Slow Cook-off Research Articles

Study on cook-off characteristics and thermal safety venting area of RBOE charge

RBOE is a new type of DNAN-based high-energy melt-cast mixed explosive, whose safety under thermal stimulation is significantly affected by heating conditions and venting area of the warhead. Based on the thermal decomposition reaction characteristics and combustion characteristics of each component of RBOE explosive, the cook-off calculation models of RBOE warhead before and after ignition were established. In addition, closed and vented warheads were designed, as well as fast and slow cook-off test devices. The cook-off characteristics and thermal safety venting area of RBOE warhead were extensively studied. The results showed that the closed RBOE warhead underwent deflagration reaction under both slow and fast cook-off conditions. The calculation result of the shell wall temperature before slow cook-off ignition response of the warhead was 454.06 K, with an error of +1.75% compared to the test result of 462.15 K, and the temperature rise rate calculated was in good agreement with the test. The calculated ignition time of RBOE warhead under fast cook-off was 161 s, with an error of +8.8% compared to the test result of 148 s, which verified the accuracy of cook-off model of RBOE warhead before ignition. According to the cook-off calculation model of the warhead after ignition and cook-off test of the vented warhead, it was determined that the thermal safety venting area was 1124.61 mm2 for fast cook-off and 530.66 mm2 for slow cook-off, effectively preventing the reaction of warhead above combustion. Therefore, this study provides a scientific basis for the thermal safety design and evaluation of insensitive warheads.

EFFECT OF HMX CONTENT ON THERMAL SAFETY CHARACTERISTICS OF MODIFIED DOUBLE-BASE PROPELLANTS

In order to explore the thermal safety characteristics of modified double-base propellants, differential scanning calorimetry (DSC) was used to study the thermal decomposition of modified double-base propellants with high melting explosive (HMX) content of 0%, 21%, and 40%, respectively. The thermal decomposition temperatures at the heating rates of 2, 5,10, and 20°C·min<sup>-1</sup> were obtained. The apparent activation energy, pre-exponential factor, reaction rate, Gibbs free energy, activation enthalpy, and activation entropy were calculated by thermal reaction kinetics analysis. The response characteristics of modified double-base propellants with different HMX contents were obtained through slow cook-off, 5 s explosion point, and methyl violet chemical stability tests to characterize the thermal safety of propellants. The insensitivity of modified double-base propellant containing HMX was further studied by flame sensitivity and mechanical sensitivity tests. The results showed that when HMX content was 21%, the apparent activation energy was the highest, the slow cook-off response was the lowest, the 5 s explosion point response temperature was the highest, the methyl violet test paper had the longest discoloration time, and the flame sensitivity and mechanical sensitivity were the lowest; With the increase of HMX content, the first decomposition peak temperature of DSC moves backward, and the apparent activation energy decreases. The slow cook-off response temperature of the double-base propellant moves to the high-temperature direction, and the response level increases accordingly. When the HMX content is 40% or more, the response level is explosive, which cannot pass the slow cook-off test. After HMX component is added into the sample, its 5 s explosion point temperature moves to high temperature, and the trend of rise is obvious. The discoloration time of methyl violet test paper is prolonged, and the thermal stability of modified double-base propellant is improved; The flame sensitivity and the mechanical sensitivity decreased, which was helpful to improve the low vulnerability of the formula.

The Flow and Heat Transfer Behavior of Liquid COMP-B3 in Slow Cook-off

The Flow and Heat Transfer Behavior of Liquid COMP-B3 in Slow Cook-off

Study and Design of the Mitigation Structure of a Shell PBX Charge under Thermal Stimulation

To study the design method and pressure relief effect of the mitigation structure of a shell under the action of thermal stimulation, a systematic research method of theoretical calculation-simulation-experimental verification of the mitigation structure was established. Taking the shelled PBX charge as the test material, the pressure relief area that can effectively reduce the reaction intensity of the charge is obtained by theoretical calculation. The influence of the pressure relief hole area, distribution mode, and other factors on the pressure relief effect is calculated by simulation. The pressure relief effect of the mitigation structure was verified by the low-melting alloy plug with refined crystal structure for sealing the pressure relief hole and the cook-off test. The research results show that the critical pressure relief area is when the ratio of the area of the pressure relief hole to the surface area of the charge is AV/SB = 0.0189. When the number of openings increases to 6, the required pressure relief coefficient decreases to AV/SB = 0.0110; When the length/diameter ratio is greater than 5, the opening at one end cannot satisfy the reliable pressure relief of the shell. The designed low-melting-point alloy mitigation structure can form an effective pressure relief channel. With the increase in AV/SB from 0.0045 to 0.0180, the reaction intensity of the cook-off bomb is significantly reduced in both fast and slow cook-off, which improves the safety of the charge when subjected to unexpected thermal stimulation.

