Testing apparatus for the spatial and temporal pressure measurements from near-field free air explosions

摘要

Accurate quantification of the loading on a structure resulting from the impingement of a blast wave following a high explosive detonation is crucial if analysts are to be able to determine the viability of protective structures. This is of particular importance in the case of near-field explosive detonations, where the magnitude of the loading is extremely high, and highly spatially non-uniform over the face of the target. This loading can result in localised failure of structural targets due to brisance or rear-face spalling (predominantly load magnitude related phenomena) or shear failure due to spatially non-uniform impulse take-up of the target (predominantly impulse related phenomenon). However, no clear and simple guidance exists on how to define the magnitude and spatial variation of very near-field blast loading. Whilst it is possible to use numerical modelling approaches to simulate the detonation, air-shock propagation and shock-structure interaction, little definitive, well controlled experimental data exists to validate such models. This paper presents an experimental methodology that has been developed in part to enable such experimental data to be gathered. The experimental rig 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. A new finite element based method is introduced which allows for correction of the effects of dispersion of the propagating waves in the pressure bars, enabling accurate characterisation of the peak pressures and impulses from these loadings.