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Research 

Presented here are the results of research performed at Los Alamos National Laboratory and at Brigham Young University

 

Numerical Validation of Heat Capacity Model for a Mixture Containing a Phase Change Material

Abstract

  A model has been proposed for predicting the variation of heat capacity with temperature in composites containing a fraction of material that undergoes a phase change. Experimental data was collected for transient heat flux through a thin plate coated with a Phase Change Material (PCM). A finite difference routine was developed which implements the effective heat capacity model. The numerical solutions were compared to the experimental data to test the validity of the model.

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PARTICLE CHARACTERIZATION OF PRESSED GRANULAR HMX

Abstract

It is widely accepted that particle size and morphology in granular beds of HE plays a large role in combustion and detonation events. This work reports the characteristics of coarse granular HMX (Class A) at a range of densities from stock density to 95% TMD. We report measurements of the particle size distribution of original granular HMX, as well as the size distribution of pressed (higher density) samples. Scanning electron microscope (SEM) pictures are presented and are found to be useful in interpreting the size distribution measurements of the granular HMX, as well as in helping to more fully characterize the state of the particles. We find that the particle size distribution changes significantly with pressing. Particles are observed to be highly fractured and damaged, especially at higher pressed densities. Also, we have found that sample preparation can significantly affect size distribution measurements. In particular, even short duration ultra-sonic or "sonication" treatment can have a significant effect on the measured size distributions of pressed HMX samples. Surface area measured by gas absorption is found to be much larger than inferred from light scattering.

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THICK WALLED DDT TUBE EXPERIMENTS

Abstract

In this paper we present initial results from a new series of deflagration-to-detonation transition (DDT) experiments in which we study the piston-initiated DDT of heavily confined granular cyclotetramethylenetetranitramine (HMX). These experiments were designed to be useful in model development and evaluation. Initial experiments have examined the effect of density, piston speed, and ignition delay on the DDT event. Often, in previous work, little material characterization is reported which makes modeling and interpretation of the experiments more difficult. In this work we measure the particle size distribution of the original granular explosives, as well as the size distribution of pressed (higher density) samples. Scanning electron microscope (SEM) pictures are presented and are useful in interpreting the size distribution measurements of the HMX and in more fully characterizing their initial condition. We find that the particle size distribution changes significantly with pressing. That is, particles are highly fractured and damaged at higher pressed densities. Also, we have found that sample preparation can significantly affect size distribution measurements. For the base case (65% TMD) two DDT experiments were performed yielding nearly identical results, indicating that reproducibility is good. Run-to-detonation, as indicated by color change and deformation of the inner wall, for the three densities (65%, 75%, and 85% TMD) considered shows a slight decrease, going from 65% to 75% TMD, but a significant increase in 85% TMD. This result is qualitatively compared with similar results reported previously for thermally ignited DDT tubes. Increasing the piston speed decreased the distance to detonation, as expected, and the effect of the ignition delay (tighter packing of the titanium boron gasless igniter) extended the distance to detonation somewhat. Future experiments are described.

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