Speaker: Leora Dresselhaus-Cooper, MIT
Program Description:
Shock waves push materials far from equilibrium, causing transformations that permanently alter the system. Characterizing the exotic phase transformations or fracture is difficult, as shock waves interact strongly with initial material defects, causing the irreversible dynamics to fluctuate significantly between samples. To understand how shock waves induce material changes, we must measure the response in-situ, measuring all of the relevant sub-nanosecond information in a single acquisition. Furthermore, the techniques must give signals that are interpretable over the large variation in pressure and temperature found in shock waves. These challenges cause much of our understanding of shocked materials to follow experimental technique development.
Using a novel a tabletop optical method, I study 150-μm diameter cylindrically converging shock waves in a quasi-2D sample. I present a novel imaging diagnostic that captures a sequence of ultrafast images in a single acquisition. With this and other diagnostics, I demonstrate how shock waves initiate explosive chemistry in 1,3,5-triaza-1,3,5-trinitrocyclohexane (RDX). While RDX has been used for industrial and weapons applications for decades, much is still unknown about the molecular mechanism by which shock waves initiate large-scale detonations. My experimental findings on single crystals of RDX in-situ and after recovery show phase transitions, fracture, deflagration and voids that give significant insight into how shock waves initiate the underlying chemistry.
