Session: 03-01-01: Annual Conference-Wide Symposium on Additive Manufacturing

Paper Number: 149558

149558 - Dynamically Tuning Porous Microstructures of Energetic Materials for Switchable Properties via a Pressure-Assisted Binder Jet Process 

Polymer-bonded energetic composites are a class of energetic materials (EMs) consisting of energetic crystals bonded together with a polymer binder. These materials usually exhibit microstructural defects, such as cracks and voids, which can lead to the formation of hotspots and initiate reactions through various localization phenomena such as void collapse. This, in turn, enhances the ignition threshold, shock sensitivity, and detonation characteristics of EMs. From a standpoint of safety, all these defects and the resulting increased sensitivity are undesirable for EMs during manufacture, storage, and transport. Effective control of these defects for specific working environments holds the promise of optimizing EM performance and ensuring safety across their applications.

We propose a “switchable” EM whose properties can be dynamically changed by switching on microstructural defects using externally applied electromagnetic fields. This capability is enabled by a pressure-assisted binder jet (PBJ) process. The PBJ process fabricates a “switchable” EM through integrating electromagnetically reactive additives into the EM in a layer-by-layer fashion. Upon exposure to microwave, the additives can react and then trigger localized defects, primarily at the particle-binder interface in EMs. Traditionally, much of the research has emphasized defects within crystals as the primary causes of EM sensitivity. However, some experimental and theoretical evidence has shown that defects within the non-crystal phase, particularly at the particle/binder interface, can also be influential. In the PBJ process, a layerwise compaction force is applied to achieve high solids fraction of energetic crystals in the EMs and thus minimize the microstructural defects or voids prior to microwave exposure.

In this presentation, we will present the operating principle of the PBJ process and investigate the process-structure-properties relationships of the process for the fabrication of “switchable” EMs. Furthermore, we will discuss the process of defect generation in EMs upon microwave exposure. To study the switched properties of EMs, different experimental tools have been employed, including X-ray micro-computed tomography, in-situ high-speed compression testing, and high-speed optical imaging. These techniques have provided valuable insights into the microstructural changes and performance characteristics of the EMs before and after microwave illumination. Additionally, numerical simulations using Abaqus/Standard have been conducted to assess the defect generation in EMs under varying conditions, such as pressures, cohesive properties, and binder thicknesses. The simulation results demonstrate the significant influence of these factors on the ability to generate defects in EMs. The applications of this approach in controlling burning behaviors of solid propellants and shock sensitivity of mock explosives will be presented. This research has the potential to significantly improve the safety of EMs by enabling the development of less sensitive EMs and facilitating in situ EM sensitization through microwave pulse.

Presenting Author: Xuan Song University of Iowa

Presenting Author Biography: Dr. Xuan Song is an Associate Professor and James A. Chisman Faculty Fellow in the Department of Industrial and Systems Engineering at the University of Iowa (UIowa). His group specializes in the design, manufacturing, and diagnostics of extreme materials that operate under high-temperature and high-strain-rate conditions. Their current interest centers on studying how gentle and versatile material forming mechanisms found in nature can be leveraged to advance next-generation manufacturing processes for ceramics and energetic materials with enhanced sustainability and multi-scale tunability. They also utilize multi-scale in-situ experimental tools, including high strain-rate compression testing, high-speed optical imaging, and high-speed thermometry, to probe the process and material dynamics under extreme environments. Dr. Song is a recipient of the US National Science Foundation CAREER Award, the US Air Force Office of Scientific Research (AFOSR) Young Investigator Award, and SME Outstanding Young Manufacturing Engineer Award. He earned his Ph.D. in industrial engineering from the University of Southern California in 2016.

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