Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session L4: Inelastic Deformation V: Polymers & Metals |
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Chair: Neil Bourne, University of Manchester Room: Hyatt Regency Constellation E |
Tuesday, August 2, 2005 3:30PM - 3:45PM |
L4.00001: High Strain Rate Response of an Elastomer Tong Jiao, Rodney J. Clifton Pressure-shear plate impact experiments are used to study the nonlinear dynamic response of an elastomer at shearing rates of $10^5$ - $10^6$ $s^{-1}$. Samples with thicknesses in the range $100 \mu m$ - $400 \mu m$ are cast between two hard steel plates. Because of the comparatively low impedance of the elastomer, longitudinal waves reverberating through the thickness of the sample -- and recorded with a laser interferometer -- can be used to determine the isentrope of the material under uniaxial strain compression. Once the sample is fully compressed the shear wave arrives and imposes a simple shearing deformation. From the transverse velocity, measured interferometrically at the rear surface of the sandwich target, the shear stress and the transverse velocity at the rear surface of the sample are determined. These measurements provide an indication of the shearing resistance of the material under pressure. When the longitudinal unloading wave arrives from the rear surface of the target, these same measurements provide an indication of the shearing resistance of the material at zero pressure. Because the sample adheres to the bounding plates the reflection of unloading waves from both the rear surface of the flyer and the rear surface of the target allows the sample to be strained in uniaxial extension. Thus, from a single experiment, one obtains the response of the elastomer in uniaxial strain compression, simple shear and uniaxial strain extension. [Preview Abstract] |
Tuesday, August 2, 2005 3:45PM - 4:00PM |
L4.00002: High Strain Rate Response of an Epoxy and a Vinyl Ester Rodney J. Clifton, Petch Jearanaisilawong, Tong Jiao Pressure-shear plate impact experiments are used to study the nonlinear dynamic response of an epoxy and a vinyl ester at shearing rates of $10^5$ - $10^6$ $s^{-1}$. Samples with thicknesses in the range $10 \mu m$ - $100 \mu m$ are formed between two hard steel plates. Because of its higher wave speed, the longitudinal wave generated at impact reaches the sample first and, after a few reverberations through the thickness of the sample, subjects the sample to a uniform state of uniaxial strain compression. Then the shear wave arrives and imposes a simple shearing deformation. From the transverse velocity, measured interferometrically at the rear surface of the sandwich target, one obtains the shearing resistance of the material under pressure. Because the sample bonds to the bounding plates, the shearing of the sample continues even after longitudinal unloading waves arrive from the rear surface of the target and reduce the nominal pressure in the sample to zero. Thus, from a single experiment, one obtains the response of the sample in simple shear -- both under pressure and without pressure. From such experiments a pressure-sensitivity of the inelastic shearing resistance is found for both the epoxy and the vinyl ester. [Preview Abstract] |
Tuesday, August 2, 2005 4:00PM - 4:15PM |
L4.00003: Microscopic Observation of Mechanism for Shear Wave Attenuation in Nylon-66 Ting Li, Zhiping Tang, Jian Cai Gupta[1] found rapid shear attenuation near the impact surface for PMMA target. However, the physical mechanism remains unknown. In this article, nylon-66 was chosen for experimental investigation by using a keyed gas gun and EMV method, since nylon-66 has the spherical grain structure, which can be observed under a polarized microscope. The similar rapid shear attenuation occurs in the present study when the impact velocity and inclination angle reach a critical value. The polarized micro-observation of recovered samples shows that near the impact surface there is a melting layer of thickness about 6-8$\mu $m, which causes the decay of the shear component propagating into the sample. The interesting thing is that there is a discontinuous crystalline layer about 2-3$\mu $m thick above the melting layer, which indicates the melting may not directly caused by the friction on the impact surface and the heat produces inside of the sample and near the surface. Further observation discloses an adiabatic shear band near the surface to cause the material failure. [1]Gupta Y M, \textit{J. Appl. Phys}. \textbf{51}(1980), 5352. [Preview Abstract] |
Tuesday, August 2, 2005 4:15PM - 4:30PM |
