Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session E2: Energetic and Reactive Materials: Reactive Materials |
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Chair: Su Peiris, AFRL Munitions Directorate Room: Grand Ballroom AB |
Monday, July 10, 2017 3:30PM - 4:00PM |
E2.00001: Enhancing Reactivity in Structural Energetic Materials Invited Speaker: Nick Glumac In many structural energetic materials, only a small fraction of the metal oxidizes, and yet this provides a significant boost in the overall energy release of the system. Different methodologies to enhance this reactivity include alloying and geometric modifications of microstructure of the reactive material (RM). In this presentation, we present the results of several years of systematic study of both chemical (alloy) and mechanical (geometry) effects on reactivity for systems with typical charge to case mass ratios. Alloys of aluminum with magnesium and lithium are considered, as these are common alloys in aerospace applications. In terms of geometric modifications, we consider surface texturing, inclusion of dense additives, and inclusion of voids. In all modifications, a measurable influence on output is observed, and this influence is related to the fragment size distribution measured from the observed residue. [Preview Abstract] |
Monday, July 10, 2017 4:00PM - 4:15PM |
E2.00002: The role of porosity and annealing in the impact fragmentation of an aluminum reactive material Joseph Hooper A reactive fragment has a unique structural requirement to survive explosive launch but then fragment catastrophically and combust upon impact. Suitable materials for this application tend to be metal composites with high ductility in compression but elastic-brittle behavior in tension. Characterizing the dynamic fragmentation of such materials is key for understanding their lethality. Here we consider a prototypical aluminum reactive frag material, formed via cold isostatic pressing of micron-scale powder followed by annealing. Samples were gun-launched into a target and recovered in a soft-catch medium of artificial snow, allowing for excellent recovery down to micron sizes and minimal contamination. Recovered fragment distributions were analyzed and compared to standard energy-balance theories. We study the effect of compaction pressure and annealing conditions on the fragmentation behavior at 500-800 m/s impacts, and find a particularly strong effect from short annealing periods. Though dynamic fracture occurs entirely along original particle boundaries in this material, recovery processes within the Al microstructure during annealing lead to a rapid decrease in the extent of fragmentation. [Preview Abstract] |
Monday, July 10, 2017 4:15PM - 4:30PM |
E2.00003: Liquid Metal Embrittled Aluminum Alloy Material in Explosive Fragmentation and Shock Loading Conditions. John Rudolphi Liquid metal embrittled (LME) aluminum alloy configurations were studied to characterize and investigate their behavior during explosive loading. Localized reductions in material strength, ductility, and toughness were created by the embrittling action of small quantities of gallium applied to aluminum. This study consisted of light gas gun experiments to quantify gallium-embrittled aluminum response to copper projectile impacts between 2.2 GPa and 18 GPa resulting in a P-u Hugoniot relationship. Microstructure conditions of tested material were characterized and indicate intergranular penetration by gallium into the aluminum alloy substrate. Embrittling agent quantity and exposure time were varied and quantified. In addition, aluminum alloy cylinders were packed with Composition C-4 explosive to observe natural fragmentation behavior in representative geometries. Some tests included a polycarbonate buffer between explosive and embrittled aluminum to induce a ``low'' pressure condition; all other tests were conducted with intimate explosive contact to the cylinder walls. Results indicate that embrittled aluminum cylinders fragment into significantly smaller particles compared to non-embrittled cylinders at both high and low pressure conditions. Microstructure analysis indicated brittle failure mechanisms in contrast to the highly-ductile failure of non-embrittled aluminum alloy. [Preview Abstract] |
Monday, July 10, 2017 4:30PM - 4:45PM |
E2.00004: Failure and fragmentation of pressed bimetallic composites Jamie Kimberley, Michael Hargather, Steven Thoma The dynamic failure and fragmentation response of pressed metallic composites is investigated experimentally using a Kolsky bar and explosive loading. The composites are made of nominally brittle and ductile metal phases, in varying ratios, to explore the effect of composition on the material strength and fragment size distribution. Dynamic compression experiments at strain rates up to 5000 /s are conducted on a Kolsky bar to measure the compressive strength of the materials. High-speed images captured during the dynamic loading provide insight to the nature of the failure mechanisms activated (e.g. brittle vs. ductile fragmentation). Explosively-driven fragmentation experiments are conducted in a shock tunnel to investigate the fragmentation behavior under shock loading which produces higher rates and induces spall failure. These experiments incorporate high-speed schlieren imaging to track the explosively driven shock and resulting fragments as they travel down range. The high-speed images from both experimental setups are correlated with postmortem measurements of the resulting fragment size distributions, providing connections between the composition, mechanical properties, and fragmentation behavior. [Preview Abstract] |
Monday, July 10, 2017 4:45PM - 5:00PM |
E2.00005: The effect of heat treatment on the dynamic behavior of explosively consolidated Ni/Al composites Qiang Zhou, Pengwan Chen, Bingbing Zhou The effect of heat treatment (HT) on the mechanical behavior of Ni/Al composites was investigated in this work. The Ni/Al composite was fabricated by explosive consolidation, and underwent HT to improve its ductility. The mechanical response and failure mechanisms of Ni/Al before and after HT were studied using a split Hopkinson bar combined with high-speed digital photograph. The Ni/Al composite before HT fractured into pieces with a yield strength of \textasciitilde 350MPa at 2500-1, showing obvious brittleness. The HT-Ni/Al composite maintained integrity with a lower yield strength of 320MPa at 2500-1, and showed apparent strain hardening during yield stage. It indicates the Ni/Al bonding was enhanced through heat treatment. Two distinct failure mechanisms, axial splitting and shear failure, were observed for the samples before and after HT, respectively. In the case of the Ni/Al composite fabricated in this work, both phases are continuous, which failure mode is dominant is determined by bonding strength. When the bonding is strong, it shows shear failure, otherwise, axial splitting. The DSC and XRD analysis were also conducted, showing no intermetallic was formed during the heat treatment and the chemical reactivity was not affected by the heat treatment. [Preview Abstract] |
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