Experiments and simulations on cookoff characteristics of a DNAN based cast explosive

AbstractIncidents caused by fire and combat operations can heat energetic materials that may lead to thermal explosion and result in structural damage and casualty, thus understanding the response of energetic materials to thermal insults is crucial for the safety design and assessment of insensitive munitions. In the present work, cookoff characteristics of a new DNAN‐based cast explosive ROL‐1 are systematically analyzed. Small‐scale slow cookoff experiments were performed and an overall reaction kinetic model including the melt‐ignition model for DNAN was developed and implemented in FLUENT. The simulated results agree well with the experimental data, which verifies the validity of the model. The large‐scale fast cookoff experiment and simulation were then performed. Ignition behaviors as well as the reaction mechanism of ROL‐1 under slow and fast cookoffs are investigated. The heat generation rates are highly correlated to the temperature gradient, liquid phase fraction, and ignition behaviors in ROL‐1. The ignition of ROL‐1 happens at around 550 K, delaying the ignition temperature of the HMX (493 K) by nearly 60 K, indicating the potential substitution of NTO for HMX. The safety of ROL‐1 has proven to stand out in comparison to a range of mixed explosives.

Comparative Study on Thermal Response Mechanism of Two Binders during Slow Cook-Off.

The HTPE (hydroxyl-terminated polyether) propellant had a lower ignition temperature (150 °C vs. 240 °C) than the HTPB (hydroxy-terminated polybutadiene) propellant in the slow cook-off test. The reactions of the two propellants were combustion and explosion, respectively. A series of experiments including the changes of colors and the intensity of infrared characteristic peaks were designed to characterize the differences in the thermal response mechanisms of the HTPB and HTPE binder systems. As a solid phase filler to accidental ignition, the weight loss and microscopic morphology of AP (30~230 °C) were observed by TG and SEM. The defects of the propellant caused by the cook-off were quantitatively analyzed by the box counting method. Above 120 °C, the HTPE propellant began to melt and disperse in the holes, filling the cracks, which generated during the decomposition of AP at a low temperature. Melting products were called the “high-temperature self-repair body”. A series of analyses proved that the different thermal responses of the two binders were the main cause of the slow cook-off results, which were likewise verified in the propellant mechanical properties and gel fraction test. From the microscopic point of view, the mechanism of HTPE’s slow cook-off performance superior to HTPB was revealed in this article.

Mechanism of AP effect on slow cook-off response of HTPE propellant

Due to safety requirements, insensitive behaviour under slow cook-off conditions is the desirable behaviour for HTPE (Hydroxyl-terminated block copolyether) propellant. In this paper, in order to study the effect of AP (ammonium perchlorate) on slow cook-off response of HTPE propellants, the slow cook-off behaviour of AP and the effect of HTPE binder on AP were investigated firstly. The results showed that, the weightlessness rate of AP was only 2.2% in closed system till heated to 250°C, but the figure was 35.91 % in opened system. Then the slow cook-off behaviour of two groups of HTPE propellants with different AP content and diameter respectively were tested. The results indicated that, as the AP content increased from 52% to 67%, or the diameter of AP decrease from 400 μm to 5 μm, the violence of slow cook-off response all increased. The possible mechanism was proposed. It expressed that, thermal damage of propellant produced during the slow cook-off test, the combustion sensitivity to pressure of damaged propellant increased as the AP content rise and the AP diameter decrease, leading a more violent response to slow cook-off.

Study on the Effect of NTO on the Performance of HMX-Based Aluminized Cast-PBX.

3-Nitro−1,2,4-triazol−5-one (NTO) is an explosive with broad application prospects. To study the effect of NTO content on the properties of HMX-based cast-PBX (polymer bonded explosive), five different HMX/NTO-based cast-PBXs were prepared and characterized by experiments and simulations. The results show that the addition of NTO is beneficial to reduce the mechanical sensitivity of cast-PBX, but will reduce the energy level of cast-PBX. We then found that with the increase in NTO content, cast-PBX showed a trend of first increasing and then decreasing in terms of mechanical properties, specific heat capacity (Cp) and thermal conductivity (λ). In addition, we found that the Gurney energy (Eg) of N30 is 2.31 kJ/g. Finally, the increase in NTO content greatly improves the thermal safety performance of the cast-PBXs, and numerical simulation of slow cook-off can be used as one reliable method to obtain the ignition location, ignition temperature and the transient temperature distribution.