L4.00004: Elastic-Plastic Behavior of U6Nb Under Ramp Wave Loading D.B. Hayes, G.T. Gray III, C. Hall, R.S. Hixson Prior shock experiments on the alloy uranium-niobium-6 wt.{\%} (U6Nb) were absent an elastic precursor when one was expected (A. K. Zurek, et. al., \underline {Journal de Physique} IV, \textbf{10 }({\#}9) p677-682). This was later explained as a consequence of shear stress relaxation from time-dependent twinning that prevented sufficient shear stress for plastic yielding. (D. B. Hayes, et. al., \underline {Shock Compression of Condensed Matter-2003}, p1177, American Institute of Physics 2004) Pressure was ramped to 13 GPa in 150-ns on eight U6Nb specimens with thicknesses from 0.5 -- 1.1-mm and the back surface velocities were measured with laser interferometry. This pressure load produces a stress wave with sufficiently fast rise time so that, according to the prior work, twins do not have time to form. Four of the U6Nb specimens had been cold-rolled which increased the yield stress. Each velocity history was analyzed with a backward integration analysis to give the stress-strain response of the U6Nb. Comparison of these results with prior Hugoniot measurements shows that the U6Nb in the present experiments responds as an elastic-plastic material and the deduced yield strength of the baseline and of the cold-rolled material agree with static results. [Preview Abstract] |
Tuesday, August 2, 2005 4:30PM - 4:45PM |
L4.00005: Effect of Heat Treatment on the Shock Response of a Zr-Based Bulk Amorphous Alloy (BAA) M.B. Walpole, Y.M. Gupta, Amit Bandyopadhyay In an earlier study,\footnote{Stefan J. Turneaure, et al., Appl. Phys. Lett. \textbf{84}, 1692 (2004)} shock wave compression of a Zr-based BAA (Zr$_{56.7}$Cu$_{15.3}$Ni$_{12.5}$Nb$_{5.0}$Al$_{10.0}$Y$_{0.5})$ resulted in an elastic-plastic, strain-softening response. To understand the observed strain-softening in the as-received samples, wave profiles were obtained from samples heat treated in vacuum at three different temperatures (30 minutes at 450$^{\circ}$C, 600$^{\circ}$C and 700$^{\circ}$C). The ambient glass transition temperature is 495$^{\circ}$C. The heat treatments resulted in less than a 2{\%} increase in density and a 4-15{\%} increase in the shear sound speed while the longitudinal sound speed increases by no more than 5{\%}. For the 600$^{\circ}$C and 700$^{\circ}$C heat treatments, 50nm and $>$100nm precipitate were observed, respectively. The samples had a nominal thickness of 3mm and were shocked to a peak stress of 9.5GPa. The measured wave profiles for the as-received and the heat-treated samples show significant differences in the overall profiles and in the HEL values. These results will be presented and discussed in terms of a continuum material response. Work supported by DOE and ARL. [Preview Abstract] |
Tuesday, August 2, 2005 4:45PM - 5:00PM |
L4.00006: Material Strength Models for Vanadium Stephen Pollaine, Thomas Lorenz, Bruce Remington, John Edwards, Ed Alley, Dave Bailey We have preliminary results of measurements of vanadium strength at 600 kb and 1 Mb, at strain rates between 10$^{7}$ and 10$^{8}$/s. The results are inconsistent with the Steinberg-Guinan [1] model, which is independent of strain rate, but can be made consistent with other models, such as PTW [2]. We show a variety of different strength models and compare them to the data. [1] DJ.Steinberg, S.G.Cochran, and M.W.Buinan, J. Appl. Phys. \textbf{51}, 1498 (1980). [2] D.L. Preston, D.L.Tonks, and D.C.wallace, J. Appl. Phys. \textbf{93}, 211 (2003). This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. [Preview Abstract] |
Tuesday, August 2, 2005 5:00PM - 5:15PM |
L4.00007: A Strength Model For Materials With Phase Change Eric Harstad, Qiuhai Zuo, Francis Addessio A material strength model has been developed for the deviatoric stress of Zr. The model takes into account different material properties for each phase and evolves separate yield surfaces for each phase. The strength model is coupled with a free energy approach for the equation of state that is applicable to high-pressure applications. The material model has been implemented into a three-dimensional Lagrangian finite-element code. Simulations of an explosively-formed projectile using the model are compared with existing material models that do not consider phase changes. [Preview Abstract] |
Tuesday, August 2, 2005 5:15PM - 5:30PM |
L4.00008: Johnson-Cook Strength Model for Automotive Steels K. Vedantam, D. Bajaj, N.S. Brar Over the last few years most automotive companies are engaged in performing simulations of the capability of individual components or entire structure of a motor vehicle to adequately sustain the shock (impacts) and to protect the occupants from injuries during crashes. These simulations require constitutive material models (e.g., Johnson-Cook) of the sheet steel and other components based on the compression/tension data obtained in a series of tests performed at quasi-static ($\sim $1/s) to high strain rates ($\sim $2000/s). One such study is undertaken by the recently formed IISI (International Iron and Steel Institute) in organizing the round robin tests to compare the tensile data generated at our Laboratory at strain rates of $\sim $1/s, $\sim $300/s, $\sim $800/s, and $\sim $2000/s on two grades of automotive steel (Mild steel and Dual Phase-DP 590) using split Hopkinson bar with those generated at high strain rate testing facilities in Germany and Japan. Our tension data on mild steel (flow stress $\sim $ 500 MPa) suggest a relatively small strain rate sensitivity of the material. The second steel grade (DP-590) tested exhibits significant strain rate sensitivity in that the flow stress increases from about 700 MPa (at $\sim $1/s) to 900 MPa (at $\sim $2000/s). J-C strength model constants (A, B, n, and C) for the two steel grades will be presented. [Preview Abstract] |
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