Begell House Inc.
International Journal of Energetic Materials and Chemical Propulsion
IJEMCP
2150-766X
12
4
2013
MODELING OF A SHORT ACTION MOTOR DISCHARGING A WEIGHT
275-306
10.1615/IntJEnergeticMaterialsChemProp.2013005392
Dan
Michaels
Technion
Alon
Gany
Faculty of Aerospace Engineering, Technion - Israel Institute of Technology,
Haifa, 3200003, Israel
interior ballistics model; short action motor; motor discharging weight; impulse augmentation
This paper investigates the interior ballistics of a unique concept for short action motors, based on a rocket-type combustion chamber discharging a weight through an exhaust tube. Depending on the overall system requirements, different kinds of propellant and weight may be considered. In the current study a system comprising a granular solid propellant and a solid weight is considered in order to capture the basic mechanisms of the impulse augmentation. A simplified lumped parameters model and a detailed two-phase flow model have been formulated and the fundamental characteristics of the propulsion system have been computed and analyzed. The study reveals that for certain system parameters with a given propellant mass the total impulse as well as the specific impulse may be significantly larger than those generated by a conventional rocket motor. The theoretical parametric investigation provides a good understanding on how different system parameters influence the in-terior ballistics processes, and can provide guidelines to the design of thrusters. Such short action motors may be beneficial for spacecraft and missile station keeping and trajectory correction, applying mini-thrusters of this kind, as well as for separating large space bodies such as missiles/launcher stages, satellites, etc.
PLATE DENT TESTS AND SEDIMENTATION OF PARTICLES IN MELT-CAST EXPLOSIVES
307-317
10.1615/IntJEnergeticMaterialsChemProp.2013005737
Patrick
Brousseau
Defence Research and Development Canada − Valcartier, 2459 Pie-XI Blvd North, Quebec, Canada G35 ix5
Serge
Trudel
Defence Research and Development Canada − Valcartier, 2459 Pie-XI Blvd North, Quebec, Canada G35 ix5
Pascal
Beland
Defence Research and Development Canada − Valcartier, 2459 Pie-XI Blvd North, Quebec, Canada G35 ix5
explosives
plate dent
sedimentation
RIGHTTRAC
GIM
A short experimental study demonstrated that the plate dent test is very sensitive to the last few centimeters of explosives at the bottom of the cylinders. The tests were performed by simply detonating an explosive cylinder with a small thickness (12.7−25.4 mm) of a different explosive (faster, slower, inert) at the bottom. The study will present how those small thicknesses influence the dent depth and hence the reported performance. Cylinders of explosives were cast and then cut to determine the extent of sedimentation of the HMX particles. Densities were taken at various places and concentrations of HMX were extrapolated from those. It was found that there was a difference of 22% in the percentage of HMX from the bottom and the top of the cylinder (66% vs. 44%; theoretical average was 52.8%). The explosive at the bottom was then significantly different and more powerful than the one at the top. The study will also demonstrate how the situation can be worse in real artillery shells. Given the results of the plate dent experiments reported before, it will be demonstrated how in theory one could be misled on the plate dent test by letting particles settle. Simple precautions can be taken to eliminate this variable and to ensure that the results of the plate dent test are meaningful. It also serves as a reminder that the composite explosives that we test, especially the melt-cast explosives, have large variations in their composition from sample to sample.
MOLECULAR MODELING: TOWARD A REALISTIC APPROACH TO MODEL ENERGETIC MATERIALS
319-333
10.1615/IntJEnergeticMaterialsChemProp.2013005416
David
Brochu
DND
Mounir
Jaidann
Defence Research and Development Canada, 2459 de la Bravoure Road, Quebec G3J1X5, Canada
Hakima
Abou-Rachid
Defence Research & Development Canada – Valcartier
Jamie
Neidert
U.S. Army Aviation and Missile Research Development and Engineering Center, Redstone Arsenal, Huntsville, Alabama 35898
Josee
Brisson
Département de Chimie, CERMA (Centre de Recherche sur les Matériaux Avancés) and CQMF (Centre Québécois sur les Matériaux Fonctionnels), Faculté des Sciences et de Génie, Université Laval, Québec, Canada G1V 0A6
energetic materials
simulation and modeling
sensitivity
HTPB
RDX
plastic-bonded explosives
Models of plastic-bonded explosives were created with the aim of studying the mechanical properties and sensitivity because the latter is one of the most important problems in relation to energetic materials. Previous models proposed in the literature used short plastic chains, which are appropriate for interaction modeling. In the present work, a model with a single, long chain was built, which is more appropriate for modeling mechanical properties. The representative hydroxyl-terminated polybutadiene (HTPB)/dioctyladipate (DOA)/cyclotrimethylenetrinitramine (RDX) system was used (81.4 w/w% of RDX and 18.6 w/w% of the amorphous HTPB/DOA phase, with a 60/40 ratio between the polymer and plasticizer). The HTPB chain was composed of 48 trans groups, 16 cis groups, and 16 vinyl groups. Due to the length of the chain, superposing the crystalline RDX cell [cleaved at the crystalline (2 0 0), (0 2 0), and (2 1 0) planes] to the amorphous HTPB/DOA cell introduced considerable void, and therefore resulted in low density−much more so than when using models with shorter chains. A compression/minimization iterative procedure was used to converge to the optimal density. Pair distributions were calculated to verify that the procedure did not lead to abnormal changes in the RDX crystal model. Comparable energies were obtained for models built with each cleavage plane, contrary to previous work with small molecules. Long chains have lower entropy and are less able to change conformations and maximize interactions with the crystal surface. Models with densities higher than the minimum value were shown to have energy stored in two main components; i.e., the internal energy was stored mainly in the bond and torsion contributions, whereas the external energy storage was performed by van der Waals interactions. These preliminary models show the potential for studying the sensitivity of explosives through molecular modeling.
