Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session L3: Soft Matter I: Polymers |
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Chair: Eric Brown, Los Alamos National Laboratory, Jennifer Jordan, Air Force Office of Scientific Research Room: Grand G |
Tuesday, June 16, 2015 3:45PM - 4:15PM |
L3.00001: High strain rate characterization of soft materials: past, present and possible futures Invited Speaker: Clive Siviour The high strain rate properties of low impedance materials have long been of interest to the community: the very first paper by Kolsky on his eponymous bars included data from man-made polymers and natural rubber. However, it has also long been recognized that characterizing soft or low impedance specimens under dynamic loading presents a number of challenges, mainly owing to the low sound speed in, and low stresses supported by, these materials. Over the past 20 years, significant progress has been made in high rate testing techniques, including better experimental design, more sensitive data acquisition and better understanding of specimen behavior. Further, a new generation of techniques, in which materials are characterized using travelling waves, rather than in a state of static equilibrium, promise to turn those properties that were previously a drawback into an advantage. This paper will give an overview of the history of high rate characterization, the current state of the art after an exciting couple of decades and some of the techniques currently being developed that have the potential to offer increased quality data in the future. [Preview Abstract] |
Tuesday, June 16, 2015 4:15PM - 4:30PM |
L3.00002: Energy absorption behavior of polyurea coatings under laser-induced dynamic tensile and mixed-mode loading Kailash Jajam, Jaejun Lee, Nancy Sottos Energy absorbing, lightweight, thin transparent layers/coatings are desirable in many civilian and military applications such as hurricane resistant windows, personnel face-shields, helmet liners, aircraft canopies, laser shields, blast-tolerant sandwich structures, sound and vibration damping materials to name a few. Polyurea, a class of segmented block copolymer, has attracted recent attention for its energy absorbing properties. However, most of the dynamic property characterization of polyurea is limited to tensile and split-Hopkinson-pressure-bar compression loading experiments with strain rates on the order of 10$^{\mathrm{2}}$ and 10$^{\mathrm{4}}$ s$^{\mathrm{-1}}$, respectively. In the present work, we report the energy absorption behavior of polyurea thin films (1 to 2 $\mu $m) subjected to laser-induced dynamic tensile and mixed-mode loading. The laser-generated high amplitude stress wave propagates through the film in short time frames (15 to 20 ns) leading to very high strain rates (10$^{\mathrm{7}}$ to 10$^{\mathrm{8}}$ s$^{\mathrm{-1}})$. The substrate stress, surface velocity and fluence histories are inferred from the displacement fringe data. On comparing input and output fluences, test results indicate significant energy absorption by the polyurea films under both tensile and mixed-mode loading conditions. Microscopic examination reveals distinct changes in failure mechanisms under mixed-mode loading from that observed under pure tensile loading. [Preview Abstract] |
Tuesday, June 16, 2015 4:30PM - 4:45PM |
L3.00003: In situ phase contrast imaging of spall and cracking in vitreous carbon, polymethylmethacrylate, and magnesium alloys Kyle Ramos, Brian Jensen, Timothy Pierce, David Montgomery, Cheng Liu, Aleksander Zubelewicz, Esteban Rougier, Adam Iverson, Carl Carlson, Dana Dattelbaum, Eric Brown, Kamel Fezzaa In impact-generated compression and tension experiments, velocimetry diagnostics are used to detect dynamically created interfaces associated with material damage by observing wave interactions with free surfaces. Interpretation of these wave interactions becomes increasingly more difficult when the interfaces are sufficiently heterogeneous and oblique to the shock front. Therefore, phase contrast imaging of gas gun driven impacts has been performed at the Advanced Photon Source. Damage nucleation, propagation, and coalescence have been studied in multiple configurations for vitreous carbon, polymethylmethacrylate, and several magnesium alloys including AZ31B and AMX602. Uniaxial tension was used for obtaining spall strength and dynamic stress intensity factors. Complex tension, created from wave release off of concave and convex surfaces, was used to investigate shear dependence and stochasticity of cracking. Phase contrast images will be presented to illustrate the range of damage responses exhibited across the different classes of material in their respective microstructure and the use of concave and convex surfaces to create complex tension in planar geometries. [Preview Abstract] |
Tuesday, June 16, 2015 4:45PM - 5:00PM |
L3.00004: Mechanical Properties and Shock Response of PMMA Jennifer Jordan, Daniel Casem, Paul Moy, Timothy Walter Polymethylmethacrylate (PMMA) is used widely in shock experiments as a window material and in explosive characterization tests, e.g. gap tests, as a shock mitigation material. In order to simulate the complex loading present in a gap test, the constitutive response of the PMMA must be well understood. However, it is not clear what characterization must be done when the PMMA material is changed, e.g. changing supplier, and the Rohm and Haas Type II UVA PMMA, which was used for many of the calibration experiments, is no longer available. In this paper, we will present characterization results on legacy Rohm and Haas Type II UVA in comparison with new PMMA grades proposed for use in gap tests. The materials are characterized in compression quasi-statically and dynamically. The quasi-static tests include simultaneous digital image correlation to determine local strain and temperature measurements. Planar shock experiments are performed to determine the compression and release response. [Preview Abstract] |
Tuesday, June 16, 2015 5:00PM - 5:15PM |
L3.00005: On the recovery and recrystallization of two thermoplastics Eric Brown, Christoph Rau, David Townsend, Neil Bourne, Phil Withers The well-known Taylor test, that follows the impact of a flat-ended cylindrical rod onto a rigid stationary anvil, is conducted over a range of impact speeds for two polymers, PTFE and PEEK. In previous work experiments and a model were developed to capture the deformation behavior of the rod after impact. A distinctive feature of these works was that a region in which there was both spatial and temporal variation of both longitudinal and radial deformation showed evidence of order in an otherwise amorphous matrix within the material. This region is imaged in a range of impacted targets at the I13 Imaging and Coherence beamline at the Diamond synchrotron. Resolution beyond the limitations given by the detector and X-ray optics were achieved using methods working in reciprocal space. Further techniques were fielded to resolve crystalline regions within the recovered polymer cylinders. [Preview Abstract] |
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