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 B2: ERM: Mechanical Testing of Energetic Materials |
Hide Abstracts |
Chair: Steve Son, Purdue Room: Grand Ballroom II |
Monday, June 17, 2019 9:15AM - 9:30AM |
B2.00001: High-Speed Infrared investigations of local heating in a Graphite-Fiber-PDMS Composite material Under dynamic loading. Stephane Boubanga Tombet, Suraj Ravindran, Addis Kidane, Frédérick Marcotte Infrared thermal imaging also often called thermography is a very evolving field in science as well as industry owning to the enormous progress made in the last 3 decades in microsystem technologies of IR detector design, electronics, and computer science. The development of high-speed IR cameras with high temporal resolution has given rise to a wide variety of demanding thermal imaging applications ranging from academics and research, industrial R{\&}D, non-destructive testing and materials testing, aerospace and defense. We have recently demonstrated the potentialities of high-speed and high-definition IR imaging in experimental mechanics by monitoring heat releases during tensile and shear tests. In the present work we have investigated heat generation dynamics in a graphite cylindrical rods embedded in a polydimethylsiloxane composite material. We were able to observe the effect of both tensile and shear stress on the fibers. The breaking was found mostly to be due to shear stress. Some tensile-stress-induced hot spots were measured with temperature nearly 22 times higher. We also observed a clear influence of the fiber alignment and density in the epoxy matrix on heat generation and the breaking dynamics of the fibers. [Preview Abstract] |
Monday, June 17, 2019 9:30AM - 9:45AM |
B2.00002: TATB Ratchet Growth and Hydrostatically-Confined PBX 9502 Caitlin Woznick, Darla Graff Thompson, Racci DeLuca The explosive TATB (2,4,6-triamino-1,3,5-trinitrobenzene) is formulated with various polymeric binders to create plastic-bonded explosives like PBX 9502 (95 wt{\%} TATB and 5 wt{\%} Kel-F binder). TATB crystals are graphitic and plate-like in nature and single crystals exhibit anisotropic thermal expansion where the direction normal to the platelet surface grows 10-20 times more than the in-plane platelet direction. Compactions of TATB, with and without binder, exhibit irreversible volume expansion, also known as ratchet growth, when thermal cycled to hot or cold temperatures. Specifically, when TATB-based compactions return to ambient after a temperature excursion away from room temperature, the volume of the specimen is slightly larger. Repeated thermal cycles can reduce the density by 1 to 2{\%}. Axial confinement on a cylindrical specimen has previously been shown by us to suppress growth in the confining direction but then to increase growth in the unconfined directions. In the current work presented here, PBX 9502 specimens were placed in cup assemblies where they were embedded in Sylgard (an incompressible silicon resin) to provide hydrostatic confinement when the assemblies were placed under different axial loads. The loaded cup assemblies were thermally cycled 10 times to hot and cold temperatures. Results show that increasing the hydrostatic confining pressure causes a decrease in the PBX 9502 volume expansion that occurs. [Preview Abstract] |
Monday, June 17, 2019 9:45AM - 10:00AM |
B2.00003: PBX 9501 versus a New Thermomechanical Density Mock: Brazilian Disk Compression Test Comparison Cheng Liu, Darla Graff Thompson, Caitlin Woznick, John Yeager, Amanda Duque, Racci DeLuca Due to safety concerns, it is a common practice to use inert surrogates or mocks to replace high explosives in complex experiments. To better understand and simulate these complex experiments, it is desirable that the inert mock can match the real explosive in a wide spectrum of parameters, like density, elastic constants, hardness, coefficient of thermal expansion (CTE), or even mechanical failure/cracking processes. We found that the pharmaceutical material idoxuridine (IDOX) mimics several single crystal properties of the HMX closely, and we have formulated IDOX with the PBX 9501 binder system to generate a new plastic-bonded mock for PBX 9501. Here, we study the mechanical performance of the formulated IDOX mock and compare to PBX 9501 using Brazilian disk compression combined with the digital image correlation (DIC) technique. Samples were tested under quasi-static loading conditions while the test temperature was varied. We thus compare the similarities and differences in their deformation, damage, and failure when subject to mechanical loading. We also investigate formulation and pressing conditions for the IDOX mock, finding that small changes in production were sufficient to enable the mock to be tailored to match specific PBX 9501 properties. [Preview Abstract] |
