Browsing by Author "Alford, Roland"

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    An experimental method of determining explosive equivalency when scaled distance approaches zero
    (International Society of Explosives Engineers, 2024-01-01) Alford, Roland; Hazael, Rachael; Critchley, Richard
    The ability to compare explosives is fundamental. Numerous methods are used and while simple conversion factors are often used, the use of TNT Equivalency (TNTe) is not a simple subject as explosives exhibit very different equivalencies depending on whether the pressure or impulse are being considered as well as other conditions. The scaled distance has been found to have a significant effect on the TNTe but due to the difficulty of taking measurements at very close ranges, no TNTe have been quoted for charges in direct contact (Z=0). This paper describes the use of a ballistic pendulum to measure the impulse from contact charges and presents some surprising results that require a two-stage propulsion, as originally described by Backofen, to be explained.
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    Are low-yield explosive ordnance disposal methods viable?
    (IMCSE, 2022-10-01) Alford, Roland; Hazael, Rachael; Critchley, Richard
    In 2021 reports began to appear online regarding a new underwater UXO clearance tech that produced a “low-yield” result. It claimed that the technology used did not cause deflagration (burning) but resulted in the munitions breaking up and scattering, causing the explosives to dissipate. The system used was referred to by the brand name Hydra-Jet.[1] Review of available material shows that at Seagreen Offshore Wind Farm, currently being constructed 27km off the Scottish coast in the North Sea [2], three sea mines were attacked using the Hydra-Jet and all three interventions either caused a detonation or a partial detonation. It is unlikely that this technology is 100% reliability and appears to show no improvement over proven low-order techniques such as shaped charges that use low-density reactive liners.[3] It is thought likely that the disruptive effect is produced by overpressure from the charge, placed at close range to the target causing high pressures that are designed to result in physical break-up of the munition rather than any more complex mechanism. The pressure readings taken of the events show that they strongly indicate that at least some of the explosives detonated. The published pressure measurements, indicating that there had been at least partial detonations, were reported to have presented a risk of harm to wildlife (harbour porpoise within approximately 4km) despite the results not having breached the operator’s licence thresholds.[4,5] The latest data from trials conducted by the national Physical Laboratories and Loughborough University might offer guidance for more stringent but achievable thresholds for future work.[6]
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    Experimental Measurement of TNT Equivalency For Contact Charges
    (Cranfield University, 2024-01-19T12:36:00Z) Alford, Roland
    The ability to compare explosives is fundamental. Numerous methods are used and while 10 simple conversion factors are often used, the use of TNT Equivalency (TNTe) is not a 11 simple subject as explosives exhibit very different equivalencies depending on whether the 12 pressure or impulse are being considered as well as other conditions. The scaled distance has 13 been found to have a significant effect on the TNTe but due to the difficulty of taking 14 measurements at very close ranges, no TNTe have been quoted for charges in direct contact 15 (Z=0). This paper describes the use of a ballistic pendulum to measure the impulse from 16 contact charges and presents some surprising results that require a two-stage propulsion, as 17 originally described by Backofen, to be explained.
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    Introducing the combustion continuum to define the transition points between burning, deflagration, and detonation regimes of energetic materials
    (Taylor and Francis, 2024-12-28) Alford, Roland; Hazael, Rachael; Critchley, Richard
    This paper introduces what the authors term Combustion Continuum which treats oxidation reactions of energetic materials as lying on a continuum in which the variable is the speed of reaction. It divides the continuum into three regions, burning, deflagration, and detonation (BDD) and defines the transition points between each region and describes various observable effects that allow definitive identification of the type of reaction. The transition point between combustion and deflagration is defined as the onset of an atmospheric shock wave, which is the first time deflagration has been defined in such a way that the point of transition can be observed and fixed. The transition point between deflagration and detonation is well defined elsewhere and is the point at which the reaction shocks-up to produce a shock wave driven detonation front. This approach contrasts with most literature that treats burning, deflagration and detonation as interrelated forms of energetic reaction with none giving precise definitions that allow a full understanding of the difference between them and most critically, how to determine whether a reaction is burning or deflagration.
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    Is TNT Equivalency Still Useful?
    (Cranfield University, 2024-01-22T14:12:55Z) Alford, Roland
    Poster contribution to the Defence and Security Doctoral Symposium 2023
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    Modular ballistic pendulum for measurement of impulse from tamped explosives
    (OneMine.Org, 2023-02-06) Alford, Roland; Hazael, Rachael; Critchley, Richard
    The ballistic pendulum is a well-established piece of test equipment originally developed for estimating the velocity of bullets and projectiles. When trying to understand the effects of different tamping methods on explosive performance, the ballistic pendulum is an excellent tool allowing calculation of explosive charge impulse. Most ballistic pendula for this application are limited to narrow impulse ranges as the pendulum mass determines the angle of swing; and a mass capable of being moved by a small charge would be far too small for a larger charge. This paper describes a modular design (the Alford Modular Ballistic Pendulum) which overcomes this problem.