Experimental characterisation of near-field blast loading using digital image correlation on thin plates

Direct measurement of near-field blast loading is seldom in the academic literature, and currently available techniques either produce a small number of discreet temporal measurements, or a single time- and area-integrated value. This limitation is addressed in the current work through the use of stereo high-speed video cameras and Digital Image Correlation (DIC); a technique typically used to determine temporally-resolved, full-field deformation of flexible plates subjected to blast loading. Herein, the focus is on the very first instants of plate response, from which distributions of initial velocity are measured, and– through conservation of momentum– specific impulse is inferred. In total, 29 experiments were performed at 5 different scaled distances covering the entire near-field range (0.17–1.03 m/kg1/3). Plate displacements were recorded at 100,000 fps and around 2100 points on the plate surface, effectively enabling full-field measurements of near-field loading distributions, which has previously been unattainable. The results are used to comment on the form and magnitude of blast loading, which ranges from highly centralised, high magnitude loading in the extreme near-field, to relatively uniform, low magnitude loading in the late far-field. The results also show distinct regions of increased localised variability in loading in the mid near-field range, and it is suggested that an idealised, deterministic loading model is not appropriate to capture the true complexity of loading in this region.