Characterising blast loading from non-spherical charges in the near-field.

Near-field blast loading from non-spherical explosive charges differs markedly from that of equivalent spherical charges, yet the extent and spatial character of these differences remain poorly quantified. This has significant implications for blast-resistant design and threat characterisation, where spherical equivalence is commonly assumed but may be inadequate for elongated charges at close range. Whilst far-field blast waves from all charge geometries converge towards a spherical form, early-time near-field loading is highly dependent on charge geometry and orientation. This work provides, for the first time, a detailed spatial and temporal dataset against which theoretical and computational predictions can be assessed.

Experiments were conducted at the Characterisation of Blast Loading (CoBL) facility, University of Sheffield, measuring reflected pressure–time histories from 200 g C4 cylindrical charges (7:1 length-to-diameter ratio) at a cleared standoff of 250 mm. Orientations spanned radial to axial, including intermediate inclinations of 22.5°, 45° and 67.5° and end-detonated variants of the radial and axial configurations. An array of up to seventeen Hopkinson pressure bars enabled simultaneous measurement of localised loading at discrete positions, capturing its spatial variability and temporal development across the target face. Results were compared with equivalent spherical charges to quantify the influence of geometry and orientation on reflected pressure and specific impulse.

Charge orientation profoundly influences near-field loading. Radially oriented cylinders impart approximately twice the total impulse of an equivalent sphere to the measurement area, whilst axially oriented charges impart approximately half, a four-fold difference between the cylindrical extremes. The transition is non-monotonic: 45° and 67.5° orientations produce lower total impulse than even the axial case, attributed to measurement positions lying within a bridging wave zone between the primary radial and end wave regions. Repeatability is high for total impulse, though considerable localised variability occurs at individual positions, consistent with chaotic near-field processes.