Modelling ‘hot-spot’ initiation in heterogeneous solid explosives

2000 ◽  
Author(s):  
N. J. Whitworth
Keyword(s):  
Hot Spot ◽  
Solid Explosives ◽  
Heterogeneous Solid

Hot-spot reaction under transient pressure conditions

1987 ◽  
Vol 413 (1845) ◽  
pp. 329-350 ◽  
Keyword(s):  
Hot Spots ◽  
Hot Spot ◽  
Thermodynamic Description ◽  
Exothermic Reaction ◽  
Pressure Change ◽  
Variable Pressure ◽  
Transient Pressure ◽  
Physical Mechanisms ◽  
Solid Explosives ◽  
Condensed Phase Explosives

The initiation of condensed-phase explosives is often caused by hot spots; that is, localized regions of high temperature created by a variety of physical mechanisms, particularly in solid explosives. Once the hot spots are created, further temperature change is governed by (i) self-heating due to chemical reaction, (ii) heat loss by conduction and radiation, and (iii) adiabatic effects due to pressure and specific volume variation. The last effect includes both self-induced pressure change due to thermal expansion against the surroundings, and externally generated pressure change when initiation is attempted by mechanical impact. This paper presents a thermodynamic description of exothermic reaction under conditions of variable pressure and volume. The reaction rate is assumed to be a function of temperature only. The effect of variable pressure enters through its influence on temperature. It is demonstrated that the effects of self-induced pressure change are small. In the case of externally generated pressure change, explosion times can be affected drastically. These results are discussed in terms of initiation by shock waves of finite duration.

scholarly journals Initiation of solid explosives by impact and friction: the influence of grit

1949 ◽  
Vol 198 (1054) ◽  
pp. 337-349 ◽  
Keyword(s):  
Melting Point ◽  
Hot Spots ◽  
Hot Spot ◽  
Threshold Value ◽  
Maximum Temperature ◽  
Melting Points ◽  
Solid Explosives ◽  
Lower Melting Point ◽  
Determining Factor ◽  
Spot Temperature

This paper describes an experimental study of the initiation of solid explosives, and in particular the effect of artificially introducing transient hot spots of known maximum temperature. This was done by adding small foreign particles (or grit) of known melting-point. The minimum transient hot-spot temperature for the initiation of a number of secondary and primary explosives has been determined in this way. It is shown that the melting-point of the grit is the determining factor , and all the grits which sensitize these explosives to initiation either by friction or impact have melting-points above a threshold value which lies between 400 and 550 ° C. Grit particles of lower melting-point do not sensitize the explosives. The same explosives initiated by the adiabatic compression of air required, for initiation, minimum transient temperatures of the same order as the threshold melting-point values. The results provide strong evidence that the initiation of solids as well as of liquids by friction and impact is thermal in origin and is due to the formation of localized hot spots. There is evidence that in the case of the majority of secondary explosives which melt at comparatively low temperatures, intergranular friction is not able to cause explosion and the hot spots must be formed in some other way. With the primary explosives which explode at temperatures below their melting-points, hot spots formed by intergranular friction can be important.

scholarly journals Modelling the Fluctuations of Reactive Shock Waves in Heterogeneous Solid Explosives as Stochastic Processes

2019 ◽  
Vol 45 (2) ◽  
pp. 295-315 ◽  
Author(s):  
David E. Kittell ◽  
Cole D. Yarrington ◽  
Jeremy B. Lechman ◽  
David L. Damm ◽  
Melvin R. Baer
Keyword(s):  
Shock Waves ◽  
Stochastic Processes ◽  
Solid Explosives ◽  
Heterogeneous Solid

scholarly journals Birth and growth of explosion in liquids and solids initiated by impact and friction

1949 ◽  
Vol 198 (1054) ◽  
pp. 350-372 ◽  
Keyword(s):  
Hot Spot ◽  
Time Lag ◽  
Mass Movement ◽  
Striking Similarity ◽  
Time Lags ◽  
Low Velocity ◽  
Viscous Liquids ◽  
Low Viscosity ◽  
Solid Explosives ◽  
First Moment

The birth and growth of explosions initiated by mechanical and thermal means have been studied. Liquid and solid explosives show a striking similarity. The point of initiation is always located at a source of local high temperature, for example, a hot wire, an electric spark, an impacted grit particle, or at a gas pocket suddenly compressed during impact. There is an appreciable time lag between the first moment of impact and the first appearance of light from the explosion. With secondary explosives the time lag depends on the conditions of impact (it could be varied from 60 to 150 μsec.), but for all the explosives studied the delays under similar conditions are approximately the same. For the primary explosives the time lags are usually much shorter, indicating that a different mechanism of initiation may be operative. The first stage of explosion in liquids is a burning which begins slowly and accelerates to speeds of 500 or even 1000 m./sec. This speed may represent, in the main, a mass movement of the gas products away from the centre of explosion. In most solid explosives (both primary and secondary) the first stage is again a slow burning which accelerates to speeds of several hundred metres per sec. A second stage of constant velocity detonation then sets in. The detonation velocity (which varies from 1100 to 2300 m./sec. according to the explosive and the physical conditions of the layer) may be identified with the low-velocity detonation in large charges, and the correct order of velocity has been explained on hydrodynamic grounds. It is suggested that the continued propagation of the low-velocity detonation stage in a liquid is made possible by the rapid breaking up of the explosive by the detonation shock front, particularly if the liquid has a low viscosity. In more viscous liquids and solids propagation is possible only if hot-spot sources are present in the explosive. The hot spots may be developed by rapid compression of gas pockets, or, if the solid has a high enough meltingpoint, by intercrystalline friction.

