Experimental measurement of specific impulse distribution and transient deformation of plates subjected to near-field explosive blasts

The shock wave generated from a high explosive detonation can cause significant damage to any objects that it encounters, particularly those objects located close to the source of the explosion. Understanding blast wave development and accurately quantifying its effect on structural systems remains a considerable challenge to the scientific community. This paper presents a comprehensive experimental study into the loading acting on, and subsequent deformation of, targets subjected to near-field explosive detonations. Two experimental test series were conducted at the University of Sheffield (UoS), UK, and the University of Cape Town (UCT), South Africa, where blast load distributions using Hopkinson pressure bars and dynamic target deflections using digital image correlation were measured respectively. It is shown through conservation of momentum and Hopkinson-Cranz scaling that initial plate velocity profiles are directly proportional to the imparted impulse distribution, and that spatial variations in loading as a result of surface instabilities in the expanding detonation product cloud are significant enough to influence the transient displacement profile of a blast loaded plate

A continuum model of nanocrystalline metals under shock loading

Nanocrystalline metals, i.e., polycrystalline metals with grain sizes in the nanometer range, have recently elicited significant interest due to their potential for achieving higher material strength, especially under shock loading, reaching strength as much twice the value under normal conditions. The main source of deformation, grain-boundary sliding, has been found to be coupled to friction-like mechanisms decreasing the proportion of sliding resistance by an amount proportional to the applied normal stress. In this work, we propose a continuum model describing the competing deformation mechanisms believed to determine the effective response of nanocrystalline materials. A phenomenological model considering grain boundary sliding and accommodation as uncoupled plastic dissipative deformation mechanisms is formulated to describe the constitutive behavior of grain boundaries. A Mohr-Coulomb friction model is then added by considering the normal stress as an inhibiter of sliding, in agreement with molecular dynamics findings. The model proposed aims at capturing the main feature of the effective behavior afforded by atomistic descriptions at a much lower cost, i.e., without the need of tracking the evolution of individual atoms. Copyright © 2006 by MIT

The Negative Phase of the Blast Load

Following the positive phase of a blast comes a period where the pressure falls below atmospheric pressure known as the negative phase. Whilst the positive phase of the blast is well understood, validation of the negative phase is rare in the literature, and as such it is often incorrectly treated or neglected altogether. Herein, existing methods of approximating the negative phase are summarised and recommendations of which form to use are made based on experimental validation. Also, through numerical simulations, the impact of incorrectly modelling the negative phase has been shown and its implications discussed