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Zirconium deformation behavior: insights from EBSD measurements.

Description: The deformation of crystal-bar zirconium was investigated as a function of strain and strain rate through electron back-scattered diffraction (EBSD) characterization. The resultant data provided spatially resolved information on microstructure and texture evolution, individual twin system activity, and subsequent strain partitioning between twinned volume and parent grains. A range of deformation conditions was represented through quasi-static compression, 4-point beam bend tests at room and cryogenic temperature, and Taylor cylinder impact experiments. Effects from the interplay between slip and twinning deformation modes on anisotropic plasticity are considered in order to address the apparent trend toward isotropy at high rates. The role of various length scales on deformation behavior will be considered, along with the implications of these length scales on the assumptions typically invoked for plasticity modeling.
Date: January 1, 2001
Creator: Bingert, J. F. (John F.); Mason, T. A. (Thomas A.); Kaschner, G. C. (George C.); Maudlin, P. J. (Paul J.) & Gray, G. T. (George T.), III
Partner: UNT Libraries Government Documents Department

Compressive properties of PBXN-110 and its HTPB binder as a function of temperature and strain rate

Description: The compressive constitutive strength behavior of PBXN-110 and its HTPB-based binder system was measured as a function of temperature (-55 C to +20 C) and strain rate (10{sup -3} and 2000 s{sup -1}). PBXN-110 is a plastic bonded explosive (PBX) with relatively high binder content that contains 88wt% HMX and 12wt% HTPB-based binder. A pure analog of the PBXN-110 binder system was tested for comparison to the strain rate and temperature dependence of the composite PBXN-110. As expected, the strength of PBXN-110 was found to exhibit strong temperature and strain rate dependence, attributable to the large fraction of the very soft HTPB binder. The strength of the pure HTPB binder analog was challenging to measure using the split Hopkinson pressure bar (SHPB) because of its extreme softness, however satisfactory results were obtained at and below room temperature by optimizing the SHPB technique. These measurements provide the basis to develop and validate predictive material strength models for PBXN-110.
Date: January 1, 2002
Creator: Blumenthal, W. R. (William R.); Thompson, D. G. (Darla G.); Cady, C. M. (Carl McElhinney); Gray, G. T. (George T.), III & Idar, D. J. (Deanne J.)
Partner: UNT Libraries Government Documents Department

Influence of temperature and strain rate on the compressive behavior of PMMA and polycarbonate polymers

Description: Compression stress-strain measurements have been made on commercial polymethylmethacrylate (PMMA) and polycarbonate (PC) polymers as a function of tcmperature (-197 C to 220 C) and strain rate. A split-Hopkinson-pressure bar (SJIPU) was used to achieve strain rates of about 2500 s-' and a servohydraulic tester was used for lower strain rate testing (0.001 to 5 s-'). The mechanical response of these transparent polymers is quite different. The strength of PC is weakly dependent on strain rate, only moderately dependent on temperature, and remains ductile to -197OC. In contrast, the strength of PMMA is linearly dependent on temperature and strongly dependent on strain rate. Significantly, PMMA develops cracking and fails in compression with little ductility ( 7 4 % total strain) at either low strain rates and very low temperatures (-197OC) or at high strain rates and temperatures very near ambient.
Date: January 1, 2001
Creator: Cady, C. M. (Carl McElhinney); Lopez, M. F. (Mike F.); Gray, G. T. (George T.), III; Idar, D. J. (Deanne J.) & Blumenthal, W. R. (William R.)
Partner: UNT Libraries Government Documents Department

Compressive Properties of a Closed-Cell Aluminum Foam as a Function of Strain-Rate and Temperature.

Description: The compressive deformation behavior of a closed-cell Aluminum foam (ALPORAS) manufactured by Shinko Wire. Co. in Japan was evaluated under static and dynamic loading conditions as a function of temperature. High strain rate tests (1000 - 2000/s) were conducted using a split-Hopkinson pressure bar(SHPB). Quasi-static and intermediate strain rate tests were conducted on a hydraulic load frame. Little change in the flow stress behavior as a function of strain rate was measured. The deformation behavior of the Al-foam was however found to be strongly temperature dependent under both quasistatic and dynamic loading. Localized deformation and stress state instability during testing of metal foams will be discussed in detail since the behavior over the entire range of strain rates indicates nonuniform deformation.
Date: January 1, 2001
Creator: Gray, G. T. (George T.), III; Liu, C. (Cheng); Trujillo, C. P. (Carl P.); Jacquez, B. (Benito); Mukai, T. & Cady, C. M. (Carl McElhinney)
Partner: UNT Libraries Government Documents Department

Crystallographic texture effects on mixed-mode strain localization for lower-symmetry metals

Description: A bifurcation analysis is used to understand the damage realized in flatplate gas-gun specimens that were machined from a highly-textured plate stock of Zr. These low-symmetry material specimens were tested to insipient failure and subsequently soft-recovered. Post-mortem data sets consisting of EBSD imaging of metallographic samples cut from the recovered targets show very different texture-dependent damage morphologies depending on the initial texturekarget orientation at impact.
Date: January 1, 2003
Creator: Maudlin, P. J. (Paul J.); Mason, T. A. (Thomas A.); Gray, G. T. (George T.), III; Bourne, N. K. & Bingert, J. F. (John F.)
Partner: UNT Libraries Government Documents Department