Microcomputed X-Ray Tomographic Imaging and Image Processing for Microstructural Characterization of Explosives

John D. Yeager,Lindsey A. Kuettner,Amanda L. Duque,Larry G. Hill,Brian M. Patterson

doi:10.3390/ma13204517

Abstract

Microstructural characterization of composite high explosives (HEs) has become increasingly important over the last several decades in association with the development of high fidelity mesoscale modeling and an improved understanding of ignition and detonation processes. HE microstructure influences not only typical material properties (e.g., thermal, mechanical) but also reactive behavior (e.g., shock sensitivity, detonation wave shape). A detailed nondestructive 3D examination of the microstructure has generally been limited to custom-engineered samples or surrogates due to poor contrast between the composite constituents. Highly loaded (>90 wt%) HE composites such as plastic-bonded explosives (PBX) are especially difficult. Here, we present efforts to improve measurement quality by using single and dual-energy microcomputed X-ray tomography and state-of-the-art image processing techniques to study a broad set of HE materials. Some materials, such as PBX 9502, exhibit suitable contrast and resolution for an automatic segmentation of the HE from the polymer binder and the voids. Other composite HEs had varying levels of success in segmentation. Post-processing techniques that used commercially available algorithms to improve the segmentation quality of PBX 9501 as well as zero-density defects such as cracks and voids could be easily segmented for all samples. Aspects of the materials that lend themselves well to this type of measurement are discussed.

Highlights

A characterization of the microstructure of high explosives (HEs) is important for constructing accurate mesoscale simulations; understanding processing–structure–property relationships, which influence initiation and detonation behavior; and quantifying production parameters
Some care should be taken before comparing the results found here for any given material to “bulk” or typical large scale material microstructure
The lighter material is the HMX, while the black constituent is void, and the intermediate grayscale material is the binder. This contrast scheme is consistent for all the CT images shown here, as the grayscale value is lighter as density increases

Summary

Introduction

A characterization of the microstructure of high explosives (HEs) is important for constructing accurate mesoscale simulations; understanding processing–structure–property relationships, which influence initiation and detonation behavior; and quantifying production parameters (i.e., lot-to-lot variations). The polymers (“binders”) can be inert and only serve to enhance stability and machinability, or they can be somewhat energetic themselves and contribute to the detonation energy [14]. Melt-castable explosives can be a single low melt temperature material (e.g., trinitrotoluene) or a mixture of explosives, where at least one component is melt-castable so it can serve as a binder (e.g., Composition B) while imparting high detonation energy [15]. As is the case in many materials, quantifying all microstructural features with a single technique is difficult if not impossible; since most explosives are relatively fragile, not to mention hazardous, obtaining accurate measurements is especially challenging

Methods

Results

Discussion

Conclusion