Mechanism of PSAN effect on slow cook-off response of HTPE propellant

ABSTRACT Due to safety requirements, insensitive behavior under slow cook-off conditions is the desirable behavior for HTPE propellant. As a low sensitivity oxidant, PSAN is used to partially replace for AP in HTPE propellant formulation to improve the slow cook-off behavior further. But the effect of PSAN on the slow cook-off behavior of propellant is inconclusive. So, in this paper, two kinds of HTPE composite propellant contained either AP as oxidant or a mixture of AP and PSAN were manufactured, named HTPE/AP/Al propellant and HTPE/AP/PSAN/Al propellant respectively. Then the slow cook-off behavior of the two propellants were tested. The results indicated that the slow cook-off response of HTPE/AP/PSAN/Al propellant was much more violent than the response of HTPE/AP/Al propellant. Then the possible mechanism was proposed. It expressed that, during the slow cook-off test, the PSAN decomposed much more than AP, the crack and hole produced in propellant grain; meanwhile the decomposition of PSAN also accelerated the decomposition of HTPE binder, the the crack and hole or AP particles could not be covered effectively by the liquefied decomposition product of HTPE binder; if the ignition occurred, the combustion of thermal damaged propellant was sensitive to pressure, leading a violent response to slow cook-off.

Numerical Simulation Research on Slow cook-off of Warhead of DNAN-based Melt-cast Explosive

RBOE explosive is a new type of DNAN-based insensitive melt-cast explosive with good thermal safety. In order to study the response characteristics of RBOE explosives under slow cook-off conditions, this study carried out a numerical simulation study of slow cook-off for the ϕ35mm×116mm RBOE cylindrical warhead. According to the thermal decomposition characteristics of each component of the explosive, the thermal reaction model of the RBOE explosive was established. Numerical simulation of RBOE warhead cook-off was carried out at a heating rate of 1K/min; the internal temperature rise curve, phase change cloud diagram and ignition cloud diagram of the warhead were obtained, and the thermal response characteristics of the RBOE explosive were analyzed.

Experimental and simulative thermal stability study of HTPE solid propellants in different scales

The hydroxyl-terminated polyether (HTPE) solid propellants are widely recognized as promising alternatives for hydroxyl-terminated polybutadiene (HTPB) propellants due to their compliance with insensitive munition characteristics of composite solid propellant. This study reports thermal stability investigation of HTPE solid propellants in different scales with the help of differential scanning calorimetry (DSC, 0.9 mg), accelerating rate calorimetry (ARC, 0.219 g), and slow cook-off (112 g) tests by taking HTPE/A3/Al/AP/PSAN composite solid propellant as an example. More importantly, for the first time, thermal decomposition kinetic parameters of HTPE solid propellant were calculated by employing iso-conversional Friedman method and using DSC experimental data at different heating rates. The simulation results of adiabatic combustion and slow cook-off of the HTPE propellant were obtained by applying the kinetic parameters in Advanced Kinetics and Technology Solutions software, which exhibited satisfied consistency with the experimental results, with less than 2% average deviation. Finally, the validated kinetic parameters were further employed to describe the large-scale thermal hazards of HTPE propellant and the predicted self-accelerating decomposition temperature of HTPE propellant in 50 kg-scale was 94.2 °C. Our simulative study provided a cogent and convenient strategy to understand thermal hazard of HTPE solid propellant in different scales during usage, storage, and transportation.

Research on the effect of the charge diameter on the slow cook-off performance of HMX base explosive

In order to study the effect of the charge diameter on the slow cook-off (SCO) performance of HMX (cyclotetramerthylenetetranitramine) based explosives, a typical cyclotetramerthylenetetranitramine based explosive was used as the research object, and the effect of the different charge diameters on the slow cook-off performance was studied. The research results show that: the charge diameter has no significant effect on the response level of the cyclotetramerthylenetetranitramine based explosives. The reaction time and ambient temperature increase with the increase of the charge diameter, and the center temperature decreases with the increase of the charge diameter. The ambient temperature and the center temperature change regularly with the increase of the charge diameter.

