Investigating the focusing effect of charge geometry with computer simulations, witness plates, and high-speed videography

Scaled distance is used to calculate a safe standoff radius from the detonation of a known mass of an explosive. It has been shown that varying only the geometry of the charge significantly overdrives regions of the blast wave potentially resulting in hazardous overpressure levels at scaled distance safe radii. Pressure transducers are used to measure overpressure surrounding spherical, cylindrical, and cubic charges to determine if bridge waves were formed at the edges between flat sides as seen in published studies of cylindrical charges. In the fireball field a witness plate is used to evaluate radial energy distribution with a novel modification to the plate dent test. In the near field blast wave overpressure is measured utilizing a novel optical time of arrival method to measure blast wave overpressure. The empirical investigations are supported with 2-dimensional computer simulations of a circle, triangle, rectangle, and star of equal dimensions to those used in the empirical testing. In the near field the overpressure from primary waves normal to the flat sides of the triangle and rectangle produced an overpressure up to 3.5 times that of the circle. For the star the significant overdriving observed in the fireball field is not seen in the near field where the blast wave resembles that of the cylinder. These two results indicate that pressures within the fireball and near fields can be significantly increased without increasing charge mass. An added benefit to breachers and researchers appears to be that when the overdriven blast wave has reached K-18 distances in the far field the pressures may have decayed below the damage thresholds used to determine K-18 safe standoff distances, but further studies are necessary to validate this observation --Abstract, page iv