Fast Cook-off Research Articles

Test design and theoretical calculation of 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 454.06K, with an error of +1.75% compared to the test result of 462.15K, 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 161s, 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.

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.

An efficient energy characteristics and explosion heat improving method of FOX-7-based aluminized explosives

Exploring new composite explosives based on 1,1-diamino-2,2-dinitroethylene (FOX-7) is significant in the field of insensitive high explosives (IHE). Despite having good detonation performance compared to RDX, FOX-7 has not been successfully applied in the preparations of aluminized explosives due to the poor explosion heat values. In this paper, the explosion heat and detonation velocity of FOX-7-based aluminized explosives were studied systematically. The experiment results showed that the explosion heat of FOX-7-based aluminized explosives are significantly lower than that of RDX-based ones, especially when the content of aluminum powder exceeds 30%. To solve this problem, a simple but effective method of adding RDX to FOX-7-based aluminized explosives was developed, leading to a huge growth of explosion heat values. Finally, in order to compare the safety performance with RDX-based aluminized explosives, the low vulnerability of the FOX-7/RDX-based aluminized explosives formulation was investigated by fast cook-off, sympathetic detonation and 12.7 mm bullet impact tests. The results showed that the safety performance of FOX-7/RDX-based aluminized explosives is better than that of RDX-based aluminized explosives, proving that good low vulnerability is kept with the addition of RDX into FOX-7-based aluminized explosives.

Vented and sealed cookoff of powdered and pressed ε-CL-20

ABSTRACT We have completed a series of vented and sealed cookoff experiments of the ε-polymorph of CL-20 in our Sandia Instrumented Thermal Ignition (SITI) apparatus using both powder and pressed pellets at nominal densities of 313 ± 8 kg/m3 and 1030 ± 4 kg/m3, respectively. The boundary temperature of our aluminum confinement cylinder was ramped in 10 minutes from room temperature to a prescribed set-point temperature ranging between 448 nd 468 K and held at the set-point temperature until ignition. A universal cookoff model (UCM) has been calibrated using the ε-CL-20 SITI data to predict pressurization and thermal ignition of ε-CL-20. The ignition model was validated by using one-dimensional time-to-explosion (ODTX) ignition data from a different laboratory. We found that a thirtyfold increase in the reaction rates due to liquefaction at 520 K could explain the high temperature ODTX cookoff data. The model gives a plausible explanation of why melting is important in fast cookoff events involving CL-20. Our model also gives support to 520 K as the liquefaction point of CL-20, which has different values in the literature.

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.

Fast cook-off modeling of HMX

The transient behavior of confined HMX in response to an external heat flux has been simulated using a detailed kinetic model. The model is spatially one-dimensional, fully transient, and consists of equations for modeling the solid (condensed) phase HMX, the gas phase, and the surrounding container for fast cook-off conditions. The condensed-phase decomposition reactions are described by semi-global, distributed kinetics. The gas phase description includes a detailed chemistry model for the combustion of HMX. A nonlinear, numerical solution of the partial differential equations results in predictions of temperature, pressure, velocity, and species fractions as a function of position and time. Predicted time-to-ignition yields good agreement with experimentally measured fast cook-off times. Temperature at ignition is found to be a function of heating rate. The ignition process for fast cook-off is consistent with laser ignition of bare HMX samples. Simulation results depend on accurate boundary conditions applied to the steel container. Pressurization rates are calculated and insight is given into the fast cook-off behavior of HMX. The main decomposition pathway is the conversion of HMX into CH2O and N2O.

A numerical study on the thermal initiation of a confined explosive in 2-D geometry

Insensitive munitions design against thermal stimuli like slow or fast cook-off has become a significant requirement for today's munitions. In order to achieve insensitive munitions characteristics, the response of the energetic material needs to be predicted against heating stimuli. In this study, a 2D numerical code was developed to simulate the slow and fast cook-off heating conditions of confined munitions and to obtain the response of the energetic materials. Computations were performed in order to predict the transient temperature distribution, the ignition time, and the location of ignition in the munitions. These predictions enable the designers to have an idea of when and at which location the energetic material ignites under certain adverse surrounding conditions. In the paper, the development of the code is explained and the numerical results are compared with available experimental and numerical data in the literature. Additionally, a parametric study was performed showing the effect of dimensional scaling of munitions and the heating rate on the ignition characteristics.

