Steady Deflagration of PBX-9501 Within a Copper Cylinder


Book Description

A copper cylinder cook-off experiment has been designed to cause steady deflagration in PBX-9501 explosive material. The design is documented and preliminary copper expansion results are presented for steady deflagration with a reaction speed of 1092 +/- 24 m/s. The expansion of reaction products from the detonation of an explosive is something that is well understood, and reasonably simulated using documented equations of state (EOS) for many explosives of interest. These EOS were historically measured using a 'standard' copper cylinder test design; this design comprised an annealed, oxygen-free high conductivity (OFHC) copper tube filled with explosive material and detonated from one end. Expansion of the copper wall was measured as a function of time using either a streak camera (for classic testing), or more recently using laser velocimetry techniques. Expansion data were then used to derive the EOS in various preferred forms - which are not discussed here for the sake of brevity. [Catanach, et. al., 1999] When an explosive deflagrates rather than detonating, simulation becomes more difficult. Reaction products are released on a slower time scale, and the reactions are much more affected by the geometry and local temperature within the reaction environment. It is assumed that the standard, documented EOS will no longer apply. In an effort to establish a first order approximation of deflagration product behavior, a cook-off test has been designed to cause steady deflagration in PBX-9501 explosive material, and to record the copper expansion profile as a function of time during this test. The purpose of the current paper is to document the initial test design and report some preliminary results. A proposal for modification of the design is also presented.




Measurement of the Flow Properties Within a Copper Tube Containing a Deflagrating Explosive


Book Description

We report on the propagation of deflagration waves in the high explosive (HE) PBX 9501 (95 wt % HMX, 5 wt% binder). Our test configuration, which we call the def1agration cylinder test (DFCT), is fashioned after the detonation cylinder test (DTCT) that is used to calibrate the JWL detonation product equation of state (EOS). In the DFCT, the HE is heated to a uniform slightly subcritical temperature, and is ignited at one end by a hot wire. For some configurations and initial conditions, we observe a quasi-steady wave that flares the tube into a funnel shape, stretching it to the point of rupture. This behavior is qualitatively like the DTCT, such that, by invoking certain additional approximations that we discuss, its behavior can be analyzed by the same methods. We employ an analysis proposed by G.I. Taylor to infer the pressure-volume curve for the burning, expanding flow. By comparing this result to the EOS of HMX product gas alone. we infer that only (almost equal to)20 wt% of the HMX has burned at tube rupture. This result confirms pre-existing observations about the role of convective burning in HMX cookoff explosions.




Deflagration Behavior of PBX 9501 at Elevated Temperature and Pressure


Book Description

We report the deflagration behavior of PBX 9501 at pressures up to 300 MPa and temperatures of 150-180 C where the sample has been held at the test temperature for several hours before ignition. The purpose is to determine the effect on the deflagration behavior of material damage caused by prolonged exposure to high temperature. This conditioning is similar to that experienced by an explosive while it being heated to eventual explosion. The results are made more complicated by the presence of a significant thermal gradient along the sample during the temperature ramp and soak. Three major conclusions are: the presence of nitroplasticizer makes PBX 9501 more thermally sensitive than LX-04 with an inert Viton binder; the deflagration behavior of PBX 9501 is more extreme and more inconsistent than that of LX-04; and something in PBX 9501 causes thermal damage to 'heal' as the deflagration proceeds, resulting in a decelerating deflagration front as it travels along the sample.




PBX 9404 Detonation Copper Cylinder Tests


Book Description

We present detonation copper cylinder test results on aged PBX 9404 (94 wt% HMX, 3 wt% CEF, 2.9 wt% NC, 0.1 wt% DPA) explosive. The charges were newly pressed from 37.5 year-old molding powder. We compare these results to equivalent data performed on the same lot when it was 3.5 years old. Comparison of the detonation energy inferred from detonation speed to that inferred from wall motion suggests that the HMX energy is unchanged but the NC energy has decreased to ≈25% of its original value. The degradation of explosives and their binders is a subject of continual interest. Secondary explosives such as HMX are sufficiently stable near room temperature that they do not measurably degrade over a period of at least several decades. For formulated systems the bigger concern is binder degradation, for which the three main issues are strength, initiation safety, and (if the binder is energetic) energy content. In this paper we examine the detonation energy of new and aged PBX 9404 (94 wt% HMX, 3 wt% tris-[beta] chloroethylphosphate (CEF), 2.9 wt% nitrocellulose (NC), 0.1 wt% diphenylamine (DPA) [1, 2]), measured via the detonation copper cylinder test. In 1959, two independent PBX 9404 accidents [3] raised serious concerns about the safety of the formulation. Over about a decade's time, Los Alamos pursued a safer, energetically equivalent replacement, which ultimately became PBX 9501. In order to accurately compare the performance of the PBX 9404 and PBX 9501 formulations, W. Campbell and R. Engelke (C & E) developed a stringent cylinder test protocol that they called the Los Alamos Precision Cylinder Test [4]. The present aging study is possible because excellent PBX 9404 data from those qualification tests endures.




