DYNAMIC COMPRESSION OF AN FE-CR-NI ALLOY TO 80 GPA

Wave profiles were measured in an Fe-Cr-Ni alloy (stainless steel 304) shock compressed to Hugoniot stresses between 7 and 80 GPa. A single- stage propellant gun was used to generate shock states and time histor ies were recorded by velocity interferometry. The particle velocity me asurements are generally consistent with impedance match calculations to +/-2%. Unloading wave velocities were obtained from analysis of the release wave profiles. Using Eulerian finite strain theory and under the assumption of fully elastic initial release, the first and second pressure derivatives of the longitudinal modulus are given by: 7.9(0.5 ) and -0.16(0.06) GPa(-1), where the numbers in parentheses are one st andard deviation uncertainties. The first and second pressure derivati ves of the adiabatic bulk modulus are: 6.4(1.0) and -0.17(0.08) GPa(-1 ). The unloading wave velocities are generally consistent with extrapo lated trends from low-pressure ultrasonic data as well as with higher stress shock measurements on an alloy of similar composition. From 1 b ar to 80 GPa, Poisson's ratio, nu, increases with Hugoniot stress, sig ma (in GPa), according to the relation: nu=0.29 + 0.0008 sigma. The Hu goniot elastic limit of 304 steel was found to be 0.35(0.12) GPa, and the initial yield stress is 0.21(0.07) GPa. The elastic precursor velo city was 5.8(0.1) km/s. Numerical simulations of the wave profiles usi ng a constitutive model that incorporates a Bauschinger effect and str ess relaxation reproduced the main features observed in the profiles. Release adiabats were also calculated from the measured wave profiles. The shear stress at unloading was determined to vary with stress acco rding to the relation: tau(0)+tau(c)=0.149+0.018 sigma, where sigma is given in GPa. (C) 1997 American Institute of Physics. [S0021-8979(97) 05921-5].