MSE Seminar Series: K.T. Ramesh, John Hopkins University
Friday, February 10, 2017
1:00 p.m.-2:00 p.m.
Room 2110, Chemical and Nuclear Engineering Building
The Mechanical Behavior of Asteroidal Materials
Most Near-Earth asteroids (NEAs) are rocky, with compositions similar to meteorites. The mechanical behavior of asteroidal materials is a critical aspect of many important questions. What is the likely strength of an incoming asteroid? What will it take to disrupt such an asteroid? What is the potential for asteroid mining, and what would an asteroid prospector seek? What will we find on the surface of an asteroid if we were to land on one (the NASA OSIRIS-REx mission seeks to do this in 2019)? Our spacecraft have shown that most asteroids appear to be covered by a loose layer of rocky material called the regolith. The presence of regolith on such airless bodies has been attributed to impact ejecta re-accumulation and gradual breakdown of boulders by micrometeorite impacts. However, ejecta velocities for these small kilometer-sized asteroids often exceed the gravitational escape velocity. What then is the source of the surface layer of rocks? This is an important question both for manned missions to the asteroids and for prospective asteroid mining operations.We examine the mechanical behavior of asteroidal materials by studying the quasistatic and dynamic mechanical properties of meteorites using traditional experiments, nanoindentation, impact, high-strain-rate and thermal fatigue experiments. We couple these experiments with analytical and computational studies of failure processes in the extreme environments associated with near Earth asteroids. Our focus is on the relative roles of impact and thermal loading on the nature of asteroids that may potentially impact the Earth. We examine the main length and timescales involved in the mechanical degradation of asteroidal materials, and then develop simple scaling laws to estimate the strengths and the time required for thermal fatigue-induced rock breakdown. Finally, we consider the implications of our work for the lifetimes of these asteroids, for asteroid mining operations, and mitigating the potential impact hazard on the Earth.
K.T. Ramesh is the Alonzo G. Decker Jr. Professor of Science & Engineering at Johns Hopkins University. His research interests are in the physics of dynamic failure, impact biomechanics, and planetary scale impact problems. Prof. Ramesh received his doctorate from Brown University in 1987. After a short stint as a postdoctoral fellow at the University of California, San Diego, he joined the Department of Mechanical Engineering at Johns Hopkins in 1988, becoming Department Chair from 1999-2002 and founding Director of the Hopkins Extreme Materials Institute (HEMI) in 2012.