Deflagration Wave Profiles


Book Description

Shock initiation in a plastic-bonded explosives (PBX) is due to hot spots. Current reactive burn models are based, at least heuristically, on the ignition and growth concept. The ignition phase occurs when a small localized region of high temperature (or hot spot) burns on a fast time scale. This is followed by a growth phase in which a reactive front spreads out from the hot spot. Propagating reactive fronts are deflagration waves. A key question is the deflagration speed in a PBX compressed and heated by a shock wave that generated the hot spot. Here, the ODEs for a steady deflagration wave profile in a compressible fluid are derived, along with the needed thermodynamic quantities of realistic equations of state corresponding to the reactants and products of a PBX. The properties of the wave profile equations are analyzed and an algorithm is derived for computing the deflagration speed. As an illustrative example, the algorithm is applied to compute the deflagration speed in shock compressed PBX 9501 as a function of shock pressure. The calculated deflagration speed, even at the CJ pressure, is low compared to the detonation speed. The implication of this are briefly discussed.




Small-scale Deflagration Cylinder Test with Velocimetry Wall-motion Diagnostics


Book Description

Predicting the likelihood and effects of outcomes resultant from thermal initiation of explosives remains a significant challenge. For certain explosive formulations, the general outcome can be broadly predicted given knowledge of certain conditions. However, there remain unexplained violent events, and increased statistical understanding of outcomes as a function of many variables, or 'violence categorization, ' is needed. Additionally, the development of an equation of state equivalent for deflagration would be very useful in predicting possible detailed event consequences using traditional hydrodynamic detonation moders. For violence categorization, it is desirable that testing be efficient, such that it is possible to statistically define outcomes reliant on the processes of initiation of deflagration, steady state deflagration, and deflagration to detonation transitions. If the test simultaneously acquires information to inform models of violent deflagration events, overall predictive capabilities for event likelihood and consequence might improve remarkably. In this paper we describe an economical scaled deflagration cylinder test. The cyclotetramethylene tetranitramine (HMX) based explosive formu1lation PBX 9501 was tested using different temperature profiles in a thick-walled copper cylindrical confiner. This test is a scaled version of a recently demonstrated deflagration cylinder test, and is similar to several other thermal explosion tests. The primary difference is the passive velocimetry diagnostic, which enables measurement of confinement vessel wall velocities at failure, regardless of the timing and location of ignition.




LASL Explosive Property Data


Book Description




Explosive Effects and Applications


Book Description

This is a broad-based text on the fundamentals of explosive behavior and the application of explosives in civil engineering, industrial processes, aerospace applications, and military uses.







Energetic Materials


Book Description

Incorporation of particular components with specialized properties allows one to tailor the end product's properties. For instance, the sensitivity, burning behavior, thermal or mechanical properties or stability of energetic materials can be affected and even controllably varied through incorporation of such ingredients. This book examines particle technologies as applied to energetic materials such as propellants and explosives, thus filling a void in the literature on this subject. Following an introduction covering general features of energetic materials, the first section of this book describes methods of manufacturing particulate energetic materials, including size reduction, crystallization, atomization, particle formation using supercritical fluids and microencapsulation, agglomeration phenomena, special considerations in mixing explosive particles and the production of nanoparticles. The second section discusses the characterization of particulate materials. Techniques and methods such as particle size analysis, morphology elucidation and the determination of chemical and thermal properties are presented. The wettability of powders and rheological behavior of suspensions and solids are also considered. Furthermore, methods of determining the performance of particular energetic materials are described. Each chapter deals with fundamentals and application possibilities of the various methods presented, with particular emphasis on issues applicable to particulate energetic materials. The book is thus equally relevant for chemists, physicists, material scientists, chemical and mechanical engineers and anyone interested or engaged in particle processing and characterization technologies.