The Effect of Ambient Pressure on Blast Reflected Impulse and Overpressure

Abstract

Reflected blast pressure and impulse for bare 226.8 g spherical C-4 charges under various atmospheric pressure conditions were studied both experimentally and numerically. Blast pressure measurements were conducted using an array of high resonant frequency tourmaline-based piezoelectric pressure transducers to record normally reflected blast pressure histories at a 61 cm standoff. The explosive detonation and pressure measurements were conducted inside a pressure vessel which allowed the ambient pressure surrounding the C-4 charge to be varied. The recorded pressure histories were analyzed for blast wave arrival time, peak reflected overpressure, and positive phase impulse. The numerical analysis of blast pressures under varying ambient conditions was conducted using an axi-symmetric Arbitrary Lagrangian Eulerian (ALE) finite element technique with LS-DYNA. Numerical predictions were carried out for a 61 cm standoff that allowed direct comparison to the measured data. Additionally, the ALE simulations considered the effects of ambient pressure on blast impulse for varying standoff distances in the range of 12.7 to 61 cm. At a 61 cm standoff, measured peak reflected pressures showed no significant effect of varying ambient pressure while normally reflected impulses increased with increasing ambient pressure. Predictions by LS-DYNA for standoffs less than 61 cm showed a decreasing effect of ambient pressure on the normally reflected impulse as the standoff distance decreased. For small standoff distances it was predicted that the effects of ambient air pressure on normally reflected impulse were not significant. As the standoff distance between the explosive charge and the reflecting structure increases, higher ambient air pressures did cause a significant increase in reflected impulse.