Shock Initiation Study of PBX-9404 PDF Download
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Languages : en
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Pressure-field histories during the sustained and short-duration shock initiation of PBX-9404 explosive (plastic-bonded HMX) have been determined with embedded Manganin gauges. Numerical integration of the conservation relations and an assumed equation of state are used to obtain the decomposition histories during the initiation process. In both cases, this process is effected by reaction originating near the impact face producing pressure pulses that overtake the shock front and enhance its strength, leading to an abrupt transition to detonation. Correlation of reaction rates to state variables suggest an Arrhenius rate form, modified to include a dependence on shock strength and an induction time. This rate is used in computer simulations of several other initiation experiments on PBX-9404.
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Languages : en
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Pressure-field histories during the sustained and short-duration shock initiation of PBX-9404 explosive (plastic-bonded HMX) have been determined with embedded Manganin gauges. Numerical integration of the conservation relations and an assumed equation of state are used to obtain the decomposition histories during the initiation process. In both cases, this process is effected by reaction originating near the impact face producing pressure pulses that overtake the shock front and enhance its strength, leading to an abrupt transition to detonation. Correlation of reaction rates to state variables suggest an Arrhenius rate form, modified to include a dependence on shock strength and an induction time. This rate is used in computer simulations of several other initiation experiments on PBX-9404.
![Nature of the Buildup to Detonation in Solid High Explosives During Plane Shock Initiation. [PBX-9404 and PBX-9502]. PDF](https://books.google.com/books/content/images/frontcover/jzmcAQAACAAJ?fife=w80-h100)
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Languages : en
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Two models for the initiation process are compared to results of experimental studies of initiation of detonation in two high explosives, PBX-9404 (HMX-based) and PBX-9502 (TATB-based), by sustained shock waves. A critical examination of the model known as single-curve buildup is made. Several comparisons are made with experimental results for the two explosives. The model describes the observed shock trajectories moderately well although it has some limitations. These are manifested by an examination of the relation between input pressure and distance of run to detonation. The data are also compared with model solutions for the initiation process which assume self-similar flow. The model can fit the experimental shock trajectory reasonably well but difficulties are encountered in attempting to complete the solution for the entire flow field. For PBX-9404, published pressure-time profiles are examined for self-similar character. The measured profiles show substantial disagreement with the similarity model.
![Short-pulse Shock Initiation of Granular Explosives. [PBX-9404]. PDF](https://books.google.com/books/content/images/frontcover/_yX_wQEACAAJ?fife=w80-h100)
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Languages : en
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An experimental investigation has examined how different rates of unloading affect the release of chemical energy in a granular explosive experiencing transient shock compression. A compressed-gas gun was used to generate two types of short-pulse shocks in the explosive PBX-9404. A shock pressure of 3.2 GPa sustained for 0.37 .mu.s was produced in both cases, but differences in flyer-plate properties resulted in different unloading histories. In one case the impact interface was rapidly unloaded by the initial release wave, while in the second case the unloading required multiple release waves over several microseconds. A VISAR system was used to observe the evolution of these two waves for distances up to 10 mm. The recorded waveforms showed that the unloading rates had a dominant effect on chemical energy release and growth towards detonation. This effect is important for considerations of critical impact criteria, and should provide a strong test for predictive shock-initiation models.
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Category : Explosives
Languages : en
Pages :
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Languages : en
Pages : 9
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Desensitization of explosives by preshocking is being studied using the well-supported plane shock waves generated by a gas gun. Evolution of the waves in the explosive is monitored using in-material multiple magnetic gauges to measure particle velocity in the lagrangian frame, over ≈ 3[mu]s of run. PBX-9404, PBX-9502 have been studied, at pressures up to 10.5 GPa. A substantial extension of the run to detonation is observed in PBX-9404, with the run beginning approximately at the end of the preshocked region. A reactive wave is observed while the preshock persists in both PBX-9404 and PBX-9501, but evidently does not contribute to the detonation wave or shorten the run to detonation. PBX-9502 is inert at pressures accessible with the gas gun, but serves to clarify the progress of multiple shocks over the off-Hugoniot EOS surface and the shock dynamics of wave coalescence.
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Languages : en
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PBX-9404 and Composition B-3 were desensitized by subjecting them to shocks in the pressure range 10 to 24 kbar. Results show that the collapse of voids, and thus the activation of hot spots by shock waves, takes time and may require more than 5 .mu.s. This time is, in a way, a counterpart of the induction time for shock initiation of a homogeneous explosive. Gittings' data are adduced to extend the results to 100 kbar and to show that at high pressures desensitization occurs in a very brief time window. When the voids have been collapsed, the relatively homogeneous explosive is resistant to detonation through an Arrhenius type of reaction because of the lower shock temperature resulting from double shocking. This conclusion is supported by experiments on single crystals of HMX and by shock temperature calculations. The time required for desensitization of PBX-9404 is related to pressure by the expression p/sup 2.2/tau = 1150. 21 references, 5 figures, 5 tables.
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Category :
Languages : en
Pages : 5
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Preshocking delays initiation of PBX-9404 and PBX-9501, relative to unshocked material. In PBX-9404 preshock experiments, a first shock of 2.3 GPa was followed 0.65 [mu]s later by a second shock of 5.6 GPa. In PBX-9501, a preshock of 2.8 GPa and 0.32 us duration was followed by an initiating shock of 6.0 GPA. Both PBX explosives show clear desensitization while the preshock persists. In PBX-9404, initiation of detonation occurs nearly as anticipated for the material, after coalescence of the preshock and main shock into a single wave. Multiple embedded magnetic gauges were used to measure the shock histories. Our data indicates a slightly longer run to detonation than expected, even though a single wave is initiating the material. A slight stress reduction at coalescence, as required by the shock dynamics, may be responsible for the overrun. A reactive waste is clearly evident while the preshock persists. The long run to detonation indicates that this reactive wave is not driving the initiation. A set of four preshock experiments were preformed on PBX-9502, which is unreactive at these pressures, to investigate the shock dynamics of the two waves in the HE.
Author: Roger Cheret
Publisher: Springer Science & Business Media
ISBN: 1461392845
Category : Science
Languages : en
Pages : 442
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This work marks a stage in the evolution of a scientific and technical field which has been developed by the Commissariat a l'Energie Atomique (CEA) over several decades. Many members of the staff of the CEA have won re nown in this field, and their work has brought it to the high degree of excel lence for which it is internationally recognized today. These scientists had to consider every aspect of the field, as it concerned: modeling, which has recourse to fluid thermodynamics, molecular phys ics, and chemistry; numerical evaluation, which relies on mathematical analysis and data processing; and experiments in the firing area, which require specific stress generators and instrumentation. Whilst this book is a testament to the activity and success of staff of the CEA, it also reviews a number ofthe advances made in the discipline. How ever, it is not intended to be an exhaustive account of those advances; it is assumed that the reader can, if desired, consult the standard monographs, and more recent, more specialized works (notably W.C. Davis and W. Fickett, and C.L. Mader). The history of the discipline is interesting in itself, and also as an illustra tion of the causes which lead to progress in a coherent body of scientific work. I should like to make some comments on this progress, of which there is a fascinating summary in the introduction, and which will figure largely throughout the work.
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Category : Acoustic phenomena in nature
Languages : en
Pages : 1126
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Author:
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Category : Acoustic phenomena in nature
Languages : en
Pages : 1120
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