Technical report | Target Plate Deformation Time-History from a Detonating Buried Charge in Various Sand Media

ABSTRACT

The present work analysed the influence of the sand/soil media for deforming a target plate in response to loading from a buried explosive charge. Flash x-ray technique was used to capture the plate deformation as a measure of the momentum transfer to the target. The target response was assessed experimentally for a variety of sands and a soil to investigate the effect of the sand parameters. The experiments used an axisymmetric cylindrical setup to enable easier comparison with numerical simulations in two-dimensions. The experiments were used to validate a two-phase model for the sand which has been implemented in the CTH hydrocode. Simulation results are in good agreement with the experiments and demonstrate a high fidelity description of the sand behaviour with the two-phase model.

Executive Summary

The present report expands on the analysis of the loading from a buried improvised explosive device (IED) for a variety of sands and soils, where it was considered for only dry calcite sand in a previous DST report. The momentum transfer to a target, which is important for vehicle occupant survivability, was assessed from the deformation of a target plate, which represents the vehicle floor. The target plate was subjected to loading from a high explosive (HE) charge buried under a layer of the sand/soil material. Flash x-ray was used to measure the target plate deformation and allowed for an evaluation of the momentum distribution in both space and time.

The experimental setup has been refined from the previous study and consists of a cylindrical axisymmetric configuration which can be simulated numerically in two-dimensions. This addresses limitations of the previous setup which consisted of a rectangular target plate that enabled a quasi-two-dimensional approximation, however, ultimately was still affected by the third dimension. The present setup enables validation of the two-phase sand model employed in the previous study [1] with a much higher accuracy using a two-dimensional simulation. Therefore, the two-phase sand model, implemented in the Sandia shock physics code, CTH, can be assessed with direct comparison of the experimental and numerical results without assumptions related to the physical third dimension. The comparison demonstrates a high fidelity of the modelling and high accuracy in predicting the plate deformation for the case of dry calcite sand. This prediction tool should allow for improved designs countering the threat and ultimately increase the survivability of vehicle occupants.

Various sands (and a soil) were tested with the present experimental setup, enabling an investigation of the influence of the sand parameters on the momentum transfer to the target plate. Parameters evaluated included particle size distribution, particle shape, type of sand (chemical composition), moisture content and density or level of initial compaction of the sand. This provides a sensitivity analysis on the influence of the various sand parameters which could be used to inform on the response of an unknown sand from a specific region of operation for the Department of Defence.