Monday, June 17, 2019 10:00AM - 10:15AM |
B2.00004: Dynamic Shearing Resistance of a Simulant of an Active Material Pinkesh Malhotra, Tong Jiao, Rodney Clifton, Pradeep Guduru Pressure-Shear Plate Impact (PSPI) experiments have been conducted to provide an experimental foundation for developing constitutive models for the mechanical response of polymer-bonded sugar (PBS) simulants of polymer-bonded explosives (PBXs). Experiments have been done on HTPB, sucrose, and a HTPB/sucrose composite at a range of pressures (3-9 GPa) and shearing rates of 10$^{\mathrm{5}}$-10$^{\mathrm{6}}$ s$^{\mathrm{-1}}$. It is shown that shear strength of HTPB is highly pressure sensitive, increasing from 120 MPa at 2.8 GPa to 470 MPa at 8.8 GPa. Sucrose, on the other hand, exhibits a nominally constant value of shear strength (\textasciitilde 300 MPa) in this range of pressures and shear strain rates. However, pronounced strain softening is observed in sucrose at high shear strains --- even a dramatic drop in shearing resistance in some cases. Based on the experimental data, constitutive models have been developed. Finite element simulations are carried out for a quasi-linear viscoelastic model for HTPB and an elastic-thermoviscoplastic model for sucrose. [Preview Abstract] |
Monday, June 17, 2019 10:15AM - 10:30AM |
B2.00005: The role of heat conduction on hot-spot formation in energetic materials Eliseo Iglesias, Babak Ravaji, Justin Wilkerson Understanding and mitigating the formation of hot-spots in energetic materials, e.g. polymer-bonded explosives (PBX), is vital to improving their overall safety. Accidental hot-spot formation can occur when heat generated via plastic dissipation overwhelms the rate of thermal conduction. It is commonly assumed that under dynamic loading conditions, e.g. strain rates in excess of 100{\%} per millisecond, that thermal conductivity is too slow to be effective, i.e. adiabatic. As such, it has become common place to carry out computational simulations of such high strain-rate deformation assuming adiabatic conditions. Here we carry out mesoscale (explicitly resolving the microstructure in PBX) finite element calculations with and without adiabatic assumptions. The effect of loading rate is studied in detail to elucidate the effect of competing timescales of loading rate versus thermal transport timescales. These calculations enable us to map out the regimes where the adiabatic assumption is appropriate and regimes where it can introduce non-trivial inaccuracies, i.e. over-predictions of hot-spot temperatures. For situations where thermal conduction plays a fairly significant factor on hot-spot formation, we experimentally investigate the implications for the design of PBX with reduced sensitivity to accidental ignition. In particular, we find that enhancing the thermal conductivity of the binder phase, e.g. through the incorporation of nanoparticles with ultrahigh conductivities, can result in the generation of cooler hot-spots and hence improved sensitivity. [Preview Abstract] |
Monday, June 17, 2019 10:30AM - 10:45AM |
B2.00006: Novel PBX formulations containing thermally-expandable microspheres for on-demand control of explosive behavior Amanda Duque, Brian Patterson, Lindsey Kuettner, William Perry, Joseph Mang Here, we present the formulation and analysis of inert Plastic-Bonded eXplosive (PBX)-surrogates loaded with thermally expandable microspheres (TEMs). TEMs consist of a thermoplastic acrylonitrile shell (10-50 microns) encapsulating a low boiling hydrocarbon. Upon heating, the TEMs expand as the shell softens while the hydrocarbon gasifies, increasing the internal pressure and expanding the particle by as much as 120 vol{\%}. We hypothesize that TEM expansion within a PBX will introduce tunable changes in local density and porosity, and ultimately the shock sensitivity. This paper focuses on microstructural details of surrogate PBX-TEM formulations, both before and after thermally-induced TEM expansion. The formulations were analyzed by scanning electron microscopy (SEM), ultra-small angle neutron scattering (USANS), and X-ray Computed Tomography (x-ray CT) under various thermal conditions. In parallel, the overall design is guided by $\pi $SURF, a recently developed hydrodynamic burn model that provides predictive capability for shock initiation response, based partly on a statistical characterization of the microstructure. Both experimental and numerical analysis suggests that TEM expansion within a PBX is a viable method to impart microstructural changes that are predicted to have a measurable, on-demand effect on the initiation sensitivity. Future work includes development of PBX-TEM formulations with HMX and shock initiation experiments. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700