ENHANCEMENT OF COMPOSITE PROPELLANT IGNITION CHARACTERISTICS BY SURFACE ABRASION
335-346
10.1615/IntJEnergeticMaterialsChemProp.2013005353
Jacquie
Hewson
Rocket Systems Engineering, Bristol Aerospace Limited, Rockwood Propellant Plant, 660 Berry Street, Winnipeg, MB, Canada R3C 2S
Robert
Le Neal
Rocket Systems Engineering, Bristol Aerospace Limited, Rockwood Propellant Plant, 660 Berry Street, Winnipeg, MB, Canada R3C 2S
propellant
ignition
rocket
During curing of composite solid rocket motor propellants, the propellant polymer tends to accumulate as a thin film adjacent to the mandrel used to form the internal bore of the propellant grain. This binder-rich layer coats the ammonium perchlorate crystals on the propellant surface and may inhibit flame propagation during rocket motor ignition. Poor flame propagation during ignition can affect both ignition performance and the reliability characteristics. Abrasion of the solid propellant bore surfaces to remove the binder-rich layer and expose the ammonium perchlorate oxidizer is a common procedure used to enhance rocket motor ignition. Abrasion of the propellant bore was evaluated as a means to enhance the ignition performance and reliability characteristics of Bristol 2.75-in. CRV7 rocket motors. Techniques were developed using wire brushes to scrub the surface of the propellant bore. Automated production processes were developed to provide uniform abrasion of the propellant surface, resulting in consistent enhancement of the rocket motor ignition characteristics. This paper describes the development of the CRV7 propellant bore abrasion process, and describes the results of the testing performed to quantify the effect of propellant abrasion on the rocket motor ignition characteristics.
THERMAL EXPLOSION SYNTHESIS OF TITANIUM HYDRIDE POWDERS
347-359
10.1615/IntJEnergeticMaterialsChemProp.2013005386
Valery
Rosenband
Faculty of Aerospace Engineering, Technion- Israel Institute of Technology, Haifa 32000, Israel
Alon
Gany
Faculty of Aerospace Engineering, Technion - Israel Institute of Technology,
Haifa, 3200003, Israel
energetic materials
titanium hydride
thermal explosion
Titanium hydride (TiH2) is used in the fields of pyrotechnics, metallurgy, and hydrogen (H2) storage. Different pyrotechnic compositions and flash powders contain mixtures of TiH2 with potassium perchlorate. Because of its high H2 content (about 4%), TiH2 is also used as a H2 storage medium. Hydrides offer a compact H2 storage option, minimizing the H2 effective volume and improving the H2 storage safety. The traditional method of TiH2 production consists of a long exposure of Ti metal to H2 at elevated temperature and pressure. This paper describes a new thermal explosion method for production of TiH2, as well as a parametric investigation using the new experimental technique to evaluate the H2 content in the resulting hydride.
CHARACTERIZING 5.56-mm CARTRIDGE PERFORMANCE WITH NOVEL MEASUREMENT TECHNIQUES
361-370
10.1615/IntJEnergeticMaterialsChemProp.2013005291
John J.
Ritter
U.S. Army Research Laboratory, RDRL-WML-D, B390, Aberdeen Proving Ground, Maryland 21005
small caliber
ignition
5.56 mm
interior ballistics
primer performance
A custom, in-house designed breech for an M16A1 Mann barrel, 5.56 mm, has been instrumented to measure the force output of an unsupported primer. In addition, the Mann barrel is designed to accept gauges at two diametrically opposed locations to simultaneously measure mid-case chamber pressure. This one-of-a-kind apparatus provides an advanced diagnostic tool to gain insight into the interactions between the primer and propellant bed of the 5.56-mm cartridge during ignition, and allows for enhanced characterization and understanding of the cartridge's interior ballistics. The experiments performed investigate the role of the primer, cartridge temperature conditioning, and charge weights in their respective effects on chamber pressures and primer forces. The results indicate the primer force measurement is an invaluable tool in evaluating the interior ballistics of the 5.56-mm cartridge and it provides information that the more standard mid-case or case-mouth pressure techniques overlook. This pioneering system-level approach provides detail into the primer/propellant interactions never before observed by analyzing the primer and propellant outputs simultaneously within a closed system. In addition, this diagnostic technique provides further early time data. It advances the initial data acquisition timeframe to when the firing pin strikes the primer, whereas previous diagnostic techniques began when the propellant gas generation is first recorded. The additional data gained through the primer force measurement provide investigators a new avenue into malfunction investigations, as well as giving formulators and designers an additional tool to characterize the performance of new primer and/or propellant formulations in search of the optimized weapon cartridge.