Strength of Materials Through RT Experiments & Multiscale Model Validation

Kristen John, California Institute of Technology

This research involves studying the strength of metals through Rayleigh-Taylor laser experiments. The goal is to determine the strength of certain metals, namely iron and tantalum, at high pressures (greater than 1 Mbar) and high strain rates (greater than 100 s-1). To achieve this, we use the Omega Laser in Rochester, N.Y., where we have performed several experiments to “impact” our metal sample using Omega’s 60 laser beams. Our sample is designed with ripples on the side. By measuring the growth of these ripples as the sample is impacted, we can study a property called the Rayleigh-Taylor instability. Using strength models, we then correlate measurements of instability growth to a measure of strength. We have conducted similar experiments at Caltech, but there we replaced the lasers with a gas gun and the metal samples with ballistic gelatin. We successfully correlated strength to growth of the Rayleigh-Taylor instability. As expected, the stronger the material, the more it suppresses instability growth. We are performing experiments at Caltech using the gas gun to impact tin, chosen because it is a soft metal and should flow upon impact. In order to validate past experiments and to help design future experiments, we are utilizing a multiscale model designed at Caltech. By running simulations and comparing the model to the Omega and gas gun experiments, we’re able to predict the behavior of these materials, estimate a value for the strength, understand the mechanics effects on the growth, validate the experiments and make design changes for future experiments. This research has astrophysics and aerospace applications and has direct applications to fusion energy. A key issue preventing fusion from occurring is the presence of Rayleigh-Taylor instabilities and this research could lead to stabilizing them.

Abstract Author(s): K. John and G. Ravichandran