignition term as well as its reaction rate is obtained through a “mixing rule” of the explosive components; new expressions for both the low-pressure slow burning term and the high-pressure fast reaction term are also obtained by establishing the relationships between the reaction rate of the multi-component PBX explosive and that of its explosive components, based on the low-pressure slow burning term and the high-pressure fast reaction term of a mesoscopic reaction rate model. Furthermore, for verification, the new reaction rate model is incorporated into the DYNA2D code to simulate numerically the shock initiation process of the PBXC03 and the PBXC10 multi-component PBX explosives, and the numerical results of the pressure histories at different Lagrange locations in explosive are found to be in good agreements with previous experimental data.

Simulation of one dimension shock initiation of condensed explosive by SPH method

Purpose This paper aims to study the ability of SPH method in simulating shock initiation process. The initiation and subsequent explosion processes of condensed explosive involve high pressure propagation and material large deformation, which increase the simulation difficulty in using traditional mesh-based method. The study aims to take the SPH method as an alternative method to shock initiation simulation. Design/methodology/approach The SPH method combined with some correct aspects is applied to simulate the shock initiation process. The condensed explosive is ignited by the impact of high speed flyer. In order to avoid the non-physical penetration between particles of high velocity flyer and condensed explosive, a particle-to-particle contact algorithm is employed. After the ignition, the detonation process of condensed explosive is represented by the ignition and growth model. A modified SPH method based on Riemann-solver is applied to smooth the numerical oscillation at shock front. Two numerical examples are implemented to illustrate the capability of SPH method in shock initiation simulation. One is the interface velocity experiment of PBX-9501. Another is the plate push experiment of PBX-9502. Both of the examples include the shock initiation process of condensed explosive. Findings Numerical results show that the shock initiation process of condensed explosive can be well predicted by SPH method. The characteristics of detonation are captured in the simulation. The measured data in numerical examples are also in good agreement with the experimental data. Research limitations/implications Because of the research purpose is to study the ability of SPH for shock initiation simulation, only one-dimension numerical examples are discussed in the paper. Therefore, researchers are encouraged to extend and test the proposed method to two or three dimension shock initiation problems simulation. Originality/value This paper provides an alternative method for shock initiation simulation. The implemented method can overcome the weaknesses of traditional mesh based method in simulation of shock initiation problems.

Special catalytic effects of intermediate-water for rapid shock initiation of β-HMX

The intermediate-water efficiently promoted the decomposition of β-HMX, corresponding to a rapid shock initiation process.

Shock initiation of explosives investigated with small partition experiment and numerical simulation

In order to investigate the shock ignition of high energy solid explosives by shock waves, we carry out Lagrangian experiments with 2-D Lagrangian technique which uses composite manganin-constantan (CMC). The effects of the shock sensitivity of pressed solid high explosives, TNT, and the effect of the lateral rarefaction wave were studied. Based on the measured pressure histories and the radial displacements, we formulate the Ignition and Growth reactive flow models for the pressed TNT. The shock initiation process simulated by Ignition and Growth model agreed well with experimental data. This pressed TNT model can be applied to shock initiation scenarios which are highly unpredictable and have not been or cannot be tested experimentally.

Revisiting Shock Initiation Modeling of Homogeneous Explosives

Shock initiation of homogeneous explosives has been a subject of research since the 1960s, with neat and sensitized nitromethane as the main materials for experiments. A shock initiation model of homogeneous explosives was established in the early 1960s. It involves a thermal explosion event at the shock entrance boundary, which develops into a superdetonation that overtakes the initial shock. In recent years, Sheffield and his group, using accurate experimental tools, were able to observe details of buildup of the superdetonation. There are many papers on modeling shock initiation of heterogeneous explosives, but there are only a few papers on modeling shock initiation of homogeneous explosives. In this article, bulk reaction reactive flow equations are used to model homogeneous shock initiation in an attempt to reproduce experimental data of Sheffield and his group. It was possible to reproduce the main features of the shock initiation process, including thermal explosion, superdetonation, input shock overtake, overdriven detonation after overtake, and the beginning of decay toward Chapman-Jouget (CJ) detonation. The time to overtake (TTO) as function of input pressure was also calculated and compared to the experimental TTO.

Critical Initiating State and 2D Lagrangian Analysis of Pressed TNT

Shock initiation experiments on the explosives pressed TNT was performed to obtain in-situ pressure/radial displacement gauge data for the purpose of determining the Ignition and Growth reaction flow model with proper modeling parameters. The pressure and radial displacement were got by manganin-constantan composite 2-D Lagrange sensor. The particle velocity, relative volume, internal energy and fraction reacted of shock initiation process has been calculated by 2-D Lagrangian analysis method.

In-situ measurements of the onset of bulk exothermicity in shock initiation of reactive powder mixtures

The shock initiation process was directly observed in different powder mixtures that produce little or no gas upon reaction. The samples of reactive powder were contained in recovery capsules that permitted the samples to be analyzed after being shocked and that allowed the initiation of reaction to be monitored using three different methods. The microsecond time-scale processes were observed via a fast two-color pyrometer. Light intensity detected from the bottom of reactive samples was slightly greater compared to inert simulants in the first 10 μs after shock arrival. However, this light was much less intense than that which would correspond to the bulk of the material reacting. Thus it seemed that only small, localized zones, or hot spots, had begun to react on a time scale of less than 30 μs. Light emissions were then recorded over longer time scales, and intense light appeared at the bottom of samples a few milliseconds to a few hundreds of milliseconds after shock arrival at the bottom of the test samples. Thus it appeared that the bulk of the material reacted as the hot spots spread via convective/diffusive means. This bulk reaction was also observed using thermocouples for a large number of mixtures and incident shock pressures. The delay time for the onset of bulk reaction was found to be not strongly dependent upon shock pressure but seemed to correlate with the burning speed of the mixtures. The shock initiation process appeared to take place via the initiation and growth of hot spots, as in high explosives, except that burning speeds are much slower in reactive powders that produce little gas.