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 K3: Experimental Developments II |
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Chair: Alan Frank, Lawrence Livermore National Laboratory Room: Hyatt Regency Constellation D |
Tuesday, August 2, 2005 1:30PM - 1:45PM |
K3.00001: Validation of a multitechnicals device aimed to reach the temperature of a material under shock loading Bruno Legrand The temperature is one of the parameters which occurs in the equations of state, to describe the behaviour of materials submitted to an intense shock (tens of GPa). Our laboratories use a multispectral pyrometer to determine the temperature. This kind of diagnostic is well known on simple experimental set-up, but it allows to obtain only one temperature measurement. The aim of this work is to validate a device able to integrate 2 simultaneous measurements of temperature, coupled with chronometry and velocity measurements, to improve our knowledge of the behaviour and of the temperature of a material under shock loading. It was necessary to resize and to characterize the existing diagnostics and taking into account the duration of the phenomena (700 ns), as well as mechanical and luminous disturbances generated by the shock. The true temperature of the shocked material is obtained from a luminance measurement with short wavelength. So the pyrometer was reconfigured. This assembly was validated on bismuth samples. The results obtained enable to consider new prospects, like the addition of a reflectivity measurement, in order to reduce uncertainty on the temperature. [Preview Abstract] |
Tuesday, August 2, 2005 1:45PM - 2:00PM |
K3.00002: The effect of sample roughness and planarity on gauge response times William Proud, Jean Wang, Daniel Cross This study presents experimental data on the significance of a sample's planarity and roughness on gauge response under shock-loading. Experiments were carried using a plate impact facility on Copper or PMMA, samples. The impact surface of the target is varied and the stress profile is recorded with piezoresistive manganin gauges. For PMMA, Velocity Interferometer System for Any Reflector (VISAR) and high-speed photography are also used. Results show that the transit times and final stresses reached for both materials are consistent with expected values calculated from Hugoniot crossing. Samples angled at one degree give an increased rise time consistent with the additional distance traversed by the shock in reaching the gauge. The siginificance of surface roughness is explicitly measured. [Preview Abstract] |
Tuesday, August 2, 2005 2:00PM - 2:15PM |
K3.00003: Piezoelectric Polymer Shock Gauges Fran\c{c}ois Bauer The science and technology of piezoelectric materials has long been dominated by the availability of specific materials with particular properties. Piezoelectric PVDF (Poly(vinylidene fluoride)) polymer and copolymers of PVDF with trifluoroethylene have shown that they have the potential for new shock-wave sensors. Since 1981 and until 1995, the piezoelectric response of PVDF has been studied in a cooperative effort with Fran\c{c}ois Bauer of ISL, France, R.A. Graham of Sandia National Laboratories and L.M. Lee of the Ktech Corporation of Albuquerque. Among the known piezoelectric polymers, the PVDF plays an important role in measuring mechanical and physical state of matter under shock loading. The present paper presents the history of the development of the PVDF shock gauge. After 24 years of research in this area, main relevant results and data obtained are summarized as well as some of original applications of the PVDF gauges. [Preview Abstract] |
Tuesday, August 2, 2005 2:15PM - 2:30PM |
K3.00004: Study of sensitivity and repeatability of piezoelectric sensors Carys Lloyd, Martin Greenaway, William Proud The sensitivity and repeatability of stress measurements obtained using commercially available piezoelectric probes have been studied for impact velocities ranging from $\sim $2 m s$^{-1}$ to $\sim $1600 m s$^{-1}$. The probes used were \textit{Dynasen} piezoelectric probes, in which the sensor element is a small ((0.4$\pm $0.05) mm thick, (1.2$\pm $0.1) mm diameter) PZT disc. The probe gives an output voltage $V(t)$ proportional to the time derivative of the force normal to the z-axis of the PZT. The stress level is obtained using the time-integrated voltage. The research presented focuses on the probe's suitability for a wide range of stress levels and pulse lengths. The pressures measured by the probe are compared directly with theoretically estimated or independently measured pressures for a range of impact velocities. The lowest velocity impact experiments were achieved using a Hopkinson Bar, intermediate velocities were performed using a SIJA (Single Impact Jet Apparatus), and highest velocity impact experiments were achieved using laser-driven aluminum flyers. The experiments found that whilst the probes' pressure measurements were often close to the estimated values, the probes demonstrated a gradual drop in sensitivity for higher velocity impacts. [Preview Abstract] |
Tuesday, August 2, 2005 2:30PM - 2:45PM |
K3.00005: A New Spin on an Old Technology: Piezoelectric Ejecta Diagnostics for Shock Environments Wendy Vogan, William Anderson, Michael Grover, Robert Hixson, Nicholas King, Steve Lamoreaux, Kevin Morley, Paulo Rigg, Gerald Stevens, William Turley, William Buttler In our investigation of ejecta, or metal particulate emitted from a surface subjected to shock-loaded conditions, we have developed a shock experiment suitable for testing new ideas in piezoelectric mass and impact detectors. High-explosive (HE) shock loading of tin targets subjected to various machined and compressed finishes results in significant trends in ejecta characteristics of interest such as areal density and velocity. Our enhanced piezoelectric diagnostics, ``piezo-pins" modified for shock mitigation, have proven levels of robustness and reliability suitable for effective operation in these ejecta milieux. These field tests address questions about ejecta production from surfaces of interest; experimental results are discussed and compared with those from complementary diagnostics such as x-ray and optical attenuation visualization techniques. [Preview Abstract] |
Tuesday, August 2, 2005 2:45PM - 3:00PM |
K3.00006: Calibration of Commercial Gauges of Varying Geometry to Measure the Lateral Component of Stress Z. Rosenberg, N.K. Bourne, J.C.F. Millett The measurement of complete stress fields in the inelastic loading of materials has proved to be necessary since in many materials the strength is not constant through the loading pulse or with increase in its amplitude. In planar shock, the strain is uniaxial and the axisymmetric stress field only requires definition of the longitudinal and lateral components. Commercial manganin stress gauges have been used to measure longitudinal stress histories for many years and have been successfully calibrated for this by several workers. Their use in the measurement of lateral stresses has reached maturity now after an understanding of the factors which affect their piezoresistive response. Recently, differing gauge geometries have been adopted. These are grid and a T-shaped gauge manufactured by Micromeasurements. It was noticed that this affected the relative resistance change measured by the gauge for nominally the same input stress. A calibration has been conducted for two differing gauge geometries using a series of experiments in which T and grid gauges were mounted side by side for the same shock. It is found that at low stress amplitudes the gauge response differs, whilst at higher stresses their response is the same. The critical value for this change in behaviour is at a relative resistance change of 0.1. The results are presented and the reasons for the differences are discussed. [Preview Abstract] |
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