Characterisation of Near-field Blast Loading

The near-field is the period of contact between the explosively generated fireball and shock-wave, prior to detaching. Loading is of extreme pressures, short timescales and subject to variability of specific impulse in terms of both spatial distribution and magnitude. Assessment of near-field loading requires evaluation of magnitude, spatial distribution and variability, including how each is affected by scaled distance.

An experimentally driven study, characterising near-field blast loading from spherical charges across five scaled distances of 0.17-1.03 m/kg1/3 is presented. The methodology utilises digital image correlation to determine full field spatial resolution of structural response and loading data. An approach to inferring specific impulse from the velocity uptake of the plate is demonstrated and assessed.

Loading data is presented as a series of specific impulse distributions, characterising the magnitude, shape profile and variability. The results of all tests fit to a bell-shaped trend of centrally normalised specific impulse, which forms the basis of a two-part rapid predictor of near-field loading. This model is validated against experimental results and compared with other fast-running models. Loading variability is rigorously assessed and shown to be greater at scaled distances less than 0.5~m/kg m/kg1/3. An investigation of early-time features in the loading reveals they do not directly influence the spread in loading magnitude. However, it is noted that greater temporal resolution within the data may reveal the effect that time of arrival has on the loading imparted across the plate.

This thesis characterises near-field loading magnitude at a spatial resolution that is not viable with direct measurement techniques across scaled distances of 0.17-1.03 m/kg1/3. Furthermore, it has provided tools with which a blast engineer can rapidly predict the loading a protective structure must withstand when exposed to close proximity explosive events.