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Zhang F.,Defence R&D CanadaSuffield | Ripley R.C.,Martec Ltd. | Yoshinaka A.,Defence R&D CanadaSuffield | Findlay C.R.,Defence R&D CanadaSuffield | And 2 more authors.
Shock Waves | Year: 2015

The detonation performance of a more than 70,000 m3 fuel spray-air cloud is experimentally investigated using dispersal of a 5,090 kg gasoline payload by a central explosive in a cylindrically stratified configuration. The large-scale explosive dispersal data are further analyzed, together with a revisit of the data from previously conducted small-scale experiments and numerical simulations, to study particle jetting instabilities. The experiments depict a dual hierarchical jet structure consisting of primary particle jets overlapped by fine particle jets on the primary surfaces. Both jet systems form within the expansion of 1.5–2 times the initial charge diameter. The fine droplet jets are numerous initially as a result of surface instabilities or fragmentation of the charge casing, while the primary jets have a limited number emerging out of the surface of fine jet structures later in time. The number of primary jets is consistent with the number of incipient radial fractures observed at the payload surface. From this fact, an instability mechanism is suggested that the formation of primary particle jets may originate in the perturbations that develop near the interior interface between explosive and payload, through non-uniform density effects or casing fragmentation, driven by the explosive detonation and subsequent expansion of the high-pressure detonation products. Numerical modeling using liquid payload fragmenting into droplet particles has been applied to investigate the proposed mechanism. The numerical results show that the high-pressure jets of detonation products, created from the interior casing fragmentation, radially fracture the payload. The resulting compressed radial filaments, developed within the payload, lead to the primary jets emerging between the radial fracture points at the payload surface. The number of interior payload filaments before payload surface bursting, and hence the number of primary jets, is controlled by the number of inner casing fragments at the explosive-payload interface. Furthermore, the number of primary jets is also influenced by the mass ratio of payload to explosive and inner casing fragment pattern, whereas the perturbations induced by minor fragments will dissipate through the large payload and not result in final filaments. © 2014, Her Majesty the Queen in Right of Canada.

Desilets S.,Canadian Department of National Defence | Brousseau P.,Canadian Department of National Defence | Chamberland D.,Canadian Department of National Defence | Singh S.,Canadian Explosives Research Laboratory | And 4 more authors.
Thermochimica Acta | Year: 2011

The decomposition of urea nitrate (UN) was studied using adiabatic and non-isothermal calorimetry techniques. Gas species released were identified and quantified in situ using TG-infrared spectroscopy/mass spectrometry and molar proportions of these gases were evaluated. A decomposition mechanism at high temperature was proposed based on the nature and sequences of gaseous species observed combined with literature data on decomposition of intermediate products formed. Non-isothermal decomposition kinetics of urea nitrate were measured using variable heating rates to give activation energies E/kJ mol-1 = 206 and 113 with preexponential factors Ln Z/min-1 = 47 and 21, in a closed and open system, respectively. In these systems the major UN decomposition step is strongly coupled to an endothermic dissociation reaction. Species remaining after this exothermic decomposition showed only minor exothermicity at higher temperatures. This is contrasted with the onset to adiabatic decomposition which occurred ∼30 °C below the apparent melting point (155-156 °C), and where solid (condensed) species are available. © 2011 Elsevier B.V. All Reserved rights.

Desilets S.,Defence RandD Canada | Brousseau P.,Defence RandD Canada | Chamberland D.,Defence RandD Canada | Singh S.,Canadian Explosives Research Laboratory | And 3 more authors.
Thermochimica Acta | Year: 2011

Aging and degradation of urea nitrate below the melting point, at 100 °C, was studied by using thermal analysis and spectroscopic methods including IR, Raman, 1H and 13C NMR techniques. It was found that urea nitrate was completely degraded after 72 h at 100 °C into a mixture of solids (69%) and released gaseous species (31%). The degradation mechanism below the melting point was clearly identified. The remaining solid mixture was composed of ammonium nitrate, urea and biuret while unreacted residual nitric and isocyanic acids as well as traces of ammonia were released as gaseous species at 100 °C. The thermal stability of urea nitrate, under extreme storage conditions (50 °C), was also examined by isothermal nano-calorimetry. © 2011 Elsevier B.V. All Reserved rights.

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