Material science experiments at the Atlas facility

Three experimental campaigns designed for fielding on the Atlas Pulsed Power facility will be discussed. The foci of these experiments will be directed toward a better understanding of three material science issues; (1) strength at high strain and high strain rate, (2) friction at material interfaces moving at high relative velocities, and (3) material failure in convergent geometry. Atlas will provide an environment for investigating these problems in parameter regimes and geometries that are inaccessible with standard techniques. For example, flow stress measurements of material strength using conventional Hopkinson bar experiments are limited to strain rates ∼ 10∧4 sec-1. Atlas will be capable of imploding metal shells to combined strains of 200% and strain rates > 10∧6 sec-1. Data obtained regimes will be used to test different constitutive strength models used in several Los Alamos hydrocodes. Dynamic friction has been investigated for nearly 300 years, but a first-principles understanding of this phenomenon does not exist. In the second set of experiments, the relative motion produced at and near the surface separating two materials, will be studied using multi-frame radiography. The motion will be produced from using a high-velocity liner to impact a segmented target having two materials with different shock speeds. The third campaign will be devoted to spall investigations. Both the effects of varying the driving pressure profile and the effect of convergence on spall will be investigated. Through proper design of an Atlas liner, shock profiles ranging from flat-top to Taylor-like pressure pulse can be produced in a suitable target, and the resultant effects of these different profiles on damage can be inferred by using VISAR to measure pull-back velocities. Atlas will also be used study the growth, or healing, of spalled material in a converged geometry.