An Eulerian–Lagrangian approach for simulating explosions of energetic devices

An approach for the simulation of explosions of “energetic devices” is described. In this context, an energetic device is a metal container filled with a high explosive (HE). Examples include bombs, mines, rocket motors or containers used in storage and transport of HE material. Explosions may occur due to detonation or deflagration of the HE material, with initiation resulting from either mechanical or thermal input. This approach is applicable to a wide range of fluid–structure interaction scenarios, the application to energetic devices is chosen because it demonstrates the full capability of this methodology. Simulations of this type are characterized by a number of interesting and challenging behaviors. These include the transformation of the solid HE into highly pressurized gaseous products that initially occupy regions which formerly contained only solid material. This rapid pressurization of the container leads to large deformations at high strain rates and eventual case rupture. Once the container breaks apart, the highly pressurized product gas that escapes the failing container generates shock waves that propagate through the initially quiescent surrounding fluid. The approach, which uses a finite-volume, multi-material compressible CFD formulation, within which solid materials are represented using a particle method known as the Material Point Method, is described, including certain of the sub-grid models required to close the governing equations. Results are first presented for “rate stick” and “cylinder test” scenarios, each of which involves detonating unconfined and confined HE material, respectively. Experimental data are available for these configurations and as such they serve as validation tests. Finally, results from an unvalidated “fast cookoff” simulation in which the HE is initiated by thermal input, which causes deflagration, are shown.

Large Scale Fast Cook-off Sensitivity Results of a Melt Castable General Purpose Insensitive High Explosive

A melt castable General Purpose (GP) Insensitive High Explosive (IHE) formulation was developed and subjected to a number of performance and sensitivity tests. The formulation consisted of a thermoplastic binder with 3-nitro-1,2,4-triazol-5-one (NTO) as the primary insensitive explosive. Other ingredients include: aluminum powder (Al), ammonium perchlorate (AP) and cyclotrimethylenetrinitramine (RDX). The detonation velocity of the explosive was measured at 7080 m/s at a density of 1.79 g/cm3 at a confined diameter of 20.3 cm. This paper is concerned with the fast cook-off (FCO) thermal sensitivity response of this composition (identified as TE-T7005) in a large scale/heavily confined test apparatus to simulate large storage quantities. Ergebnisse der Cook-off Empfindlichkeit im Großversuch bei einem schmelzgießfähigen allgemein verwendbaren unempfindlichen Hochleistungssprengistoff Eine schmelzgießfähige, allgemein verwendbare Formulierung eines unempfindlichen Hochleistungssprengstoffs (IHE) wurde entwickelt und zahlreichen Leistungs- und Empfindlichkeitstests unterworfen. Die Formulierung besteht aus einem thermoplastischen Binder aus 3-Nitro-1,2,4-triazol-5-on (NTO) als primärer unempfind-licher Sprengstoff. Andere Zusätze enthalten Aluminiumpulver, Ammoniumperchlorat und RDX. Die Detonationsgeschwindigkeit des Sprengstoffs wurde gemessen zu 7060 m/s bei einer Dichte von 1,79g/cm3und einem Durchmesser der Verdämmung von 20,3 cm. Diese Arbeit befaßt sich mit der thermischen Empfindlichkeit beim schnellen Cook-off Test(FCO) des als TE-T7005. bezeichneten Sprengstoffs in einem Großversuch bei starker Verdämmung, um große Lagermengen zu simulieren. Résultats de la sensibilité cook-off lors d'un essai à grande échelle sur un explosif à haute puissance, insensible, coulable par fusion, à usage général On a développé une formulation d'explosif à haute puissance insensible (IHE), coulable par fusion, à usage général et on l'a soumise à de bombreaux tests de puissance et de sensibilité. La formulation est composée d'un liant thermoplastique avec le 3-nitro-1,2,4-triazol-5-one (NTO) en tant qu'explosif primaire insensible. D'autres additifs contiennent de la poudre d'aluminium, du perchlorate d'ammonium et du RDX. On a mesuré une vitesse de détonation de l'explosif de 7060 m/s pour une densité de 1,79g/cm3 et un diamétre de confinement de 20,3 cm. Ces travaux portent sur la sensibilité thermique, lors d'un test d'échauffement rapide (FCO), de l'explosif portant la désignation TE-T7005 dans le cadre d'un essai á grande échelle avec confinement important en vue de simuler de le stockage de grandes quantités.

Sensitivities of azide polymer propellants in fast cook-off, card gap and bullet impact tests

Sensitivities of GAP propellants and BAMO/NMMO propellants were evaluated. The fast cook-off test, card gap test and bullet impact test were employed to characterize the propellant samples. All the samples tested here showed no reaction other than burning. In the fast cook-off test, ignition time was dependent on the confinement and propellant composition. In the card gap test, the double base propellant was found to have a higher sensitivity than AP-based composite propellant. In the bullet impact test, the case material played an important role in the sensitivity. The case made of carbon fiber-reinforced plastics (CFRP) was effective in mitigating the sensitivity to the bullet impact. As a whole, AN-based composite propellants had relatively lower sensitivity.

