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THE BEHAVIOR OF AN ELASTOMER AT HIGH PRESSURES AND HIGH STRAIN RATES

Tong Jiao (Brown University), Rodney Clifton (School of Engineering, Brown University)

Eringen Medal Symposium in honor of G. Ravichandran

Tue 9:00 - 10:30

Salomon 001

Pressure-shear plate impact (PSPI) experiments have been conducted to study the mechanical response of an elastomer (polyurea – a block co-polymer) at high pressures (up to 9GPa) and high strain rates:10^5-10^6s^-1. In order to enable the direct measurement of the thickness-averaged nominal strain rates of the sample  as well as the tractions on both of its interfaces with the bounding linear elastic plates, a new symmetric pressure-shear plate impact (SPSPI) configuration has been developed. This enhancement of the information obtainable from SPSPI experiments is made possible by using a symmetric configuration for which the velocity of the mid-plane of the sample is known from symmetry to be one-half of the impact velocity. Thin (e.g. 70m thick) layers of polyurea are cast onto the impact faces of both a WC flyer plate and a WC anvil plate. A diffraction grating is copied onto the rear surface of the anvil plate to enable the interferometric measurement of both normal and transverse components of the rear-surface velocity. One-dimensional elastic wave theory is used to obtain tractions and particle velocities at the sample/anvil interface from the measured rear-surface velocities. From symmetry, the tractions and particle velocities at the flyer/sample interface are obtained as well. In this way, nominal strain-rate histories are obtained for both longitudinal and shear strains. Integration of these strain rates, and use of the measured traction histories, provides dynamic stress-strain curves that provide insight for developing constitutive models for elastomers at the high strain rates and pressures of these experiments.