Stephanie Hagelberg

CHARACTERIZING THE EFFECTS OF RATCHET GROWTH ON PBX 9502

Pressed composites of TATB (2,4,6‐trinintro‐l,3,5‐benzenetriamine) undergo irreversible volume change when subjected to thermal cycling. Using micro x‐ray computed tomography and ultra‐small angle neutron scattering, we have characterized the micro‐structure of as‐pressed and ratchet grown specimens of PBX 9502, a TATB‐based composite, thereby distinguishing the effects of ratchet growth from the effects of density alone. Porosity differences are shown to effect mechanical properties, presented here, with ongoing efforts to evaluate sensitivity and/or performance effects.

DENSITY‐DEPENDENT ACOUSTIC PROPERTIES OF PBX 9502

We have measured the longitudinal and shear acoustic velocities of PBX 9502 as a function of density for die‐pressed samples over the range 1.795 g/cc to 1.888 g/cc. The density dependence of the velocities is linear. Thermal cycling of PBX 9502 is known to induce irreversible volume growth. We have measured the density dependence of the volume growth for a subset of the pressed parts and find that the most growth occurs for the samples with lowest initial density. The acoustic velocity changes due to the volume growth are significant and reflect damage in the samples.

A STUDY OF THE SHOCK SENSITIVITY OF PBX 9501 DAMAGED BY COMPRESSIVE LOADING

We have studied the effects of damage caused by compressive loading on the shock sensitivity of the plastic bonded explosive PBX 9501. PBX 9501 consists of 95 wt. % HMX and 5 wt. % nitroplasticized Estane binder. The binder is a mixture of 49 wt. % Estane® 5703 (BF Goodrich), 49 wt. % Nitroplasticizer (a eutectic mixture of bis(2,2‐dinitropropyl)formal and bis(2,2 dinitropropyl)acetal), and 2 wt. % Irganox® 1010 stabilizer. PBX 9501 cubes, 25.4 mm on a side, were compressed to various uniaxial loads in an Instron machine. After loading, 10×10 mm cross‐sections, 3.5 mm thick, were taken from the center of each cube. These slices were then subjected to nearly identical 35 kbar shocks. Transmitted shock wave profiles were measured using interface velocimetry (VISAR). Comparison of shock wave growth is a measure of shock sensitivity. Results on four samples indicate little change in sensitivity caused by compressive loading.

The Poly‐rho Test as a Tool for Screening Explosive Performance

A screening test was developed that can be used to decide if a new synthesized/formulated explosive might warrant further development. The test consists of a rate stick composed of 12.7 mm diameter by 12.7 mm high pellets of different densities ordered from lowest to highest, with ignition occurring at the low‐density end of the stick. This “Poly‐rho” test yields detonation velocities over a range of densities using only the small amount of the explosive typically generated by the synthetic organic chemist at an early stage of the scale‐up process. The amount of material required is far less than that required for the typical rate stick series. Poly‐rho tests on two explosives commonly used at Los Alamos National Laboratory, PBX 9501 and PBX 9502, were conducted and the results compared with empirical detonation‐theory predictions and others’ explosive experiments. There was good agreement in both cases.