Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session V1: Composites and Polymers I: Mechanics of PBXs |
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Chair: Phil Rae, Los Alamos National Laboratory Room: Grand Ballroom II-III |
Thursday, June 30, 2011 4:00PM - 4:15PM |
V1.00001: Temperature Dependent Equations of State for HMX-based Composites Melvin Baer, S. Root, R. Gustavsen, T. Pierce, S. DeFisher, B. Travers In order to examine the temperature dependence of the equation of state (EOS) of two HMX-based explosives, PBX9501 and PBXN9, samples were subjected to shockless compression using the Sandia VELOCE magnetic compression system. Prior to compression, the energetic composites were heated to temperatures up to 155$^{\circ}C$, just below the HMX $\beta -\delta $ phase transition at atmospheric pressure conditions. The phase transition is explored at higher stress conditions when subjected to near isentropic loading. A Velocity Interferometer System for Any Reflector (VISAR) was used to measure particle velocity of the transmitted compression wave. The velocity profile data was analyzed using forward/backward integration methods along with an optimization method to determine unreacted EOS parameters. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U. S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Thursday, June 30, 2011 4:15PM - 4:30PM |
V1.00002: Strain-rate master curves for a PBX and binder Daniel Drodge, David Williamson, Stewart Palmer, William Proud Many studies have been performed, using several different experimental techniques, to characterise the mechanical response of Polymer Bonded Explosives (PBX). Here we draw together a range of techniques, namely Dynamic Mechanical Analysis, quasi-static compression, Hopkinson Bar and ultrasonics, to produce a master curve. This was performed with a UK PBX and its binder, and the shift-factors required to produce a consistent master curve were consistent with previous findings, and furthermore implied that a simple linear conversion between strain-rate and frequency is acceptable, the constant of proportionality being $2\pi$. This has been cited before as a consequence of the Cox Merz rule. The benefit of this approach is that a wider range of mechanical testing data can now be employed in code validation. [Preview Abstract] |
Thursday, June 30, 2011 4:30PM - 4:45PM |
V1.00003: Time-Temperature Superposition Applied to PBX Mechanical Properties Darla Thompson, Racci DeLuca The use of plastic-bonded explosives (PBXs) in weapon applications requires a certain level of structural/mechanical integrity. Uniaxial tension and compression experiments characterize the mechanical response of materials over a wide range of temperatures and strain rates, providing the basis for predictive modeling in more complex geometries. After years of data collection on a wide variety of PBX formulations, we have applied time-temperature superposition principles to a mechanical properties database which includes PBX 9501, PBX 9502, PBXN-110, PBXN-9, and HPP (propellant). The results of quasi-static tension and compression, SHPB compression, and cantilever DMA are compared. Time-temperature relationships of maximum stress and corresponding strain values are analyzed in addition to the more conventional analysis of modulus. Our analysis shows adherence to the principles of time-temperature superposition and correlations of mechanical response to the binder glass transition and specimen density. Direct ties relate time-temperature analysis to the underlying basis of existing PBX mechanical models (ViscoSCRAM). Results suggest that, within limits, mechanical response can be predicted at conditions not explicitly measured. LA-UR 11-01096. [Preview Abstract] |
Thursday, June 30, 2011 4:45PM - 5:00PM |
V1.00004: Mechanical Failure of a Plastic Bonded Explosive vs Confining Pressure Donald Wiegand, Kevin Elllis, Claire Leppard EDC37 fails by crack growth between 0.1 and about 7 MPa and by yield and plastic flow between about 7 and at least 138 MPa. In the low pressure range the compressive strength increases with pressure due to a threshold stress which also increases with pressure. The threshold stress is due to friction between crack surfaces and must be overcome for crack growth. In the higher pressure range the yield strength also increases with pressure but at a much lower rate. In the low pressure range the threshold stress for crack growth is less than the yield strength so primarily crack growth is observed while in the higher pressure range the yield strength is less the the threshold stress for crack growth so that only yield is observed. Thus at moderately low confining pressures greater than 7 MPa crack growth does not take place and so processes depending on crack motion such as frictional heating will not take place. [Preview Abstract] |
Thursday, June 30, 2011 5:00PM - 5:15PM |
V1.00005: Taylor Impact Tests and Simulations on PBX 9501 Brad Clements, Darla G. Thompson, D.J. Luscher, Racci DeLuca Taylor impact tests have been conducted previously on plastic bonded explosives (PBXs) to characterize the stress state of these materials as they impact smooth and flat steel anvil surfaces at speeds of $\sim $100m/s (i.e. Christopher, et al, 11th Detonation Symposium). In 2003, C. Liu and R. Ellis (unpublished, Los Alamos National Laboratory) performed Taylor tests on PBX 9501 up to speeds of 115 m/s, capturing impact images. In the work presented here, we have extended these tests to velocities of 200 m/s using a composite-lined gun barrel and no specimen sabot. Specimen images are used to validate the thermo-mechanical constitutive model ViscoSCRAM. ViscoSCRAM has been parameterized for PBX 9501 in uniaxial stress configurations. Simulating Taylor impact experiments tests the model in situations undergoing extreme damage. In addition, experimental variations to specimen confinement and friction are introduced in an attempt to establish ignition thresholds in this velocity regime. [Preview Abstract] |
Thursday, June 30, 2011 5:15PM - 5:30PM |
V1.00006: Study on Dynamic Fracture and Mechanical Properties of a PBX Simulant by Using DIC and SHPB Method Zhongbin Zhou, Pengwan Chen, Fenglei Huang The deformation and fracture of a polymer bonded explosive (PBX) simulant, a particulate composite, were studied in this work. A pre-cracked semi-circular bending (SCB) specimen was dynamically loaded by a split Hopkinson pressure bar (SHPB). The failure process of the specimen was recorded by using a high speed camera. Based on the recorded images corresponding to the loading steps, the displacement and strain fields were determined by using digital image correlation (DIC) method. The displacement vector fields indicate that the specimen fractures under tensile stress. The strain distribution in front of the preset crack can be used to predict the propagation of the crack initiated from the tip of the pre-crack. In addition, the dynamic fracture toughness of the SCB specimen was measured. The fracture toughness values are 1.45MPa$\cdot$m$^{1/2}$, 1.52MPa$\cdot$m$^{1/2}$ and 1.85MPa$\cdot$m$^{1/2}$ corresponding to strain rates 380s$^{-1}$, 450s$^{-1}$ and 625s$^{-1}$, respectively. The results indicate that the fracture toughness show strong strain rate dependence. [Preview Abstract] |
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