Bradley White

Ignition and growth modeling of detonation reaction zone experiments on single crystals of PETN and HMX

It has long been known that detonating single crystals of solid explosives have much larger failure diameters than those of heterogeneous charges of the same explosive pressed or cast to 98 – 99% theoretical maximum density (TMD). In 1957, Holland et al. demonstrated that PETN single crystals have failure diameters of about 8 mm, whereas heterogeneous PETN charges have failure diameters of less than 0.5 mm. Recently, Fedorov et al. quantitatively determined nanosecond time resolved detonation reaction zone profiles of single crystals of PETN and HMX by measuring the interface particle velocity histories of the detonating crystals and LiF windows using a PDV system. The measured reaction zone time durations for PETN and HMX single crystal detonations were approximately 100 and 260 nanoseconds, respectively. These experiments provided the necessary data to develop Ignition and Growth (I&G) reactive flow model parameters for the single crystal detonation reaction zones. Using these parameters, the calculated...

Impact Initiation of Reactive Aluminized Fluorinated Acrylic Nanocomposites

The initiation of aluminized fluorinated acrylic (AlFA) nanocomposites during modified Taylor impact tests was investigated. Samples were impacted against a steel or sapphire anvil at a nominal velocity of 150 m/s. A framing camera was used to capture head-on and side-profile impact images for the sapphire window and steel plate rigid anvils, respectively. Correlations were drawn between both experimental setups to determine the initiation locations and reaction times. Reactions were found to initiate at an intermediate radius on the impact face of the pellet at a time near full compaction. From simulations, the highest strains and temperatures were found at radii similar to those observed in experiments at the time of ignition. Off-normal impacts produced higher localized straining and temperatures on one-half of the pellet. The copper projectile, used for delivery, was revealed to aid in a shear assisted reaction by helping to drive the pellet material outward as the projectile deformed radially.

Computational studies of the skid test: Evaluation of the non-shock ignition of LX-10 using HERMES

We perform computational studies to evaluate the non-shock ignition response of LX-10 (95wt.% HMX, 5wt.% Viton A) during a skid impact test. We employ the HERMES (High Explosive Response to MEchanical Stimuli) model for LX-10 for Skid test calculations investigating the influence of drop height and angle on the pressure, strain-rate, strain, and ignition states. While grit is typically present in skid tests, it was not considered in these continuum-scale calculations. We found that the incident angle has a much more significant influence on pressure, strain-rate, strain, and ignition states than drop height. The peak HERMES ignition parameter value, Ign, is nearly one order of magnitude higher for an incident angle of 45° than for 14°. Peak Ign values occur at the contact patch where shear deformation is highest and is a result of the shear-dependence in the ignition criteria. While peak Ign values for Steven Tests were approximately 60, the skid test had a much smaller value < 2 for the scenarios considered in this study. The discrepancy in ignition values suggest that grit-explosive interactions play a significant role in skid test response. Since the peak ignition values are much less for the 14° impact angles, the role of the grit may be more important at lower incident angles. Future work should include meso-scale calculations to resolve the localized grit interactions that underpins these shear ignition mechanisms.

Mesoscale simulations of particle reinforced epoxy-based composites

Polymer matrix composites reinforced with metal powders have complex microstructures that vary greatly from differences in particle size, morphology, loading fractions, etc. The effects of the underlying microstructure on the mechanical and wave propagation behavior of these composites during dynamic loading conditions are not well understood. To better understand these effects, epoxy (Epon826/DEA) reinforced with different particle sizes of Al and loading fractions of Al and Ni were prepared by casting. Microstructures from the composites were then used in 2D plane strain mesoscale simulations. The effect of varying velocity loading conditions on the wave velocity was then examined to determine the Us-Up and particle deformation response as a function of composite configuration.