Dissertation
Pressure-assisted additive manufacturing of energetic composites: processing science and applications
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2023
DOI: 10.25820/etd.006996
Abstract
Binder jetting is a widely used technique in additive manufacturing that has found numerous applications. However, it suffers from processing limitations that lead to poor green densities in the final parts. To address this issue, a novel process called pressure-assisted binder jetting (PBJ) has been developed, enabling layer-by-layer compaction of the powder bed and improving the density of printed objects. In-depth analysis of the heterogeneous stress network has been conducted to further enhance the density of PBJ prints. The unique characteristics of powder density and binder deposition in the PBJ process offer an opportunity to overcome existing challenges in the fabrication of energetic materials such as propellants and polymer-bonded explosives. While conventional fabrication techniques in energetics can achieve desirable density, solids loading, and mechanical properties, they lack the flexibility required to construct complex structures or modify grain gradients, both of which play a crucial role in determining thrust profiles in propellants and detonation evolution in polymer-bonded explosives. While various additive manufacturing techniques have shown improvements in complex geometric fabrication, they often come at the expense of other important features. PBJ, on the other hand, has demonstrated promising capabilities in both avenues of energetics. It has enabled the construction of propellants with excellent resolution of complex features, offering one of the few methods to incorporate gradients within the grain structure. Furthermore, satisfactory results have been achieved in terms of density, solids loading, and mechanical properties. In the case of polymer-bonded explosives, similar outcomes have been observed, but an additional level of control was desired. By selectively depositing microwave reactive thermites in printed polymer-bonded explosives, it became possible for switchable control of defect-induced porosity, a crucial factor influencing safety and performance. Detailed investigations have been carried out to map the process and fabrication parameters and understand their impact on the generation of defects. The results exhibit great promise in producing polymer-bonded explosives that offer both safety in handling and excellent ignition and performance characteristics in real-world applications
Details
- Title: Subtitle
- Pressure-assisted additive manufacturing of energetic composites: processing science and applications
- Creators
- Levi Kirby
- Contributors
- Xuan Song (Advisor)Yong Chen (Committee Member)Chao Wang (Committee Member)Albert Ratner (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Industrial Engineering
- Date degree season
- Summer 2023
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.006996
- Number of pages
- xx, 170 pages
- Copyright
- Copyright 2023 Levi Kirby
- Grants
- FA9550-20-1-0700, United States Air Force Office of Scientific Research (United States, Arlington) - AFOSR
- Language
- English
- Date submitted
- 06/24/2023
- Description illustrations
- illustrations, tables, graphs
- Description bibliographic
- Includes bibliographical references (pages 159-170).
- Public Abstract (ETD)
- Binder jetting is a widely utilized additive manufacturing technique with a range of applications. However, it is hindered by processing limitations that lead to inadequate green densities in the final parts. To overcome this challenge, a novel process known as pressure-assisted binder jetting (PBJ) has been developed. PBJ addresses this concern by implementing layerwise compaction of the powder bed, effectively improving the density of printed objects. In-depth analysis of the heterogeneous stress network has been conducted to further enhance the density of PBJ prints. The unique selectivity of powder density and binder deposition in the PBJ process presents a valuable opportunity to address existing deficiencies in the fabrication of energetic materials, specifically propellants and polymer-bonded explosives. While traditional fabrication techniques in energetics can achieve desirable density, solids loading, and mechanical properties, they lack the flexibility necessary for constructing complex structures or modifying grain gradients. These factors play a crucial role in guiding thrust profiles in propellants and the evolution of detonation in polymer-bonded explosives. Although numerous additive manufacturing techniques have shown advancements in complex geometric fabrication, they often come at the expense of other important features. In the case of PBJ, its capabilities were investigated and demonstrated great promise in both energetics domains. Propellants were constructed with excellent resolution of intricate features, offering one of the few methods for incorporating gradients within the grain structure. Furthermore, the density, solids loading, and mechanical properties were all found to be satisfactory. Similarly, polymer-bonded explosives yielded comparable results, although there was a desire for an additional level of control. By selectively depositing microwave reactive thermites in printed polymer-bonded explosives, it became possible for switchable control of defect-induced porosity, a critical factor influencing safety and performance. Detailed mapping of the process and fabrication parameters was studied to understand their influence on the degree of defects generated. The results exhibit great promise in producing polymer-bonded explosives that not only ensure safety during handling but also offer excellent ignition and performance characteristics in practical applications.
- Academic Unit
- Industrial and Systems Engineering
- Record Identifier
- 9984454541502771
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