Numerical analysis of cook-off behavior of cluster tubular double-based propellant

To study the thermal security of solid rocket motors filled with cluster tubular double-based propellants, a 3-D transient heat transfer and cook-off response model was established. This was based on the global reaction model of double-based propellants, which follows the first-order Arrhenius law. Under the conditions that the fast cook-off ambient temperature is 600 ~ 1000 K and the slow cook-off heating rate is 1.8 ~ 5.4 K/h, the cook-off response characteristics of the tubular charge are numerically predicted. The results show that, in the case of fast cook-off, propellant begins thermal decomposition reaction at 420 K. The ignition position is close to the end faces on both sides of the propellant. The radial cross-sectional area of the ignition increases as the environment temperature increasing, but the ignition position does not change. In the case of slow cook-off, the incoming heat and release heat from the propellant decomposition reaction (start at 360 K) to heighten the temperature of the propellant. After reaching the ignition temperature, the thermal decomposition reaction accelerates, and the ignition occurs. Ignition areas are symmetrically distributed at both ends, and the ignition area moves from the inside to the outside as the heating rate increases.

Synchrotron Based Measurement of the Temperature Dependent Thermal Expansion Coefficient of Ammonium Perchlorate

AbstractAmmonium perchlorate is commonly used as an oxidizer in solid rocket propellant. Having a knowledge of its thermal expansion properties is essential for its application in different environments. Knowledge of thermal expansion properties is also useful for the prediction of propellant mechanical properties and response of propellant slow cook off applications. X‐ray diffraction analysis was performed on ammonium perchlorate at temperatures ranging from 260 K to 500 K. From there, Bragg peaks were indexed by fitting theoretical values of 2θ to the 2θ values of peaks obtained from the experiment. The Miller indices along with the 2θ values were then used to solve for the lattice parameters at each temperature. The lattice parameters, in nanometers, range from 0.9201 to 0.9373, 0.5805 to 0.5865, and 0.7439 to 0.7535 for a, b, and c, respectively. The measurement of the lattice parameter expansion leads to the determination of the temperature dependent thermal expansion coefficients within the temperature range. The lattice parameter values also lead to the determination of strain and stress on the ammonium perchlorate crystal. Direct measurement of the strain within the crystal lattice provides a more accurate measurement method over traditional optical‐based techniques.

Preparation and thermal properties study of HNIW/FOX-7 based high energy polymer bonded explosive (PBX) with low vulnerability to thermal stimulations

ABSTRACTFor modern munitions, high energy explosives are expected to reduce vulnerability and improve safety. In this study, based on the formulation of PAX-11 (94 wt% HNIW, 2.4 wt% CAB, 3.6 wt% BDNPA/F), FOX-7 is used as a portion replacement for HNIW to decrease vulnerability. To further decrease mechanical sensitivities and prevent static electricity, 0.5 wt% graphite is added to the surface of PBXs. A series of HNIW/FOX-7 based polymer bonded explosives (PBXs) with different formulations are prepared and mechanical sensitivities, thermal stabilities, detonation velocities, and slow cook-offs are studied to evaluate the energy and hazard of these PBXs. Additionally, finite element numerical simulations are utilized to study the transient temperature distributions, ignition time and ignition locations of the PBX cylinders during slow cook-off. Based on the results of this study, we obtain a high energetic low vulnerable PBX formulation (54 wt% HNIW, 40 wt% FOX-7, 2.4 wt% CAB, 3.6 wt% BDNPA/F, 0.5 wt% additional graphite) that balances energy and vulnerability. This formulation passes the slow cook-off test and detonation velocity reaches 8776 m·s−1, which can be used in the warhead of the high explosive anti-tank cartridge.

Thermal hazards evaluation of insensitive JEOL-1 polymer bonded explosive

Thermal stimuli is one of the major external stiumuli resulting from an overheated explosion of a munition. In order to evaluate the influence of external thermal stiumuli on the thermal hazards of JEOL-1 (32 wt% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 32 wt% 3-nitro-1,2,4-triazole-5-one (NTO), 28 wt% Al and 8 wt% binder system) explosive, accelerating rate calorimeter (ARC) is used to study the adiabatic thermal decomposition properties of JEOL-1 molding powders, and the slow cook-off properties of JEOL-1 are studied by experimental test and numerical simulation. The activation energy Ea, pre-exponential factor A, mechanism function f(α) and self-accelerating decomposition temperature (SADT) of adiabatic thermal decomposition of JEOL-1 molding powders are obtained according to ARC results. The response level of JEOL-1 polymer bonded explosive (PBX) columns exposed to an engulfing liquid pool fire is examined by the slow cook-off test. The ignition location, ignition temperature, ignition time and the transient temperature distributions of JEOL-1 PBX columns during the slow cook-off are obtained by numerical simulation. It can be concluded from this study that JEOL-1 is a low vulnerable explosive with high thermal safety.

