Blast Waves

The Negative Phase of the Blast Load

“…Bryant et al [10] provided both numerical and experimental examples of situations where the Figure 1. Idealised pressure-time profile for a reflected blast wave negative phase causes adverse target response, and also highlighted the limitations of shock tube testing to accurately replicate free-field negative phase pressures and impulses, on account of the inability of a shock tube to replicate the effect of the rising fireball [11]. Whilst these studies show that the negative phase cannot be ignored for certain blast scenarios, and indeed some effort has been undertaken to define the situations where ignoring the negative phase is un-conservative, there remains some uncertainty on the issue of how to properly model the form of the negative phase pressure-time history.…”

“…In free-field blast experiments, the rising fireball creates a lower pressure near the ground surface, which draws in the surrounding air. This has the effect of further lowering the air density, which has already been over-expanded after the shockwave has passed, and hence results in larger negative phase impulses at larger stand-off distances [11]. , giving a period of zero pressure between the linear positive and negative phase.…”

Fireball and shock wave dynamics in the detonation of aluminized novel munitions

“…The RDX detonation pressure is roughly two orders of magnitude greater than the case strength for a typical steel case. For the mild steel case in the present work, it is reasonable to assume that less than 1% of the detonation energy is required to rupture the steel casing material [32]. The test articles in the present work are considered moderate to heavily cased charges because the 27.2-kg steel case in the present work gives case-to-charge mass ratios that range from 1.6 to 4.…”

“…A case-to-charge mass ratio in this range could result in the casing fragment kinetic energy that is about 50% of the detonation energy [32]. In other words, up to about half of the detonation energy could be used in propelling the case fragments.…”

“…In other words, up to about half of the detonation energy could be used in propelling the case fragments. Less than 1% of the detonation energy is lost in the form of thermal and visible radiation [32]. The remainder of the detonation energy is available to generate a blast wave.…”