Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session T6: SMGPB: Shock Waves in Polymers |
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Chair: William Proud, Imperial College London Room: Broadway III/IV |
Thursday, June 20, 2019 2:00PM - 2:15PM |
T6.00001: Shockwave interactions with additively-manufactured polymer structures Dana Dattelbaum, Brittany Branch, Brian Patterson, Axinte Ionita Control of structural topology, via a bottom-up approach, is now possible through the continuing maturation of additive manufacturing techniques. For example, new classes of porous materials with increased strength-to- density ratios, novel thermal and acoustic properties, and even ``metamaterial'' properties such as negative Poisson ratios have been recently realized by tailoring deformation mechanisms and structural instabilities. \textit{It is the control of organizing features at the mesoscale that has led to a revolution in tailoring materials' mechanical properties and function. }However, extensions to dynamic, high strain rate, large strain conditions have been scarcely explored. Here we will present the results of traditional plate impact methods applied to organized polymer architectures, using velocimetry and x-ray phase contrast imaging at the Advanced Photon Source. These methods allowed for the characterization of the mechanisms of shock wave propagation, localization, and compaction in the structures. In particular, we have investigated the role of interfaces on stress localization within the structures. The experimental results will be discussed in the context of finite element simulations of the same structures, including progress on topological optimization for desired dynamic response. [Preview Abstract] |
Thursday, June 20, 2019 2:15PM - 2:30PM |
T6.00002: Shock Propagation and Deformation of Additively-Manufactured Polymer Foams with Engineered Porosity David Lacina, Christopher Neel, Jonathan Spowart, Geoffrey Frank, Andrew Abbott, Brittany Branch Additively-manufactured (AM) polymeric structures containing multiple length scales of engineered porosity have been developed to promote enhanced shock dissipation and shockwave propagation directionality (i.e. a ``shock diode''). Light gas-gun planar impact studies of both cube-shaped and asymmetrically shaped specimens, with porosities built in different ``fractal'' geometries, have been carried out. Equation of State information, in-situ particle velocity profiles, and deformation histories were obtained using photon Doppler velocimetry (PDV), embedded electromagnetic gauges, and high-speed video, respectively. The results of this work show that certain asymmetrical fractal geometries do induce a degree of directionality in shockwave propagation. Anisotropy in the Hugoniot for some of these AM polymeric structures was also observed and has been attributed to AM print orientation. This data has been used to validate a finite element analysis model for the dynamic impact of printed solids. These results also provide information which AM manufacturing can use to tune shock properties of AM printed structures to obtain more favorable shock response behavior. [Preview Abstract] |
Thursday, June 20, 2019 2:30PM - 2:45PM |
T6.00003: Reactive wave structures in shock compressed polyimide Rachel Huber, Dana Dattelbaum, Lee Gibson, Richard Gustavsen, Stephen Sheffield Polyimide (PI, (-OC$_{\mathrm{2}}$NC-C$_{\mathrm{2}}$O-)$_{\mathrm{n}})$ is a thermoplastic polymer that is chemically-robust at elevated temperatures and pressures thereby lending itself to a multitude of extreme condition applications. When shocked to pressures greater than \textasciitilde 18 GPa, PI is suspected to dissociate from polymer structure to a product mixture, due to a ``cusp'' in the principal Hugoniot. Above the cusp, a multiple wave structure is expected due to volume changes (densification) along the reaction coordinate. From historical work, PI has a volume change of \textasciitilde 20{\%}; larger than polysulfone (PSF), and other extended polymer chain structures, for example. To better understand the reactants to products transition in PI, a series of gas-gun driven plate-impact experiments were conducted on PI, and particle velocity wave profiles were measured using both embedded electromagnetic particle velocity gauges and optical velocimetry (VISAR and PDV). Here, we present an analysis and interpretation of the two-wave structure in shocked PI and the loci of the unreacted and product Hugoniot states, as well as the decomposition reaction rate(s). LA-UR-19-21573 [Preview Abstract] |
Thursday, June 20, 2019 2:45PM - 3:00PM |
T6.00004: Improved Polymer Equations of State Katie Maerzke, Joshua Coe, J. Tinka Gammel Polymers are pervasive in the modern world. They are used in a wide variety of applications for such tasks as structural support, impact mitigation, and maintenance of engineering tolerances. Yet polymer equations of state are the most underdeveloped of any material class. Polymers pose several unique modeling challenges. Like high explosives, they react and chemically decompose under sufficiently strong shock compression. We model this using two equations of state, one of the unreacted material and one for the decomposition products. Unlike high explosives, polymers typically exhibit a reduction (rather than increase) in volume upon reaction. Moreover, the molecular structure of polymeric materials results in thermal and shock compression properties that are different from metallic solids. Modeling these behaviors requires more sophisticated physics models. Polymer foams introduce additional complications, such as compaction and an ``anomalous'' volume expansion upon reaction. These modeling challenges will be discussed in the context of recent equations of state for polyethylene and a poly(dimethylsiloxane)-based foam. [Preview Abstract] |
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