Mutation Spectrum in Patients with Wiskott-Aldrich Syndrome and X-linked Thrombocytopenia: Identification of Twelve Different Mutations in the WASP Gene

1996 ◽  
Vol 75 (04) ◽  
pp. 546-550 ◽  
Author(s):  
Marianne Schwartz ◽  
Albert Békássy ◽  
Mikael Donnér ◽  
Thomas Hertel ◽  
Stefan Hreidarson ◽  
...  
Keyword(s):  
Base Pair ◽  
Hot Spot ◽  
Missense Mutations ◽  
Nucleotide Substitutions ◽  
Exon 2 ◽  
Wiskott Aldrich Syndrome ◽  
Base Pair Deletion ◽  
Reliable Diagnosis ◽  
Wasp Gene ◽  
Detection Of Mutations

SummaryTwelve different mutations in the WASP gene were found in twelve unrelated families with Wiskott-Aldrich syndrome (WAS) or X-linked thrombocytopenia (XLT). Four frameshift, one splice, one nonsense mutation, and one 18-base-pair deletion were detected in seven patients with WAS. Only missense mutations were found in five patients diagnosed as having XLT. One of the nucleotide substitutions in exon 2 (codon 86) results in an Arg to Cys replacement. Two other nucleotide substitutions in this codon, R86L and R86H, have been reported previously, both giving rise to typical WAS symptoms, indicating a mutational hot spot in this codon. The finding of mutations in the WASP gene in both WAS and XLT gives further evidence of these syndromes being allelic. The relatively small size of the WASP gene facilitates the detection of mutations and a reliable diagnosis of both carriers and affected fetuses in families with WAS or XLT.

Challenges to immigrant associations and NGOs in contemporary Greece

2013 ◽  
Vol 10 (3) ◽  
pp. 342-358 ◽  
Author(s):  
Apostolos G. Papadopoulos ◽  
Christos Chalkias ◽  
Loukia-Maria Fratsea
Keyword(s):  
Civil Society ◽  
Economic Crisis ◽  
Hot Spot ◽  
Geographical Range ◽  
Legal Form ◽  
Social Actors ◽  
Governmental Organizations ◽  
Non Governmental Organizations ◽  
Migrant Integration ◽  
Concentration Patterns

The paper explores the challenges faced today, in a context of severe economic crisis, by immigrant associations (ΙΜΑs) and Non-Governmental Organizations (NGOs) in Greece. The data analysed here was collected between October 2009 and February 2010 and incorporates references to all recorded migration-related social actors operating in Greece. The paper takes into account such indicators as legal form, objectives, financial capacity and geographical range of activity, concluding with a typology of civil society actors dealing with migration issues. This study aims at informing the migration policymaking and migrant integration processes. By a spatial hot-spot clustering of IMAs and NGOs, we also illustrate the concentration patterns of civil society actors in Greece.

Sun Load Analysis and Testing on Automotive Front Lighting Products

2020 ◽  
pp. 116-122
Author(s):  
Emre Öztürk ◽  
Mehmet Aktaş ◽  
Tunç Şenyüz
Keyword(s):  
Prolonged Exposure ◽  
Hot Spot ◽  
Load Test ◽  
Angle Of Incidence ◽  
The Sun ◽  
Solar Simulator ◽  
Automotive Lighting ◽  
Inclination Angles ◽  
Plastic Parts ◽  
Load Simulation

The purpose of this research is to reach good correlation between sun load simulation and solar focusing test for exterior automotive lighting products. Light coming from sun is highly collimated (parallel rays) and focusable from lenses with concave structure. Focusing incidence leads to a hot spot on lens surrounding plastic parts which may cause melting failures at high temperature zones. Sun load simulation is performing to eliminate risk of discoloration, deformation, out gassing, coating failures and fire with prolonged exposure from field. Irradiance values in W/m2 defined in simulation as heat source depending of an angle of incidence of the sun radiation. At first step, simulation is performing with 5 degree intervals to define the critical zones then intervals decreased to 2 degree to detect the critical azimuth and inclination angles. Critical azimuth and inclination angles is checking with ray trace analysis to check the bouncing of sun rays and possible solution to eliminate focuses with design solutions. After numerical analysis to release and validate the automotive lighting products regarding the sun load test, measurement with first parts is necessary. Measurement is performing for all critical angles which have been detected at simulation with thermal camera under ultra high-collimation solar simulator. Measured temperatures are settled according to environment conditions and correlation is checking with simulations.

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