Observations from Preliminary Experiments on Spatial and Temporal Pressure Measurements from Near-Field Free Air Explosions

Abstract

It is self-evident that a crucial step in analysing the performance of protective structures is to be able to accurately quantify the blast load arising from a high explosive detonation. For structures located near to the source of a high explosive detonation, the resulting pressure is extremely high in magnitude and highly non-uniform over the face of the target. There exists very little direct measurement of blast parameters in the nearfield, mainly attributed to the lack of instrumentation sufficiently robust to survive extreme loading events yet sensitive enough to capture salient features of the blast. Instead literature guidance is informed largely by early numerical analyses and parametric studies. Furthermore, the lack of an accurate, reliable data set has prevented subsequent numerical analyses from being validated against experimental trials. This paper presents an experimental methodology that has been developed in part to enable such experimental data to be gathered. The experimental apparatus comprises an array of Hopkinson pressure bars, fitted through holes in a target, with the loaded faces of the bars flush with the target face. Thus, the bars are exposed to the normally or obliquely reflected shocks from the impingement of the blast wave with the target. Pressure-time recordings are presented along with associated Arbitary-Langrangian-Eulerian modelling using the LS-DYNA explicit numerical code. Experimental results are corrected for the effects of dispersion of the propagating waves in the pressure bars, enabling accurate characterisation of the peak pressures and impulses from these loadings. The combined results are used to make comments on the mechanism of the pressure load for very near-field blast events.

Experimental Measurement of Specific Impulse Distribution and Transient Deformation of Plates Subjected to Near-Field Explosive Blasts

“…An alternative, developed in 1914 by Bertram Hopkinson, is the apparatus now known as the Hopkinson pressure bar (HPB) [9], consisting of a length of cylindrical bar which propagates an elastic stress pulse along its axis to be recorded by sensitive equipment situated a safe distance from the loaded end. Whilst it is now more commonly used in its 'split' form for high strain-rate material testing [10], the HPB is still a valuable tool for measuring highmagnitude, short-duration loading [11][12][13][14][15][16]. HPBs are used in this study at UoS to record the spatial and temporal distribution of loading acting on a rigid target located close to an explosive.…”

Displacement timer pins: An experimental method for measuring the dynamic deformation of explosively loaded plates

“…The experimental proof-of-concept presented in this article was chosen specifically for a case where existing numerical modelling approaches can offer suitable verification [2]. In concept, however, the DTP approach is not limited by this requirement and can be used for measuring deflection of complex target geometries and materials, confined or internal explosions, and vehicle undersides subjected to shallow buried explosives.…”

“…When a blast wave resulting from a high explosive detonation interacts with a structure located close to the explosive, the magnitude of the resulting transient blast load is extremely high and highly spatially non-uniform over the face of the structure [1,2]. This has the potential to cause significant damage to key building components, and poses a considerable risk to vehicles and civilians, particularly if the explosive is buried within a soil and its effects are focussed vertically by the surrounding soil mass.…”

A review of Pochhammer–Chree dispersion in the Hopkinson bar

“…Using one-dimensional stress wave theory, Davies was able to link the longitudinal particle velocity and radial displacement to the stress in the bar, that is the applied pressure). In more recent HPB experiments, axial and/or radial strain in the bar is most frequently measured using electrical resistance or semi-conductor strain gauges mounted on the bar perimeter, for example Puckett andPeterson (2005a, 2005b), Cloete and Nurick (2016), Rigby et al (2015Rigby et al ( , 2016, Tyas and Ozdemir (2014) and Tyas et al (2016).…”