INSENSITIVE MUNITIONS PROPULSION PROGRESS

Increasing interest in the application of thrust-managed, solid-propellant rocket motors for future missiles has prompted a desire to learn how these motors might react to the stimuli involved in the MIL-STD 2105B1 insensitive munitions (IM) hazards tests. An opportunity became available for the Insensitive Munitions Advanced Development (IMAD) Propulsion Project to obtain four experimental, dual-pulse (two chamber) rocket motors; these motors were subjected to the fast cookoff, slow cookoff, bullet impact, and fragment impact IM hazards tests. These motors had steel cases with a bulkhead separating one pulse from the other. The propellant for each pulse grain was a nitrate-ester-plasticized, reduced-smoke, hydroxyl-terminated polyether (HTPE) propellant. Reactions in the IM hazards tests were classified as follows: fast cookoff, deflagration (fail); slow cookoff, explosion (fail); bullet impact, burn (pass); and fragment impact, explosion (fail). In the cookoff tests, the aft pulse (pulse 1) reacted first followed by the forward pulse (pulse 2). Delay times between the reaction of pulse 1 and pulse 2 were 5 seconds for the fast cookoff and 45 seconds for the slow cookoff tests. It was unexpected when pulse 1 reacted first, because this pulse's chamber consisted of thicker insulation. In the impact tests, the projectiles and fragments were aimed at the pulse 2 chamber resulting in the reaction of this pulse with no accompanying reaction from pulse 1. The implication of these results is that separate chamber, pulsed motors containing a relatively insensitive propellant such as the HTPE propellant will probably provide less collateral damage than motors in which an equivalent amount of propellant is contained in one chamber.

Simple Calculation Methods for Munitions Cookoff times and temperatures

AbstractSimple one‐dimensional quasi‐static heat transfer calculations can be used to estimate fast cookoff times of cylindrical munitions with metal cases. The most critical parameter for the thermal analysis is the heat flux to the ordnance from the fire. One must remain aware that heating will be different for transparent flames of propane or methane test fires than they are for the opaque smoky flames of wood and jet‐fuel fires. Good values for material thermal conductivities and energetic material ignition behavior are also needed. Low‐conductivity composite cases cannot be analyzed in the same way because case mechanical failure is the primary initial failure path, rather than thermal conduction leading directly to ignition of the energetic material. Reaction violence cannot be calculated in a simple way with the present state of the art.Simple hand analysis of slow cookoff problems is limited to simple symmetric shapes of the type that were published over 30 years ago involving constant boundary temperatures. Modern computers, using finite‐difference codes can be used to readily solve problems with varying boundary temperatures to predict time to cookoff. However, as this paper shows, quasi‐static solutions of symmetric shapes (slabs, cylinders and spheres) can be obtained with desktop computer spreadsheets that give the same results as the finite‐difference codes. There are no a priori methods for predicting the violence of the slow cookoff reaction. These same comments apply as well to intermediate cookoff heating rates (greater than 3.3 K/h).Calculations by the methods of this paper place tools for designing experiments to explore cookoff behavior and for designing ordnance to meet insensitive munitions requirements on virtually every desktop.

Thermomechanical Properties of Rocket Propellants and Correlation with cookoff behaviour

AbstractThe cookoff behaviour of several plasticized HTPB/AP and HTPB/RDX propellants has been evaluated using the standard Small‐Scale Cookoff Bomb (based on the NWC design) and a modified version of the standard equipment (whereby the reaction violence can be measured quantitatively) to investigate the effects of (1) plasticizer level on the thermomechanical properties and its role in moderating the cookoff response, and (2) heating rate. A change from slow to fast cookoff behaviour was observed for the plasticized HTPB/RDX propellants; the measured pressures/energy output at the slow heating rate were much lower than those at the fast heating rate for the same propellants. The thermal distribution/gradient at various positions and depths in the cylindrical propellant specimen, during fast and slow cookoff, were measured in order to understand the reversal in the severity of the response shown by the plasticized RDX propellants when the heating rate was changed. Thermomechanical properties of the propellants were measured and correlated with cookoff behaviour, to provide further insight into the cookoff mechanisms.

Low‐Sensitivity Explosive Compounds for Low Vulnerability Warheads

AbstractLooking for explosives for Low Vulnerability Ammunitions leads to an interest in explosive molecules less sensitive than the usual nitramines (RDX, HMX). If TATB is quite convenient in terms of sensitivity, its performance is too low.The researches described here are related to synthesis and use of NTO (nitrotriazolone), another insensitive molecule. The synthesis by nitration of TO (triazolone) is easy and the two steps from available starting materials have been optimized.A comparison of desensitivation of PBX either by TATB or by NTO have been made. The sensitivity levels were found equivalent while the detonation velocity of the NTO based PBX was slightly higher. Unfortunately in this case, the failure diameter would be larger.The last part relates to an extensive characterization in terms of performance and vulnerability to fast cook off, slow cook off, bullet impact, shock sensitivity and sympathetic detonation of a NTO and HMX based PBX. This PBX, B 2214, was one of the first examples of explosive composition showing no sympathetic detonation, even in 248 mm large diameter.

Assessing the response of naval armament stores in credible accident environments

Abstract The paper reviews the credible accident environments to which an armament store could be subjected in service. The current fast cook-off, slow cook-off and impact tests for naval armament stores are described. The extent to which theoretical studies are needed to further the understanding of the response of stores in these environments is discussed.