Session B03: Detonation Propagation I

Experimental and Modeling Analysis of Detonation in a Confined Circular Arc of DAAF-Based Explosive

Detonation models for high explosives are typically calibrated from experiments with simple charge geometry, such as cylinders and slabs, which may be unconfined or confined. Applying these models to a geometry where the detonation wave must turn due the shape of the charge can provide assurance that the model can predict detonation performance in more complex systems. Here, we describe a newly developed test consisting of a circular arc of a 95% DAAF and 5% FK-800 explosive confined on the inner and outer surfaces by 2 mm thick titanium alloy sheets. Utilizing radiography from the LANL pRad facility, 21 images of the arc detonating and driving the titanium sheets outward were captured. In addition, 16 PDV probes were used to measure the motion of the inner confiner plate. Here, we show these results, their analysis, and compare them to model predictions.   

A CREST Reactive Burn Model for a TATB-Based Explosive

CREST is an entropy-dependent reactive burn model for shock initiation and detonation of explosives in hydrocode calculations. This paper describes the development and initial testing of a CREST model for an explosive that comprises 95% by weight TATB and 5% Kel-F800 and having a nominal density of 1.905 g/cm³. Following other recent CREST models, the equations of state are fitted to available shock Hugoniot, sound speed and overdriven detonation wave data, while the reaction rate coefficients are calibrated using an automatic method to fit sustained-shock gas-gun data and the explosive’s detonation size-effect curve. It was found that the optimal reaction rate from the automatic parameterization was subsequently unable to predict recent detonation corner turning data used for validation purposes. Subsequent analysis of parameter sets close to the “best” found reaction rates that gave significant improvement to the corner turning data with only slight reductions in the quality of fit to the standard calibration data; one of these was chosen for the reaction rate in the final model. The implications of these findings for the future calibration of reactive burn models for TATB-based explosives will be considered and discussed.

 

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Ballistic Studies with Reactive Material Projectiles

Two important conclusions about the combustion of reactive materials under extreme loading are rooted in their ignition and energy release. From a physical perspective, there is an art to designing experiments that characterize the combustion of a reactive materials as a function of formulation, environment, and loading conditions. Thermodynamics dictates that if an impact induced reaction can be contained in a semi-sealed constant volume chamber, then transient pressure measurements reveal information about thermal energy buildup and release. From an understanding of thermal energy exchange, further conclusions about ignition sensitivity and energy release rates with the environment can be realized. Advances in diagnostics also enable two-dimensional transient temperature measurements of condensed phase materials. Specifically, high-speed cameras are modified to provide a thermal perspective of ballistic impact events. When applied to reactive material projectiles, thermography allows observation of energy transport through a fragmentation field. The role of condensed phase temperatures from reacting fragments on heating the gaseous environment is important. In this presentation, vented chamber calorimetry and thermography experiments reveal information about the ignition sensitivity and energy transport of reactive material projectiles impacting a target plate at velocities up to 1200 m/s. Multiple reactive material formulations will be discussed including projectiles composed of pure metal (aluminum), two metals (intermetallic), and metal and metal oxide (thermite). The projectiles are examined in inert gas (argon) and ambient air environments. The environmental influence on ignition and energy transport is significant. The experimental observations provide a foundation for understanding the influence of varied parameters including formulation, environment, and loading conditions on reactive material performance in terms of ignition and energy generation.   

Experimental and Computational Study on Detonation Propagation in 2D Circular Arcs of PBX 9502 for Varying Inner Radius and Thickness

The dynamics of detonation diffraction in an unconfined 2D circular arc of the TATB-based insensitive high explosive PBX 9502 was investigated previously by Short et al. (Combust. Flame, 196, 129-143, 2018). In the current study, we describe a combined experimental and computational analysis of the effect of varying inner arc surface radius and arc thickness on detonation propagation in unconfined circular arcs of PBX 9502. Experimentally, we study the change in angular speed and shape of the detonation for two arcs with the same inner radius but two different thicknesses, and a third arc with a larger inner radius. We also examine the modified geometry effects through a newly-calibrated Wescott-Stewart-Davis reactive burn model for PBX 9502.  In particular, we show how the structure of the subsonic detonation driving zone evolves with changing inner radius and thickness.