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 Z6: SMGPB: Soft Materials II |
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Chair: Jennifer Jordan, Los Alamos National Laboratory Room: Galleria South |
Friday, June 21, 2019 11:00AM - 11:15AM |
Z6.00001: Temperature Effects on Dynamic Response of a Simple Polymer Structure William Proud, David Sorry, Gareth Tear The temperature dependance of polymers is well known. From the 1950s onward semi-empirical relationships such as the Williams-Landel-Ferry (WLF) have been used to predict flow and, by extension, strain rate properties of polymers. Group Interaction Modelling, from the 1990s onwards, has been increasingly used to predict a range of static and dynamic properties from knowledge of the chemical structure. In a series of parallel developments the analysis of loading systems such as the Split Hopkinson Pressure Bar (SHPB) has moved from the application of analytic relationships to the use of complete modelling of the loading system and the sample. In this paper a simple structure, a tubular polymer specimen is loaded over a range of stresses, strain rates and pulse shapes in a SHPB. The sample temperature is varied from that which results in brittle response to a flow response. Changing the diameter of the central hole in the sample shows the effect of the structure on the response. Overall this study gives insight into how the polymer failure envelope changes with temperature and strain rate. [Preview Abstract] |
Friday, June 21, 2019 11:15AM - 11:30AM |
Z6.00002: A tensile split Hopkinson pressure bar for low impedance materials David Williamson A split Hopkinson pressure bar that is specifically designed for testing low impedance materials in uniaxial tension is discussed. The input and output bars are each 2.5 m long and formed of titanium alloy tubes and are of low mechanical impedance (Grade 9 alloy, 16 mm outside diameter, 1mm wall thickness). Tensile pulses are generated by the action of an impedance matched striker-tube which is coaxial to, and rides over the top of, the input-tube. The striker tube is propelled along the input-tube away from the specimen by a gas-gun with a wrap-around breech to strike a stop mounted at the end of the input-tube. The subsequent compressive pulse is inverted to become tensile by reflection from a free surface, and propagates back up the input-tube to interact with the specimen, causing it to be placed into a state of uniaxial tension with associated displacement rates of between 0.5 and 5 meters per second. In addition to force-displacement information obtained from strain gauges mounted on the bars, sample deformation is monitored using high-speed video and sample strains are extracted using digital image cross-correlation. Recent results from experiments on highly filled particulate composites with polymer matrices are presented. [Preview Abstract] |
Friday, June 21, 2019 11:30AM - 11:45AM |
Z6.00003: Low and high strain rate compressive properties and aging study of Sylgard 184 with varying amounts of plasticizer and crosslinker Tomislav Kosta, Thomas Krawietz, Jesus Mares We present the quasi-static and high strain rate compressive mechanical properties of Sylgard 184, a Dow Corning commercial variant of polydimethylsiloxane (PDMS), and four variants. The four variants are composed of Sylgard 184 with various amounts of plasticizer and crosslinker. For each of the five materials we present the quasi-static and dynamic compressive properties measured via Instron load frame and Kolsky bar. Additionally, we present a curing/aging study of Sylgard 184 where we measure the compressive properties as a function of natural aging in the time period following sample manufacture. This work is motivated by the wide interest of Sylgard 184 across numerous communities from biomechanics to flexible electronics. While PDMS has been characterized in the literature, efforts appear to have been focused on low strain rates and here we extend the characterization to the high strain rate regime with the intent of measuring the shock response in the future. [Preview Abstract] |
Friday, June 21, 2019 11:45AM - 12:00PM |
Z6.00004: Time and Temperature Dependent Adhesion in Viscoelastic Materials Lewis Lea, Nicholas Taylor, David Williamson An experimental method is presented for studying the interfacial strength between constituent materials in polymer bonded composites. Macroscopic spherical caps of filler material are loaded into compression against a half-plane of the polymer matrix material, and then unloaded through tension and subsequent adhesive breakdown. The entire experiment is contained in an environmental chamber, temperature variations are achieved through a combination of liquid nitrogen cooling and resistive air heating, tuned using an environmental controller. The displacement of the spherical cap, contact force and contact surface are all directly empirically measured. The measured work of adhesion required to separate the two surfaces is related to the thermodynamic work of adhesion scaled by a factor due to mechanical loss during debonding. In a viscoelastic material the measured work of adhesion is therefore expected to be both rate and temperature dependent. Recent results are presented on experiments relevant to high fill fraction particulate composites with polymer matrices. Particular attention is paid to the interplay between deboning rate and temperature for viscoelastic materials, and the extension of the technique to a variety of loading profiles. [Preview Abstract] |
Friday, June 21, 2019 12:00PM - 12:15PM |
Z6.00005: Generation and propagation of shock wave trains in free liquid jets. Claudiu Stan, Gabriel Blaj, Philip Willmot, Mengning Liang, Jason Koglin, Andrew Aquila, Joseph Robinson, Raymond Sierra, Sébastien Boutet The shock structures that form in supersonic gas jets, discovered by Mach and Salcher 130 years ago, are a common sight in the exhaust of jet and rocket engines. The technology to produce sustained supersonic liquid jets out of a solid nozzle does not exist yet, but we discovered that similar shock trains can form in nearly stationary liquid jets ablated by femtosecond X-ray laser pulses. The shock trains were produced as an initial shock reflected multiple times at the surface of the jet. Using time-resolved optical imaging, we observed a range of nonlinear wave propagation phenomena either common to the gas jets (oblique shock reflections) or unique to liquids (negative pressures, cavitation). We estimated the positive and negative pressure excursions in the shock train using the velocities of shocks and of the expansion of cavitation bubbles. Although the shock amplitude decayed rapidly, trains with up to 6 shocks could be generated. For a brief period, the shock trains represent an extremely intense sound wave (\textasciitilde 270 dB, re: 1 \textmu Pa) that is fundamentally limited to amplitudes just below those that would damage the wave propagating medium in a single oscillation cycle. [Preview Abstract] |
Friday, June 21, 2019 12:15PM - 12:30PM |
Z6.00006: Modeling of an advanced wedge test Christopher Romick, Tariq Aslam, Cindy Bolme, Kyle Ramos The objective of an advanced wedge test is to offer a diagnostic that provides both spatial and temporal resolution, such that the interaction of multiple materials in the presence of an oblique shock can be examined. The materials' spatial and temporal behavior, including the deflection angle and particle velocity, can be measured using photon Doppler velocimetry and/or x-ray phase contrast imaging. However, it is not clear if the deflection of a material interface will dramatically affect the experimentally obtained values from those predicted by the semi-analytic shock polar analysis or those from a full time-dependent simulation of such an interaction. Therefore, several of these interactions are first examined for two non-reactive materials with shock polar analysis to obtain a leading order estimate of the expected behavior. This is followed by the examination of these material interfaces with a full time-dependent simulation using a ghost fluid methodology which utilizes nominally fifth-order spatial and third-order temporal discretizations. These two results are then compared with those obtained from advanced wedge test experiments. Lastly, the material interface of a high explosive impinging on an inviscid, inert material is examined. [Preview Abstract] |
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