Preparation and performances characterization of HNIW/NTO-based high-energetic low vulnerable polymer-bonded explosive

To satisfy the energy and security requirements of the explosives, it is necessary to develop high-energetic low vulnerable explosive. As the representatives of high-energetic explosives and low vulnerable explosives, hexanitrohexaazaisowurtzitane (HNIW) and 3-nitro-1,2,4-triazole-5-one (NTO) are used to research high-energetic low vulnerable polymer-bonded explosive (PBX) in this study. Based on the formulation of PAX-11 (94 mass% HNIW, 2.4 mass% CAB, 3.6 mass% BDNPA/F), some HNIW is replaced by NTO to reduce the vulnerability of the PBX during this work. Solution−water suspension method was used to prepare a series PBXs with different formulations. The explosion probability method, differential scanning calorimeter and accelerating rate calorimeter are used to evaluate the hazards of different PBX molding powders. And the thermal vulnerabilities, mechanical properties and energy levels of PBX columns are assessed by slow cook-off tests, tensile strengthes and detonation velocities, respectively. Moreover, finite element numerical simulations are adopted to study the transient temperature distributions, ignition time and ignition locations of the PBX columns during slow cook-off. The investigated results show that when the mass fraction of HNIW and NTO is 50% and 44%, respectively, the PBX passes the slow cook-off test and the detonation velocity reaches 8685 m s−1. To balance the energy and vulnerability of the PBXs, we obtain a high-energetic low vulnerable PBX formulation (50 mass% HNIW, 44 mass% NTO, 2.4 mass% CAB, 3.6 mass% BDNPA/F, 0.5 mass% additional graphite) which can be used in the warhead of the high-explosive anti-tank cartridge.

Mechanism and characteristics of thermal action of HMX explosive mixture containing high-efficiency fuel

In this study, the thermal stability and detonation properties of three types of explosives were investigated. Results indicated that nanoaluminum powder improved the detonation properties of HMX by increasing the specific surface area of HMX, which substantially increased the explosion heat and power. The decomposition temperatures of the three explosives containing aluminum hydride, ammonia borane, and nanoaluminum powder during slow cook-off at heating rates of 1.5 and 10°C min–1 were measured as 246°C and 241°C, 256°C and 261°C, and 238°C and 264°C, respectively. The explosives containing hydrogen storage materials swelled; however, the nanoaluminum powder was only slightly peeled off at the edge of the grains during cook-off. Differential scanning calorimetry (DSC) curves of the explosives containing hydrogen storage materials exhibited endothermic and exothermic peaks before the major exothermic reaction peak during the cook-off tests. In contrast, only one weak peak was observed in the DSC curve of the explosive containing nanoaluminum powder before the major exothermic reaction. In addition, the additives and adhesives catalyzed the slow cook-off decomposition, which caused the transformation of HMX crystals and accelerated the thermal decomposition reaction of HMX. The addition of high-density hydrogen storage materials to HMX resulted in detonation heats and explosion powers much greater than cure HMX. This improved performance was attributed to the hydrogen storage materials in the explosives participating in a secondary reaction in the reaction zone at the instant of the explosion, effectively realizing complementary lossless energy and thus greatly improving the explosive power of the explosives.

Investigation of heat transfer and heterogeneous reactions during the slow cook off of a composite propellant

In this work, a new modelling of interactions between components of aluminium/ammonium perchlorate/HTPB propellant during slow heating is presented. The phenomenon was previously described by experimental approaches performed in the laboratory. Heat and mass balance will be considered both in the solid and gas phases. The interaction of the decomposition products of both ammonium perchlorate and HTPB binder is shown thanks to previous experiments and a specific numerical model allows us to reproduce this trend. Mass and heat transfers are taken into account in each particle of ammonium perchlorate and inside the matrix of the HTPB binder. The chemical reaction in the gas phase is in interaction with the adsorption desorption of several species with regard to the surface grains. The whole set of equations is solved thanks to Comsol multiphysic solver and the numerical results are compared with mass loss measurements by means of a thermogravimetric device.

고체 추진기관 둔감화 점화 장치의 반응

This paper describes the results of study on reaction of insensitive igniter in which a pyrosensor is automatically sensing the rate of risk of fire or explosion of solid rocket motor exposed to an unexpected fire and makes the rocket motor burn itself safely. The Slow Cook Off(SCO) test following the regulation of MIL-STD-2105D was carried out with a rocket motor loaded with HTPB propellant, in which a thermal pyrosensor igniter was installed. The auto-ignition temperature measured was approximately and it corresponded to Type V(Burning) reaction in SCO test, while the temperature by Kissinger equation was calculated to be .