Calculation of jet characteristics from hydrocode analysis

Abstract

The penetration performance of a shaped charge jet is affected strongly by factors such as straightness, stretch rate, and breakup time. Straightness is related to manufacturing tolerances, assembly techniques, and system integration features. Stretch rate and breakup time are controllable features of charge design. A higher stretch rate is desirable for short standoff performance. The stretch rate is easily altered by a change of explosive or modification of the angle with which the detonation wave sweeps the liner surface, however, an increased stretch rate generally results in a decreased breakup time. Many of the recent gains in shaped charge performance have been made possible by increasing the effective breakup time of the jet. Several models exist for calculating breakup time. They include analytic models, such as Chou & Carleone’s dimensionless strain rate model, and empirical or semi-empirical models such as Walsh’s theory and those proposed by Pearson, et al. These models can be applied to raw hydrocode calculation data and used to determine a Jet Characterization (JC) file. The JC file can then be used to perform further calculations, such as Penetration Versus Stand Off (PVSO) curves. This paper details adaptation of the Chou & Carleone model for predicting breakup time using hydrocode data. The hydrocode is used to determine the physical parameters of the jet which are then extrapolated back to a virtual origin for breakup time calculation. This results in a model that is design independent, relying on hydrocode determination of jet variables. The model implementation will be discussed, and comparisons of predicted jet characteristics will be made to test data for several charge geometries.